Date of Award:

5-1-1999

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Committee Chair(s)

James A. Gessaman

Committee

James A. Gessaman

Committee

Barrie K. Gilbert

Committee

Edmund D. Brodie

Abstract

The numbers of eagles occupying either the Willard Canyon roost or the Ogden Bay roost exceeded the combined total of other communal roosts documented in Utah. These roosts are among the largest known communal roosts in the lower 48 states, and the largest documented winter roosts within the McKenzie-Intermountain Flyway. During the winters of 1997-98 and 1998-99 I surveyed several Bald Eagle (Haliaeetus leucocephalus) roost sites in northern Utah to document their geographic location, habitat, and occupancy. I conducted surveys from December 1997 to April 1998 and December 1998 to April 1999. Most winter roosts were communal, as defined by the presence of three or more birds at sunset. Fourteen roosts were regularly used, and more than 100 eagles regularly occupied two roosts. One of these sites is up Willard Canyon where larger Douglas-firs (Pseudotsuga menzeisii) were the preferred roost trees. Willard Canyon had maximum annual occupancies of 227 eagles on 18 March 1998, and 363 on 15 January 1999. The other major communal roost, located on the Ogden Bay Waterfowl Management Area, had maximum occupancies of 153 on 2 February 1998, and 264 on 18 February 1999. Roost trees were in a stand of cottonwood (Populus sp.) and willow (Salix sp.) snags. The Weber River basin had several small communal roosts usually occupied by fewer than 20 birds at a time. These roosts were in groves of narrow-leaf cottonwood (Populus angustifolia) on stream banks, or in side canyons. Similar, small communal roosts existed near the Salt Creek Waterfowl Management Area. Eagles occupied the majority of the roosts regularly within seasons and between years.

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