Cuckoos repeatedly lay eggs in the same host nest in order to increase the likelihood of their brood being accepted by host parents reports research published in Nature Communications. The work suggests that this method disrupts the cognitive processes used by foster parents to identify their own eggs and reduces the risk of the cuckoo’s eggs being rejected.
Many species of cuckoo lay their eggs in the nests of others and have developed strategies, such as mimicking the appearance of host eggs, so as to evade rejection. In response, host birds have established methods for distinguishing their own eggs from the cuckoos. As well as using prior knowledge of their own eggs, they appear to scan for differences in colour, pattern, and size and then discard eggs that don’t fit their internal template. By studying a cuckoo finch native to sub-Saharan Africa and their hosts, the tawny-flanked prinia, Martin Stevens and colleagues show that an increased number of cuckoo eggs laid in any nest leads to disruption of these discriminatory processes in host birds and a greater acceptance of parasitic eggs. The team demonstrate that higher numbers of parasitic eggs laid leads to the host requiring larger differences in colour in order to correctly identify their own brood and reject the cuckoo eggs.