Above: A non-migratory fork-tailed flycatcher. Photo: Alex Jahn

 

THE TINY TROPICAL fork-tailed flycatcher (Tyrannus savana) is known to rustle its wings to communicate, but two subspecies “speak” in different dialects, new research has found.

T. s. monachus spends all its time in northern South America whereas T. s. savana is a long-distance migrant, breeding in the southern part of the continent but overwintering in the north of South America. Birds of this migratory race make a higher-pitched sound in flight, probably thanks to their thinner feathers, evolved for flying long distances.

“We knew that migratory and non-migratory fork-tailed flycatchers are diverging genetically, potentially now representing different species, and that males differed in flight feather modifications. So, here we wanted to know if those modifications produced sounds for communication, if they differed between the two sub species, and whether the differences could be associated with the differences in movement behaviour,” said Valentina Gómez-Bahamón, a researcher at Chicago’s Field Museum and lead author of a study published in Integrative and Comparative Biology.

The researchers discovered that it is the males’ flight feathers that make the noise, when flying very fast and when fighting, for example in the breeding season. The sound is caused by feather fluttering. It was also observed in early morning courtship displays and when attacking potential predators.

Ms Gómez-Bahamón added: “We don’t know if the birds perceive the differences and whether they prefer their own sound for mating. When they are together in the wintering grounds of the migratory group (which coincides with the breeding season of the non-migrants) they do not mate with each other. Future experiments testing the birds’ reactions to playback of these sounds will hopefully allow us to know if they distinguish each other.”

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