Scale‐dependent habitat use by fall migratory birds: vegetation structure, floristics, and geography

Animal habitat selection is a central focus of ecology and conservation biology. Understanding habitat associations in migratory animals is particularly complicated because individuals have variable habitat requirements during the annual cycle, across their geographic range, along migratory routes, and at multiple spatial scales. We studied habitat associations of 16 fall Nearctic–Neotropical migratory land birds at two spatial scales at a stopover site along the northern Yucatan coast to examine scale‐dependent habitat use, identify proximate cues shaping birds' distributions, and evaluate similarities in habitat use between our tropical stopover site and temperate sites. We addressed scale‐dependent habitat associations in two ways, by (1) quantifying species' distributions among and within broad vegetation types and (2) comparing migrants' associations with architectural gradients between the two spatial scales. We also evaluated the relative importance of vegetation architecture and floristics in explaining migrants' distributions within broad coastal vegetation types. Bird species were nonrandomly distributed among broad‐ and fine‐scale vegetation types, and patterns of habitat use varied between the two scales. Moreover, birds had different preferences for vegetation architecture at the two scales, which may reflect trade‐offs between competing demands and/or reduced variation in vegetation at the small scale in our study. These findings illustrate the manner in which spatial scale and range of vegetation variation influence perceptions of animal–habitat associations. Within broad coastal vegetation types birds refined their distributions in relation to architectural and floristic attributes, which provided them with redundant and/or complementary information regarding the distribution of suitable habitat. We suggest that the relative importance of architecture and floristics is likely scale‐dependent. Habitat use at our site was similar to that observed at temperate stopover sites for almost all species, indicating that habitat affinities are maintained along the migratory route for these eastern populations despite latitudinal changes in environmental factors. We highlight examples of similar patterns observed in other migratory and nonmigratory animals to illustrate the generality of these patterns beyond en route land birds and our tropical site. We also indicate where we expect to see differences and outline areas of research that merit greater attention in order to advance our understanding of animal habitat selection.