New pattern recognition software has shed light on the
evolutionary arms race between cuckoos and the birds they
Cuckoos are well-known for their parasitic behaviour. Instead of
raising their own young, they sneak into the nests of other birds,
lay their eggs and let their oblivious victim feed and care for
It isn't just a matter of having an extra mouth to feed: baby
cuckoos hatch earlier, grow faster, and will usually kick out their
host's eggs or children.
To combat this threat, birds have developed techniques for identifying cuckoo eggs and
removing them before they can hatch and wreak havoc.
Now a study published in Nature Communications has
examined in fine detail how shell patterns help birds differentiate
between their own eggs and unwanted cuckoo eggs.
Researchers from University of Cambridge and University of
Harvard looked at hundreds of eggs from eight species of birds
known to be targeted by the common cuckoo and found that they had
evolved unique "recognisable signatures" with the markings on their
Eggs with a very high or low density of markings had poorly
identifiable signatures, while those where the space between
markings was higher had more easily identifiable signatures.
The pattern recognition software used, dubbed
NaturePatternMatch, was designed to be as close as possible to bird
pattern recognition, though the researchers admit it has
"Many aspects of avian pattern recognition remain poorly
understood, so our model provides a roughly analogous
representation rather than a complete description of the cognitive
processes involved in avian pattern perception," they write in the
In addition, although an ideal strategy to combat cuckoos would
be to have eggs that were highly similar within a single clutch,
but still variable across a species, the researchers found that
different species of birds had evolved different strategies.
The brambling bird, for example, had a high variation within a
single clutch but less variation across the species. Their eggs
have very sparse markings. The garden warbler on the other
hand has more dense markings, but within a single clutch the eggs
are very similar.
Both strategies help make their eggs more recognisable, which
correlated with data for the birds' ability to reject cuckoo
Of course, the evolutionary arms race goes on, with cuckoos in
turn constantly adapting to even better mimic their victims' eggs.
But now we have a slightly better insight into what's going on in
those birds' brains.