Content uploaded by Carrie Elizabeth Gray
Author content
All content in this area was uploaded by Carrie Elizabeth Gray on Aug 04, 2014
Content may be subject to copyright.
BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit
publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to
critical research.
Body Mass in Common Loons (Gavia immer) Strongly
Associated with Migration Distance
Author(s): Carrie E. Gray, James D. Paruk, Christopher R. DeSorbo, Lucas J.
Savoy, David E. Yates, Michael D. Chickering, Rick B. Gray, Kate M. Taylor,
Darwin Long, IV, Nina Schoch, William Hanson, John Cooley and David C.
Evers
Source: Waterbirds, 37(sp1):64-75. 2014.
Published By: The Waterbird Society
DOI: http://dx.doi.org/10.1675/063.037.sp109
URL: http://www.bioone.org/doi/full/10.1675/063.037.sp109
BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the
biological, ecological, and environmental sciences. BioOne provides a sustainable
online platform for over 170 journals and books published by nonprofit societies,
associations, museums, institutions, and presses.
Your use of this PDF, the BioOne Web site, and all posted and associated content
indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/
page/terms_of_use.
Usage of BioOne content is strictly limited to personal, educational, and non-
commercial use. Commercial inquiries or rights and permissions requests should be
directed to the individual publisher as copyright holder.
64
Body Mass in Common Loons (Gavia immer) Strongly Associated
with Migration Distance
Carrie e. Gray1,*, James D. Paruk1, ChristoPher r. Desorbo1, LuCas J. savoy1, DaviD e. yates1,
miChaeL D. ChiCkerinG1, riCk b. Gray1, kate m. tayLor1, Darwin LonG, iv1, nina sChoCh1,
wiLLiam hanson1, John CooLey2 anD DaviD C. evers1
1Biodiversity Research Institute, 19 Flaggy Meadow Road, Gorham, ME, 04038, USA
2Loon Preservation Committee, 183 Lees Mill Road, Moultonborough, NH, 03254, USA
*Corresponding author; E-mail: carrie.gray@briloon.org
Abstract.—During 25 field seasons between 1988 and 2012, Biodiversity Research Institute captured and
uniquely color-banded 2,730 adult Common Loons (Gavia immer) on breeding territories in 11 States and seven
Provinces throughout North America. Body mass was obtained from each individual; tarsus and bill measurements
were obtained from more than half the birds banded. Clinal variation in body mass, tarsal width and bill length was
observed. Body mass varied from 2,700 g to 7,600 g; loons from populations in the upper Great Lakes and central
Canada were smallest, and size increased to the east and west. Examination of band return and satellite tracking
data resulted in three migration distance groups: < 1,500 km; 1,500-3,500 km; and ≥ 3,500 km. Body mass was
inversely related to migration distance. Males were significantly larger (> 20%) than associated females, and within-
pair differences increased with decreasing migration distance (i.e., males from coastal States were proportionally
larger than their mates compared to interior State pairs). Received 26 February 2013, accepted 18 June 2013.
Key words.—clinal variation, Common Loon, Gavia immer, migration distance.
Waterbirds 37 (Special Publication 1): 64-75, 2014
Intraspecific variation of morphological
features in birds has been observed across
geographic ranges (Ainley 1980; McGilli-
vray 1989; Leafloor and Rusch 1997; Ashton
2002). The trend for body size to be larger
in cooler climates and smaller in warmer
climates (often represented by latitude) is
known as Bergmann’s rule when it occurs
among closely related species or James’s rule
when it occurs within species (James 1970;
Blackburn et al. 1999). The basis is that larg-
er body size will be favored in cool climates
because lower surface area to mass ratios re-
sult in reduced heat loss and, thus, apparent
increased survival. There is strong evidence
for similar variation within species; howev-
er, many exceptions to the rule have been
observed, particularly among migratory vs.
sedentary species (James 1970; Blackburn
et al. 1999; Ashton 2002; Meiri and Dayan
2003). In birds, this may be attributed to a
decreased load-carrying capacity of an indi-
vidual associated with increased body mass
(Hedenström and Alerstam 1992, 1997).
Further, migration speed is diminished with
increased body size for birds that use flap-
ping flight, resulting in increased migration
times and, thereby, constraining the migra-
tion distances that larger-sized birds are
capable of completing during their annual
life cycle (Hedenström and Alerstam 1998;
Alerstam et al. 2003; Hedenström 2003; Hein
et al. 2012). For example, among three spe-
cies of European swans, the smallest species
(Cygnus bewickii) had the longest migration
distance, the largest species (C. olor) the
shortest distance, and the mid-sized species
(C. columbianus) an intermediate distance
between the smallest and largest species
(Cramp and Simmons 1977). This pattern
has also been observed in Atlantic alcids
such as Thick-billed Murre (Uria lomvia; Vau-
rie 1965), Atlantic Puffin (Fratercula arctica;
Moen 1991), Razorbill (Alca torda; Barrett et
al. 1997) and Dovekie (Alle alle; Wojczulanis-
Jakubas et al. 2011).
Loons are a small monophyletic group
(Gaviiformes) consisting of five species
worldwide (Sibley and Ahlquist 1990; Lind-
say 2002; Evers et al. 2010). They are heavy-
bodied piscivorous birds known as divers in
the Old World due to their foot-propelled
diving foraging strategy. Loons are a classic
K-selected species with long life expectancy,
delayed sexual maturity, and low fecundity;
their mating system is socially and geneti-
boDy mass in Common Loons 65
cally monogamous (Piper et al. 1997). The
Common Loon (Gavia immer) has the larg-
est geographic range of the loon species
in North America and is the only one that
breeds in the contiguous USA (Sibley and
Ahlquist 1990; Lindsay 2002), which makes it
a good candidate to examine within-species
variation. The annual life cycle of the Com-
mon Loon varies little across its broad geo-
graphical range in that it breeds on fresh-
water lakes throughout the northern USA,
including Alaska, and Canada north to the
southern edge of the taiga shield, and mi-
grates to coastal areas in the fall, including
the Atlantic and Pacific Coasts, Gulf of Mex-
ico, and Gulf of California. Satellite tracking
data indicate that the duration of migration
and the timing of arrival on the wintering
grounds appear to vary within and among
populations (U.S. Geological Survey 2013;
Biodiversity Research Institute, unpubl.
data). These differences among populations
seem to be associated with differences in mi-
gration distance. For example, northeastern
USA Common Loon populations typically
arrive in coastal wintering areas within a day
of departure from breeding areas, whereas
upper midwestern USA Common Loon pop-
ulations that travel up to seven times the dis-
tance of northeastern USA Common Loons
may take up to a few weeks to complete
their fall migration (U.S. Geological Survey
2013). Less information is available regard-
ing migration timing of Common Loon pop-
ulations in interior Canada. However, lim-
ited satellite tracking data suggest that they
travel the greatest migration distances of all
North American Common Loons and may
take up to 2 months to complete their fall
migrations (Confederated Salish and Koote-
nai Tribes 2008; Paruk et al. 2014).
