By Susan Milius
For the first time, scientists have found a bird species–Australia’s superb fairy-wren–that can spot a murderer.
The killers are chicks of a particularly aggressive cuckoo species. The crime begins when the cuckoo mothers sneak an egg into a non-cuckoo nest, duping foster parents into all the work of childcare. After the intruder chick hatches, it kills its young nestmates by shoving them overboard.
Any human being can spot that something’s wrong in the invaded nest, since the cuckoo chick quickly grows ridiculously big, up to six times the size of its foster parent. Some victimized species catch the fraud in the egg stage and roll the cuckoo egg out of the nest. Yet to the bemusement of biologists, no bird had been known to catch the obvious cuckoo once the chicks hatched.