Relationships between Shorebird
and Benthos Distribution at the
Western Treatment Plant
Danny I. Rogers, Richard Loyn, Shanaugh McKay,
David Bryant, Robert Swindley and Phil Papas
2007
Arthur Rylah Institute for Environmental Research
Technical Report Series No. 169
Arthur Rylah Institute for Environmental Research Technical Report Series No. 169
Relationships between shorebird
and benthos distribution at the
Western Treatment Plant
Danny I. Rogers, Richard Loyn, Shanaugh McKay,
David Bryant, Robert Swindley and Phil Papas
Arthur Rylah Institute for Environmental Research
123 Brown Street, Heidelberg, Victoria 3084
November 2007
Arthur Rylah Institute for Environmental Research, Department of Sustainability and
Environment. Heidelberg, Victoria.
Report produced by:
Arthur Rylah Institute for Environmental Research
Department of Sustainability and Environment
PO Box 137
Heidelberg, Victoria 3084
Phone (03) 9450 8600
Website: www.dse.vic.gov.au/ari
© State of Victoria, Department of Sustainability and Environment 2007
This publication is copyright. Apart from fair dealing for the purposes of private study, research, criticism or review
as permitted under the Copyright Act 1968, no part may be reproduced, copied, transmitted in any form or by any
means (electronic, mechanical or graphic) without the prior written permission of the State of Victoria, Department
of Sustainability and Environment. All requests and enquires should be directed to the Customer Service Centre,
136 186 or email customer.service@dse.vic.gov.au
Citation
Rogers, D.I., Loyn, R., McKay, S., Bryant, D., Swindley, R. and Papas, P. (2007). ‘Relationships between shorebird and
benthos distribution at the Western Treatment Plant’. Arthur Rylah Institute for Environmental Research Technical
Report Series No. 169. (Department of Sustainability and Environment: Heidelberg).
ISBN 978-1-74208-223-3 (Print)
ISBN 978-1-74208-224-0 (Online)
ISSN 1835 3827 (Print)
ISSN 1835 3835 (Online)
Disclaimer
This publication may be of assistance to you but the State of Victoria and its employees do not guarantee that the
publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore
disclaims all liability for any error, loss or other consequence which may arise from you relying on any information
in this publication.
Cover page photo: Adult Red-necked Stint foraging on the shoreline of 5W Lagoon, Western Treatment Plant.
Photographer: Danny Rogers.
Authorised by the Victorian Government, Melbourne.
Printed by: NMIT Printroom, 77-91 St Georges Road, Preston 3072
Contents
List of tables and figures ........................................................................................................................ ii
Acknowledgements ................................................................................................................................. iii
Summary ................................................................................................................................................... iv
1
Introduction ...................................................................................................................................... 1
2
Methods ............................................................................................................................................. 4
2.1
Measurement of shorebird usage of foraging sites ........................................................ 4
2.2
Measurement of benthos abundance ................................................................................. 5
3
Results ............................................................................................................................................... 8
3.1
Tidal flat attributes and shorebird foraging areas .......................................................... 8
3.3
Changes in bird and benthos biomass distribution ......................................................18
4
Discussion
4.1
4.2
4.3
.......................................................................................................................21
Foraging distribution of Red-necked Stints ....................................................................21
Distribution of edible biomass ..........................................................................................22
Relationships between Red-necked Stint and benthos distribution ..........................23
5
References .......................................................................................................................................26
Appendix 1. High tide shorebird counts at the WTP, 2004-2007. ................................................28
Appendix 2. Low tide shorebird counts at the WTP, 2004-2007. .................................................29
i
List of tables and figures
Figure 1. Bird foraging areas at the WTP. ......................................................................................... 22
Figure 2. Calculation of bird-foraging hours for a site .................................................................. 23
Figure 3. Relationship between abundance of foraging Red-necked Stint and amount of seagrass cover on tidal flats abutting the WTP ....................................................................... 23
Figure 4. Relationship between abundance of foraging Red-necked Stint and width of tidal
flats abutting the WTP ............................................................................................................ 24
Figure 5. Map of distribution of biomass edible for Red-necked Stints on the tidal flats
abutting the WTP ..................................................................................................................... 25
Figure 6. Relationship between edible biomass and distribution of foraging Red-necked
Stints abutting the WTP in March 2005 .............................................................................. 26
Figure 7. Changes in distribution of edible biomass and of foraging Red-necked Stint,
between March 2005 and March 2006................................................................................. 27
Figure 8. Relationships between edible biomass and numbers of foraging Red-necked Stints
in February and March 2006.................................................................................................. 29
Table 1. Stomach contents of Curlew Sandpipers and Red-necked Stints in other studies . 30
Table 2. Attributes of tidal foraging areas at the WTP .................................................................. 31
Table 3. Red-necked Stint numbers in tidal foraging areas of the WTP .................................... 32
Table 4. Total biomass of benthos in tidal foraging areas of the WTP ...................................... 33
Table 5. Edible biomass of benthos in tidal foraging areas of the WTP .................................... 34
Table 6. Comparisons of biomass at the WTP with other wetland systems ............................. 35
ii
Acknowledgements
We are grateful to Melbourne Water for commissioning this study and to Will Steele for his
continued support. Our simultaneous counts program would not be possible without the
skilful assistance provided by a large number of volunteers: We thank regular team leaders
Ken Harris, Tania Ireton and Charlie Smith, Dave Torr, Jeff Davies, Will Steele, Ken Rogers,
Ken Gosbell, Dale Tonkinson, Jimmy Gunn – and some 50 other volunteers: Adrian Boyle,
Amanda Bush, Alice Ewing, Andrew Silcocks, Noel, Asha and Brenna Billing, Barnaby Briggs,
Birgeitta Hansen, Claire Appleby, Chris Hassell, Craig Morley, Charles Smith, Doris Graham,
Dean Ingwersen, David McCarthy, Dawn Neylan, David Wilson, Gina Hopkins, Ed McNabb,
Frank Farr, George Appleby, Howard Plowright, Heidi Zimmer, Inka Velthiem, Joan
Broadberry, Jen Spry, Jean Thomas, Joy Tansey, Keith Johnson, Lauren Beasley, Luke Einoder,
Lyn Easton, Mark Barter, Maarten Hulzebosch, Liz Gower, Nathan Detroit, Naomi Hall, Penny
Johns, Peter Gower, Richard Walsh, Rob Clemens, Sant Cann, Shirley Cameron, Sue Charles,
Dale Tonkinson and John Stoney; we apologise to a few others whose names never made it
onto a data sheet. Mike Nicol helped with the collection and processing of benthos samples;
statistical advice on the design of the benthos sampling program was provided by Joanne
Potts.
3
Summary
The Western Treatment Plant (WTP) attracts large numbers of shorebirds, including
migratory species that breed in northern Asia and are subject to international agreements to
protect migratory birds and their habitats. These shorebirds are among the principal
biological assets that contributed to the site being listed as a wetland of international
significance under the Ramsar Convention. Melbourne Water manages the WTP and needs to
conserve habitat for shorebirds, while meeting core commitments to treat wastewater.
Melbourne Water has recently upgraded its treatment processes through an Environment
Improvement Project to meet a number of requirements set by the Victorian Environment
Protection Authority as part of Melbourne Water’s accredited discharge licence. There is a
risk that shorebird habitat values in tidal flats will decline if nutrient levels from adjacent
effluent outfalls are reduced through the Environment Improvement Project. Hence,
Melbourne Water is examining management options to offset any such change in shorebird
habitat values. This will assist Melbourne Water to meet its obligations to protect shorebird
habitat under legislation, including the Commonwealth Environment Protection and
Biodiversity Conservation Act 1999.
This report focuses specifically on the problem of whether macrozoobenthos and shorebird
abundance are related at the WTP. Although it seems plausible that relationships of this kind
exist, studies commissioned by Melbourne Water have shown that the relationships between
nutrient, benthos and bird abundance are complex and difficult to assess. We carried out
coupled surveys of shorebird distribution and abundance, and of benthos distribution and
abundance. Bird distribution and abundance were assessed through a series of
“simultaneous counts”, in which teams of volunteers were based at the main shorebird
foraging and roosting sites of the WTP, and counted the birds present and foraging at each
site at approximately hourly intervals. All shorebird species were counted, but only the data
collected on the most common migratory species, the Red-necked Stint (Calidris ruficollis),
are presented in this report. The data obtained were used to calculate the number of birdforaging hours per site. This is the most robust daily index of the importance of particular
sites to foraging shorebirds that can be made at the WTP.
Benthos was core-sampled from the top 5 cm of sediment, with a minimum of four samples
collected from each bird-foraging area, and an equal number of cores taken from lower (only
exposed on the lowest spring tides) and upper tidal flats. The biomass of macrofauna (larger
than 0.25 mm) was assessed for each sample, as was the biomass of macrofauna ingestible
for Red-necked Stints. These values were calculated for each bird-foraging area for
comparison with the data available on bird-foraging hours per site.
The first coupled survey (early March 2005) was broad in its scale, with benthos sampled
from all known intertidal foraging sites for Red-necked Stints at the WTP. Benthos
abundance was patchy and there was little evidence for a direct relationship between
benthos abundance and distance from active sewage outfalls. Such a relationship may exist
on small scales, but not on the scale of distances covered by shorebirds (up to 10 km) in
their typical daily movements at the WTP. The relationship between bird and benthos
abundance was complex and unclear, partly because some sites with high benthos
abundance held few shorebirds. Some of these sites were suspected to be unsuitable as
shorebird habitat for geomorphological reasons, as they had narrow or predominantly rocky
shorelines. In subsequent surveys, attention was therefore focussed on the eight birdforaging areas known from past observations to hold the largest numbers of foraging
shorebirds. The high numbers of shorebirds seen at these sites at some stage in the past
4
four years (at least 2,000 individuals at each) demonstrate that they do not have
geomorphological characteristics that make them unsuitable for foraging shorebirds.