A geographic cline in the body size of the
Common Loon (loons) has been observed
across its North American range and appears
to coincide with the differences in migration
distance, where interior breeding loons are
smallest and size increases to the east and
west (Rand 1947; Storer 1988; Evers et al.
2010). The increased physiological cost of a
larger body size during migration may create
a selection pressure that favors smaller body
sizes for loons with long migration distances.
However, an opposing selection pressure
for large body size may exist for loons that
migrate shorter distances. A central char-
acteristic on which several life history traits
may depend is individual body size, includ-
ing survival and fecundity (Boag and Grant
1981; Alisauskas 1987; Promislov and Harvey
1990; Sedinger et al. 1995). Loons are highly
territorial during the breeding season, and
competition for quality breeding territories
often results in aggressive interactions be-
tween individuals and pairs (Paruk 1999; Pip-
er et al. 2008; Piper 2011). Piper et al. (2000)
found that larger-sized loons were less likely
to be usurped from their territories dur-
ing these interactions compared to smaller
loons. Loons are also highly vocal during
the breeding season and produce an array
of calls, the yodel being the most complex
and used solely by males often in response
to territorial intrusions. Mager et al. (2007a)
confirmed that variability in the dominant
frequency of a male’s yodel is influenced by
body size, with larger males producing lower
frequency yodels. Further, loons appeared
to respond with more alarm to lower pitch
yodels compared to higher pitched yodels
during callback surveys (Mager et al. 2007b).
Over a 25-year period (1988-2012), the
Biodiversity Research Institute, with the
help of multiple collaborators, banded 2,730
adult Common Loons on their breeding
territories in 11 States and seven Provinces
throughout the species’ range in North
America. Of those individuals, 536 breed-
ing pairs were sampled (i.e., the male and
female of a territorial pair were captured
and banded within the same breeding sea-
son). These significant banding efforts have
resulted in the largest known collection of
morphological data on Common Loons.
We analyzed these data in an effort to deter-
mine if body size features, such as body mass,
tarsus width, and bill length, are linked to
differences in migration distance. We pre-
dicted that loon populations inhabiting the
interior part of the continent with ostensibly
longer migration distances will have smaller
morphological features than coastal ones
with much shorter migrations. We were also
66 waterbirDs
interested in how size differences between
pair members changed, if at all, across their
range. If being larger is more important for
a male than a female to defend and hold its
territory, then selection should favor larger
males relative to females when the distance
between breeding and wintering areas is de-
creased. Our prediction was that size differ-
ence between pair members would increase
as migration distance decreased.
methoDs
Study Area
During the breeding season (June-August) from
1988 to 2012, Common Loons were targeted for cap-
ture and banding efforts in their breeding territories
on freshwater lakes and ponds in the following States
and Provinces: Alaska, Alberta, Maine, Manitoba, Mas-
sachusetts, Michigan, Minnesota, Montana, New Bruns-
wick, New Hampshire, New York, Nova Scotia, Ontario,
Quebec, Saskatchewan, Vermont, Washington, and Wis-
consin.
Capture and Measurements
Adult loons were captured on their breeding lakes
with a replicable night-lighting technique (Evers 1993,
2001). Spotlights (400,000 to 1.5 million candle power)
were used to search lakes, and tape-recorded and mim-
icked calls were used to attract loons to the boat where
they were netted with large landing nets, restrained,
and transported to shore. All loons were marked with
U.S. Geological Survey aluminum or stainless steel
bands, and a unique plastic, colored leg band combina-
tion glued with an acetone-based derivative. The follow-
ing measurements were also taken using a standardized
protocol developed by Evers (2001): bill length, width
and depth; culmen; right and left tarsal width; and body
mass. Males were distinguished from females based on
yodel calls given before and/or after capture. In some
cases gender was determined by placing several drops
of blood on a cotton pad, which was sent to a genetics
lab for analysis. Sexing was accomplished by amplifying
a portion of the W-linked EE0.6 sequence and a control
sequence from the spindlin gene on the Z chromosome
with PCR (polymerase chain reaction). Female birds
showed two bands on an agarose gel (~150 and 300
base pairs; the Z and W fragments, respectively) and
male birds had a single band (~150 base pairs; the Z
fragment) (Itoh et al. 2001).
Migration Distance Categories
Migration distances between breeding and winter-
ing grounds were determined from wintering band
return and satellite tracking data (Table 1). Only
Common Loons banded on breeding territories and
recovered outside of the breeding area during the pe-
riod when loons are expected to be on the wintering
grounds and not in migration (i.e., December, Janu-
ary, and February) were included in the development
of the migration distance categories. Although loons
may be found in wintering locations outside of these
months, it was necessary to be conservative in the selec-
Table 1. Migration distance (km) from breeding to wintering areas of Common Loons in North America deter-
mined from band recoveries and satellite tracking data. BRI = Biodiversity Research Institute.
Population
Migration Distance Traveled (km)
Data Source nMean ± SD Range
Band Recoveries
Maine 12 450 ± 223 190-950 BRI Banding Records
Michigan 5 2,660 ± 344 2,200-3,000 BRI Banding Records
Minnesota 4 2,869 ± 415 2,600-3,475 BRI Banding Records
Montana 3 1,967 ± 153 1,800-2,100 BRI Banding Records
New Hampshire 8 284 ± 103 175-500 BRI Banding Records
New York 3 800 ± 368 575-1,225 BRI Banding Records
Quebec 4 1,931 ± 383 1,600-2,475 BRI Banding Records
Washington 3 275 ± 150 125-425 BRI Banding Records
Wisconsin 11 2,550 ± 299 2,200-2,950 BRI Banding Records
Satellite Tracking
Alberta 1 4,700 4,700 Confederated Salish and Kootenai Tribes 2008
Alaska 2 286 ± 10 279-293 J. Schmutz, pers. commun.
Maine 7 498 ± 313 172-1,050 BRI, unpubl. data; Kenow et al. 2009
Minnesota and Wisconsin 4 — 1,884-2,121 Kenow et al. 2002
New Hampshire 2 154 ± 3 152-156 Kenow et al. 2009
New York 5 430 ± 60 362-527 Kenow et al. 2009
Saskatchewan 3 4,005 ± 451 3,694-4,522 Confederated Salish and Kootenai Tribes 2008;
Paruk et al. 2014
boDy mass in Common Loons 67
tion of recovery data to avoid inclusion of loons recov-
ered during migration in locales that did not represent
full migration distances between breeding and winter-
ing areas. Straight-line distances between breeding
territory locations and winter recovery locations were
measured in ArcGIS (Environmental Systems Research
Institute 2011). The same method was used to measure
the distance between breeding and winter locations for
the Biodiversity Research Institute’s unpublished satel-
lite tracking data. Distances were also obtained from
colleagues with unpublished satellite tracking data
through personal communication and from the peer-
reviewed literature (Confederated Salish and Kootenai
Tribes 2008; U.S. Geological Survey 2013; Paruk et al.
