Mammals are animals that are born with fur or hair. Mammals produce live young which they nourish with milk. They are warm-blooded and have the most highly developed nervous system of all the animals. A mammal usually has four limbs and a four-chambered heart. The largest mammal is the blue whale at 100 feet in length. The smallest mammals are shrews, mice, and bats. Many are less than two inches long, excluding the tail length. Click on the name of the animal below to see a picture of its tracks and some natural history information about it. I have also included some personal notes about each species. The species below are primarily those that can be found in northern California and the west. Some of them are found throughout the U. S. As I do more research, I will add species that are found in other areas. Keep checking this page for updates.