Does Beginning of Spring Represent a Critical Period in Annual Cycle of Capercaillie (Tetrao urogallus, Tetronidae, Galliformes)?

Abstract

In European Russia, the clutch size of capercaillie varies depending on the spring density of population and simultaneously on combination of different variants of vegetation that reflect influence of the various environmental factors. Late snow thawing, dense vegetation, scarcity of field layer foods or high density of birds seem to aggravate the competition for limited food resources and nesting sites. These factors permit to consider (1) the beginning of spring as one of the critical periods in annual cycle of Capercaillie determining realization of the potential fecundity of hens, and (2) mean clutch size as the relative monitoring index of saturation by birds of the natural carrying capacity.