2009 NORTHEASTERN NATURALIST 16(4):501–518
Composition of Eiders Harvested in Newfoundland
Scott G. Gilliland1,* and Gregory J. Robertson2
Abstract - Somateria mollissima (Common Eider) is an important game species
throughout its circumpolar range, including eastern Canada and northeastern United
States. In eastern Canada, the largest harvest of Common Eiders occurs in Newfoundland;
however, the age, sex, and subspecific composition (S. m. borealis and dresseri
are both present) of this hunted population is not well quantified. The species, subspecies,
age, and sex composition of the harvest was determined by examining heads
collected from 1672 eiders (including Somateria spectabilis [King Eider]), taken
mostly by hunters, from 1980–1996. Band-recovery information for Common Eiders
banded in Newfoundland and Labrador were also summarized, including data from a
release program of hand-reared ducklings in northern Newfoundland from 1988–1996.
The composition of the eider harvest varied across the province. In northern and eastern
areas, borealis Common Eiders made up the bulk of the harvest. King Eiders were
also taken in these areas. In southern areas, most Common Eiders taken were dresseri.
Sex ratios tend to be near 1:1, and immature birds comprised most of the harvest.
Recovery distributions showed that Common Eiders breeding in Newfoundland and
Labrador were mainly taken within the province, but also contributed to harvests in
Québec and Nova Scotia, and to a lesser extent, Maine. Hand-reared ducklings had
direct recovery rates of 0.047 and were most likely to be recovered within the province
in the year of banding, but contributed to harvests in Atlantic Canada and New England
as they aged. The harvest of eiders in Newfoundland varies regionally and seasonally;
therefore specific harvest regulations could be implemented to manage the variety of
populations present in the province throughout the year.
Introduction
Somateria mollissima L. (Common Eider) is a wide-ranging circumpolar
species that has a long history of utilization by people. The largest of the sea
ducks, Common Eiders have been, and continue to be, an important source
of meat, eggs, and down to northern aboriginal peoples. More recently, recreational
harvests have developed in the southern areas of their range and
sustainable down-collection industries have been developed at some breeding
areas (Bédard et al. 2008).
In eastern North America, Common Eider numbers were depleted
at the turn of the 20th century, and were one species specifically considered
in the Migratory Bird Treaty negotiated between the United States and
Canada. Unlike most ducks, Common Eiders vary across their range in size
and other morphological features, leading to the recognition of 7 subspecies
worldwide. In eastern North America, 2 of these sub-species are present: the
1Canadian Wildlife Service, Environment Canada, 6 Bruce Street, Mount Pearl,
NL A1N 4T3, Canada. 2Wildlife Research Division, Environment Canada, 6 Bruce
Street, Mount Pearl, NL A1N 4T3, Canada. *Corresponding author - scott.gilliland@
ec.gc.ca.
502 Northeastern Naturalist Vol. 16, No. 4
S. m. dresseri (American) and S. m. borealis (Northern) subspecies (Mendall
1980). The American Common Eider breeds from southern Labrador south
to New England, and winters within this range, with most of the northern
breeding populations of American Common Eiders moving south to some
degree in winter (Goudie et al. 2000). The Northern subspecies breeds in
Labrador and north throughout the eastern Canadian Arctic and Greenland;
some move south ahead of the ice to Québec and Newfoundland in the nonbreeding
season, while others move east to winter in Greenland (Mosbech et
al. 2006). Along the coast of Labrador, an intermediate form (intergrades) of
the 2 subspecies is found breeding (Mendall 1980, 1986).
The coast of insular Newfoundland is an important wintering area for
both Somateria spectabilis L. (King Eider) and Common Eiders (Reed and
Erskine 1986), and the Common Eider is one of the most important game
birds in Newfoundland and Labrador (Wendt and Silieff 1986). The size of
the Common Eider population breeding in insular Newfoundland is small
(7000 pairs of dresseri; S.G. Gilliland, unpubl. data); hence, most of the
100,000+ eiders that over-winter in Newfoundland waters (Gilliland et al.
