How information about predation in mixed-species bird flocks changes through the breeding cycle in a subtropical, limestone forest

Background/Question/Methods: Conservation strategies that incorporate species interactions have the potential to protect multiple species simultaneously. In many Mixed-species bird flocks, there are "nuclear" species that can produce calls that encode information about predation, so that "following" species in flock can eavesdrop and consequently adjust their anti-predator behavior. Yet how dependent are following species on information derived from nuclear species, and how do they adapt when it is missing? We setup 6 1-km transects in the Nonggang National Nature Reserve, Guangxi Province, southern China and monitored each transect 2-3 times each month from Jan. 2017 to Feb. 2018. Especially, we observed bird responses to two kinds of predator threats under the conditions with and without nuclear species: an imminent attack by a moving predator, as simulated by a thrown stick and the presence of a stationary predator, as simulated by Glaucidium brodiei model and playback (control experiments used the model and playback of the Streptopelia chinensis)

Results/Conclusions: Flock density decreased dramatically from 2.1 flocks/km (n=27) in non-breeding seasons (NBS) to 0.5 flocks/km (n=38) in breeding season (BS), and the individuals of the nuclear species in flocks also decreased from 4.8 per flock to 1.9 per flock. Consequently, the amounts of vocalization provoked by nuclear species in playback experiment and moving predator experiment decreased significantly from NBS to BS. However, follower species showed an opposite strategy. When tested in the flock, more following species responded to playback at BS (6.4/ trial, n=9) than NBS (2.5/ trial, n=28). Similarly, when tested outside of the flock, more species responded to playback at BS (4.5/ trial, n=90) than NBS (2.2/ trial, n=59). We found strong seasonal changes in both flocking (decrease in BS) and mobbing intensity (increase in BS). The flow of information among birds thus undergoes a profound transformation from a system in which information is made mostly by one nuclear species, to one in which many species must produce their own information.