Short-Term Response of Forest Birds to Experimental Clearcut Edges

Abstract

Abstract Numerous studies have addressed the potential consequences of increasing the density of edges through human activities, but most have documented responses to existing edges. Here, we monitored the response of seven forest bird species to experimentally created edges around five plots (10 ha, n = 3; 25 ha, n = 2) in the boreal mixed-wood forest of Alberta, Canada. We also mapped bird detections in six control plots (10 ha, n = 5; 25 ha, n = 1). The focal species were Least Flycatcher (Empidonax minimus), Red-eyed Vireo (Vireo olivaceus), Yellow-rumped Warbler (Dendroica coronata), Black-throated Green Warbler (D. virens), Ovenbird (Seiurus aurocapilla), Mourning Warbler (Oporornis philadelphia), and White-throated Sparrow (Zonotrichia albicollis). In the two breeding seasons following experimental clearcutting, we quantified birds' responses to edges in the absence of substantial edge-induced changes in vegetation by comparing the distribution of detections between treatment and control plots. We predicted that forest-edge specialists would be attracted to edges, forest-interior specialists would avoid them, and interior-edge generalists would show a neutral response. None of these predictions was consistently supported among plots and years, except in the Mourning Warbler. However, none of the significant responses was the opposite of predictions. We also predicted that postharvest colonization of treated plots would mainly involve forest-edge specialists, whereas most local extinctions would involve forest-interior specialists. Only the colonization of 10-ha fragments followed the predicted pattern. The relatively neutral response to forest edges we observed suggests that, in general, boreal forest birds do not respond to the edge itself or to proximate cues of edge proximity. Rather, significant responses may be delayed until edge-to-interior gradients in vegetation are established. Respuestas a Corto Plazo de las Aves de Bosque a Bordes Creados Experimentalmente por Tala Rasa