The Neomorphus ground cuckoos live in forests in Central and South America, where they often follow herds of wild peccaries so they can feed on the invertebrates that the peccaries disturb as they plough through the leaf litter.
Ecologists have noticed that when the cuckoos clap their beaks together they sound a lot like the tooth clacks the peccaries make to deter large predatory cats. To find out whether this is just coincidence or evidence of mimicry, Cibele Biondo at the Federal University of ABC in Brazil and her team analysed the cuckoo and peccary sounds, and compared them with the beak clapping sounds made by roadrunners – close relatives of the ground cuckoos.
Logically, the cuckoos should sound most similar to roadrunners, given that the two are closely related. But the analysis suggested otherwise. “The acoustic characteristics are more similar to the teeth clacking of peccaries,” says Biondo.
She suspects that cuckoos have something to gain by imitating the peccaries, particularly in the dark, dense forests where predators rely on hearing as much as vision. “Cuckoos may deceive predators by making it appear that peccaries are present when they are not,” says Biondo.
Dave Gammon at Elon University in North Carolina is intrigued by the findings. He wonders whether the acoustic similarities can be explained by the cuckoos and peccaries producing similar sounds in response to some features of their shared environment – in other words, that the similarities are the result of convergent evolution rather than mimicry.
Biondo and her colleagues have considered alternatives too. For instance, by making the same sounds, cuckoos and pigs could be teaming up to protect each other. The birds could be taking on the role of guards while peccaries ward off attackers, for example.
Gammon isn’t convinced that the two species need to make similar calls to recognise and respond to each other. But he thinks there could be more going on. “It will be interesting to see what additional evolutionary insights are made,” he says.
Biondo’s team now hopes to conduct experiments in the field to explore further. “It could be a challenge due to the rarity and elusive behaviour of both species,” says Biondo.