Management and Conservation Article
Habitat Use by Migrant Shorebirds in Saline Lakes of the
Southern Great Plains
ADRIAN E. ANDREI,1,2 Texas Tech University, Box 42125, Lubbock, TX 79409-2125, USA
LOREN M. SMITH, Department of Zoology, Oklahoma State University, Stillwater, OK 74078, USA
DAVID A. HAUKOS, United States Fish and Wildlife Service, Texas Tech University, Box 42125, Lubbock, TX 79409-2125, USA
JAMES G. SURLES, Department of Mathematics and Statistics, Texas Tech University, Box 1042, Lubbock, TX 79409-1042, USA
ABSTRACT Shorebirds migrating through the Southern Great Plains of North America use saline lakes as stopovers to rest and replenish
energy reserves. To understand how availability of invertebrates, salinity, freshwater springs, vegetation, and water influence the value of saline
lakes as migration stopovers, we compared lakes used and not used by migrant shorebirds. Shorebirds used lakes that had freshwater springs,
mudflats and standing water, sparse vegetation (1% cover), low to moderate salinities (x̄ ¼ 30.87 g/L), and mean invertebrate biomass of 0.79
g/m2. Lakes that were not used were generally dry or had hypersaline water (x̄ ¼ 82.56 g/L), lacked flowing springs and vegetation, and had few
or no invertebrates (x̄ ¼ 0.007 g/m2). Our results suggest that reduced spring flows and increased salinity negatively affect availability of
shorebird habitats and aquatic invertebrates. We recommend preservation of the freshwater springs discharging in the saline lakes. Because the
springs are discharged from the Ogallala aquifer, which is recharged through the playa wetlands, the entire complex of wetlands in the Great
Plains and the Ogallala aquifer should be managed as an integral system. ( JOURNAL OF WILDLIFE MANAGEMENT 72(1):246–253;
2008)
DOI: 10.2193/2007-144
KEY WORDS freshwater springs, invertebrates, migration stopovers, Ogallala aquifer, saline lakes, shorebirds, Southern Great
Plains.
Tens of thousands of shorebirds migrating through interior
North America use saline lakes in the Southern Great Plains
(SGP) of west Texas and eastern New Mexico, USA, as
stopovers to replenish energy reserves (Andrei et al. 2006).
These saline lakes are key habitats not only for migrant
shorebirds, but also for nesting shorebirds and sandhill
cranes (Grus canadensis; Iverson et al. 1985, Reeves and
Temple 1986, Conway et al. 2005, Andrei et al. 2006). The
approximately 45 saline lakes are discharge wetlands deeply
incised into the short-grass prairie (Brüne 1981, Reeves and
Reeves 1996). Abundant springs fed by the Ogallala aquifer
historically discharged in the saline lakes (Brüne 1981), but
in the past few decades, spring flows have been reduced due
to declining aquifer levels (Triplet 1998, Sophocleous 2000).
It is unclear how reduced hydroperiods may affect
availability of shorebird foraging habitats and prey in the
saline lakes. Further, it is unknown how migrant shorebirds
select among the saline lakes and which lakes are most
valuable as stopovers.
During migration, shorebirds select wetlands that offer
sparse vegetation, mudflats, and shallow water, where
foraging conditions are favorable (Weber and Haig 1996,
Davis and Smith 1998). However, reduced spring flows in
saline lakes may result in higher salt concentrations. At
increased salinity levels, invertebrates spend more energy
osmoregulating and less energy growing and reproducing
(Herbst 1992, 1999). Thus, increased salinities in the SGP
saline lakes may reduce availability of prey needed by
shorebirds to replenish energy reserves and continue
1
E-mail: andreia@lincolnu.edu
Present address: Department of Agriculture, Lincoln University of
Missouri, 820 Chestnut Street, Jefferson City, MO 65101, USA
2
246
migration at a time when most shorebird populations in
the Western Hemisphere are declining (Brown et al. 2001,
Fellows et al. 2001, International Wader Study Group
2003).
We compared lakes used and not used by migrant
shorebirds during spring and summer–autumn to understand how availability of water, invertebrates, and salinity
influence use of saline lakes as migration stopovers. Our
objectives were to 1) evaluate habitat characteristics such as
water depth, invertebrate availability, vegetation cover, and
salinity at lakes used and not used by shorebirds; 2) estimate
the effect of salinity on invertebrate availability; and 3)
propose management recommendations for shorebirds
migrating through the SGP.
STUDY AREA
We conducted the study on saline lakes in Andrews, Bailey,
Castro, Dawson, Gaines, Lamb, Lynn, Parmer, and Terry
counties in northwest Texas and in Curry, Lea, Quay, and
Roosevelt counties in eastern New Mexico (Fig. 1). We
located the saline lakes defined by Reeves and Reeves (1996)
and surveyed all lakes for which landowner permission was
granted. We surveyed 21 lakes during spring 2002, 25 lakes
during autumn 2002, and 27 lakes during spring and
autumn 2003.
