Study focuses on Seward Peninsula gyrfalcons
As part of the University of Alaska Fairbanks Strait Science lecture series Michael Henderson of the Peregrine Fund talked last week on the gyrfalcon, the world’s largest falcon. They can weigh up to about four and a half pounds and their wingspan can measure four feet. While the peregrine falcon, smaller cousin to the gyrfalcon, is considered the world’s fastest animal, gyrfalcons are thought to be faster in straight powered flight. Their large size makes them a favorite of falconers and birders alike. “Many people spend a lot of time and money each year just to get to Nome to see these birds,” said Henderson.
The gyrfalcon’s large size allows it to take large prey, as large as a crane. They typically nest on cliffs, often on stick nests built by other birds, particularly ravens, rough legged hawks, and golden eagles. They also nest on bare ledges, in trees and on man-made structures. To a certain extent, they compete with peregrine falcons for nesting sites.
Gyrfalcons are monogamous. Both parents perform the parental duties including hunting, defense of nest, incubating and brooding. During the early season the males do more hunting and less brooding. They lay three or four eggs per clutch and only one clutch per year. If the nest is destroyed by a storm or collapses there will be no more eggs that year. They lay the eggs around April and the nestlings fledge in July. During the spring, when the snow is falling, the bird incubating the eggs might be completely covered in snow. But they will stay on the nest.
It was formerly believed that there are subspecies of gyrfalcon. Their physical appearance can differ from bird to bird but recent DNA analysis shows there is only one variety. They are a monotypic species with no subspecies. While there are no distinct color varieties the coloration of individuals can range from very dark to nearly white, with most being right in the middle in an intermediate gray.
Gyrfalcons breed farther north than any other diurnal raptor. Most of the population is non-migratory and spend all winter in the Arctic and sub-Arctic. They are, however, seen as far south as Idaho and Montana. Breeding age adults stay close to their home territory as they start breeding in early spring.
The willow ptarmigan and the rock ptarmigan are critical prey for the gyrfalcon. They are often the only prey available at certain times of the year. During the breeding time, the abundance of ptarmigan enables the gyrfalcon to achieve the physical vitality needed for breeding. During the short summer, they feed on ground squirrels, shore birds, songbirds and sea birds.
The extreme northern weather prevalent in the gyrfalcon range has protected them from being disturbed by humans, but climate change is starting to affect them. The greatest temperature changes are happening above the 55 degree latitude line, which overlaps with the gyrfalcon’s circumpolar distribution. With the warmer temperatures comes an increase in precipitation and storms are getting more intense. The rain motivates the bird’s prey to take cover and it can kill nestlings who have no defense against cold and wet storms. Climate change is bringing dramatic changes to the Arctic landscape. Earlier and warmer springs increase the size and distribution of shrubs on the tundra. This affects the distribution of wildlife and disrupts functions of the ecosystem.
Also, warmer temperatures and changing ecology exposes Arctic wildlife to new diseases to which they lack immunity. Better conditions for mosquitos means more vectors delivering disease. The top predators are an indicator species that can reveal disruptions within their ecosystem. They rely on the health of the lower tiers of the food web. The gyrfalcon has been identified as an effective sentinel species. Recent evidence suggests the population on the Seward Peninsula is in decline.
Henderson is focusing on consistent raptor monitoring to keep an eye on the population and identify any behavioral changes taking place. His program has several objectives. The first is to keep a finger on the pulse of the raptor population and identify any changes that might be happening. The Department of Fish and Game is monitoring about 600 sites to learn how many birds are breeding, where they are, and what is the rate of success. They band nestlings with colored bands which can be read with a scope or with a camera, identifying the individual bird. They collect feathers and blood samples which can tell the tale of nest health and also provide genetic samples. Seventy motion activated cameras at nesting sites also provide valuable information. Over two million photos have given insight into how many eggs have hatched, how many nestlings grew to maturity, and how and when mortalities happened. In one case the cameras recorded a nest collapse in which an adult picked up the five-day old nestling in its beak and flew five miles to an alternate nest. This had never been seen before.
Secondly the program is trying to learn the dietary habits of the raptors and the importance of prey species throughout the breeding season. During the 2014 to 2015 season they recorded 40 different prey species from 15 different families. The most important were ptarmigan and Arctic ground squirrels.
Lastly, they look at diseases which may afflict the birds. Falcons are susceptible to new diseases. They will be testing for avian malaria and influenza along with others.