Three coupled surveys conducted subsequently (October-November 2005, February 2006
and March 2006) showed that benthos abundance varied over time, with the location of the
areas richest in benthos changing from survey to survey. The causes of these changes are
unknown, but they provide a natural experiment: if shorebird numbers are influenced by
benthos abundance, then the distribution of foraging shorebirds should change in response
to changes in benthos distribution. This proved to be the case, with significant relationships
between bird and benthos distribution being found in surveys in February 2006 and March
2006, despite benthos distribution changing substantially between the two surveys.
Although the analyses carried out in this study need to be refined, they are sufficient to
confirm that there is a positive relationship between benthos and shorebird abundance at
the WTP at sites that are geomorphologically suitable for large numbers of foraging
shorebirds.
5
Relationships between Shorebird and Benthos Distribution at the Western Treatment Plant
1
Introduction
The Western Treatment Plant (WTP) is one of two main sewage treatment plants for
Melbourne, serving approximately 1.6 million people on the western side of the city. It
covers an area of 10,851 ha on the west coast of Port Phillip Bay, near the town of Werribee,
and is owned and managed by Melbourne Water. The area has long been renowned as a
habitat for large numbers of migratory and resident shorebirds, as well as significant
populations of other waterbirds. Its value for these birds has been recognised with the
nomination of the area to the list of Wetlands of International Importance under the
Convention on Wetlands (commonly known as the “Ramsar Convention”).
Shorebird habitats at or near the WTP are managed by two State government agencies.
Melbourne Water manages the WTP above high tide mark and is the committee of
management for the coastal reserve from the mouth of the Little River to the mouth of
Werribee River. Parks Victoria manages the intertidal habitats between the Little River
mouth and Kirk Point, as well as coastal, intertidal and sub-tidal habitats at The Spits (Figure
1). Areas managed by Parks Victoria constitute The Spits Nature Conservation Reserve,
which includes the most important coastal intertidal shorebird foraging habitats in the area.
The shorebirds are one of the principal Ramsar Convention values of the WTP and adjacent
habitats, and the migratory species are listed on the JAMBA and CAMBA migratory bird
agreements. For this reason, shorebirds are subject to the provisions of the Commonwealth
Environment Protection and Biodiversity Conservation Act 1999 (the ‘EPBC Act’).
Melbourne Water has implemented an Environment Improvement Plan at the WTP, including
major treatment upgrades between January 2003 and December 2004 to provide a more
sustainable future operation. Implementation of the Plan is a condition of Melbourne Water’s
Environment Protection Authority (EPA) accredited discharge licence. Many of the Plan’s
objectives are being delivered through an Environment Improvement Project including
(amongst other things) the progressive upgrade of sewage treatment processes. One of the
primary goals of the Project has been to progressively reduce the annual load of nitrogen
discharged into the bay from and average of 3,600 tonnes in 2001 to a target of 3,100
tonnes by January 2005.
Concern has been expressed that the reduction in nutrient loads to the nearby parts of Port
Phillip Bay from the WTP may result in ecological changes in the enriched and highly
productive intertidal flats, with a consequent decline in the numbers of shorebirds using the
area. Initial investigations (PPK Environment and Infrastructure Pty Ltd 2000) showed that
the relationship between nutrients and shorebird foraging densities is complex and difficult
to assess due to high levels of natural variability in nutrient levels in the near-shore flats and
the many possible pathways by which these nutrients reach the organisms on which
shorebirds feed.
The uncertainty associated with predicting the impact of the Environment Improvement
Project on shorebird numbers foraging in the intertidal habitats has led to the adoption of
an adaptive management approach to its implementation. In addition, Melbourne Water has
commissioned or supported a number of studies to improve understanding of the responses
of benthos to changes in nutrient levels (e.g. Morris and Keough 2001, 2002; Morris and
Metcalf 2004), and of the feeding habitat requirements of shorebirds (e.g. PPK Environment
and Infrastructure Pty Ltd 2000; Loyn et al. 2002; Beasley 2004; Rogers et al. 2004, Rogers
and Loyn 2007).
Arthur Rylah Institute for Environmental Research Technical Report Series No. 169
1
1
2
3
4
5
6
7
8
12
10
14
9
11
13
15
16
17
Figure 1. Bird foraging areas (shaded pink) at the WTP; areas where birds concentrate and benthos was sampled are overlaid in red. These
intertidal areas do not have formal names, but we have listed the unofficial names used in this survey.
Establishing whether or not there is a relationship between benthos abundance and
shorebird foraging densities is difficult in general (Goss-Custard et al. 2006) and has proved
problematic at the WTP. A pilot study by PPK Environment and Infrastructure Pty Ltd (2000)
reported that a relationship occurred in one survey, but this was not universally accepted.
Criticisms made of the study included the possibility that the low-tide counts used as an
index of intensity of bird-foraging were may have been skewed by local movements, and that
high densities of birds seen in two transects that dominated the study might have been a
reflection of tidal flat width (which was not assessed) rather than benthos abundance.
This report documents a more detailed study of the relationship between shorebird and
benthos abundance. The study differs from previous work at the WTP in using bird-foraging
hours as a robust measure of the importance of specific sites to feeding shorebirds, in
repeated sampling, and in restricting some analyses to sites known to have a sufficient tidal
flat area for large numbers of foraging shorebirds. The study focuses on the most common
shorebird species at the WTP, the Red-necked Stint Calidris ruficollis (see cover photograph).
This species is a long-distance migrant, which breeds in the Siberian tundra and migrates
annually to Australia; it uses the WTP as a non-breeding area, with most individuals foraging
on the intertidal flats during low tide (Loyn et al. 2002).
Arthur Rylah Institute for Environmental Research Technical Report Series No. 169
3
2
Methods
2.1
Measurement of shorebird usage of foraging sites
In January 2004, a program of “simultaneous counts” was initiated at the WTP. These
shorebird surveys were carried out during a single day by seven small teams of volunteers,
who counted the number of shorebirds present at their allotted sites at approximately
hourly intervals. In addition, the number of shorebirds foraging was recorded. Fourteen such
surveys have been conducted since the program began: one in October (2005), one in
November (2005), three in December (2004, 2005, 2006), three in January (twice in 2004,
once in 2005), four in February (2004, 2005, 2006, 2007) and two in March (2005, 2006).
Five additional low tide and high tide counts (including an assessment of the number of
birds foraging) were made as part of an existing monitoring program (July 2005, June 2006,
December 2005, and January 2007). Each of these surveys included one complete high tide
count and one complete low tide count of the entire WTP, including the abutting tidal flats,
for consistency with monitoring methods already established at the WTP (Loyn et al. 2002).
Complete low tide and high tide surveys of this kind were also carried out on days when we
conducted simultaneous counts.
The intertidal foraging areas surveyed are shown in Figure 1. The break-up of the coastline
into specific sites was based on the practicalities of shorebird counts; most of the sites we
used, have clear geographical boundaries and are all small enough to be surveyed reasonably
quickly, usually in less than fifteen minutes. The foreshore between Little River Mouth and
Lake Borrie Outfall is a rather long stretch of coastline that can hold especially large
numbers of shorebirds; a marker was set up half-way along this beach, so it could be divided
into two shorebird foraging sites.
Radio-telemetry studies (Rogers et al. 2004) and the simultaneous counts program (Rogers
and Loyn 2007) have shown that a good deal of shorebird movement occurs during low tide
at the WTP. Some sites, such as the lagoon of North Spit, are used more intensively on
ebbing than on rising tides, and there is a tendency for birds at most sites to move northeast as the tide ebbs. Accordingly, single counts of a particular site done at the nadir of low
tide, or the peak count obtained in the low tide period, do not necessarily correspond well
with the number of birds that use the site in question. Data from the simultaneous counts
were used to calculate bird-foraging hours per site in the four hours before, and the three
hours after the nadir of low tide (Figure 2). This included the full period over which the
intertidal flats were exposed on the survey days in question (tides rise more quickly than
they ebb at the WTP). The number of bird-foraging hours per site was calculated separately
for each species; only data for Red-necked Stints are presented in this report. In this species,
the number of bird-foraging hours per site was closely correlated with the average number
of foraging Red-necked Stints observed in counts carried out at each foraging site when the
tidal flats were partially or fully exposed (r = 0.886, n = 40). We used the average number of
foraging Red-necked Stints at each given site through a low tide period as our index of bird
abundance for comparisons with benthos abundance, as our measure of benthos abundance
in each shorebird foraging area was an average from a number of sampling points, many of
which were only exposed when the tide was at its lowest.
The count made at the peak of high tide for each shorebird survey is presented in Appendix
1, and the count made at the nadir of low tide in each shorebird survey is presented in
Appendix 2.
Arthur Rylah Institute for Environmental Research Technical Report Series No. 169
4
Tide Height
No. of
Red-necked
Stints
12:00
15:00
18:00
Time
Figure 2. Calculation of bird-foraging hours for a site. The dotted line indicates tide height. The
number of bird-foraging hours is given by the area under the curve (shaded grey) and is considered a
more representative indication of the value of a site to foraging shorebirds than the maximum low tide
count (upper black dot) or the count at the nadir of low tide (lower black dot).