2009; Canadian Wildlife Service, St. John's, NL, Canada, unpubl. data)
must originate from breeding areas along the coasts of Labrador, northern
Québec, and the eastern Canadian Arctic. Since 1975, when regular harvest
surveys began, the harvest of Common Eiders in Newfoundland has ranged
from 4500 to over 23,000 birds, averaging 11,500 birds, and is usually the
largest harvest of Common Eiders of all the provinces in Canada (Gendron
and Collins 2005). Due to inherent biases in the these surveys (Chardine
et al. 2008, Wendt and Silieff 1986), these estimates likely underestimate
the true level of harvest. Previous descriptions of eiders wintering in
Newfoundland were based on anecdotal observations (see Gillespie and
Learning 1974), but indicated that of the two subspecies of Common Eiders
present, the borealis subspecies comprised the majority of wintering
birds (Reed and Erskine 1986). Gillespie and Learning (1974) indicated
that borealis were found primarily off the north, east, and southeast coasts
of Newfoundland, whereas smaller numbers of dresseri wintered off the
south and southwest coasts of the island.
Information on the species and subspecies composition of eiders wintering
in Newfoundland is important as dresseri and borealis Common Eider
and King Eider populations face different environmental conditions and
anthropogenic pressures (Reed and Erskine 1986). The breeding population
of dresseri in Newfoundland is currently depressed but is showing signs of
recovery, while borealis birds breeding in Canada and Greenland are showing
different regional trends and face different harvest pressures (Chaulk et
al. 2005, Christensen and Falk 2001, Gilliland et al. 2009, Merkel 2004a).
It is also not possible to distinguish subspecies during aerial surveys, so
estimates of subspecies composition are essential for determining the size of
these wintering populations from aerial survey data.
The purpose of this paper was to summarize several data sets useful
for management of eiders in Newfoundland and Labrador, with the overall
2009 S.G. Gilliland and G.J. Robertson 503
goal of obtaining a better understanding of how Common Eider populations
are structured and utilized in eastern North America. We compiled
information from collections of eiders of both species shot by hunters, and
information from recoveries of Common Eiders banded in Newfoundland
and Labrador. Specifically we describe the spatial and temporal distribution
of the age, sex, species, and sub-specific composition of eiders harvested in
Newfoundland. The spatial and temporal distributions of band recoveries of
eiders banded in Newfoundland and Labrador were analyzed to determine
the contribution of the local breeding populations to the harvest. We also
estimate juvenile recovery rates and adult survival rate from a data set of
hand-reared pre-fledging Common Eiders released in northern Newfoundland
as part of efforts to re-build local populations, and comment briefly on
the contribution of these hand-reared birds to harvest.
Methods
Examination of harvested bird carcasses
Demographic and morphological measurements from 1672 Common
Eiders and King Eiders were collected in insular Newfoundland, primarily
of birds taken between 1981 and 1996, with a focus during 1985–1987 (n =
972) and 1994–1995 (n = 364), while a small portion of the collections occurred
before 1980 (n = 12). The data were compiled from several sources:
birds collected under various scientific collection permits (n = 20), confiscations
of birds that were taken illegally (n = 137), and eider heads collected
from hunters (n = 1535). For the bulk of the sample that came from hunters,
individuals in communities where eider hunting is common were contacted
and asked to supply heads from birds they had shot. Therefore, the sample
cannot be treated as randomly collected, but opportunistically collected from
a representative set of communities that regularly hunt eiders. The legal
eider-hunting season in Newfoundland spanned approximately 107 days
from late November to 10 March in 1980–1997; in 1998, the season was
reduced to approximately 78 days, ending at the end of February. Daily bag
limits were 12 eiders from 1980–1990 and 6 eiders from 1990–2000 (with a
further reduction to only 3 eiders in the month of February from 1997–2000).
