The spatial response of male Hooded Warblers to edges in isolated fragments

We tested whether Hooded Warblers (Wilsonia citrina) avoided abrupt forest edges by radiotracking males breeding in small, isolated forest patches (0. 5-2.0 ha) in northwest Pennsylvania. Because territory edges were synonymou s with abrupt forest edges in all cases, we compared space use patterns wit h males radiotracked in a nearby continuous forest (150 ha), where we defin ed edge from territorial boundaries. Based on the proportion of edge to cor e area, males in both habitats avoided the area within 20 m of the edge, im plying that males responded to the presence of territory edge rather than f orest edge. Surprisingly, however, males in isolated fragments used the edg e area significantly more than males in continuous forest, even when measur ed against the relative amount of edge area within each territory. Elevated levels of edge use were not related to distance of nests to edges, nest st age, or time of day. We conclude that the presence of physical edges is not the sole determinant of territorial space use in this species and there ar e likely additional social factors influencing occupancy rates in small, is olated woodlots. Therefore, definitions of forest-interior species based on edge use need to be reconsidered.