2.2
Measurement of benthos abundance
Benthos samples were taken from the top 5 cm of sediment with a cylindrical corer, 5 cm in
diameter, and then placed directly in sample jars for future laboratory examination. Ethanol
was used as a preservative. It is traditional to take larger, deeper cores in studies of
intertidal benthos (e.g. Gill et al. 2001; van Gils et al. 2005 a,b). Smaller samples were taken
at the WTP in order to reduce laboratory processing time, and hence to increase the number
of samples we could process. Previous benthos studies at the WTP had shown the benthic
fauna to be extremely abundant and dominated by small animals, so only small cores were
required to capture enough animals for analytical purposes. At most sites it would have
been possible to take considerably deeper cores, as the sediment above the shell-grit layer
was at least 30cm deep at some sites. However, benthic animals buried more than 5 cm
below the surface are beyond the reach of the bill-tips of the three most common shorebird
species at the WTP (Red-necked Stint, bill length 16-22 mm; Curlew Sandpiper Calidris
ferruginea, bill length 32-43 mm; and Sharp-tailed Sandpiper Calidris acuminata, bill length
22-27 mm; bill measurements from Higgins and Davies 1996). Moreover, observations at the
WTP have shown that these species rarely probe deeply into the mud, usually taking prey
from the top centimetre or so of sediment (Loyn et al. 2002; Beasley 2004; pers. obs.).
In the first broad-scale benthos survey, benthos samples were taken from all tidal birdforaging areas known in the WTP. All samples were collected between March 4th and 7th,
2005, immediately after a simultaneous shorebird count conducted on March 3rd, 2005. Five
Arthur Rylah Institute for Environmental Research Technical Report Series No. 169
5
replicate cores were taken at each site. Benthos samples were taken along two transects
within each bird-foraging area. One sample in each transect was taken from high in the
intertidal area (from mudflats or sand flats exposed on all low tides) and the other was taken
from low in the intertidal area (from mudflats or sand flats only exposed on spring low
tides). In most bird-foraging areas, samples were taken at four points. In two bird-foraging
areas with very broad tidal flats (the eastern and western sides of the mouth of Little River),
two additional samples were taken at mid-tide levels, and in one bird-foraging area (the
coast south of Murtcaim Outlet), only two samples were taken, as tide levels prevented
sample collection in the lower intertidal zones. Selection of benthos sampling points within
these constraints was random, except that microhabitats that were unsuitable for foraging
shorebirds (such as rocks or deep channels) were avoided.
Three additional benthos surveys were carried out in 2005-2006 (13 Oct. - 14 Nov. 2005; 5-9
Feb. 2006; 6-8 Mar. 2006). Each of these surveys was accompanied by a simultaneous
shorebird count (8 Oct. and 5 Nov. 2005; 6 Feb. 2006; 4 March 2006). Sampling design was
altered in these surveys. Analyses from the first survey had shown that little was gained by
taking and processing five replicate cores and a single core was considered sufficient.
Sampling was restricted to eight bird-foraging areas known to be capable of holding large
shorebird numbers. Within these bird-foraging areas, sample sites (especially at mid-tidal
levels) were added to the array so that interpolative spatial techniques can be used to
generate density maps of benthos abundance along the shores of the WTP (these analyses
are in progress and are not included in this report). The sampling array used in these three
surveys included the points sampled in the first survey. As the benthos surveys were held at
intervals of at least a month, and as sampling points were located by handheld GPS (only
accurate to c. 3 m), it is very unlikely that our repeated sampling of the same sites
influenced the local benthos abundance.
A number of habitat attributes were recorded at each benthos sampling point. These
included time, width of tidal flat, distance of sampling point to the nearest vegetation on
shore, penetrability, grain-size, sediment type, depth of anoxic layer, and percentage cover
of sea-weed and bird abundance within 5 m of the sampling point. These data were collected
for a spatial analysis that has yet to be completed, but a brief summary is provided in this
report.
Benthos samples taken at a few inland ponds on some of the surveys. Only one set of these
samples (at Walsh’s Lagoon during the first benthos survey) had been processed at the time
this report was prepared. The results from these samples at Walsh’s Lagoon are mentioned
briefly in this report, for a rough comparison with tidal flats.
Under laboratory conditions, a 50% sub-sample of each sediment core was flushed through a
250 micron sieve and the residue sorted under a stereo microscope. All animals extracted
from the residue were identified to broad structural categories (e.g. gastropod; small bivalve)
and counted. A representative sample from each category was dried and weighed and the
average weight per animal calculated (Total weight/No. animals weighed). The benthic
biomass at each site was then calculated by summing the weights of each animal category:
∑ (No. animal A x weight animal A) + (No. animal B x weight animal B) + ....
Animals found in the benthos samples were not identified beyond order or family level, but
the specimens were retained and can be identified more precisely in the future if this is
deemed necessary. One reason for using general biomass (rather than more refined
identifications) as a measure of prey availability was that little is known about the diets of
the three most abundant shorebird species of the WTP (Red-necked Stint, Curlew Sandpiper
Arthur Rylah Institute for Environmental Research Technical Report Series No. 169
6
and Sharp-tailed Sandpiper). Studies of stomach contents of Red-necked Stints and Curlew
Sandpipers at other Australian sites indicate that a diversity of small invertebrate prey is
taken (Table 1). The differences in diet found between sites in Western Port Bay (Dann 1999)
and a site in Tasmania (Thomas and Dartnall 1971) suggest it is unlikely that these shorebird
species have highly selective diets; it is more likely that the prey taken depends on local prey
availability. Therefore, studies carried out at other sites cannot be considered reliable
sources of information on the exact prey types of shorebirds at the WTP, but they provide
information on the maximum size of prey that can be ingested. Using the criteria in Thomas
and Dartnall (1971; broadly consistent with data presented in different format by Dann
1999), the following benthic animals were regarded as potential prey for Red-necked Stints:
soft animals (such as dipteran larvae and amphipods) less than 12 mm long and 3 mm wide;
and hard-shelled animals (such as gastropods and bivalves) less than 5 mm long and 3 mm
wide. In addition, we treated polychaetes less than 50 mm long as edible, as DR observed
several Red-necked Stints eating onuphid polychaetes up to 50 mm long in the course of
benthos sampling at the WTP in March 2005. Only c. 2% of the 27,878 polychaetes captured
in the core samples were greater than 12 mm long. It is possible that the number of large
polychates was underestimated because such animals were able to burrow deeper than 5 cm
and could thus avoid capture in core samples.
For each bird-foraging area, we used the average of the core samples processed as the
measure of biomass. Biomass estimates were converted to g dry mass m-2 for ease of
comparison with data in published literature.
Table 1. Stomach contents of Curlew Sandpipers and Red-necked Stints in Western Port Bay, Victoria
(Dann 1999) and south-eastern Tasmania (Thomas and Dartnall 1971). Dann (1999) measured
biovolume of different prey types, and Thomas and Dartnall reported the percentage of stomachs
examined containing specific prey types; these different measures of prey abundance are not directly
comparable.
Number
examined
Prey Type
Polychaetes
Gastropods
Crabs
Amphipods
Ostracoda
Bivalves
Seeds
Insect larvae
Curlew Sandpiper
Western Port
SE Tas
Red-necked Stint
Western Port SE Tas
n = 11
% biovolume
n = 17
% biovolume
63.3%
21.4%
31.8%
0.1%
0.0%
0.2%
0.5%
0.0%
n = 58
% of
stomachs
12.0%
67.2%
7.0%
17.2%
0.0%
25.9%
39.6%
58.6%
0.0%
68.3%
31.8%
0.2%
0.0%
0.0%
0.0%
0.0%
n = 59
% of
stomachs
3.3%
32.0%
3.3%
38.9%
18.6%
4.9%
13.5%
c. 38.5 %
Arthur Rylah Institute for Environmental Research Technical Report Series No. 169
7
3
Results
3.1
Tidal flat attributes and shorebird foraging areas
The tidal flats of the WTP are generally narrow, broadening around the mouth of Little River
(up to 300 m wide on the lowest spring tides) and on the lagoon inside The Spits (Table 2).
On neap low tides, these are often the only areas where expanses of tidal flat broader than
20 m are exposed, except for promontories of small boulders and the sand flat between
Beacon Point and Kirk Point. Most of the tidal flats are firm, with a sand or fine sand
substrate. Most of them have patchy sea-grass cover, ranging from sparse (around Little
River Mouth) to extensive (lower tidal flats west of Beacon Point).
Numbers of foraging Red-necked Stints in each of the intertidal foraging areas are
summarised in Table 3. These data come from 19 low-tide surveys of the WTP carried out
since January 2004, including 14 simultaneous counts in which counts were made at
approximately hourly intervals.
There was no clear relationship between substrate type and Red-necked Stint abundance,
with large numbers of the species found foraging in sites with both fine sediments (e.g. the
lagoon of North Spit) and coarse sediments (e.g. the western bank of Little River Mouth,
where birds often fed in high densities on the shingle bank bordering the river channel). Nor
was there an obvious relationship between the percentage of sea-grass cover and the number
of foraging Red-necked Stints at a site, with high numbers of Red-necked Stints found both
at sites with and without abundant sea-grass (Figure 3).
No. of feeding Red-necked Stint
6000
5000
4000
3000
2000
Maximum count
Average count
1000
0
0.0
0.1 0.2 0.3 0.4 0.5 0.6
Proportion of Sea-grass Cover
0.7
Figure 3. Maximum (black circles) and average (grey triangles) counts of Red-necked Stint plotted
against proportion of sea-grass cover at each foraging site. The trend lines were fitted by Lowess
smoothing.
Arthur Rylah Institute for Environmental Research Technical Report Series No. 169
8
Table 2. Attributes of intertidal foraging areas at the WTP in the benthos survey undertaken in early March 2005. Except where stated, tidal flats in all sites
are firm (walking humans sink less than 2 cm) and any anoxic layer is at least 5 cm below the surface.
Site
Substrate type
Approximate width of Tidal
Flats (m)
Other Attributes
Approximate
length of coastline
(m)
Percentage of
area covered by
sea-grass or seaweed
1. East of 145W Outlet
2. Little River Mouth East
3. Little River Mouth West
Fine dark sand
Sand to coarse sand
Fine to coarse sand
Spring low
tides (>0.15
m)
220
200
300
4. Borrie Outlet
Sand
100
50
540
3%
5. Beacon Point
6. Coast N of Beach Rd
7. Rocks S of Beach Rd
8. Kirk Point
9. Kirk Bay
10. Murtcaim Beach
11. NN Spit Coast
12. NN Spit Lagoon
Fine sand
Fine sand
Rocks on sandy bed
Rocks on sandy bed
Sand
Sand, pipi shells
Coarse sand
Silt to fine sand
200
200
50
70
50
20
60
200
40
10
10
40
20
5
5
200
1180
1200
1000
540
720
580
640
620
64%
33%
50%
50%
25%
40%
53%
47%
13.
