A
new study has found that crows living in large social groups are healthier than
crows that have fewer social interactions.
The
research, led by Dr Claudia Wascher of Anglia Ruskin University (ARU), has been
published this week in the journal Animal Behaviour. Dr Wascher and her
colleagues studied a population of captive carrion crows over a six-year
period. They monitored the behaviour of the crows in different sized groups and
measured friendship by ranking the birds using a sociality index.
At
the same time, they studied the crows' droppings to measure for the presence of
coccidian oocyst, a gastrointestinal parasite that can represent an important
health threat for birds.
Increased
exposure to parasites and disease transmission is considered as one of the
major disadvantages of group living. This new study, however, shows the
opposite effect.
The researchers
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.
The
study did not find a connection between health and the crow's dominance within
the group, but found that male crows (33%) were slightly more likely to carry
the parasite than females (28%).
Dr
Wascher, Senior Lecturer in Biology at Anglia Ruskin University (ARU), said:
"Crows are a highly social bird and we found that crows with the strongest
social bonds excreted fewer samples containing coccidian oocyst, which is a
common parasite in birds.
"It
is a commonly-held belief that animals in larger groups are less healthy, as
illness spreads from individual to individual more easily. 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.
"It
could also be that healthier crows are more sociable. However, as 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."
See:
Posted by Dr. Tim Sandle, Pharmaceutical Microbiology Resources (http://www.pharmamicroresources.com/)
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