The approximately 45 saline lakes formed through a
combination of dissolution of salts and wind deflation
(Reeves and Reeves 1996), and the hydroperiods depended
on precipitation and springs fed by the Ogallala aquifer
(Brüne 1981). Originally short- to mid-grass prairie, the
SGP was one of the most intensively cultivated regions in
the Western Hemisphere (Bolen et al. 1989). Preceding and
during data collection, precipitations recorded in Lubbock,
The Journal of Wildlife Management
72(1)
Figure 1. Location of saline lakes and shorebird study area in the Southern
Great Plains of New Mexico and Texas, USA, during spring and autumn of
2002 and 2003 (after Reeves and Reeves 1996).
Texas, were below the 48-cm average (2001: 32.9 cm; 2002:
47.6 cm; 2003: 20.9 cm; National Oceanic and Atmospheric
Administration 2004).
METHODS
Field and Laboratory Methods
Invertebrate availability, vegetation cover, and salinity.—
We collected invertebrates weekly in each lake throughout
spring and summer–autumn of 2002 and 2003. We assigned
30-m transects in areas with the highest shorebird use in the
used lakes and in the areas that would be considered optimal
shorebird habitat (i.e., mudflats interspersed with shallow
water) in the lakes where shorebirds were not present (used
lakes: spring 2002, n ¼ 13; autumn 2002, n ¼ 12; spring
2003, n ¼ 15; autumn 2003, n ¼ 15; nonused lakes: spring
2002, n ¼ 4; autumn 2002, n ¼ 5; spring 2003, n ¼ 5; autumn
2003, n ¼ 3). Along transects, we collected invertebrates at
random points by taking 5 5 3 10-cm benthic core samples
and 5 water column samples (2,000 mL vol; Swanson
1978, 1983; Davis and Smith 1998). We took water column
samples from areas that had water depths .3 cm because
water depths ,3 cm were too shallow for the water column
device to effectively collect invertebrates. To determine
Andrei et al.
Habitat Use by Migrant Shorebirds
relative abundance of mobile invertebrates, we used 5 pitfall
traps partially filled with water and detergent installed for a
period of 24 hours on moist mudflats and dry mudflats in
areas used by shorebirds (Luff 1975, van den Bergh 1992).
We did not sample invertebrates in lakes that were
completely dry. We washed all samples through a 0.5-mm
sieve and preserved invertebrates in 80% ethanol. We
counted and identified invertebrates to family, oven dried
them to constant mass at 658 C, and weighed them
(Peterson 1979a, b; McAlpine et al. 1981; Pennak 1989;
Merritt and Cummins 1996).
We used a laser rangefinder to measure and estimate
percent cover of vegetation in each lake and noted presence
or absence of flowing springs. Between March and
December 2003, we used a portable salinity meter to
measure salinity of surface water associated with most
invertebrate availability samples. We measured salinity
associated with invertebrate samples in lakes that had at
least some standing water during 2003 (used lakes: n ¼ 9;
nonused lakes: n ¼ 4).
Habitat use and availability.—We surveyed all shorebirds weekly during spring (10 Mar–15 Jun 2002 and 2
Mar–7 Jun 2003) and summer–autumn (7 Jul–9 Nov 2002
and 7 Jul–8 Nov 2003). We used binoculars and a spotting
scope to count all shorebirds within each lake from one
location on the edge of the lake or by walking around the
edge of the lake when not all shorebirds were visible from
one location. We minimized bias associated with conducting
surveys on the same lake at the same time on consecutive
weeks by randomly assigning weekly survey times for each
lake to 1 of 3 diurnal periods: early day (sunrise–1100 hr),
midday (1100–1500 hr), and late day (1500 hr–sunset;
Bergan et al. 1989). We estimated percentage cover of dry
flats, mudflats and shallow water (,4 cm depth), moderate
water (4–16 cm depth), and deep water (.16 cm depth) in
all lakes during each shorebird survey. We estimated percent
cover of each water-depth type within each lake by
measuring with a meter stick and by estimating depth
relative to the length of shorebirds legs when shorebirds
were present, (Baker 1971, Davis and Smith 1998). For
lakes where shorebirds were either not present or not
dispersed throughout each water-depth type, we estimated
percentage cover of each water depth by measuring water
depths with a meter stick at 1-m intervals along 3–6
transects within each lake (depending on lake size and water
coverage) and plotting the water depths on maps of each
lake.
