By PATRICIA SIMPSON
For a long time, the only squirrels found at Mission Trails Regional Park were California ground squirrels (Otospermophilus beecheyi). But in 2016, an iNaturalist user photographed a fox squirrel (Sciurus niger) on a trail west of Kumeyaay Lake. No one reported another fox squirrel in the park on iNat until April 2019 and since then, seven more observations have been posted, including one by skylukr (bit.ly/2uhjARI). This new population of non-native critters seems to be confined to an urban border of the park, just east of Kwaay Paay Peak Trail (off of Father Junipero Serra Trail).
The fox squirrel is a tree squirrel and as the name indicates, it excels at living among trees, where it nests in empty cavities and forages. It is grey and orange in color and sports a bushy tail that often perks up and lines its back to form an “S” shape. In contrast, the California ground squirrel holds its tail directly behind the body, usually on the ground or sometimes hanging straight down if the animal is perched. The ground squirrel is also stockier and more muted in color and its eyes are lined with a distinct white ring.
According to the San Diego Natural History Museum, fox squirrels might have been introduced to the Los Angeles Area around 1904 from Tennessee or the Mississippi Valley. They have been expanding their territory ever since. In San Diego, there has been a well-established population in Balboa Park for many years (since 1929 according to most sources), but in the last few years, more and more fox squirrels have been reported in other parts of the county.
The impact of fox squirrels on the native squirrel population in San Diego has not been studied. It is probable that the impact on California ground squirrels is minimal as the two species have different habitat and nesting preferences. However, as the fox squirrel population moves east toward San Diego’s mountains, the Western gray squirrel (Sciurus griseus) species may be affected. Both Western gray and fox squirrels are tree squirrels and would most definitely compete for habitat and food, according to a study by Los Angeles County Fish and Wildlife.
To help scientists better understand the current distribution of squirrels in San Diego County, please take photos of them, post on iNaturalist.org and join the Southern California Squirrel Survey at bit.ly/3bmU4ez.
— Patricia Simpson is a trail guide at Mission Trails Regional Park.