Population composition and perching habitat of wintering bald eagles, Haliaeetus leucocephalus, in northcentral Michigan

Abstract

From 15 November 1989 to 15 February 1990, biweekly aerial surveys of the Au Sable, Manistee, and Muskegon rivers, Michigan, detected 54 adult and 33 immature bald eagles (Haliaeetus leucocephalus) with a high of 19 between 1-15 January. Adults peaked prior to immatures and appeared to leave earlier. Thirteen deciduous and four coniferous species were identified among 55 perch trees. Adults perched nearly equally in coniferous (43%) and deciduous trees (57%), whereas immatures used mostly 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. 408.9, P = 0.017) and on terrain that had a greater mean slope (40.6% vs. 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 the more densely populated Muskegon River.