2014; J. Schmutz, pers. commun.). Three broad migra-
tion distance groups were developed based on these
data: short-distance (< 1,500 km), moderate-distance
(1,500-3,499 km), and long-distance (≥ 3,500 km). The
short-distance migration category included Common
Loons sampled in Alaska, Maine, Massachusetts, New
Brunswick, New Hampshire, New York, Nova Scotia,
Vermont, and Washington. The moderate-distance mi-
gration category included loons sampled in Michigan,
Minnesota, Montana, Ontario, Quebec, and Wisconsin.
The long-distance category included loons sampled in
Alberta, Manitoba, and Saskatchewan. Loons banded in
States or Provinces without band recovery or satellite
tracking data, including Manitoba, Massachusetts, New
Brunswick, Nova Scotia, Ontario, and Vermont, were as-
signed to a migration distance category based on their
geographic location relative to nearby populations with
known wintering locations.
Statistical Analysis
Statistical analyses were performed in Microsoft EX-
CEL and JMP (SAS Institute, Inc. 2010). Banding records
of adult male (n = 1,419) and female (n = 1,311) Common
Loons sampled on breeding territories as part of research
conducted by the Biodiversity Research Institute between
1988 and 2012 were evaluated for differences in body
mass, tarsus width, and bill length. Normality of sample
distributions was checked with the Shapiro-Wilk test, and
homogeneity of variance was examined with the Bartlett
test. We examined the effects of latitude of breeding loca-
tion, longitude of breeding location, the compound effect
of latitude and longitude of breeding location (latitude
x longitude), and migration distance category on body
mass using a general linear model (GLM) framework.
Candidate models of suites of covariates were ranked with
Akaike Information Criterion adjusted for small sample
size (AICc). The model with the lowest AICc and those
having ΔAICc ≤ 2 had the most statistical support, values
between 4 and 7 had considerably less support, and those
> 10 had virtually no support (Burnham and Anderson
2002). The Akaike weight was also considered when deter-
mining the relative amount of statistical support for each
model. The relationship between body mass and tarsus
width and body mass and bill length were determined with
simple linear regression. Differences in tarsus width and
bill length among migration distance categories were ex-
amined with analysis of variance (ANOVA). Pairwise com-
parisons between categories were conducted with Tukey’s
honestly significant difference (HSD) test. All tests were
considered significant at P < 0.05.
The relationship between male and female body
mass within breeding pairs was examined with linear re-
gression for short-distance migrant breeding pairs (n =
415) and moderate-distance migrant breeding pairs (n
= 138). The variation in body mass, tarsus width, and bill
length between a male and female of a breeding pair
were tested for differences between short-distance and
moderate-distance migrant breeding pairs using Stu-
dent’s t-test. Small sample size precluded inclusion of the
long-distance category in the breeding pair analyses.
resuLts
Body Mass
Body mass ranged from 2,700 g to 6,200
g in females (n = 1,311) and from 4,350 g to
7,600 g in males (n = 1,419). The top sup-
ported model included longitude, latitude,
longitude x latitude, and migration distance
for males and females, although migration
distance accounted for the greatest variation
in body mass (Table 2). Body mass decreased
with increased migration distance in males
and females (Fig. 1). Tukey’s HSD tests indi-
cated that female short-distance migrant least
squares mean (LSM) body mass [x – = 4,505 g
(SE = 23)] was significantly greater than fe-
male moderate-distance migrants [x –= 3,719
g (SE = 20)] (P < 0.001), and both of those
groups were significantly greater than female
long-distance migrants [x – = 3,430 g (SE =
74)] (short to long: P < 0.001; moderate to
long: P < 0.001). Similarly, LSM body mass
of male short-distance migrants [x – = 5,727 g
(SE = 27)] was significantly greater than male
moderate-distance migrants [x – = 4,661 g (SE
= 21)] (P < 0.001), and both of these groups
were greater than long-distance migrants [
x –
= 4,244 g (SE = 84)] (short to long: P < 0.001;
moderate to long: P < 0.001). Among State
and Province populations, male and female
Common Loons in Maine and New Hamp-
shire had the greatest arithmetic mean body
masses compared to loons sampled in any
other States or Provinces (Appendix).
Tarsal width ranged from 20.0 mm to
28.6 mm in females and 21.1 mm to 30.8
mm in males. Right tarsal width was mod-
erately correlated with body mass (females:
68 waterbirDs
r2 = 0.29, F681 = 275.39, P < 0.001; males: r2
= 0.34, F723 = 375.27, P < 0.001). ANOVA
results indicated significant differences in
tarsal width among the migration distance
categories for both sexes (females: F702 =
105.21, P < 0.001; males: F748 = 201.10, P <
0.001) (Fig. 2). Pairwise comparisons with
Tukey’s HSD test showed that short-distance
migrants [females: = 24.86 mm (SE = 0.05),
n = 536; males: = 26.87 mm (SE = 0.05), n
= 558] had greater tarsal widths than mod-
erate-distance migrants [females: x – = 23.46
mm (SE = 0.11), n = 131, P < 0.001; males: x –
= 24.86 mm (SE = 0.11), n = 153, P < 0.001];
both of these groups were greater than the
long-distance migrants [females: x – = 22.68
mm (SE = 0.21), n = 36; short to long: P <
0.001; moderate to long: P = 0.003] [males:
x – = 24.12 mm (SE = 0.21), n = 38; short to
long: P < 0.001; moderate to long: P = 0.005].
Among State and Province populations, the
largest tarsal widths were observed in Alaska
(Appendix).
Table 2. Model selection results examining the effects of migration distance category (MD), latitude of breeding
location (Lat), longitude of breeding location (Long), and the compound effect of latitude and longitude of breed-
ing location (Lat*Long) on the body mass of female (n = 1,311) and male (n = 1,419) Common Loons sampled
across their North American breeding range from 1988 to 2012. Models are ranked according to Akaike Informa-
tion Criterion adjusted for small sample size (AICc). The table shows the variables included in the model, number
of estimated parameters (K), differences between model Akaike Information Criterion adjusted for small samples
size (ΔAICc), AICc weights (wi), and the amount of variation explained by the model (r2).
