‘Masters of deception’ cuckoos evolving into new species

Many cuckoos like to outsource their parenting.

These medium-sized birds lay their eggs in the nests of other bird species, tricking the unsuspecting hosts into raising their chicks. In some cuckoo species, the chicks grow alongside the host’s offspring. In others, the cuckoo chicks eject the hosts’ babies from the nests. This deception can be costly for the hosts who spend their time and energy raising another bird’s babies. So, some host birds have evolved ways to recognize and remove cuckoo eggs and chicks from their nests. This pressure to avoid detection is, in turn, driving several new cuckoo species to emerge, a study published in May has found.

Let’s consider the little bronze-cuckoo (Chrysococcyx minutillus) and the shining bronze-cuckoo (C. lucidus). Both these species abandon their eggs in the nests of songbirds like the gerygones (Gerygone spp.). But how do these cuckoos stay “hidden” from the hosts?

To find out, a team of researchers examined multiple lines of evidence including two decades of field observations and DNA samples from several historical museum cuckoo specimens.

They found a distinct trend: both species of bronze-cuckoos are masters of deception. They have evolved into several subspecies, each targeting a different host bird. Each of these subspecies produces babies that closely resemble the appearance of the hosts.

“Cuckoos are very costly to their hosts, so hosts have evolved the ability to recognize and eject cuckoo chicks from their nests,’’ Naomi Langmore, lead author of the study and a professor at the Australian National University, Canberra, said in a statement. “Only the cuckoos that most resemble the host’s own chicks have any chance of escaping detection, so over many generations, the cuckoo chicks have evolved to mimic the host chicks.”

The researchers found another clear pattern: parasitic cuckoos that like to remove the host’s babies from the nest have higher rates of speciation—that is, they splinter into new species more often—than parasitic cuckoos that grow along with the host’s offspring, as well as cuckoos that are not parasitic.

“This finding is significant in evolutionary biology, showing that coevolution between interacting species increases biodiversity by driving speciation,” co-author Clare Holleley, a scientist at the Australian National Wildlife Collection within CSIRO, Canberra, said in the statement.