Our paper “Categorical identity signatures can reduce host error rates during brood parasitism” has been published in the journal PLoS Biology. This paper was led by Tanmay Dixit, in collaboration with Cameron Blair, Jess Lund, Claire Spottiswoode, and several other collaborators. In this paper, we combined fieldwork in Choma on hosts of the cuckoo finch with simulations. We showed that hosts that lay categorical egg signatures (e.g. their eggs are either white or blue) are more successful at rejecting cuckoo finch eggs – and avoiding rejecting their own – than hosts laying a continuous range of signatures (e.g. not only whites and blues but also intermediate pale blues).

The paper explains how it is that these categorical signatures reduce the rates both of these errors – rejecting own eggs and accepting cuckoo finch eggs. For instance, a bird laying categorical signatures could accept eggs of the same category as hers (e.g. blue, with small speckles) but reject all eggs of different categories (e.g. white eggs with small speckles, or blue eggs with large blotches). If she does this, then she will effectively never reject her own eggs – they are always of the same category. However, depending on the number of categories, it might be very unlikely that a cuckoo finch egg is of the same category. Thus she may also be good at rejecting cuckoo finch eggs. This is true of zitting cisticolas parasitised by cuckoo finches in Zambia – the image shows the range of egg signatures that zitting cisticolas exhibit.

It has long been thought that hosts that are good at rejecting a brood parasite’s eggs will run a greater risk of rejecting their own too. Our paper shows that actually categorical variation allows hosts to successfully avoid rejecting their own eggs, even while being good at rejecting cuckoo finch eggs.

You can read the paper at https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3003667 (please contact us if you cannot access it).