Some years ago when working in Cambridge as a research assistant studying a population of wild jackdaws, me and my colleague Alex Thornton got fascinated by the huge flocks of jackdaws and their massive roosts during the winter months. Every night, we observed hundreds to thousands of birds coming to roost and again leaving collectively in the early morning. What struck us even more was that the mass departures often happened almost instantaneously, in a matter of seconds. How did the birds manage to make such a collective, coordinated decision and under such low light conditions?
In a new paper published in Current Biology, we show that it is the birds calling that primes them to leave. Using audio recorders we found that, the louder and the more the birds call, and the more their intensity increases, the quicker the birds leave the roost. Using playback experiments 🔊 we were able to confirm it is really the calling that drives the mass departures, with birds leaving the roost considerably earlier when jackdaw calls were played, while control playbacks did not have any effect.
Our study suggests that, through their calls, jackdaws appear to effectively signal their willingness to leave. This provides large groups with a means to achieve a consensus to perform cohesive, collective decisions, such as when to leave from the roost. This may be important as by staying in large flocks the birds may reduce their risk of predation and have various foraging benefits, which is critical during the short days and harsh conditions of the winter months 🌨.
The photo is of one of our study roosts, taken sometime after sunset, which shows the blurred shapes of jackdaws and rooks closely roosting together against the purple sky.
#sciencepaper #flocking #birdbehaviour #fieldwork #ecology #animalbehaviour #corvids
6 months ago