Last laugh: Scientists expose role of female cuckoo’s evil ‘chuckle’
PARIS — The common cuckoo, notorious for evading parental duty by hiding her eggs in the nests of other brooding birds, is even more devious than previously thought, scientists revealed on Monday.
After laying an egg, the female distracts the owner of the nest — a reed warbler in this case — essentially by frightening the poor bird out of its wits, they said.
The cuckoo gives a “chuckle” that mimmicks the call of the sparrow hawk — which loves to snack on warbler flesh — before abandoning her egg among the warbler’s clutch and flying off to freedom.
“This hawklike chuckle call increases the success of parasitism by diverting host parents’ attention away from the clutch and toward their own safety,” a duo of Cambridge University researchers wrote in the journal Nature Ecology & Evolution.
“As a result, the female cuckoo might have ‘the last laugh’ in this particular battle.”
The bird has also adopted “remarkable secrecy and speed” in depositing its egg, said the team.
For this reason, scientists have battled to understand why the cuckoo would risk exposure by “chuckling” so soon after committing its crime.
The Cambridge team theorized the purpose was to distract the warbler with fear.
To test this, they played the recorded calls of male and female cuckoos, a sparrow hawk, and a random, nonthreatening bird — a collared dove, to reed warblers.
Only the male cuckoo makes the signature sound copied in pendulum clocks. The female utters a laughterlike “kwik-kwik-kwik” not dissimilar in frequency to the sparrow hawk’s “kiii-kiii-kiii”.
The warblers reacted with the same vigilance to female cuckoo calls as to hawk calls, and diverted attention away from their clutch.
In a further test, the team played the female cuckoo call to tits — birds which are also eaten by sparrow hawks but are not targeted by cuckoos for fostering duties.
In tits, too, “cuckoo calls increased vigilance as much as hawk calls”.
“Our results show that the female cuckoo enhances her success by manipulating a fundamental trade-off ... between clutch- and self-protection.”