Possession limits were twice the daily bag limit.
Where possible, we recorded the following information for each bird:
species (King or Common Eider), sex, age of males based on plumage
(adult: after second year, immature: second-year or hatch-year), and date
and location of the collection. Females cannot be reliably age based on
plumage alone. We also took the following complete set of bill measurements
from 1182 birds: culmen midline, exposed culmen, nostril extension,
and frontal extension (Mendall 1980, 1986). Data were recorded on standardized
data sheets to help ensure repeatability of measurements, and the
bulk of the data was collected by 3 experienced biologists familiar with
eiders. Information was incomplete for some birds; hence, sample sizes
vary across the various summaries of the database.
504 Northeastern Naturalist Vol. 16, No. 4
Following Mendall’s (1986) key, we used 4 bill measurements to classify
Common Eiders into 1 of 4 subspecies classes: dresseri, borealis,
borealis-dresseri intergrades, and “borealis or intergrade.” Because our
primary interest was to determine if Common Eiders originated within
the breeding range of S. m. borealis (High Arctic and Low Arctic population
groups; Reed and Erskine 1986), or within the breeding range of S. m.
dresseri (Atlantic population breeding group; Reed and Erskine 1986), we
collapsed the three S. m. borealis subspecies classes (borealis, intergrades
and “borealis or intergrades”) into a “borealis-type” class. We assumed
that all Common Eiders classified as dresseri originated from the Atlantic
population breeding group.
The data collections were made from several locations. For the purposes
of our analysis, we pooled samples into 5 coastal areas: 1) Northeast Coast,
2) Bonavista, 3) Avalon, 4) Burin, and 5) South Coast (Fig. 1). Additionally,
to maintain sufficient sample sizes in examining temporal patterns in the
subspecies composition, we further pooled the three northeastern coastal areas
(Northeast Coast, Bonavista, and East Avalon; the Northeastern Coastal
Zone), and the 2 southern coastal areas, (Burin and South Coast; the Southern
Coastal Zone).
Band recoveries
Banding and recovery data for all the Common Eiders banded in Newfoundland
and Labrador were provided by the Bird Banding Office, Canadian
Wildlife Service, for recoveries up to January 2000. Between 1983 and 1996,
857 adult female Common Eiders were banded in Groswater Bay and Table
Bay in Labrador, and St. John Bay, Hare Bay, and Grey Islands in northern
Newfoundland from 1983–1996. During 1988–1996, 3413 hand-reared
ducklings were banded and released at Hare Bay and Sacred Bay in northern
Newfoundland, and 156 hand-reared ducklings were banded and released in
1990 and 1991 at Oderin Island, in southern Newfoundland (Fig. 1; more on
this hand-rearing program below). Our analyses were restricted to recoveries
of these birds shot between September and April. We summarized the temporal
and spatial distribution of these recoveries.
A Common Eider propagation project was initiated in 1988, and was
intended to increase the relatively small number of Common Eiders that
nested in Hare Bay, Newfoundland. Smaller initiatives were undertaken at
Sacred Bay and Oderin Island. Eider eggs were collected from colonies in
Newfoundland, Nova Scotia, and Québec, and incubated to hatch. The ducklings
were dry-brooded until they were four-weeks old, moved to a holding
facility adjacent to a small eider colony, and allowed access to salt water for
one to two days before being released.
For the hand-reared ducklings released at Hare Bay, Sacred Bay, and
Oderin Island, we determined the sex ratio at release and tested for differences
in spatial patterns of direct recoveries (shot in the year immediately
following banding) and indirect recoveries (shot one or more years after
banding) (recovery type) using a chi-square test for goodness of fit (Zar
2009 S.G. Gilliland and G.J. Robertson 505
1984). We ensured data were homogeneous before pooling across release
sites and years, and determined if there were different spatial patterns
Figure 1. Locations of Common Eider banding sites in Labrador and Newfoundland,
primary locations where eiders were collected by hunters, and delineation of coastal
areas used for data summaries.
