Biological Projects

Raptors:
Twenty-one raptor species have been identified on the Togiak Refuge. The most abundant of these are bald eagles, northern harriers, rough-legged hawks, and short-eared owls. In addition, osprey, golden eagles, merlins, gyrfalcons, peregrine falcons, great horned owls, snowy owls, northern hawk owls, and boreal owls are observed each year. Less frequent or few observations are made for the remaining species.

Raptors are predators at the top of complex food chains and are sensitive indicators of the health of the environment. Therefore, raptors are important species to monitor.

From 1985-1989 aerial surveys were flown to record the activity and productivity of nesting bald eagles (Haliaeetus leucocephalus). These surveys were commenced again in 1999, have continued annually, and may show changes over time with nesting bald eagles. Although these aerial surveys target bald eagle nests, we record data from all raptor nests encountered.

To conduct these aerial surveys, Togiak Refuge staff fly to known bald eagle nest locations in early June to see which nests are active. During the course of these flights, new nests are located and observed. All active nests are then looked at again in late July to observe the productivity of each nest (how many chicks are present and assumed to fledge).

For the surveys flown from 1985-1989, brood sizes averaged 1.73 bald eagle chicks per successful nest, while the surveys conducted from 1999-2003 averaged 1.57 bald eagle chicks per successful nest. However, rates of nest activity were higher in the period from 1999-2003 (average of 80%) than in the period from 1985-1989 (average of 69%).

Here is an example of a single year's data. In 2001, 50 bald eagle nests, 2 rough-legged hawk (Buteo lagopus) nests, 1 golden eagle (Aquila chrysaetos ) nest, and 2 great gray (Strix nebulosa )/great horned owl (Bubo virginianus) nests were observed. Nest productivity data was gathered from 44 bald eagle nests (1.82 chicks per nest), 1 rough-legged hawk nest (3.00 chicks per nest), and 1 unidentified large-owl nest (1.00 chicks per nest). In addition, we have locations of nests previously used by other species that were either not observed or were inactive. These represent 2 gyrfalcon (Falco rusticolus ) nests, 2 osprey (Pandion haliaetus ) nests, and 5 peregrine falcon (Falco peregrinus ) nests.

For more information regarding the activity and productivity of nesting bald eagles, contact the Togiak National Wildlife Refuge.