Robert M. Yerkes was assistant professor of comparative psychology at Harvard University, managing editor of the Journal of Animal Behavior, and editor of the Animal Behavior Series.
Elephant populations continue to dwindle in Tanzania.
With proper safeguards, water currents can be harnessed out of sight.
Barely pulled back from the brink of extinction, California condors are still being poisoned by lead-based ammunition.
Vulnerable everywhere in the wild, lions already face regional extinction.