Researchers convened August 12-15 at the American Ornithologists’ Union 2009 meeting in Philadelphia, Pa. They presented their latest findings on the evolution of female songs, the unexpected vocal anatomy of sage grouse and the perils of traffic noise for forest birds.
PHILADELPHIA—It’s not her latitude. It’s her lifestyle. A new study may help explain why birdsong is more of a guy thing in temperate regions but plenty of females join the chorus in the tropics.
Jordan Price of St. Mary’s College of Maryland in St. Mary’s City and his colleagues used New World blackbirds to study the evolution of female song. The group includes both tropical and temperate species, some with female singers and some without.
Looking at the pattern of female singing on a family tree of 65 blackbird species, the researchers concluded that the original blackbirds founding the lineage had female singers. As the lineage diversified into modern species, the capacity for female song disappeared at least 11 times, Price reported August 15.
Among blackbirds, then, the question isn’t why some females sing but why some don’t. Dividing the blackbird species into tropical and temperate dwellers yields only a rough correlation with the occurrence of female song, Price said. Instead he found a tighter correlation by looking at lifestyle.
Among most of the blackbird species that stay in one region year round and breed in monogamous, territorial pairs, females still sing. But in birds that have left behind that way of life, such as migratory orioles and colonially breeding grackles, females typically have lost their songs. It’s how the birds live, rather than where, that reveals the most about female song, he said. — Susan Milius
PHILADELPHIA—Those famous sage grouse ballooning out their chests during courtship calls in nature documentaries have a vocal system that is very different from what biologists had thought.
Sage grouse belong to the group of galliform birds that includes chickens. Yet a chance discovery with a new microphone setup has raised the possibility that studying the vocal anatomy of chickens has misled biologists. Sage grouse turn out to have an unchickenlike, double-barreled sound source with the capacity to produce two sounds at once, Alan Krakauer of the University of California, Davis reported August 15.
For courtship, sage grouse use the singles-bar approach: Males gather at one place to strut and call as females review what’s on offer. Krakauer and Gail Patricelli, also at Davis, set out an array of 24 microphones on a sage grouse display ground in Wyoming to record the males’ seductive “coo-pop-whistle-pop” calls. Deploying an array of microphones allowed researchers to record a large number of males and triangulate calls to identify which male made which noise.
Some of the recordings caught a second, slightly lower whistle before a male’s final pop. Such ghostly whistles have shown up now and then in previous recordings at male gathering places. But thanks to the new microphone array, Krakauer and Patricelli could see that the ghost whistle wasn’t an inadvertent recording of some other male’s noise. One male can make two simultaneous whistles, Krakauer said.
Biologists have found this capacity in songbirds, which can create a different sound on each side of their vocal sound-source organ, the syrinx. Chickens, though, have a one-cluck-at-a time syrinx, so biologists had expected similar limitations in related birds.
Dissecting vocal organs from a sage grouse (found already dead) confirmed the capacity for a double source of vibrations, Krakauer said. The Davis researchers hitched the syrinx to air suction hoses, working with vocal specialist Franz Goller of the University of Utah in Salt Lake City. Mechanically pulling air through each side of the syrinx led to its own vibrations.
Since then, the researchers have tested three other galliform birds — Japanese quail, the greater prairie chicken and the sharp-tailed grouse — and found the unexpected two-sided sound capacity in all three. — Susan Milius
LOW-VOICED BIRDS
PHILADELPHIA—Traffic noise may be driving birds with low-pitched calls away from forests.
Of eight species surveyed in a new study, the two with the calls most likely to get lost in the din of traffic were unexpectedly rare in woodlands near highways, Sarah Goodwin of the University of Delaware in Newark reported August 13.
Traffic typically rumbles at 3 kilohertz or below, Goodwin said. Several earlier studies had found that urban populations of certain birds such as great tits have higher-pitched calls compared with rural cousins. Goodwin looked for a more drastic reaction: just avoiding noisy places.
She got the idea, she said, while selecting sites for an earlier bird survey in the sprawl around Washington, D.C. So many of the possible spots had so much traffic noise that she had to reject them because she couldn’t hear birds well.
To see if birds also shun habitat based on noise, she looked for eight species in 30 places in wooded national parks. Half the study sites hummed with readily audible traffic noise and half had more peace and quiet. To reduce confounding factors such as unhealthful effects of roadside exhaust, she chose study plots at least 100 meters from a road edge. She checked each plot weekly during the spring and summer for woodland birds with diverse calls and lifestyles, including Carolina wrens, wood thrushes and scarlet tanagers.
When she analyzed the presence of birds and the plot characteristics, she found that noise was the strongest factor explaining the loud spots’ rarity of two species: yellow-billed cuckoo and white-breasted nuthatch. Those birds vocalized mostly in the traffic-din range, she said.
