Dispersal of Little EgretsEgretta garzettafrom Northern Spanish Atlantic Colonies

Abstract

We studied the movements of little egrets Egretta garzetta from breeding colonies in northern Spanish Atlantic estuaries using sighting data of colour-ringed birds. Data on 304 resightings of 95 out of 457 little egrets ringed as chicks in two colonies on the southern Bay of Biscay were analysed. Most egrets (68.9%) were observed less than 50 km from their natal colonies and thus exhibited low dispersal, supporting the view that these birds belong to a resident population breeding along the coasts of the Bay of Biscay. Nearly all resightings (95.5%) occurred in estuaries across an east-west axis corresponding to the Atlantic coast of northern Spain and had a west-biased dispersal direction. We suggest that the recently formed northern Atlantic Spanish population is a consequence of a westward colonisation pattern originating in the French Atlantic colonies.