The San Diego Natural History Museum is closely collaborating with MVZ to resurvey as many sites as possible statewide (learn more about the Grinnell Resurvey Project). This resurvey effort first kicked off in 2003 with resurvey of Yosemite National Park, and grew to include a multi-year resurvey of other areas of California, including the San Jacinto Mountains.

Through a collaborative NSF grant in 2015, we extended our resurvey work to 32 sites in the Mojave Desert region, mostly in Joshua Tree National Park and Mojave National Park, and primarily focused on small mammals but with some supplemental bird resurveys at springs. MVZ collaborators concurrently resurveyed small mammals at Death Valley National Park, and had completed the Mojave Desert bird resurvey effort earlier (Iknayan and Beissinger 2018).

Our resurvey work is already producing significant results and publications. Highlights so far include notable range extensions or increases for the Zone-tailed Hawk, Rufous-crowned Sparrow, and Baja Pocket Mouse, and declines in the chipmunks and several woodland birds in Joshua Tree National Park.

Through ecophysiology modeling, our collaborators at UC Berkeley showed that the rodent community was relatively stable but the bird community collapsed over the last century of climate change in the Mojave Desert. Small mammals were able to reduce their exposure, mostly by staying underground during the day, while birds had much higher cooling costs, and tended to disappear from sites that both warmed and dried. Learn more about the study here, which was published in the February 5, 2021 issue of Science.

Complementary to large-scale analysis across species and sites, the Museum is also providing interpretation of faunal changes within a natural history context through detailed species accounts that draw heavily from historic field notes and photos. These will be published for each region, and consider observational changes at a finer scale, site by site, and species by species.

We are also making use of other regional studies and data for a complete picture of range shifts. Although our resurveys show many northward or upslope range shifts as expected from climate warming, we identified 52 nesting bird species whose southern California ranges have expanded southward or downslope over the past century (learn more). However, of the seven mammal species reaching southern range limits in our study areas, three have undergone major northward retractions (Tremor et al. 2019). The southernmost populations of the chisel-toothed kangaroo rat (Dipodomys microps), in Joshua Tree National Park, and of the lodgepole chipmunk (Tamias speciosus) and Humboldt's flying squirrel (Glaucomys oregonensis), in the San Jacinto Mountains, are now extirpated. The Baja pocket mouse (Chaetodipus rudinoris), previously known to range north only to extreme southeastern California, has now spread north into Joshua Tree. Data from other collections suggest the spread had begun by the 1970s.

Despite the general collapse of the bird community in the Mojave Desert, our resurveys have also revealed small but notable range expansions and/or increases in Mojave National Park of the Zone-tailed Hawk (Buteo albonotatus), Gilded Flicker (Colaptes chrysoides), Black-tailed Gnatcatcher (Polioptila melanura), Crissal Thrasher (Toxostoma crissale), and Rufous-crowned Sparrow (Aimophila ruficeps). However, in Joshua Tree NP, declines were more frequent, primarily in shrub and woodland species, including nine of birds plus the chipmunk Tamias obscurus. These changes appear correlated with increased cover of grass, shrubs, cacti, and Joshua trees in Mojave National Park, and with a decrease in pinyon-juniper woodland in Joshua Tree National Park. A spread of the California Towhee east into Joshua Tree National Park represents the single counterexample in that area.

Photo credits above | (Left) Chipping Sparrow (Spizella passerina), Santa Rosa Mountain. (Right) Desert Pocket Mouse (Chaetodipus penicillatus), Joshua Tree National Park. Photos by Jack Daynes.