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Fighting Counterfeit Eggs

June 26, 2014

Common cuckoos trick other birds into raising their young. But the hosts have evolved some defenses.

Transcript

BOB HIRSHON (host):

Fighting phony eggs. I’m Bob Hirshon and this is Science Update.

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An adult Reed Warbler raises a much larger Common Cuckoo. To trick their hosts into accepting foreign eggs, cuckoos have evolved egg mimicry. Using a new pattern recognition tool, NATUREPATTERNMATCH, researchers show that host birds have evolved individual egg pattern signatures, which allow them to distinguish their own eggs from those of a cuckoo cheat. NATUREPATTERNMATCH extracts visual features, here represented by magenta vectors (center). Three eggs each (represented in different rows) laid by three different Great Reed Warblers are shown here (right). (David Kjaer, left, and Mary Caswell Stoddard/Natural History Museum, UK, center, right) 

Common cuckoos lay their eggs in the nests of other birds, tricking them into raising their young. They get away with this by laying eggs that look almost identical to those of the host parents, according to Harvard evolutionary biologist Mary Caswell Stoddard.

MARY CASWELL STODDARD (Harvard University):

So w e can think of this sort of like the cuckoo being the counterfeiter, it’s forging the patterns of the host egg.

HIRSHON:

But the cuckoos don’t always get away with the ruse. Stoddard and her colleagues used a mathematical algorithm to identify signature patterns that may help host birds distinguish their own eggs from those of cuckoos. They found that host species which have experienced the most intense egg mimicry from cuckoos have also evolved the most recognizable patterns.

STODDARD:

From an evolutionary standpoint, I think we’ll find that visual signatures may be a very powerful defense against parasite trickery.

HIRSHON:

I’m Bob Hirshon, for AAAS, the science society.