506 Northeastern Naturalist Vol. 16, No. 4
of recovery type using a heterogeneity χ2 test (Zar 1984). We then used
recoveries of hand-reared ducklings released in Hare Bay and Sacred Bay
to estimate juvenile recovery rates (f ’) and adult (1+ year old) survival (S),
using Program MARK (White and Burnham 1999). Because there were only
a small number of hand-reared ducklings released from Oderin Island in
southern Newfoundland, we excluded them from this analysis. As we were
constrained by a data set that only included juvenile marked birds, juvenile
survival rates (S’) and adult recovery rates (f) could not be calculated
(Brownie et al. 1985). However, if juvenile survival is held constant over
time, adult survival rates are estimable (Barker and Buchanan 1993). Computationally,
this is achieved by combining juvenile survival rates and adult
recovery rates in a single parameter θ (Barker and Buchanan 1993). Model
fitting was done by sequentially fitting models with fewer parameters. The
global model allowed for sex and time (t) variation in all rates (S, f ’, and θ).
Akaike’s information criterion (corrected for small sample sizes; AICc) was
used to assess model fit. Reduced parameter models of juvenile recovery
rates (f ’) were built first as they do not influence calculations of the other
parameters in the model. Once the best-fitting parameterization for f ’ was
found, θ was modeled. Finally the parameter of interest, adult survival S,
was modeled with the best-fitting parameterizations of f ’ and θ. Due to the
relatively sparse data, we could not calculate meaningful estimates of the
variance inflation factor (ĉ). Sufficient data were not available to estimate
adult survival rates from birds banded as adults, and their recovery rates
were previously reported in analyses by Krementz et al. (1996).
Results
Examination of harvested bird carcasses
King Eiders constituted 10% of the birds examined (n = 1672), and most
were taken in the Northeast Coastal Zone (Fig. 2, and specifically in the eastern
portion of this zone [Fig. 1]). Males constituted 54.7% of the population,
and the sex ratio did not significantly deviate from 1:1 (χ2 =1.5, df = 1, P =
0.22), or vary across the non-breeding season (χ2 =4.3, df = 5, P = 0.50). The
majority of male King Eiders were immature birds (85%, n = 91).
The sub-specific classification for Common Eiders was: 25% dresseri,
20% borealis, 2% intergrades, and 53% “borealis or integrade” (n = 1205);
285 birds were not classified because of missing data. The combined “borealis-
type” class comprised 75% of the sample. The sex ratio of harvested birds
did not vary detectably over the non-breeding season (χ2 = 3.8, df = 6, P =
0.70), with 49% males, which did not detectably differ from a 1:1 ratio (χ2 =
0.48, df = 1, P = 0.49). The majority of male Common Eiders were immature
birds (60%, n = 706).
Along the Northeast Coast, Bonavista, and the Avalon areas, the majority
of Common Eiders were the borealis-type (Fig. 2), primarily taken from
January to March (Fig. 3). Along the South Coast and Burin coastal areas,
the majority was dresseri (Fig. 2), and the largest harvests were in November
2009 S.G. Gilliland and G.J. Robertson 507
and December (Fig. 3). In the Northeastern Coastal Zone, borealis-type
eiders dominated the harvest from October to April, while in the Southern
Coastal Zone, dresseri was dominant in all months except April (Fig. 4).
Figure 2. Species
composition of eiders
(King and Common
Eider) and subspecific composition of
Common Eiders in
each coastal area for
eiders hunted in Newfoundland,
1980–
1996 (sample sizes in
parenthesis).
508 Northeastern Naturalist Vol. 16, No. 4
Figure 3. Seasonal distribution
of Common
Eiders collected from
hunters in Newfoundland
from 1980–1996.
