Climate Change Effects on an Out-of-Control Population: The Case of the Snow Goose

The Migratory Bird Treaty Act was enacted in 1918 as an effort to conserve migratory birds within North America and aimed to maintain or increase populations of various migratory birds, including waterfowl. These efforts have been successful in most species, but now waterfowl managers face a problem of overpopulation in snow geese (Ducks Unlimited, n.d.). These birds have grown substantially in population size as population estimates indicate numbers exceeding 15 million geese (Ducks Unlimited, n.d.). They have also expanded their breeding and nesting ranges throughout the Canadian Arctic and Sub-Arctic. The over-grazing of these areas has caused snow geese to find new habitat, and have destroyed vegetation that is crucial for foraging in snow geese (Peterson et. al, 2013). Other problems that are related to climate change include the decreased fitness in snow geese, reduced body size and condition of goslings, and new predation risks.

Snow geese have breeding grounds in the northern parts of Canada, but overpopulation and climate change are causing ranges to expand. Source: Environment Canada


Snow geese are the main driving force in the habitat degradation in the Hudson Bay area. They impact the vegetation and soil in a negative manner, which creates large patches of barren ground and makes it difficult for these habitats to recover even after the geese have moved out of the habitat (Peterson et. al, 2013). Also, climate change has caused these geese to inhabit new areas and degrade them as well (Peterson et. al, 2013). This causes problems for fitness and survival of geese, as lower resources decrease reproductive success and gosling survival. Aubry et. al. (2013) studied the effects of climate change, phenology, and habitat degradation on the body condition in snow goose goslings. Their findings show that goslings that live within the center of populations where habitat degradation was the worst had lower body condition and lower survival rates. Also, warmer winters and summers due to climate change result in lower body condition

This image shows an area that has been fenced off to keep snow geese out. The landscape around it has been destroyed by over-foraging of snow geese. Source: Wek’eezii Renewable Resources Board

scores for goslings, likely due to the reduced forage nutrition in plants (Aubry et. al, 2013). These factors could lower snow goose populations as they are reducing their nutrition and destroying their habitat.

Another change that has been observed is the difference in timing of migrations in snow goose populations. Climate change has caused a change in weather patterns and has altered the timing of snow goose migrations. These migrations appear to be happening earlier in the year, and geese are returning to their breeding grounds and nesting at earlier times (Bety et. al, 2004). It has been shown that geese that arrive earlier have better reproductive success than late-arriving geese. However, there are costs associated with arriving too early (Bety, 2004). These costs include harsh conditions in early spring that increase adult maintenance costs, less food availability, and increased predation (Bety et. al, 2004). It is shown that there is a benefit to arriving a few days earlier than average, but too early can decrease reproductive probability (Bety et. al, 2004). This indicates that birds that arrive at their breeding grounds much earlier than average have decreased fitness.

This table shows the changing in migration times and arrival and departure dates of snow geese. Source: Bety et. al, 2004

Climate change and the early arrival of snow geese to their breeding grounds have caused an increase of nest and adult predation and new predators are also a threat. Rockwell and Gormezano (2009) studied the effects of climate change on the arrival of polar bears on the nesting grounds of snow geese. The earlier melting of ice in the Hudson Bay has caused polar bears to come to shore earlier and reduced their predation on ringed seals. this has caused them to have a nutrient deficiency (Rockwell and Gormezano, 2009). This causes increased predation to snow goose nests, as the eggs provide the nutrients that the polar bears are lacking. These nests are easily preyed upon by polar bears and if this trend continues to increase, many snow goose colonies could suffer massive declines (Rockwell and Gormezano, 2009).

