Birds use Distinct Markings to Avoid being Tricked by Cuckoos: Cambridge Researchers

Some birds have evolved distinct signature patterns to recognize eggs. These markings help the birds fight cuckoo bird invasion, University of Cambridge researchers have found.

The parasitic Common Cuckoo lays its eggs in other birds' nests. Their hatchlings are born murderers, who instinctively push hosts' eggs out of the nest.

Researchers have now found that some birds might counter cuckoos strategy by evolving specific signature for their own brood.

For the study, Dr Mary Caswell Stoddard at the Harvard University and Professor Rebecca Kilner and Dr Christopher Town at the University of Cambridge developed a new computer vision tool called NATUREPATTERNMATCH.

"We harnessed the same computer technology used for diverse pattern recognition tasks, like face recognition and image stitching, to determine what visual features on a bird's eggs might be easily recognised," explained Stoddard in a news release.

Researchers used the tool to examine pigmentation pattern of hundreds of eggs of eight species of birds. These birds are common targets of cuckoos.

The team found that some host bird species have distinct blotches of pigments on the eggs that might help them recognize their own brood from the foreign ones. Researchers said that bird species that have been the primary target of cuckoos have more distinct looking eggs than other bird species.

According to the researchers, cuckoos and their hosts are in a sort of co-evolutionary arms race. If host birds make different patterns of eggs, then over time even cuckoos develop techniques to outsmart them.

Researchers found that host birds have evolved different strategies to counter the trickery of cuckoos. Some birds have complex markings across the species, while other birds have different marks for each brood, meaning that each female bird has its own signature. According to researchers, each technique is equally effective in helping host birds recognize foreign eggs and kill them before they harm their own brood.

The team plans to use NATUREPATTERNMATCH to study other complex patterns in the nature.

Related studies have shown that host birds have "maiden aunts" that help fight parasitic birds.

"The ability of Common Cuckoos to mimic the appearance of many of their hosts' eggs has been known for centuries. The astonishing finding here is that hosts can fight back against cuckoo mimicry by evolving highly recognisable patterns on their own eggs, just like a bank might insert watermarks on its currency to deter counterfeiters," said Stoddard.

The study is published in the journal Nature Communications.