Abstract
Individual animals across many different species occasionally ‘adopt’ unrelated, orphaned offspring. Although adoption may be best explained as a by-product of adaptive traits that enhance parental care or promote the development of parental skills, one factor that is possibly important for the likelihood of adoption is the history of cooperative interactions between the mother, adopted offspring and adopter. Using 652 h of behavioural samples collected over four months, we describe patterns of allogrooming and food sharing before and after an instance of non-kin adoption between two adult female common vampire bats (Desmodus rotundus) that were captured from distant sites (340 km apart) and introduced to one another in captivity. The first female died from an illness 19 days after giving birth. The second female groomed and regurgitated food to the mother more often than any other group member, then groomed, nursed and regurgitated food to the orphaned, female pup. The substantial increase in alloparental care by this female after the mother's death was not observed among the 20 other adult females that were present in the colony. Our findings corroborate previous reports of non-kin adoption in common vampire bats and are consistent with the hypothesis that non-kin adoption can be motivated, in part, by a history of cooperative interactions.
Highlights
Animals are most likely to care for others’ young in groups where members are related and helpers can gain indirect fitness benefits [1,2], as in most cooperative breeding societies [3,4]
Our observations suggest that adoption is influenced by the history of cooperative interactions between mother, offspring and adopter, more evidence is needed to test this hypothesis
The probability of non-kin adoption in vampire bats and whether it affects the fitness of adopters remains unclear, especially outside of captive conditions, but we can make two testable predictions
Summary
Animals are most likely to care for others’ young (i.e. alloparental care) in groups where members are related and helpers can gain indirect fitness benefits [1,2], as in most cooperative breeding societies [3,4]. Alloparental care towards either kin or non-kin could result in direct fitness benefits for the helper (e.g. group augmentation [5,6]). Individuals adopt kin, through which they might gain indirect fitness benefits [1,11]. Individuals adopt familiar nonkin (e.g. chimpanzees: [12]; cercopithecines: [13]; muriquis: [14]; phocid seals: [15]), or unfamiliar or seemingly unfamiliar non-kin (e.g. dolphins: [16]; Barbary macaques: [17]; Rhesus macaques: [18]). Whether or not adopting non-kin is adaptive remains unclear
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