Greater Snow Goose
The Greater Snow Goose is a large migratory
bird that breeds principally in the Eastern Canadian
High Arctic, from North Baffin Island to North Ellesmere
Island, with some birds also breeding in West Greenland.
Geese come to the Arctic during the summer because the
tundra provides good conditions to breed and raise goslings.
For the rest of the year, geese migrate south to avoid
the harsh Arctic winter.
During the migration, Greater Snow Geese follow a relatively
specific route. Each year, they leave the Arctic at the end of
August and migrate south through Central Quebec where they stage
from 6 to 8 weeks, replenishing their reserves in tidal marshes
along the St. Lawrence River. From the St. Lawrence estuary, a
900-km non-stop flight south brings geese to their wintering grounds
in the U.S. mid-Atlantic States, from New Jersey to South Carolina.
In spring, Greater Snow Geese depart from their wintering grounds
in late March, once again spending 6 to 8 weeks in the St. Lawrence
estuary before leaving for their Arctic breeding grounds (3,000
km north of the St. Lawrence). Birds leave the St. Lawrence estuary
between 15 and 25 May to arrive on their breeding grounds in late
May early June.
Like many other goose species, the Greater Snow Goose has seen
its population size dramatically increasing since the 1960s. One
of the main factors thought to be responsible for this expansion
in recent years is the extensive use of agricultural fields which
provide them with an unlimited food resource during winter (US
east coast) and migratory stopovers (along the St. Lawrence River
in southern Quebec). A consequence of this population explosion
is that Greater Snow Geese are imposing a large stress on their
fragile Arctic breeding habitats. In order to remediate to this
situation and limit the goose population, management actions during
spring, autumn and winter have been undertaken since 1999.
As Bylot Island has the largest
breeding colony of Greater Snow Geese in the Canadian High Arctic, it provides an exceptional
setting for the study of the species’ breeding ecology and
its impact on the Arctic habitat. From late May to early June,
thousands of Snow Geese migrate to Bylot Island to reproduce.
Upon their arrival, they concentrate in areas such as south facing
hills and creeks, where the snow melts first and uncovers the
vegetation. Geese initially feed in those areas but quickly move
to the lowland areas, their preferred habitat for nesting and
rearing their brood, as snow-melts progresses.
The actual number of geese breeding on Bylot Island varies remarkably
from year to year. In good breeding years, up to 70,000 adults
have been observed on the island during the summer but in poor
breeding years, the number of adults can be as low as 2,000. The
variation in the number of birds spending the summer on the island
is dictated by spring weather conditions and breeding success.
Geese cannot build their nest before nesting sites are snow-free.
When snowmelt is delayed, many birds may forego breeding because
not enough time will be left to complete the reproduction before
autumn freeze up. Among nesting birds, many will also loose
their nest to egg predators and will not renest. More than 90%
of geese that are not able to reproduce or lose their nest leave
the island in early summer for other Arctic regions. As it is
the case for many water birds, geese molt (shed and replace) all
their flight feathers at once every summer, which leaves them
flightless and vulnerable to predators. Non-breeders or failed
nesters thus leave the island for molting areas that provide a
better protection against predators, unlike parental birds that
stay with their young and molt with them on Bylot Island.
The distribution of Snow Geese on Bylot varies throughout the
summer. During the nesting period in June and early July, geese
are mostly concentrated in a 63 km² area a few kilometers
north of Dufour Point near the coast. In this colony, nest density
is high, averaging over 400 nests per square kilometer. In years
of high reproductive effort (number of geese breeding), the main
colony expands, and other nesting areas are also used elsewhere
on the island, although less intensively. After hatching, many
families leave the nesting colony and disperse throughout the
island, concentrating in areas that have a high density of wetlands.
These sites offer a high abundance of plants preferred by goslings,
and many ponds that provide a refuge for families in case of attacks
by predators. Families can move up to 50 kilometers in a few days
to settle on a suitable brood-rearing area on the island. In late
summer, many families move to upland areas, sometimes high up
on mountain slopes. Depletion of food in wetland areas combined
with an abundance of fruiting plants in upland areas at that time
explain these movements.
In order to monitor the number and distribution of Snow Geese
on Bylot Island, we conducted aerial surveys during
the brood-rearing season at 5-year intervals between 1983 and 2008. Besides
numbers and distribution, surveys also provide information on
age (adult or goslings), reproductive status (breeding or non-breeding)
and types of habitat used by geese.
The reproduction of geese, which is their most important activity
during the summer, is monitored annually by our research team
since 1989 on Bylot Island. The parameters studied include those
related to the chronology of nesting such as the date at which
birds start laying their eggs (laying date) and the date that
eggs hatch (hatching date); a measure of the reproductive effort
such as the density of nests in the colony and the number of eggs
per nest (clutch size); and finally their nesting success (nests
are considered successful if at least one egg hatches).
||The follow up of geese continues during the
summer when birds move to the brood-rearing area. The most
important activity during this period is the capture and
banding of large number of goose families in late summer.
