In the early hours of the morning, large groups of hundreds or even thousands of birds perched on their communal perches overnight take off in sudden mass movements. These starts, perfectly timedoccurs in low-light conditions and in complex habitats where access to visual cues is often limited. How do birds coordinate in this way without seeing each other? Scientists have investigated western crows (corvus monedula) and got a big surprise: these birds also use a ‘democratic’ process to begin their flight. They do it “by consensus”According to a study published in ‘Current Biology’.
The researchers discovered that the crows began to squeak as the flight time approached. They do this until the noise is loud enough to show it.some consensus“In the group. I got to this once”acoustic arrangement‘, they fly in flocks.
“Like humans, large groups of animals use decision-making processes to overcome their individual differences and reach a kind of democratic compromise.”, explains Alex Thornton of the University of Exeter and co-author of the study.
The choice of jackdaw for the study was not accidental: it is a very noisy and sociable crow. wintering roosts consisting of thousands of individuals from different age classes and breeding colonies.
To understand the potential role of vocalizations in coordinating mass departures, the researchers collected acoustic and video data during the winter months from six tunnels in Cornwall, United Kingdom, and measured the vocalization intensity just before and just before the groups took off.
Instant mass outputs
Mass exits were always almost instantaneous, always in less than eight seconds, and in some cases even just one second. In addition, the birds always stayed together in harmonious flocks after they left, which means “a unanimous decision», the authors conclude.
However, takeoffs were sometimes delayed by rain or fog, leading the researchers to conclude: changes in the size of calls serve as a source of information and synchronization.
To test their hypothesis, the researchers played squeaks with loudspeakers to entice the crows to fly earlier than usual.
The experiment confirmed their suspicions: they were able to accelerate the start of the flight by an average of six and a half minutes. And on the few occasions when the collective squeaks weren’t loud enough, the birds took off in small groups rather than all at once.
No doubt: departure time has always been about calls inside the roost. Some jackdaws began to sing long before dawn, but only when almost all of the jackdaws squeaked did the flock begin to fly.
“Jackdaws seem to actively signal their willingness to leave through their calls.“to provide large groups a means of reaching consensus and making collective and cohesive exits from the roost”, the scientists emphasize.
This ‘democratic’ system has many advantages. “By agreeing on leaving the nest early and in large flocks, the birds It reduces the risk of predation, facilitates access to useful nutritional information and potential mates, and extends the time available for foraging on short days and harsh winter conditions.» collects the work.
Fear of human discomfort
The final results are clear: «Our observational data show that consensus is reached by the effect of call accumulation (excitation) up to the point where collective exits (activation) can be triggered. Our experiments are Strong evidence for a causal link between the timing of calls and mass departures. This work provides important insights into the mechanisms underpinning the mass movements of large groups of animals under natural conditions.”
The data collected in this study combines already existing data on ‘acoustic consensus’ in two other species, heathland (meerkat) and bees (Apis sp.), dances combine acoustic signals. Only in these two previous cases were small groups and their respective members studied, something that jackdaws do not.
The authors claim that their experiments provide: empirical evidence “for sound-mediated consensus decision making in large vertebrate groups”.
They believe that there are types such as rooks (corvus frugilegus), red-winged thrushes (Turdus iliacus), starling (Sturnus vulgaris) can behave just like jackdaws. And geese proved to be (Anser sp.) and swans (Cignus sp.) call each other before moving in together.
Scientists are concerned that human activities will also affect acoustic communication in nature. “As human impacts on wildlife increase, human disturbances such as light or noise pollution are likely to affect the ability of groups of animals to communicate and reach consensus decisions.Thornton finishes.
A very social and noisy breed
jackdaws detailed social behaviororganized for both breeding and foraging noisy groupsAs detailed in ‘The Birds of Spain Guide’ by Seo/BirdLife.
With black and ash plumage, these birds breed in a wide variety of places, from rocky cliffs to old buildings, cliffs and hollow trees.
Jackdaws unlike other crows obvious vegetarian habitshowever, during the rearing of chickens they catch a wide variety of invertebrates and some small vertebrates.
This plentiful in Spain and fairly homogeneously distributed throughout the Peninsula, where it is missing only a large part of the Cantabrian coast and the Pyrenees. Less so in Galicia, at some points in the Guadalquivir valley, and in parts of Catalonia and southern Meseta. Although it lives in Ceuta as stated in the Seo/BirdLife guide, it is absent in the Balearic Islands, Canary Islands and Melilla.
Populations of this species for the whole of Europe are estimated at between 5.3 and 29 million pairs; Between 420,000 and 530,000 live in Spain.
Some authors have documented a particular territorial expansion of the jackdaw over a century, particularly in Scandinavia and Siberia. in Spainby contrast, data from Seo/BirdLife’s bird watching program SACRE is a Slight reduction in troops between 1998 and 2005.
Reference report: https://www.cell.com/current-biology/fulltext/S0960-9822(22)00601-7
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