One of fewer than 10 woodland caribou (Rangifer tarandus caribou) in US zoos, Costello the caribou would stand patiently anywhere in exchange for a reward of grape leaves. Meanwhile in the wild, woodland caribou are nearly absent from the lower 48 states because they rely on old-growth forest habitat. Just a few holdouts still cross from Canada into northern Idaho and Washington. The total U.S. population is 40 individuals.