Jonathan C. Slaght/ Wildlife Conservation Society Russia

Listening for a Safe Neighborhood

For humans, eavesdropping on your neighbors is considered rude. But for owls raising a family, it's essential. Researchers in Spain have found that some owls take the alarm calls of other owl species into account before deciding where to nest. The birds aren't the only animals known to listen in on their neighbors, but examining how animals use alarm calls to decide on the best areas to raise young hasn't been done before.

Many animals use alarm calls to alert friends and family of impending danger. But in some situations, alarm calls from a member of another species can be more informative than those from a member of your own species, says Daniel Blumstein, a behavioral ecologist at the University of California, Los Angeles, who was not involved in the new research. He points to studies that demonstrate that different species, such as mule deer and yellow-bellied marmots, are more likely to listen to one another if they have the same predators.

Since little owls (Athene noctua) and scops owls (Otus scops) breed in the same area of southeastern Spain and share similar resources, biologist Deseada Parejo of the Spanish National Council for Research in Almeria, Spain, wanted to find out whether they relied on alarm calls to help pick breeding sites. The researchers used little owl calls because the birds are supposedly better informed about habitat quality since they are year-round residents of the study area.

Parejo and two colleagues set up nest boxes in three kinds of experimental plots: risky plots (those with a lot of alarm calls), nonrisky plots (those with only contact calls), and control plots (those with no calls at all). To minimize the chances that resident and migratory owls would respond to the familiarity of the caller rather than the information in the call, all of the recordings were of little owls that didn't live in the area.

Little owls preferred risky and nonrisky plots over control areas, but scops owls preferred the control and nonrisky plots, the team reports today in the Proceedings of the Royal Society B. Little owls laid more eggs in nests on nonrisky plots than on risky plots, but scops owl clutch size didn't correlate with where they nested.

Parejo says that little owl preference for the nonrisky and risky plots could be a function of their attraction to other little owls rather than a response to information in the alarm calls. But the fact that they laid larger clutches in nonrisky plots suggests that they were cuing in to something about the alarm calls, she says.

The authors speculate that the little owls could be interpreting threat levels of risky and nonrisky plots and laying eggs accordingly. Small clutch sizes in a risky environment could shorten the time a nest is exposed to predators, reduce the number of feeding trips parents make that could attract a predator, or help the adults save energy for a second nest if the first one fails.

Parejo adds that it makes sense for scops owls to use the information in little owl alarm calls to make decisions about their nest sites. The study confirmed the team's hypothesis that because little owls and scops owls share similar resources, such as nesting habitats, it would be advantageous for the less-informed scops owl to listen to what the better-informed little owls had to say about predation risk.

It's an interesting idea, Blandine Doligez, a behavioral ecologist at the French national research agency who works in Lyon, writes in an e-mail. But she cautions that the study's small sample size calls for additional work—perhaps with songbirds that allow for larger sample sizes—to flesh out the paper's conclusions.

"What's missing from this is drilling down and really looking at the mechanisms," Blumstein says. He'd like to know how these owls are using information in alarm calls to make their decisions and thinks it would be a good avenue for future research. But Blumstein likes how this study combines research in different areas, such as in alarm calls and breeding behavior. It demonstrates that "species need other species," he says.