Model K ΔAICcwir2
Females
MD1+Lat2+Long3+Lat*Long4 5 0.000 0.909 0.66
MD + Lat + Long 4 5.552 0.057 0.66
MD + Long 3 6.559 0.034 0.66
MD + Lat 3 19.284 0.000 0.65
MD 2 167.335 0.000 0.65
Lat*Long 3 386.360 0.000 0.54
Lat+Long 2 962.297 0.000 0.29
Long 1 1,007.851 0.000 0.26
Lat 1 1,221.432 0.000 0.13
Males
MD+Lat+Long+Lat*Long 5 0.000 0.999 0.74
MD + Lat + Long 4 14.443 0.001 0.74
MD + Long 3 20.443 0.000 0.73
MD + Lat 3 49.510 0.000 0.73
MD 2 177.257 0.000 0.73
Lat*Long 3 529.061 0.000 0.62
Lat+Long 2 1,308.043 0.000 0.34
Long 1 1,350.686 0.000 0.32
Lat 1 1,638.399 0.000 0.16
Figure 1. Differences in body mass (g) among short
(< 1,500 km), moderate (1,500-3,499 km), and long (≥
3,500 km) distance migration categories for male and
female Common Loons banded on breeding territories
in Canada and the United States, 1988 to 2012. Box-
and-whisker plots represent median, interquartile range,
overall range, and outlier values of body mass (g). Short-
distance migrants: females: n = 791, males: n = 813; mod-
erate-distance migrants: females: n = 489, males: n = 572;
long-distance migrants: females: n = 31, males: n = 34.
boDy mass in Common Loons 69
Bill length ranged from 63.5 mm to 97.5
mm in females and 72.0 mm to 100.1 mm in
males. Bill length was weakly correlated with
body mass in both sexes (females: r2 = 0.20,
F737 = 182.97, P < 0.001; males: r2 = 0.10, F758 =
86.77, P < 0.001). ANOVA results indicated
that significant differences in bill length
were observed among the distance migra-
tion categories for both sexes (females: F757
= 90.45, P < 0.001; males: F790 = 70.06, P <
0.001) (Fig. 3). Pairwise comparisons with
Tukey’s HSD test showed that the bill length
of short-distance migrants [females: = 84.01
mm (SE = 0.19), n = 593; males: = 88.13
mm (SE = 0.18), n = 600] was greater than
the moderate-distance migrants [females: =
80.78 mm (SE = 0.41), n = 133, P < 0.001;
males: = 85.86 mm (SE = 0.36), n = 155, P
< 0.001]. Both of those groups had greater
bill lengths than the long-distance migrants
[females: x – = 73.72 mm (SE = 0.83), n = 32,
P < 0.001; males: x – = 79.81 mm (SE = 0.74),
n = 36; short to long: P < 0.001; moderate to
long: P < 0.001]. Among State and Province
populations, the longest bill lengths were
observed in Massachusetts (Appendix).
Breeding Pairs
Minimal correlation was detected be-
tween female body mass and the body mass
of its male mate among short-distance mi-
grant pairs (r2 = 0.07, F414 = 32.29, P < 0.001).
However, a slightly stronger correlation was
noted within pairs in the moderate-distance
migrant category (r2 = 0.20, F137 = 33.36, P
< 0.001). Small sample size precluded the
regression analysis of body mass for breed-
ing pairs in the long-distance migration cat-
egory. Male loons invariably weighed more
than their female mates, and the difference
increased with decreased migration distance
(Fig. 4). Male short-distance migrants aver-
aged 25% more in body mass [x – = 1,293 g
(SE = 22), n = 415] than their female mates.
In comparison, male moderate-distance
migrants averaged 21% more in body mass
[x – = 875 g (SE = 38), n = 138] than their fe-
male mates, which was significantly less than
the body mass difference observed within
short-distance migrant pairs (t551 = -10.46, P
< 0.001).
Tarsal diameter showed a similar pat-
tern as body mass; the tarsus of male short-
Figure 2. Differences in tarsus width (mm) among short
(< 1,500 km), moderate (1,500-3,499 km), and long
(≥ 3,500 km) distance migration categories for male
and female Common Loons banded on breeding ter-
ritories in Canada and the United States, 1997 to 2012.
Box-and-whisker plots represent median, interquartile
range, overall range, and outlier values of tarsus width
(mm). Short-distance migrants: females: n = 536, males:
n = 558; moderate-distance migrants: females: n = 131,
males: n = 153; long-distance migrants: females: n = 36,
males: n = 38.
Figure 3. Differences in bill length (mm) among short
(< 1,500 km), moderate (1,500-3,499 km), and long
(≥ 3,500 km) distance migration categories for male
and female Common Loons banded on breeding ter-
ritories in Canada and the United States, 1997 to 2012.
Box-and-whisker plots represent median, interquartile
range, overall range, and outlier values of bill length
(mm). Short-distance migrants: females: n = 593, males:
n = 600; moderate-distance migrants: females: n = 133,
males: n = 155; long-distance migrants: females: n = 32,
males: n = 36.
70 waterbirDs
distance migrants was = 2.1 mm (SE = 0.14;
n = 139) larger than their female mates,
which was greater than the tarsus width dif-
ference observed within moderate-distance
migrant pairs [x –= 1.37 mm (SE = 0.24), n =
43] (t180 = -2.43, P = 0.02) (Fig. 5). The bills
of male short-distance migrants were = 4.69
mm (SE = 0.49; n = 122) larger than their
female mates and the bills of male moderate-
distance migrants were x – = 4.14 mm (SE =
0.82; n = 43) greater in size than their mates
(Fig. 5). No significant differences in male
and female bill length were detected in ei-
ther group. Small sample size precluded the
comparison of tarsus widths and bill lengths
for breeding pairs in the long-distance mi-
gration category.
DisCussion
Body masses of Common Loons varied by
approximately two to threefold across their
breeding range with females ranging from
2,700 g to 6,200 g and males ranging from
3,250 g to 7,600 g. The heaviest males were
larger than Yellow-billed Loons (G. adamsii)
reported to date (Evers et al. 2010, 2014),
which were once considered as being the
largest of all the loon species (North 1994).
The body of the loon is streamlined to re-
duce drag while pursuing prey underwater,
and this is further achieved by holding the
wings very close to the body while swimming
(Barr 1973). Consequently, loon wings are
very narrow, 20 percent shorter than pre-
dicted for a bird of its size, and heavily cam-
bered (McIntyre 1988). The resultant trade-
off is one of the highest wing-loading ratios
of any breeding bird in North America (2.45
g/m2), which requires a runway of approxi-
mately 200 m to achieve lift (Poole 1938;
Welty and Baptista 1988). Once airborne,
loons beat their wings rapidly (~240 times/
min; Evers et al. 2010) and fly 112-129 kph
to keep their bodies aloft (Kerlinger 1982).