Every August since 1990, we round up several thousands of
geese in nets over a few days and mark all birds with a small
metal leg band, and many adult females with a plastic neck-collar.
Marking individuals is very important to study the survival
and movements of long-lived birds like geese. Measurements
and weighting of captured goslings further provides information
on their growth during the summer. Plant production in wetland
areas preferred by goose families is also monitored annually
Population Number and Trends
Aerial surveys indicate that the total number of breeding adult
Snow Geese on Bylot Island has greatly increased from 1983 to
1993, passing from 16,600 birds to 55,000 birds (a 12.7% increase
per year). Following the peak of 1993, the number of breeding
adults declined to 37,600 in 1998 and remained stable through
2003 (36,900). The 2008 survey showed a slight decrease in the number of breeding adults (29,800).
It should be noted, however, that 1993 was a record
year of reproduction, which may have slightly inflated the size
of the breeding population compared to subsequent years.
The same trend was observed for goslings. Their number increased
from 26,500 in 1983 to a peak of 86,500 birds in 1993, and then
decreased to 59,100 in 1998 and remained stable in 2003 (58,000) with a slight decrease in 2008 (51,400).
The number of non-breeding adults generally followed the same
trend except that numbers peaked in 1998 (23,100 compared to 8,900
in 1983), and then dropped to 10,900 in 2003 and increased to 12,800 in 2008.
Brood Distribution and Densities
Brood densities varied among years, following the same trends
observed in the breeding population. In 1983, when the population
was low, the average brood density (5.2 broods per km²) was
more than three times lower than that observed in 1993 (17 per
km²). During that period, the increase in brood density was
much greater in low quality habitats (mostly upland; from 0.8
brood per km² in 1983 to 12.1 broods per km² in 1993)
than the good quality habitats (wetland areas; from 16.4 broods
per km² in 1983 to 29.9 broods per km² in 1993).
This indicates that as the Snow Goose population increased, its
distribution on Bylot Island also changed. At low breeding numbers,
brood distribution was characterized by few areas of high and
moderate brood densities, with a large part of the south plain
presenting low brood densities (e.g. 1983 and 1988). With the
increasing numbers, the area of high to moderate densities greatly
expanded, leaving only a small area with low brood densities (1993
Since 1989, the average laying date of Snow Geese on Bylot Island
was 12 June (minimum: 6 June, maximum: 20 June). Annual variations
in the average egg laying date are strongly related to weather
conditions in spring, being earliest when snow-melt is early and
latest when it is late. We did not detect any temporal trends
in laying dates. However, it should be noted that laying was late
for the first years following the instauration of a spring hunt
in Québec (1999-2002). Therefore, this factor may mask
any possible long-term temporal trend that could be a consequence
of change in local conditions in spring.
|Incubation has a set time length in birds, and for Greater
Snow Geese hatching always occurs 23 to 24 days after the
last egg is laid. Hatching is synchronous within a nest and
all eggs usually hatch within 24 hours. Therefore, egg hatching
dates follow the same trends as laying dates: if geese lay
their eggs early one year, eggs will hatch early too. The
average hatching date on Bylot Island is 9 July (minimum:
3 July, maximum: 15 July) with no detectable long-term trend.
Annual estimates of nest densities provide an indication of yearly
reproductive effort. As mentioned, the reproductive effort largely
reflects spring weather conditions and therefore varies from year
to year. Nest densities is estimated since 1994
on Bylot Island, in an area located within the main nesting colony
of the Island. The average nest density in the
area was 457 nests per km² (minimum: 42, maximum: 1053) with
no obvious temporal trend.
overall average clutch size of Snow Geese on Bylot Island
is 3.7 eggs per nest (minimum: 3.1, maximum: 4.4). The clutch
size influences the length of the laying period as laying
interval between each egg is about 34 hours. The clutch
size shows a strong inverse relationship with the laying
date: it is large when geese lay their eggs early and small
when they lay their eggs late in the season. A reduced clutch
size in late years is probably because females have a reduced
physical condition due to limited feeding opportunities
and a shorter summer to raise their brood. We did not find
any temporal trends in clutch size but, as with laying dates,
clutch size was small in years following the instauration
of a spring hunt in Québec (1999-2002).
Nesting success represents the proportion of all nests that hatched
at least one egg. On Bylot Island, the main cause of nesting failure
for Snow Geese is predation. In decreasing order of importance,
the main predators are the Arctic Fox, Parasitic Jaeger, Glaucous
Gull and Common Raven. On average, nesting success is 67% but
this parameter varies considerably among years (minimum: 14%,
maximum: 90%). Environmental conditions and, most importantly,
predator density determine nesting success. Success is low when
the reproductive effort is reduced due to late snow-melt. Nesting
success also tends to show periodic variations due to cyclic fluctuations
in lemming abundance (see Lemmings).
When lemmings are low such as in 1995 and 1999, predators like
foxes and jaegers will turn to geese and rob many eggs, leading
to poor nesting success. This effect is amplified in areas where
the density of goose nests is low, such as in areas away from
the main colony. We did not detect long-term trend in nesting
success, possibly due to these periodic fluctuations.