Geography Reference
In-Depth Information
Less obvious pollutants af ect an even wider range of city animals. Our
penchant to light the night sky disorients insects and birds, and also confuses
reptiles, notably sea turtles. On beaches around the world, when the tide is
high and the moon slight, female turtles emerge from the dark sea. On legs
built for swimming, they paddle across the sand to the dunes where they use
their hind l ippers to excavate a niche suitable for one hundred or more leath-
ery eggs. After covering all signs of their actions, the mothers reverse course
and return to the sea. About two months later baby turtles dig out of their
sandy incubators and orient toward bright horizons. Naturally, this would
lead them away from a dark shore and into the sea. But because of shore light-
ing, the bright horizon today is often an inland town or lighted yard, which
leads the hatchlings astray. Well-lit shores may also cause gravid females to
delay or abort landings, reducing the use of otherwise healthy nesting habi-
tat. Lighting af ects sedentary species as well. Toad tadpoles develop more
slowly under the lights because they stay away from illuminated, though pro-
ductive, shallows. Some diurnal reptiles and amphibians, including a variety
of geckos, anoles, skinks, toads, and tree frogs, actually benei t from night
lights, which allow them to forage under the streetlamps that are so attractive
to insects.
Among the perils of city life that birds and other animals share, the most
uniformly serious one is the domestic cat that ventures out-of-doors. In sub-
urban Canberra, Australia, cats eat around a half million small animals each
year. Most are nonnative small mammals, more than three hundred thousand
per year. Native reptiles are also frequent victims, about thirty thousand per
year. Few cats kill amphibians, though upwards of i ve thousand frogs, toads,
and salamanders a year may die by the paw. A similar pattern holds in the
United States, where cats kill 6.9 to 20.7 billion small mammals each year.
Suddenly the slaughter of more than three hundred million vertebrates—
birds, herps, and mammals—on U.S. roads seems tiny. Cats eat at least an
