Zoom / The wren is a small brown bird found across the Americas. A study in Costa Rica found that these birds change their song in town to counter the effects of human-made noise.
Larry Keller, Lititz Pa./Getty Images
Dawn is breaking in San José, the capital of Costa Rica. The city is still asleep, but early risers are greeted by a beautiful symphony: Hummingbirds, corn eaters, yigüirros (clay thrushes), yellow-breasted cardinals, blue tanagers, house wrens, warblers and other birds announce that a new day has arrived.
Soon the incessant noise of vehicles and their horns, construction, street vendors and more take over, shaping the soundscape of the frenetic routine of hundreds of thousands of people who travel and live in this city. Then the songs of the birds will slip into the background.
“Birdsong has two main functions in males: it is to attract females and also to defend their territory against other males,” explains Luis Andrés Sandoval Vargas, an ornithologist at the University of Costa Rica. For females in the tropics, he adds, the primary role of their song is to defend territory. Thus, to communicate in cities, to ensure the security of their territory and to find partners, birds must find ways to counter the effects of anthropogenic noise, that is to say the noise produced by humans.
"The main effect of urban development on song is that many birds sing at higher frequencies," says Sandoval Vargas. Studies over the past 15 years have shown, for example, that blackbirds (Turdus merula), great tits (Parus major) and ring-necked sparrows rufous (Zonotrichia capensis) sing higher, with higher minimum frequencies, in urban than in rural settings.
But the response of birds to anthropogenic noise can be more complex than that, as Sandoval Vargas discovered when studying house wrens (Troglodytes aedon). House wrens are small brown birds (about 10 centimeters tall and weighing 12 grams) that feed on insects and tend to live near humans. In Costa Rica, they are found almost everywhere but especially in abundance in the cities. "Males sing almost year-round and sing for many hours during the day, and much of their behavior is mediated by vocalizations," Sandoval Vargas explains. But what makes them ideal for studying adaptations to urban environments is that most components of their song are in the same frequency range as the noise we humans produce.
Over two years, taking advantage of the house wren breeding season, from April to June, Sandoval Vargas and his team recorded the song of male house wrens at four locations in Costa Rica and also recorded ambient noise. Although all four sites are in urban areas, levels of human-generated noise are different at each site, ranging from very high and medium-high to medium-low and low.
The study, published in 2020 in the International Journal of Avian Science, focused on the repertoire of sound elements: the variety of unique sounds that, when combined together to others, shape the characteristic song of a bird. -which are produced by House Wrens.
As scientists expected, house wrens tended to sing with higher pitches in places with more anthropogenic noise. But that's not all they discovered.
They also found that, in general, the size of the birds' repertoire decreased as anthropogenic noise increased, particularly when birds were exposed to levels of anthropogenic noise above the usual noise to which they were accustomed. The researchers observed the same trend at the individual level: the same bird offered a smaller song repertoire on louder days than on quieter days.
A reduced repertoire can affect the way these birds learn their sonic language, as songbirds need to hear themselves and other birds to crystallize their son...
Zoom / The wren is a small brown bird found across the Americas. A study in Costa Rica found that these birds change their song in town to counter the effects of human-made noise.
Larry Keller, Lititz Pa./Getty Images
Dawn is breaking in San José, the capital of Costa Rica. The city is still asleep, but early risers are greeted by a beautiful symphony: Hummingbirds, corn eaters, yigüirros (clay thrushes), yellow-breasted cardinals, blue tanagers, house wrens, warblers and other birds announce that a new day has arrived.
Soon the incessant noise of vehicles and their horns, construction, street vendors and more take over, shaping the soundscape of the frenetic routine of hundreds of thousands of people who travel and live in this city. Then the songs of the birds will slip into the background.
“Birdsong has two main functions in males: it is to attract females and also to defend their territory against other males,” explains Luis Andrés Sandoval Vargas, an ornithologist at the University of Costa Rica. For females in the tropics, he adds, the primary role of their song is to defend territory. Thus, to communicate in cities, to ensure the security of their territory and to find partners, birds must find ways to counter the effects of anthropogenic noise, that is to say the noise produced by humans.
"The main effect of urban development on song is that many birds sing at higher frequencies," says Sandoval Vargas. Studies over the past 15 years have shown, for example, that blackbirds (Turdus merula), great tits (Parus major) and ring-necked sparrows rufous (Zonotrichia capensis) sing higher, with higher minimum frequencies, in urban than in rural settings.
But the response of birds to anthropogenic noise can be more complex than that, as Sandoval Vargas discovered when studying house wrens (Troglodytes aedon). House wrens are small brown birds (about 10 centimeters tall and weighing 12 grams) that feed on insects and tend to live near humans. In Costa Rica, they are found almost everywhere but especially in abundance in the cities. "Males sing almost year-round and sing for many hours during the day, and much of their behavior is mediated by vocalizations," Sandoval Vargas explains. But what makes them ideal for studying adaptations to urban environments is that most components of their song are in the same frequency range as the noise we humans produce.
Over two years, taking advantage of the house wren breeding season, from April to June, Sandoval Vargas and his team recorded the song of male house wrens at four locations in Costa Rica and also recorded ambient noise. Although all four sites are in urban areas, levels of human-generated noise are different at each site, ranging from very high and medium-high to medium-low and low.
The study, published in 2020 in the International Journal of Avian Science, focused on the repertoire of sound elements: the variety of unique sounds that, when combined together to others, shape the characteristic song of a bird. -which are produced by House Wrens.
As scientists expected, house wrens tended to sing with higher pitches in places with more anthropogenic noise. But that's not all they discovered.
They also found that, in general, the size of the birds' repertoire decreased as anthropogenic noise increased, particularly when birds were exposed to levels of anthropogenic noise above the usual noise to which they were accustomed. The researchers observed the same trend at the individual level: the same bird offered a smaller song repertoire on louder days than on quieter days.
A reduced repertoire can affect the way these birds learn their sonic language, as songbirds need to hear themselves and other birds to crystallize their son...
Zoom / The wren is a small brown bird found across the Americas. A study in Costa Rica found that these birds change their song in town to counter the effects of human-made noise.
Larry Keller, Lititz Pa./Getty Images
