Nutrient reserve dynamics of non-breeding Mute Swans (Cygnus olor) on the lower
Great Lakes.
Biology 4999E
April 8, 2009
Investigator:
Amanda Richman, Honours Student
Department of Biology, University of Western Ontario
Email: arichman@uwo.ca
Supervisor:
Dr. Scott Petrie, Executive Director
Long Point Waterfowl
Email: spetrie@bsc-eoc.org
Signed: ___________________
Co-Supervisor:
Dr. Robert Bailey, Professor
Department of Biology, University of Western Ontario
Email: drbob@uwo.ca
Advisors:
Dr. Jeremy McNeil, Professor
Department of Biology, University of Western Ontario
Email: jmcneil2@uwo.ca
Dr. Beth MacDougall-Shackleton, Professor
Department of Biology, University of Western Ontario
Email: emacdoug@uwo.ca
Abstract
Little is known about the nutrient reserve dynamics of Mute Swans (Cygnus olor)
throughout the moult and winter periods, particularly for birds residing at high latitudes in
North America. I analyzed abdominal fat and protein reserves of Mute Swans (n=177)
collected from the lower Great Lakes during the non-breeding season. Lipid (abdominal fat)
and protein (leg + breast muscle) reserves were determined to be good predictors of total
body fat and protein. Lipid reserves increased between the pre-moult and wing-moult periods
then remained stable between the wing-moult and post-moult periods. Protein reserves were
similar among pre-moult, wing-moult, and post-moult adults. Although not significant, adults
appeared to acquire fat and protein after moult and prior to winter. Abdominal fat increased
throughout moult, whereas protein reserves were not statistically significant. Juvenile protein
and lipid reserves did not differ between sexes. Juvenile fat reserves increased throughout fall
and winter. Juveniles also underwent substantial structural and muscle growth during fall and
early winter, this pattern began to slow and stabilize during late winter. Results support my
hypothesis that moult is not an energetically demanding activity in Mute Swans in North
America, likely due to the ready availability of submerged aquatic vegetation in coastal
wetlands. Observed protein and lipid reserve dynamics suggest that, at least during average
winters on the lower Great Lakes, adult Mute Swans can acquire sufficient food to maintain
reserves. Juvenile Mute Swans did not appear to be energetically stressed during their first
winter. It would seem that coastal wetlands associated with the lower Great Lakes are
suitable habitat for Mute Swans to winter, breed, and raise young.
2
Introduction
Mute Swans (Cygnus olor) are endemic to Eurasia, but were introduced to North
America in the late 1800s and early 1900s for zoos, captive collections, and estate ponds
(Allin and Husband, 2003; Petrie and Francis, 2003; Tatu et al., 2007a). Intentional and
accidental release of captive swans resulted in the establishment of populations along the
northeastern Atlantic and Pacific coasts of the United States. More recently, Mute Swans
began colonizing the lower Great Lakes, establishing resident populations on the coastal
wetlands associated with lakes Michigan, St. Clair, Erie, and Ontario (Petrie and Francis,
2003). These lower Great Lakes wetlands also provide important habitat for tens of
thousands of diving ducks, geese, and native swans during migration and winter (Knapton
and Petrie, 1999).
Mute Swans differ from all native waterfowl species in that they are herbivorous, do
not dive for food and do not field-feed in North America (Andersen-Harild, 1981; Allin and
Husband, 2003; Tatu, et al., 2007b). Therefore Mute Swans on the lower Great Lakes must
satisfy all their nutritional requirements through the consumption of submerged aquatic
vegetation. The presence of the large Mute Swan populations on the lower Great Lakes
provides a unique opportunity to study the nutrient reserve dynamics of a large-bodied
herbivorous waterfowl species in a north-temperate environment. More specifically, little is
known about how members of the tribe Cygnini (swans) acquire and allocate nutrients during
flight feather replacement between June to October (hereafter moult) or winter.
