by Bruce Batt, Ph.D.
Most populations of North American geese nest in Arctic and subarctic regions. This may seem a poor plan, as the Arctic is a cold and rugged place most of the year. Arctic-nesting geese have only a very narrow window of time to arrive, establish a nest site, lay eggs, incubate, hatch and raise young, and sustain a full molt of body and flight feathers before making their amazing migrations to climes farther south for the fall, winter, and spring.
So what special adaptations allow Arctic geese to handle all this?
For one, most Arctic geese actually spend the majority of the year on agricultural and other habitats in the settled regions of the continent farther south—it's just too cold to be an Arctic goose for very long. Exceptions to this pattern are the Pacific and Atlantic brant and the emperor goose, which live on natural coastal habitats throughout the year.
Geese are remarkably preadapted to take advantage of the enormous agricultural landscapes they live in most of the year. Starting in the fall, families of many western continental geese arrive in Prairie Canada and immediately have access to farm fields that have abundant supplies of waste grains, peas, beans, and lentils from the recent harvest. The young birds are only about 12 weeks old and are nutritionally near depletion after flying across the vast boreal forest. Some young geese don't survive the flight.
The abundant waste crops allow the geese to restore their body reserves quickly. The young continue to grow and get stronger for the continuing migration that lies ahead. Most biologists believe that the food supply on farm fields is vastly superior to and more predictable than the native prairie on which the birds evolved. The birds almost certainly enjoy higher survival rates for the next seven or eight months than they would have in the vast bison pastures that they encountered in prehistoric times. This “food subsidy” continues until spring, when the geese are back in Prairie Canada before their last flight to the breeding grounds in May.
Spring is a time of constant eating as the birds store fat that will fuel their migration and provide most of the energy they need to breed. These are the last substantial meals female geese will have for the next six or seven weeks. The Arctic breeding grounds will be frozen when the geese arrive, and females must incubate constantly to avoid predation and shorten the incubation period as much as possible.
The birds get remarkably fat in the spring. They are fatter than at any time of the year just as they leave for the breeding areas in May. Snow geese shot during the extended conservation season in Prairie Canada are literally “grease balls” with thick layers of fat under the skin and throughout the gut. Indeed, the livers of these birds are similar to those of force-fed domestic geese used to make goose liver pâté. The first person to figure out how to make goose liver pâté must have harvested geese in the spring.
These large reserves of fat are a critical hedge against the birds' arriving to find the breeding grounds covered in snow and not yet warm enough for nesting. Some body reserves are absorbed by the birds to sustain them until they can nest. This is a critical period of time. If snow cover lasts too long, the geese will use so much of their body reserves that they will not have enough energy left to nest. In some years, such as 1992, whole regions of the Arctic have been affected by delayed snow melt, and entire populations will fail to raise young.