Thus, the physiological cost of transport for
loons is high (Hill et al. 2008), and the fit-
ness benefits associated with optimal time
management in migratory species (Alerstam
and Lindström 1990) would likely favor a
small body size for loons that perform long-
distance migrations.
The heaviest loons recorded were from
Maine and New Hampshire, which winter
within the Gulf of Maine south to Long Is-
land Sound—a distance of less than 500
km. In contrast, significantly smaller loons
breeding in the upper Great Lakes region
winter in the Gulf of Mexico—a distance of
greater than 1,500 km. Satellite movement
data of Common Loon migration indicate
that northeastern USA loons can arrive at
their wintering locations in 1 day, whereas
Figure 4. Mean plus standard error difference in body
mass (g) between male and female Common Loons of a
breeding pair according to migration distance category.
Short-distance migration (< 1,500 km): n = 415; moder-
ate-distance migration (1,500-3,499 km): n = 138.
Figure 5. Mean plus standard error difference in right
tarsus diameter (mm) and bill length (mm) between
male and female Common Loons of a breeding pair ac-
cording to migration distance category. Short-distance
migration (< 1,500 km): tarsus diameter (n = 127), bill
length (n = 116). Moderate-distance migration (1,500-
3,499 km): tarsus diameter (n = 44), bill length (n = 51).
boDy mass in Common Loons 71
interior loons have a protracted migration
of 4 to 10 weeks (Kenow et al. 2002, 2009;
Paruk et al. 2014; Biodiversity Research Insti-
tute, unpubl. data). The geographical gradi-
ent in body size revealed by our data (i.e.,
interior breeding populations in the upper
Great Lakes region and central Canada are
smallest in size and increase to the east and
west) supports the model that small body
size is favored over large body size in birds
using flapping flight for long-distance mi-
grations (Hein et al. 2012). It also supports
our original prediction that body size in
Common Loons is inversely related to mi-
gration distance between breeding and win-
tering areas. Similar variation in body size
has been observed in Canada Geese (Branta
canadensis), a species with 11 recognized
subspecies (Mowbray et al. 2002). However,
despite great differences in body size among
Common Loons, the geographic variation
was clinal and the designation of subspecies
originally proposed by Bishop (1921) for
smaller individuals in central North America
is not recommended.
Although many bird species have been
shown to adhere to Bergmann’s and James’s
Rules (James 1970; Ashton 2002; Meiri and
Dayan 2003), no strong support for a rela-
tionship between body size and latitude, and
therefore temperature, was found in Com-
mon Loons. For example, breeding loons
in Alaska were larger than those in the in-
terior of the continent; however, they were
not larger than breeding loons in the north-
eastern USA. It is expected that endotherms
with larger body sizes are favored in cooler
environments due to a decreased surface
area to volume ratio, which serves to mini-
mize heat loss. However, studies have shown
that feather mass and structure are perhaps
more important than body size with regard
to thermoregulation in birds (Scholander
1955; Geist 1987). It has also been proposed
that larger body size is favored in more sea-
sonal environments because larger animals
can store more fat and can use those stores
for greater survival during seasonal stress
(Boyce 1979; Lindstet and Boyce 1985).
Common Loons migrate in stages (Kenow
et al. 2002, 2009; Paruk et al. 2014), which
allows them to replenish fat stores along
their route, and so are likely not in need of
greater fasting endurance during seasonal
resource shortages.
Male loons were typically 22% heavier
than females in all migration categories.
Similarly, male diving seabirds may be up
to 25% larger than females and it has been
noted that they feed on larger prey items
and have different nitrogen isotopic signa-
tures (Croxall 1995; Bearhop et al. 2000,
2006; Forero et al. 2002, 2005). Barr (1973)
examined the digestive system of Common
Loons and concluded that males likely feed
on larger fish than females. Furthermore,
our data have shown that male loons have
larger bills than females, which supports the
belief of trophic segregation between the
sexes in Common Loons. Another potential
factor favoring size differences in loons is
that males engage in aggressive intra-sexual
contests for territories that can potentially
result in fatalities, whereas females do not
engage in such contests as often (Piper et al.
2008; Piper 2011). Piper et al. (2000) found
that 40% of loon territory changes between
years were due to usurpation by intruder
loons. Body size, muscle mass and strength
are intercorrelated in many animals (Le
Boeuf 1974; Whitham 1979; Dodson 1997;
Zeh 1997), and large body size is gener-
ally associated with an advantage in fighting
ability among a broad spectrum of animals
(Andersson 1994). If larger males are more
likely than smaller males to retain territo-
ries and/or mates, then selection should
favor larger-sized individuals. However, it is
unclear at this time if larger females experi-
ence fitness benefits. Among breeding pairs,
little correlation was detected between male
body size and that of its female mate. The
difference in body size was less pronounced
in pairs that migrated moderate distances
compared to short-distance migrant pairs,
suggesting that males, freed from the ener-
getic and physiological costs associated with
longer migration, increased in size relative
to females.
For body size (phenotypic variation) of a
species to be considered an adaptation, the
differences must also be genetic (Stillwell
72 waterbirDs
2010). Limited genetic research has been
conducted on Common Loons (Dhar et al.
1997; McMillan et al. 2004); more results will
be forthcoming (A. Lindsay and A. McMil-
lan, pers. commun.). Barbraud et al. (1999)
concluded that body size differences in Snow
Petrels (Pagodroma nivea) across a broad geo-
graphic scale were at least partly attributable
to genetic variation. Larger-sized petrels as-
sociated with coastal environments made sig-
nificantly shorter foraging trips compared
to smaller-sized individuals in more interi-
or environments. It was suggested that the
larger individuals made shorter trips to off-
set the increased energetic costs associated
with flapping flight for larger-bodied birds.
Across North America, Common Loons un-
dertake short, moderate, and long-distance
migrations between their seasonal environ-
ments. Our findings suggest that the body
size of regional populations is strongly influ-
enced by migration distance. Migration has
evolved as a strategy to maximize fitness in a
seasonal environment (Alerstam et al. 2003),
and, although we did not test for genetic dif-
ferences between our sampling areas, it is
likely that there is some genetic component
to body size variation in Common Loons.
However, we recognize the caveat of making
adaptive conclusions from phenotypic data
(Gienapp et al. 2008).