Flight feather replacement increases energetic cost so birds must increase
consumption or catabolize reserves during that time (Birkhead and Perrins, 1986; Ryley and
Bowler, 1994). Annual timing and location of moult depends largely on the timing of other
3
life cycle events (eg. breeding and migration), body condition and food availability (Van
Dijk and Van Eerden, 1991). Mute Swans (generally) moult sometime between June and
October leaving birds flightless for 6-8 weeks (Van Dijk and VanEerden, 1991), thereby
potentially limiting their access to preferred foods (Mathiasson, 1973; Birkhead and Perrins,
1986; Perrins, 1991). Because Mute Swans have never been collected throughout the
moulting period, it is not known if this period in their annual cycle is energetically
demanding (due to increased energetic and nutritional costs associated with feather growth or
reduced access to preferred foods).
Mute Swans residing on the lower Great Lakes overwinter on or very close to their
breeding sites. Potential advantages of this strategy include reduced mortality and energetic
costs associated with migration, possible reductions in density-dependent mortality factors
(Petrie, 2005) and early access to breeding territories. However, there are potential costs of
wintering at northern latitudes, including reduced availability, accessibility and quality of
food (Allin and Husband, 2003; Petrie, 2005). Also, increased thermoregulation costs
necessitate higher rates of food consumption or acquisition of large fat stores prior to periods
of thermal stress (Birkhead and Perrins, 1986; McKinney and McWilliams, 2005). Mute
Swans likely have a thermoregulatory advantage over small-bodied waterfowl due to their
low surface area to volume ratio (McKinney and McWilliams, 2005), and so possibly have a
higher capacity for overwintering in a north-temperate environment than native species.
However, Mute Swans are possibly constrained by the fact that they do not field feed (unlike
overwintering dabbling ducks, geese, and native swans) or dive for food or eat macroinvertebrates (unlike overwintering sea ducks and diving ducks).
4
Objectives and Hypotheses
The primary objectives of this study were to investigate Mute Swan nutrient reserve
dynamics during summer moult and winter in the lower Great Lakes. Results of this study
will advance understanding of how a large bodied waterfowl species residing in a northtemperate environment allocates nutrients during these two potentially energetically
demanding periods in their annual cycle, while feeding solely on submerged aquatic
vegetation.
My objective for the moulting period (July-Oct) was to determine if moulting adult
Mute Swans maintain endogenous reserves during the flightless period and how this changes
throughout the season from pre-moult to post-moult. I hypothesized that male and female
Mute Swans would maintain endogenous fat and protein reserves throughout moult since
submerged aquatic vegetation is readily available at moulting areas during summer on the
lower Great Lakes. This prediction is also based on the fact that Mute Swans are large and
dominant with few predators (Petrie and Francis, 2003), which should enable them to
effectively forage during the flightless period.
For the wintering period, my objective was to determine levels and temporal changes
in protein and lipid reserves in adult Mute Swans (Nov-Mar). I hypothesized that adults
would acquire fat and possibly protein in preparation for winter and that they would
subsequently catabolize reserves throughout winter due to unfavourable weather as well as
reduced food quality, availability and accessibility.
Juvenile Mute Swans have different energetic requirements than adults throughout
late summer and winter, primarily because they continue to grow and replace body feathers
5
during this time (Mathiasson, 1980). I studied changes in body condition throughout fall and
winter of their first year (July-Mar), to test the hypothesis that there would be no sex-related
differences in juvenile fat or protein reserves because both sexes are undergoing the same
physiological demands and processes associated with growth. I also predicted that fat and
protein reserves would increase through summer and fall and that fat would subsequently
decline during winter due to harsh conditions and reduced food availability, while protein
would stabilize due to reduced growth.
Methods
Adult and juvenile Mute Swans (n=177) were collected (shotgun and rifle) in coastal
wetlands associated with Long Point Bay and Lake St. Clair from Mar 2001 to Nov 2004,
tagged for identification and returned to the Long Point Waterfowl Avian Energetics Lab.
