Breeding ecology of the horned grebe, Podiceps auritus, in southwestern Manitoba.

Abstract

Nesting horned grebes selected permanent, open ponds with peripheral stands of emergent vegetation. This reflected their dependence on open water feeding areas and emergent nesting cover, and possibly alleviated competition with pied-billed grebes Podilymbus podiceps. Annual variation in initiation of 1st clutches was related to spring weather conditions. Clutch size varied from 3-8 eggs and decined significantly as the nesting season progressed. Nest losses were high, with predators accounting for at least 54% of the total egg loss. Following nesting failure, pairs made up to 3 renesting attempts. Asynchronous hatching resulted in considerable age and size differences between 1st and last hatched chicks of a brood. Brood division, parental aggression and selective feeding of smaller chicks appeared to be adaptations for reducing the competitive disparities among chicks that resulted from asynchronous hatching.-from Authors