Terrestrial Mammals at CNM

Medium-Sized Mammals:

Typically the most activity occurs at night (with the exception of Audubon’s cottontail), which is why most of the following images are captured by motion-triggered cameras.

Grey Fox (NPS photo):

The gray fox (Urocyon cinereoargenteus californicus) is a small, omnivorous canid that feeds mostly on cottontail rabbits as well as birds and berries. Gray foxes have short legs compared to other foxes, which make them more adept at climbing trees.



Once a common sighting in the Point Loma peninsula, the coyote (Canis latrans) has been absent for the last decade at Cabrillo National Monument. Similar to a German shepherd in looks, though much smaller, the coyote will feed on rabbits, small mammals, birds, and reptiles – it will eat just about anything it can catch. Coyotes do very well near humans, scavenging landfills and garbage cans for morsels.


Common Raccoon (NPS photo):

Raccoons (Procyon lotor psora) are abundant at Cabrillo National Monument. Like coyotes, raccoons are very opportunistic scavengers, and will eat almost anything – their diet is made up of invertebrates, plant materials, and small vertebrates like lizards and mice. Raccoons at Cabrillo National Monument also forage in the tidepools for marine invertebrates.


Virginia Opossum (NPS photo): Non-native!

The Virginia opossum (Diadelphis virginianus) is the only marsupial in North America north of Mexico. About as big as a housecat, this species is also opportunistic, successfully living in urban environments by rummaging through trash cans. The opossum is not native to the Western United States, and it is thought that they were introduced during the Great Depression, possibly as a source of food.


Striped Skunk (NPS photo):

The striped skunk (Mephitis mephitis holzneri), an extremely recognizable character by sight and smell, is a common inhabitant of Cabrillo National Monument. Males will have a “harem” of females during mating season, and will defend them from other males that approach. This skunk species primarily feeds on insects, but will also eat lizards, mice, and bird eggs when readily available. Skunks do not have many predators, as their defense is an excellent repellent.


Feral Cat (NPS photo): Non-native!

It is not known how cats were introduced to Cabrillo. Whether these are free-roaming cats that have large territories, or completely feral, one thing we know: they are destructive to the natural environment and the animals that struggle to live in it. Cats can introduce diseases that our wildlife populations are unable to handle. Cats are known predators, and in addition to killing for food, cats will kill animals for the “sport” of it. This unfortunately includes native lizards, small mammals, and birds. Please think twice before letting your cat outside, let alone releasing it into the wild. Many cats that are released into the wild don’t do so well – they can get in fights with other native mammals, such as raccoons, or they could be bitten by a rattlesnake. There are many rescue groups that will find a cat a good home and give it the loving care it needs.


Small Mammals:

Audubon’s Cottontail (photo Warren Tam VIP):

Part of the lagomorph order that includes rabbits, hares, and pikas. A small rabbit with a short, white tail, the Audubon’s cottontail (Sylvilagus audubonii) is a favorite food item for every large predator. At Cabrillo, the cottontail’s predators include snakes, foxes, and raptors.


Crawford’s Grey Shrew (photo Warren Tam VIP):

The shrew is actually an insectivore, not a rodent – so it is not at all related to a mouse. Actually, shrews are more closely related to hedgehogs than they are mice. You may have heard that some species of shrews are venomous. This particular species is not. They spend much of their time underground or hunting at night, and they have poor vision, so shrews have an excellent sense of smell, and like bats, can echolocate to get around and find prey.

This species is one of the smallest desert mammals, at birth being about the same size as a honeybee. A baby will reach adult size after about four weeks, when it will be about 2 inches long – which includes its tail.

These critters are extremely voracious eaters, needing to consume about 75% of their body weight every day due to their high metabolism. They will eat a variety of invertebrates, lizards, and small mice.


Rodents: The rodent family, which includes many species from rats and mice to porcupines, is generally characterized as having upper and lower incisors that grow continuously and usually have a yellow to orange enamel. The name rodent comes from the Latin word “rodere,” which means “to gnaw.” Many of the mice species are tough to differentiate until they are “in hand” and measured, which is why some of the animals are pictured being handled by experienced biologists.