14.
15.
16.
17.
Fine to coarse sand
Fine sand
Coarse sand
Fine sand to sand
Coarse sand
400
200
30
300
10
350
150
3
200
3
480
1000
1140
800
800
11%
31%
25%
48%
28%
N Spit Channel
N Spit Lagoon
N Spit Coast
S Spit Lagoon
S Spit Coast
Neap low tides
(0.3-0.45 m)
Not exposed
70
100
380
480
700
5%
1%
5%
Has a shingle bank beside
river
Shingle bank developing at
Outlet
Soft, with anoxic layer 1-4
cm below surface
Many shingle channels
Table 3. Numbers of foraging Red-necked Stints in intertidal areas of the WTP. Data are from 4 low tide counts and 14 simultaneous counts carried out
between 2003 and 2007.
Site
Number of
low tide
counts when
RNS present
Maximum count
of Red-necked
Stints
Average No. of Rednecked Stints when
exposed
Comments
1. East of 145W Outlet
2. Little River Mouth East
3. Little River Mouth West
4. Borrie Outlet
5. Beacon Point
6. Coast N of Beach Rd
7. Rocks S of Beach Rd
8. Kirk Point
9. Kirk Bay
10. Murtcaim Beach
11. NN Spit Coast
12. NN Spit Lagoon
13. N Spit Channel
14. N Spit Lagoon
15. N Spit Coast
16. S Spit Lagoon
17. S Spit Coast
28
27
37
35
42
23
58
50
17
25
32
47
18
38
36
24
13
2390
3690
4500
1950
3600
2376
1100
500
80
161
572
4601
4530
5460
360
762
68
762
937
1029
594
652
169
106
49
17
25
77
705
539
281
24
110
11
Only used on lowest tides
Numbers peak on rising tides; used on neaps
Numbers increase as tide ebbs; used on neaps
Numbers peak early during ebb of tide
Numbers peak on ebbing tide; birds stay longer during neaps.
Relationships between Shorebird and Benthos Distribution at the Western Treatment Plant
In contrast, plots of the width of tidal flats against the number of Red-necked Stints foraging
in tidal areas suggest that Red-necked Stints prefer to feed on broad tidal flats (Figure 4).
Linear regressions showed a statistically significant relationship on spring low tides:
Number foraging = 300.19 (±500.66) + (12.067*width); R2 = 0.545, P = 0.001.
In reality, the relationship between Red-necked Stint abundance and tidal flat width is likely
to interact with other variables: even if we recorded all of these other variables
systematically, a complete multivariate analysis would be problematic given the number of
parameters to be estimated on the basis of data from only 17 bird-foraging areas.
Nevertheless, it would be prudent in subsequent analyses to be aware that width of tidal
flats may constrain Red-necked Stint abundance in some way.
There are only ten sites in which Red-necked Stints were recorded in thousands, including
six on the relatively broad tidal flats centred on the mouth of Little River, and three on the
lagoon at North Spit (Table 2). Maximum counts on the narrower tidal flats between Beach
Road and Kirk Point, and on the seaward side of the Spits, were of fewer than 500 birds, with
the exception of a single count of 1100 Red-necked Stints on the narrow rocky shoreline
south of Beach Road. This latter count is somewhat misleading, as it involved birds that only
fed at the site for a few minutes; the largest of the other 57 low tide counts made at this site
was of only 400 birds. In subsequent comparisons of Red-necked Stint abundance with
benthic biomass, it would therefore be sensible to only include sites where Red-necked Stints
are known, on occasion, to feed in large numbers. Presumably these sites lack any
geomorphological constraints (perhaps width of tidal flat) that may limit abundance of Rednecked Stints at other sites.
Number of Red-necked Stints
6000
5000
4000
3000
2000
Maximum count
Average count
1000
0
0
100
200
300
400
Width of tidal flat (m)
500
Figure 4a. Relationship between numbers of foraging Red-necked Stints and width of tidal flats (on
spring tides >0.15 m) at the WTP. The lines represent simple linear regressions.
Arthur Rylah Institute for Environmental Research Technical Report Series No. 169
11
Relationships between Shorebird and Benthos Distribution at the Western Treatment Plant
Number of Red-necked Stints
6000
5000
4000
3000
2000
Maximum count
Average count
1000
0
0
100
200
300
Width of tidal flat (m)
400
Figure 4b. Relationship between numbers of Red-necked Stints and width of tidal flats (on neap tides of
0.30-0.45 m) at the WTP. The lines represent similar linear regressions.
3.2
Broad scale patterns of benthos distribution
Total biomass of macrobenthic fauna, presented as g dry mass m-2, is summarised in Table 4.
Biomass in our samples was sometimes dominated by a small number of large bivalves,
gastropods or crabs which were too large to be ingested by Red-necked Stints. Excluding
such animals from our analyses allows us to calculate the edible biomass (Table 5). Edible
biomass was usually dominated by worms (almost entirely polychaetes) or bivalve spat.
Bivalves appeared to constitute a larger proportion of the biomass in March and November
2005 than in February and March 2006. However differences in diversity between sites have
not been tested, as samples were not identified to species level.
A direct comparison of biomass between sites is difficult, as only dry mass was measured.
Biomass of benthos is typically reported as Ash-free Dry Mass (AFDM) in g m-2. In calculating
this value, the dry mass is measured, the sample is then incinerated (burning off the
digestible component of the benthos), and the residue weighed; AFDM is obtained by
subtracting the mass of the indigestible residue from the dry mass.
The dry masses obtained from the WTP for worms, insect larvae (nearly all soft-bodied
dipterans) and small crustaceans are likely to be quite close to AFDM, as these animals have
few indigestible hard parts. Bivalves and gastropods were weighed with their shells, and
their dry masses would thus have been substantially higher than AFDM. In benthos samples
from Roebuck Bay, north-western Australia, AFDM of bivalves was on average 7.6% (range 266%) of dry mass, and that of gastropods was 20.0% (range 4 to 42%) of dry mass. There was
a large range of variation because of differences in morphology between species. Assuming a
similar ratio of shell to digestible matter occurred in the Victorian samples, the AFDM of
gastropods in the samples taken in March 2005 can be calculated as 4.9 g AFDM m-2, that of
Arthur Rylah Institute for Environmental Research Technical Report Series No. 169
12
Relationships between Shorebird and Benthos Distribution at the Western Treatment Plant
bivalves as 2.3 g AFDM m-2 and the total biomass as 23.3 g AFDM m-2. The data can also be
broken up to calculate the AFDM of total biomass at freshwater sites (Walsh’s Lagoon) and
intertidal sites at the WTP. These are crude approximations, but they serve as a rough point
of comparison with biomasses calculated in other wetland systems (Table 6).
Although this comparison is crude, it is apparent that biomass of benthos in the WTP,
especially in the intertidal zone, is very high. The biomass observed is even more remarkable
when one considers that core samples were only 5 cm deep, thus probably failing to catch
large deeply buried animals that were sampled in most of the comparative studies available.
On the scale of this study, there was no evidence for a gradient of biomass abundance
centred on the outfalls of the WTP (Figure 5). High biomass levels were found near outfalls
on tidal flats from the mouth of Little River to 145W Outlet (an area traditionally used by
large numbers of Red-necked Stints), but also at important Red-necked Stint foraging areas
relatively far from outfalls (south-west of Beacon Point, and on the north-eastern part of the
Spit Lagoons). There was no clear relationship between abundance of benthos and that of
foraging Red-necked Stints (Figure 6):
Number foraging = 53.54 (± 1,788.77) + (224.051 (± 140.74). biomass)
0.132)
(R2 = 0.145, P =
In part, this may have been because the tide did not go out far enough to expose the tidal
flats east of the mouth of Little River on the day that the simultaneous count took place in
March 2005,. More importantly, high biomass was found at some sites where Red-necked
Stints did not feed in large numbers (e.g. the narrow rocky shoreline south of Beach Road,
and on the narrow coastline on the seaward side of South Spit). Width of coastline in itself
could not explain the variation observed, as adding it to the above model did not improve it
substantially (R2 = 0.173, P = 0.264). The effect of tidal flat width on numbers of foraging
Red-necked Stints does not appear to be linear and probably interacts with other variables.
Arthur Rylah Institute for Environmental Research Technical Report Series No. 169
13
Relationships between Shorebird and Benthos Distribution at the Western Treatment Plant
Table 4. Biomass of benthos (g dry mass m-2) in the intertidal foraging areas of the WTP. Number of sample
sites is given in the first data column; the final six columns express biomass of subgroups as a percentage of
total biomass.
Site name
Date
n
1. East of 145W Outlet
March '05
Nov '05
Feb '06
Feb '06
March '05
Nov '05
Feb '06
March '06
March '05
Nov '05
Feb '06
March '06
March '05
Nov '05
Feb '06
March '06
March '05
Nov '05
Feb '06
March '06
March '05
Nov '05
Feb '06
March '06
March '05
March '05
March '05
March '05
March '05
March '05
Nov '05
Feb '06
March '06
March '05
Nov '05
Feb '06
March '06
March '05
March '05
March '05
March '05
4
7
7
7
6
5
5
5
10
19
13
19
4
13
13
13
4
5
5
5
4
16
16
16
4
4
4
2
4
4
9
9
9
4
7
7
7
4
4
4
4
2. Little River Mouth East
3. Little River Mouth West
4. Borrie Outlet
5. Beacon Point
6. Coast N of Beach Rd.
7. Rocks S of Beach Rd.
8. Kirk Point
9. Kirk Bay
10. Murtcaim Beach
11. NN Spit Coast
12. NN Spit Lagoon
13. N Spit Channel
14.
