Junco hyemalis es una especie común en los bosques de pino montanos a lo largo de Norte América, pero durante aproximadamente 25 años una población aislada se ha reproducido exitosamente en un excepcional entorno urbano en el sur de California. Sin embargo, ni los hábitats urbanos ni los naturales han sido estudiados con detalle alguno en cuanto a las presiones de selección que pueden ejercer sobre la comunicación animal. Los hábitats urbanos son evolutivamente nuevos, aunque hasta cierto punto pueden parecerse acústicamente a hábitats rocosos como los acantilados y cañones. El hábitat urbano se encuentra en expansión alrededor del mundo y un creciente número de especies, incluyendo muchas aves, se ven obligadas a comunicarse acústicamente entre edificios y sobre el concreto. Las propiedades de la transmisión del sonido difieren entre hábitats y pueden conducir la evolución de señales acústicas en distintas direcciones. La degradación de las señales acústicas durante su transmisión constituye una presión de selección importante para los animales que dependen de la comunicación vocal. Although the pattern of song divergence was not consistent and it is difficult to draw firm conclusions from this single urban population, our transmission results suggest that echoes could be important in shaping urban birdsong. There were also no differences in trill rates, but we did find a significantly higher minimum frequency in the urban junco population compared to three of four forest populations. Despite the presence of relatively short urban songs, there was no significant shortening overall. We expected environmental selection in urban habitat to favor shorter songs with higher frequencies and slower trill rates. Transmission properties differed significantly, resulting in tails of reflected sound with gradually declining amplitude in the forest and in multiple discrete echoes in the urban environment. We investigated potentially divergent selection pressures on junco songs, using sound transmission experiments with artificial sound stimuli, in natural forest habitat and in this urban habitat. Dark-eyed Juncos ( Junco hyemalis) commonly inhabit montane pine forests across North America, but for about 25 years an isolated population has been successfully breeding in an urban environment in southern California.
Neither urban nor these natural habitats have been studied in any detail for the selection pressure they may exert on animal communication.
Urban habitats are evolutionarily new, although to some extent they may acoustically resemble rocky habitat such as cliffs and canyons. Urban habitat is expanding worldwide and an increasing number of species, including many birds, must now communicate around buildings and over concrete. Sound transmission properties differ among habitats and may drive the evolution of vocal signals in different directions. Degradation of acoustic signals during transmission presents a challenging selection pressure for animals dependent on vocal communication.