Dominance behaviour of female vampire bats

Female vampire bats (Desmodus rotundus) are a model for the study of cooperation in behavioural ecology, but we know very little of their conflict. This gap in knowledge is surprising given that competition over resources, and thus conflict, is an expected consequence of group living (Clutton-Brock & Huchard, 2013). Further, it is important to understand how vampire bats compete and resolve conflict because there is evidence to suggest that patterns of conflict are associated with patterns of cooperation (e.g. Schino & Aureli, 2008). We aimed to address this gap by observing competitive interactions occurring over food within a captive colony of 33 vampire bats which included adult females and their young aged 5 months and younger. To understand whether there was a pattern to competitive interactions we looked for evidence of a dominance hierarchy. We found strong evidence for a weakly linear dominance hierarchy, tested using three standard metrics: directional consistency, Landua’s h’, and triangle transitivity. Randomised Elo-ratings showed that the hierarchy was not steep. We also found no evidence that rank was predicted by body size, sex, age, reproductive status, social group origin, or kinship. Taken together, these results strongly indicate that vampire bat social interactions are predominantly egalitarian. To put our results in a broader context, we compared dominance hierarchy metrics in female vampire bats to 172 published datasets from other taxa. Female vampire bat dominance was less linear and less steep than over 95% of other taxa. This indicates that female vampire bats are exceptional in their lack of a strict dominance hierarchy. Our results are consistent with the prediction that egalitarian or low-sloped hierarchies will occur in species characterised by symmetrical and reciprocal cooperative relationships which supports the biological market theory of cooperation