Seasonality modulates habitat cover effects on avian cross-boundary responses and spillover

Species cross-boundary response is a key mechanism affecting species
spillover into agricultural fields. However, temporal changes in edge
permeability, which may depend on the seasonal availability of resources
in both matrix and native habitats, remain poorly understood. Here we
tested how edge crossing behavior and the associated spillover of birds
into sun coffee plantations respond to landscape structure and
seasonality. We monitored the movement of six insectivorous understory
bird species (four forest-specialists and two forest-generalists) using an
automated telemetry system along a gradient of forest cover (7-60%) during
two seasons (dry vs. wet) at nine sampling sites at the Brazilian Atlantic
forest. We monitored 116 individuals and obtained a total of 15,129 bird
detections across seasons. Bird resistance to crossing edges was strongly
driven by an interaction between seasonality and forest cover in the
surrounding landscape, with higher resistance to crossing edges along the
dry season and in landscapes with lower amount of forest cover.
Furthermore, spillover patterns in plantations were driven by an
interaction between forest cover and distance from forest edges, but this
was most pronounced for forest-specialist bird species. Forest-specialists
moved more intensively and farther from edges in more forested landscapes,
whereas forest-generalists showed similar patterns of occupation
regardless of forest cover and isolation. Our study contributes to a
better understanding of avian cross-boundary responses and spillover in
response to landscape structure across seasons and the factors driving
bird movement decisions in anthropogenic landscapes. There are a myriad of
possible mechanisms governing movement decisions, and these mechanisms may
interact in complex ways and remain important foci for research within
fields of tropical ecology and evolution in the tropics.