Information, predation risk and foraging decisions during mobbing in great tits Parus major

Tomaximise survival during foraging animalsmust decide when and for how long foraging should be interrupted in order to avoid predators. Previous experiments have shown that birds that hear other individuals’alarm calls resume feeding later than those that see a flying predator.However, the responses of prey animals to enemies are highly context-dependent. We therefore investigated how birds respond to a threat less serious than a flying hawk depending on different amount of information about the predator. We used Great Tits dyadswhere one individual saw a perchedmodel predator (sender), whereas the other individual could only hear the conspecific’s mobbing calls (receiver). The sender responded appropriately as shown by comparing their responses to how they responded to a control.We also found that while senders were exposed to the predator, receivers became more wary and reduced their activity level. However, despite the receivers having less information about predation risk they still did not prolong the time they took to resume foraging. Hence, once the mobbing ceased (and consequently the transmission of information about the predator stopped) therewas no effect of only having second-hand information. This also shows that receiver’s rely upon the sender’smobbing calls suggesting that mobbing calls may act as honest signals of the prevailing predation risk. In conclusion, our results support the view that responses of prey to predators are highly context-dependent and that birds’ anti-predator responses are a result of an interaction between the amount of information and the level of the threat.

Lind, F. Jongren, J. Nilsson, D. Schonberg Alm & A. Strandmark, Ornis Fennica 82:89-96. 2005