These egg varieties are no accident -- they’re an anti-counterfeit strategy. Some birds lay lookalike eggs in other species’ nests to trick the foster parents into raising their chicks. While the impostors try to go undetected, their victims evolve more distinctive eggs to make them harder to fake. Duke graduate student Eleanor Caves analyzed the color patterns of hundreds of eggs from 11 African warbler species and the cuckoo finches that imitate them. Warblers don’t just pattern their eggs to foil the cuckoo finch forgeries, she found -- for even better security they avoid egg overlap with nearby warbler species too.