Reed wablers use social learning to defend themselves against cuckoos

Jeremy Hance
June 04, 2009

The cuckoo bird is famous for its parental strategy: rather than raise its own children it infiltrates the nest of an unsuspecting bird of a different species, replacing that bird’s eggs with its own; when the cuckoo babies are born the ‘adoptive’ parents end up unwittingly rearing young that is not theirs. However, at least one bird species—the reed wabler—has learned to defend itself against such clever incursions.

Scientists describe the relationship between the cuckoo and the reed wabler as an ‘arms race’: when once one species establishes a new defense, the other begins a new strategy. In a new study published in Science reseachers have discovered a new weapon employed by the reed wablers in the arms race with cuckoos: social learning.

Reed wabler nest parasitized by common cuckoo, larger eggs is the parasitic egg. Image courtesy of Science and AAAS.
"Studies of co-evolutionary arms races between brood parasites and hosts have emphasised genetic adaptations and counter adaptations; however, our field experiments show that transmission through social learning provides a mechanism by which hosts can adjust their nest defence and so respond rapidly to changes in parasitism," said Dr. Justin Welbergen.

Scientists at the University of Cambridge discovered that reed wablers will attack in unison cuckoos when they enter the wablers’ territory. This behavior is taught byway of inexperienced wablers observing their fellows. There are risks with such attacks, however, since such attacks can lead to injuries with the wablers and, in the ruckus, expose them to predators.

In order to test the reed wabler’s willingness (or foolhardiness) to put their selves in danger, scientists from the University of Cambridge sent non-cuckoo species, such as parrots, into the reed wablers territory to see what would happen. The answer: nothing. This suggested that reed wablers have used social learning in their defensive behavior, so that they only attack when confronted with a true threat, like the cuckoo.

"Our previous work showed that reed warblers distinguish cuckoos from other nest enemies and adjust their defences according to local parasitism risk,” says Welbergen. “Our current work demonstrates that reed warblers can use social information to fine-tune their defences to the nature of the local threat."

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Jeremy Hance (June 04, 2009).

Reed wablers use social learning to defend themselves against cuckoos.