Sixty-seven (male: n=39, female: n=28), 60 (male: n=35, female: n=25), and 44 (male: n=25,
female: n=19), swans were used in the moult, overwinter, and juvenile analyses, respectively.
Measurements of the: skull (mm) and culmen width (mm), as well as the length of the tarsus
(mm), body length without tail feathers (cm) and ninth primary (cm) were taken. These data
were used in a principal component analysis (PCA) to correct nutrient reserves for variation
related to differences in structural size (Petrie, 2005). Swans were weighed and then frozen
for further processing.
Birds were dissected and sex and age were determined by examination the gonads
and presence or absence of a bursa, respectively. The weight (g) of one breast (including
pectoralis and supracaracoideus), leg (less bone) and abdominal fat, as well as the entire
digestive tract, full and empty, were recorded to calculate ingesta-free body mass.
6
A subset of birds (n=11 male; n=12 female) were used in a proximate analysis to
determine if lipid (abdominal fat) and protein deposit (leg + breast muscle) are good
indicators of somatic reserves. These carcasses were cut into small pieces, ground three times
in a Hobart meat grinder and then dried at 90˚C until constant mass was reached. Dried
carcass homogenate was then put through a coffee grinder to ensure the sample was ground
fine and even. A 10g subsample of dry homogenate was put in a Soxhlet system where lipids
were removed using petroleum ether solvent. The proportion of lipid obtained was then
applied to the dry weight of the bird to determine total body fat.
The remainder of each sample of lean dry homogenate was weighed, put in a muffle
furnace overnight at 550˚C to burn off any tissue remaining following lipid removal. The
difference between the means before and after gave an estimate the protein content, which
was then applied to determine the lean dry mass of the entire bird. For a more detailed
description of methods see Afton and Ankney (1991).
Statistical Analyses
Least-squares linear regression was used to determine the relationships between total
carcass protein and protein deposit (breast + leg muscle) and between total carcass lipid and
abdominal fat mass. I used log transformed data for all analyses to increase linearity and
decrease variance in the data. Principal Component Analyses (PCA) were performed on the
correlation matrix of body length, tarsus length, and culmen width measurements from 1) all
pre-moult, wing-moult and post-moult adult Mute Swans; 2) all overwintering adults and 3)
all juveniles (Table 1).
Two separate Analyses of Covariance (ANCOVA) were used on the data from all
7
adult birds during the moulting season to assess potential sources of variation in lipid
(abdominal fat) and protein (breast + leg muscle) deposits using a model that included effects
for moult status (pre-moult, wing-moult, or post-moult), sex (male and female), body size
(PC1) and all two-way interactions. I also used two separate ANCOVAs to assess sources of
variation in lipid (abdominal fat) and protein (breast + leg muscle) reserve indices of adult
Mute Swans in wing-moult with a model that included effects for sex, ninth primary length (a
proxy for time in wing moult), body size (PC1), and all two-way interactions.
For analysis of overwintering (Nov-Mar) adult nutrient reserves, I used two separate
ANCOVA to evaluate sources of variation in lipid (abdominal fat) and protein (breast + leg
muscle) reserve indices by specifying a model that included effects for size (PC1), ordinal
date, and all two-way interactions. I assigned ordinal date by setting the first day of the
collection period to 1 and subsequent days numbered accordingly.
To analyze juvenile reserves, I used ANCOVA to evaluate sources of variation in
lipid (abdominal fat) and protein (breast + leg muscle) reserve indices by specifying a model
including effects for sex, body size (PC1), ordinal date, and all two-way interactions. All
statistical analyses were done using SPSS 16.0 (2007).
Results
Comparison of Lakes:
No significant differences were observed in abdominal fat or protein deposit of birds
from lakes Erie and St. Clair during adult moult, adult overwinter, or juvenile analysis (Table
2), so data were pooled across sites.
