Friday, October 13, 2017

Milbert's Tortoiseshell

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.

Tuesday, October 10, 2017

Quaking Aspen (Populus tremuloides)

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 tolerate temperatures from -70 degrees Fahrenheit to 110 degrees Fahrenheit.  The trees have smooth, white bark that does not peel, but is marked with dark scars at the locations of previous years' branches.  (Be careful not to confuse the smooth white bark of aspens with the peely white bark of birch trees.  Birches are in a completely different plant family from aspens.  While aspens are members of Salicaceae, with willows, poplars and cottonwoods, birches belong to the family Betulaceae, with alders and hazels.)

A grove of Quaking Aspens in full autumn kit is a magnificent sight to behold.  But each grove hides a secret that is not readily apparent to the casual on-looker.  One grove appears to be made up of hundreds of trees, but is in fact one single organism.  Genetically the trees are clones, shoots derived from one root system.  The trees reproduce asexually, the underground system of roots sending up new shoots until acres and acres are covered in a grove of identical aspen trees.  The trees are capable of reproducing by the normal method of flowering and setting seed, but do so only under specific conditions.

Aspen groves far exceed California's famed Bristlecone Pines (Pinus longaeva) in age, and may be in the running for the title of "world's oldest  living thing" along with the Creosote Bush of the desert southwest (which are also clones).  Scientists believe the oldest aspen clone is 80,000 years old.  This clone is named "Pando" (Latin for "I spread") and is located in the Fishlake National Forest of central Utah.  With over 40,000 individual trunks spread across an area of 106 acres and an estimated weight of over 6,000 tons, Pando may be considered Earth's largest living organism.  (Though actually, a honey fungus in the mountains of Oregon is considered by many to be the largest.  Sorry, blue whale.)

Interestingly, within a clone of aspens each tree exhibits identical branching structure and all of the trees will simultaneously change color in the fall, from green to the same varying shades.  One clone can be distinguished from another by the color of its fall foliage. 

But you might be wondering, why, exactly, do leaves change color in the first place?

First, we need a quick refresher on photosynthesis, the process upon which all life on earth is built. 

During photosynthesis, plants take in water and carbon dioxide from their environment and with the aid of sunlight captured by chlorophyll molecules, convert it into sugar (usable energy for the plant) and oxygen.  The equation looks like this:
carbon dioxide (6CO2) + water (6H2O) --------> glucose (C6H12O6) + oxygen (6O2) 

As we see from the equation, the plant molecules chlorophyll, found in chloroplasts, are a vital part of the process of photosynthesis.  Chlorophyll itself is unstable and readily breaks down in the presence of sunlight, so plants are required to produce it at a constant rate throughout the growing season.  The production of chlorophyll requires warm temperatures and adequate sunlight.

As long as temperatures and light conditions are favorable, chlorophyll is produced and photosynthesis carries on.  But many species of deciduous (winter-dormant) trees only photosynthesize during the favorable months of the growing season, going dormant to conserve energy at other times.  It is as these preparations for dormancy are made that we begin to notice a change in leaf color.

Lower temperatures and shorter days bring about the miraculous change in leaf color of many species of deciduous trees.  Red pigments (anthocyanins) and yellow pigments (carotenoids) are present year-round in leaves, but are masked during the growing season by green chlorophyll.  With fewer hours of daylight and the cooler temperatures of autumn, trees are triggered to grow membranes between branches and petioles (leaf stems), slowing the supply of nutrients to the leaves.  Chlorophyll production drops and photosynthesis slows down.  Without green chlorophyll to mask the other colors, the familiar reds and golds of autumn are allowed to shine for a brief time before the leaves drop from the trees and the trees become dormant for the winter. 

Underneath the thin bark of aspens is a green photosynthetic layer that allows the trees to photosynthesize to some extent during the dormant period.  Aspen trees grow year-round, providing a valuable source of browse for deer and elk during tough winters. 

Predicting peak fall color is tricky, since it is influenced by environmental conditions and not likely to occur at exactly the same time each year.  According to what I've read, a growing season with ample moisture followed by a dry, sunny fall with cool days and frost-free nights produces the best fall color in aspens.  From what I've seen so far, the trees are looking good this year in the Sierra!

Click on the video above to see aspens shimmer in the breeze!
(View the video in full screen and make sure it is set to HD for best results.)

Monday, October 9, 2017

Hoary Commas: Woodland Butterflies at Yosemite and Tahoe

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 cracks and crevices of logs and trees, and may emerge to fly on warm days.  Once the weather warms up in the spring, they emerge to breed and the cycle is complete.

The underside of the Hoary Comma's wings provide excellent camouflage as they hibernate in
cracks in logs and trees. 

