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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.

Snow Goose - Grande Oie des neiges © Gilles Gauthier

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).

geese in banding net - oies dans le filet de baguage © Joël Bêty 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 (see Plant Monitoring section).



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 and 1998).


Breeding Ecology

Laying Date

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.


Hatching Date

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. Greater Snow Goose goslings - oisons de la Grande Oie des neiges © Anna M. Calvert


Nest density

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.


Clutch Size

Greater Snow Goose eggs - oeufs de Grande Oie des neiges © Marie-Christine Cadieux

The 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

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.