Functional connectivity in forest birds: evidence for species-specificity and anisotropy

Abstract

Functional connectivity is assumed to play a critical role in population dynamics in fragmented landscapes. Although it is generally summarized as an isotropic metric, functional connectivity may be anisotropic, i.e. may vary as a function of movement axis and direction. In addition, variation in functional connectivity among species within the same landscape has rarely been examined. Here, we asked to what extent the functional connectivity of managed forest landscapes is species-specific, and whether there is evidence for directional anisotropy in functional connectivity for two species of forest songbirds. We performed 6-km reciprocal translocations between two pairs of sites and we monitored return times of territorial male Ovenbirds (Seiurus aurocapilla; n = 47) and Black-throated Green Warblers (Setophaga virens; n = 37) in northwestern New Brunswick, Canada. Each landscape was dominated by deciduous forest and comprised a 500- to 900-m wide strip of conifer plantation perpendicular to the movement axis. Homing time was shorter for Black-throated Green Warbler than for Ovenbird and anisotropy in functional connectivity was detected in the Ovenbird in one of the landscapes. Differences between species may reflect the Ovenbird’s narrower habitat and foraging niche. Our results indicate that spatially-explicit population models should account for variability in functional connectivity among species, even when they are closely related. Our findings also suggest that anisotropy can be present under specific conditions.