2009 S.G. Gilliland and G.J. Robertson 509
Band recoveries
Up until 2000, there had been 243 recoveries of Common Eiders
banded in Newfoundland and 57 recoveries of birds banded in Labrador
(includes all wild and hand-reared birds of all ages). These recoveries
occurred in coastal areas of eastern Canada and the New England States
(Fig. 5). The majority of the recoveries were on the island of Newfoundland;
54% (31 of 57) of recoveries from birds banded in Labrador and
79% (192 of 243) of recoveries from birds banded in Newfoundland, were
on the island of Newfoundland. Within Newfoundland, 60% of recoveries
were within the Northeastern Coastal Zone, while the remaining 40%
were in the Southern Coastal Zone (n = 165).
Recovery of hand-reared ducklings. The sex ratio at release did not
deviate significantly from a 1:1 ratio of males to females (χ2 = 0.518, 1 df,
Figure 4. Seasonal
distribution of the
Common Eider
harvest by sub-species,
for the Northeastern
and Southern
Coastal zones
for eiders hunted
in Newfoundland
from 1980–1996
(sample sizes in
parenthesis).
510 Northeastern Naturalist Vol. 16, No. 4
P = 0.472, n = 3569) and was homogeneous across years and release sites
(χ 2 = 11.1, df = 9, P = 0.94, n = 3569). Recoveries of ducklings released from
the Northern Peninsula occurred from Table Bay, Labrador south to Massachusetts
(Fig. 5). The majority of recoveries (80%) were in Newfoundland
and St. Pierre and Miquelon, with smaller numbers occurring in Labrador
Figure 5. Recovery distributions of hand-reared Common Eiders released at Hare Bay
(a) and Sacred Bay (b), Newfoundland, and wild female Common Eiders captured at
breeding colonies in southeastern Labrador (c) and northern Newfoundland (d).
2009 S.G. Gilliland and G.J. Robertson 511
(1%), Québec (5%), Nova Scotia (8%), and the New England States (5%).
Within Newfoundland, in the Northeastern Coastal Zone, most recoveries
were made late in the fall and early winter, while recoveries in the Southern
Coastal Zone were similar from November to March, except for a notable
peak in December (Fig. 6). Recoveries from Newfoundland, St. Pierre and
Miquelon, Labrador, Quebec, and the New England States were pooled
(Nova Scotia was kept separate) to examine regional patterns of recovery
type, and differed among areas (χ 2 = 37.9, df = 3, P > 0.001, n = 226). The
primary difference in the pattern of direct and indirect recoveries was that a
larger proportion of the indirect recoveries occurred in Nova Scotia and the
New England States than expected (Fig. 7).
Juvenile recovery rates of hand-reared ducklings banded only in northern
Newfoundland were best modeled with time variation, with little evidence
of a difference between the sexes (Table 1). The mean juvenile recovery
rate (based on a random effects model) was 0.047 ± 0.007 (SE). θ was best
modeled as a constant. Models with time variation or constant adult survival
were similarly well supported, while there was only weak support for a sex
difference. Due to sparse data and poor estimation of time-specific survival
rates, model averaging was not useful, so the constant adult survival rate of
0.715 ± 0.051, with a 95% profile likelihood interval of 0.605 to 0.803, is
presented. Direct recovery rates of hand-reared ducklings released at Oderin
Island in southern Newfoundland in 1990–91 were high, at 0.147 ± 0.028 (23
of 156 banded ducklings).
Figure 6. Seasonal distribution of band recoveries reported by hunters for Common
Eiders banded in Newfoundland and Labrador, and recovered in the Northeastern
Coastal and Southern Coastal zones of Newfoundland.
512 Northeastern Naturalist Vol. 16, No. 4
Discussion
The composition of eiders harvested in Newfoundland varies considerably
across the province. In northern and eastern areas, King Eiders are taken
in some number, with borealis-type Common Eiders making up the bulk of
Figure 7. Geographic distribution of direct (hatch-year) and indirect (after-hatchyear)
band recoveries for hand-reared Common Eiders released in Newfoundland
(sample sizes in parenthesis).