15.
16.
17.
N Spit Lagoon
N Spit Coast
S Spit Lagoon
S Spit Coast
Total
biomass
97.8
32.3
25.7
49.7
87.1
35.2
32.5
41.3
79.6
57.2
23.4
31.6
19.0
16.9
19.9
15.1
39.7
16.2
1.9
10.5
110.6
3.8
8.3
13.6
140.5
0.6
2.2
5.2
50.9
69.6
25.0
14.1
8.2
8.0
1138.2
65.2
6.7
158.6
248.4
2.1
25.0
Gastropods
0.0
0.0
0.1
0.2
0.0
0.3
0.0
0.9
0.7
0.1
0.1
0.9
0.0
0.0
0.0
0.5
0.3
0.0
0.0
0.0
12.4
0.1
0.0
0.0
131.0
0.0
0.0
0.0
41.8
12.9
7.5
0.2
0.3
0.2
5.7
0.0
0.0
122.7
138.4
0.0
22.0
Bivalve
Worms
85.3
20.9
2.4
9.1
83.9
24.8
9.0
12.4
71.2
49.6
2.7
7.4
15.1
9.4
1.0
0.8
34.0
15.0
0.0
0.0
79.1
2.2
0.3
0.2
2.3
0.0
0.1
0.0
4.7
51.0
12.3
2.3
2.3
1.5
1.6
0.4
0.5
31.1
1.4
0.7
2.8
11.3
7.6
18.7
33.7
2.9
7.5
22.1
23.1
7.5
4.8
18.3
20.3
2.6
3.8
18.5
13.4
5.3
0.7
1.7
9.9
8.2
0.9
6.9
12.8
7.2
0.6
0.2
3.1
3.1
4.3
2.4
7.2
3.7
2.2
2.8
2.6
2.6
2.2
5.1
1.1
0.2
Arthur Rylah Institute for Environmental Research Technical Report Series No. 169
14
Crustacea
1.2
2.3
1.0
3.2
0.2
2.6
1.3
2.5
0.2
1.9
0.4
0.5
0.0
0.9
0.3
0.4
0.2
0.5
0.1
0.6
0.5
0.6
1.1
0.5
0.0
0.0
1.9
2.1
1.3
0.2
2.8
0.2
0.6
3.5
4.5
3.2
3.5
0.1
0.4
0.3
0.0
Inedible
phyla
0.0
1.5
3.5
3.5
0.1
0.0
0.1
2.4
0.0
0.8
1.9
2.5
1.3
2.8
0.1
0.0
0.1
0.0
0.1
0.0
10.4
0.0
0.0
0.1
0.0
0.0
0.0
0.0
0.0
1.2
0.0
4.2
1.3
0.6
1123.6
59.0
0.1
2.5
103.1
0.0
0.0
Relationships between Shorebird and Benthos Distribution at the Western Treatment Plant
Table 5. Biomass of edible benthos (g dry mass m2) for Red-necked Stints in the intertidal foraging
areas of the WTP. Number of sample sites is given in the first data column; the next five columns
express biomass of subgroups as a percentage of edible biomass, and the final column presents edible
biomass as a proportion of the total biomass present.
Site name
Date
n
Edible
biomass
Gastropods
Bivalve
Worms
Crustacea
Inedible
phyla
1. East of 145W Outlet
March '05
Nov '05
Feb '06
Feb '06
March '05
Nov '05
Feb '06
March '06
March '05
Nov '05
Feb '06
March '06
March '05
Nov '05
Feb '06
March '06
March '05
Nov '05
Feb '06
March '06
March '05
Nov '05
Feb '06
March '06
March '05
March '05
March '05
March '05
March '05
March '05
Nov '05
Feb '06
March '06
March '05
Nov '05
Feb '06
March '06
March '05
March '05
March '05
March '05
4
7
7
7
6
5
5
5
10
19
13
19
4
13
13
13
4
5
5
5
4
16
16
16
4
4
4
2
4
4
9
9
9
4
7
7
7
4
4
4
4
97.8
30.8
22.2
46.2
67.0
35.2
32.5
38.9
79.6
32.2
21.5
28.4
17.7
14.1
19.9
14.7
39.7
16.2
1.9
10.5
57.8
3.8
8.3
13.6
9.5
0.6
2.2
3.5
8.8
67.8
22.6
10.0
6.9
7.0
9.3
6.3
6.7
33.6
6.9
2.1
3.0
0.0%
0.0%
0.5%
0.5%
0.0%
1.0%
0.0%
2.1%
0.9%
0.1%
0.6%
2.7%
0.0%
0.0%
0.1%
3.1%
0.7%
0.0%
0.7%
0.0%
11.2%
3.0%
0.1%
0.2%
93.2%
0.0%
0.0%
0.0%
82.2%
18.5%
30.1%
1.8%
3.1%
2.4%
0.5%
0.1%
0.4%
77.4%
55.7%
0.0%
88.1%
87.3%
64.9%
9.3%
18.3%
96.4%
70.5%
27.9%
30.0%
89.5%
86.7%
11.5%
23.4%
79.7%
55.7%
5.2%
5.3%
85.5%
92.8%
0.0%
0.0%
71.5%
57.3%
3.8%
1.8%
1.7%
0.0%
5.3%
0.0%
9.2%
73.3%
49.1%
16.3%
28.5%
18.8%
0.1%
0.6%
7.4%
19.6%
0.6%
32.7%
11.2%
11.5%
23.6%
72.6%
67.8%
3.3%
21.2%
68.1%
55.9%
9.4%
8.4%
78.3%
64.1%
13.6%
22.7%
93.3%
88.6%
13.2%
4.2%
91.6%
93.9%
7.4%
22.6%
83.2%
94.1%
5.1%
99.8%
10.2%
59.7%
6.1%
6.2%
9.8%
51.1%
44.5%
27.4%
0.2%
3.9%
39.3%
1.4%
2.1%
53.1%
0.8%
1.2%
7.0%
3.9%
6.4%
0.3%
7.4%
4.1%
6.1%
0.2%
3.3%
1.6%
1.6%
0.0%
5.2%
1.4%
3.0%
0.5%
3.0%
7.7%
6.1%
0.5%
17.1%
12.8%
3.9%
0.0%
0.2%
84.5%
40.3%
2.6%
0.3%
11.1%
1.6%
7.2%
43.2%
0.4%
5.0%
52.9%
0.0%
0.1%
14.2%
0.0%
0.0%
4.5%
17.6%
13.2%
0.0%
0.0%
4.1%
12.1%
0.0%
1.4%
9.2%
9.7%
6.7%
16.3%
1.2%
3.0%
0.0%
0.0%
7.7%
6.1%
9.3%
0.0%
11.3%
3.9%
0.0%
0.0%
0.0%
0.0%
0.0%
1.7%
0.0%
30.8%
23.8%
7.9%
98.7%
1.5%
18.8%
1.6%
41.5%
0.0%
0.0%
2. Little River Mouth
East
3. Little River Mouth
West
4. Borrie Outlet
5. Beacon Point
6. Coast N of Beach Rd
7. Rocks S of Beach Rd
8. Kirk Point
9. Kirk Bay
10. Murtcaim Beach
11. NN Spit Coast
12. NN Spit Lagoon
13. N Spit Channel
14.
15.
16.
17.
N Spit Lagoon
N Spit Coast
S Spit Lagoon
S Spit Coast
Arthur Rylah Institute for Environmental Research Technical Report Series No. 169
15
Percent
biomass
edible
100.0%
95.5%
86.3%
92.9%
77.0%
100.0%
100.0%
94.0%
100.0%
56.3%
91.9%
89.9%
93.3%
83.7%
100.0%
97.0%
100.0%
100.0%
100.0%
100.0%
52.3%
100.0%
100.0%
100.0%
6.8%
100.0%
100.0%
66.9%
17.4%
97.5%
90.1%
70.8%
83.4%
86.7%
0.8%
9.6%
100.0%
21.2%
2.8%
100.0%
11.9%
Relationships between Shorebird and Benthos Distribution at the Western Treatment Plant
Table 6. Biomass (expressed as g AFDM m-2) of benthos at the WTP, compared with benthic biomass
reported from other sites in other studies.
Location
Biomass (g AFDM
Reference
-2
m )
Freshwater habitats
Walsh’s Lagoon, WTP
Oregon, USA (agricultural wetlands)
Intertidal flats
WTP
Coorong, SA
Tasmania
Roebuck Bay, WA
South Africa
West Africa
Korea
Netherlands
Germany
6.77 (0.9-13.0)
This study
0.44 (0.09-1.41)
Taft and Haig (2005)
57.34 (0-423)
This study
Dittmann et al. 2006
0.4-2.6
1.7-42.5
12.5 (0.07-167)
4.7-20.4
17
3.1 – 51.9
c. 25
50
Pepping et al. 1999
Scharler and Baird 2005
Wijnsma et al. 1999
Doornbos and Groenendijk
1986
Ysebaert et al. 2003
Scheiffarth and Nehls 1997
Arthur Rylah Institute for Environmental Research Technical Report Series No. 169
16
13.0
4.8
19.4
6.0
10.1
29.7
12.7
20.2
14.2
1.2
13.4
6.5
2.8
6.8
7.7
10.5
10.8
4.1
Average edible biomass for
Red-necked Stints in birdfeeding areas sampled in early
March 2005
0.6
Figure 5. Biomass (in g dry mass m-2) edible to Red-necked Stints in the intertidal bird-foraging areas at the WTP in early March 2005. The black
arrows indicate sewage outfalls.
