BUTTERFLIES OF THE KERN RIVER VALLEY

by Dan Cooper

One hundred thirty five (UPDATE: 138 through Feb, 2002, BB) butterfly species have been collected in the peaks, canyons, and valleys in and around the Kern Valley, representing more than half the species known from California. Because butterflies are strongly tied to specific vegetation communities, the variety and proximity of the habitats in and around the Kern Valley allows a wide variety of butterflies to coexist within a small area. Additionally, the isolated mountain ranges surrounding the Kern Valley represent an integration zone between Sierran and Southern California montane butterflies.

Mirroring the distribution of native vegetation in California, the current variety of butterflies has evolved from two distinct groups, each tied to an ancient floristic province from the Tertiary Era (until about 2 million years before present). The Holarctic group, which featured taxa that extended from temperate North America to Europe and Asia via the Bering Strait landbridge, dominates most of the montane butterflies of our local mountains. One, the Clodius Parnassian (Parnassius clodius baldur), found on exposed ridges high in the Greenhorn Mountains north to Yosemite, is among the more sought-after species by local butterfly enthusiasts due to its strict habitat preferences and short flying time in early summer. Other Holartic groups include coppers and ringlets, distinctive members of montane and alpine insect fauna in the mountains of the western U.S.

A second group of butterflies, the Sonoran assemblage, originated in the subtropical floristic province that developed in northwestern Mexico and the American Southwest. Many of the chaparral and dry woodland plants of California may be traced to this ancient floristic province. Members of the skipper family (Hesperidae), which includes dozens of confusing orange-and-brown look-alikes, are Sonoran, as are the metalmarks (Riodinidae).

When the Sierra Nevada and the mountains surrounding the Los Angeles Basin appeared a couple million years ago in the Pliocene, evolution of the modern butterfly flora of California began in earnest.  Solid geological barriers (as opposed to shifting climatic barriers) began to separate organisms into the discrete "bioregions" that remain today.  The Kern River Valley itself, which separates the contiguous Sierra Nevada from the mountains to the south, has hindered genetic exchange of montane butterflies, which has resulted in substantial differences in the butterfly taxa of the mountains north and south of the valley.  Nearly 30 species occur in the southern Sierras that are absent from the Greenhorn Mountains immediately to the southwest. 

Working opposite ecological barriers, the low passes through the mountains east and west of the Kern Valley have allowed flora from outside its borders to persist here, providing channels for butterfly species to enter areas.  At on time, a Central Valley flora probably extended up the lower Kern Canyon to Weldon. Riparian species such as the boldly-colored Lorquin's Admiral (Liminitis l. lorquini) and the jagged-edged Satyr Anglewing (Polygonia satyrus neosatyrus) occur in the valley riparian forest along the South Fork Kern River as outposts from lowland populations west of the valley.  Similarly, the Mojave Desert and Great Basin ecosystems periodically invaded the Kern Valley (and, to an extent, the Central Valley), which has resulted in several desert butterfly species occurring here, including the Eunus Skipper (Psuedocopaeodes eunus), a highly localized species whose larvae require the desert salt grass of the valley's alkali meadows.

Finally, the biology of butterflies themselves also accounts for their high diversity.   Unlike birds, butterfly diversity shows considerable variation within habitats due to feeding preferences of both the larval and adult stages.  Nectaring adults of a butterfly species are often restricted to certain plant genera or to a few genera with a family, as well as being tied to a particular habitat type.  Caterpillars of butterfly species are often restricted to a single species of plant.  Thus, the region's high level of floral diversity within the numerous habitats has enabled the coexistence of so many non-overlapping butterfly taxa.

Not surprisingly, the Kern Valley area is one of the  most exciting places to study butterflies in the state.  Twenty years ago, lepidopterists Thomas and John Emmel named the Piute Mountains one of the five locales with the greatest potential to hold new butterfly records for Southern California, based on their position between the Sierras and the Transverse Range.  Today the Piutes are just as little-studied as back then, so who knows which of their quiet meadows or canyons is harboring California's next new butterfly?

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