Seasonal and between-sex differences in the diet of Black Grouse Tetrao tetrix.

Abstract

Capsule Dietary differences between sexes and seasons reflected diversity in plant availability and habitat preferences.
Aims To analyse Black Grouse diet through the identification of plant and invertebrate material found in the crop.
Methods Crops were dissected and the content categorized into plant species and components (i.e. leaf, stem, flower, fruit and seed). Multivariate analysis was used to test for seasonal, sex- or location-related differences in the diet.
Results Plant fragments accounted for 98% of the diet and included 53 plant species or taxa. Invertebrates made up the remaining 2%. Diet varied significantly between seasons and sexes. Both sexes ate more ericaceous shrubs in autumn and winter, with females eating more than males. The plant parts eaten varied seasonally. In summer, fruits, flowers and seeds were favoured over leaves, which dominated in winter.
Conclusions With few trees, birds were reliant upon Heather in autumn and winter.