DEMOCRACY IS LOUD & NOISY
'Democracy' governs mass jackdaw take-offs
IMAGE: JACKDAWS ROOSTING view more
CREDIT: ALEX THORNTON
Jackdaws use a "democratic" process to decide when to leave their roosts en masse, new research shows.
In winter, jackdaws roost in groups of hundreds or even thousands, and it is common for most or all of the birds to take flight in a sudden mass departure around sunrise.
In the new study, a team led by the University of Exeter recorded the rising racket of jackdaw calls that happens before mass departures at various roosts in Cornwall.
By combining this with tests in which pre-recorded jackdaw calls were played at a colony, the team found evidence that the birds' calls are used in a form of "consensus decision-making".
"After roosting in a large group at night, each jackdaw will have a slightly different preference about when they want to leave, based on factors like their size and hunger," said Alex Dibnah, who led the study as part of a Masters by Research at Exeter's Penryn Campus in Cornwall.
"However, it's useful to reach a consensus. Leaving the roost together has various benefits, including safety from predators and access to information such as where to find food.
"Our study shows that by calling out jackdaws effectively ‘cast a vote’ and, when calling reaches a sufficient level, a mass departure takes place."
The research team – which included the University of Cambridge and Barcelona's Centre for Ecological Research and Forestry Applications – also found:
- Mass departures happened almost instantly, with all departing birds in the air within less than five seconds on average.
- These departures took place in the period from 45 minutes before sunrise to 15 minutes afterwards. Rain and heavy cloud tended to delay departures.
- When the intensity of calling rose more steeply, birds departed earlier.
- Playing recordings of roosting calls brought forward the time of the first mass departure by an average of more than six minutes.
- Recordings of wind noise did not lead to earlier mass departures, suggesting that the birds respond specifically to calls of their fellow birds (not to noise in general).
Jackdaws did not always leave their roost in mass departures. If the level of calling did not rise sufficiently, roost members failed to reach a consensus and instead left in a stream of small groups.
Commenting on the wider significance of the research, Professor Alex Thornton – of Exeter's Centre for Ecology and Conservation – said: "It helps us to understand how really large groups of animals can coordinate their actions – something that has rarely been tested in detail before.
"Also, our findings provide further evidence that vocalisations are really fundamental in allowing some species to reach group decisions – so we need to investigate what happens when we as humans create noise pollution that might influence how information spreads through these social groups.
"The next stage of our research will look into this."
The research was funded by the Human Frontier Science Program.
The paper, published in the journal Current Biology, is entitled: "Vocally-mediated consensus decisions govern mass departures from jackdaw roosts."
JOURNAL
Current Biology
METHOD OF RESEARCH
Observational study
SUBJECT OF RESEARCH
Animals
ARTICLE TITLE
Vocally-mediated consensus decisions govern mass departures from jackdaw roosts
ARTICLE PUBLICATION DATE
23-May-2022
Noisy jackdaw birds reach “consensus” before taking off
Peer-Reviewed PublicationVIDEO: OVER A THOUSAND JACKDAWS PERFORMING A SUDDEN AND FAST MASS DEPARTURE THAT LASTS ONLY SECONDS, WITH BIRDS TRAVELLING IN ONE COHESIVE FLOCK IN THE SAME DIRECTION. view more
CREDIT: DIBNAH ET AL./CURRENT BIOLOGY
On cold, dark winter mornings, small black crows known as jackdaws can be heard calling loudly to one another from their winter roosting spots in the U.K. before taking off simultaneously right around sunrise. Now, researchers who’ve studied their daily activities in unprecedented detail report evidence that these groups of hundreds of individuals rely on a “democratic” decision-making process to coordinate with one another and take to the skies all at once. The findings are reported in the journal Current Biology on May 23.
“Like humans, large animal groups can use decision-making processes to overcome their individual differences and reach a kind of ‘democratic’ consensus,” says Alex Thornton (@CornishJackdaws) of the University of Exeter.
Previous studies had investigated consensus decision-making in animal groups that were relatively small or made up of family members, he explained. What struck them about the jackdaw roosts was their sheer size. Not only are their groups large, they also include individuals of different ages, sexes, family groups, and colonies all spread across the treetops.
It’s not likely that all those different individuals would just naturally prefer to take off at precisely the same moment. And, yet, sticking together has advantages, such as reducing the risk of predation and giving individuals information from their peers about where to find food. The researchers wanted to explore how the birds decide when it is time to go.
To look more closely, Thornton and colleagues, including first author Alex Dibnah (@alexdibnah01), recorded hours and hours of audio and video of six different jackdaw roosts in Cornwall, U.K. over the course of the winter months. The size of the roosts varied from 160 to almost 1,500 individuals. They quantified the intensity of the birds’ calls leading up to and right after they took off in flight.
The evidence shows that the timing of departure is tightly linked to calling intensity within the roost. While on some mornings, the birds left in a stream of small groups over about 20 minutes, most of the time they set out in mass departures, with hundreds of birds taking off within about 4 seconds of each other.
On most mornings, they found that calling intensity increased over the hour before the biggest group departure. It sometimes got delayed by rain or heavy cloud cover. They concluded that changes in calling intensity could serve as a reliable source of information, enabling the birds to synchronize their daily takeoffs.
To confirm cause and effect, the researchers played the sounds of conspecifics calling to them to see if they could get the birds to take off earlier than they otherwise would have. And they found that they could. By adding calls into the mix, the birds took flight an average of about 6.5 minutes earlier.
“Through their calls, jackdaws appear to effectively signal their willingness to leave, providing large groups with a means of achieving consensus to perform cohesive, collective departures from the roost,” the researchers write.
They say the observational data indicate that consensus is achieved as the intensity of calls build to a point that triggers them to act. The playback experiments help to show a causal link between calling intensity and takeoff. Together, they offer new insight into the ways that animals make decisions about mass movements in nature.
It is also notable that, on the few occasions when the intensity of calling did not build up sufficiently, the birds apparently failed to reach consensus. As a result, they took off in “dribs and drabs” instead of all at once.
In future studies, researchers hope to learn more about how human activities may affect these dynamics.
“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 says.
CAPTION
Jackdaws roosting in a tree
CREDIT
Jolle Jolles
This research was supported by the Swedish Research Council, the Human Frontier Science Program, the Whitten Lectureship in Marine Biology, the Royal Society Dorothy Hodgkin Research Fellowship, and a Severo Ochoa Postdoctoral grant through the Spanish Program for Centres of Excellence.
Current Biology, Dibnah et al. “Vocally mediated consensus decisions govern mass departures from jackdaw roosts” https://www.cell.com/current-biology/fulltext/S0960-9822(22)00601-7
Current Biology (@CurrentBiology), published by Cell Press, is a bimonthly journal that features papers across all areas of biology. Current Biology strives to foster communication across fields of biology, both by publishing important findings of general interest and through highly accessible front matter for non-specialists. Visit http://www.cell.com/current-biology. To receive Cell Press media alerts, contact press@cell.com.
J
CAPTION
Jackdaws roosting in a tree
CREDIT
Jolle JollesOURNAL
Current Biology
METHOD OF RESEARCH
Experimental study
SUBJECT OF RESEARCH
Animals
ARTICLE TITLE
Vocally mediated consensus decisions govern mass departures from jackdaw roosts
ARTICLE PUBLICATION DATE
23-May-2022
No comments:
Post a Comment