Birder’s Notebook: Gyrfalcon––A top predator of the North
It was an exciting day when in late February a gyrfalcon shot across the road before me in pursuit of ptarmigan––my first sighting all winter. Gyrfalcons have been a consistent and interesting feature of winters in the Nome area, and their absence this winter has been perplexing during a time when ptarmigan, the mainstay of their winter diet, seem particularly plentiful.
An iconic predator of the tundra, the gyrfalcon is a year-round resident of the circumpolar north. They breed only in arctic and subarctic regions of the globe and generally winter as close to their breeding territories as food availability allows.
Because gyrfalcons are arctic specialists, most inhabit remote and inaccessible places. However, on the Seward Peninsula they are one of the most abundant raptors, second only to the rough-legged hawk. The Nome road system provides a front-row seat to observe these magnificent predators in action.
The gyrfalcon is the world’s largest falcon. They are fast and powerful on the wing and thrilling to watch as they hunt, powering low over the landscape with fast wing beats, occasionally striking a ptarmigan and driving it to the ground. Ravens and foxes often are watching, too, and sometimes manage to steal a falcon’s skillfully captured prey.
Gyrfalcons are a well-studied species on the Seward Peninsula. In 1998, now-retired Fish and Game biologist Peter Bente began an annual aerial survey program to assess abundance and breeding success of gyrfalcons and other raptors on the peninsula. Today, Fish and Game biologist Travis Booms continues to build on this valuable, long-term data set.
In 2014, the Peregrine Fund, a renowned raptor conservation organization, in partnership with the Alaska Department of Fish and Game, launched the Gyrfalcon and Tundra Conservation Program, overseen by Michael Henderson. The next Birder’s Notebook will focus on this collaborative research investigating the effects of climate change on gyrfalcons and the ecosystem on which these birds depend.
Gyrfalcons are monogamous and form long-term pair bonds. Both sexes incubate, brood, hunt and defend the nest, but the male generally does more hunting and less brooding than the female.
Because breeding pairs are resident on the Seward Peninsula, they are here to begin egg laying in April, before winter has released its grip. Ptarmigan are courting and conspicuous then and relatively easy to catch. According to Henderson,
despite inclement weather, early nesters tend to have better success than pairs that nest later.
By foregoing migration, breeding pairs are also in position to defend their territories from other pairs and to claim choice nesting sites before the arrival of migratory raptors that might compete for the same limited, cliff-face nesting ledges.
Gyrfalcons do not build their own nests. Instead, they typically occupy stick nests previously built by golden eagles, rough-legged hawks and ravens. If no stick nest is available, gyrfalcons may nest on a bare cliff ledge or occasionally in trees or on man-made structures.
According to Booms, last summer was a good one for gyrfalcons on the Seward Peninsula, with many occupied nesting sites and many nestlings. He banded what was perhaps a record number of nestlings last June. However, survival of the young is unknown.
Young gyrfalcons fledge in July. The fledglings remain in the vicinity of their nest for up to several weeks, staying in contact with their parents and siblings. The parents continue to feed their young for four to six weeks after fledging.
The young falcons migrate, often showing up along the coast to hunt waterfowl during fall migration. It is common to see juvenile gyrfalcons and occasionally adults along Safety Sound, perched on driftwood or Iditarod Trail markers, or hunting along the shoreline.
Where the young falcons winter is unknown. Henderson said gyrfalcons do not tolerate tracking transmitters well, so little is known about their movements. Small, tailmounted transmitters are being tested on gyrfalcons. If they prove successful, much can be learned about the birds’ localized and longdistance travels.
The gyrfalcon’s large size enables it to take prey up to the size of a crane, but that is not the norm. In winter their diet consists almost entirely of ptarmigan and they will travel as needed to find them. Both willow and rock ptarmigan are taken.
Cameras placed at nest sites by the Peregrine Fund have documented a shift in diet as nesting progresses. As ptarmigan begin nesting their plumage becomes cryptic, their behavior becomes secretive and they become increasingly difficult to hunt. The falcon’s diet then transitions to ground squirrels, supplemented with a variety of songbirds, shorebirds, lemmings and voles.
When hunting, these focused predators most often fly fast and low over the ground but may make high-speed dives from the sky to strike prey on the ground or in flight. After impact they usually drive prey to the ground rather than grabbing it in the air with their talons. You also may see them scanning or launching from a power pole or tall willow.
I have seen gyrfalcons successfully prey on ptarmigan five times. In two of those cases, the ptarmigan were quickly stolen by ravens. I know of another snatched by a fox. Gyrfalcons, ravens and foxes make an interesting trio. A fox can sometimes be an asset to a falcon by flushing otherwise unattainable ptarmigan from the willows. However, being watched by cunning ravens seems to be nothing but trouble for a gyrfalcon. These fascinating interactions make me wonder how often the falcon’s hunting prowess is for naught.
I still wonder where the gyrfalcons have been this winter but am pleased that at least one is now hunting over the landscape near my home at Banner Creek. Perhaps ptarmigan have been so abundant near their nesting cliffs that the falcons had no need to roam this far to find food.
Here’s hoping they occupy their nest sites next month and have another productive year.
This article was published incomplete in the March 23 edition and is printed in it’s entirety in this week’s edition.