Some Aspects of the Ecology of Migrant Shorebirds

During migration, shorebirds form dense multispecific aggregations within relatively uniform and limited marine littoral habitats. The amount of available feeding space in the habitats frequented fluctuates widely with the daily and seasonal changes in the tidal rhythm. Shorebird species broadly overlap in their periods of peak abundance, inter— and intrahabitat distributions, and in the food organisms preyed upon. However, the totality of species differences and the transient character of migratory assemblages apparently minimizes interspecific interactions that might result in competitive exclusion. The staggering of peak population densities and differences in distribution is most pronounced among morphologically similar species. The number of individuals and species that occur in an area is apparently determined by the amount of available feeding space and the physical diversity of the habitat. Food appears to be generally abundant relative to the requirements of the birds in all the habitats studied. The environmental conditions encountered during migration and the interactions with other individuals have evidently been important factors in the evolution of morphological and behavioral differences among shorebird species. Individuals must be as able to survive during the nonbreeding season as they are during the breeding season.