Population increase and nest-site selection of Cattle Egrets Bubulcus ibis at a new colony in drylands of north-east Algeria

Abstract

Colony occupation by Cattle Egrets Bubulcus ibis at an arid location in north-east Algeria lasted from mid-March or April to August. The colony, which was founded in 2003, increased from 124 pairs in 2007 to 250 pairs in 2011 and the density of nests from 0.36 to 0.73 nests m⁻² in the same period. The number of trees used for nesting increased from 16 trees in 2007 to 40 in 2011. The average height of nesting trees ranged from 12.8 士 3.0 m in 2007 to 13.6 土 2.9 m in 2011, whereas the average height of nests varied between 11.5 土 2.5 m and 13.2 土 2.9 m. Cattle Egrets built their nests mainly on strong primary branches of trees (30%) or secondary branches at the periphery of the tree's crown (29%). Numbers of nests sited in a tree were significantly influenced by the species of tree and the diameters of its trunk and crown, as well as by the horizontal and vertical positions of nests within the tree.