Sunday, October 1, 2017

Elegant Terns at Moss Landing Harbor

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 to human disturbance and habitat loss.  Due to their limited breeding range, Elegant Terns are listed as vulnerable or near threatened.  

In Mexico, breeding colonies of Elegant Terns are often associated with colonies of Heermann's Gulls and Caspian Terns, the smaller terns probably seeking the protection offered by the larger species.  Terns are highly social birds, nesting on the ground in colonies with thousands of birds packed closely together.  Nests are little more than scrapes on the ground, and a clutch consists of just one or two eggs.  A few days after hatching, chicks are old enough to leave the nest and join the other chicks of the colony, which gather together in a large group called a "crèche."  During this time, adult terns feed only their own chick(s), able to single out their young from the crowd by sound.

During the late summer and early fall, after the breeding season is finished, Elegant Terns leave their breeding grounds and move north along the coast of California to feed.  Occasionally, but rarely, they reach as far north as southern Washington.  Elegant Terns return south in October, spending the winter along the coast of central and south America, as far south as Peru and Chile.

Elegant Terns are a strictly coastal species, almost never found inland.  They commonly concentrate in large numbers around estuaries and bays (like Moss Landing).  Like other terns, Elegant Terns feed on fish which they spot from above while flying, and catch by making spectacular plunging dives into the water.  Watching a flock of terns is a great form of entertainment!

Thursday, September 28, 2017

Western Pygmy-Blue Butterfly

While I was supposed to be looking for Sandhill Cranes and early-season Greater White-fronted Geese at Merced National Wildlife Refuge yesterday, a much smaller winged creature caught my eye.  Flying low near the ground around a patch of heliotrope flowers were several tiny fluttering gems.  Since I strive to be an equal-opportunity naturalist, I crouched down on the ground to devote some time to studying these little butterflies, Western Pygmy-Blues (Brephidium exile).

According to Kaufman's Field Guide to Butterflies of North America, this species is abundant in salt flats, salt marshes, deserts and other alkaline areas collectively thought of as wastelands.  The plants they were visiting, Heliotropium curassavicum, are also generally associated with similar conditions: common names include Salt heliotrope, Alkali heliotrope and Seaside heliotrope.  Salt-bush (Atriplex spp.), Lambsquarters (Chenopodium album), other members of the goosefoot family, as well as Russian thistle (Salsola tragus) are larval foodplants of the Western Pygmy-Blue.  And these plants certainly are abundant in the San Joaquin Valley, particularly around our wildlife refuges.

With a wingspan of only half an inch, this easily-overlooked butterfly is thought to be the smallest butterfly in North America, if not the world.  While the birds were calling (literally) it was nice to spend a little time on the ground admiring these lesser-appreciated beauties. 

P.S.  These heliotrope flowers are incredible: growing in inhospitable, alkaline soils, and still blooming in the valley at the end of September after months without any rain to speak of.  And I think they're just gorgeous!

Wednesday, September 27, 2017

Wetland Report: Sandhill Cranes Return to the Great Central Valley!

Reports of Sandhill Cranes (Antigone canadensis) in the Great Central Valley have been trickling in for the last couple of weeks.  The migrants usually start turning up in our fields and wetlands around mid-September, after the journey from their summer breeding grounds in the far north.  I've been looking forward to the arrival of the cranes, and was able to take a quick trip out to see them yesterday.

Sandhill Cranes at Merced NWR

As of this week (the week of September 25th) nearly 1,000 Sandhill Cranes have returned to one of my favorite wetlands in the valley, Merced National Wildlife Refuge.  By Thanksgiving, somewhere around 20,000 cranes will have settled in for the winter at this one location alone!  The air is already filled with their unique croaking call, and their elegant dancing forms bring the wetlands back to life once again.

Greater White-fronted Geese at Merced NWR

In addition to the cranes, an unseasonably large flock of Greater White-fronted Geese has arrived at the refuge.  They are a little early; these birds don't typically show up in large numbers until closer to November.  Northern Shovelers and American Coots have taken up residence on wetland ponds, while Black-necked Stilts and Greater Yellowlegs wade in the shallows.  Resident White-faced Ibis are abundant, as are Red-winged Blackbirds and our trusty plovers, the Killdeer.  Also present is a large flock of American White Pelicans.

Most of the wetlands are flooded now, or at least partially so, and new birds will be arriving at a constant rate through the fall.  Waterfowl numbers peak during the winter with the arrival of myriad duck species, Tundra Swans, Snow Geese and Ross's Geese. 

