Summer diet preferences of a declining steppe bird as revealed by DNA metabarcoding

Abstract Agricultural intensification is one of the main threats to steppe bird populations, leading to habitat degradation and the reduction of food resources. The Little Bustard ( Tetrax tetrax ), a highly endangered bird species in Europe, is particularly vulnerable to the loss of seminatural habitats containing such resources. Understanding its diet composition is crucial for the development of effective conservation strategies. Here, we describe Little Bustard diet composition and preferences during summer, which includes the chick rearing period, using DNA metabarcoding of faeces. Diet quality at this stage is critical for the adults to face reproduction costs (e.g. male display or parental investment by females) and for juveniles to ensure their survival and recruitment. Additionally, we identified arthropod taxa selected or avoided by Little Bustards by comparing the sequencing results with the estimated availability of these taxa in the study area (obtained from pitfall traps and sweep netting). Our findings suggest that arthropods are more relevant than plants in Little Bustard diet in this period and inform about the relevance of wild vs cultivated species in their diet. Among arthropods, the most commonly detected orders were Orthoptera, Coleoptera, and Lepidoptera, while the most consumed plant families were Asteraceae, Fabaceae and Brassicaceae. The analyses of arthropod preferences showed that Little Bustards select Orthoptera, Lepidoptera, Hemiptera, and Dermaptera among insects and avoid Hymenoptera and Aranea. Our results reinforce the importance of natural vegetation patches as feeding habitats, but also of cultivated habitats like rain-fed alfalfa, if managed to resemble natural grasslands, where Little Bustards can find the arthropods needed.