From backyard gardening to mountain climbing, outdoor activities are on the wane as people around the world spend more leisure time online or in front of the tube, according to findings published this week in the Proceedings of the National Academy of Sciences.

"There's a real and fundamental shift away from nature -- certainly here [in the United States] and possibly in other countries," said Oliver Pergams, visiting research assistant professor of biological sciences at the University of Illinois at Chicago.

Pergams and Patricia Zaradic, a fellow with the Environmental Leadership Program, Delaware Valley in Bryn Mawr, Pa., had previously reported a steady decline in per capita visits to U.S. national parks since the late 1980s -- which correlated very strongly with a rise in playing video games, surfing the Internet and watching movies. The researchers call this recent shift to sedentary, electronic diversions "videophilia." And they don't see it as healthy progress.

"The replacement of vigorous outdoor activities by sedentary, indoor videophilia has far-reaching consequences for physical and mental health, especially in children," Pergams said. "Videophilia has been shown to be a cause of obesity, lack of socialization, attention disorders and poor academic performance."

In the new study, Pergams and Zaradic sought to gather and analyze longitudinal survey data on various nature activities from the past 70 years -- including the 20 years since U.S. national park visits began their ongoing decline.

"We felt that national park visits in the U.S. were a pretty good proxy for how much people were involved in nature," said Pergams. "But we wanted to see if people were going less to other nature-related venues or participating less in nature recreation activities, both here and in other countries."

The biologists examined figures on backpacking, fishing, hiking, hunting, visits to national and state parks and forests. They found comparable reliable statistics from Japan and, to a lesser extent, Spain.

They found that during the decade from 1981 to 1991, per-capita nature recreation declined at rates from 1 percent to 1.3 percent per year, depending on the activity studied. The typical drop in nature use since then has been 18-25 percent.

As biologists, the researchers are also concerned about the ecological implications.

"We don't see how this can be good for conservation," Pergams said. "We don't see how future generations, with less exploration of nature, will be as interested in conservation as past generations."