Stinking decorations protect nests.

The common waxbill's habit of adorning its nests with fur plucked from carnivore scat turns out to discourage attacks from predators.

In southern Africa, these songbirds build enclosed grass nests on the ground, explains Justin G. Schuetz of Cornell University. The birds share their habitat with a goodly number of rodents and snakes that hunt for eggs.

Schuetz knew from old descriptions that the birds follow the unusual practice of pecking at scat left by servals and other carnivores. The waxbills then bring home lumps of excreted fur to tuck into the walls of their nests. "I could find some of the nests just by sniffing," says Schuetz.

A few other bird species have arranged macabre decorations when in captivity, for example, draping dead insects or dead nestlings on the top of nests. However, Schuetz couldn't find any report of experiments on how such decorations function in the wild.

The researcher set out 78 wicker imitation nests, lining half of them with fur from scat. As bait in each nest, he added two market finch eggs about the same size as a waxbill's.

During the 16 days that Schuetz monitored the imitation nests, he found a higher survival rate for eggs in the scat-adorned wicker. The potential egg eaters may have interpreted the stench as a danger sign indicating the presence of species that usually hunt them, says Schuetz.

He speculates that scat may lose some of its repulsive punch as days go by. He's seen waxbills take their latest scat haul and dunk it in a stream before carrying the wad home. Perhaps wetting the scat freshens up the odor, he says.