Page last updated at 09:36 GMT, Monday, 25 May 2009 10:36 UK

Climate link to mockingbird songs

By Victoria Gill
Science reporter, BBC News

The tropical mockingbird's elaborate tune puts the brown trembler mockingbird to shame

Unpredictable weather seems to stimulate chatter among birds - as well as humans - according to researchers.

A team of US scientists has found that mockingbirds living in variable climates sing more elaborate songs.

Complex tunes, sung by males to impress females, are likely to signal the birds' intelligence.

Published in Current Biology, the findings suggest that females seek mates with superior singing skills - smart enough to survive harsh climes.

Carlos Botero, a researcher from the National Evolutionary Synthesis Center in North Carolina, led the study.

He and his colleagues compared recordings of 29 species of mockingbird, studying patterns in their songs including the number of different notes, the number of syllables and the birds' abilities to mimic other sounds.

Researcher, Carlos Botero
Carlos Botero's approach to song recording

His team then compared weather patterns in the birds' habitats with the patterns in the songs.

Dr Botero told BBC News that it was "very exciting" to see a strong correlation between song complexity and climate.

"The birds are not born knowing how to sing; they have to learn," he explained. The fact that the males sing more variable tunes in a more variable climate could demonstrate the "sexual selection of intelligence".

This means that females may be looking for a tuneful signal that their prospective partner is a good catch.

Singing challenge

Local climate patterns are good indicators of how challenging life is in a given location, Dr Botero explained.

"Survival and reproduction become more complicated when weather patterns are unpredictable because you don't know when food will be available or how long it will be around.

"In really difficult or demanding environments you would expect females to be choosier."

White breasted thrasher mockingbird
St Lucia's white breasted thrasher sings a simple song

He added that researchers might be able to use this simple, measurable behaviour in the birds, to provide clues about the evolution of important human developments such as language, music and art.

Sandra Vehrencamp from Cornell University, who was also involved in the study said that, to fully test this explanation, the team would need to design an intelligence test for the male birds, and examine their relative breeding success.

During the course of the study, Dr Botero embarked on a solitary month-long tour of South America, seeking out elusive birds and recording their songs.

Thanks to his expedition, some key gaps in the library of birdsong at Cornell University, where he was based during the study, are now filled.

"I had to try to visit as many different countries as possible at exactly the right time - when the birds were breeding," he said, adding that some of the remote locations he visited were like "mockingbird paradise".

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