Yet another often asked question with a multilayered answer! Deer arrived on Angel Island by walking, swimming, and taking the boat. Angel Island was connected to the surrounding land about 10,000 years ago, so it’s possible that the deer could have walked here. Deer can also swim and, especially during rutting season, have been seen swimming in the waters off Angel Island and Tiburon. When the military was on the island they over-hunted the deer, and eventually brought in more by boat so they could continue hunting.
As there are no predators that eat deer on Angel Island, deer began to become overpopulated when the military left in the 1960s and hunting ceased. When the island’s severely overpopulated deer herd was threatened with starvation, many deer were trapped and transported off the island. Currently, park policy is to cull some of the deer population whenever it is required in order to maintain a healthy herd (although this has not been necessary for about 20 years.