In conclusion, the morphometric data
collected from multiple Common Loon
populations across North America indicate
that short-distance migrants do not have
the physical constraints of long-distance mi-
grants and, therefore, selection favors larger
individuals that can more effectively com-
pete for limited high quality breeding terri-
tories. Further research on the heritability of
body size and other characteristics in loons
will likely better characterize underlying rea-
sons for geographically based variability in
Common Loon morphology.
aCknowLeDGments
All birds were banded in accordance with the gen-
eral conditions and specific authorizations of permits
granted by the USGS Bird Banding Laboratory, Cana-
dian Wildlife Service, and individual States and Prov-
inces. During the 25 years of this study, numerous
people (> 400) contributed to the capture and banding
of Common Loons. We offer each of them our sincere
gratitude and appreciation for their diverse contribu-
tions. However, we would like to thank especially the
following individuals for their dedicated service and
commitment to loon research and conservation and as
contributors of this project: Patty Baumgartner, Gael
Bissell, Neil Burgess, Louise Champoux, Dan Clark,
Peg Comfort, Cory Counard, Ariel Davila, Mary Derr,
Jeff Fair, Mark Fuller, Patty Freeman, Mark Fuller, Wing
Goodale, Ginger Gumm, Chris Hammond, Eric Han-
son, Jerry Hartigan, Jeff Hines, Liz Jozwiak, Larry Kal-
lemeyn, Joseph Kaplan, Gary Lee, Sarah Lord, Myron
Lysne, Andrew Major, Denny Masse, Amy McMillan,
Michael Meyer, Ken Munney, Kyle Murphy, Shearon
Murphy, Larry Neel, Matt O’Neal, John Ozard, Justin
Paugh, Dan Pepin, Chris Persico, Dan Poleschook, Amy
Sauer, Tony Scheuhammer, Joel Schmutz, Rocky Spen-
cer, Sally Stockwell, Keren Tischler, Harry Vogel, Lucy
Vlietstra, Mark Wayland, Jeff Wilson, Michael Yates, and
Sarah Yates. Our banding efforts started 25 years ago
at Seney National Wildlife Refuge, Michigan, and we
would like to extend our gratitude to Mike Tansey, Ref-
uge Manager, and Richard Urbanek, wildlife biologist,
who welcomed us into their backyard. We had no idea
we were embarking on a lifetime of devoted work.
Literature CiteD
Ainley, D. G. 1980. Geographic variation in Leach’s
storm-petrel. Auk 97: 837-853.
Alerstam, T. and Å. Lindström. 1990. Optimal bird mi-
gration: the relative importance of time, energy, and
safety. Pages 331-351 in Bird Migration: Physiology
and Ecophysiology (E. Gwinner, Ed.). Springer-Ver-
lag, Berlin, Germany.
Alerstam, T., A. Hedenström and S. Åkesson. 2003.
Long-distance migration: evolution and determi-
nants. Oikos 103: 247-260.
Alisauskas, R. T. 1987. Morphometric correlates of age
and breeding status in American coots. Auk 104:
640-646.
Andersson, M. 1994. Sexual selection. Princeton Uni-
versity Press, Princeton, New Jersey.
Ashton, K. G. 2002. Patterns of within-species body size
variation in birds: strong evidence for Bergmann’s
rule. Global Ecology and Biogeography 11: 505-523.
Barbraud, C., H. Weimerskirch, G. G. Robertson and
P. Jouventin. 1999. Size-related life history traits:
insights from a study of snow-petrels (Pagodroma
nivea). Journal of Animal Ecology 68: 1179-1192.
Barr, J. F. 1973. Feeding biology of the Common Loon
(Gavia immer) in oligotrophic lakes of the Canadian
shield. Ph.D. Dissertation, University of Guelph,
Guelph, Ontario, Canada.
Barrett, R. T., T. Anker-Nielsen and Y. V. Krasov. 1997.
Can Norwegian and Russian Razorbills Alca torda be
identified by their measurements? Marine Ornithol-
ogy 25: 5-8.
boDy mass in Common Loons 73
Bearhop, S., R. A. Phillips, D. R. Thompson, S. Waldron
and R. W. Furness. 2000. Variability in mercury con-
centrations of Great Skuas Catharacta skua: the influ-
ence of colony diet and trophic status inferred from
stable isotope signatures. Marine Ecology Progress
Series 195: 261-268.
Bearhop, S., R. A. Phillips, R. McGill, Y. Cherel, D. A.
Dawson and J. P. Croxall. 2006. Stable isotopes indi-
cate sex-specific and long-term individual foraging
specialization in diving seabirds. Marine Ecology
Progress Series 311: 157-164.
Bishop, L. B. 1921. Description of a new loon. Auk 38:
364-370.
Blackburn, T. M., K. J. Gaston and N. Loder. 1999.
Geographic gradients in body size: a clarification
of Bergmann’s rule. Diversity and Distributions 5:
165-174.
Boag, P. T. and P. R. Grant. 1981. Intense natural
selection in a population of Darwin’s finches
(Geospizinae) in the Galapagos. Science 214: 82-85.
Boyce, M. S. 1979. Seasonality and patterns of natural
selection for life histories. American Naturalist 114:
569-583.
Burnham, K. P. and D. R. Anderson. 2002. Model selec-
tion and multimodel inference: a practical informa-
tion-theoretic approach, 2nd ed. Springer Science
and Business Media, Inc., New York, New York.
Confederated Salish and Kootenai Tribes. 2008. Migra-
tion of Common Loons after staging on Flathead
Lake, Montana. Report submitted to the Montana
Fish, Wildlife, and Parks Commission, Kalispell,
Montana.
Cramp, S. and K. E. L. Simmons (Eds.). 1977. Hand-
book of the birds of Europe, the Middle East and
North Africa: the birds of the Western Palearctic,
vol. I: ostrich to ducks. Oxford University Press, Ox-
ford, U.K.
Croxall, J. P. 1995. Sexual size dimorphism in seabirds.
Oikos 73: 399-403.
Dhar, A. K., M. A. Pokras, D. K. Garcia, D. C. Evers, Z.
J. Gordon and A. Alcivar-Warren. 1997. Analysis of
genetic diversity in common loon Gavia immer using
RAPD and mitochondrial RFLP techniques. Molec-
ular Ecology 6: 581-586.
Dodson, G. N. 1997. Resource defense mating system in
antlered flies, Phytalmia spp. (Diptera: Tephritidae).
Annals of the Entomological Society of America 90:
80-88.
Environmental Systems Research Institute (ESRI).
2011. ArcGIS v. 10.1. ESRI, Redlands, California.
Evers, D. C. 1993. A replicable capture method for adult
and juvenile Common Loons on their nesting lakes.
Pages 214-220 in Proceedings from the 1992 Confer-
ence on the Loon and Its Ecosystem: Status, Man-
agement and Environmental Concerns (F. Stock-
well, Ed.). North American Loon Fund, Holderness,
New Hampshire.
Evers, D. C. 2001. Common Loon population studies:
continental mercury patterns and breeding territory
philopatry. Ph.D. Dissertation, University of Minne-
sota, St. Paul.
Evers, D. C., J. D. Paruk, J. W. McIntyre and J. F. Barr.
