(CN) — The call of the jackdaws in the early hours of the morning is “democracy” at work.
A study published in Current Biology focuses on six roosts of these small black crows in and around the county of Cornwall in southern England. Study authors Alex Thorton, Alex Dibnah and their colleagues observed the roosts’ daily activities, studying hundreds of jackdaws in the process. Previous studies on this subject focused on smaller groups or family members, which brought a set of challenges.
“Working with wild animal populations is always a challenge,” Thornton said in an email. “Alex Dibnah, who led the study, had to overcome many challenges. Aside from the often challenging weather conditions of winter fieldwork, one particular obstacle is that Cornwall, where we conducted the work was historically a tin and copper mining area and there are lots of old, disused mineshafts around. The mineshafts are often overgrown with vegetation, so Alex had to be extra careful to avoid falling into them when working”.
The authors studied jackdaws of different ages, sexes, family groups, and colonies spread across the treetops. They recorded hundreds of hours of audio and video of the roosts and quantified the intensity of the birds’ calls soon before and right after they took flight.
They found the intensity of the jackdaws’ calls reached a peak in the hour before the biggest group departure. The authors suggest that during this time, the birds communicated with each other about best time to leave.
“The decisions are “democratic” in the sense that group members signal their preferences (by calling) and a consensus is reached based on the combined preferences of the group,” Thornton said.
When asked if the roosts had a hierarchy for decision-making, Thornton said, “In the recordings it is not possible to pick out the calls of individuals when hundreds or thousands of birds are calling together, so at the moment we do not know if each bird has an equal say (is it “one bird, one vote"?) or if there is any kind of hierarchy. This would be very interesting to try to understand in future work.”
During their observations, the study authors saw departure delays when it rained or there was heavy cloud cover, indicating that the birds called out to each other to wait for ideal flying weather.
On some mornings, the birds left in small groups in intervals of about 20 minutes. Most of the time, hundreds of birds took off within four seconds of each other.
To test this, the researchers played the sounds of other jackdaws calling to them to see if they would take off earlier than normal. It worked: on average, the birds took flight 6.5 minutes earlier.
The researchers believe the jackdaws developed this system to deter predators. With this “democratic” communication, the birds can signal their willingness to leave, information about weather patterns and achieve a consensus before they depart.
Notably, the study reported, sometimes the intensity of the calling did not sufficiently build up. When this happened, the birds couldn't reach a consensus on when to leave and departed in smaller groups as a result.
The researchers hope to use future studies to understand how human may impact future roosts.
“As human impacts on wildlife grow, we are very interested in understanding to understand whether and how human disturbance — for instance, from light and noise pollution — may affect animal groups’ abilities to communicate and reach consensus decisions,” Thornton said in a statement accompanying the study.