Specialist or generalist? It depends. Context-dependent habitat relationships provide insight into forest disturbance effects for a boreal bird species

Abstract

Understanding how disturbance affects species is a critical component of management in the boreal forest, particularly for disturbance specialist species that often help initiate the succession process through seed dispersal, nutrient cycling, and other means. Unfortunately, emulation of natural disturbance rarely incorporates the disturbance response of those specialist species, which may be potentially sensitive to disturbance characteristics because they are attracted to resources provided by the disturbance itself. Identifying disturbance specialist species and the reasons they occur in post-disturbance habitat is thus a priority for maintaining biodiversity in managed forests. We compared two types of habitat use to fill this information gap for a potential boreal forest disturbance specialist, the Common Nighthawk (Chordeiles minor). The Common Nighthawk is of particular interest to forest managers because this wide-ranging species is declining and listed as of conservation concern in multiple jurisdictions. We used passive acoustic monitoring to survey for nighthawks at 326 locations in the boreal forest of northeastern Alberta, Canada where land use pressure for resource extraction is high. We used an occupancy modelling framework to evaluate two hypotheses for why nighthawks use post-disturbance habitat: nesting or foraging resources. The nesting resource hypothesis was supported by all three lines of evidence that we examined. First, time since disturbance negatively affected territorial habitat use, but not extraterritorial habitat use, confirming that this species is only a disturbance specialist for the territorial component of its home range. Second, territorial habitat use differed between disturbance types, with a higher probability of habitat use for post-harvest and abandoned well sites, which are more likely to have lower amounts of residual vegetation. For our third line of evidence, open pine forest mitigated the effects of time since disturbance for territorial habitat use for all three disturbance types, but especially for postfire areas. We conclude that breeding Common Nighthawks require a combination of open habitat for nesting and wetland areas for foraging and provide industry-specific recommendations for incorporating the Common Nighthawk into boreal forest management plans. Our research emphasizes that understanding the context-dependence of species responses to disturbance provides insights that facilitate effective forest management. We advocate that understanding the behavioural context of habitat use can provide this insight and is often more likely to be aligned with the operational scale of forest management.