Forest fragmentation affects step choices, but not homing paths of fragmentation-sensitive birds in multiple behavioral states

Abstract

Theory predicts that movement limitation due to landscape fragmentation can reduce population viability. Understanding how landscape heterogeneity influences movement is thus critical for testing theory and developing conservation strategies. Consequently, studies are needed that link movement data with landscape features influencing dispersal. We used experimental translocations to test whether forest fragmentation constrains movements of two fragmentation-sensitive bird species. We also tested for evidence of multiple behavioral movement phases (i.e., exploring, homing) and evaluated whether fragmentation effects varied between them. Over two breeding seasons we translocated territorial Wood Thrushes (Hylocichla mustelina; n = 36) and Ovenbirds (Seiurus aurocapilla; n = 19) 1–1.2 km across landscapes spanning a fragmentation gradient and recorded spatial (movement path) and temporal (return time) homing data using VHF transmitters and receivers. Ninety-one percent of individuals returned home, taking up to 72.2 h. Movements of 98% of returning birds indicated distinct exploring (i.e., short, undirected movements and course reversals) and homing (i.e., large, fast steps towards home) movement phases. Both species chose steps minimizing gap exposure in both phases. However, landscape fragmentation had no negative effect on homing times or path straightness. Our results suggest movement limitation does not drive fragmentation sensitivity in these species. Discrepancy between step- and path-level analyses either indicate that fine-scale movement data do not reflect landscape connectivity, or that artificially motivated animals respond unnaturally to behavioral barriers. Given evidence for dichotomous movement behavior, future studies linking these behaviors to life stages will elucidate when and how landscape features influence movement.