Effects of season, understorey vegetation density, habitat edge and tree diameter on patch-use by bark-foraging birds

1. We provided equal feeding opportunities for bark-foraging bird species across seasons, cleared and uncleared woody understories, edge-to-interior habitat and tree diameters in a deciduous oak forest in north-eastern Illinois, USA, to determine habitat preferences of these bird species. We determined habitat preferences by quantifying patch-use intensity. 2. Patch-use intensity was greater in the breeding season than in the non-breeding season, and in interior than in edge habitat. In addition, however, we found interactions among the habitat variables. For instance, these bird species showed significant preferences for foraging in woodland interior habitat and on large diameter trees in the breeding season, but not in the non-breeding season. 3. Foraging preferences were further affected by understorey clearing, with preference for interior over edge habitat reversed in the cleared habitat in the non-breeding season. This effect may reflect unintended consequences of topography, an uncontrolled factor outside the experiment protocol. 4. Overall, the results suggest that patch-use results from the response of the bird species to effects of vegetation variation from edge to interior habitat on both microclimate and predation risk. Those effects of vegetation may disappear or diminish when understorey vegetation is removed or reduced.