How Red-wings Elude Eavesdroppers

Red-winged Blackbird by Donald Metzner

The oak-a-lee song of a male Red-winged Blackbird is unmistakable as it reverberates through the spring air, warning other males to stay off his territory and away from the females in his harem. Because the message is meant to be heard throughout the bird's territory, it radiates more widely than calls intended just for mates, according to a study published in the May 2007 issue of Behavioral Ecology and Sociobiology.

Calls meant for fewer birds or one bird—such as courtship or copulation vocalizations—are more narrowly directed to prevent eavesdropping by rivals or predators, the study suggests. Lead author Gail Patricelli began the study as a postdoctoral fellow at the Cornell Lab of Ornithology and finished her analyses at the University of California at Davis.

Patricelli's team placed eight microphones in a ring around a calling perch. They also mounted three cameras to confirm the bird was a Red-winged Blackbird and to determine the direction it was facing in relation to the microphones. The scientists recorded five types of calls and measured their acoustic radiation patterns.

Patricelli found the checks, cheers, ti-ti-ti, and t'chit calls were all "significantly directional," while the oak-a-lee song was moderately directional, falling between alarms and courtship calls.

"This is because songs are used in two ways," says Patricelli. "They are used in direct interactions with specific birds and they can also be used as a broad advertisement, where omnidirectional calls are more effective at spreading the message widely—such as alarm or alert calls meant to communicate with neighboring males and females in a male's harem."

—Pat Leonard

For permission to reprint all or part of this article, please contact Laura Erickson, editor, Cornell Lab of Ornithology, 159 Sapsucker Woods Rd., Ithaca, NY, 14850. Phone: (607) 254-1114. email: lle24@cornell.edu