Statistical Analyses
Invertebrate availability, vegetation cover, and salinity.—
We summarized invertebrate taxa available in all lakes by
aggregate percent dry mass and percentage occurrence
(Prevett et al. 1979). For analyses, we conservatively defined
used lakes as those in which we observed 1 shorebird
during a migration season (i.e., spring or autumn) and
nonused lakes as those where we observed no shorebirds
during a migration season. We averaged invertebrate
familial richness, biomass (i.e., dry mass/m2), and density
247
(i.e., individuals/m2) within each lake during each season of
each year, and we used analysis of variance (ANOVA) to
determine differences in biomass, density, and familial
richness of invertebrates between used and nonused lakes.
Richness, biomass, and density were dependent variables,
whereas lake type (i.e., used or nonused), year, and season
were independent variables. We also averaged biomass and
density of 7 families of invertebrates (i.e., Chironomidae,
Tipulidae, Corixidae, Ceratopogonidae, Artemiidae, Stratiomyidae, and Ephydridae) within each lake during each
season and year. These families represented the most
abundant invertebrates in benthic-core, water-column, and
pitfall-trap samples and also represented .90% of prey
taken by American avocets (Recurvirostra americana), least
sandpiper (Calidris minutilla), lesser yellowlegs (Tringa
flavipes), and Wilson’s phalarope (Phalaropus tricolor) during
our study (Andrei 2005). For each invertebrate family, we
used factorial ANOVAs to test for differences in biomass
and density between used and nonused lakes, seasons, and
years. Following significant (P , 0.05) main effects and
nonsignificant (P . 0.05) interactions, we used separate 1way ANOVAs to compare biomass, density, and richness of
invertebrates between used and nonused lakes.
Because percentage cover of vegetation and presence or
absence of flowing springs did not change between weekly
surveys, we used each lake during each season of each year as
replicates. Due to the binomial distribution of data, we used
logistic regression models and odds ratios with 95%
confidence intervals (Allison 1999, Bland and Altman
2000) to examine the effect of presence of springs and
vegetation on probability of lakes being used by shorebirds.
We used odds-ratio estimates to calculate the probabilities,
likelihood-ratio chi-square statistics to test significance of
logistic regression models, and Wald chi-square to test the
effect of each variable (Agresti 1996, Quinn and Keough
2002).
We assumed that measurements of salinity recorded
within a lake were not independent of each other. Therefore, we averaged across seasons salinity samples collected
within each lake, and we used an independent-sample t-test
to compare salinities of lakes used with those not used by
shorebirds (used: n ¼ 9; nonused: n ¼ 4). Similarly, we
averaged biomass and familial richness of all invertebrates
collected in benthic-core and water-column samples by lake
and across seasons and used nonlinear regression analyses to
examine potential effects of salinity on biomass and familial
richness of all invertebrates (Zar 1996). Average salinity
within each lake was the independent variable, whereas
mean biomass and mean familial richness within each lake
were dependent variables. Further, we used separate
regression analyses to examine potential relationships
between salinity and biomass of Chironomidae (nonbiting
midges), Ceratopogonidae (biting midges), Tipulidae (crane
flies), Ephydridae (brine flies), and Artemiidae (brine
shrimp).
Habitat use and availability.—To examine availability
of water depth types to all shorebirds using the saline lakes
248
during migration, we categorized lakes by shorebird use (%
of all shorebirds obs/season) into nonused lakes, lightly used
lakes (0–1% of all shorebirds obs/season), moderately used
lakes (1–10% of all shorebirds obs/season), and heavily used
lakes (.10% of all shorebirds obs/season). We averaged
percentage cover of each water-depth type within each lake
for each season of each year (i.e., lakes were replicates).
Within each water depth, we used a factorial ANOVA to
compare percentage cover between seasons and years and
among lake use categories. Following significant (P 0.05)
interactions in ANOVAs, we used ANOVAs and Fisher’s
least significant difference tests to compare percentage cover
of water depth among lake use categories within each season
of each year. We present means 6 standard error. We used
the Statistical Analysis System (SAS Institute Inc., Cary,
NC) for all analyses.
RESULTS
Invertebrate Availability, Vegetation Cover, and Salinity
We identified 44 families of macroinvertebrates from
benthic-core, water-column, and pitfall-trap samples collected in the saline lakes. The most abundant order was
Diptera, which accounted for 65.94–84.10% of aggregate
dry mass within each season (Table 1). Within Diptera, the
most abundant families were Chironomidae, Ephydridae,
Tipulidae, and Ceratopogonidae.