8
Major fat and protein deposits as predictors of total reserves:
Least-squares regression indicated that protein (breast + leg muscle) and abdominal
fat deposits were reliable predictors of total somatic protein (r2= 0.79, p<0.001, F1,21=76.51,
b=0.70±0.01) and total somatic lipid reserves (r2= 0.882, p<0.001, F1,12=157.14,
b=7.33±0.13) respectively, in Mute Swans (Figure 1).
Adult Wing Moult:
In the analysis of abdominal fat throughout the wing-moult period (pre- moult, wingmoult, post-moult), moult status was nearly significant (p=0.069; Figure 2) but neither size,
sex, or any of the interactions were significant (Table 3). Generally, abdominal fat increased
throughout moult, mostly between pre-moult and active wing-moult, and remained fairly
stable in mid- to late-moult (Figure 2). Back transformation of parameter estimates showed
that birds in the pre-moult group have 70% less fat than those in the post-moult group, and
birds in the wing-moult group have 23% less fat than those in the post-moult group.
Both sex and size, as well as the resulting interaction significantly affected protein
content (Figure 3) but the moult periods did not (Table 3). Larger swans generally have
larger protein reserves than do smaller swans. Also, after correcting for structural differences
it was determined that, for any given body size, males usually have more protein than do
females.
Abdominal fat in active wing-moulting Mute Swans was not significantly affected by
sex, primary feather length, size, or any interactions (Table 4). Back transformation of the
parameter estimates showed that females had 18% less fat than did males during wing-moult.
Protein deposit in moulting adult Mute Swans was unaffected by size and primary feather
9
length but sex had a significant effect (Table 4), and back transformation of estimates
revealed that females had 18% less protein than males.
Overwintering Adults
Sex was the only significant source of variation for abdominal fat in adult Mute
Swans during the winter period (Table 5). Although there was not a significant change in
abdominal fat in either sex during winter, males and females appeared to have somewhat
diverging trends in body fat, with a slight decrease in males and increase in females,
respectively, in late-winter (Figure 4). Back transformation of the parameter estimates
showed that females had 68% more abdominal fat than did males during late- winter.
Regarding protein deposit, there was a significant interaction involving size (PC1)
and date (Table 4). Protein deposit did not change throughout winter in male Mute Swans;
however females showed a minor increase (Figure 5). Back transformation of parameter
estimates revealed that adult males have 26% more protein then adult females do at any
given time. Early in winter, there is a greater increase in protein deposit in adult Mute Swans
compared to later in the season when there is less of an increase in protein deposit with size.
Juveniles
As hypothesized, no significant differences in fat or protein reserves between sexes
were found (Table 6). I hypothesized that juvenile fat reserves would increase through
summer and fall and then decline during winter. However, male and female juveniles started
off in early fall with very low fat, but levels steadily increased until late-winter (Figure 6)
and resulted in ordinal date being the only significant source of variation in abdominal fat
10
and protein deposit in juveniles (Table 6). However, noise in the data for the end of
November may have confounded the strength of these results. Due to a rapid increase in early
fall, there was a significant seasonal change in protein content (Figure 7). Back-transformed
parameter estimates indicated that females had 5% less protein than did males throughout
their first year (Figure 7). The trend found in juvenile growth rate, indexed by culmen width
(mm) over time, resembles that of protein deposit over time (Figure 8).
Discussion
Prior to this study, it was unclear if moult was energetically expensive in large bodied
waterfowl and this question had never been studied in Mute Swans using the lower Great
Lakes. Wing-moult in Mute Swans occurs after breeding (July to Oct), leaving birds
flightless for 6-8 weeks (Birkhead and Perrins, 1986). Data collected on breeding and nonbreeding Mute Swans resident on the lower Great Lakes suggest that birds lose significant
amounts of fat prior to moult (DeHaan, unpublished data), which leaves them to enter moult
with low fat reserves. The loss of reserves during mid-summer when submerged aquatic
vegetation is readily available suggests a strategy to reduce wing loading, thereby enabling
birds to regain flight capabilities earlier than if they had maintained large lipid stores. This
would enable birds to regain access to distant food sources and avoid predators.
