For female vampire bats an equal chance to rule the roost – sciencedaily
Female vampire bats establish an egalitarian community within a perch rather than a society based on a clear hierarchy of dominance that is often seen in animal groups, suggests a new study.
Researchers observed more than 1,000 competitions for food among a colony of 33 adult and juvenile female bats living in captivity, assigning a rank to each bat based on a calculation of wins and losses in those contests. .
The team found that, unlike many mammalian societies, the higher-ranking animal didn’t necessarily win all food fights, and there was a random ranking order – no specific measured quality gave a bat a better chance of domination. , so that any adult female had an equal chance of ranking very high or very low on a dominance scale in the roost.
Traditionally, research on group-living animals – especially primates – in the wild has focused on how a dominance structure plays a role in survival, longevity, and healthy offspring, and later considered the importance of friendship in these same communities.
Lead author of the study, Gerald Carter, worked in reverse order. His research on highly social female vampire bats, whose behaviors resemble what has been observed in certain groups of primates, has focused on cooperation, finding that vampire bats make “friends” through a gradual build-up of trust and show signs of maintaining these friendships in nature.
“We realized that we didn’t know anything about the dominance among female vampire bats, so this is a first step in the direction of trying to identify how similar they are to primates in this way,” he said. said Carter, assistant professor of evolution, ecology and organism biology at Ohio State University. “We can say quite clearly that they are certainly not like some of the well-studied primates. They do not have a very clear social rank that they consistently apply.”
The study is published today (July 7, 2021) in the journal Royal Society Open Science.
The research team videotaped 1,023 competitive interactions for food over three months in a captive colony of common vampire bats at the Smithsonian Tropical Research Institute (STRI) in Panama. The colony consisted of 24 adult females captured at two remote sites as well as nine young bats – four males and five females.
Winners and losers were identified from five types of blood meal feeder events: displacement of a feeder bat by an intrusive bat with or without physical contact; maintaining a feeder bat in position following the approach of another bat, with or without contact; and a bat nearby waiting to eat until a feeding bat has left the feeder.
The researchers assigned a social rank to individual bats based on wins and losses and found great variability in the ranking of adult female bats, with virtually no predictor of how these community arrangements played out. . No association was found between body size, age and reproductive status and dominance rank, and common grooming and food-sharing behaviors of vampire bats were not associated with rank. social. Being linked to each other had no effect. The only possible predictor detected, when young males were excluded, was the smaller forearms in the more dominant adult females.
Compared to the data that exists on the female yellow baboon and female long-tailed macaque communities, vampire bats were also much less likely to show a consistent pattern of victories by the more dominant members of the community.
“Basically with these primates almost 100% of the time the dominant individual wins,” Carter said. “With vampire bats, even when you have two individuals within 10 rows of each other, the more dominant individual doesn’t necessarily replace the other.”
The results suggest that young males are subordinate to adult females, and the same is likely true of adult males as they are smaller than female vampire bats. Previous research has shown that male vampire bats compete and fight – and within a colony, males tend to focus on establishing territory rather than social relationships.
A comparison of group-level dominance measures between female vampire bats and 14 other documented female mammal groups – including African elephants, bison, and many primates – placed bats in 12th or more. 15th in the overall dominance ranking, depending on the metric used.
Although the study of animals in captivity alone does not provide all the answers, research suggests that vampire bats live in “more fluid and open communities,” Carter said. A fluid and open society is different, but not necessarily better, than a group characterized by domination and hierarchy, he noted. A clear power structure actually helps prevent conflict.
“In a group of animals that are always together, it’s really important to determine who is dominant, because when you encounter food, you all encounter that food together,” he said.
“With vampire bats, they have this society inside a tree, and all the relationships are established. But we think vampire bats don’t hunt as a stable group – they come out, get out. feed and return together. So what that means is that they don’t always encounter a food resource together and they have to decide who is going to have access to it first. “