2010. Common Loon (Gavia immer). No. 313 in The
Birds of North America Online (A. Poole, Ed.). Cor-
nell Lab of Ornithology, Ithaca, New York. http://
bna.birds.cornell.edu/bna/species/313, accessed
10 January 2013.
Evers, D. C., J. A. Schmutz, N. Basu, C. R. DeSorbo, J.
Fair, C. E. Gray, J. D. Paruk, M. Perkins, K. Regan, B.
D. Uher-Koch and K. G. Wright. 2014. Historic and
contemporary mercury exposure and potential risk
to Yellow-billed Loons (Gavia adamsii) breeding in
Alaska and Canada. Waterbirds (Special Publication
1) 37: 147-159.
Forero, M. G., K. A. Hobson, G. R. Bortolotti, J. A.
Donazar, M. Bertellotti and G. Blanco. 2002. Food
resource utilization by the Magellanic Penguin eval-
uated through stable-isotope analysis: segregation
by sex and age and influence on offspring quality.
Marine Ecology Progress Series 234: 289-299.
Forero, M. G., J. Gonzalez-Solis, K. A. Hobson, J. A.
Donazar, M. Bertellotti, G. Blanco and G. R. Borto-
lotti. 2005. Stable isotopes reveal trophic segrega-
tion by sex and age in the Southern Giant Petrel in
two different food webs. Marine Ecology Progress
Series 234: 289-299.
Geist, V. 1987. Bergmann’s rule is invalid. Canadian
Journal of Zoology 65: 1035-1038.
Gienapp, P., C. Teplitsky, J. S. Alho and J. A. Mills. 2008.
Climate change and evolution: disentangling envi-
ronmental and genetic responses. Molecular Ecol-
ogy 17: 167-178.
Hedenström, A. 2003. Scaling migration speed in
animals that run, swim and fly. Journal of Zoology
(London) 259: 155-160.
Hedenstrom, A. and T. Alerstam. 1992. Climbing per-
formance of migrating birds as a basis for estimating
limits for fuel-carrying capacity and muscle work.
Journal of Experimental Biology 164: 19-38.
Hedenström, A. and T. Alerstam 1997. Optimum fuel
loads in migratory birds: distinguishing between
time and energy minimization. Journal of Theoreti-
cal Biology 189: 227-234.
Hedenström, A. and T. Alerstam 1998. How fast can
birds migrate? Journal of Avian Biology 29: 424-432.
Hein, A. M., C. Hou and J. F. Gillooly. 2012. Energetic
and biomechanical constraints on animal migration
distance. Ecology Letters 15: 104-110.
Hill, R. W., G. A. Wyse and M. Anderson. 2008. Animal
physiology. Sinauer Associates, Sunderland, Massa-
chusetts.
Itoh, Y., M. Suzuki, A. Ogawa, I. Munechika, K. Murata
and S. Mizuno. 2001. Identification of the sex of a
wide range of carinatae birds by PCR using primer
sets selected from chicken EE0.6 and its related se-
quences. Journal of Heredity 92: 315-321.
James, F. C. 1970. Geographic size variation in birds and
its relationship to climate. Ecology 51: 365-390.
Kenow, K. P., M. W. Meyer, D. C. Evers, D. C. Douglas
and J. Hines. 2002. Use of satellite telemetry to iden-
tify Common Loon migration routes, staging areas
and wintering range. Waterbirds 25: 449-458.
74 waterbirDs
Kenow, K. P., D. Adams, N. Schoch, D. C. Evers, W. Han-
son, D. Yates, L. Savoy, T. Fox, A. Mahor, R. Kratt
and J. Ozard. 2009. Migration patterns and winter-
ing range of Common Loons breeding in the north-
eastern United States. Waterbirds 32: 234-247.
Kerlinger, P. 1982. The migration of Common Loons
through eastern New York. Condor 84: 97-100.
Leafloor, J. O. and D. H Rusch. 1997. Clinal size varia-
tion in Canada Geese affects morphometric discrim-
ination techniques. Journal of Wildlife Management
61: 183-190.
Le Boeuf, B. J. 1974. Male-male competition and repro-
ductive success in elephant seals. American Zoolo-
gist 14: 163-176.
Lindsay, A. R. 2002. Molecular and vocal evolution in
loons. Ph.D. Dissertation, University of Michigan,
Ann Arbor.
Lindstet, S. L. and M. S. Boyce. 1985. Seasonality, fasting
endurance, and body size in mammals. American
Naturalist 125: 873-878.
Mager, III, J. N., C. Walcott and D. Evers. 2007a. Macro-
geographic variation in the body size and territorial
vocalizations of male Common Loons (Gavia im-
mer). Waterbirds 30: 64-72.
Mager, III, J. N., C. Walcott and W. H. Piper. 2007b. Male
common loons, Gavia immer, communicate body
mass and condition through dominant frequencies
of territorial yodels. Animal Behaviour 73: 683-690.
McGillivray, W. B. 1989. Geomorphic variation in size
and reverse size dimorphism of the Great Horned
Owl in North America. Condor 91: 777-786.
McIntyre, J. W. 1988. The Common Loon: spirit of
northern lakes. University of Minnesota Press, Min-
neapolis, Minnesota.
McMillan, A., M. J. Bagle and D. C. Evers. 2004. Char-
acterization of seven polymorphic microsatellite
loci in the Common Loon (Gavia immer). Molecular
Ecology 4: 297-299.
Meiri, S. and T. Dayan. 2003. On the validity of Berg-
mann’s rule. Journal of Biogeography 30: 331-351.
Moen, S. M. 1991. Morphologic and genetic variation
among breeding colonies of the Atlantic Puffin
(Fratercula arctica). Auk 108: 755-763.
Mowbray, T. B., C. R. Ely, J. S. Sedinger and R. E. Trost.
2002. Canada Goose (Branta canadensis). No. 682
in The Birds of North America Online (A. Poole,
Ed.). Cornell Lab of Ornithology, Ithaca, New York.
http://bna.birds.cornell.edu/bna/species/682, ac-
cessed 14 January 2013.
North, M. R. 1994. Yellow-billed Loon (Gavia adamsii).
No. 121 in The Birds of North America Online (A.
Poole, Ed.). Cornell Lab of Ornithology, Ithaca,
New York. http://bna.birds.cornell.edu/bna/spe-
cies/121, accessed 14 January 2013.
Paruk, J. D. 1999. Territorial takeover in the Common
Loon. Wilson Bulletin 111: 116-117.
Paruk, J. D., D. Long, IV, S. L. Ford and D. C. Evers. 2014.
Common Loons (Gavia immer) wintering off the Loui-
siana coast tracked to Saskatchewan during the breed-
ing season. Waterbirds (Special Publication 1) 37: 47-
52.
Piper, W. H. 2011. Troubled waters. Natural History 1:
22-26.
Piper, W. H., K. B. Tischler and M. Klich. 2000. Territory
acquisition in loons: the importance of take-over.
