dDNA metabarcoding reveals dietary niche partitioning between sympatric Iberian sandgrouse and bustards

The study of dietary niche partitioning is of great importance for understanding community structure and species coexistence, particularly if these are threatened. Here we used DNA metabarcoding from faeces to assess the diet of four threatened steppe birds (two bustards and two sandgrouse), with the aim of better understanding their dietary requirements, trophic interactions and potential threats. We found seasonal and interspecific differences in their plant diet, with greater importance of cultivated plants during autumn and winter (around 50% of their diet) than spring. Despite differences, plants of the genus Convolvulus and of the family Brassicaceae were frequently consumed by all species. In spring, poppies were a considerable part of their diet, and could be used as a source of carotenoids or for their anti-parasitic properties. Furthermore, the results also showed a dietary niche partitioning between species, with a marked segregation between bustards and, to a lesser extent, between sandgrouse. Diet similarity was generally higher between species from different orders that occur in mixed-species flocks (bustard - sandgrouse) than between species from the same order. This partitioning was probably related to a stratification in habitat use rather than to specialization and might prevent competition to some extent. However, the homogenization of trophic resources resulting from agricultural intensification could pose an important threat, particularly during autumn, when weeds are scarcer and the most abundant trophic resource are sown seeds, which are often treated with pesticides.