My results show that Mute Swans were able to increase fat and maintain protein
reserves during moult. Since adult swans on the lower Great Lakes initiate moult with low fat
reserves, the reported trend would reveal that food is readily available on the moulting
grounds. Therefore, moult is not an overly energetically demanding activity for these birds as
they were able to satisfy the increased nutritional requirements of moult through dietary
11
intake (Birkhead and Perrins, 1986). This is supported by the fact that Mute Swans in
Denmark (Andersen-Harild, 1981) and in England (Bacon and Coleman, 1986) were able to
maintain a stable body weight during moult. In the Netherlands, however, Mute Swans have
been shown to lose weight throughout moult, which was attributed to low food availability
on moulting grounds (Van Dijk and Van Eerden, 1991).
Increased energy expenditure related to thermoregulation combined with declining
food availability and accessibility (senescence, depletion, ice cover) during winter could
result in birds being in a negative energy balance, particularly during harsh winters. This
could result in swans losing body mass as winter progresses, which has been shown to affect
winter survival and reproductive success in the following breeding season (Drewien and
Bouffard, 1994). Lower Great Lakes wintering Lesser Scaup (Aythya affinis) showed a
similar trend in lipid reserves as Mute Swans, with females increasing nutrient reserves by
spring whereas males experienced no change or a slight loss in lipid reserves (Badzinkski and
Petrie, 2006). McLandress and Raveling (1981) reported an increase in fat and protein
storage in late winter for a population of Giant Canada Geese (Branta canadensis) in midNorth America. Geese studied in the previously mentioned paper migrate a very short
distance, and so increases in protein and fat reserves were attributed to nutrient storage for
egg laying in females and territory defense in males. In contrast, weight loss during winter
has been reported for several species of waterfowl (Owen and Cook, 1977; McLandress and
Raveling, 1981; Reineke et al., 1982; Limpert, et al., 1987), including Mute Swans in Europe
(Andersen-Harild, 1981). This weight loss has been attributed to reducing wing loading prior
to early spring migration (Limpert et al, 1987). The increase in female Mute Swan abdominal
fat over winter in the current study suggests that birds are able to acquire sufficient energy
12
from lower Great Lakes wetlands and that there is no selective advantage to reduce wing
loading. This is most likely because Mute Swans that winter on the lower Great Lakes do not
move far between wintering and breeding areas, so incur limited flight costs.
There may be some behavioural mechanisms that influence timing of nutrient storage
and catabolism that differs between the sexes. Males started to catabolize lipid reserves by
mid- to late-winter, which could be due to increased energetic costs associated with
beginning to seek out and defend breeding and feeding territories, as well as mates. In
contrast, females stored body fat during late winter, likely in preparation for breeding. Fat
storage at this time is quite possibly facilitated by males that defend them and their territory.
Mute Swans are likely able to access enough nutrients from their habitat to maintain and
increase their fat reserves, but may not be acquiring enough nutrients high in protein to help
with storing extra protein reserves. This, however, is not necessarily concerning because
Mute Swans on the lower Great Lakes are non-migratory and so they do not need to increase
protein deposits prior to spring to the extent that migratory waterfowl do (McLandress and
Raveling, 1981; Lindstrom and Piersma, 1993).
Little is known about growth and development of swan juveniles. Muscles provide
added heat generation capacity and also help to decrease the surface area to volume ratio of
the body (Liu et al., 2006), so there are nutritional advantages to storing body protein prior to
winter. Also, juvenile Mute Swans continue to gradually moult their feathers through their
first winter (Birkhead and Perrins, 1986), so extra body fat and protein are needed to replace
feathers and for thermoregulation. Juvenile growth is rapid in late summer and early fall, but
as winter approaches growth slows and remains steady as birds approach adult size (Figure
8), which is the same trend as that seen in juvenile protein deposit over time (Figure 7). This
13
would reveal that changes in abdominal fat or protein deposit coincided with continued
growth.
