Local and Long-Range Movements of Bald Eagles Associated with the Autumn Concentration in Glacier National Park, Montana

Abstract

A concentration of bald eagles (Haliaeetus leucocephalus) along lower McDonald Creek in Glacier National Park was first recorded in November 1939, when 37 were observed (Shea 1978). On that occasion and during each subsequent autumn, bald eagles have congregated to feed on spawning kokanee salmon (Oncorhynchus nerka). Kokanee is a non-native species, first introduced in the Flathead River drainage (in which McDonald Creek occurs) in 1978. Preliminary data suggest that there may be nearly 1,000 bald eagles now stopping at the Glacier concentration annually, although maximum counts are well below this level because of a high turnover rate. The northern subspecies of the bald eagle was classified as endangered in February 1978 under the aegis of the Endangered Species Act of 1973 and subsequent amendments. This conveys a high level of responsibility upon managers of lands and waters used by bald eagles and demands a commitment to effective habitat management. The purpose of our research is to provide information essential to such management - knowledge of movement patterns, spatial and temporal distributions, numbers, and morhpology - directly benefiting not only Glacier National Park managers, but all public agencies, industrial corporations and private land owners responsible for bald eagle habitat. This report summarizes the first part of the fourth year of a study of the ecology of Bald Eagles associated with the Glacier concentration. At this writing eagles are being tracked in the western states. Most data from this autumn have not yet been analyzed.