Table 1. Model selection results for hand-reared Common Eiders released at 4 weeks of age in
northern Newfoundland, 1998–1996.
Model Number of
ModelA AICc ΔAICc likelihood parameters Deviance
St, f ’t, θ 2135.1 0.00 1.000 20 84.7
S, f ’t, θ 2135.3 0.20 0.927 11 103.0
Ssex, f ’t, θ 2137.3 2.10 0.347 12 103.0
Ssex*t, f ’t, θ 2145.7 10.5 0.005 29 77.0
Ssex*t, f ’t, θsex 2147.1 12.0 0.003 30 76.4
Ssex*t, f ’t, θt 2160.3 25.2 0.000 38 73.2
Ssex*t, f ’t, θsex*t 2172.5 37.4 0.000 47 67.0
Ssex*t, f ’sex, θsex*t 2181.1 46.0 0.000 40 89.9
Ssex*t, f ’, θsex*t 2183.6 48.5 0.000 39 94.5
Ssex*t, f ’sex*t, θsex*t 2184.4 49.3 0.000 56 60.3
AS = adult (1+ year) survival rate, f ’ = juvenile recovery rate, and θ = product of juvenile survival
rate and adult recovery rate.
2009 S.G. Gilliland and G.J. Robertson 513
the harvest. Along the south coast of Newfoundland, dresseri-type birds
predominated. However, both regions had mixes of the two sub-species in
their harvest—notably, some proportion of borealis were taken throughout
the season along the southern coasts of Newfoundland.
Sexes appeared to be equally represented in the harvest of King and Common
Eiders in the province. In many ducks, males comprise a larger portion
of the harvest, and often there are more males in the population (Johnson et
al. 1992). Sex ratios in the long-lived sea ducks, notably eiders, are probably
closer to even (Swennen et al. 1979). Data from the Species Composition
Survey (SCS) for Common Eiders taken in Newfoundland 1972–2006, show
a slight female bias in the harvest (45% male; Gendron and Collins 2005).
In Greenland, sex ratios of hunted birds were slightly male biased (57%) for
Common Eiders, and even for King Eiders (Merkel 2004b). Similarly, males
comprised 58% of the Common Eider harvest in Denmark (Noer et al. 1995).
Large portions of the harvest comprised immature birds. This was expected,
as immature waterfowl, including eiders, tend to be more susceptible to
harvest (Joensen 1974). The SCS for Common Eiders taken in Newfoundland
1972–2006, show 60% of male eiders taken were immature (Gendron
and Collins 2005), the same value found in our study. Similarly, hunters in
Greenland took mostly immature birds (76–96% of Common Eiders and
56–92% of King Eiders harvested; Merkel 2004b), while 45% of the harvest
in Denmark comprised immature Common Eiders (Noer et al. 1995).
The temporal, spatial, species, subspecies, age, and sex distributions
based on information collected from hunters, will reflect to a degree, the
overall distribution of animals, but temporal and spatial patterns in hunting
effort and sampling intensity, as well as differences in vulnerability to hunting
among cohorts (e.g., age or sex) will lead to biases. We suspect the sex,
species, and sub-specific composition of the harvest to reasonably reflect the
overall eider populations in the region. The age structure of the harvest is not
likely to reflect the population due to the higher vulnerability of immature
birds. Temporal patterns in harvest, however, are more difficult to interpret,
as they will reflect bird movements, local abundance of birds, and the behavior
of hunters.
The eider duck hunting season has generally lasted from late November
to 10 March or late February over the study period. Because so few of our
collections occurred outside the hunting season, the composition of eiders
observed during the early fall and the spring may not fully reflect the distribution
of eiders during these periods. The weather and sea-ice limits, and
in some circumstances enhances, hunting opportunities in Newfoundland.
