Quirky and amazingly social: Researchers have gleaned new insights into the personal relationships between vampire bats. The meaning of the bond obviously goes beyond the mutual care in the colony: Friends animals leave the sleeping place separately, but they apparently find each other in their bloodthirsty hunting activities. The scientists suspect that the animals may speak to each other using special noises.
Their diet has inspired many a horror story: While other bat species hunt insects, the vampire bats (Desmodus rotundus) tap the blood of larger animals such as cattle. The bats, which are widespread in warm regions of America, land on their victims at night, scratch their skin with their sharp teeth and then lick the escaping blood. The bizarre fellows spend the day in colonies of up to several hundred animals, which are often in hollow trees.
In these roosts, the animals show an astonishingly complex social behavior, which scientists have been researching for some time. They have already been able to document that each animal has its own personal social network within the colony – the females in particular develop intensive relationships with certain individuals. Not only do they seek to be close to friends and clean each other in the neighborhood, they even feed unsuccessful social partners with blood that has been choked up.
How far does the friendship go?
So far, however, it has remained unclear whether the friendly behavior is limited to the contacts within the quarters or whether vampire friends also make common cause on their night outings. Simon Ripperger and Gerald Carter from Ohio State University in Columbus have now pursued this question using sophisticated technology at an experimental colony in Panama: They equipped some female bats, whose friendly relationships were known from previous observations, with proximity sensors. The mini-computers were so small and light that the bats could carry them like a kind of backpack. The devices then recorded the interactions between the test animals on their nocturnal excursions to the neighboring pasture.
The evaluations showed: The bats usually leave the roost individually – apparently they do not break out in social groups or together with partners to search for food. But as the evaluations of the proximity sensors showed, the befriended females often came together again far from their sleeping place. This was not the case with animals of the colony that were not socially connected. “We show that the social bonds of vampire bats are not limited to personal hygiene and sharing food in the roost, but that connected individuals even hunt together, which illustrates the complexity of their social relationships,” the researchers say.
Coordination is emerging
As they explain, the data suggest that the befriended individuals meet at their animal victims and go about their bloody goings there together. This could indicate that they are making targeted contact with each other. “Somehow they come together in the cattle pasture – we think they coordinate,” says Carter. They may also exchange information about victims or access to a wound that has already been opened. This collaboration could reduce the time and effort involved in the animals’ bloody diet, the researchers speculate.
Video and audio recordings of vampire bats while they are eating support the thesis that sound communication plays a role at the meetings, the researchers report: During the investigations, Ripperger noticed a certain type of vocalization that is apparently related to foraging. “I could see that the bats called when they were alone on a cow,” says Ripperger. So far, however, there are still questions unanswered. Perhaps the researchers can now gain more precise insights into the communication of the mysterious beings of the night through further investigations.
Source: Ohio State University, Article: PLoS Biology, doi: 10.1371 / journal.pbio.3001366