Migrating Tortoiseshells

California Tortoiseshell

In August while climbing Mount Lassen (Lassen Volcanic National Park CA) Leonard and I were surrounded by literally thousands of California tortoiseshells (Nymphalis californica). The butterflies were hitting us, landing on us, covering the snow and talus  and filling the sky. What a magical experience!! For a couple weeks in late summer millions of California tortoiseshells migrate over Mount Lassen. Leonard and I were fortunate to accidentally have chosen a day to summit when the spectacle was occurring.

I could not find any definitive explanation for this phenomenon. However, California tortoiseshells that overwinter as adults in California’s Central Valley and Inner Coast Range have an early generation in place. This early generation seasonally moves north and east upslope to the higher elevations of the Klamaths, Sierra Nevada and Cascades. There they have another generation whose larvae (caterpillars) feast on the abundant Ceanothus species. In the late summer and early fall this generation returns downslope to their winter home. Depending on weather conditions and food supply, the returning tortoiseshells are often part of a population explosion. On their return the butterflies ride warm currents up and over the young volcanic crater. I like this reason best.

Common ravens (Corvus corax) are the most frequent predators on the California tortoiseshells migrating over Lassen Peak. Leonard and I saw many of these corvids noisily cawing while feasting on the butterflies that landed on the snow and rocks.

Many of the migrating butterflies displayed tattered wings and looked worse for wear –¬† such as this specimen. I am not posting any other photographs because I just could not adequately capture the numbers of tortoiseshells surrounding us. The pictures are black blurs against the background.

More information on California tortoiseshell butterflies can be found in my previous post: “California Tortoiseshell” on 07-29-16.

Leonard and I were so happy to see this spectacle.

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Antelope Ground Squirrel

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Antelope ground squirrels (Ammospermophilus leucurus) are hyperactive. They never stop moving! While exploring Grimes Point Archeological Site along Nevada Highway 50 east of Fallon NV, Leonard and I came upon this cute little guy (gal?). We sat down and it … Continue reading

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Great Basin Bristlecone

This gallery contains 9 photos.

Leonard and I just returned from a week exploring Great Basin National Park and other historical, geological and botanical sites along Nevada Highway 50. For me, one of the highlights of the trip was hiking to the Great Basin Bristlecone … Continue reading

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This gallery contains 9 photos.

According to the literature, chicory (Cichorium intybus) flower heads are blue, rarely white. In June, Leonard and I discovered blue, white and distinctly pink chicory flower heads between the North and South Elkins Barns at Ash Creek Wildlife Area near … Continue reading

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Knobcone Pine

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Knobcone pines (Pinus attenuata) are rather short-lived with a life-span averaging about 60 years. A small tree, this native species varies in form and size depending whether it grows in an exposed or sheltered area. In extremely poor sites it … Continue reading

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Gray Dagger Moth Caterpillar

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While walking through an alder thicket on the Paradise Meadow Trail at Lassen Volcanic National Park (California), I noticed a caterpillar gorging itself on alder leaves. I took a couple photographs hoping to identify the caterpillar. Not being an entomologist … Continue reading

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Mountain Sorrel

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Mountain sorrel (Oxyria digyna) is an important circumpolar and circumboreal plant. Caribou, geese and musk oxen eat its leaves while lemmings, voles and Arctic hares prefer the roots for nourishment. The leaves, high in Vitamin C, were used by the … Continue reading

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