For now, the heat of summer is lingering a little longer, and at first glance it seems that a dry desolation still hangs over the wetlands and surrounding uplands.  But there is life here!  Several species of butterflies flit about the upland vegetation - I counted whites and blues, skippers and Monarchs just at a glance - and dragonflies and damselflies buzz over the wetlands.  Yes, there is abundant life here in the valley!

Tuesday, September 26, 2017

Celebrate A Conservation Success Story During Sea Otter Awareness Week!

Every year during the last week of September, citizens have the chance to join marine institutions and researchers in celebrating one of our cutest keystone species: the sea otter (Enhydra lutris).  But there is much more to these large members of the weasel family than their winsome demeanor and dog-like appearance. 

Sea otters are a keystone species, a species upon which the health of their entire ecosystem is largely dependent.  During the 18th and 19th centuries, sea otters were hunted to near-extinction for their valuable pelts.  Before the 1700's, the range of the sea otter extended in a continuous belt around the Pacific, from Japan to Baja California.  Today, sea otter numbers are slowly recovering, but their distribution remains fragmented and patchy throughout their former range. 


By the early 1900's, excessive hunting left just a handful of southern sea otters (Enhydra lutris nereis) surviving along the Big Sur coast - and nowhere else in California.  Monterey Bay was devoid of sea otters, and its biologically rich forests of giant kelp were suffering greatly.  The presence of sea otters ensures healthy kelp forests, as the otters prey on sea urchins, which in turn consume kelp.  Without the otters, kelp forests are overgrazed by sea urchins and biodiversity plummets.  During the early- and mid-20th century, Monterey Bay was something of a barren wasteland - nothing like the thriving kelp forests we see today!

Eelgrass beds, which act as nurseries for many types of fish and mollusks, also require otters in order to thrive.  Sea otters prey on crabs, and crabs feed on sea slugs.  Sea slugs feed by scraping algae off blades of eelgrass.  Without otters, crab populations boom, which causes sea slug numbers to drop and allows algae to thrive, essentially suffocating the eelgrass.  Effects of the failure of eelgrass beds can be felt throughout the food web.

In addition to being a keystone species in their ecosystem, sea otters are also an indicator species; the health of the sea otter population reflects the overall health of the greater marine ecosystem. 

Sea otters were protected under the Endangered Species Act in 1977.  Thanks to herculean efforts by research and conservation groups, sea otter populations in California have risen and these marine mammals can now be found from Half Moon Bay in San Mateo county to Point Conception in Santa Barbara county. 

But sea otters are not out of the woods yet (or should I say, not out of the kelp forests yet? Bad pun fully intended).  Infectious diseases and parasites still threaten otter populations, and may be caused by highly contaminated coastal waters.  Oil spills are absolutely detrimental to sea otters (and other sea life!), as oil destroys the insulating properties of otters' fur and leads to hypothermia (sea otters are the only marine mammals that do not have insulating blubber, and instead rely on well-groomed thick fur).  Ingesting and inhaling oil is fatal for marine life as well.

If you get the chance, take time this week to learn more about the role sea otters play in their ecosystem, and to appreciate the efforts conservationists have made over the last few decades to ensure the survival of this incredible species.  It is a beautiful time of year to visit Monterey Bay, which is one of the best places to see sea otters in the wild!

For more information about Sea Otter Awareness Week, visit their website:

Friday, September 22, 2017

Fall Goings-on in Central California

Every year after the long, hot summer, I eagerly await the arrival of fall.  The transition between seasons may be gradual or abrupt, but each year there is one moment when you sense it: change is coming.  There is a hint of autumn in the smell of the air, a certain color to the morning light, a crispness in the breeze that has long been absent.  As dusty browns mellow into pleasant gold and the cool wind blows, creatures begin to stir.

The wild world is waking up after a drowsy summer.

Yosemite Valley (mid-November of last year)

In central California, the changing of the seasons is not as vividly dramatic as New England postcards, but it can be just as markedly beautiful if you know where to look.  Fall is an excellent season to see wildlife, as many species are on the move.  Shorebirds and songbirds migrate, Sandhill Cranes and other northern breeding birds return to the valley from the Arctic; monarch butterflies migrate to their overwintering grounds on the coast; salmon make their way from the Pacific all the way up valley rivers to spawn.  Fall offers the last good opportunity to see Humpback and Blue whales off the coast before they begin their southern migration, and is the time to see (and hear) Tule Elk during their rut season.  And of course, the star of the autumn woods will always be fall foliage!

Below is a list of some of my favorite fall goings-on in central California.

Cedar Waxwings arrive in the Central Valley every autumn


* Shorebird and seabird migration along the coast.  September is peak season, and Monterey Bay is a great location for birding (I love Point Pinos and Moss Landing).

