Investigating the role of matrix habitat use in determining avian area-sensitivity

The absence of some species from small habitat patches has long posed a challenge for conservationists, yet the underlying mechanisms that cause this "area-sensitivity" remain poorly understood. Capacity of a species to extend their activities into the surrounding matrix habitat represents one potential determinant of area-sensitivity. Species may be able to occupy smaller patches if they can utilize matrix habitat beyond patch boundaries, whereas area-sensitive species may be restricted to larger patches due to their inability to utilize the surrounding matrix. We investigated the potential role of matrix utilization in determining area-sensitivity by mapping the movements of two shrubland-obligate passerines with contrasting patch area requirements in shrub-dominated forest openings ranging in area by nearly an order of magnitude. Our findings were consistent with our predictions; the less area-sensitive chestnut-sided warbler (Setophaga pensylvanica) exhibited greater use of matrix habitat than the highly area-sensitive prairie warbler (S. discolor). Furthermore, chestnut-sided warblers that occupied smaller openings used mature forest more than conspecifics in larger patches, yet forest use by prairie warblers was unrelated to opening size. Chestnut-sided warblers foraged as frequently in mature forest as within shrubland, whereas prairie warblers foraged significantly more in openings compared to forest. The findings of this study suggest that the ability or inclination of a species to utilize surrounding matrix habitat explains at least some of the observed variation in area-sensitivity in songbirds and potentially other taxa.