California Ground Squirrel (photo Patricia Simpson VIP):

The most commonly seen terrestrial mammal at Cabrillo National Monument, the California ground squirrel has a grey-brown pelage with a long, fluffy tail. Interestingly, this squirrel has co-evolved with rattlesnakes, exhibiting behaviors such as tail flagging. Squirrels that flag their tail while in proximity of a rattlesnake are much less likely to be attacked than those that do not. Tail flagging lets the rattlesnake know that their presence is known, and also alarms other squirrels in the area. Squirrels have also been observed chewing rattlesnake skin sheds, presumably to camouflage their scent to their predators. For more information about this research, check out the work by Rulon Clark of SDSU: http://www.bio.sdsu.edu/pub/clark/Site_3/Project_Homepage.html


Bryant’s Woodrat (photo Patricia Simpson VIP):

Also known as the San Diego desert woodrat (Neotoma bryanti), this packrat makes a very large mound-shaped nest called a “midden” in vegetation, preferably in agave or cactus stands. These large woodrats are solitary and extremely defensive of their nests and of water sources – including succulent plants like Shaw’s agave, found at Cabrillo National Monument. 


San Diego Pocket Mouse (photo Don Endicott VIP):

The San Diego pocket mouse (Chaetodipus fallax) is closely related to the kangaroo rat – and like the kangaroo rat, can utilize its large hind feet and long tail to burst into a fast gallop to get away from predators. They are “granivores,” and will forage mainly on seeds from plants.


California Vole (NPS photo):

The California vole (Microtus californicus) is characterized by its relatively dark fur and small ears. Their diet is made up of plant material and they tend to favor non-native plants such as wild oats and brome grass (both found at Cabrillo National Monument). Though they are seen as an agricultural pest, they are very beneficial to their environment – like other rodents, the vole’s burrowing habits help aerate soils.


House Mouse (NPS photo): Non-native!

The house mouse (Mus musculus) is named because of its preference for living in association with humans. It is an introduced species originating from Asia. This species is the most common animal used in scientific research. 


California Mouse (photo Melissa Stepek SDNHM):

The California mouse (Peromyscus californicus) is a large mouse that has a very long tail and very large ears. In contrast to most rodent species, the California mouse is generally monogamous.


Northern Baja Deer Mouse (photo Patricia Simpson VIP):

Formerly known as the cactus mouse, the Northern Baja deer mouse (Peromyscus fraterculus) is a small mouse species native to Southern California and the Baja peninsula. This species is very common at Cabrillo National Monument.

Deer Mouse (photo Warren Tam VIP):

The deer mouse (Peromyscus maniculatus) is a species that can carry hantavirus. This species is characterized by its large beady eyes and white feet. Diet includes invertebrates, seeds, fruits, and sometimes fungi. They will typically breed when food is plentiful, rather than in a specific season. 


Western Harvest Mouse (photo Warren Tam VIP):

The western harvest mouse (Reithrodontomys megalotis) is a small mouse native to the western United States, Mexico and British Columbia. Its diet consists of seeds that are stored underground, and insects such as grasshoppers and caterpillars. This is a very common mouse species at Cabrillo National Monument. 


Botta’s Pocket Gopher (photo Warren Tam VIP):

During monthly herpetofauna surveys in March 2017, CABR biologists and wildlife VIPs discovered a cute little furry critter hiding in a cup in a pitfall bucket (a 5-gallon bucket situated in the ground). This was something they had never seen before, and it turns out, had never been caught in the 20+ years of monitoring. Though it is not on the park’s official species list, there are records for the Botta’s pocket gopher (Thomomys bottae) in the San Diego Natural History Museum, where it had been historically observed and recorded on adjacent Navy land in Point Loma.

Why haven’t we seen the Botta’s pocket gopher before? It could be due to the massive rains San Diego has been having this winter, increasing food supplies and thus activity for a variety of wildlife. This particular species is also difficult to capture in pitfall traps because it spends a lot of its life underground.

Botta’s pocket gophers feed strictly on plants, including shoots and grasses, and even bulbs, roots and tubers. Though viewed as a pest in many households, pocket gophers are beneficial to the environment because they can aerate soils up to a depth of almost a foot. They can be found in a variety of soils, including very hard packed clays. Unlike many other types of gophers, these particular gophers can dig with their teeth, which don’t wear down as quickly as claws can.