Feeding Red-necked Stints
2000
1500
1000
500
0
0
10
20
Edible biomass (g dry mass sq m)
30
Figure 6. Edible biomass of benthos in each tidal foraging site, plotted against the number of Rednecked Stint foraging hours during the low tide of 5 March 2005. There was no significant relationship
between the two (R2=0.145, n = 19, P =0.132).
3.3
Changes in bird and benthos biomass distribution
Edible biomass available to Red-necked Stints was measured in four benthos surveys. Data
are presented for eight tidal flats known to support large numbers of foraging Red-necked
Stints at times (Figure 7). The presence, at times, of large numbers of Red-necked Stints at
these sites indicates that they did not have geomorphological or other attributes that made
them unsuitable for foraging. Within these sites, benthos abundance varied over time; it was
lower at almost all foraging sites in the survey of November 2005 than it was in other
surveys carried out in February and March. The distribution of the areas of highest benthos
abundance also varied over time. For example, in March 2005 benthos abundance was
relatively high in western sites (North of Beach Road, and in The Spit Lagoon); in March 2006
benthic abundance in these sites had declined, yet it had increased substantially in sites at
and east of the mouth of Little River.
Foraging distribution of Red-necked Stints varied over the same period (Figure 7). The data
obtained in the simultaneous counts carried out in March 2005 and November 2005 are of
limited used for comparisons with benthos distribution, as the shorebird counts were
carried out on low tides that did not go out far enough to expose the tidal flats east of Little
River, or to expose wide expanses of tidal flat between Little River and Beacon Point.
However, in the spring tide surveys undertaken in February and March 2006, changes in Rednecked Stint foraging distribution coincided reasonably well with changes in the distribution
of edible biomass, at least in the east of the study area. In general, at sites where there was a
substantial increase in benthos abundance (e.g. east of 145W Outfall, and at Little River
Mouth West), there was a corresponding increase in bird abundance. Similarly, a substantial
decline in benthos abundance at “Borrie Outfall” (Lake Borrie Outfall) coincided with a
substantial decrease in bird abundance.
Arthur Rylah Institute for Environmental Research Technical Report Series No. 169
18
40
Mar.
30
20
2005
10
0
0
1
2
3
4
5
6
Site Number
7
8
9
Edible biomass
50
40
Nov.
30
20
2005
10
0
0
1
2
3
4
5
6
Site Number
7
8
9
Edible biomass
50
40
Feb.
30
20
2006
10
0
0
1
2
3
4
5
6
Site Number
7
8
9
Red-necked Stint feeding hours
Edible biomass
50
1600
Red-necked Stint feeding hours
Feeding Red-necked Stints
1600
Red-necked Stint feeding hours
Edible biomass
1600
40
Mar.
30
20
2006
10
0
0
800
400
0
0
1
2
3
4
5
6
Site Number
7
8
9
1
2
3
4
5
6
Site Number
7
8
9
1
2
3
4
5
6
Site Number
7
8
9
1
2
3
4
5
6
Site Number
7
8
9
1200
800
400
0
0
1200
800
400
0
0
1600
1
2
3
4
5
6
Site Number
7
8
Edible biomass
Edible biomass
50
1200
1200
800
400
0
0
9
Figure 7. Average edible biomass (graphs in left column), and foraging abundance of Red-necked Stints
(graphs in right column) in eight important tidal flats at the WTP. Edible biomass is expressed as g dry
mass m2; foraging abundance is expressed as number of Red-necked Stint foraging hours per hour at
low tide. The sites, numbered along the X-axis, are: 1. East of 145W Outlet; 2. Little River Mouth East; 3.
Little River Mouth West; 4. Borrie Outlet; 5. Beacon Point; 6. Coast N of Beach Rd; 7. NN Spit Lagoon; 8.
N Spit Channel. Location of these sites is shown in Figure 1.
Arthur Rylah Institute for Environmental Research Technical Report Series No. 169
19
Confining our attention to the surveys of February and March 2006 (when all tidal flat areas
were exposed), it is clear that there was a positive relationship between edible biomass and
abundance of foraging Red-necked Stint (Figure 8). Foraging theory suggests that the
relationship between density and prey abundance should be some kind of asymptotic gain
function, but with only eight data points, it is not possible to fit a curvilinear function, .
Nevertheless, the relationship proved to be statistically significant when modelled with
linear regression without a constant (it was assumed that if no prey was present, there
should be no foraging birds):
In February 2006:
Average number foraging = (30.843± 5.791) x biomass (R2 = 0.802; P = 0.001);
In March 2006:
Average number foraging = (26.185± 4.549) x biomass (R2 = 0.826; P = 0.001).
Arthur Rylah Institute for Environmental Research Technical Report Series No. 169
20
4
Discussion
4.1
Foraging distribution of Red-necked Stints
It is unlikely that benthos abundance is the only factor that influences foraging distribution
of Red-necked Stints on the intertidal flats of the WTP. Our data showed that there were
areas along the foreshore that were seldom or never used by large numbers of Red-necked
Stints, although they could (at least sometimes) support high benthic biomass. One feature
that these seldom-used tidal flats had in common was that they were relatively narrow;
typically less than 50 m wide even on the lowest spring tides. Red-necked Stints may prefer
foraging on relatively broad tidal flats for two reasons, not mutually exclusive. First, foraging
on narrow tidal flats forces Red-necked Stints close to shoreline vegetation which may
conceal predators. Birds of prey, notably Whistling Kite (Haliastur sphenurus), Swamp
Harrier (Circus approximans) and Australian Hobby (Falco longipennis) are common at the
WTP and often follow shorelines when hunting, probably using the shoreline vegetation as
cover so they can make a close approach to potential prey on tidal flats. The further birds on
tidal flats are from tall cover, the harder it will be for birds of prey to approach them
without being detected from long range. Red-necked Stints may therefore benefit from
foraging on broad tidal flats because the possibility of predation is reduced, or because on
broad tidal flats there are lower energetic costs associated with alarm flights forced by close
approach of a predator.
A second potential benefit of foraging on broad tidal flats is that they have a larger surface
area, so Red-necked Stints need not feed at such high densities. The relationship between
density of foraging Red-necked Stints and the area of tidal flat is unlikely to be simple.
Foraging Red-necked Stints at the WTP do not scatter uniformly over exposed tidal flats;
they tend to concentrate at the tide-edge (possibly as prey is more easily detected there), and
thus occur at high densities even when the tidal flat area is large. However, as the tide line
moves more quickly over a broad tidal flat than a narrow one, the amount of time that Rednecked Stints spend feeding at any particular point on a tidal flat is likely to be higher if the
tidal flat is narrow. Narrow tidal flats may therefore be depleted of prey more rapidly than
are broad tidal flats.
Although the cause of any preference for broad tidal flats by Red-necked Stints at the WTP
remains unknown, it is clear that the relationship between tidal flat width and the number of
foraging Red-necked Stints is strong, and could in theory be modelled. To do so, it would be
ideal to have an exposure map of the tidal flats of the WTP, so that the width and area of
tidal flats could be estimated at particular heights of tide. Tide height is measured by the
Port of Geelong at six-minute intervals at the nearby Point Richard’s tide gauge, so with an
exposure map it would be possible to calculate width and area of tidal flats associated with
all shorebird counts (including individual counts carried out at hourly intervals during the
simultaneous counts program).
An adequate exposure map is not yet available for the tidal flats of the WTP, so we
attempted to control for the effects of tidal flat width by restricting our analyses to sites
considered broad enough to support large numbers of foraging Red-necked Stints. We were
able to identify such sites by examining data collected in a large number of low tide counts
carried out over the past few years on a variety of dates and tide conditions. While we
consider this step reasonable, it does have the drawback of reducing sample sizes, as it
reduces the number of sites that can be used in comparisons of benthos and bird density.
Arthur Rylah Institute for Environmental Research Technical Report Series No. 169
21
4.2
Distribution of edible biomass
One of the problems with comparisons of the distribution of benthos and foraging
shorebirds is that they need to be sampled on different scales. Shorebirds can be identified
and counted at long range with telescopes, so it is possible for observers to do complete
counts of the number of birds on a specific tidal flat. Indeed counting foraging stints in
smaller areas is impractical, as they are mobile at low tide, and are likely to only spend short
periods on specific points of mud. Previous radio-telemetry and the simultaneous counts
program at the WTP have shown that Red-necked Stints may move several kilometres in the
course of a low tide, with many birds routinely foraging on The Spit Lagoon as the tide ebbs
and then moving as far as 145W Outfall (8 km away) at the nadir of low tide. In addition to
longshore movements like these, Red-necked Stints also tend to follow the tide edge as the
tide ebbs (pers. obs.).
In contrast, the benthic animals on which small shorebirds feed can only be sampled on
small scales, as identifying and counting them is a time-consuming laboratory task. To
compare the distribution of benthos and shorebirds, it is therefore necessary to sample
benthos from specific points, and use the data obtained from these points to estimate
benthos density in the surrounding bird-foraging area. In this study we simply used the
average from our sampling points. The number of sampling points at upper and lower tidal
flats was equivalent in all sampling areas, so zonation effects (e.g. higher densities of
animals at lower tidal levels) are unlikely to have caused systematic biases between sites in
our assessment of biomass. We therefore consider the use of averages adequate for the
simple analyses carried out in this report. However, a better estimate could be developed
through use of spatial statistical techniques to generate density maps of benthos on the tidal
flats, and this is a priority for future research at the WTP.
