ABSTRACT
Abstract. Climate change can alter the timing of biological events differently across members of an ecosystem, changing the nature of ecological interactions and the efficacy of evolutionary strategies. Mismatches in phenology have been reported between breeding songbirds and their food resources in north temperate ecosystems, especially for long-distance migrants and dietary specialists. Far less attention, however, has been paid to periods outside the breeding season. The success of songbird migration, like breeding, should also be determined by the degree of matching between bird and resource phenologies. Here, we tested if habitat patch use for songbirds along the migratory route was predicted by (a) habitat characteristics that varied throughout the migration season, (b) static characteristics, or (c) a combination of the two variable types. We tested for these patterns in four families of songbirds that ranged from specialists to generalists and across four stopover sites along the Gulf of Maine. Dynamic habitat characteristics alone predicted patch use in all four families better than static variables or a combination of dynamic and
static characteristics. Regardless of mean dietary niche breadth, mist net captures indicated that all four families shifted their apparent patch use throughout the season as a function of ripe fruit abundance, invertebrate biomass, vegetation defoliation, and soil moisture. The best predictors of patch use were different for short-versus longdistance migrants across the two most commonly captured families, but all species and migration strategies were sensitive to phenological changes. Our results suggest that migratory songbirds assess patch quality within a stopover site differently through time. Variation in the timing of stopover arrival thus results in different habitat selection behaviors. The potential therefore exists for timing mismatches that reduce individual fitness. We recommend that conservationists prioritize stopover habitats where landscape-scale phenological heterogeneity maintains benefits to migrants throughout the season.
