A survey of mockingbird species links variable environment and song complexity
“You’ve got to suffer if you want to sing the blues” may apply to mockingbirds too.
In the Mimidae family, of mockingbirds and thrashers, the species with the more elaborate male courtship songs tend to be those living in the more challenging climates, says Carlos Botero of the National Evolutionary Synthesis Center in Durham, N.C.
Virtuoso birdsong, Botero explains, means precision in repeated elements, abundant variety in tweets and trills plus dead-on mimicry of other sounds, whether from neighboring bird species or car alarms. Mockingbird species that excel in such performance tend to breed in zones of hard-to-predict and highly variable temperature and precipitation, Botero and his colleagues report online May 21 in Current Biology.
Like other songbirds, mockingbirds and their relatives have to learn the vital singing skills for wooing and warring. If climate has something to do with brain evolution and learning, as some scientists have long hypothesized, then bird music may reveal the effects, the researchers propose.
“Nobody has looked at climate and bird song before,” Botero says.
This proposed link is important, says Daniel Sol of the Autonomous University of Barcelona in Spain, “because it suggests that sexual selection can also be affected by climatic variability.” That influence, he adds, “is key to understand the possible impact of climate change on biodiversity.”
Collecting data to test for a climate-song relationship was “horrendously difficult,” Botero says. He traveled through remote locations recording birds, and he and his colleagues sorted through some 1,700 recordings of species in the mockingbird family, coming up with 98 suitable ones. The recordings come from 29 species, the majority of the known members of the family.
At the flashier extreme, brown thrashers in North America sing repertoires of more than a thousand syllable types. And then there are pearly-eyed thrashers. “I like these guys a lot, but they do not shine in their vocal versatility,” he says. Their repertoires run to 20 kinds of syllables.
For climate data, Botero and his colleagues analyzed temperature and precipitation records for roughly the last 200 years from the Global Historical Climatology Network. Tropical forests, home to several thrashers, offered the most predictable and least variable habitats. At the other extreme lie drier, higher-altitude scrub habitats and deserts. Statistical tests found links of varying strengths between various singing skills and climate factors.
To explain how climate might influence bird music, Botero says he’s looking to the evolutionary process called sexual selection, in which mating choices shape species’ traits.
Animals get pickier in choosing their mates in harsh places, he says. There, picking a lousy mate can have especially bad consequences. Male birds in challenging habitats may be under extra pressure to prove themselves attractive in their courtship serenades.
And when variety in climate is part of that challenge, superior learning ability and a gift for innovation may prove particularly attractive. As Botero puts a female bird’s dilemma: “If I mate with this guy and something weird happens, then will he be able to come up with a solution to the problem?”
How accomplished a bird is in learning to sing might indicate superior brain power then. In the climate-song link, “the possibility is that we’re seeing sexual selection on measures of intelligence,” Botero says.
“Intriguing” is what Caroly Shumway research fellow at Brown University, has to say about the paper. It has convinced her that there’s a link between climate and singing ability in songbirds. As for explaining what causes the link, she says she’d like to see the researchers explore other hypotheses too.
Botero, C.A., et al. 2009 Climatic patterns predict the elaboration of song displays in mockingbirds. Current Biology 19(July 14):1-5. doi: 10/1016/j.curb.2009.04.061