Post‐fledging spatial dispersion and movement behaviour differs between cavity‐nesting and open‐cup nesting passerines

Abstract

Spatial dispersion and movement behaviour of siblings vary across animal taxa and can affect fitness. The factors underlying why species differ in movement behaviour of young and why some species form family groups while other species have dispersed young have rarely been addressed. We tested a hypothesis that siblings should be more dispersed in space and move less in species that have offspring with poor locomotor abilities to reduce the chance of the loss of the whole brood. In contrast, siblings should aggregate and move more when their mobility and ability to avoid predators is strong. We tested this hypothesis using songbirds because cavity‐ versus open‐cup‐nesting species strongly contrast in nesting strategy. Offspring of species that nest in cavities leave the nest with well‐developed wings and initially are more mobile and incur lower predation rates than fledglings of species that nest in open‐cups. We used radiotelemetry to track fledglings of three cavity‐ and three open‐cup‐nesting songbird species to test whether young differ in spatial dispersion and movement behaviour between nest types. We found that mobile young of cavity‐nesting species moved farther on a daily basis but remained more aggregated as a family than the less mobile young of open‐cup‐nesting species. Movement distances increased with mobility as young aged, especially in open‐cup‐nesting species, but families of open‐cup‐nesting species remained dispersed throughout the first week after fledging. This variation in spatial dispersion and movement behaviour of young can have important implications for parental care strategies and juvenile survival.