Geography Reference
In-Depth Information
century ago. As mynas spread across the island, they diversii ed in size, be-
coming smaller and more similar in size between the sexes in southern rela-
tive to northern cities. Small size may rel ect food scarcity or may be a re-
sponse to the need for respiring mynas to limit water loss in the cooler and
drier south. Regardless of the reason, the rapid change is striking.
House sparrows also quickly evolved size and plumage dif erences after
they were introduced to cities around the world. I could see these dif erences
among the many sparrows at the Burke Museum just as I could measure dif-
ferences among juncos. Sparrows from the dry steppe of Kazakhstan were
diminutive and buf y in color. Those from France and Buryatia, Russia, were
similar, with pronounced gray caps and rusty capes—traits missing from our
local Washington birds.
Professor Richard Johnston, of the University of Kansas, documented the
evolution of racial dif erences in house sparrows half a century ago. House
sparrows were introduced to North America in the 1850s and vary consider-
ably in size, shape, and coloration. As they colonized cities in various
regions—cold or dry places such as Detroit, Michigan; Sisseton, South Da-
kota; and Edmonton, Canada—and warm or humid places such as Phoenix,
Arizona; Gainesville, Florida; Honolulu, Hawaii; and Mexico City, Mexico—
their physiques evolved. In cold climates, sparrows are large and have rela-
tively short appendages. Large sparrows are known to survive winter storms
better than small ones, perhaps owing to larger fat and muscle reserves, better
insulation, and an increased ability to retain heat than small and lanky birds.
Sparrows are also typically large in dry, western cities where small birds
would rapidly lose precious moisture with each breath. In warm climates
sparrows are small and have long appendages, allowing them to quickly shed
excess heat and keep cool. As is true of many birds that live in humid, coastal
settings, the sparrows of Vancouver, Canada, are exceptionally dark. All these
dif erences evolved rapidly, over fewer than i fty years.
 
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