Lakes used by shorebirds had greater (F1,64 ¼ 162.33, P ,
0.001) familial richness of invertebrates than nonused lakes
(Table 2). There were no lake type 3 season 3 year (F1,64 ¼
1.23, P ¼ 0.271), lake type 3 season (F1,64 ¼ 1.08, P ¼
0.307), or lake type 3 year (F1,64 ¼ 3.05, P ¼ 0.085)
interactions in the analysis of familial richness. Biomass of
invertebrates was greater (F1,64 ¼ 29.77, P , 0.001) in used
lakes than in nonused lakes (Table 2). There were no lake
use 3 year (F1.64 ¼ 1.22, P ¼ 0.27), lake use 3 season (F1,64 ¼
1.40, P ¼ 0.24), or lake use 3 season 3 year (F1,64 ¼ 2.76, P ¼
0.10) interactions for invertebrate biomass.
Invertebrate density was greater (F1,64 ¼ 30.03, P , 0.001)
in used lakes than in nonused lakes (Table 2). There were no
lake use 3 season 3 year (F1,64 ¼ 2.25, P ¼ 0.14), lake use 3
season (F1,64 ¼ 0.63, P ¼ 0.43), or lake use 3 year (F1,64 ¼
0.01, P ¼ 0.92) interactions for invertebrate density.
Chironomidae, Ceratopogonidae, Corixidae, Ephydridae,
and Tipulidae were more abundant in lakes used by
shorebirds than in nonused lakes. Biomass and density of
Stratiomyidae and Artemiidae did not differ between used
and nonused lakes (Table 2, Appendix).
Salinity was greater (t12 ¼ 4.10, P , 0.001) in nonused
lakes (x̄ ¼ 82.56 g/L, SE ¼ 18.93, n ¼ 4) than in lakes used
by shorebirds (x̄ ¼ 30.87 g/L, SE ¼ 2.72, n ¼ 9). Invertebrate
biomass was a function of salinity (r2 ¼ 0.87, F1,11 ¼ 77.81, P
, 0.001), with biomass decreasing sharply between 20 g/L
and 40 g/L (Fig. 2). Salinity also influenced familial richness
of invertebrates (r2 ¼ 0.79, F1,11 ¼ 42.65, P , 0.001).
Locations with high mean salinity had fewer taxa in benthos
and the water column (Fig. 2). Dry weights of Chironomidae (r2 ¼ 0.40, F1,11 ¼ 7.40, P ¼ 0.02), Ceratopogonidae
The Journal of Wildlife Management
72(1)
Table 1. Seasonal aggregate percent dry mass and percent occurrence of macroinvertebrates in benthic core, water column, and pitfall traps from shorebird
foraging areas in saline lakes of the Southern Great Plains of northwest Texas and eastern New Mexico, USA, during spring and summer–autumn, 2002–
2003.
Class
Aggregate %
Order
Spring
Family
Branchiopoda
Anostraca
Artemiidae
Arachnida
Aranea
Gnaphosidae
Salticidae
Lycosidae
Insecta
Coleoptera
Anthicidae
Byrrhidae
Carabidae
Cincidelidae
Coccinelidae
Curculionidae
Elateridae
Euglenidae
Heteroceridae
Hydrophilidae
Malachiidae
Staphilinidae
Hemiptera
Aphididae
Corixidae
Hebridae
Saldidae
Heteroptera
Anthocoridae
Veliidae
Diptera
Agromyzidae
Calliphoridae
Ceratopogonidae
Chironomidae
Culicidae
Dolichopodidae
Drosophilidae
Ephydridae
Muscidae
Mycetophylidae
Sarcophagidae
Sphaeroceridae
Stratiomyidae
Syrphydae
Tabanidae
Tachinidae
Tipulidae
Homoptera
Cicadellidae
Hymenoptera
Formicidae
Sphaecidae
Lepidoptera
Lycaenidae
Orthoptera
Acrididae
Thysanoptera
Thripidae
Andrei et al.
