When a mourning dove lifts off the ground into flight, the wings whistle. It's a non-vocal sound much like the whistling sound displaying male woodcocks make in the spring. And it's typical for many members of the pigeon family.
It's also typical that pigeons and doves do not make vocal alarm calls. Robert Magrath of the Australian National University in Canberra wondered if the sounds of wing whistles varied depending on the circumstances. Perhaps a certain type of wing whistle served as an alarm. This seemed reasonable because a frightened bird takes off faster and at a steeper angle than a calm bird just moving from place to place.
Magrath and a student tested his idea with crested pigeons. They set up 13 feeding stations and recorded normal takeoff wing whistles. Then to collect sounds of a startled takeoff, they flew a glider shaped like a hawk over individual feeding pigeons. The sound of the wing whistle of startled birds was louder and faster. Listen to both sounds at http://sciencenow.sciencemag.org/feature/data/wingsound.wav .
Then they tested flocks of pigeons by playing the recorded sounds. None of 15 flocks responded in any way to the normal wing whistle. When these same flocks heard the wing whistle of startled birds, however, 11 of the 15 flocks flew off.
Because the wing whistle of alarmed birds is louder than normal takeoff whistles, Magrath varied the volume of the sounds. Normal wing whistles made louder did not alarm feeding pigeons. But when they reduced the volume of the alarmed wing whistles, three of the 15 flocks flew off, and the others became alert and looked around for danger.
Magrath concluded in a recent report in the "Proceedings of the Royal Society B" that it is the faster tempo of the startled wing whistle, not loudness, that signals alarm. He attributes the sound to a narrow outer feather on the wing.
Next time you watch mourning doves in the backyard or hunt them in the field, listen for differences in wing whistle between calm and alarmed individuals.
Mourning dove hunting is regulated with migratory waterfowl. The early season ended recently, additional seasons run Oct. 24-Nov. 28 and Dec. 26-Jan. 2.
Scott Shalaway is a biologist and author. He can be reached at http://scottshalaway.googlepages.com and RD 5, Cameron, WV 26033.