Sneaky Cuckoo Finch Hoodwinks Other Birds by Laying Multiple Eggs in their Nests

Researchers have learned that African cuckoo finches -- quirky parasite birds that lay their eggs in the nests of other birds -- have a better chance of hoodwinking the host bird by surreptitiously laying more than one egg in the nest.

Bird experts from University of Exeter and University of Cambridge discovered that when the African cuckoo finch lays more than one egg in the nest of an African tawny-flanked prinia, the host birds find it more difficult to differentiate the impostor's eggs from their own.

This added level of secrecy further ensured that the host bird will not reject the cuckoo finch chicks upon their hatching, and essentially secures the foster chicks a free ride at the host bird's expense.

The researchers say this finding helps explain why the African cuckoo finch commonly lays more than one egg in the host's nest. What's more, the cuckoo finches' eggs, which are shades of blue and ocher, beautifully imitate the color palate of the host bird's eggs. Ornithologists contend that the mimicry has evolved over time to combat picky foster parents rejecting or removing foreign eggs in their nest.

"Egg rejection depends on hosts accurately discriminating parasitic eggs from their own," the University of Exeter researchers said in a statement. "To do so they must first carry out the sensory task of detecting small differences in egg colors and patterns between their eggs and the parasite's. They must then also correctly identify which eggs are parasitic, to ensure that they don't mistakenly reject any of their own eggs. This is a cognitive task relying on an ability to process the sensory information and compare it to a memorized template of what their own eggs look like."

The presence of multiple imitation eggs causes a conflict of sensory and cognitive mechanisms that leads the host birds to become uncertain about which eggs are truly their own.

"Our work shows that by laying multiple eggs in each host nest, the cuckoo finch has evolved a novel strategy, in addition to egg mimicry, to defeat host defenses and increase its reproductive success. Laying several eggs in a host nest causes confusion in host defenses, and when combined with effective mimicry, they can outwit the hosts and help more of their young to be reared," said University of Exeter's Martin Stevens.

"In the future it would be great to know whether other brood parasites have similar strategies, and whether there is any way that hosts can fight back in the arms race against the cuckoo finch," Stevens said.

Stevens and his colleagues' work is published in the journal Nature Communications.