Do Canada Geese Ever Leave Chicago?

It’s no secret, Canada geese have done an incredible job adapting to the human-altered landscape of Illinois. They thrive on agricultural crops, in the ponds that intersperse urban and suburban neighborhoods, and even parks in downtown Chicago. The adaptability of Canada geese to metropolitan areas has contributed to increases in abundance and a shift in their winter distribution, with geese now staying farther north in winter than they did historically. However, we know little about how Canada geese use metropolitan areas and what about these areas allow geese to overwinter there.

Canada geese that winter in Illinois are generally from two breeding populations. One population, the temperate-nesting population, breeds across the Midwest and southern Canada, and may migrate from more northern breeding areas, or remain throughout the year in the area where they breed. The other population is the subarctic-nesting population which breeds along the southern portions of Canada’s Hudson Bay. Geese from this population must migrate away from the inhospitable tundra during winter. Historically they migrated as far as Alabama, Mississippi and Arkansas, but have made several large-scale shifts north over the last several decades, most recently from southern Illinois to the northern portion of Illinois. Individuals from both populations now spend the entire winter in the Chicago area despite seemingly brutal weather and poor-quality food.

Animals should make decisions that maximize their chances of survival. Canada geese choose where to spend the winter based on trade-offs between climate conditions, food and risk of predation. Metropolitan areas offer relatively low-quality food (i.e. turf grasses in city parks and sports fields) but safety from hunters and predators. Rural areas pose risk from hunters and other predators but have access to energy rich grains. To survive the winter, geese must balance their need to acquire the energy they need to survive, while avoiding being shot or eaten.

They balance these trade-offs through their behaviors (i.e. moving less/conserving energy) and choosing where they go (i.e. parks versus cornfields). These choices extend to regional levels and include the decision to migrate south or remain in metropolitan areas. Our goal is to examine these trade-offs by investigating what proportion of geese leave the Chicago area and when they do, what factors influence their departure.

GPS transmitters mounted to neck collars were used to track the movement of Canada geese in the Chicago area. We captured and GPS tagged 105 geese during winter and the breeding season in the Chicago area from 2014 to 2019. Geese were tracked and individuals classified as wintering in rural areas, wintering in urban areas, or leaving Chicago for more southern areas. The surrounding landscape and breeding region of geese that did or did not leave the city were compared. Of the 87 geese captured in winter, 30 nested in southeast Wisconsin, 14 in Thunder Bay, Ontario and 7 along Hudson Bay in Ontario during the subsequent breeding season after capture (Fig. 1). We calculated the probability of geese migrating south of Chicago based on their breeding region, their home range and weather conditions.

Between 2014 and 2019, 32 of 153 geese migrated out of the Chicago area in winter (animation). Breeding region was an important factor with only 13 percent of geese that nested in Chicago departing but 28 percent of Wisconsin breeding geese departed. Departure from the city was also correlated to the proportion of urban development in the surrounding area, with geese wintering in more highly developed areas being less likely to leave.

A period of abnormally cold temperatures occurred in late January 2019, which consisted of average lows of around -7° for a week. During that time, only 9 of our 32 GPS tagged geese migrated south. Despite going to hunted areas, all 9 of those geese survived while 20 percent of those that stayed in urban areas died. Though we could not confirm cause of death for all geese with transmitters, we did observe several incidences of dozens of geese that apparently froze or died of exposure while roosting on frozen waterbodies.

While staying in urban areas where they are safe from hunters might be a good strategy in more mild winters, harsher winters might tip the scale in favor of migrating south. We suspect that those individuals that choose to stay may be in such poor condition that they are unable to move out the city during those extreme events, leaving them no other choice but to remain and tough it out. We are currently working to better understand the effects of winter weather on movements and survival of Canada geese, with the overall goal of informing management of Canada geese in huntable areas and reduce conflicts in urban areas.

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Ryan Askren is a PhD Candidate at the University of Illinois – Illinois Natural History Survey. Michael Ward, PhD, is an Associate Professor and Senior Ornithologist with the University of Illinois – Illinois Natural History Survey.