Sunday, July 03, 2005

Green Cars, Splatometers, and Road Kill

When we hear talk about developing “green cars” that do not damage the environment because they use clean fuels such as hydrogen, we should remember the British experiment with the “splatometer.”

British scientists were worried about the decline of their country’s bird population. The population of field birds, such as larks, sparrows, buntings, and finches, was declining dramatically For example, the number of tree sparrows in Britain declined by 90 percent in the last 25 years. They thought the cause might be a reduction in the number of insects available for the birds to eat.

In 2004, they counted insects by attaching “splatometers” to cars. A splatometer is a small piece of plastic, about the size of a postcard, that is attached to the front of a car. After driving, the researchers counted the number of insects on the splatometer, and they found that it hit only about one insect every five miles, much less than they expected.

These scientists theorized that insect population was declining because farms were using more pesticides. But a rough order-of-magnitude calculation shows that cars themselves are responsible for killing a huge number of insects:

  • The average area of the front of a car is more than 100 times the size of a splatometer, so we can conservatively assume that, for every five miles driven, 100 insects are killed.
  • Americans travel about 10,000 vehicle miles per capita per year, so they kill 200,000 insects per capita.
  • There are 300,000,000 Americans, so the total number of insects killed by cars in the United States each year is 60,000,000,000,000 (60 trillion).

Assuming that Americans kill about as many insects per mile as the British, the number of insects killed by cars each year in America alone is 10,000 times as great as the world’s total human population.

Because insects are at the base of the food chain, there is no doubt that this causes a significant decline in the population of amphibians, reptiles, and birds.

In addition, it is estimated that cars kill about 100,000,000 vertebrates in the United States each year. This estimate seems conservative, since about 900,000 killings of deer are reported each year, and judging from the roadkill you see on American roads, the number of lizards, squirrels, possums, and other small animals killed must be more than 100 times the number of deer. Some species, such as Florida Panthers, are threatened with extinction because roads filled with cars have fragmented their habitat.

No doubt, we should shift to cars that do less damage to the environment, such as hybrids, but if we want to live in an ecologically rich world, we must also drive less.


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