Where Young Golden Eagles From Denali Spend the Summer: Across All of Alaska

By Carol L. McIntyre, National Park Service, and Stephen B. Lewis, U.S. Fish and Wildlife Service. From Alaska Park Science.

A golden eagle soaring above Denali National Park and Preserve. NPS.

Studying migratory animals is hard: as the ecologist David Lack observed in 1954, a migrant may breed in one place and die in another hundreds of miles away. For birds that travel thousands of miles a year it is harder still. Alaska had recorded 521 naturally occurring bird species as of January 2018, many of them international migrants. To conserve them, including golden eagles (Aquila chrysaetos), NPS and U.S. Fish and Wildlife Service managers need to know where, when and how they travel, and how conditions along the way affect their survival and breeding. For most migratory birds raised in Alaska's parks, including golden eagles, that information is thin.

Territorial and non-territorial eagles

An eagle's age and social status shape how it moves.

• Territorial eagles belong to the breeding population: they hold and defend a nesting territory, try to raise young when conditions allow, and stay in and near it through the breeding season.
• Non-territorial eagles hold no territory and do not breed, and they roam widely. Some are actively trying to join the breeding population and return to Alaska with the breeders, from late February through March. Others are not, and return much later, from mid-April to late May.

Figure 1: Locations of golden eagles captured in Denali, 2014–2016. Left, a territorial adult male stays near his nesting territory; right, 20 non-territorial second- and third-year eagles range across much of Alaska and northwest Canada (note the different scales). NPS.

This article is about the second group: second- and third-year eagles not yet trying to breed. They are the breeding population's future, yet little is known about them or about natal dispersal, the journey from the nest where a bird hatched to the place it first breeds, which in golden eagles can take many years. Their movements and needs differ sharply from those of breeders, so conservation plans built on nesting territories may miss them, and the areas they use are usually less protected. Their survival may matter all the more because migration adds to the risk of dying. Lightweight tracking tags have begun to make them possible to follow.

Golden eagles have become a conservation concern in the United States, with worries about human causes of death: habitat loss, electrocution on power lines, contaminants, collisions with vehicles and illegal shooting. The Fish and Wildlife Service, which manages the species, has expanded its research.

Denali's eagles in history

Naturalists Charles Sheldon, Joseph Dixon and Adolph Murie all saw that the northern foothills of the Alaska Range, now in Denali, held a large concentration of nesting golden eagles. Dixon counted the eagle among the area's outstanding birds and urged that it be preserved, and Murie understood that Denali's eagles migrated and faced new hazards in the south. Their work inspired the golden eagle studies that began in Denali in 1987. (Mount McKinley National Park, established a century before the NPS celebrated it in 2017, was enlarged and renamed Denali National Park and Preserve in 1980 by the Alaska National Interest Lands Conservation Act.)

• 1987–1996: nestlings were banded. Recovered bands showed migration routes and wintering areas across western North America, and eagles killed by electrocution, shooting and vehicles showed how events thousands of miles away affected birds from a protected park.
• From 1997: satellite tags tracked juveniles and second- and third-year eagles year-round, giving some of the first estimates of survival and continental movements for migratory golden eagles in North America. Young eagles wintered from central Alberta's grasslands to central Mexico's high deserts.
• The surprise was summer: many tagged eagles spent most of the breeding season hundreds of kilometres from Denali, often in the Brooks Range or on the Arctic Coastal Plain, where other scientists had long seen young eagles without suspecting they came from Denali.

What the recent tracking shows

Tracking from 2014–2016, a collaboration of the NPS, the Fish and Wildlife Service, the U.S. Geological Survey and the Alaska Department of Fish and Game, pooled with the late-1990s data, showed great variety:

• some eagles wandered all season without settling; others wandered, then settled for long spells;
• four eagles, tagged in the late 1990s and in 2015, spent much of June to August in the western National Petroleum Reserve-Alaska (NPR-A), showing the area's use by Denali eagles over many years;
• at least two eagles tagged in 2015 each travelled over 3,100 miles (5,000 km) during the 2016 breeding season, passing through the same part of southwestern Alaska, one in May and one in September; individuals also used different areas from year to year;
• two non-territorial eagles tagged elsewhere, in the Mentasta Mountains (Wrangell-St. Elias) in late March 2015 and near a Denali nest in early April 2015, also ranged statewide, including the Seward Peninsula.

Federal lands they use

Beyond the NPR-A, the eagles were located in 27 other federally managed areas in Alaska and three in Yukon, from Arctic, Yukon Delta, Togiak and Yukon Flats national wildlife refuges to Gates of the Arctic, Katmai, Kobuk Valley, Lake Clark and Wrangell-St. Elias parks, the Tongass National Forest and several wild and scenic rivers. Individual eagles visited from 2 to 17 such areas in a season, and for some, most locations fell on federal land. Because conservation on federal land may be simpler than on private land, that matters.

The NPR-A, managed by the Bureau of Land Management and of growing interest for oil and gas, stands out. Six Denali eagles spent part of the season in its western half; four spent between 36.6% and 53.7% of the breeding season there, arriving in early to mid-June and staying into late August or early September. Observers counted 32, 33 and 30 golden eagles near its bluffs in 2012, 2013 and 2016, at least 75% of them in subadult plumage in 2012 and 2013 and at least 90% in 2016. The authors conclude that parts of the NPR-A are important to non-territorial eagles, including Denali's, and that conservation and management there, and statewide eagle plans, should say so.

A statewide strategy

Although the samples are small, the tracking shows many second- and third-year eagles using much of interior and northern Alaska in summer, so protecting what they need takes a statewide conservation strategy. Eagles summering in different regions face different conditions, and conserving them means working at the scale of the landscape and the whole year, with every agency and organisation that manages the lands they use. Over the next five years the partners plan to track dozens more eagles in Denali and other Alaska parks with solar-charged GPS-GSM tags that could last for years, to measure survival by season and age, dispersal and lifetime breeding success.

Sources

• Carol L. McIntyre and Stephen B. Lewis, "Statewide Movements of Non-territorial Golden Eagles in Alaska During the Breeding Season: Information for Developing Effective Conservation Plans," Alaska Park Science 17(1), National Park Service. https://www.nps.gov/articles/aps-17-1-10.htm
• The article says the eagles were found in 27 federal areas besides the NPR-A; its table lists 26 areas including the NPR-A.
• Six tracking maps in the original are drawn on a licensed commercial base map and are not reproduced here.
• Words on this page from people and organisations outside the federal government are paraphrased; rewritten in hubnx's own words.