Identifying the Peregrine Falcons on Alaska’s Coast

Posted by on Jan 12, 2016

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A new study sheds light on the Peregrine Falcons which populated an area in Alaska after retreating glaciers opened it to colonization. Though earlier researchers believed that this new habitat was filled by the subspecies from nearby coastal areas, the researchers found an inland subspecies in this area.

Icy Bay, the study site, was entirely glaciated as recently as 1887. Since then, glacier fronts in the area have retreated, though a glacier still meets the water in one part of the bay. During this period, rocky outcrops and cliffs overlooking open ocean were exposed, creating suitable nesting habitat for Peregrines.

There are three subspecies of Peregrine Falcons that live in the United States, the American, the Arctic, and Peale’s. All of these are found in Alaska. They are just a fraction of the 19 subspecies that are found worldwide. Previous work had assumed that the distribution in Alaska corresponded tightly to habitat types, with the Arctic subspecies found in the far north of the state, a second subspecies inland, and a coastal subspecies near the Gulf of Alaska to the south.

Previous Distribution Peregrine

Map of distribution of Peregrine Falcon subspecies, as understood previously. Source: Journal of Raptor Research.

As the authors write, some reports described the classification of the Peregrine Falcons of the Lost Coast, the area between the western and eastern panhandles of Alaska, as unclear. The new study provided a definite answer for the particular research site, Icy Bay.

Authors Stephen Lewis and Michelle Kissling work in the area did not begin not with Peregrines. They first focused on the Kittlitz’s Murrelet as the Fish and Wildlife Service considered whether it should be categorized as an endangered species. This status could allow for action to be taken to protect the bird’s habitat. Though the murrelet was later deemed ineligible, the project allowed additional scientific work on other bird species as well. Taking advantage of this possibility, the researchers gathered data on Peregrines and Bald Eagles.

To clarify the subspecies to which Icy Bay Peregrines belonged, the authors needed to capture them in order to take close measurements, and to attach tracers that would allow them to track migratory behavior. This work required them to face challenging conditions. In an email, Lewis wrote that Icy Bay, has “dynamic,” or changing, ice conditions.  He stated, “depending on the weather conditions, winds, and tide, the ice in the bay could be contracted deep into the fjords or spread throughout the entire bay. That could change on a daily basis or even within a day.” The authors navigated icy waters in 14-foot inflatable skiffs to reach Peregrine nests on shore.

Glacier Bay Ice Low Tide

Sea ice blocks exposed by falling tide in Icy Bay. Courtesy of Margaret Olson/Flickr. (The crumbly mourrain material of the cliffs in the background makes poor nesting ground, but exposed rock in other parts is quickly capitalized upon by nesting Peregrines, according to Lewis.)

Once ashore, protocols on animal capture and release were followed to ensure the birds’ safety. The researchers weighed and measured the captured birds, which included 6 adults and hatchlings, as well as noting their coloration of the captured birds. GPS tracking devices were also attached.

In determining the subspecies of the birds, researchers looked to size. They knew that the coastal subspecies, which travels long distances over open ocean in search of the seabirds on which it feeds, was larger than the other two, which capture smaller prey and travel shorter distances. But they found that size characteristics varied too much within the subspecies to serve as a clear delineator. It was coloration–specific details of stripes on the throat—which provided the first strong clue that the captured birds were of the American, or anatum, subspecies, rather than the expected Peale’s subspecies.

Peregrine-Sitka

A Peregrine Falcon at a raptor recovery center in Sitka, Alaska. Courtesy of Harvey Barrison/Flickr.

Strong confirmatory evidence of this classification was found through the tracking devices. The devices provided data on the long-distance migration of the birds. Radio tags identified the birds as having wintered in southern Mexico and as far south as Uruguay (some birds managed to lose their tags, including one who fell off the radar over Brazil). The American Peregrine is understood to be a much greater traveler than Peale’s, supporting the classification of the Icy Bay Peregrines as American.

The finding contradicted the widely-held view of distribution of Peregrine subspecies in Alaska, which indicated that Peregrines of the Peale’s subspecies would be the most likely inhabitants of Icy Bay. The previous belief also represented a theory that the existing coastal species would move in to occupy new coastal areas opened by receding glaciers. In finding that the Icy Bay Peregrines were of the American, rather than the Peale’s subspecies, the study provides one case study that indicates the complexity of the movement of birds and other animals into areas that are exposed as glaciers retreat.

 

 

 

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