Geography Reference
In-Depth Information
Singing soprano may be ef ective, but it has costs. Though it gets around
urban noise, it does not penetrate walls or other urban obstructions as well as
low-frequency sound. High frequencies are also perceived as less threatening
by other males and may not be readily recognized by potential mates. These
miscues could reduce a male's reproductive output, though if females and
males continue to evolve in similar acoustic environments, one would expect
recognition of a singer's full repertoire to improve. In fact, as urban messages
come to dif er substantially from rural ones, they may ef ectively isolate popu-
lations and enable the evolution of distinct species. In Australia, silvereyes
may be heading down that path. Birds in the city and nearby rural areas dif er
in song. These dif erences in language are not yet limiting gene l ow, which
may explain why urban and rural silvereyes also have no morphological dif-
ferences, despite singing dif erent songs. Perhaps in time this will change.
A unique aspect of cultural evolution in subirdia is the potential coevolu-
tionary relationship that can develop between birds and people. As our cul-
ture changes, we may select for cultural changes in birds. The changed song
of birds in response to our changing modes of transportation is a case in
point. But this ef ect is mostly one way, from people to birds. The way people
and corvids—birds of the family Corvidae, including jays, crows, rooks, ravens,
jackdaws, and magpies—interact leads to frequent and reciprocal, coevolu-
tionary adjustments in our cultures.
Corvids are common components of urban bird communities throughout
the world. Interacting with people favors cultural adjustment in these birds
because human attitudes and important resources regularly and rapidly
change. Three aspects of human culture appear especially important to cor-
vid culture: persecution, provision of new food, and creation of new opportu-
nities. The power of persecution is evident in the nest defense culture of crows
and ravens. American crows and common ravens in the western United States
aggressively defend their nests in cities and towns where shooting is outlawed
and in general where persecution is frowned upon, but they quietly retreat out
