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KODIAK: Survey Measures Pulse of Bald Eagle Population
Alaska Region, September 12, 2007
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The Kodiak Archipelago supports a robust population of resident bald eagles, estimated at 2,500-2,800 birds. Photo: Steve Hillebrand/USFWS
The Kodiak Archipelago supports a robust population of resident bald eagles, estimated at 2,500-2,800 birds. Photo: Steve Hillebrand/USFWS - Photo Credit: n/a

People who visit Kodiak frequently comment about its abundant bald eagle population, particularly when birds concentrate along the coast in winter. In fact such observations correspond with the picture revealed by Refuge eagle surveys. Since 1963, wildlife biologists have routinely monitored the Refuge's eagle population.  As such, this survey is one of the longest-running on the Refuge and in Alaska. For the past 30 years the survey has been operated by Refuge Biologist Denny Zwiefelhofer.  

Survey results over the years documented a dramatic increase in the number of active nesting eagles followed by a slight decline or leveling of breeding numbers. From 1982 to 2002 active nests increased from 200 to over 600. In 2007, 429 active nests were found, a decrease of 30%. This decline suggests that the population may have reached the maximum number the Refuge can support. Correspondingly, nest success and production surveys revealed increases in the 1980's and 1990's followed by declines in the 2007 survey. Of the 429 active nests seen in May, 206 (48%) were successful in fledging 305 young eagles. The production rate measured in 2007 (0.7 young per active nest) was markedly lower than the rate of 2002 (0.9 young per active nest) and 1963 (1.1 young per active nest). The 2007 rate is considered sufficient for maintaining the population, assuming that survival of fledged immature birds and adults remains high.

Despite sustained high rates of nest success and productivity in the 1960s and 1970s, the population of nesting adults showed minimal change. This suggests either that some local factors were limiting survival of immature or adult eagles or that birds fledged in Kodiak emigrated from the island and never returned. Emigration is unlikely since Denny has documented that the eagles of Kodiak are homebodies; those reared on the islands apparently make them their lifelong residences. On the other hand, a combination of factors--deficient food supply, contaminants (e.g., lead), and human action (e.g., Alaska sponsored a bounty hunt on eagles until 1952)--probably limited survival of older birds.

Despite declines observed in 2007, the Refuge’s non-migratory population of bald eagles remains healthy, maintaining its status as one of the most abundant in North America.


Contact Info: Kristen Gilbert, 907-786-3391, Kristen_Gilbert@fws.gov



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