Mathiasson (1980) found male and female juvenile Mute Swans of the Swedish west
coast are relatively close in body weight as they grow, with females being slightly lighter
than males. They also found that juvenile growth is exponential at first then slows throughout
the first year. In the current study, juveniles were also of similar size, with males being
insignificantly larger. Protein deposit increased exponentially at first then leveled off at
relatively the same time as growth slowed and leveled off, indicating that juveniles are able
to access enough nutrients for growth as well as to maintain nutrient reserves through winter.
That no decrease was noted in juvenile abdominal fat or protein over the study period
suggests that they were not energetically stressed to the point where body condition was
compromised or they needed to catabolize protein reserves for energy and warmth.
Average winter temperatures during the study period (2001-2004) were not
substantially different from the long term average (Figure 8) (Environment Canada, 2008), so
Mute Swans are apparently capable of maintaining reserves during most years. It seems that
North American Mute Swans have found a comparable niche to their native habitat in
Europe. Additional research should be conducted to determine how Mute Swan body
condition is influenced during harsh winters.
Conclusions
Because birds did not store nutrients prior to moult and were able to maintain and
even increase nutrient reserves during that time it can be concluded that, in a north-temperate
environment, moult was not a nutritionally stressful period for Mute Swans. Although it is
14
apparent that abdominal fat increased and protein deposit remained stable, the effect of moult
on protein and fat deposits may be more apparent if larger sample sizes were collected.
Patterns observed in the dynamics of protein and lipid reserves suggest that, at least during
average winters on the lower Great Lakes, adult Mute Swans were able to acquire sufficient
food to enable them to maintain reserves throughout winter. Juvenile Mute Swans did not
appear to be energetically stressed through their first winter as they continued to grow and
store nutrients during that time. It would seem that during average winters the lower Great
Lakes is an ideal area for Mute Swans to winter, breed and raise young as they are able to
produce healthy individuals that are likely to reach adulthood. However during harsh winters
juveniles may not be able to maintain reserves and body condition may be compromised.
Further research is could be done to determine effects of harsh winters on adult and juvenile
Mute Swans.
Acknowledgements
Financial support was provided Long Point Waterfowl, the Bluff’s Hunting Club, the
Ontario Federation of Anglers and Hunters, the Catherine and Fredrik Eaton Charitable
Foundation, Long Point Waterfowlers’ Association, Aylmer Order of Good Cheer, S. C.
Johnson & Son, Inc., and Mees Pierson, Ltd. I would like to thank Bird Studies Canada and
Canadian Wildlife Service for logistical support, as well as the numerous hunters and wildlife
professionals who participated in specimen collections and laboratory assistance. I also thank
S. Shannon Badzinsk, Robert Bailey, Jeremy McNeil, and Beth MacDougall-Shackleton for
assisting with manuscript development.
15
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17
List of Tables
Table 1. Standard coefficients of PCA of Mute Swans physiological variables. Standard
coefficients of principal component analysis of A. Adult Mute Swans during the entire
moulting season, including pre- and post-moulting birds (July-Oct); B. Overwintering adult
Mute Swans (Nov-Mar); C. Juvenile Mute Swans during the entire non-breeding (July-Mar)
season. Measurements used were culmen width (mm), tarsus length (mm), and body length
(cm).
1
Component
2
A. Moult
Log culmen width
Log tarsus length
Log body length
Eigenvalue
Percent variance
0.057
0.013
0.013
0.004
63.88
-0.010
0.037
0.010
0.002
27.92
-0.003
-0.007
0.020
0.000
8.21
B. Overwinter
Log culmen width
Log tarsus length
Log body length
Eigenvalue
Percent variance
0.002
0.187
0.006
0.035
96.99
0.020
<0.001
0.019
0.001
2.095
-0.012
<0.001
0.013
0.000
0.913
C. Juvenile
Log culmen width
Log tarsus length
Log body length
Eigenvalue
Percent variance
0.004
0.299
0.005
0.090
88.75
0.098
-0.002
0.009
0.010
9.63
-0.004
<0.001
0.040
0.002
1.62
3
18
Table 2. Results from comparison of residuals between Lake Erie and Lake St. Clair
(2001 to 2004). Residuals from analysis of covariance (ANCOVA) were found for protein
deposit and abdominal fat in Lake Erie and Lake. St Clair and compared between lakes for
adult Mute Swans during the entire moulting season, including pre- and post-moulting birds
(July-Oct); overwintering adult Mute Swans (Nov-Mar); juvenile Mute Swans during the
entire non-breeding (July-Mar) season.
