If, at dawn, you are tired of hearing incessant squawks under the windows, tell yourself that you are probably attending … a referendum! Researchers have discovered that ravens, the raven, seek consensus before flying in large numbers from the treetops where they usually spend the night. To reach this conclusion, Alex Debne of the University of Exeter, UK, and his colleagues recorded and photographed six groups of birds nesting in Cornwall, across the English Channel. About 130 hours of audio and 55 hours of video allowed them to examine the collective decision-making process by communities of over 1,400 birds!
The article, published in Current Biology on Monday, explains that crows leave their nocturnal homes less than an hour before or shortly after sunrise. In nearly two-thirds of the cases studied (21 out of 33 AM), the majority or all individuals flew within five seconds. Other times the corvids took off in small groups, about twenty minutes passing, at most, between the first and last convoy. Two opposing events owe nothing to chance.
Maintaining group cohesion…
The researchers found that most often, the jaws sharpened during the hour before the departure of the main group of crows. Once a certain threshold was crossed, the crows left en masse, forming a swarm in the sky. Conversely, on days when this noise level was not reached, take-off occurred in drops and falls, as if the birds had not come to a consensus.
To confirm the link between vocalization and group declension, scientists have used tricks. In some cases, they broadcast the sounds of crow cries among the trees themselves! And in doing so, they had caused a hasty departure. On the other hand, when they released the sound of the wind recordings, the take-off occurred at the expected time. So it was not the general rise in volume that determined the crows, but the call of the majority of their peers.
“For birds scattered in the trees, it is difficult to see other members of the group, especially because it can be so many and it is dark early in the morning. Acoustic cues are a useful way to convey information in these conditions,” said study co-author Alex Thornton. This “democracy” bait? to maintain group cohesion, answers the study: in order to reduce the risk of predation, to enhance foraging and to ensure “better access” to potential partners.
…. and overcoming differences
Interested in ravens for ten years, a team from the University of Exeter naturally pushed their study of these birds even further. “In principle, similar decision-making processes may occur in other bird species. It would be interesting to know! Until now, research on the role of vocal cues in collective decisions of animals has focused only on bees and small groups of vertebrates, which include less than fifty Individuals, like meerkats, have also been known to communicate in very complex ways, but using pheromones instead.
“Bees and ants live in family groups where the interests of the members of the group all align because they are all relatives and thus share genes. In contrast, groups of crows consist of a wide variety of individuals, from many different family groups. This means that individual preferences for timing of leaving the roost are likely to They vary widely and there is a high potential for conflict of interest,” says Alex Thornton. Individuals will have different levels of hunger, which in turn will influence when they want to leave to fetch food. We were particularly interested in understanding how animals can overcome their differences and reach consensus in such circumstances. »
The team’s next work should focus on the consequences of human activities (such as light and noise pollution) on the animals’ ability to make collective decisions. The stars of these studies: always corvids, which, in recent decades, have been shown by several studies, but also other types of birds such as greenfinch, red-winged or even starling.