As they do every Fall, monarch butterflies (Danaus plexippus) continue to arrive on the coastline of California to spend the winter. They have come from throughout western North America, but the majority come from the foothills and lower elevations of the Sierra Nevada. This year, as in years past, I start to see them leisurely migrating as singles through the Central Valley beginning in August. Enroute and especially once they get to the coast, they feed greedily on the nectar from the flowers of Pride of Madeira (Echium candicum) and mule fat (Baccharis salicifolia). I have seen adults whose abdomens are so fat that you wonder how they are able to fly, but the internal food supply will help them survive the winter.
With the shortening day length, the monarchs form Temporary Bivuoacs, sites where the monarchs form clusters of individuals on the branches of the trees. The butterflies continuously stream in and out of the Temporary Bivuoacs and these sites persist because of the constant immigration of animals; Temporary Bivuoacs usually have a good source of nectar. When the air temperature drops, the movement of the monarchs stops, and the sites where they spend the cold months of the year are known as Wintering Colonies. Interestingly, during mild winters or in southern California, Temporary Bivuoacs may persist through the entire winter. The only way to accurately determine if a site is a Temporary Bivuoac or a Wintering Colony is to mark individual butterflies to see if there is any movement of the animals.
In late January into February, the monarchs leave the sites; some stay around the general area, but the majority head into the coast range, especially the areas located in western Kern and San Luis Obispo counties, or into the foothills of the Sierra Nevada.
Another observation - efforts to conserve California monarchs that focus solely on protecting the Temporary Bivuoacs and Wintering Colonies are doomed to failure. The conservation of the spring and summering grounds in the foothills and lower elevation of the Sierra Nevada is critical. In the past twenty years, there has been a burst of ranchettes and development in these areas. Some of the most favored areas for the residential development, and agriculture, especially vineyards, may be best places for milkweed, the foodplant of the monarch.
There are three rare insects that could be living in coastal San Mateo County in northern California - the endangered Ohlone tiger beetle (Cicindela ohlone), endangered Myrtle's silvespot butterfly (Speyeria zerene myrtleae), and the alledgedly extinct Strohbeen's parnassius butterfly (Parnassius clodius strohbeeni).
The Ohlone tiger beetle is only known from a handful of native grasslands to the south in Santa Cruz County, but the coastal grasslands south of Pacifica to Ano Nuevo State Reserve have not been surveyed for the animal, or Myrtle's silverspot butterfly, for that matter. Myrtle's was last seen in San Mateo County back in the 1950s, but few collectors have looked for it there, most going p to Marin County to get specimens. Stohbeen's parnassius - last seen in 1958 - an another extinct animal that may rise from the dead (like the "extinct" Palos Verdes blue butterfly) - that an intrepid and observant biologist may find in an isolated coastal canyon in San Mateo County. Look for it near bleeding heart (Dicentra formosa), the hostplant of the caterpillar. Butterfly collectors, bird watchers, and others have a habit of going where they know their prey is found; few trailblaze into new areas. In fact, there was a scientific paper published in the 1990s that described how most rare plant records are found within a few miles, if that far, of roads, because some biologists evidently don't walk very far from their cars.
Coastal grasslands are a beautiful and vanishing habitat in California. Richard Minich did a fantastic job of reconstructing the pre-European vegetational communites in the Golden State in his book California's fading wildflowers Los Legacy and Biological Invasions. One of my treasured possessions is the San Franciso Wild in the City, a poster that maps the vegetation of the San Francisco pennisula prior to 1750.
Yesterday, the Federal Register published a notice on the petition to list the Sacramento Valley tiger beetle (Cicindela hirticollis abrupta) as an endangered specis under the Endangered Species Act. This insect was found only in the northern Central Valley of California. The petition was denied because intensive surveys for the animal failed to located any extant populations. The species probably became extinct in the late 1980s or early 1990s when water flows from the Oroville Dam on the Feather River flooded the last remaining population.
I work in the wildlife protection field. Mainly endangered species. My favorite endangered species are the California tiger salamander, Queen Alexandre's birdwing butterfly and the Ohlone tiger beetle.