Nav: Home

Friends help female vampire bats cope with loss

May 23, 2017

Female vampire bats form strong social bonds with their mothers and daughters as they groom and share regurgitated meals of blood. They also form friendships with less closely related bats. Gerry Carter, post-doctoral fellow at the Smithsonian Tropical Research Institute (STRI), and colleagues discovered that unrelated friends are important backup support when family members go missing.

When they remove a major food donor, like a mother or daughter, from a bat's social network, females who previously built up more friendships with non-relatives cope better with their loss. They score more food than do female bats who only invest in close kin.

"Is it better to have a few strong social bonds or a greater number of weaker social ties?" asks Carter. "Theory suggests you should always invest in the cooperative partner that provides the best returns. But clearly, a social animal should not put all its social time and energy in just one relationship, especially in an unpredictable social environment. That's like putting all your eggs in one basket."

"Females don't begin reproducing until they are two years old," said co-author Gerald Wilkinson professor of biology at the University of Maryland. "They only have one pup per year, so the number of closely related females tends to be low."

"Vampire bats who feed more non-relatives don't usually do better at getting fed when they are hungry," Carter said. "So why cultivate non-kin "friends"? We discovered that on the rare occasion that they lose a major food donor, they do much better. Their social network of food donors is wider and more robust." 

Vampire bats live on the edge. If they do not get enough to eat, it does not take long before they die of starvation. Their close relatives and friends often step in, sharing blood meals. Strengthening relationships by feeding a possible donor is one way to increase the chances of being fed. Having a larger number of potential donors is another. Carter calls the balance between these two strategies "social bet hedging".

To understand how social bet hedging works for vampire bats, Carter's team monitored social interactions in a captive colony of about 30 marked common vampire bats (Desmodus rotundus) for four years. They worked out how the bats were related based on their genes. Carter removed individual females from the group for a 24-hour fasting period. Just before returning them to the group, he removed one of the bat's key food donors, usually its mother or daughter. Then he looked at how each bat coped with this change to its social network.

Common vampire bats are native to the American tropics and sub-tropics, where they often feed on cattle, especially where forests have been replaced by pastureland. "It's not uncommon that a bat goes out to forage and fails to get food, and it's not uncommon that her closest relative will have switched to a different roost that night," Carter said. "We're recreating a situation that vampire bats might face fairly often."

Social bet hedging might exist in other species, including our own. Other studies have shown that baboons that lose a close relative to a predator will begin grooming more individuals in their group. There is also evidence that humans are happier with quality over quantity, yet people living in unpredictable social environments tend to value more friendships over a few stronger ones. "It would be particularly interesting to test the extent to which human collaborative or friendship networks are shaped by decisions to invest in relationship quantity or quality," the authors conclude. "The social bet-hedging hypothesis provides a new dimension to why animals form and maintain social groups" said Damien Farine, a former post-doctoral fellow at STRI who is now principal investigator at the Max Planck Institute for Ornithology and University of Konstanz in Germany, and co-author of the study.
-end-
Funding for this study was from the Ford Foundation and a grant from the U.S. National Science Foundation, the American Society of Mammalogists, and the Animal Behavior Society.

The Smithsonian Tropical Research Institute, headquartered in Panama City, Panama, is a part of the Smithsonian Institution. The Institute furthers the understanding of tropical nature and its importance to human welfare, trains students to conduct research in the tropics and promotes conservation by increasing public awareness of the beauty and importance of tropical ecosystems. STRI website: http://www.stri.si.edu.

Carter, Gerald G, Damien R. Farine, Gerald S. Wilkinson. 2017. Social bet-hedging in vampire bats. Biology Letters.

Smithsonian Tropical Research Institute

Related Bats Articles:

Bats are the major reservoir of coronaviruses worldwide
Results of a five-year study in 20 countries on three continents have found that bats harbor a large diversity of coronaviruses (CoV), the family of viruses that cause severe acute respiratory syndrome coronavirus (SARS) and Middle East respiratory syndrome coronavirus (MERS).
Friends help female vampire bats cope with loss
When a female vampire bat loses a close relative, she may starve, because she depends on her mother and daughters to share blood by regurgitation.
Some bats develop resistance to devastating fungal disease
Bat populations in some places in North America appear to have developed resistance to the deadly fungal disease known as white-nose syndrome.
The tale of the bats, dark matter and a plastic surgeon
What happens when a plastic surgeon meets a bat expert zoologist and a paleobiologist?
Roads 'a serious threat' to rare bats
Roads present a serious threat to bat populations, indicating that protection policies are failing.
Study documents African monkeys eating bats
Primates and bats may interact directly, but their behavioral and predator-prey interactions are poorly documented, and detailed reports of their interactions have been rare, until now.
Skull specializations allow bats to feast on their fellow vertebrates
Over their 52-million-year history, a few bats have evolved a taste for their fellow vertebrates.
Bats' flight technique could lead to better drones
Long-eared bats are assisted in flight by their ears and body, according to a study by researchers at Lund University in Sweden.
What bats reveal about how humans focus attention
Researchers discover how a bat's brain determines what sounds are worth paying attention to.
How bats recognize their own 'bat signals'
A new Tel Aviv University study identifies the mechanism that allows individual bats to avoid noise overlap by increasing the volume, duration and repetition rate of their signals.

Related Bats Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Anthropomorphic
Do animals grieve? Do they have language or consciousness? For a long time, scientists resisted the urge to look for human qualities in animals. This hour, TED speakers explore how that is changing. Guests include biological anthropologist Barbara King, dolphin researcher Denise Herzing, primatologist Frans de Waal, and ecologist Carl Safina.
Now Playing: Science for the People

#532 A Class Conversation
This week we take a look at the sociology of class. What factors create and impact class? How do we try and study it? How does class play out differently in different countries like the US and the UK? How does it impact the political system? We talk with Daniel Laurison, Assistant Professor of Sociology at Swarthmore College and coauthor of the book "The Class Ceiling: Why it Pays to be Privileged", about class and its impacts on people and our systems.