Long-term research examines population changes in Arctic breeding geese
More than 15 million Ross’s and Lesser snow geese migrate to the Canadian Arctic every spring, making them one of the most abundant Arctic wildlife species. Despite extensive annual harvests by southern hunters – about 700,000 of these “light geese” are harvested each year in North America – populations of both species have increased by more than 700 per cent since the 1970s, prompting researchers to ask why there was such an increase, and what impacts higher goose populations may be having on their Arctic habitats.
Dr. Ray Alisauskas, a research scientist with Environment and Climate Change Canada (ECCC), has been studying the population ecology of light geese and their impact on Arctic ecosystems since the late 1980s. This long-term work allows us to track the status of key Arctic ecosystems, as well as ensuring that the harvest of snow geese is sustainable over the long term.
Dr. Alisauskas’ work links to ECCC’s regulations and policies under the Migratory Birds Convention Act, 1994. For example, the setting of guidelines around hunting season and bag limits are based on a science evaluation of light geese population status and trends of migratory game birds.
Light geese breed in many large colonies in the Arctic, and Dr. Alisauskas has focused his long-term research program on a large colony at Karrak Lake in the Queen Maud Gulf Migratory Bird Sanctuary, Nunavut (starred on the map below (Figure 1)). The Queen Maud is the largest federally owned protected area.
Nearly one million geese nested on the tundra around Karrak Lake occupying an area of 280 km2 in 2016, making it the second-largest known concentration of breeding geese in the world.
The increase in light goose populations was likely due to the availability of additional winter food on farm fields in the United States. On their Arctic breeding grounds, nesting geese and their goslings forage voraciously after hatch, and this modifies the vegetation in and around colonies.
“It is astonishing to fly over a large colony like Karrak Lake and see the landscape speckled with geese. You also see visible changes to the landscape, such as areas that are grazed down to exposed peat,” said Dana Kellett, a wildlife research technician, who has worked at Karrak Lake for more than 20 years.
Wildlife populations cannot increase forever, and recently Dr. Alisauskas and his team have shown that numbers of light geese appear to be stabilizing. Megan Ross, a graduate student in Dr. Alisauskas’ program, carried out analyses of long-term breeding data from Karrak Lake to understand why population growth has stabilized.
The answer appears to be that breeders are producing fewer young than before.
“In years where birds arrived at the breeding colony in poorer body condition, they produced fewer eggs and fewer goslings survived,” said Ross.
Not only are breeders arriving at the breeding sites in poorer body condition, but the timing of food availability for goslings on the breeding ground has changed. When adults arrive to nest, the colony is mostly snow-covered, with little or no food available. To get around this food shortage, geese accumulate fat and protein during foraging stops on their trip north. These stored food reserves allow them to lay and incubate eggs quickly upon arrival at the colony, but their ability to do so has declined recently.
The timing of hatching by goslings to coincide with peak “green up” is key to breeding success, but Ross has shown that the rate of green up has accelerated over the past 20 years, likely due to climate change. It has long been known that late snow melt delays green up and reduces the number of goslings produced, but the accelerated timing of green up also reduces breeding success by creating a mismatch between the timing of hatching and the availability of high quality vegetation. This pattern has been confirmed by analysis of long-term remote sensing data by Dr. David Douglas, a scientist with United States Geological Service, who collaborated in the study.
According to Ross, the acceleration in the timing of green up, in addition to reduced nutrition of breeders because of high populations of geese, has resulted in “a decline in gosling size, gosling survival and, ultimately, the number of goslings present on the brood-rearing area near the end of summer. Basically, if goslings hatch late, they miss out on having access to high quality vegetation. The Arctic summer is short and goslings need high quality food to grow fast enough to successfully migrate south.”
This long-term research is part of international agreements with the United States and Mexico under the North American Waterfowl Management Plan, notably the Arctic Goose Joint Venture. The ECCC research team has shared these and other research findings with colleagues at various international scientific conferences and these results will be published in the journal Ecology.
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