|Aim It is generally believed that the migration programme constrains the
dispersal and hence range sizes of migratory bird species. This conclusion is based
on analyses of breeding ranges of migratory versus non-migratory (resident)
terrestrial bird species, and rests on the assumption that there are no ecological or
evolutionary constraints on extending the non-breeding range. To investigate this
assumption, the abilities of migrant and resident terrestrial species to colonize
new wintering areas were compared.
Location Three major wintering regions of long-distance migrants: South
America, sub-Saharan Africa and the Indian Subcontinent.
Methods It was determined whether the relative numbers of residents and shortand
long-distance migrants were the same in those species that have dispersed to
a novel wintering region as in the source species pools.
Results At the species level, long-distance migratory species are more likely to
have non-breeding ranges that include more than one of the above regions than
resident species. This indicates that the dispersal of migratory species is less
constrained than that of resident species. The pattern holds irrespective of the
inclusion or exclusion of species associated with coastal, freshwater and wetland
habitats, and also holds for ecological groups such as aerial feeders. The pattern is
most pronounced between the regions separated by the strongest dispersal
barriers (South America and sub-Saharan Africa).
Main conclusions It is unlikely that the migration programme per se constrains
dispersal, but rather that difficulties in establishing new non-breeding areas
prevent range expansions in migrant species.|