Coastal Shorebirds Delay Maturity More Than Inland Ones

Delaying the age of first breeding will lower lifetime reproductive output unless compensated for by increased fecundity or survival. Yet, in many migratory shorebird species (Charadriiformes) individuals delay their first return migration to the breeding grounds until they are several years old. Using data from non-breeding and breeding season counts of shorebirds in the non-breeding areas, recaptures, and long-term banding studies, we assess the age of first return migration (as a measure of maturity) for 37 shorebird species that have migrated to Australian non-breeding grounds. We provide a comparative analysis of the association between the measure of maturity and habitat use during the non-breeding period, contrasting coastal and inland wetland habitats. After controlling for latitudinal and phylogenetic covariates, we found a positive relationship between body size and the age of first return migration. However, there was still a stronger relationship with the type of non-breeding habitat used. Coastal shorebird species delayed maturity more than species that spend the non-breeding season in non-tidal inland wetlands. This finding expands on previously identified ecological and physiological differences between coastal and inland shorebirds and leads to questions on the environmental characteristics embodied in the habitat contrast. We propose that the complicated tidal dynamics and differences in prey make it more difficult to become an individually competent coastal (rather than inland freshwater) forager.