Because the Garden is only open during the day, visitors are unlikely to see most mammals as they tend to be nocturnal. Exceptions are squirrels and Homo sapiens. Mammals are also quite wary, so even during an early visit, when one might encounter a skunk or opossum still out foraging, it pays to be quiet and observant. One more reason that mammals are rarely seen is that most require large territories, so if the Hartman Prehistoric Garden is included in an individual's range, it would only wander through occasionally. Within the area around Town Lake and Zilker Park, there are numerous mammals, such as white-tailed deer, nutria and other rodents, and rabbits. Perhaps one of the most renowned species that inhabits downtown Austin is the Mexican free-tailed bat. During the summer, a large colony of these animals lives under the Congress Avenue bridge that crosses Town Lake. When the bats arrive in the spring, they number about 1.5 million individuals. The nightly spectacle of that many animals flying out to feed draws crowds of onlookers. The colony happens to consist of pregnant females and, once they give birth, the number of bats doubles. Needless to say, that many nursing insectivores eat an enormous amount of insect flesh every night.
The list below includes mammals that have definitely been spotted in the garden or who leave their telltale signs of habitation.
