Foraging behaviour of an omnivorous bird varies in mixed-species groups

In mixed-species groups (MSGs), individuals from different species may locate and communicate about the presence of predators and prey quickly and accurately but may compete for food and favourable positions in the flock. Thus, foraging behaviour is likely to change when individuals participate in MSGs compared with single-species groups (SSGs). In a highly seasonal tropical environment, the foraging behaviour of omnivorous birds may also vary with fluctuations in food availability, weather, and breeding conditions. Here, we observed the foraging behaviour (food item consumed and foraging substrate) of an insectivorous-granivorous songbird, the Coal-crested finch (Charitospiza eucosma), in a savanna in central Brazil, while simultaneously sampling the grass seed production. Birds were more likely to consume grass seeds and forage on lower vertical strata (i.e., ground or herbaceous layers) in MSGs than in other social contexts (SSGs, pair or alone), suggesting they are facing interference competition from other species in MSGs or obtaining antipredator benefits in MSGs that enable them to explore preferred food resources in microhabitats more exposed to predators. As expected, Coal-crested finches were more likely to feed on grass seeds and forage on lower vertical strata when grass seed production is abundant, suggesting that they switch their diet according to the availability of their main food items: grass seeds and invertebrates. Weather and breeding seasonalities had small effects on foraging behaviour. Our results show that MSGs may have a major role in the foraging behaviour of omnivorous birds even considering the seasonal mismatching of their main food items. Highlights We studied the foraging behaviour of an insectivorous-granivorous songbird in a savanna in central Brazil. Coal-crested finches forage more on grass seeds and lower vertical strata in mixed-species groups than in single-species groups. Birds forage more on grass seeds and lower vertical strata during the circannual peak in grass seeds production. Foraging behaviour was weakly affected by weather and breeding seasonalities.