Much of the previous benthos work carried out on the tidal flats of the WTP has focussed on
the “outfall” effect. Sediments near the nutrient-rich sewage discharge points are believed to
hold very high densities of invertebrates and to have a different species composition than
sites further away (Poore and Kudenov 1978; Davies and Brown 1995; PPK Environment and
Infrastructure Pty Ltd 2000; Morris and Metcalf 2004). Our sampling did not show a clear
gradient in biomass from sewage outfalls. In part this was probably because we only
examined edible biomass, and did not consider benthic animals at species level. We suspect
Red-necked Stints target foraging areas providing abundant food rather than being selective
about the prey species taken; moreover, the diets of shorebirds at the WTP are poorly
known. A consideration likely to be of greater importance was the scale of our sampling;
radio-telemetry and the simultaneous counts program have shown that the Red-necked
Stints of the WTP move considerable distances along the shoreline at low tide, so for the
benthos data we collected to be compared with data on bird abundance, it was necessary to
use a sampling program that covered c. 10 km of shoreline. The gradients in benthos
abundance from sewage outfalls are likely to be more localised, only operating over a few
hundred metres (Morris and Keough 2002). On the scale at which we sampled, benthos was
generally more abundant at outfalls around Little River Mouth and 145 W Outfall than it was
elsewhere, but abundance was generally patchy and varied considerably over time. It would
be of interest to examine the outfall effect over a still larger geographical area, in case the
entire 10km stretch of coastline that we sampled was influenced by nutrient discharge from
WTP outfalls.
Arthur Rylah Institute for Environmental Research Technical Report Series No. 169
22
4.3 Relationships between Red-necked Stint and benthos
distribution
The causes of temporal variation in benthos abundance at the WTP remain unclear. In a 16month study carried out by Morris and Metcalf (2004), benthos abundance on the tidal flats
of the WTP varied over time, with responses varying from species to species but with an
apparent tendency for benthos abundance to be lowest in late summer (February and March).
They suggested that high summer temperatures and anoxic conditions caused by rotting
seaweed may cause a seasonal reduction in benthos abundance across the entire shoreline.
Our data were consistent with the idea that something causes broad-scale temporal variation
in benthos abundance at the WTP. However, in this study, benthos abundance in a November
survey was markedly lower than in three surveys carried out in February and March. Clearly
there is a great deal to be learned about temporal trends in benthos abundance at the WTP.
Given that the variation is very substantial (e.g. average biomass in the November 2005 was
only c. 25% that found in the March 2006 survey), a long-term benthos monitoring study to
unravel the nature of seasonal trends in benthos abundance at the WTP would be of great
value.
The benthos sampling we carried out at the WTP was consistent with previous studies (e.g.
PPK Environment and Infrastructure Pty Ltd 2000; Morris and Metcalf 2004) in finding
benthos to be extremely abundant relative to that found in studies at other sites (Table 6). It
would be of considerable interest to know if this abundance approaches the point, predicted
by foraging theory, at which any further increase in prey abundance has a negligible effect
on intake rates, because the intake rate has reached the maximum level dictated by
constraints such as food-handling times (Holling 1959), the time needed to digest food (van
Gils et al. 2005a, b), or interference competition from other birds attracted to a rich feeding
area (van Gils and Piersma 2004). If prey abundance at the WTP is at this level, then in theory
benthic densities could decline considerably before having any impact on foraging success
(and hence numbers) of Red-necked Stints.
Our data suggest this scenario is unlikely to apply. Restricting our attention to those
foraging areas with an established history of holding large numbers of Red-necked Stints
(hence presumably having the geomorphological and other attributes needed by this
species), we found a strong positive relationship between prey abundance and numbers of
foraging Red-necked Stints. This relationship could be described effectively with a linear
function. We did not have enough data points to assess whether the relationship could be
described equally effectively with an asymptotic gain function, but the effectiveness of the
linear regressions suggests that benthic densities of at least most of the sites we sampled
were well below any asymptotic level at which intake rates cannot improve further. It
therefore seems reasonable to conclude that Red-necked Stint numbers at the WTP could be
affected by environmental changes that cause detectable reductions in the amount of
benthos.
The strength of the relationship between benthic biomass and Red-necked Stint foraging
abundance indicates that it should be possible to unravel the functional response (i.e. the
relationship between food intake rates and the density of prey) and construct robust
foraging models. Van Gils et al. (2004) have outlined the requirements of carrying-capacity
models, and have stressed that if they are based only on the functional response and prey
abundance data, they calculate “Giving-up Density” rather than the critical intake rates that
determine the carrying capacity of a site. Foraging models are considerably more powerful if
they include: (1) indices of habitat availability, including changes over time; (2) estimates of
Arthur Rylah Institute for Environmental Research Technical Report Series No. 169
23
the energetic costs associated with specific foraging sites; (3) estimates of the predation
costs associated with specific foraging sites. At the WTP, much of this data is available or
can be collected cheaply. With an exposure map, it will be possible to model foraging habitat
area at all conditions of tide (thus making construction of dynamic foraging models
possible). Energetic costs of commuting between foraging areas and roosts can be calculated
with physiological theory (e.g. Rogers et al. 2006), as radio-telemetry and the simultaneous
counts program have given us a good understanding of shorebird movements in the WTP at
low tide. The relationship between tidal flat width and foraging shorebird abundance may be
a helpful tool in developing an index of predation costs. Robust carrying-capacity models for
shorebirds at the WTP thus appear achievable and would be of considerable management
value, as they would allow prediction of the effects of changes in benthic biomass on
shorebird abundance, and they could be used to calculate target biomasses needed to
maintain shorebird populations.
Arthur Rylah Institute for Environmental Research Technical Report Series No. 169
24
Feeding Red-necked Stints
Feeding Red-necked Stints
1200
A
1000
800
600
400
200
0
0
10
20
30
Edible biomass (g dry mass sq m)
40
10
20
30
40
Edible biomass (g dry mass sq m)
50
1500
B
1000
500
0
0
Figure 8. Relationships between edible biomass and average number of foraging Red-necked Stints at
each foraging site when tidal flats were exposed, in February 2006 (A) and March 2006 (B).
Arthur Rylah Institute for Environmental Research Technical Report Series No. 169
25
5
References
Beasley, L. (2004). ‘Habitat use by Three Species of Sandpiper at the Western Treatment Plant, Victoria’.
Honours Thesis. (School of Ecology and Environment, Deakin University: Melbourne).
Dann, P. (1999). Foraging behaviour and diets of red-necked stints and curlew sandpipers in southeastern Australia. Wildlife Research 27, 61-68.
Davies, S. and Brown, V. (1995). ‘Effect of Effluent from Western Treatment Plant on Benthic Biota:
Monitoring Studies 1983-84’. Research Report 16. (Melbourne Water PLC: Melbourne).
Dittmann, S., Cantin, A., Noble, W. and Pocklington, J. (2006). ‘Macrobenthic Survey 2004 in the Murray
Mouth, Coorong and Lower Lakes Ramsar Site, with an Evaluation of Food Availability for
Shorebirds and Possible Indicator Functions of Benthic Species’. (Department of Environment and
Heritage: Adelaide).
Doornbos, G. and Groenendijk, A.M. (1986). Nakdong estuary barrage and reclamation project:
preliminary results of the botanical macrozoobenthic and ornithological studiesa. Biological
Conservation 38, 115-142.
Gill, J.A., Sutherland, W.J. and K. Norris. (2001). Depletion models can predict shorebird distribution at
different spatial scales. Proceedings of the Royal Society of Biological Sciences 268, 369-376.
Goss-Custard, J.D., West, A.D., Yates, M.G., Caldow, R.W.G., Stillman, R.A.S., Castilla, J., Castro, M,
Dierschke, V, Durell, S.E.A. le V. , Eichhorn, G, Ens, B.J., Exo, K.-M., Fernando, P.U.U., Ferns, P.N.,
Hockey, P.A.R., Gill, J.A., Johnstone, I, Kalejta-Summers, B., Masero, J.A. Moreira, F., Nagarajan, R.,
Owens, I.P.F., Pacheco, C., Perez-Hurtado, A., Rogers, D., Scheiffarth, G., Sitters, H. Sutherland, W.J.,
Triplet, P., Worrall, D.H., Zharikov, Y., Zwarts, L. and Pettifor, R.A. (2006). Intake rates and the
functional response in shorebirds Charadriiformes eating macroinvertebrates. Biological Reviews
81, 501-529.
Higgins, P.J. and Davies, S.J.J.F. (1996). ‘Handbook of Australian, Antarctic, New Zealand and Antarctic
Birds. Volume 3: Snipes to Pigeons’. (Oxford University Press: Melbourne).
Holling, C.S. (1959). Some characteristics of simple types of predation and parasitism. Canadian
Enomology 91. 385-398.
Loyn, R.H., Lane, B.A., Tonkinson, D., Berry, L., Hulzebosch, M., and Swindley, R.J. (2002). ‘Shorebird use
of Managed Habitats at the Western Treatment Plant’. (Arthur Rylah Institute for Environmental
Research and Brett Lane & Associates: Melbourne).
Melbourne Water (2000). ‘Ramsar and Conservation Management Plan’. (Melbourne Water: Melbourne).
Morris, L. and Keough, M. J. (2001). Vertical migration of infaunal invertebrates in response to dosing
with secondary treated sewage effluent: a microcosm experiment. Journal of Aquatic Ecosystem
Stress and Recovery 9, 43-65.
Morris, L. and Keough, M. J. (2002). Organic pollution and its effects: a short-term transplant
experiment to assess the ability of biological endpoints to detect change in a soft sediment
envirnment. Marine Ecology Progress Series 225, 109-121.
Morris, L. and Metcalf, S. (2004). ‘Western Treatment Plant Conservation Management Program:
Analysis of Exisiting Zoobenthos Samples’. Internal PIRVic report No. 11, Department of Primary
Industries. [NOT FOR CITATION WITHOUT PERMISSION]
Pepping, M, Piersma, T, Pearson, G and Mavaleye, M. (1999). ‘Intertidal Sediments and Benthic Animals
of Roebuck Bay, Western Australia’. Report No. 199-3. (Netherlands Institute of Sea Research: Den
Burg).
