The nightjar and the ant: a tale of a lose-lose game

Birds and ants co-occur in most terrestrial ecosystems and engage in a range of interactions. Competition, mutualism and predation are prominent examples of these interactions, but there are possibly many others that remain to be identified and characterized. This study provides quantitative estimates of the frequency of toe amputations resulting from ant bites in a population of migratory red-necked nightjars (Caprimulgus ruficollis) monitored for 15 years (2009-2023) in S Spain and identifies the attacker(s) based on taxonomic analyses of ant-mandible remains found on injured toes. Less than 1% of examined adults (N = 369) missed one or more toes. The analysis of ant remains identified African army ants (Dorylus sp.) as the primary cause of toe amputations in nightjars and revealed that body parts of the attacker may remain attached to the birds even after intercontinental migration. No cases of severe damage were observed in juveniles (N = 269), apart from the mandible of a Messor barbarus –a local ant species– attached to one of the teeth of the characteristic comb of the medial toe of nightjars. The incidence of ant-bite damage may appear unimportant for nightjar populations, but this might not be true if only birds that manage to survive their injuries and potential complications (e.g. severe bleeding and sepsis from opportunistic infections) return from the tropics. More field studies, ideally in tropical areas, that incorporate routine examination of ant-induced injuries into their protocols are needed to understand the true incidence and eco-evolutionary implications of antagonistic ant-bird interactions.