Moult
Overwinter
Juvenile
t
1.04
0.77
1.52
Abdominal Fat
p
df
0.30
65
0.44
58
0.14
42
t
0.75
0.12
1.62
Protein Deposit
p
df
0.46
65
0.91
58
0.11
42
19
Table 3. Results from analysis of covariance for the moult season (July to Oct). Results
of analysis of covariance (ANCOVA) on abdominal fat and protein deposit in adult Mute
Swans during the entire moulting season (July to Oct), including pre-, wing-, and post-moult
birds. The model incorporated main effects and all two-way interactions.
Dependent
Variable
Sex
df=1
Abdominal F=0.079
Fat
p=0.779
Protein
Deposit
Size
df=1
F=0.179
p=0.674
Moult Sex*Moult Size*Moult Size*Sex
Error
Status
Status
Status
df=2
df=2
df=2
df=1
df=57
F=2.786
F=1.134
F=1.407
F=0.479 MS=0.356
p=0.069
p=0.329
p=0.253
p=0.492
F=9.700 F=11.134 F=0.545
p=0.003 p=0.001 p=0.463
F=0.013
p=0.911
F=0.066
p=0.798
F=5.842
p=0.019
MS=0.006
20
Table 4. Results from analysis of covariance for active wing-moult Mute Swans. Results
of analysis of covariance (ANCOVA) on abdominal fat and protein deposit in adult Mute
Swans in active wing-moult. The model incorporated main effects and all two-way
interactions.
Dependent
Variable
Size*
Primary
Length
df=1
F=0.007
p=0.935
Size*Sex
Error
df=1
F=0.019
p=0.890
Sex*
Primary
Length
df=1
F=0.049
p=0.826
df=1
F=0.446
p=0.509
df=35
MS=0.343
F=0.049
p=0.826
F=0.046
p=0.832
F=0.256
p=0.616
F=2.615
p=0.116
MS=0.008
Sex
Size
Primary
Length
Abdominal
Fat
df=1
F=0.229
p=0.635
df=1
F=0.041
p=0.840
Protein
Deposit
F=6.581
p=0.015
F=2.010
p=0.165
21
Table 5. Results from analysis of covariance for overwinter (Nov to Mar). Results of
analysis of covariance (ANCOVA) on abdominal fat and protein deposit in adult male and
female overwintering Mute Swans (Nov to Mar). The model incorporated main effects and
all two-way interactions.
Dependent
Variable
Sex
Size
Date
Sex*Date
Size*Date
Size*Sex
Error
Abdominal
Fat
df=1
F=7.074
p=0.010
df=1
F=1.569
p=0.215
df=2
F=2.514
p=0.118
df=2
F=0.392
p=0.534
df=2
F=0.813
p=0.371
df=1
F=0.811
p=0.372
df=56
MS=0.093
Protein
Deposit
F=16.608
p<0.001
F=7.079
p=0.010
F=7.915
p=0.007
F=2.969
p=0.091
F=6.525
p=0.013
F=1.650
p=0.205
MS=0.002
22
Table 6. Results from analysis of covariance for juveniles (July to Mar). Results of
analysis of covariance (ANCOVA) on abdominal fat and protein deposit in male and female
juvenile Mute Swans during the entire non-breeding season (July to Mar). The model
incorporated main effects and all two-way interactions.