% occurrence
Autumn
Spring
Autumn
2002
2003
2002
2003
2002
2003
2002
2003
0.21
0.21
0.21
5.20
5.20
1.95
2.98
0.27
94.58
18.23
0.48
0.55
2.50
10.79
0.95
0.00
0.74
0.50
0.45
0.40
0.00
0.87
5.76
0.09
2.24
0.82
2.61
0.00
0.00
0.00
65.94
0.34
0.00
7.54
26.43
0.00
0.00
0.05
11.53
0.00
0.00
0.00
0.02
2.02
0.00
1.84
0.05
16.12
0.57
0.57
1.02
1.02
0.00
3.00
3.00
0.00
0.00
0.06
0.06
1.86
1.86
1.86
5.25
5.25
1.35
3.72
0.18
92.93
19.86
0.45
0.00
3.70
13.17
0.66
0.00
0.00
0.27
0.17
0.00
0.26
1.18
9.14
0.04
4.68
0.27
4.15
0.00
0.00
0.00
62.99
0.00
0.00
7.15
32.25
0.22
0.00
0.00
16.36
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
7.01
0.00
0.00
0.26
0.26
0.00
0.17
0.17
0.45
0.45
0.06
0.06
0.09
0.09
0.09
0.72
0.72
0.10
0.00
0.62
99.17
8.88
0.68
0.67
1.06
4.90
0.00
0.71
0.00
0.42
0.44
0.00
0.00
0.00
6.35
0.01
4.85
0.00
1.49
0.13
0.00
0.13
79.32
0.00
0.15
5.34
60.35
0.00
0.02
0.06
5.10
0.00
0.01
0.00
0.00
3.11
0.01
0.00
0.00
5.18
0.19
0.19
1.49
1.49
0.00
2.81
2.81
0.00
0.00
0.00
0.00
1.64
1.64
1.64
2.35
2.35
2.29
0.00
0.06
95.47
7.79
0.51
0.00
5.47
0.00
0.00
0.00
0.00
0.32
0.96
0.00
0.00
0.53
1.45
0.05
0.73
0.00
0.67
0.37
0.02
0.35
84.10
0.02
0.00
8.51
39.99
0.31
0.00
0.06
12.73
0.07
0.00
0.85
0.00
11.10
0.00
0.12
0.00
10.34
0.43
0.43
1.27
0.93
0.34
0.00
0.00
0.00
0.00
0.06
0.06
0.64
0.64
0.64
0.55
0.55
0.10
0.25
0.20
98.83
4.21
0.30
0.10
1.58
0.30
0.05
0.00
0.05
0.69
0.10
0.25
0.00
0.79
4.79
0.54
1.53
0.84
1.88
0.00
0.00
0.00
87.26
0.94
0.00
28.80
17.34
0.00
0.00
0.30
20.26
0.00
0.00
0.00
0.05
0.89
0.00
0.15
0.05
18.48
0.35
0.35
1.28
1.28
0.00
0.74
0.74
0.00
0.00
0.20
0.20
4.11
4.11
4.11
0.50
0.50
0.06
0.28
0.16
95.35
2.39
0.25
0.00
1.06
0.25
0.03
0.00
0.00
0.37
0.03
0.00
0.03
0.37
4.75
0.25
3.33
0.25
0.93
0.00
0.00
0.00
87.58
0.00
0.00
25.06
36.80
0.53
0.00
0.00
17.06
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
8.13
0.00
0.00
0.25
0.25
0.00
0.19
0.19
0.06
0.06
0.13
0.13
0.31
0.31
0.31
0.41
0.41
0.08
0.00
0.33
99.28
1.74
0.26
0.10
0.26
0.15
0.00
0.05
0.00
0.79
0.13
0.00
0.00
0.00
4.46
0.08
4.02
0.00
0.36
0.28
0.00
0.28
91.39
0.00
0.05
26.50
53.02
0.00
0.08
0.20
5.93
0.00
0.03
0.00
0.00
1.36
0.03
0.00
0.00
4.22
0.13
0.13
0.79
0.79
0.00
0.49
0.49
0.00
0.00
0.00
0.00
2.40
2.40
2.40
0.42
0.42
0.25
0.00
0.17
97.17
1.40
0.13
0.00
0.55
0.00
0.00
0.00
0.00
0.34
0.21
0.00
0.00
0.17
1.35
0.25
0.76
0.00
0.34
0.59
0.04
0.55
92.91
0.04
0.00
32.18
30.88
0.76
0.00
0.29
15.50
0.08
0.00
0.04
0.00
3.45
0.00
0.34
0.00
9.35
0.21
0.21
0.50
0.42
0.08
0.00
0.00
0.00
0.00
0.21
0.21
Habitat Use by Migrant Shorebirds
249
Table 2. Familial richness, biomass (g/m2), and density (no. of individuals/
m2) of 7 invertebrate families collected from saline lakes used and not useda
by shorebirds in the Southern Great Plains, USA, during spring and
summer–autumn migration, 2002–2003.
Nonused lakes
x̄
Familial richness
0.32Ab
Biomass
0.007A
Density
57.22A
Chironomidae biomass
0.0003A
Chironomidae density
0.71A
Tipulidae biomass
0.0004A
Tipulidae density
3.85A
Corixidae biomass
0.00003A
Corixidae density
0.35A
Ceratopogonidae biomass 0.0007A
Ceratopogonidae density 15.62A
Ephydridae biomass
0.005A
Ephydridae density
38.68A
Artemiidae biomass
0.005A
Artemiidae density
1.40A
Stratiomyidae biomass
0.001A
Stratiomyidae density
0.001A
SE
Used lakes
x̄
SE
0.12
2.06B
0.06
0.001
0.79B
0.06
9.28
2,615.85B 223.90
0.0001
0.38B
0.05
0.65
1,117.13B 207.37
0.0001
0.05B
0.01
2.71
184.29B 33.60
0.00001
0.04B
0.01
0.35
95.36B 22.00
0.0002
0.04B
0.006
4.23
648.33B 91.73
0.001
0.08B
0.01
6.14
350.38B 44.00
0.001
0.08B
0.01
0.67
52.57A 14.09
0.00
0.02A
0.01
0.00
34.75A 18.79
a
Nonused lakes: spring 2002, n ¼ 4 lakes; autumn 2002, n ¼ 5; spring
2003, n ¼ 5; autumn 2003, n ¼ 3. Used lakes: spring 2002, n ¼ 13; autumn
2002, n ¼ 12; spring 2003, n ¼ 15; autumn 2003, n ¼ 15.