Poore, G.C.B. and Kudenov, J.D. (1978). Benthos around an outfall of the Werribee Sewage Treatment
farm, Port Phillip Bay, Victoria. Australian Journal of Marine and Freshwater Research 29, 157167.
PPK Environment and Infrastructure Pty Ltd (2000). ‘Little River to Beacons Point Shorebird Study’.
Unpublished report prepared for Melbourne Water. (PPK Environment and Infrastructure Pty Ltd:
Melbourne).
Rogers, D.I., Loyn, R.H., Taylor, I. and Beasley, L. (2004). ‘Radio-telemetry of Red-necked Stints at the
Western Treatment Plant, Feb-Mar 2004’. Informal interim report for Melbourne Water. (Arthur
Rylah Institute for Environmental Research: Heidelberg).
Arthur Rylah Institute for Environmental Research Technical Report Series No. 169
26
Rogers, D.I. and Loyn, R.H. (2007). ‘Shorebird Monitoring at the Western Treatment Plant. Section 5.4 in
Melbourne Water 2007’. Western Treatment Plant: Environment Protection and Biodiversity
Compliance Report for 2006.
Scharler, U.M. and Baird, D. (2005). A comparison of selection ecosystem attributes of three South
African estuaries with different freshwater inflow regimes using network analysis. Journal of
Marine Systems 56, 283-308.
Schieffart, G. and Nehls, G. (1997). Consumption of benthic fauna by carnivorous birds in the Wadden
Sea. Helgoländer Meeresunters 51, 373-387.
Steele, W. (1996). ‘An annotated bibliography of inter-relationships between waterbirds and changes in
effluent flows – with particular reference to the Western Treatment Plant, Victoria. RAOU Report
No. 112, Royal Australasian Ornithologists’ Union, Melbourne.
Taft, O. W. and Haig, S.M. (2005). The value of agricultural wetlands as invertebrate resources for
wintering shorebirds. Agriculture, Ecosystems and Environment 110, 249-256.
Thomas, D.G. and Dartnall, A.J. (1971). Ecological aspects of the feeding behaviour of two calidrine
sandpipers wintering in south-eastern Australia. Emu 71, 20-26.
van Gils, J.A., Edelaar, P., Escudero, G. And Piersma, T. (2004). Carrying capacityr models should not
use fixed prey density thresholds: a plea for using more tools of behavioural ecology. Oikos 104,
197-204.
van Gils, J.A. and Piersma, T. (2004). Digestively constrained predators evade the cost of interference
competition. Journal of Animal Ecology 273, 386-398.
van Gils, J.A, de Rooij, S.R, van Belle, J., van der Meer, J., Dekinga, A., Piersma, T. and Drent, R. (2005a).
Digestive bottleneck affects foraging decisions in red knots (Calidris canutus). I. Prey choice.
Journal of Animal Ecology 74, 105-119.
van Gils, J.A, Dekinga, A., Spaans, B., Vahl, W.K., Piersma, T. (2005b). Digestive bottleneck affects
foraging decisions in red knots (Calidris canutus). II Patch choice and length of working day,
Journal of Animal Ecology 74, 120-130.
Wijnsma, G., Wolff, W., Meijeboom, A., Duiven, P. And de Vlas, J. (1999). Species richness and
distribution of benthic tidal flat fauna of the Banc d’Arguin, Mauritania. Oceanologica Acta 22,
233-243.
Ysebaert, T., Herman, P.M.J., Meire, P.M., Craeymeersch, J.A., Verbeeck, H. and Hiep, C.H.R. (2003). Large
scale spatial patterns in estuaries: estuarine macrobenthic communities in the Schelde estuary,
NW Europe. Estuarine, Coastal and Shelf Science 57, 335-355.
Arthur Rylah Institute for Environmental Research Technical Report Series No. 169
27
Appendix 1. High tide shorebird counts at the WTP, 2004-2007.
Species
19
Jan.
2004
31
Jan.
2004
16
Feb.
2004
11
Dec.
2004
29
Jan.
2005
1
1
7
14
9
Latham's Snipe
Black-tailed Godwit
14
Feb.
2005
3 Mar.
22 Jul.
8 Oct.
5 Nov.
6 Feb.
4 Mar.
2005
22
Dec.
2005
2005
2005
2005
20
7
14
5
10
Eastern Curlew
1
Marsh Sandpiper
39
22
15
11
7
8
9
2
Common Greenshank
17
40
53
23
54
43
31
24
2006
2006
11
11
13
23
9
5
34
25
8
1
1
1
1
2
1
Wood Sandpiper
27
1
3
4263
6172
3
Red Knot
12
2
1
1
2
1
32
113
30
2
37
244
67
41
38
83
32
1
42
41
22
2
1
2
1
2007
1
3
1
6261
8404
6085
3
1
1
1
8455
6373
8040
7978
11632
765
2877
4737
Long-toed Stint
Pectoral Sandpiper
2
1
Sharp-tailed Sandpiper
2706
1034
1107
3906
5882
3405
1442
Curlew Sandpiper
800
1629
2013
546
768
929
585
Ruff
4
2
7411
12370
1
1
46
47
36
23
3805
7620
2630
10
55
987
3736
1715
1
21
60
366
371
267
327
246
Banded Stilt
262
780
2
20
1
Red-necked Avocet
904
431
10
615
812
Pacific Golden Plover
19
30
4
5
Grey Plover
176
65
24
28
28
27
77
203
234
242
194
4
41
65
18
12
15
95
Double-banded Plover
1
14
160
Black-fronted Dotterel
2
2
45
Red-kneed Dotterel
70
74
36
14
2
1
144
67
Wader sp.
25
2
3092
1279
870
1811
892
7
1
1
43
26
16
42
38
30
1
1
1
1
6
408
200
252
302
191
268
205
213
6
217
334
211
63
913
13
1
22
9
20
1
1
1
9
15
9
127
4
17
97
1
1
11
1
12
101
1
35
194
3
2897
367
1
Sooty Oystercatcher
Black-winged Stilt
717
1
2924
1
27
8494
1189
Red-necked Phalarope
Total
15 Jul.
1
1
Ruddy Turnstone
Masked Lapwing
27
Jan.
2007
1
Common Sandpiper
Red-capped Plover
10
Feb.
2007
5
Terek Sandpiper
Pied Oystercatcher
16
Dec.
2006
1
Bar-tailed Godwit
Red-necked Stint
26
Jun.
2006
45
16
3
5
147
1061
610
1078
14
8
16
8
34
4
120
66
2
12
4
79
18
28
2
2
47
27
37
111
68
114
65
125
89
309
64
78
34
76
172
89
15910
12769
14176
1560
4735
8485
12785
24854
14495
1709
11488
14635
9976
912
420
13679
10805
7997
12195
Appendix 2. Low tide shorebird counts at the WTP, 2004-2007.
Species
19
Jan.
2004
31
Jan.
2004
16
Feb.
2004
11
Dec.
2004
29
Jan.
2005
14
Feb.
2005
3 Mar.
2005
22
Jul.
2005
8 Oct.
5 Nov.
2005
2005
Latham's Snipe
Black-tailed Godwit
22
Dec.
2005
6 Feb.
4 Mar.
2006
2006
26
Jun.
2006
12
1
1
8
6
1
Bar-tailed Godwit
1
11
18
7
10
2
1
1
11
11
14
1
11
30
28
1
Marsh Sandpiper
40
32
18
10
5
47
11
2
Common Greenshank
11
19
9
57
27
48
14
19
Wood Sandpiper
1
1
2
1
20
Jul.
2007
9
2
2
32
1
1
2
16
36
106
20
2
15
230
55
50
31
83
33
11
27
47
29
2
1
2
1
10412
8432
446
Terek Sandpiper
1
Common Sandpiper
1
Ruff
1
2
4
2
Grey-tailed Tattler
1
1
Ruddy Turnstone
3
10
7
Red Knot
10
1
8680
15984
10401
8060
13959
7083
5486
706
5194
3377
Long-toed Stint
Pectoral Sandpiper
2
1
1
Sharp-tailed Sandpiper
4097
4984
2120
2326
3377
3305
1163
Curlew Sandpiper
1303
1634
1144
737
918
553
193
8038
9036
4055
1
6
1
2
2
847
4209
3190
5430
2038
2
419
1004
1939
535
Broad-billed Sandpiper
2
2
Red-necked Phalarope
1
18
19
32
46
49
57
41
27
30
37
20
14
Black-winged Stilt
433
730
120
290
295
241
126
Banded Stilt
353
527
47
15
1
49
1
Red-necked Avocet
544
723
320
790
910
93
42
11
16
38
11
31
10
29
7
176
1
18
353
Pacific Golden Plover
158
331
223
10
Double-banded Plover
27
9
Black-fronted Dotterel
1
1
6
1
203
37
1
1
2
3172
1334
1378
380
1655
1387
3
28
20
32
423
185
275
278
16
31
1
1
158
206
128
138
215
97
1084
3
16
16
22
9
48
103
180
1
36
196
5
1
8
5791
5
6
Grey Plover
14
80
859
1
19
Sooty Oystercatcher
Red-capped Plover
27
Jan.
2007
1
Eastern Curlew
Pied Oystercatcher
10
Feb.
2007
1
16
Little Curlew
Red-necked Stint
16
Dec.
2006
27
11
1
29
144
119
6
1482
640
13
2
1170
24
35
22
88
3
8
15
2
18
3
30
4
121
Red-kneed Dotterel
1
3
1
1
2
5
2
27
Masked Lapwing
44
60
8
47
70
116
41
48
76
96
15
168
105
60
5
74
107
42
Oriental Pratincole
2
Total
15551
24730
14258
12440
19645
11678
7204
1547
6707
8825
12698
17439
8266
1837
11203
14751
12888
878
ISBN 978-1-74208-223-3 (Print)
ISBN 978-1-74208-224-0 (Online)
ISSN 1835 3827 (Print)
ISSN 1835 3835 (Online)