BALD EAGLE NEST SITE SELECTION AND PRODUCTIVITY RELATED TO HABITAT FEAUTURES.

Jeremy E. Guinn and James W. Grier.
Department of Zoology, North Dakota State University, Fargo, North Dakota 58105

Bald eagle (Haliaeetus leucocephalus) populations declined dramatically between 
1930 and 1970 due to several reasons.  One of the causes often cited is habitat 
loss.  However, essential habitat requirements of nesting bald eagles are not 
well understood.  Furthermore, recent gains in the number of eagles have not 
been associated with a large-scale recovery of “typical” eagle habitat.  The 
goal of this project was to determine the relationship between bald eagle 
nesting habitat features and productivity.  A large sample of nests across 
several different habitat zones was used to reduce the amount of variation seen 
in past studies.  Minnesota has a large breeding bald eagle population, four 
distinct ecoregions, and a history of bald eagle nest monitoring, providing an 
ideal location for this project.  The primary objectives of the study were to 1) 
examine habitat characteristics at nest sites and an equal number of random 
sites and 2) obtain at least two years of productivity for each nest.  

A sample of 116 nests was chosen along with 166 random habitat sites, each 
stratified according to the four ecoregions of the state.  Habitat evaluation at 
each site consisted of 1) physical examination of trees within 100 m of the nest 
and 2) evaluation of aerial photographs and land use maps to determine habitat 
types within 1 km of the nest.  Productivity data for each nest was obtained via 
two groups of aerial surveys to determine the number of nestlings prior to 
fledging.  

Trees associated with nest sites were larger in diameter than trees at random 
sites.  Nest trees were among the tallest trees at the nest site, but usually 
were not “supercanopy” trees.  Nest tree species varied according to the 
available trees in the area.  The most frequently chosen nest trees were 
cottonwoods, white pines, red pines and quaking aspen.  Land use within 1 km of 
the nest varied greatly between nest sites.  Mean distance to shoreline was 
similar to those reported for eagle nests in other studies.  Bald eagle habitat 
may not be as limited as once thought.  Eagles in Minnesota use a large variety 
of habitats with different land use types within 1 km of their nest.  Eagles 
have shown the ability to reproduce successfully in areas once considered sub-
optimal nesting habitat. Protection of shoreline habitat for nesting and 
foraging purposes continues to be a concern.

Keywords:  Bald Eagle, Nest Site Selection, Shoreline Ecology, Endangered 
Species, Haliaeetus leucocephalus