b
x̄ with the same letter within a row are not different (P . 0.05).
(r2 ¼ 0.50, F1,11 ¼ 11.18, P ¼ 0.006), and Tipulidae (r2 ¼
0.42, F1,11 ¼ 8.20, P ¼ 0.02) decreased at salinity levels
between 30 g/L and 40 g/L (Fig. 3). Biomasses of
Ephydridae (r2 ¼ 0.24, F1,11 ¼ 3.50, P ¼ 0.09) and
Artemiidae (r2 ¼ 0.06, F1,11 ¼ 0.14, P ¼ 0.72) were low
but were not negatively influenced by salinity (Table 2).
Vegetative cover, when present, was 1% (nonused lakes,
spring 2002: x̄ ¼ 0.22% cover, SE ¼ 0.14; autumn 2002: x̄ ¼
0.15%, SE ¼ 0.14; spring 2003: x̄ ¼ 0.12%, SE ¼ 0.11; x̄ ¼
0.09%, SE ¼ 0.08. used lakes, spring 2002: x̄ ¼ 0.67%, SE ¼
0.15; autumn 2002: x̄ ¼ 0.50%, SE ¼ 0.12; spring 2003: x̄ ¼
0.53%, SE ¼ 0.18; autumn 2003: x̄ ¼ 0.63%, SE ¼ 0.13).
All lakes that had flowing springs also had vegetation and
were used by migrant shorebirds. Lakes without flowing
springs did not have vegetation. There was no lake use 3
season 3 year interaction in logistic regression (v21 ¼ 0.03, P
¼ 0.855) but there was a lake-use effect (v21 ¼ 16.44, P ,
0.001). The probability of a lake being used by shorebirds
given that it had vegetation and springs was 0.88. The
probability of a lake being used by shorebirds when it lacked
vegetation and flowing springs was 0.44 (odds ratio ¼ 9.10,
CL ¼ 3.13–26.49).
Habitat Use and Availability
Mean percent cover of dry flats was greater (F3,84 ¼ 9.42, P
, 0.001) in lightly used (93.55 6 8.38%) and moderately
used (72.19 6 6.93 %) lakes than in nonused (46.84 6
5.90%) and heavily used (41.07 6 9.02%) lakes. There
were no lake use 3 season 3 year (F3,84 ¼ 1.43, P ¼ 0.24),
lake use 3 year (F3,84 ¼ 0.73, P ¼ 0.54), or lake use 3 season
(F3,84 ¼ 0.52, P ¼ 0.67) interactions.
250
Figure 2. Regression models for the effect of salinity on the biomass and
familial richness of invertebrates collected in saline lakes of the Southern
Great Plains of New Mexico and Texas, USA, March–December 2003.
Mean percent cover of mudflats and shallow water (,4
cm) varied by lake use 3 year 3 season (F3,84 ¼ 3.33, P ¼
0.02). There were no lake use 3 season interactions during
2002 (F3,38 ¼ 1.94, P ¼ 0.14) and 2003 (F3,46 ¼ 2.02, P ¼
0.12). In 2002, heavily used (19.06 6 2.19%) and
moderately used (12.79 6 1.72%) lakes had greater (F3,38
¼ 21.07, P , 0.001) percent cover of mudflats and shallow
water than lightly used (2.48 6 0.15%) and nonused (0.56
6 0.05%) lakes. Similarly, in 2003, heavily (16.29 6
3.42%) and moderately (13.32 6 2.56%) used lakes had
greater (F3,46 ¼ 7.76, P , 0.001) cover of mudflats than
lightly used (5.82 6 0.79%) and nonused (0.45 6 0.06%)
lakes.