Generally the weather, and its effect on sea conditions, is too severe to allow
unrestricted access to areas suitable for sea-duck hunting. This limitation is
especially true along the eastern portions of the Avalon Peninsula in January
and February, so samples from this region of the Avalon were limited. The
sea-ice that forms along the coast of Labrador and the eastern Canadian Arctic
moves southward along northeastern Newfoundland in January through
514 Northeastern Naturalist Vol. 16, No. 4
April. Sea-ice both affects the duck hunter’s access to specific hunting areas
and the locations of eider concentrations along the Northeast Coast. Sea-ice
can serve as a barrier to hunters, but also has a calming effect on seas and
will concentrate the eiders, making them more vulnerable to hunting if they
can be reached. It is not known whether the composition of eiders harvested
during heavy ice conditions would be the same in conditions with less ice.
Nevertheless, the geographical distribution of our sample generally reflects
previously described distributions of wintering eiders (Canadian Wildlife
Service, St. John's, NL, Canada, unpubl. data; Gillespie and Learning 1974)
and hunting effort (Wendt and Silieff 1986) in Newfoundland.
Affiliations and movements
American Common Eiders are harvested throughout the hunting season
in Newfoundland and are the dominant subspecies of Common Eider
taken along the South Coast, Burin Peninsula, and the French islands of St.
Pierre and Miquelon. While they comprise a smaller component of the take
along the Northeast Coast, this area over-winters the largest concentration
of eiders in the province, and significant numbers of dresseri-type Common
Eiders likely over-winter in this area. The temporal patterns of band
recoveries for the hand-reared eiders released from the Northern Peninsula
suggest that these birds begin their southern migration by November, with a
pulse of birds that moves through the Northeast Coast during the fall. Some
birds appear to stop and winter along the Northeast Coast, but most move
to the South Coast and French islands to winter. As these birds aged, they
were more likely to be recovered in locations south of Newfoundland, likely
a function of a developing migration strategy and integration with the wild
populations as they matured. In spite of being hand-reared, these birds did
migrate seasonally, as is typical of wild eiders. The eiders that breed along
the south coast of Labrador have similar movement patterns to the birds from
the Northern Peninsula, although a larger proportion of these birds move to
wintering areas around the Mingan and Anticosti Islands in Quebec, and the
Maritime Provinces (Bourget et al. 1986).
There is less information from which to determine the timing of migration,
or the breeding affiliations for borealis and King Eiders. A large
number of Common Eiders were classified in the “integrade” or “borealis or
integrade” categories, suggesting many of the birds harvested in Newfoundland
may be breeding in Labrador. However, Mendall’s key was developed
with a limited number of samples of northern birds from a restricted number
of sites, so this conclusion is somewhat tenuous. For birds breeding farther
north in Arctic Canada, some move south to Newfoundland waters to
winter, but many winter in Greenland (Lyngs 2003, Mosbech et al. 2006),
while Common Eiders marked as breeding in Greenland have not been recovered
in Newfoundland. These patterns suggest that many of the borealis
Common Eiders wintering in Newfoundland (and Québec) are likely from
more southerly breeding areas for the subspecies, but samples are limited
and more work (banding and telemetry) is needed to fully understand the
2009 S.G. Gilliland and G.J. Robertson 515
sources of Common Eiders wintering in Newfoundland. Northern Common
Eiders arrive at wintering areas in Newfoundland by November, but the
temporal patterns of the eider harvest (assuming our data reflect relative
level of harvest) suggest most arrive in northeastern Newfoundland, their
primary wintering area, between December and March. As for King Eiders,
Mehl et al. (2004) has shown that this species may range widely in winter,
and although sample sizes were limited, they had evidence that individual
birds wintered in different ocean basins (Pacific and Atlantic) in subsequent
seasons. The harvest of King Eiders in eastern North America is very small
overall; only in Greenland are significant numbers taken (Merkel 2004b).