Animal Behaviour 59: 385-394.
Piper, W. H., C. Walcott, J. N. Mager and F. J. Spilker.
2008. Fatal battles in common loons: a preliminary
analysis. Animal Behaviour 75: 1109-1115.
Piper, W. H., D. C. Evers, M. W. Meyer, K. B. Tischler, J.
D. Kaplan and R. C. Fleisher. 1997. Genetic monog-
amy in the common loon (Gavia immer). Behavioral
Ecology and Sociobiology 41: 25-31.
Poole, E. L. 1938. Weights and wing areas in North
American birds. Auk 55: 511-517.
Promislov, D. E. L. and P. H. Harvey. 1990. Living fast
and dying young: a comparative analysis of life-his-
tory variation among mammals. Journal of Zoology
220: 417-437.
Rand, A. L. 1947. Geographical variation in the loon,
Gavia immer. Canadian Field-Naturalist 61: 193-195.
SAS Institute, Inc. 2010. JMP v. 9. SAS Institute, Inc.,
Cary, North Carolina.
Scholander, P. F. 1955. Evolution of climatic adaptation
in homeotherms. Evolution 9: 15-26.
Sedinger, J. S., P. L. Flint and M. S. Lindberg. 1995. En-
vironmental influence on life-history traits: growth,
survival and fecundity in black brant (Branta berni-
cla). Ecology 76: 2404-2414.
Sibley, C. G. and J. E. Ahlquist. 1990. Phylogeny and
classification of birds: a study in molecular evolu-
tion. Yale University Press, New Haven, Connecti-
cut.
Stillwell, R. C. 2010. Are latitudinal clines in body size
adaptive? Oikos 119: 1387-1390.
Storer, R. W. 1988. Variation in the Common Loon
(Gavia immer). Pages 54-65 in Papers from the 1987
Conference on Loon Research and Management
(P. Strong, Ed.). North American Loon Fund, Mer-
edith, New Hampshire.
U.S. Geological Survey. 2013. Common Loon migration
study. Unpublished report, U.S. Department of the
Interior, Geological Survey, Upper Midwest Environ-
mental Sciences Center, La Crosse, Wisconsin. www.
umesc.usgs.gov/terrestrial/migratory_birds/loons/
migrations.html, accessed 31 May 2013.
Vaurie, C. 1965. The birds of the Palearctic fauna: non-
Passeriformes. Witherby, London, U.K.
Welty, J. C. and L. Baptista. 1988. The life of birds, 4th
ed. Saunders College Publishing, New York, New
York.
Whitham, T. G. 1979. Territorial defense in a gall aphid.
Nature 279: 324-325.
Wojczulanis-Jakubas, K., D. Jakubas, J. Welcker, A. M.
A. Harding, N. J. Karnovsky, D. Kidawa, H. Steen,
L. Stempniewicz and C. J. Camphuysen. 2011. Body
size variation of a high-Arctic seabird: the dovekie
(Alle alle). Polar Biology 34: 847-854.
Zeh, J. A. 1997. Polyandry and enhanced reproductive
success in the harlequin beetle-riding pseudoscor-
pion. Behavioral Ecology and Sociobiology 40: 111-
118.
boDy mass in Common Loons 75
Appendix. Body mass, right tarsus width, and bill length of adult male and female Common Loons banded on breeding territories in Canada and the United States, 1988-2012.
State
Males Females
Body Mass (g) Tarsus Width (mm) Bill Length Body Mass (g) Tarsus Width (mm) Bill Length (mm)
Mean (SE) nMean (SE) nMean (SE) nMean (SE) nMean (SE) nMean (SE) n
Canadian Provinces
Alberta 3,963 (75) 24 24.48 (0.23) 29 79.45 (0.82) 26 3,255 (65) 23 22.77 (0.22) 30 72.80 ( 0.92) 24
Manitoba 4,156 (131) 8 23.00 (0.44) 8 81.24 (1.48) 8 3,341 (128) 6 22.40 (0.55) 5 76.10 (1.85) 6
New Brunswick 5,420 (111) 11 26.70 (1.25) 1 90.16 (2.42) 3 4,562 (90) 12 NA 83.99 (1.71) 7
Nova Scotia 5,751 (87) 18 26.96 (0.36) 12 87.86 (1.12) 14 4,461 (68) 21 25.06 (0.33) 14 83.14 (1.13) 16
Ontario 4,927 (99) 14 — — 3,646 (104) 9 NA NA
Quebec 4,867 (53) 49 25.22 (0.21) 36 86.52 (0.69) 37 3,819 (50) 39 23.85 (0.21) 33 81.26 (0.83) 30
Saskatchewan 3,792 (261) 2 22.60 (1.25) 1 — 3,267 (221) 2 21.1 (1.23) 1 77.55 (3.20) 2
U.S. States
Alaska 5,667 (77) 23 28.22 (0.51) 6 82.10 (1.16) 13 4,429 (63) 23 25.48 (0.50) 6 75.52 (1.51) 9
Maine 5,982 (18) 409 26.93 (0.07) 283 87.91 (0.24) 296 4,672 (16) 400 24.89 (0.08) 266 84.41 (0.26) 300
Massachusetts 5,666 (64) 33 26.18 (0.26) 23 90.31 (0.84) 25 4,672 (56) 31 25.25 (0.27) 20 85.92 (0.94) 23
Michigan 4,605 (33) 126 24.40 (0.34) 14 89.08 (0.76) 30 3,662 (30) 108 23.97 (0.46) 7 84.77 (1.07) 18
Minnesota 4,310 (33) 126 24.57 (0.17) 53 85.13 (0.79) 28 3,497 (31) 105 22.83 (0.19) 43 80.37 (0.83) 30
Montana 4,690 (54) 47 25.40 (0.19) 43 82.60 (0.66) 40 3,863 (45) 48 23.98 (0.19) 42 78.79 (0.71) 41
New Hampshire 5,972 (28) 170 26.85 (0.12) 115 88.72 (0.37) 129 4,679 (25) 155 24.84 (0.11) 114 84.23 (0.41) 120
New York 5,593 (33) 123 26.90 (0.13) 95 88.83 (0.42) 101 4,295 (29) 119 24.75 (0.12) 97 83.50 (0.46) 97
Vermont 5,490 (111) 11 26.79 (0.40) 10 88.17 (1.32) 10 4,374 (90) 12 24.60 (0.39) 10 83.44 (1.36) 11
Washington 5,132 (95) 15 25.96 (0.35) 13 81.49 (1.40) 9 4,032 (78) 16 24.24 (0.41) 9 79.43 (1.43) 10
Wisconsin 4,550 (26) 210 22.73 (0.47) 7 87.34 (0.94) 20 3,651 (23) 180 21.72 (0.50) 6 81.36 (1.21) 14