This graph shows the overlapping and advancing of snow goose nesting times and the arrival times of polar bears to nesting grounds. Source: Rockwell and Gormezano, 2009

These factors could eventually lead to a crash in snow goose populations as their resources could become depleted, their fitness levels drop, and they are at greater risk of predation. However, management actions are being implemented to decrease populations to sustainable levels. Changes in hunting regulations, as well as governmental intervention, are being used to control the overpopulation of snow geese. Historically, snow goose hunting seasons

Spring snow goose hunting seasons are one-way overpopulation is being managed. Source: Northern Skies Outfitters

have been during the fall migration and strict regulations were implemented to protect from overharvesting of populations. Now, spring seasons have opened in the United States and Canada to increase harvest numbers in snow geese (Lefebvre et. al, 2017). These seasons also reduce restrictions on hunting, such as allowing more than three rounds of ammunition to be loaded in a firearm at a time, allowing electronic calls and baiting, and an allowing more birds to be harvested ( Lefebvre et. al, 2017). The spring conservation harvests have had an impact on the reproductive ability of snow geese, as clutch sizes were smaller, laying date was later, and a decrease in reproductive activity. These effects were shown to be caused by the energy decreases and foraging decreases due to the disturbance caused by spring hunting (Lefebvre et. al, 2017).

Also, governmental agencies have enacted management plans to help control the populations and protect habitat. The U.S. Fish and Wildlife Service in conjunction with the Canadian Wildlife Service released a management plan in 2007 to control snow goose populations. Some of the efforts include nest and egg destruction, reproductive inhibitors, and mechanical, biological, and chemical control. The destruction of eggs and nests has little evidence of success in population controls, as geese will often lay additional eggs if the first clutch is destroyed (U.S. Fish and Wildlife Service, 2007). However, reproductive inhibitors such as conjugated linoleic acids have been observed to reduce eggs hatch rates (U.S. Fish and Wildlife Service, 2007). Mechanical control such as shooting and trapping have also been effective in reducing populations. Biological controls such as predators are effective at population control but may have unforeseen impacts on the rest of the habitat. Chemical controls such as poisons in bait are also being used to control snow goose populations but may cause mortality in unintended species (U.S. Fish and Wildlife Service, 2007).

The Canadian Wildlife Service has made management plans in conjunction with The U.S. Fish and Wildlife Service. Source: USGS

The U.S. Fish and Wildlife Service have made management plans in conjunction with the Canadian Wildlife Service. Source: U.S. Fish and Wildlife Service

The overabundance of snow goose populations is due to climate change and the ability of snow geese to thrive in many conditions, including warmer than average conditions. Snow geese continue to destroy their habitats and cause widespread destruction of the vegetation in the Hudson Bay region. Although management actions have been successful in slowing the growth of these populations, monitoring of these populations is crucial as snow geese can easily take advantage of changing environments and resources, and equilibrium numbers are challenging to maintain.






Aubry LM, Rockwell RF, Cooch EG, Brook RW, Mulder CPH, and Koons DN. (2013). Climate change, phenology, and habitat degradation: drivers of body condition and juvenile survival in lesser snow geese. Glob. Ch. Bio. 19:149-160.

Bety J, Giroux JF, and Gauthier G. (2004). Individual variation in timing of migration: causes and reproductive consequences in greater snow geese (Anser caerulescens atlanticus). Behav. Eco. And Sociobio. 57(1):1-8.

Humburg DD. (n.d.). Light goose dilemma: despite increased harvests, populations of these arctic-nesting geese continue to grow. Ducks Unlimited.

Lefebvre J, Gauthier G, Giroux JF, Reed A, Reed ET, and Belanger L. (2017). The greater snow goose Anser caerulescens atlanticus: managing an overabundant population. Ambio 46(2):262-274.

Peterson SL, Rockwell RF, Witte CR, and Koons DN. (2013). The legacy of destructive snow goose foraging on supratidal marsh habitat in the Hudson Bay lowlands. Arct. Antarct. and Alp. Res. 45(4):575-583.

Rockwell RF, and Gormezano LJ. (2009). The early bear gets the goose: climate change, polar bears, and lesser snow geese in western Hudson Bay. Pol. Bio. 32(4):539-547.

U.S. Fish and Wildlife Service. (2007). Alternatives. In: Final environmental impact statement: light goose management. U.S. Depart. of the Inter. pp 9-25.

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