Biologists with CNM and the San Diego Natural History Museum teamed up to monitor and inventory bat species beginning in 2015; specifically setting up a protocol to record echolocation calls on a seasonal basis as well as looking for any signs of the Mexican long-tongued bat (Choeronycteris mexicana), which is a suspected pollinator of the Shaw’s agave (Agave shawii), a rare plant of management concern.

Bat echolocation calls are recorded on a small device called an Anabat. This device records any ultrasonic call inaudible to the human ear, and saves it into graphical form (Fig 1). Bat species have unique call frequencies and shapes that an experienced bat biologist can then interpret and determine species.

Initial results show that more than triple the amount of calls recorded were in the fall compared to any other season, which may mean that bats are using the peninsula as a migratory stopover in the fall. Although the Mexican long-tongued bat was not detected during these surveys, the first detection of the Yuma myotis (Myotis yumanensis) was recorded, along with nine other species already known to use the peninsula.

Figure 1. Example sonogram of a Mexican free-tailed bat (Tadarida brasiliensis) call. Calls that are slanted are “search phase” calls; more vertical and closer together indicate a “terminal buzz,” signifying that this bat is in pursuit of an insect or in close proximity to some sort of obstacle it needs to navigate. Note that the duration of this particular sonogram is less than one second!


California Myotis (photo Drew Stokes SDNHM):

A very small bat that weighs 3.5 to 5.5 grams, the California myotis (Myotis californicus) can fit in the palm of your hand. It can be found all the way from British Columbia to Guatemala. These bats are most active at sunset when they search for insects near watering areas. This species is common to the San Diego area.


Western Mastiff Bat (NPS photo):

The Western mastiff bat (Eumops perotis) is not only the largest bat in San Diego but in all of North America, with a wingspan of almost 2 feet. Contrary to most other bat species, this bat’s call is at a low enough frequency that it can be heard by the human ear. Mastiff bats enjoy eating insects, especially moths, which make up around 80% of their diet.


Pocketed Free-tailed Bat (NPS photo):

Named for a small fold, or “pocket” in the wing membrane, the pocketed free-tailed bat (Nyctinomops femorosaccus) is a regular visitor to Cabrillo National Monument.


Big Free-tailed Bat (NPS photo):

The big free-tailed bat (Nyctinomops macrotus) is a migratory species that comes through Cabrillo National Monument during the fall and spring. Their range extends from South America to Canada.


Mexican Free-tailed Bat (photo USFWS):

The Mexican free-tailed bat (Tadarida brasiliensis) is the most common species of bat that visits Cabrillo. Around 20 million of these bats emerge from Bracken cave in central Texas where they can show up on a Doppler radar. This bat flies higher than other bats, reaching altitudes of 3300 meters.


Big Brown Bat (photo USGS):

The big brown bat (Eptesicus fuscus) ranges from Alaska to South America. This bat has adapted well to a changing habitat, often roosting in man-made structures.


Western Red Bat:

The Western red bat (Lasiurus blossevillii), named for its distinct reddish coloration, is a solitary species – they do not roost in large groups. Instead, individuals prefer to roost in trees on their own. They will, however, migrate and forage together.


Hoary Bat (photo Paul Cryan USGS):

This species is named “hoary” bat (Lasiurus cinereus) because of the white tips to the hairs on its body. This species particularly likes to hunt for moths.

 Yellow Bat (photo Drew Stokes SDNHM):

This species, named for the color of its fur, can be found in the southwestern United States and in Mexico. Yellow bats (Lasiurus xanthinus) prefer to roost in dead palm fronds.


Western Pipistrelle/Canyon Bat (photo USGS):

Lovingly referred to as “pips” by folks in the bat community, the canyon bat (Parastrellus Hesperus) is the smallest bat species in North America, weighing in at 3-5 grams.


Yuma Myotis:

The Yuma myotis (Myotis yumanensis) is a bat species that is especially dependent on water sources. A keen eye might see these bats foraging over open water. These guys are not picky eaters, and will eat just about any insect that happens to be around.


Last revised 25-Jun-17