Brood parasites take the stress out of parenting by letting someone else do it for them, unceremoniously dumping their eggs in the nests of hard-working, involuntary foster parents who end up raising the intruder thinking it’s their own. The behavior is seen among cuckoos who use their spade-like immature beaks to scoop out any stepsiblings from the nest in one of the more murderous, deceitful adoption tales of our time.

A new study published in the journal Evolution has discovered the clever way a parasitic finch species in Africa has evolved to ensure its offspring goes undetected by the unsuspecting foster mom, by mimicking the behavior of their nest buddies.

Working in the savannahs of Zambia, the team collected images, recordings, and videos of these crafty finches called the indigobirds and whydahs of the genus Vidua. Their footage revealed a highly specialized form of mimicry that was convincing enough to allow the parasitic chicks safe passage in the nest, with the parents being none the wiser even when their adopted children grew to almost twice the size of their biological offspring.

The finches seek out the nests of a particular species of grassfinch and dump their egg among a fresh clutch belonging to the nest’s creator. The absent parent then gets the heck out of there, safe in the knowledge their child will be incubated by someone with, presumably to their mind, considerably more time on their hands. When the egg hatches, the adoptive parent will feed them alongside their own chicks as the bald intruder performs a wiggly dance that gives it the appearance of a 90’s egg alien, as seen in the above video.

Vidua finches have hustled hard to pull off this great deception as grassfinches have unusually unique nestlings, with each species exhibiting a different appearance, begging calls, and begging movements. Over time, the intruders have scrubbed up on their improvisation skills, pulling off a bespoke performance catered to the particular greenfinch species whose nests they invade.

As the team’s data showed, the performances were authentic. Brood-parasitic Vidua finches were able to copy the movements, calls, and even adopt the unique coloration of their hosts’ offspring, mirroring the bright coloration found in the inside of their mouths. The display this creates as they waggle, open-mouthed begging for food brings real context to the phrase, “a face only a mother could love”.

"The mimicry is not only amazing in its own right but may also have important implications for how new species of parasitic finches evolve," said study author Professor Claire Spottiswoode in a statement.