Cabrillo National Monument and the Point Loma Peninsula are home to several species of mammals. Gray foxes are commonly seen in the park, especially near closing time – they seem to know when it’s time for visitors to go home and they can regain the park for their nocturnal wanderings. Raccoons make their way around Cabrillo at night as well, and are efficient predators: they prey both on terrestrial and intertidal organisms. Coyotes are rarely seen here, preferring the northern end of Point Loma.
Cottontails and squirrels are frequently seen throughout the year, and their populations spike after particularly rainy winters: the abundance of grasses makes for easy foraging.
A few bat species are found in the Point Loma area, including the Mexican long-tongued bat. Many bats rely on sonar to navigate and hunt in the dark; the small populations of bats on Point Loma may be due to signals from Navy research facilities that interfere with the bats’ ability to use sonar in areas where those signals are transmitted.
Seldom seen, the voracious desert shrew has adapted to the dry slopes of Point Loma. Pocket mice are common, and are most abundant during the summer months. The California mouse is the largest white-footed mouse in the country and is so big that it is often mistaken for a small woodrat.
Coastal Sage Scrub Spotlight: The Desert Shrew
Contributed by former Cabrillo National Monument Biological Technician Tiffany Duffield
The coastal sage scrub habitat houses many creatures that thrive in its Mediterranean climate characterized by dry, warm summers and cool, damp winters. The structure of the scrub provides shade to these creatures, protecting them from overheating and providing cover which keeps them out of view from predators. During our herpetology surveys, we find many types of organisms utilizing the brush and soil in the coastal sage environment. A few include striped racer snakes, rattlesnakes, alligator lizards, side-blotched lizards, salamanders, mice, desert shrews, and many terrestrial arthropods. One of these organisms, the desert shrew (Notiosorex crawfordi), is often found in our herpetology traps, yet when people hear we have shrews, they are often surprised. At first glance one would think the desert shrew is a gentle and timid creature. However, the shrew’s metabolism forces it to be a vicious predator.
The desert shrew is a small mammal similar to a mouse, but much smaller in size. They have dark gray fur on top and pale gray fur underneath. A few characteristics to note when identifying a shrew rather than a mouse are the size, snout length, and eye size. The size of the shrew is much smaller than a mouse. The average length of the desert shrew (including its tail) is 3.5 inches, and its tail is only about 1/3 of its total size. The shrew also has a more pronounced pointed snout than a mouse. This aids them in foraging; you can observe the shrew twitching it’s snout and following its nose to a nearby meal. The eyes of a shrew are beady, whereas a mouse has larger eyes. The shrew’s eyes are so small they look the size of a pin head. Though small, the beady eyes also help in locating food; in fact it has been found that the eyes are more accurate in searching for food than the nose is. Using both its eyes and nose, the shrew forages day and night because it has a very high metabolism. It is estimated that the shrew must eat every few hours in order to survive.
The desert shrew is an insectivore and has a vast selection of food within the coastal sage scrub of CabrilloNational Monument. A typical entrée might include crickets, cockroaches, flies, grasshoppers, moths, beetles, earwigs, and centipedes. As mentioned earlier, the shrew must eat every few hours to ensure survival. This means the shrew may resort to cannibalism to keep up its metabolism. If the shrew is searching for its next meal and then stumbles upon a carcass of a bird, lizard, or another small mammal (including another shrew), it will consume that to hold it over for another few hours. It is estimated that the shrew eats 75% of its body weight each day.
In addition to cannibalism giving the shrew a bad reputation, its manners while eating are not exactly what we would call “polite.” Shrews are known to immobilize their prey by first eating the legs and then moving onto the core of the meal. Thus the shrew’s reputation of a vicious predator.
Although the shrew may seem like an atrocious animal roaming the coastal sage scrub, it is just one of the creatures that helps keep all elements of the ecosystem in balance. The only known predators of the shrew are owls. Though there is the possibility of snakes eating shrews, as snakes do eat other small mammals and lizards. The shrew also utilizes the vegetation to build its nest; some components that have been found in shrew nests are leaf litter, twigs, grasses, dried vegetation, and even cacti spines. It is obvious that although some organisms, such as the desert shrew, may appear fierce in their habits, they are simply ensuring their survival and helping to keep the ecosystem in balance.