Do eggs go cuckoo under UV light?

The first study of museum egg collections with ultraviolet (UV) light detectors has led to what the two researchers in the project call “a sobering conclusion.”

Decades of research may need rethinking because people’s eyes don’t see eggs the way birds’ do, say Michael Cherry from the University of Stellenbosch in South Africa and Andrew T.D. Bennett of the University of Bristol. People don’t see UV wavelengths, but birds do.

The look of an egg matters particularly in studies of birds, such as cuckoos, that lay eggs in other species’ nests. Some nest tenants heave the cuckoo’s egg overboard. Others tend to it faithfully, even when it doesn’t look at all like their own eggs, at least to human eyes. Feeding the stowaway means the foster parents often starve their own offspring.

In museums, Cherry and Bennett scrutinized 21 clutches of eggs that Africa’s red-chested cuckoo, Cuculus solitarius, had invaded. Hosts represented a total of 10 other species, including the cape robin. The researchers report their egg review in the March 22 Proceedings of the Royal Society of London B.

The robins’ eggs didn’t look at all to human volunteers like cuckoo eggs. In the UV range, however, the cuckoo and cape robin eggs strongly resemble each other. It’s too early to say how important UV vision is for egg recognition, the team cautions, but it’s time for a bird’s-eye view.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.