Trophic association between herons in the Albufera de Valencia paddy fields (Eastern Spain).

Full article

Published:

Volume 45(1), June 1998. Pages 29-34.

Language:

Spanish

Original title:

Asociación trófica de ardeidas en el arrozal de la Albufera de Valencia.

Keywords:

foraging associations, herons, niche overlapping, paddy fields, Spain.

Abstract:

This study analyses the patterns of intra and interspecific association of the six heron species breeding colonially at the Albufera of Valencia (Eastern Spain), while foraging in the paddy fields surrounding colonies, within the framework of the adaptative values of gregariousness. The spatial distribution of feeding groups was not uniform, but clumped, probably reflecting the patchy distribution of the food resources in the study area. The application of Cole's Coefficient of Interspecific Association to the observed associations indicated that only Little Egret-Cattle Egret (Egretta garzetta-Bubulcus ibis) and Grey Heron-Purple Heron (Ardea cinerea-Ardea purpurea) make up positive, although weak, associations. Single-species groups of egrets seem to be the most stable association. The local overabundance of food resources in the paddy fields seems to be the main factor which allows the unstable association of species with some overlapping in foraging-niche (mainly concerning hunting strategy). The mean size of the single or mixed groups of Cattle Egrets and Little Egrets was of approximately 8 individuals for both species. We were not able to distinguish between nuclear and attendant species in mixed flocks of Little Egrets and Cattle Egrets.