Egg wars.

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Eggs of cuckoo finches and tawny-flanked prinias have grown more colorful in the last 40 years--a sign that the neighbors are locked in an evolutionary arms race. African cuckoo finches (Anomalospiza imberbis) dump their eggs (inner circle shown at left) into the nests of tawny-flanked prinias (Prinia subflava). By laying eggs that mimic prinia clutches (outer circle), cuckoo finches trick the prinia into caring for the finch young. Over the last decades, both birds have evolved a greater diversity of egg colors: As prinias developed new hues to defend against invaders, cuckoo finches retaliated with new fakes, researchers from the University of Cambridge in England report in the May American Naturalist. The team found a greater color variety in eggs from both species collected in Zambia in 2007-2009 compared with eggs collected in 1969-2002. And recent cuckoo finch eggs better match recent prinia eggs than do older cuckoo finch eggs, indicating the cuckoo finches evolved in response to the prinias, the team says.