By Susan Milius
Nothing but fear itself can actually be dangerous for nesting birds.
Song sparrows protected from attack but subjected to recordings of predator yowls and leaf-crunching approach noises raised 40 percent fewer offspring in a year compared with neighbors living amid innocuous noises, says population ecologist Liana Zanette of the University of Western Ontario in Canada. Predators do not need to kill a single prey to have a big effect, she says.
Scary noises, broadcast where the sparrows nested in the wild, took a toll throughout the breeding season, Zanette and her colleagues report in the Dec. 9 Science. The alarmed sparrows laid fewer eggs to begin with, and they proved such skittish and cautious parents that they reared a smaller percentage of hatchlings than neighbors did.