Direct recovery rates of hand-reared eiders averaged close to 5%, and
varied annually. Adult female Common Eiders breeding in Atlantic Canada
had recovery rates around 1% (Krementz et al. 1996), considerably lower
than juvenile birds. Once again, higher susceptibility of juveniles to harvest
was expected, and these data show juveniles may be 5 times more
susceptible to harvest. However, this analysis was based on hand-reared
birds, which may have higher than usual recovery rates. Interestingly, direct
recovery rates of birds released at Oderin Island, which unlike Hare
Bay and Sacred Bay, does not have a local breeding population, had very
high direct recovery rates of 15%. With no adult birds to accompany, these
young birds may have been more vulnerable to harvest. Although this study
was not designed to assess the relative importance of releasing hand-reared
birds in to an area with or without local wild populations, the difference in
recovery rates would suggest releasing birds to an area with a remaining
wild population may be beneficial.
Krementz et al. (1996) documented a survival rate of 0.87 for adult
breeding females in Atlantic Canada, so the adult survival rates of 0.71
shown in our study are low for Common Eiders, although not unheard of
in over-hunted populations (H.G. Gilchrist, Environment Canada, Ottawa,
ON, Canada, pers. comm.). However, the survival rate has wide confidence
intervals, and a number of assumptions were required to obtain this estimate.
The survival rate assumes that survival reaches a plateau after one year of
age, which is likely not the case for a bird that shows delayed maturation.
The constraints imposed in our modeling efforts may have biased estimates
of adult survival rates; however, Barker and Buchanan (1993) showed that
any bias introduced by constraining juvenile survival rate to be constant
did not bias adult survival rates too much, if juvenile survival rates did not
fluctuate widely. Finally, released birds were hand-reared, and for a variety
of reasons may not have survival rates comparable to wild adult birds once
they reached maturity. As such, we would not recommend using the value
of 0.71 as the current estimate of adult survival of Common Eiders breeding
in Newfoundland, but rather suggest this estimate may indicate that prebreeding
age classes have reduced survival rates and that harvest rates or
natural mortality of hand-reared birds may have been relatively high over
the period of study (1988–2000).
516 Northeastern Naturalist Vol. 16, No. 4
Management implications
Currently, the species, age, and sex composition of the duck harvest in
Canada, including eiders, is estimated from the Species Composition Survey.
This survey uses duck wings, collected from hunters, to determine the
composition of the harvest. However, there are no criteria for classifying
the sub-species of Common Eiders using wing characteristics. The subspecific composition of the eider duck harvest is an important demographic
parameter to monitor for the management of Common Eiders in eastern
North America and Greenland. The results of this study show that considerable
demographic information on the eider duck harvest can be obtained
from the collection of eider heads, and we believe a regular, and statistically
valid, annual collection of eider heads would be worth considering.
The timing and relative contribution of borealis and dresseri to harvest
were different between the Northeastern Coastal and the Southern Coastal
zones. Because the size and productivity of these populations are different,
they may benefit from different harvest management regimes. Depending on
management goals, seasons could be varied within these zones to modify the
sub-specific composition of the harvest. For example, if protection of locally
breeding dresseri was the priority, the hunting season in the Northeastern
Coastal Zone could be delayed; possibly allowing a large portion of migrating
dresseri to pass through this area before the hunt begins. Similarly, if
protection of borealis was of concern, the seasons could be adjusted. For
example, the eider season in the Northeastern Coastal Zone could be closed
in the latter part of the winter, when hunting mortality will likely have the
largest effect on population growth, while the season in the Southern Coastal
Zone need not be affected.
Acknowledgments
We thank Ian Goudie, who provided unpublished data, and Jean-Pierre Savard,
who reviewed an earlier version of this paper. Pierre Ryan coordinated the collection
in Newfoundland, Canada, and Rodger Etcheberry the collection in St. Pierre
and Miquelon, France. Lance Woolaver measured all the heads, and Rina Nickols
compiled the initial data summaries. Finally, we thank all the hunters who provided
the heads used in this study.
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