Our paper “When perfection isn’t enough: host egg signatures are an effective defence against high-fidelity African cuckoo mimicry” has been published in the journal Proceedings of the Royal Society B. This study was led by Jess Lund, and carried out with Tanmay Dixit, Mairenn Attwood, Silky Hamama, Collins Moya, Martin Stevens, Gabriel Jamie, and Claire Spottiswoode.

This study was inspired by the impressive mimicry of fork-tailed drongo eggs by the eggs of their specialist brood parasite, the African cuckoo. We first showed that, according to drongo vision, this mimicry was almost perfect at the population level. This is illustrated in the image: panel (a) shows naturally parasitised drongo clutches, each with an almost inseparable African cuckoo egg (the bottom right egg in each case). Panel (b) shows the range of drongo and cuckoo egg types – cuckoos mimic all drongo egg types, and do so with near-perfect accuracy.

Does this mean that cuckoos will fool drongos most of the time? Using field experiments and simulated parasitism events, we showed that the high degree of variability in drongos eggs – creating individually-distinctive ‘signatures’ – means that in fact drongos would successfully reject cuckoo eggs the vast majority of the time. In other words, egg signatures mean that even perfect mimicry is not good enough.

This study was also covered by several press outlets, including The Guardian (https://www.theguardian.com/science/2023/jul/26/spot-the-difference-why-drongos-are-likely-to-clock-african-cuckoo-eggs-94-of-the-time?) and the University of Cambridge (https://www.cam.ac.uk/stories/drongos-versus-cuckoos).

Open access link: https://doi.org/10.1098/rspb.2023.1125