Animals tend to be healthier in smaller groups, where there’s less risk of disease and aggro, but that doesn’t appear to be the case with crows.
A new study from Anglia Ruskin University, UK, suggests crows living in large social groups are healthier than those that have fewer social interactions.
Claudia Wascher and colleagues spent six years studying a captive population of 36 carrion crows (Corvus corone) in northern Spain, monitoring their behaviour when in different sized groups and measuring friendship by ranking them using a sociality index.
At the same time, they studied the birds’ droppings to measure for the presence of coccidian oocyst, a gastrointestinal parasite that can represent an important health threat.
Increased exposure to parasites and disease transmission is considered one of the major disadvantages of group living. However, Wascher’s team found that crows with strong social bonds, living with more relatives and in larger groups, excreted a significantly smaller proportion of droppings containing parasites than less sociable crows.
No connection was found between health and a crow’s dominance within the group, but male crows (33%) were slightly more likely to carry the parasite than females (28%).
“It is a commonly-held belief that animals in larger groups are less healthy, as illness spreads from individual to individual more easily,” says Wascher.
“We also know from previous studies that aggressive social interactions can be stressful for birds and that over time chronic activation of the physiological stress response can dampen the immune system, which can make individuals more susceptible to parasites.
“Therefore, the results from our six-year study, showing a correlation between sociability and health, are significant. It could be that having close social bonds reduces stress levels in crows, which in turn makes them less susceptible to parasites.”
Of course, it could be that healthier crows are just more sociable, but Wascher says the nature of their study group suggests otherwise
“[A]s many of the birds we studied were socialising within captive family groups, dictated by the number of crows within that family, we believe that social bonds in general affect the health of crows, and not vice versa,” she says.
The findings are published in the journal Animal Behaviour.
Nick Carne is the editor of Cosmos Online and editorial manager for The Royal Institution of Australia.
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