On a quest years ago to find burrowing owls while teaching an environmental studies course, UC Davis professor Barry Wilson pressed a stethoscope to the ground. Cars slowed to watch; one girl asked, "Mommy, is that man listening to the heartbeat of the Earth?" Can environmental scientists ever truly measure the "health" of ecosystems? In the new book "Multiple Stresses in Ecosystems" (Lewis Publishers), co-editor Wilson notes that each level of the hierarchy of life may present different acceptable definitions of health. Given the complexity of the webs of life within ecosystems, Wilson concludes that finding one acceptable indicator of health, "the heartbeat" of any ecosystem is unlikely. One reason, Wilson says, "is the lack of quantifiable one-to-one relationships between the success of an individual species and the ecosystem in which it lives. The whole is indeed more than the sum of its parts." Book co-editors are Joseph Cech Jr., UC Davis professor of wildlife, fish and conservation biology, and Donald Crosby, UC Davis professor emeritus of environmental toxicology. Wilson is a professor of avian/animal sciences and environmental toxicology; one of his projects concerns the impact of chemicals on agricultural ecosystems.