Abstract
The Kirtland's warbler (Dendroica kirtlandii Baird) is an endangered songbird that nests in northern Lower Michigan in ecosystems dominated by young jack pine (Pinus banksiana Lamb.). An ecological, multifactor approach was used to determine the range and characteristics of landform-level ecosystems supporting the warbler and to compare the spatial and temporal patterns of warbler occupation among these ecosystems. Using an ecosystem rather than a strictly biological approach, the landforms occupied by the warbler are very diverse. Twelve landforms were identified based on 61 sites currently or formerly occupied by the warbler. Average annual jack pine height growth, an indicator of stand structural features that influences initial warbler colonization and duration of occupancy, differed significantly among landforms, resulting in marked differences in warbler occurrence in time and space across the breeding range. Landforms with favorable growing conditions for jack pine were colonized earliest and were occupied for the shortest duration, whereas landforms with unfavorable growing conditions were colonized relatively late but were occupied longest. Different ecological factors, such as the spatial position of landforms, microclimate, soil texture, or a combination of these factors, may account for favorable or unfavorable growing conditions for jack pine, which in turn affects the timing and duration of warbler occupancy. The classification and description of ecosystems occupied by the warbler provides an ecological framework for warbler management, especially when plantations rather than wildfire are the primary source of warbler habitat. FOR. SCI. 49(1):140–159.