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.
So how do events play out in a normal breeding season? A clear model of what happens can be seen with snow and Ross's geese nesting at the large Karrak Lake colony south of Queen Maud Gulf in Canada 's central Arctic. Dr. Ray Alisauskas of the Canadian Wildlife Service has studied these geese for the past 16 years. In an average year, the first snow geese arrive by June 1, and the first Ross's geese, about three days later. However, the average date of nesting at the Karrak Lake colony is about June 11. In any given year, all nests are started over a range of about three weeks—a synchrony imposed by short Arctic summers. If conditions are ideal, the first eggs are in nests the day after the birds arrive. By June 16, incubation starts on the average full clutch of 3.5 eggs. Average hatch occurs on July 3. The first Ross's geese are flying by August 15, and the first snow geese by August 22. The young of both species can sustain flight by August 31, just ahead of the first major freeze of the year between September 10 and 15, when most geese leave the Arctic for the prairies.
This remarkable series of events has been compressed into just over 90 days. But not all goes so smoothly every year. In late springs when cold and snow persist, the birds can't start nesting immediately because their eggs will freeze. They must use fat reserves simply to sustain their own lives. This is a necessary trade-off between energy for survival and energy for reproduction. As time goes by, fat reserves get smaller until about the third week of June, when it is no longer worth trying to nest because the young will not have time to mature enough to fly south. For the few geese that try, their young may die right on the breeding colony or en route to the Canadian prairies. Geese stubborn enough to nest late put their own lives at risk because they may become too emaciated to make it across the boreal forest. Natural selection is very tough on birds that make such mistakes.
A late spring on the Arctic breeding grounds typically leads to a challenging fall for hunters because having few young in the flocks makes it much more difficult to attract birds within shooting range. Every adult has had at least seven months of experience the previous year with decoy spreads and goose calls, so they are wary of joining other birds on the ground, as they may not actually be geese. The average snow goose lives another seven years once it survives the first year of life. These old-timers have accumulated at least 49 months of experience flying from roosts to feeding areas where hunters may wait. Making mistakes here can be deadly too, so most of these survivors know how to avoid decoy spreads.
The pattern at Queen Maud Gulf is repeated on all goose colonies across the northern breeding areas from Baffin Island to Alaska's North Slope to the Hudson Bay Lowlands and northern Quebec. From year to year, the unforgiving northern climate is the most important single variable that affects the size and age structure of the fall flight of Arctic geese.