Arctic Life/Arctic Animals/Birds/Birds Adaptations
Food supply competition
While the Arctic contains many resources, they are spread over a wide area – there is not enough food available in the tundra to feed many individuals in one place. Sometimes, therefore, it is necessary for individuals to move from one area to another in order to maximize the amount of food they or their offspring can obtain.
Many geese and ducks in the Arctic perform "moult migrations" – special midsummer journeys to areas outside the breeding grounds. As soon as incubation begins and there are no more breeding opportunities, males and non-breeding individuals leave the nesting grounds. They fly to an area, often further north, which is rich in food and isolated from predators. Lake Hazen, Ellesmere Island, is one such destination. The food supply in these moulting areas, although rich, may not last long enough for birds to breed there successfully. However, for a few weeks, they are ideal places for male birds to gain the nutrients – especially protein – needed to grow new feathers and to prepare for the fall migration. By moving away to feed and moult, males leave more food for their mates and offspring – like raiding the neighbor's fridge while saving the food at home for your family.
Because the summer is so short, it is critical for birds to make the most of it by nesting as early as possible. Gyrfalcons get a head start by wintering in the Arctic, and thus have the first pick of nesting cliffs in spring. Early nesting means that their offspring are already leaving the nest, while other birds have only just hatched, ensuring a good supply of easy prey for the young falcons as they learn to hunt.
Geese do not winter in the Arctic, but return very early, often before the snow has left the tundra. They store up energy, feeding heavily in the south, because there is little or no food available when they reach their breeding grounds. By the time their eggs have hatched, however, summer has arrived and there is plenty of new vegetation to eat. Many shorebirds and ducks also nest early. Unable to leave their eggs exposed to the cold, females of the common eider duck do not eat or drink for a full month while they incubate their eggs! Once the young hatch they are cared for by "aunty" ducks, while the exhausted and half-starved females recuperate in preparation for their southward migration.
Part of a young bird's development occurs inside the egg, and part of it occurs outside after the chick has hatched. Different species of birds go through these two stages at different rates. Many groups of arctic birds, such as waterfowl and shorebirds, have precocial young, which complete most of their development inside the egg. Precocial young are covered in warm fuzz and can walk or swim and often feed themselves within hours of hatching. Other birds, particularly the "perching birds" such as pipits and buntings, have altricial young. These chicks hatch with their eyes closed, completely naked and helpless. They must be tended constantly by their parents for approximately two weeks.
Breeding in the Arctic has to be done in a hurry because the summer is extremely short. The faster young can develop, the better. Although altricial hatchlings must be carefully fed, protected and kept warm, these chicks take much less time overall to develop than precocial young. Young snow buntings, for example, are fully grown and independent only 4 weeks after the eggs are laid, while the precocial young of semipalmated sandpipers, which are approximately the same size, take six weeks from egg-laying to fledging.
Rapid development allows birds to mate, lay eggs, rear offspring and leave again in a very short window of time. This strategy is particularly important to the small arctic land birds, which cannot store enough food to survive periods of scarcity in the early spring or late fall. Although precocial birds take slightly longer overall to develop, these birds have a distinct advantage: they make better use of available food resources. These active chicks can scatter from the nest and search for food separately, so they don't compete with each other in the same small area – an advantage on the tundra, where food is more thinly distributed. Because they are fuzzy and can run away, they are also more able to escape predators, and less likely to get cold than naked hatchlings.
Because the Arctic has fewer food resources than southern areas, birds living on the tundra have had to adapt their diets to what is available. Terrestrial birds that would normally eat only insects or seeds often have to feed on both, over the course of the summer, because there is not enough food for them to specialize. During the breeding season, female birds need lots of protein to form their eggs, which they get by eating insects – mainly midges, blackflies, and mosquitoes. Later in the summer, these insects die off and the birds switch to eating seeds, berries or other plant matter.
Rivers, lakes and ponds in the Arctic have far less vegetation than southern freshwater environments. Many birds that rely on aquatic plants in the south do not fare well in tundra lakes and rivers. In the Arctic, diving ducks that are adapted to feed on invertebrates – which are plentiful in arctic freshwater – have an advantage over dabbling ducks, which are herbivorous. In fact, only one of eight duck species in the Arctic – the northern pintail – manages to survive in the North solely on a diet of plants.
The biggest challenge to wintering in the North is the lack of food. Only eleven species of birds are capable of surviving the long, cold arctic winter: gyrfalcons, northern ravens, snowy owls, common redpolls, willow and rock ptarmigans, Ross' gulls, ivory gulls, thick-billed murres, dovekies, and black guillemots. And even these hardy species move slightly south in the depths of winter, probably to avoid the 24-hour darkness of the northernmost polar regions.
While marine birds move to polynyas, areas of the Arctic Ocean where the water does not freeze, the few terrestrial birds that winter in the Arctic have had to adapt their feeding strategies to make use of what is available. Lemmings and voles, the favourite prey of snowy owls and ravens, are hard to find in winter, as they hide in burrows under the snow. These predators are therefore forced to turn to scavenging to survive, eating from carcasses left by polar bears and wolves. During the time when seals come onto the ice to give birth, owls and falcons also scavenge the placentas left when the pups are born. Ravens cache food, hiding items and then returning to eat them later – if they have not been stolen by another raven!
As for the plant eaters, ptarmigans feed mainly on dwarf willow and birch, scraping through the shallow snow in windswept areas to find food. The common redpoll, a seed-eating bird, searches for food in areas of exposed ground or in lemming burrows under the snow. This bird's tiny size means that it loses heat very quickly. Therefore, in order to minimize exposure to the cold, it picks up seeds quickly and stores them in a special sac inside its throat, then moves to a more sheltered area such as a burrow to digest its meal in relative comfort.
Although the icy darkness of an arctic winter may seem daunting, lack of food is the biggest problem for birds during the cold season: terrestrial insects are killed by frost, plants and seeds lie covered in snow, and both marine and fresh waters are sealed over with ice. Most arctic birds resolve this difficulty by heading south for the winter and 85% of them migrate to areas where more food is available – from southern Canada to the sunny coasts of Mexico or even the farthest tip of South America!
In some species, males begin to store up energy for migration as soon as they have finished breeding, getting out early and leaving the females to raise the chicks. This is because as the short summer progresses, resources become fewer and competition grows more fierce. As soon as their offspring are able to look after themselves, the females follow the males, leaving the juveniles behind to fend for themselves. As soon as the young birds can fly well enough to migrate successfully, they too leave the Arctic – a remarkable journey, given that they have no adults to show them the way!
Even birds that normally winter in the Arctic sometimes move south in search of food. For example, in years when lemmings are scarce in the Arctic, snowy owls travel to southern Canada where more prey are available.
While ducks, geese, and shorebirds return to the north as early as possible in order to breed quickly, other arctic birds delay their arrival until the weather warms. This allows them to feed for longer in the south and means that when they do arrive in the North, food is readily available. Marine birds such as the alcids must wait until openings in the sea ice have formed, in order to be able to catch fish. Razorbills, in particular, take advantage of the extra food available in their Atlantic wintering grounds in the spring, before heading north to breed.