As male fork-tailed flycatchers zip around, their wings can produce a high-pitched trilling. New research shows these whistles have dialects and may be used for communication.
Fork-tailed flycatchers (Tyrannus savana) have two subspecies: one that migrates annually between northern and southern parts of South America and another that resides year-round in the north of the continent. Valentina GĂłmez-BahamĂłn at the Field Museum in Illinois and her colleagues studied the two populations.
They collected and analysed audio and video recordings of the migratory birds in flight. The researchers found that curious notches on the tips of the flight feathers â long, rigid feathers that help produce lift and thrust â on the wings of males made a chirping noise when they flapped quickly.
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The males produced these wing sounds during aerial fights with other males, as well as in dawn displays, suggesting that they may be used to communicate with mates.
The team then found that these notched feathers differed in shape between the populations.
âFeathers of migrants are thinner in different parts of the feather and longer than feathers of sedentary birds,â says GĂłmez-BahamĂłn.
This may be the result of differing evolutionary pressures on flight. A longer, thinner wing shape is better suited for long-distance migration, for example.
The team found that subtle variation in wing sounds matched up with the two flycatcher subspecies, with migratory birds making higher-pitched noises. It is possible that evolution of the physical shape of the wing and feathers has spawned wing noise dialects as a side effect.
If the noises are used to communicate with mates, Gómez-Bahamón says she wonders whether the different dialects might interfere with interbreeding, helping to split the species in two. Going forward, she wants to verify that the feather dialects are truly widespread in fork-tailed flycatchers and that the birds actually fancy their own fluttering.
âWe know they sound different, but we donât know if [the birds] like their own sound as opposed to the other sound,â says GĂłmez-BahamĂłn.
Integrative and Comparative Biology
