Natural History Journal

In days gone by, California's Great Central Valley was crisscrossed by a handful of free-flowing rivers carrying snowmelt from the Sierra Nevada to water fertile grasslands below.  Natural flood plains were regularly inundated with nutrient-rich silt, and wetlands of tule reeds and myriad wildlife flourished.  Today, the rivers persist in a somewhat diminished state, rigidly controlled by upstream reservoirs and dams.  Fruit and nut orchards, vineyards and housing developments have spread across the valley, to the very edges of river bluffs.  The view west, down the Tuolumne River in Stanislaus County. Earlier this year, flooding was a major concern in many areas along the rivers, the water flowing fast and strong.  But last year, like many years, the Tuolumne River was low and fairly calm, allowing for natural explorations of the riverine ecosystem.  Now, in the fall, the river has returned to its placid state.  When the riv...

I am not exactly the biggest snake fanatic you'll ever come across, but I have learned to appreciate the role these legless reptiles play in the wide variety of ecosystems they inhabit.  Several times this year I've crossed paths with Mountain Garter Snakes ( Thamnophis elegans elegans ) while hiking in the Sierra Nevada, and one snake in Tuolumne Meadows was kind enough to pose for a few photos.   The Mountain Garter Snake is a subspecies of the Western Terrestrial Garter Snake, found in the Sierra Nevada mountains.  These snakes have a prominent yellow dorsal stripe, along with a lighter stripe on each side of the body.  They range in length from 18 inches to 43 inches (three and a half feet!) and prefer to inhabit damp areas, retreating beneath vegetation or rocks and logs when threatened.  Other subspecies and species of garter snakes tend to be more aquatic and regularly take to the water.  Garter snakes give birth to live young, ...

Milbert's Tortoiseshell ( Aglais milberti ), a striking and unmistakable Lepidopteran, is typically a butterfly of mountain meadows.  I found this individual "puddling" in a meadow near Lake Tahoe, along with a  Hoary Comma .  Commas and Tortoiseshells are closely related members of the Brush-foot family (Nymphalidae). Many butterflies are attracted to damp soil and engage in a common behavior known as "puddling."  While we typically picture butterflies delicately sipping nectar from flowers, many species obtain their nutrients from a surprising variety of sources, including rotting fruit, sap, dung, carrion and mud.  It is believed that butterflies, especially males, obtain salts and minerals from mud. The brown underside of the wings provides camouflage as these butterflies hibernate during the winter.  Also note the butterfly's extended proboscis (feeding organ) taking in nutrients from the mud.

As temperatures drop and hours of daylight decrease, autumn steals quietly across the Sierra Nevada.  There is no pomp, no great fanfare to accompany the change of seasons, like there is in the east.  Here in the west, the change is more subtle, but perhaps all the sweeter in its humility.  Undoubtedly, the star of the western autumnal show is the Quaking Aspen ( Populus tremuloides ).  All across the mountainous west, stands of delicate aspen trees burst into glorious autumn color: liquid gold and pure sunshiny yellows are most common, but under the right conditions, leaves become brilliant shades of flame orange, salmon pink and even vivid crimson.  Each heart-shaped leaf is attached to the branch by a long, flattened petiole (leaf stem) which allows the leaves to dance and shimmer at the slightest breeze, hence the common name "quaking" and Latin specific epithet "tremuloides." Aspens prefer moist soil and abundant sunlight, and ...

Commas, members of the family of butterflies known as the Brushfoots, are typically woodland butterflies.  I've seen several Hoary Commas ( Polygonia gracilis ) fluttering about Sierra Nevada woodlands recently, and always stop to admire them.  Many species of commas rarely feed on flower nectar, instead obtaining nutrients from tree sap, carrion, dung and mud.  The Hoary Comma, found predominately in the mountains of the western part of the North American continent, is more likely to visit flowers than other species of commas.    The main larval foodplant for the Hoary Comma is currant ( Ribes spp .), and eggs are laid on petioles (leaf stems) and the undersides of leaves.  Hoary Commas have a lifespan of about one year.  Breeding takes place in the spring, and eggs hatch in the summer.  Commas overwinter as adults by hibernating during the winter, often in the crack...

The harbor in Moss Landing is a great place to see thousands of Elegant Terns ( Thalasseus elegans ) in the later summer and early fall.  They gather on the jetty and dry spits of land in large numbers, making quite the to-do and drawing a good amount of attention while they are here.  (Watch a flock of terns sometime and you'll understand what I mean!)  But very soon they will leave our shores to migrate south for the winter. Only five breeding colonies of Elegant Terns are known today, down from twelve colonies historically.  Between 90 and 97% of all Elegant Terns breed on Isla Rasa in the Gulf of California.  One other breeding colony is found off the coast of Mexico, and since the mid-1900's three breeding colonies have become established on the coast of southern California.  This is the most restricted breeding range of any North American tern, making Elegant Terns vulnerable t...