Snow Geese, from Île-aux-Oies to Bylot Island

An article by Valérie Levée, science journalist.

Like a last stop before hitting the motorway, the Greater Snow Geese make a stop along the St Lawrence each spring. This is where they refuel before resuming their flight to their nesting grounds in the Arctic. This stopover has consequences for the dynamics of the ecosystem thousands of kilometres further north. 
Pierre Legagneux is a biology professor at Université Laval and a researcher at the Centre national de la recherche scientifique (CNRS) in France. He summarises research on the Greater Snow Goose and its place in the Arctic ecosystem, carried out in collaboration with Gilles Gauthier, professor emeritus at Université Laval, Joël Bêty and Dominique Berteaux, professors at Université du Québec à Rimouski, and Dominique Fauteux, a researcher at the Canadian Museum of Nature. 

Fattening up before leaving

At the end of the twentieth century, geese were able to stop and feed on the banks of the St. Lawrence without suffering the pressure of hunting, which was banned in the spring. But things changed in 1999 when spring hunting was introduced in Quebec to regulate the goose population, which had reached one million individuals. Allowing such an overpopulation to graze the slow-growing tundra threatened to cause local desertification. In 2009, the United States also liberalised hunting, and since then the population has remained at around 600,000 birds. 
But this increased hunting pressure is not without effect on the geese's diet, and the Covid-19 pandemic provided an opportunity to demonstrate this. In the spring of 2020, with hunting at a standstill, Pierre Legagneux's team went to Île-aux-Oies, near Montmagny, to weigh the geese and monitor their feeding behaviour using high-tech transmitters. “The geese were already in very good condition when we started catching them at the beginning of May,” says Pierre Legagneux. As they were already well fattened, they did not want to feed in the fields as they do in other years (Professor Legagneux's team replicated this same monitoring in 2019 and 2021-2023). In the absence of hunting, the geese were already ready to continue their northward migration and were only waiting for favourable weather conditions to take off. 

“Hunting has a direct effect on mortality, but also, and above all, indirectly via disturbance. They find it harder to feed over long periods, and fattening takes longer,” concludes Pierre Legagneux.

Geese are sensitive to multiple stressors, as Frédéric Letourneux showed during his PhD research. Thousands of geese are ringed each summer, and the subsequent observations of these geese are used to estimate their survival. As some geese also wear a collar weighing a few grams to increase the number of resightings, Frédéric Letourneux found that wearing a collar reduces the survival rate, but only in recent years. In fact, the effect of the collar only became apparent in 1999, when spring hunting was introduced, and it increased as hunting intensified. Since then, Professor Legagneux's team has stopped using collars on geese and is working on a prototype for an ultralight smart ring.

If hunting pressure disrupts feeding, faster fattening could be beneficial for the geese. For her master's thesis, Maëliss Hoarau tested this hypothesis by modulating the dose of corticosterone in geese, knowing that at low doses this hormone induces a mobilisation of energy that encourages geese to eat more. The research team captured geese at l’Île-aux-Oies and inserted a small corticosterone tablet or a placebo under their skin. They also fitted them with a GPS to track their movements and an accelerometer to record their head movements as they foraged for food. 

“We were able to confirm that geese given corticosterone ate more and migrated an average of two days earlier, and sometimes as much as six days earlier. This link between fattening and departure date was not previously known,” reports Pierre Legagneux.

Impacts in the Arctic

Taken together, these studies show that feeding and fattening affect the flight of geese to their Arctic nesting sites. However, this flight does not guarantee reproduction, as the stressors encountered in the south can be carried over later and influence the geese's breeding decisions.
For his master's project, Thierry Grandmont studied the effects of stress on reproduction by keeping geese in captivity for 2 days during their stopover at Ile-aux-Oies.  These geese, which were ringed and fitted with transmitters, were then tracked to Bylot Island in the Arctic. 

“We found that the geese that had been stressed migrated like the others but reproduced less. They chose to skip a breeding event, a classic strategy for long-lived species”, explains Pierre Legagneux. 

Geese that can live for more than 20 years can afford to skip one year and start again the following year. 

But the reproduction of these geese has repercussions on the food web, as Frédéric Dulude-de Broin illustrated during his doctoral project by analysing nine years of data on seven species in an Arctic ecosystem. If goose reproduction is good and the number of eggs increases, an Arctic fox's home range shrinks because it does not have to travel as far to steal eggs and feed. As a result, several foxes can share the goose colony, increasing the density of foxes in the area. The foxes are also quick to attack the Golden-Plover that nest among the geese. “Some birds decide to stop nesting in the heart of the colony, where it's almost always a failure, choosing to nest on the periphery” observes Pierre Legagneux. 

However, in addition to the stresses experienced in the south, goose reproduction also depends on local factors, particularly the presence of lemmings, foxes’ other preferred prey.

“If there are lots of lemmings, foxes have something else to eat and the geese's reproductive success increases,” explains Pierre Legagneux. 

During his master's degree, David Bolduc also showed that the lemming population is partly controlled by the ermine, making this predator another key to goose reproduction. 

To learn more :

Bolduc B., Fauteux D., Gauthier G., & Legagneux  P. (2025). Seasonal role of a specialist predator in rodent cycles: Ermine–lemming interactions in the High Arctic Ecology, 106 (1) e4512

https://doi.org/10.1002/ecy.4512

Grandmont T., Fast P, Grentzmann I., Gauthier G., Bêty J.& Legagneux P. (2023) Should I breed or should I go? Manipulating individual state during migration influences breeding decisions in a long-lived bird species. Functional Ecology 37(3),602-613

https://doi.org/10.1111/1365-2435.14256

Hoarau M., Angelier F., Touzalin F., Zgirski T., Parenteau C., & Legagneux P. (2022) Corticosterone: foraging and fattening puppet master in pre-breeding greylag geese. Physiology & Behavior, 246, 15 March 2022, 113666

https://doi.org/10.1016/j.physbeh.2021.113666

LeTourneux F., Grandmont T., Dulude-de Broin F., Martin M.-C., Lefebvre J., Kato A., Bêty J., Gauthier G., & Legagneux P. (2021). COVID19-induced reduction in human disturbance enhances fattening of an overabundant goose species. Biological Conservation, 255, March 2021, 108968

https://doi.org/10.1016/j.biocon.2021.108968

LeTourneux F., Gauthier G., Pradel R., Lefebvre J., & Legagneux P. (2022). Evidence for synergistic cumulative impacts of marking and hunting in a wildlife species. Journal of Applied Ecology. 59(11) 2705-2715

https://doi.org/10.1111/1365-2664.14268