Image credit: Rob Shearer.
While most geese migrate between breeding grounds in the north and their more southerly wintering grounds, about
3.4 million remain in one location throughout the year. The most abundant species of goose in North America, the Canada
goose, primarily breeds in Canada and Alaska.
However, breeding and wintering grounds overlap in the northern latitudes of the contiguous United States. In these areas, many resident populations of geese exploit favorable conditions to stay put year-round.
In the early 20th century, hunters captured geese and clipped their flight feathers, making them live decoys to draw in migrating
waterfowl (a practice banned in 1935). Successive generations of these “captive” geese never learned natural migratory behavior,
establishing many resident populations. Other human activities have led to overwintering geese because of improved access to
winter food sources: agriculture leaves behind seeds and grain, irrigation systems keep lakes and ponds from freezing, cities create warm micro-climates, decreasing snow cover and providing access to green vegetation. Evidence also suggests that a warming climate may be extending wintering grounds farther north. These factors have encouraged populations of geese to save their energy and stay the winter in lower latitudes.
Although hundreds of thousands of geese continue to migrate through Denver, thousands more now stay put. About 700 live year-round just in City Park near the Museum. The geese are here to stay.
By John Demboski, PhD, curator of vertebrate zoology, and Andrew Doll, ornithology fellow.