About 1% of bird species parasitise the nests of other species, tricking their unwitting hosts into raising their chicks, generally at the expense of the host’s own clutch. Working with Claire Spottiswoode and Martin Stevens we investigated the visual cues tawny flanked prinia Prinia subflava use when deciding whether to eject parasitic eggs. Each female prinia lays a unique type of egg, hugely varied in colour and pattern from other females. This makes it difficult for the cuckoo finch Anomalospiza imberbis – their natural brood parasite – to match the exact colour of any given prinia female.
We used a series of egg swapping experiments to determine whether the prinia reject the “odd one out” (which wouldn’t work if their own eggs are outnumbered by the parasite’s), or a template matching method, whereby they reject anything that doesn’t match their internal/memorised egg model.