VANISHING TRACKS <i> by Darla Hillard (Arbor House/William Morrow: $19.95; 332 pp.) </i>

The snow leopard is, according to Darla Hillard, the least-studied endangered species on Earth. From 1981 to 1985, Hillard assisted wildlife biologist Rodney Jackson in a project to study the dwindling snow leopard population in its natural habitat: mountainous western Nepal. From a camp located two weeks’ hike away from the nearest airstrip, the pair set to work learning the animal’s habits. They set ingenious traps for the shy leopards in order to put radio collars on them and track their movements. Photographing them was also a trick; they solved the problem by rigging concealed cameras with hidden pressure mats in the animals’ runs. Their work also turns up evidence of poaching; they report that a snow leopard coat can fetch as much as $60,000 on the black market. The tale of their research is fascinating both as an adventure story and as a glimpse at the habits of one of the rarest big cats.