Geography Reference
In-Depth Information
the successful behavioral solutions to these challenges and opportunities.
This is the process of social learning—observing and following the actions of
others. Learning, the analogue to heredity in genetic evolution, enables ac-
tions to wax and wane in frequency as populations adapt. If you thought ge-
netic evolution was fast, hold on! Cultural evolution is even faster; it need not
wait for one generation to inherit genes from its parents but can produce
change within a generation.
The highway a block from my backyard sounds like a river of moderate
size. It surges at rush hour and slows to a trickle at other times, but I can always
hear it. Birds hear it as well. It is not just this sort of noise that af ects the acous-
tics of urban environments. Buildings disrupt sound waves and alter sound
channels, creating a complex mosaic of loud and quiet spaces throughout the
city. To communicate ef ectively, birds must adjust to the hum of the city; they
must avoid the noise, sing louder, or alter the pitch and tempo of their voices.
Indeed, social learning and cultural evolution allow them to do all of this.
Urban birds rise earlier than rural birds. The morning songs, or dawn cho-
rus, start sooner in the city than in the country. In Spain, spotted starlings and
house sparrows sing earlier on noisy streets than on quiet ones. In the United
States, American robins sing earlier, and even well into the night, in cities rela-
tive to rural lands. These adjustments in timing rel ect the stimulating ef ect of
urban lighting as well as the active avoidance of rush-hour trai c noise.
We talk loudly in noisy places, and birds also raise their voices in the
noisy city. Nightingales sing louder on weekdays when urban noise is extreme
but quickly hush their voices when the city quiets down on weekends. Noisy
miners are noisier near busy Australian streets than near quite ones. These
facultative changes in volume likely rel ect the energetic costs of singing
louder, something birds quickly avoid. Other more subtle adjustments in the
tune of urban birdsong are less costly and now known from several species.
The great tit is a signature of European subirdia. Having a bold demeanor
and wearing a smart suit of green and yellow with a black vest, these supersized
