Bald Eagle Behavior and Productivity Responses to Climbing to Nests

Abstract

Several persons have recently investigated the effects of various types of human disturbance, including research methods, on the productivity of bald eagles (Haliaeetus leucocephalus). This paper presents data on the behavior and productivity of bald e;agles in response to climbing to nests to band nestlings in northwestern Ontario during 196S68. Nests in 24 territories in 1966, and nests in an additional 12 territories in 1967, were climbed to. Subsequent productivity ( 1967-68) of these territories did not differ significantly (P > 0.05) from that of 54 territories in 1967 and 64 territories in 1968 which were censused only from a distance with the aid of binoculars. The percentage of territories with young during 196S68 varied between 53 and 74, and the number of young per nest with young ranged from 1.4 to 1.7. Declines in bald eagle populations have caused concern for the future of particular populations and, in fact, for this species (Robbins 1960, Sprunt 1963). In attempting to assess the causes of the declines, several persons have investigated the potential effects of various human activities on the eagle's life cycle ( Stickel et al. 1966, Mathisen 1968, Hickey and Anderson 1968 ) . Hancock ( 1966:91 ) suggested that some research methods, particularly climbing to nests, may seriously interfere with the eagles' productivity in subsequent years. If Hancock is correct, such a disturbance could cause serious problems for research based upon climbing to nests; consequently many persons became greatly concerned. The purpose of this paper is to present data on behavior and subsequent productivity of bald eagles during an ecological study involving climbing to nests in northwestern Ontario during 196S68. I would like to thank the following persons for valuable criticisms during the proJect and the writing of this paper: J. J. Hickey, A. Sprunt, IV, C. R. Sindelar, S. Postupalsky, H. C. Mueller, D. D. Berger, 1 Supported, 1967 and 1968, by grants from the Nation!al Audubon Society. 2 Present address: Laboratory of Ornithology, Cornell University, Ithaca, New York 14850. Frances and F. N. Hamerstrom, Jr., Joyce Grier, and my brother, J. B. Grier, assisted with fieldwork. In addition, the Ontario Department of Lands and Forests, Canadian Wildlife Service, U. S. Fish and Wildlife Service, and well over a hundred individuals gave further aid.