Breeding ecology of the Horned Grebe, Podiceps auritus, in southwestern Manitoba

Abstract

Nesting Horned Grebes, Podiceps auritus, studied in 1974 and1975 in pothole marsh habitats near Minnedosa, Maniteba, 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 first clutches was related to spring weather conditions.Clutch size varied from 3 to 8 eggs and declined 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 three renesting attempts.Asynchronous hatching resulted in considerable age and size differences between first 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.The reproductive biology of Horned Grebes in southwestern Manitoba suggests ecological parallels with grebes of the genera Rollandia and Tachybaptus which are also adapted to nesting in unstable marsh habitats.