Report Nr. 3103 Studies of Bald Eagles, Ospreys, and Other Raptors, 1986

This summary of field research activities during the 1986 breeding season is for the information of funding groups, supporters, and cooperators, to keep them up to date on some aspects of ongoing work with Ospreys, Bald Eagles, and other raptors in Michigan and certain adjacent areas in the Great Lakes region. While the reproductive success of Bald Eagle populations has been monitored in several parts of their breeding range for various lengths of time (in Michigan for 26 years), reliable information on survival rates is mostly lacking and the currently available band recovery data are still insufficient for calculations of life equations. The aerial surveys undertaken by DNR biologists, author observations and those of the handing teams, and reports from other natural resource agencies together located 122 breeding areas (territories) occupied by Bald Eagle pairs in 1986. Pairs were seen at three additional breeding sites, but no occupied nests were found there. No eagle activity was noted this year at seven sites which were occupied in 1985, and at eight sites only single adults were observed. The aerial surveys by the DNR and my more detailed observations in my principal study area together located 158 breeding sites occupied by Osprey pairs. The outcome of nesting was determined for all 158 nests, of which 102 (65%) were productive and a total of 200 young were raised to fledging or near-fledging age. The statewide productivity was 1.27 young/occupied nest - the second highest on record (1.56 in 1985) since these surveys were started in 1965 and well above the minimum level needed to maintain an Osprey population. During the past decade Michigan's Osprey population has increased by 98%, at a mean annual growth rate of 7.3%.