Migratory Routes Increasingly Threatened

One of the significant but little-noted shortcomings of wildlife preserves is that they only protect animals that stay put. Biologists who study large-scale animal migrations worry that many of nature’s most spectacular feats of persistence and survival are threatened by habitat loss and development. For instance, each winter pronghorn antelope travel 300 miles south from the Grand Teton Mountains in northwestern Wyoming to a flat mesa where wind clears the snow from grass. At four points their route narrows to about a hundred yards wide, and one of those bottlenecks has been developed into a natural gas field. Similar difficulties face caribou, monarch butterflies, wildebeests, and scores of other peripatetic creatures. Some migratory routes — like that of the whooping crane of the southern U.S. — have been restored, but given the wide swaths of land required for such projects, many biologists fear that species unfortunate enough to require summer homes may be destined for decline.