The Key Deer is a subspecies of white tailed deer. These tiny deer are only found on a few islands in the Florida Keys. It is the smallest race of North American Deer. Scientists believe white tailed deer migrated to the Keys during the last ice age, when the glaciers were a continuous ridge of land. The glaciers receded and became islands and the deer became isolated from the mainland and evolved to be smaller in order to adapt to limited resources. They are approximately 25-30 inches at the shoulder. Males weigh 55-75 lbs and females weigh 45-65 lbs.

They primarily feed on red Mangrove, but are also known to eat at least 60 other species of plants. They can drink brackish water, but they must have a supply of fresh water in order to survive. Two thirds of the Key deer population is found on Big Pine Key and No Name Key, the only two keys with significant permanent fresh water.

Key deer have a naturally low reproduction rate. Breeding occurs all year. The average adult doe gives birth to 1.08 fawn per year. The fawns weigh 2-4 lb. at birth.

The Key deer is an endangered species. In 1955, there were only about 50 Key deer left. This was probably due to uncontrolled hunting and habitat destruction. A study completed in 2000 showed an estimated population of 700-800 Key deer.

Key deer are sometimes killed by free roaming dogs. Their small size makes them especially vulnerable to attacks. Rigorous control of free roaming dogs is essential to the survival of Key deer. Mosquito ditches are also a danger. Mosquito ditches are man made ditches containing gambusia, a fish that feeds on mosquitoes. While this may be beneficial to humans, they are often lethal to the deer. Key deer, especially, the young, sometimes fall into these ditches and drown.

Feeding of Key deer by humans causes many problems. The deer often lose their natural fear of humans, making them susceptible to poachers. Consumption of foods that are not a part of their natural diet can have adverse effects on their natural behavior and appearance. Deer often gather in large numbers near public feeding areas, making them more susceptible to contagious diseases and fighting. Gathering near places populated by humans makes them vulnerable to human related accidents. Illegal roadside feeding contributes to roadkills. Motor vehicles present a significant threat to the Key deer, with road kills accounting for up 70 percent of annual mortality.. Motor vehicles kill an average of 45 deer annually. Cessation of all roadside feeding and underpasses to allow deer to cross roads safely could greatly reduce this number, as could reduction of speed limits in certain areas.