The outcome of two years of field experiments has been published today in Scientific Reports. Our previous work has shown that reed warblers are much less likely to reject an odd egg from their nest than they were in the past, and that this correlates well with the local risk of parasitism. But, how do they assess this risk?
The decision to remove an egg is not without its own risks - hosts may remove the wrong egg, or break their own by mistake. Close surveillance of their nests to attack a laying cuckoo is also risky because of the cuckoo's similarity to a hawk - attacking a 'cuckoo' could end up being a deadly mistake.
Here we show that reed warblers only reject an egg when they can combine information gathered from seeing a cuckoo at their nest, with that gained by observing their neighbours mobbing a cuckoo next door. In other words, neither social nor personal information is sufficient - instead a wide source of information is required.
See the press release here
(Image by Richard Nicoll www.richardnicollphotography.co.uk)