How the Sneaky Cuckoo Finch Fools Parent Birds with Multiple Eggs

There's more than one way to fool a bird--and cuckoo finches are well aware of that fact. Known for laying their eggs in the nests of other birds, cuckoo finches rely on other species to raise their young. Now, scientists have discovered that cuckoo finches that lay more than one egg in their victims' nests have a better chance at tricking host parents into raising their young.

When adult cuckoo finches lay their eggs, they don't build their own nests. Instead, they find the nests of other birds. While the parents are away, a cuckoo finch will quickly lay her eggs and then fly away. These cuckoo finch eggs eventually hatch and are raised at the host's expense.

In order to learn a little bit more about this behavior, the researchers examined African cuckoo finches and their African tawny-flanked prinia hosts. They found that the cuckoo finches commonly laid more than one egg in the same host nest. In addition, the eggs themselves beautifully mimicked those of their hosts.

These techniques are apparently necessary. Picky parents will sometimes reject eggs and be able to distinguish parasitic eggs from their own. The result is the removal of the foreign eggs from the nest.

"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," said Martin Stevens, one of the researchers, in a news release. "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."

Egg rejection depends on multiple factors. The host has to accurately discriminate parasitic eggs from their own. This relies on them detecting small differences in egg colors and patterns and correctly identifying the parasitic egg. Otherwise, they risk rejecting their own eggs. The fact that the cuckoo finch uses multiple strategies means that this rejection is far less likely to happen.

Currently, the researchers plan to look at other brood parasites in order to determine if there are similar strategies being used. For now, though, it seems as if the cuckoo finch has evolved the perfect strategy to trick would-be parents.

The findings are published in the journal Nature Communications.