Coverage by moderate water depth (4–16 cm) varied by
lake use 3 year 3 season (F3,84 ¼ 2.99, P ¼ 0.03). During
2002 there was a lake use 3 season interaction (F3,38 ¼ 2.99,
P ¼ 0.01). During spring (F3,17 ¼ 8.82, P , 0.001), mean
percent cover of moderate water depth was greater in heavily
(21.60 6 2.94%) and moderately (16.19 6 2.40%) used
lakes than in lightly (0.0 6 0.0%) and nonused (0.0 6
0.0%) lakes. During autumn (F3,21 ¼ 27.77, P , 0.001),
heavily used lakes (13.26 6 2.94%) had the most moderate
depth water, whereas percent cover did not differ among
moderately used (2.61 6 2.22%), lightly used (0.0 6
0.0%), and nonused (0.0 6 0.0%) lakes. During 2003 there
was no lake use 3 season interaction (F3,46 ¼ 1.76, P ¼ 0.17)
The Journal of Wildlife Management
72(1)
lightly used (0.0 6 0.0%), or nonused (0.0 6 0.0%) lakes.
During 2003, there was no lake use 3 season interaction
(F3,46 ¼ 2.55, P ¼ 0.07) by deep water. Percent cover of deep
water was greater (F3,46 ¼ 6.17, P ¼ 0.001) in heavily used
lakes (15.35 6 3.58%) than in moderately (5.83 6 2.69%),
lightly (0.0 6 0.0%), and nonused lakes (0.0 6 0.0%).
DISCUSSION
Figure 3. Regression models for the effect of salinity on the biomass of
Chironomidae, Ceratopogonidae, and Tipulidae collected in saline lakes of
the Southern Great Plains of New Mexico and Texas, USA, March–
December 2003.
in percent cover of moderate depth water. Percent moderate
water depth was greatest (F3,46 ¼ 13.93, P , 0.001) in
heavily used lakes (17.23 6 2.37%) and did not differ
among moderately used (3.93 6 1.78%), lightly used (0.0
6 0.0%), and nonused (0.0 6 0.0%) lakes.
There was a lake use 3 season 3 year interaction (F3,84 ¼
7.48, P , 0.001) in analyses of coverage by deep water (.16
cm). During 2002, there was a lake use 3 season interaction
(F3,38 ¼ 7.02, P , 0.001). During spring (F3,17 ¼ 13.23, P ,
0.001), average percent cover of deep water was greater in
heavily used (30.44 6 4.90%) lakes than in moderately used
(4.46 6 4.01%), lightly used (0.0 6 0.0%) and nonused
(0.0 6 0.0%) lakes. Similarly, during autumn (F3,20 ¼
19.68, P , 0.001), heavily used lakes had more deep water
(46.59 6 4.91%) than moderately used (1.17 6 0.10%),
Andrei et al.
Habitat Use by Migrant Shorebirds
Invertebrate Availability, Vegetation Cover, and Salinity
Higher abundances of invertebrates in lakes used by
shorebirds compared to nonused lakes indicate that prey
availability was an important factor for shorebirds to
remain on the lakes initially selected for water availability.
Invariably, lakes that had flowing springs also had
mudflats and shallow water, low salinities, invertebrates,
and sparse vegetation. Patches of herbaceous vegetation in
the vicinity of springs discharging into the lakes may
function as visual clues indicating favorable stopover sites
to flying shorebirds. The small percent vegetation coverage
(0–1%) was likely due to the effects of salinity (Bertness et
al. 1992). Extensive algal mats present on mudflats during
summer and autumn (A. Andrei, Texas Tech University,
unpublished data) indicate that microalgae, rather than
macrophytes, may account for most primary productivity
(Hart and Lovvorn 2003). Invasive salt cedar (Tamarix
spp.) formed dense stands on several saline lakes (A.
Andrei, unpublished data), which may alter hydroperiods
of saline lakes through high evapo-transpiration, further
reducing the availability of water (Cleverly et al. 2002,
Dahm et al. 2002).
Salinity was lower in used lakes than in nonused lakes and
played an important role in the distribution and abundance
of invertebrates. Overall, we found most invertebrate
biomass at salinities ,40 g/L. Stratiomyidae, Artemiidae,
and Ephydridae did not differ between used and nonused
lakes, likely because of their tolerance to high salinities. The
amount of water, influenced by precipitation, spring flow,
and evaporation, determines the salinity levels in saline
lakes. In turn, salinity plays an important role in structuring
invertebrate communities and may alter secondary productivity (Williams 1998, Wolfram et al. 1999, Herbst 2006).
Prolonged periods of drought and cessation of flow in the
springs may cause lakes to increase salinity levels .40 g/L or
to dry completely. Completely dry lakes were not used by
migrant shorebirds, whereas salinities .40 g/L reduced
invertebrate biomass and richness. Similar to other hypersaline waters where salinities were .40 g/L (Herbst 2004,
Silberbush et al. 2004), only brine shrimp (Artemia spp.) and
brine flies (Ephydra spp.) were present, whereas lakes with
salinities .120 g/L had no invertebrates. Thus, the saline
lakes may cease to serve as wetlands for shorebirds to forage
and replenish energy reserves if declines of the water tables,
drying of springs, and salinization continue. Decreasing
numbers of available stopovers will likely have a further
negative impact on populations of shorebirds migrating
through the Great Plains (Skagen and Knopf 1993).
