Birds teach passwords to their unborn chicks to detect impostors
If you’ve been reading my blog for a while, you might remember a post about cuckoos and brood parasitism. Basically, cuckoo mothers lay eggs in other birds’ nests, and when the cuckoos hatch, they kick out the other hatchlings and take all the food for themselves. For the mothers of the non-cuckoo species, it’s not so simple to detect the impostors because the eggs are elaborately colored to almost perfectly mimic those of the host species. That mothers can’t tell which eggs are impostors is a serious problem, because it means her offspring die and she thus can’t pass on her genes.
At least some species have come up with an ingenious solution: they teach their young a password, while they are still in the egg, which the young will repeat after being born to prove that they’re the real deal.
She kept 15 nests under constant audio surveillance, and discovered that fairy-wrens call to their unhatched chicks, using a two-second trill with 19 separate elements to it. They call once every four minutes while sitting on their eggs, starting on the 9th day of incubation and carrying on for a week until the eggs hatch.
When Colombelli-Negrel recorded the chicks after they hatched, she heard that their begging call included a single unique note lifted from mum’s incubation call. This note varies a lot between different fairy-wren broods. It’s their version of a surname, a signature of identity that unites a family. The females even teach these calls to their partners, by using them in their own begging calls when the males return to the nest with food.
These signature calls aren’t innate. The chicks’ calls more precisely matched those of their mother if she sang more frequently while she was incubating. And when Colombelli-Negrel swapped some eggs between different clutches, she found that the chicks made signature calls that matches those of their foster parents rather than those of their biological ones. It’s something they learn while still in their eggs.
When a cuckoo chick emerges, the parent can tell that it’s an impostor and can abandon the nest to form a new brood without wasting energy on the cuckoo. What an amazing adaptation! These sorts of stories are absolutely incredible to me, and they really demonstrate the awesome power of evolution.