INFORMED BIRDS

We know that there is variation across time and space in the ways that hosts defend themselves from parasitism.  We also now know that this is usually because of behavioural plasticity, rather than rapid genetic changes among populations. There are costs to removing cuckoo eggs, or mobbing adult cuckoos; so how do hosts best match their defences to risk?

Our work with reed warblers and Common cuckoos in the UK showed that hosts use both personal and social information to fine-tune their behaviour (see here and here), and the way they use social information has consequences for cuckoos.  As reed warblers pay attention to the specifics of the information provided when neighbours mob cuckoos, rare colour forms have an advantage (see here).

But what happens when hosts and cuckoos become allopatric? Geographic mosaic theory of coevolution predicts that there will be hot and cold spots of selection - and the rate at which defences can be attained, upregulated, or lost will determine how coevolution proceeds. We are now focussing on the range expansion of reed warblers into Finland to investigate whether social information use and plasticity in defences changes as hosts escape, and what might happen should cuckoos reinvade.

How about cuckoos? Females specialise on different host species, producing extraordinary diversity in mimetic egg colours. But how do cuckoos tune their offspring to match the host’s chick-rearing environment? This is being studied in a nest-box using population of redstarts in Oulu, northern Finland by PhD student Teresa Abaurrea.