A new study, published in Nature Ecology & Evolution, has found that Common Cuckoo is even more devious a species than previously given credit for.
Cuckoos are notorious for evading parental duty by laying their eggs in the nests of other, smaller, brooding passerines, typically Reed Warblers or Meadows Pipits. After laying an egg, the female cuckoo distracts the nest owner by frightening it with a call that mimicks that of Eurasian Sparrowhawk.
The call, which is described as a ‘chuckle’, is uttered just before the female cuckoo departs the host’s nest. Adopting what the researchers described as “remarkable secrecy and speed” in depositing an egg, it has long been perplexing why a cuckoo would call so soon after laying. The team hypothesised that uttering the call was to distract the host species with fear, in order to frighten it off while the cuckoo made its bid to escape undetected.
To test the theory, they played recordings of male and female Common Cuckoos, a Eurasian Sparrowhawk and a random, non-threatening species (a Collared Dove) to Reed Warblers. Female cuckoos utter kwik-kwik-kwik, not dissimilar in frequency to sparrowhawk’s kiii-kiii-kiii, and the team observed that the warblers reacted with the same vigilance when both were played, diverting attention away from their clutch. The warblers ignored both male cuckoo and Collared Dove calls.
In a further trial, the team also played female cuckoo calls to tits, a family often targeted for food by sparrowhawks but not for fostering duties by cuckoos. The female cuckoo call also increased vigilance among tits, despite cuckoos posing no threat to them. The team concluded that this suggested that both tits and warblers mistook the female cuckoo call for that of a sparrowhawk, even though the two sound quite different to the human ear.
The behaviour of a species tricking another into raising their own young is known as brood parasitism. In the case of Common Cuckoo, it is conducted at the expense of the foster parents’ own offspring, which are usually ejected from the nest by the cuckoo chick. To avoid getting caught, cuckoos have developed severak devious tricks, such as matching its egg colour to that of its target.
The team concluded: “Our results show that the female cuckoo enhances her success by manipulating a fundamental trade-off ... between clutch- and self-protection.
“This hawk-like chuckle call increases the success of parasitism by diverting host parents’ attention away from the clutch and towards their own safety. As a result, the female cuckoo might have ‘the last laugh’ in this particular battle.”
York, J E, and Davies, N B. 2017. Female cuckoo calls misdirect host defences towards the wrong enemy. Nature Ecology & Evolution. doi:10.1038/s41559-017-0279-3