Seasonal changes in invertebrate diet of breeding black-necked cranes (Grus nigricollis).

Abstract

Invertebrates greatly support the growth, development, and reproduction of insectivorous birds. However, the influence of human activity (e.g., pesticide use, deforestation, and urbanization) inevitably leads to a decrease in global arthropods. The diversity and variation in invertebrate diet influence the food composition of birds, especially species living in rapidly changing environments, such as the Tibetan Plateau. However, little is known of the seasonal variation in invertebrate diet in response to environmental changes. Here, we characterized the invertebrate diet composition in pre- and post-breeding black-necked crane (Grus nigricollis) using fecal metabarcoding. We identified 38 invertebrate genera; the top three were Tipula (82.1% of relative abundance), Ceramica (3.0%), and unclassified_Hymenoptera (2.5%), with Tipula predominated the diet in both seasons. We also observed 20 and 16 unique genera in the pre- and post-breeding periods, and the genera composition was distinct between seasons (R = .036, p = .024). In pre-breeding, black-necked cranes tended to consume more diverse foods, and individual cranes exhibited greater heterogeneity at the genus level. At the genera and species level, pre-breeding black-necked cranes showed a wider dietary niche than post-breeding cranes. We observed season-specific features, with Tipula (common crane fly) and Stethophyma (grasshoppers) being enriched in the post-breeding period and Ceramica (moth) being more abundant in the pre-breeding period. Three Tipula species had the greatest importance in discriminating between seasonal diets. This study demonstrated a seasonal pattern of invertebrate diet in the black-necked crane, suggesting diet composition in response to resource and species availability. These results elaborate on the foraging ecology of highland birds and can inform the management of black-necked crane conservation.