POPULATION COMPOSITION AND PERCHING HABITAT OF WINTERING BALD EAGLES,HALIAEETUS-LEUCOCEPHALUS, IN NORTHCENTRAL MICHIGAN

From 15 November 1989 to 15 February 1990, biweekly aerial surveys of the Au Sable, Manistee, and Muskegon rivers, Michigan, detected 54 adu lt and 33 immature Bald Eagles (Haliaeetus leucocephalus) with a high of 19 between 1-15 January. Adults peaked prior to immatures and appea red to leave earlier. Thirteen deciduous and four coniferous species w ere identifed among 55 perch trees. Adults perched nearly equally in c oniferous (43%) and deciduous trees (57%), whereas immatures used most ly deciduous perches (85%, P = 0.034). Coniferous perches were taller (23.2 m vs. 18.9 m, P = 0.029), in denser stands (577.6 stems/ha vs. 4 08.9, P = 0.017) and on terrain that had a greater mean slope (40.6% v s. 19.9%, P = 0.008) than deciduous trees. Perch DBH was greater than both nearest-tallest DBH (P = 0.003) and surrounding stand DBH (P < 0. 001). Distance from perch trees to potential human disturbance varied with tree type, between structures and roadways, and was greatest on t he more densely populated Muskegon River.