By Paul Carter – July 2020
In June 2020 I took three one-night trips to the Big Bear Lake area in the San Bernardino Mountains east of Los Angeles; spending about 3 hours each night looking for Humboldt’s Flying Squirrel (Glaucomys oregonensis), seen on the Castle Rock Trail. The trip list of 15+ mammals included a Black Bear with three cubs seen on Skyline Drive.
I spent most of my first trip (June 10) on the northern side of Big Bear Lake; Charles Hood joined me for the second night (June 16) and we focused on Skyline Drive on the south side of the lake, without flying squirrel. On my third trip (June 29) Charles was in Big Bear Lake at a cabin with his wife, but once I sent a text saying I had found a flying squirrel he headed my way.
About 400 m up the Castle Rock trail there are two benches and I was there at dusk to record bats and then search for flying squirrel. At 8.40 pm (40 minutes after sunset) I photographed a flying squirrel in a tree about 20 m northeast of the benches; having found it with a thermal scope. It appeared quite soon after sunset suggesting that it might have been nesting in that tree or one close by; and stayed about 25 minutes, feeding on the mid-level branches of the one tree. It had left by the time Charles arrived, but he had fortunately scoped one on his walk up (about 150m northwest of my sighting).
Dates and Areas Visited
June 10: Castle Rock trail (day), Road 3N16, Delamar Mountains Road (night).
June 11: Hanna Flat area, Wildhorse Meadows Rd (rough in parts).
June 16: Town Trail and Skyline Drive (eastern section at night).
June 17: Skyline Drive (2N10) and 2N11 to Mill Creek.
June 29: Forest Ranger Rd, Castle Rock Trail (dusk and night).
June 30: Forest Ranger Rd.
Castle Rock Trailhead and the “Two Benches” point (34.234270° -116.959250°) are shown on the Google Earth base map below.
Logistics
A day/annual National Forest Adventure Pass is needed in many areas; I bought a one-year pass ($30) at the Valero depot shop between Running Springs and Arrowbear Lake on Road CA-18 up to Big Bear lake; day passes are $5/day.
Mammal Trip List: 2020 June
- Black-tailed Jackrabbit (Lepus californicus)
- California Ground Squirrel (Otospermophilus beecheyi)
- Golden-mantled Ground Squirrel (Callospermophilus lateralis)
- Western Gray Squirrel (Sciurus griseus)
- Humboldt’s Flying Squirrel (Glaucomys oregonensis)
- Lodgepole Chipmunk (Neotamias speciosus)
- Merriam’s Chipmunk (Neotamias merriami)
- Large-eared Woodrat (Neotoma macrotis)
- Pinon or North American Deer Mouse (Peromyscus sp)
- Mule Deer (Odocoileus hemionus)
- Black Bear (Ursus americanus)*
- Big Brown Bat (Eptesicus fuscus)**
- Little Brown Myotis (Myotis lucifugus)**
- California Myotis (Myotis californicus)**
- Western Red Bat (Lasiurus blossevillii)**
* Black Bear were introduced to the mountains in the 1930’s (Landis, 2019).
** All the bat ID s above were based on Echo Meter Touch 2 Pro recordings; records of Pallid Bat seemed to refer to the Big Brown Bat (the device was alternating between the two species for what I think was the same bat) and are excluded.
Images
Lodgepole Chipmunk (Neotamias speciosus) at Big Bear Lake with distinct white outer stripe
Notes on Humboldt’s Flying Squirrel in the San Bernardino Mountains
The split of Glaucomys oregonensis from Glaucomys sabrinus is described by Arbogast et al (2017). They noted that the 2 populations from San Bernardino and Plumas counties “possess unique genetic variation that could be an important component of the overall genetic variation of the newly recognized species, G. oregonensis”.
The San Bernardino mountains mark the most southern extreme of the current range of Humboldt’s Flying Squirrel. The subspecies here is Glaucomys oregonensis californicus (Southern California Flying Squirrel or San Bernardino Flying Squirrel). They are thought to be extinct in the Mount San Jacinto range (south of San Bernardino Mountain); last seen in the 1990s.
The “Flying Squirrels of South California” project website set up by San Diego Natural History Museum (in collaboration with the U.S. Forest Service and the U.S. Fish & Wildlife Service) includes a map showing survey results; owl pellet evidence; citizen science records; and some iNaturalist records. The map indicates that the squirrels are widespread across the mountains, with numerous records from camera traps and bird feeder visits in suburban areas e.g. at Big Bear Lake. I did not come across reports or photos from mammal-watching type visits. Cameras placed on bald eagle nests show flying squirrels as frequent visitors e.g. 13 Dec 2019 and 29 March 2020. The “Flying Squirrels of South California” website showed a record of flying squirrel at an eagle nest about 350 m to the east of Castle Rock Trail and there are other records in the woods 1 – 2 km to the west.
References
Arbogast BS, Schumacher KI, Kerhoulas NJ, Bidlack AL, Cook JA, Kenagy GJ (2017). Genetic data reveal a cryptic species of New World flying squirrel: Glaucomys oregonensis. Journal of Mammalogy 98(4):1027–1041. https://doi.org/10.1093/jmammal/gyx055.
Landis M (2019). Those black bears you see in Southern California, this is how they arrived. The Sun. 2019 Jan 7.
Reid F (2006). Peterson Field Guide to Mammals of North America: Fourth Edition (Peterson Field Guides).
San Diego Natural History Museum. The “Flying Squirrels of South California” project website (http://flyingsquirrels.sdnhm.org/). Viewed June 2020.