California Ground Squirrel (Otospermophilus beecheyi) This is the most common mammal in the Reserve and can be seen feeding near the mouth of its burrows. It is diurnal and leaves well-marked trails where it lives. It can be seen both in the upland and lowland areas, but prefers dry rocky soil to live in. It is considered a pest by many, but its ringing call is very distinctive and they are very pleasant animals to watch as they industriously raise their families and sun themselves on the rocks.
Valley Pocket Gopher (Thomomys bottae) Gophers are very common but will seldom be seen above the ground. They do spend a lot more time above ground than most people think and can occasionally be seen cautiously moving from one area to another with their tiny eyes and small ears testing each movement and sound of the environment. Most of the time they stay underground eating roots and occasionally you can see a blade quiver and suddenly disappear directly into the ground before your eyes. The burrows are quite extensive and can be interconnected for a distance of 50 feet. They dig to the surface of the ground in the excavations and then refill the hole with the soil, Although they are the scourge of many gardeners, they are part of the ecosystem.
Pocket Mice (Perognathus) There are two species of Pocket Mice, the California Pocket Mouse (P. californicus) and the San Diego Pocket Mouse (P. fallax), both of which are found in the Reserve. The California Pocket Mouse lives in more brushy areas than the San Diego Pocket Mouse which is more adapted to a drier environment. Both are named because of the fur-lined pouches which they fill with seeds and take back to the burrows to be stored and eaten later. They are mouse-sized animals with long tails and a tuft of hair on the end.
Pacific Kangaroo Rat (Dipodomys agilis) The kangaroo rats are remarkable animals which can live without any surface water. They manufacture their own or extract it from the food that they eat. They live underground and close the entrance to their burrows in the daytime so they can maintain adequate moisture and heat control in their burrow system. The total length, including the long tail, is about 12 inches and when seen at night, they are hopping around with their elongated hind legs and long tail with a large tuft of hair on the end dragging on the ground. When excited they can leap straight into the air and land two or three feet from where they started. They are very gentle creatures and spend their active hours filling their cheek pouches with seeds and trying to avoid predators.
Western Harvest Mouse (Reithrodontomys megalotis) These nocturnal mice can be found in the lowland areas and are one of the few rodents that are active on moonlit nights. They are well adapted to living in the coastal marsh area since they can drink sea water and excrete the salt. Pregnant females can be seen every month of the year and raise a family in small round nests built of grass leaves that are above the ground. They line the inside of the nest with fur and raise from four to six young.
Deer Mice (Peromyscus ) There are three species of deer mice that live in the area: the California Mouse (P. califomicus) which is a rather large mouse about 10 inches in length with very large prominent ears; the Deer Mouse (P. maninclatus), which is a smaller mouse, about 7 inches long and can be distinguished from the others because its tail is shorter than the body length. The Cactus Mouse (P. eremicus) is about 8 inches long and inhabits the drier parts of the Reserve. The population of these mice is usually very dense, and they serve as a very basic food supply for many of the carnivores which live in the area. All are nocturnal and feed on larvae and pupae of insects as well as seeds and plant material. Some species breed in the fall, others breed all year round, but all produce litters numbering from 3 to 6 young with a gestation period of 22 to 25 days.
Grasshopper Mouse (Onychomys torridus) These are rather small mice which can be distinguished from the deer mice by the fact that the tail is less than 70 percent of the body length. They live in grassy areas and are fond of feeding on insects and other arthropods that live in the grass. They are one of the most vocal of the rodents and can sometimes be heard squeaking in the grass, giving their alarm call or possibly fighting each other. They breed all year round and raise a family at the end of a short underground burrow. They are a very beneficial mouse within a very important part of the ecosystem because they feed on the arthropods which, if uncontrolled, could do a considerable amount of damage to the plant life.
California Meadow Mouse (Micrstus californicus) This common mouse lives in a well-defined series of burrows and is one of the few rodents that are active during the daytime. They prefer to live in meadows and grassy environments. They have very small ears and short tails and give the general appearance of being somewhat near-sighted when they are looking at you from the safety of their burrow.
House Mouse (Mus musculus) The ubiquitous house mouse will be found wherever people are. It can be identified by its solid gray-brown color, and the hairs on the tail are so scarce that the tail has a scaly appearance. It will be found near the office and any other human habitation.
Common Rat (Rattus rattus) This is another animal that lives wherever people are. It too has a scaly tail with few hairs. It will be seen wherever people are because it has lived with them for generations.
Wood Rat (Neotoma) There are two species of wood rats that live in the Reserve: the Dusky-footed Wood Rat (N. fuscipes) and the Desert Wood Rat (N. lepida). Both these species build a rather complex nest, the dusky-footed wood rat with small sticks and the desert wood rat using pieces of cholla or beaver-tail cactus. The nests of the former can reach an amazing size of 3 to 4 feet high by 5 or 6 feet long. The desert wood rat is slightly smaller than the dusky-footed wood rat and has a tail about three-quarters the length of the head and body. The dusky-footed wood rat has a tail the same length as the head and body. They are primarily herbivores and breed in the springtime. The young stay attached to the teats of the mother while she is in the nest and if disturbed she will leave the nest and scurry away with the young family attached to her.