A team of biologists led by Claudia Wascher from Anglia Ruskin University, (Cambridge, UK) have found that the strength of social connections of black crows (Corvus Corone) depends on the health of their digestive system. Among the 36 birds living in captivity in flocks, couples and families, the least coccidian oocysts in the litter was found in those individuals who spent more time in each other’s company.
Communication with relatives in many respects determines the survival rate of social animals: uniting in groups, representatives of these species get their comrades-in-arms who help them get food, look after offspring and defend themselves from enemies. It is interesting that the loss of even one member of the formed group can significantly affect the survival of individuals: for example, occurs in killer whales.
Moreover, the benefits of social contacts within a group of animals are not always obvious. For example, birds from the Corvidae family are distinguished by a highly developed intellect, which, in essence, should help them to survive effectively alone; at the same time, they unite in groups and even form strong ties, preferring some relatives to others.
They suggested that social connections within a group of black crows may correlate with the spread of parasites. To do this, they studied a population of 36 birds living in captivity in a large open enclosure in conditions similar to natural.
As in the natural habitat, crows in the aviary were united either in flocks (from three young individuals), or in pairs (a female and a male of reproductive age), or in families (a pair of birds and their chicks). Researchers managed to conduct more than a thousand observations of bird communication lasting about five minutes each: on the basis of this, they separately considered the social proximity of individuals (how often they sit together and clean each other’s feathers), as well as cases of hostile behaviour.
In order to estimate the spread of parasites in crows, the scientists collected 760 samples of litter, which calculated the number of coccidian oocysts and nematode eggs. In total, coccidia was found in 235 samples of litter from 26 individuals, and nematodes – in 69 samples of 23 individuals.
Scientists found that the number of coccidia oocysts in the crows litter correlates with how strong friendships they form: in other words, the more time individuals spent with each other, showing affiliative behaviour, the lower the probability of finding coccidia in their litter (p <0.001 ) Moreover, the more individuals were in a close group, the less often parasites were found in their litter.
The spread of nematodes eggs in the litter, in turn, with the socialization of crows did not correlate: perhaps this is due to the fact that nematodes for the studied group of birds in principle not so frequent.
The formation of strong ties within the group, thus, brings the black crows significant advantages in health matters, and more specifically – protection against parasites. Of course, the nature of the connection found is not exactly clear, but the authors of the work suggest that strong social ties are the reason for the lesser spread of parasites, and not a consequence, since, in captivity, crows cannot control the size of their social group – one of the determining factors for the correlation found.