Preliminary investigation of bald eagle distribution, productivity and nest site requirements in Northern Ontario

Abstract

Bald eagles {Haliaeetus leucocephalus alascanus) have been declared an endangered species in Ontario. For protection of bald eagles from behavioural and habitat disturbance, their nests are defined as Areas of Concerns by the Ontario Government. To direct the management of these areas, the Ontario Ministry of Natural Resources reviewed the available literature and produced the Ontario Management Guidelines. However, the information available on Northern Ontario's bald eagles is limited, referring to the Lake of tire Woods Area only. To study bald eagles and evaluate Ontario's guidelines I gathered and analyzed data from across Northern Ontario on bald eagle habitat (1990, 1991, 1992), the effect of timber management on their reproduction (1990) and bald eagle distribution (1990). Data were analyzed univariately and I developed logistic regression models for topographical, limnological and vegetation characteristics. Variables important for defining the probability of a nest occurring include lake dimensions, stand density and tire availability of super-dominant, accessible perch trees. Of the models developed, two had practical implications: a limnological model which could be used to define potential foraging lakes and thus prevent unnecessary surveys and a vegetation model which could be used to evaluate habitat quality. Natality rates of bald eagles did not differ significantly among areas harvested according to guidelines, harvested without reference to the guidelines and undisturbed. The habitat features of forests, surrounding Northern Ontario bald eagle nest sites are similar to elsewhere except for a greater significance of perch trees. This justifies the Ontario Ministry of Natural Resource's use of available data, but the guidelines may underestimate the number of large perch and nest trees in optimal bald eagle habitat.