SETTLEMENT IN NOVEL HABITATS INDUCED BY SOCIAL INFORMATION MAY DISRUPT COMMUNITY STRUCTURE

Birds may colonize new habitats because of introduction, changing environmental conditions, and/or altered social or environmental cues. However, aside from introduced (often invasive) species, little is known about the consequences of such colonizations for members of existing communities. If the realized niche is influenced by the presence or absence of heterospecific competitors, then addition of a species to a novel habitat or location could result in extirpation or avoidance if members of the existing community are subdominant. Alternatively, if for some species heterospecific cues are the primary means for collecting information about a site's quality, heterospecific attraction could occur. To test these predictions, we experimentally induced free-living Black-throated Blue Warblers (Dendroica caerulescens) to colonize a novel environment within their existing range. We used dynamic occupancy modeling to test for the dynamics of colonization and local extinction as a function of our experimental treatment. We found strong evidence for dynamic occupancy by birds during the breeding season; colonizations and extirpations were common. Although dynamics were not generally well explained by our experimental introduction of Black-throated Blue Warblers, we found some support for the heterospecific-avoidance hypothesis; three of the four species we examined that prefer early seral forests tended to abandon a site once Black-throated Blue Warblers occupied it. We suggest that heterospecific interactions should be considered when species' distributions are projected in relation to climate change. Our results provide a caution that managers broadcasting a species' song to increase its abundance should consider the technique's effects on the broader community.