Dependent
Variable
Sex
Size
Date
Sex*Date
Size*Date
Size*Sex
Error
Abdominal
Fat
df=1
F=3.240
p=0.079
df=1
F=1.310
p=0.260
df=1
F=133.02
p<0.001
df=1
F=0.003
p=0.958
df=1
F=0.858
p=0.360
df=1
F=0.013
p=0.910
df=40
MS=0.097
Protein
Deposit
F=0.301
p=0.586
F=0.117
p=0.734
F=96.21
p<0.001
F=0.629
p=0.433
F=2.219
p=0.145
F=2.197
p=0.147
MS=0.016
23
List of Figures
A
B
Figure 1. Proximate analysis for abdominal fat and protein deposit in Mute Swans.
Results from least-squares linear regression on A. Abdominal fat and B. Protein deposit. This
was done on a subset of birds (n=11 male; n=12 female) as a proximate analysis to determine
if abdominal fat and protein (leg + breast) deposit are good indicators total body fat and total
protein content.
24
Abdominal Fat (g)
Pre-Moult
Wing-Moult
Post-Moult
Moult Status
Figure 2. Abdominal fat in adult Mute Swans during the moulting season (July to Oct).
Mean (±SE) abdominal fat (g) of combined adult male (n=38) and adult female (n=30) Mute
Swans during pre-moult, wing-moult, and post-moult. (*Differences between periods were
marginally significant (p=0.069)).
25
Protein Deposit (g)
β=188.82
β=314.66
PC1
Figure 3. Protein deposit relative to principle component scores for adult Mute Swans
in active wing-moult. The relationships between protein (breast + leg) deposits (g) and body
size indices (principle component [PC1] scores) of adult male (─) () and adult female (--)
(β=314.66) Mute Swans collected during pre-moult, wing-moult, and post-moult periods.
26
Abdominal Fat (g)
Ordinal Date (Time)
Figure 4. Trends in abdominal fat over time during winter in adult Mute Swans (Nov to
Mar). Relationships between abdominal fat deposits (g) and ordinal date (day 1 = first day of
collection; vertical lines represent division between months) for 38 adult male (─) and 23
adult female (--) Mute Swans collected during winter (Nov to Mar).
27
Protein Deposit (g)
Ordinal Date (Time)
Figure 5. Trends in protein deposit over time in overwintering adult Mute Swans (Nov
to Mar). Relationships between protein deposit (g) and ordinal date (day 1 = first day of
collection; vertical lines represent division between months) for 38 adult male (─) and 23
adult female (--) Mute Swans collected during winter (Nov to Mar).
28
Abdominal Fat (g)
Ordinal Date (Time)
Figure 6. Abdominal fat over time in juvenile Mute Swans (July to Mar). Relationship
between abdominal fat deposits (g) and ordinal date (day 1 = first day of collection; vertical
lines represent division between months) in 24 juvenile male (─) and 21 juvenile female (--)
Mute Swans collected form early fall to late winter.
29
Protein Deposit (g)
Ordinal Date (Time)
Figure 7. Juvenile Mute Swan protein deposit over time (July to Mar). Relationship
between protein (leg + breast) deposit (g) and ordinal date (day 1 = first day of collection;
vertical lines represent division between months) in 24 juvenile male (─) and 21 juvenile
female (--) Mute Swans collected from early fall to late winter.
30
Culmen Width (mm)
Ordinal Date (Time)
Figure 8. Growth of juvenile Mute Swans over time (July to Mar). Relationship between
culmen width (mm) and ordinal date (day 1 = first day of collection; vertical lines represent
division between months) in 24 juvenile male (─) and 21 juvenile female (--) Mute Swans
collected form early fall to late winter (July to Mar).
31
Temperature (˚C)
Year
Figure 9. Winter temperature trends from 1990 to 2008 in London Ontario. Mean
annual winter (Nov-Mar) temperature (˚C) recorded at London, Ontario from 1990 to 2008.
This location was chosen for its close proximity to Long Point, Ontario as well as more
extensive weather data. Time between vertical lines represents study period (2001-2004).
Horizontal line (--) represents long-term average temperature (Data from Environment
Canada 2008).
32