251
Habitat Use and Availability
Water depth is an important factor determining shorebird
use of wetlands (Hands et al. 1991, Verkuil et al. 1993,
Skagen and Knopf 1994). Shallow water may be more
important than other factors, such as invertebrate density, as
a habitat selection cue for shorebirds, (Helmers 1992, Safran
et al. 1997, Davis and Smith 1998). In general, lakes that
had mudflats and a range of water depths attracted the most
birds. Deeper lakes (16 cm) appear attractive to large
numbers of Wilson’s phalaropes (Andrei et al. 2006).
Through evaporation, deeper lakes become shallower and
attract other shorebirds. If adequate surface water is present
during spring and autumn, saline lakes attract and serve as
migration stopovers for tens of thousands of shorebirds
(Andrei et al. 2006).
Invertebrate communities in saline lakes differed from
those in neighboring playa wetlands (Anderson 1997, Davis
and Smith 1998) of the region. Unlike playa wetlands,
Diptera (midges, biting midges, crane flies, and brine flies)
larvae were dominant in salt lakes, and there were no
pulmonate gastropods (wheel snails – Planorbidae), segmented worms (Hirudinea), or roundworms (Oligochaeta).
Beetles such as Dytiscidae were absent in saline lakes,
whereas Hydrophilidae were rarely present. Overall, the
familial richness of invertebrates found in the saline lakes
indicates that these wetlands contribute to the biodiversity
of the SGP, as long as they are not dry.
MANAGEMENT IMPLICATIONS
The freshwater springs extended the hydroperiods of the
lakes and maintained relatively low levels of salinity, which
were conditions necessary for development of aquatic
invertebrates. To maintain the saline lakes as shorebird
habitats, management and conservation should focus on
preservation of freshwater springs and groundwater. Because
the springs are fed by the Ogallala aquifer and the aquifer is
recharged through playa wetlands, the entire complex of
wetlands in the SGP and the Ogallala aquifer should be
regarded and preserved as an integral system (Osterkamp
and Wood 1987, Nativ 1992, Smith 2003).
ACKNOWLEDGMENTS
Research was funded in part by Texas Tech University,
United States Fish and Wildlife Service, Playa Lakes Joint
Venture, and Texas Parks and Wildlife. L. M. Smith was
supported by the Caesar Kleberg Foundation for Wildlife
Conservation. We thank W. Johnson and S. McMurry for
comments on the manuscript. We thank all landowners for
allowing us access to their properties. I. Wennihan, E.
Black, and A. Andrei sorted invertebrates. This is manuscript T-9-1135 of the College of Agricultural Sciences and
Natural Resources, Texas Tech University.
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Appendix. Analyses of variance of biomass and density by season, year, and lake use (used or not used by shorebirds) of the most abundant invertebrate
families collected from benthic, water-column, and pitfall-trap samples in saline lakes of the Southern Great Plains, USA, during spring and autumn
shorebird migrations, 2002–2003.
Biomass
Family
Factor
Chironomidae
Ceratopogonidae
Corixidae
Tipulidae
Ephydridae
Andrei et al.
Lake
Lake
Lake
Lake
Lake
Lake
Lake
Lake
Lake
Lake
Lake
Lake
Lake
Lake
Lake
Lake
Lake
Lake
Lake
Lake
use
use
use
use
use
use
use
use
use
use
use
use
use
use
use
use
use
use
use
use
3 season
3 yr
3 season 3 yr
3 season
3 yr
3 season 3 yr
3 season
3 yr
3 season 3 yr
3 season
3 yr
3 season 3 yr
3 season
3 yr
3 season 3 yr
Habitat Use by Migrant Shorebirds
Density
F
P
F
P
11.53
2.13
1.57
3.02
13.26
0.08
0.13
0.60
4.25
0.01
0.11
1.79
4.70
0.29
0.15
0.06
9.08
1.13
1.05
0.57
,0.001
0.149
0.214
0.086
,0.001
0.775
0.722
0.445
0.043
0.939
0.737
0.185
0.038
0.597
0.697
0.812
0.003
0.292
0.309
0.570
6.66
0.59
0.19
1.99
11.89
0.59
0.01
1.56
4.29
0.01
0.04
1.44
7.20
0.57
0.03
0.05
15.83
1.84
1.88
0.03
0.012
0.446
0.661
0.163
,0.001
0.447
0.926
0.222
0.042
0.936
0.847
0.234
0.012
0.455
0.855
0.819
,0.001
0.179
0.174
0.969
253