* Songbird migration in the Central Valley.  During the fall, the diversity of songbirds in the valley is at its highest.  Try riparian areas and wetlands (wildlife refuges) in the valley as well as near the coast.

* Sandhill Cranes return to the Central Valley!  These impressive birds return in September, but their numbers will peak near the end of November.  Look for them in valley wetlands (especially Merced National Wildlife Refuge).

* Monarch migration.  These well-known butterflies are migrating across the Central Valley now, so you may spot one at any time.  But the best chance to see monarchs en masse is at their overwintering sites along the coast, most notably in Pacific Grove and Santa Cruz, between November and February.

* Tule elk rut.  If you're not even sure what that means, it's time for a trip!  Visit the San Luis National Wildlife Refuge or Point Reyes National Seashore to experience the bugling of bull elk.

Salmon run.  The fall run of Chinook Salmon takes place each year as these special creatures make their journey from the sea to freshwater spawning grounds in rivers across the Central Valley.  November seems to be the peak of the salmon run, and the bridge over the Stanislaus River in Knight's Ferry is a great place to watch.

Pinecrest Lake (October)

Fall colors:

The star of the fall foliage show across the western United States is the Aspen.  But other deciduous trees put on quite the display as well.  Look for Big Leaf Maple, Black Oak, Mountain Dogwood, Black Cottonwood, willows and even golden ferns!  Also of note, Poison Oak, a beautiful keystone species in our woodlands, develops lovely red fall color (just don't touch it!).

* Eastern Sierra: Mono and Inyo counties are well-known for their splendid show of Aspens, which generally reach peak color in mid-to-late October.

* Western Sierra: Lassen, Plumas and Tahoe National Forests put on a display of mellow fall color in October and even into November.  More southerly national forests are worth investigating as well, like El Dorado, Stanislaus and Sierra National Forests.  In my experience, fall color in Yosemite Valley seems to peak during the first two or three weeks of November.

* North Coast: Not to be left out, Big Leaf Maples and other trees color the north coast forests of California as well. 

In California's forests, expect pockets of color rather than sweeping New England hillsides of fiery red maples.  Often, hidden gems of color are found along rivers and streams.  Weather plays a big role in intensity and timing of fall colors, so no two years are quite the same.  But the fall color show lasts quite a while in California, slowly progressing from high elevations to low over the season.

Black Oaks turn yellow and reddish-bronze in the fall

Even though summer is over, the outdoors are as enticing as ever!  Hiking, camping, wildlife viewing - it only gets better as the season progresses.  Don't let changing seasons keep you indoors; mild fall temperatures are ideal for exploring the wonderful world of nature!  Head out to explore today!

Thursday, September 21, 2017

California Sister Butterfly

I have lamented before my lack of entomological knowledge.  Yet, armed with field guides, binoculars, a hand lens and the trusty internet, I slog on in my attempt to learn more about the fascinating world of insects.  Perhaps most interesting to me (and every other nature-loving child or adult, I imagine) are butterflies, if for no other reason than that they are often the most conspicuous!  (I also love finding other lepidopterans - namely moths - as well as dragonflies and damselflies.)

An abundance of butterflies seem to be out and about in our local wild lands this time of year.  I'm working on honing my butterfly identification skills (though personally, I find them even more difficult and flighty than warblers!) 

An easy butterfly to start with is the California Sister (Adelpha bredowii californica).  They are frequently seen in California's foothills and at mid-elevations in the mountains, most frequently in oak woodlands and mixed coniferous forests.  Oaks (Quercus spp.) are the larval host plant for California Sisters, meaning the larvae feed exclusively on native oaks.  (You begin to see the great value in preserving and planting California native plant species!)  Adults feed on rotting fruit and sometimes flowers, and can be found sipping at mud puddles, an act known as "puddling."  Essential minerals and amino acids are derived from the mud.

Many butterflies have surprisingly short lifespans; some species don't even feed as adults, but reproduce immediately and then die.  The lifespan of an adult California Sister is about one month long.  California Sisters are active from spring to fall; during one season there are two generations, or broods, of butterflies.  This means that this particular species goes through the whole reproductive cycle (egg, larva, pupa, adult) twice during the season (spring to fall).  (Monarch butterflies go through this process four times during one season.)  The first generation emerges in the spring, reproduces and dies; the second generation then reproduces in the summer or fall and dies, leaving its offspring to overwinter as larvae and emerge in the spring as the first generation of the following season. 
If you too are interested in learning more about the butterflies of California and the rest of North America, I can recommend two resources I have found particularly helpful.  (I'm sure there are many more than just two good ones out there, however!)
For a more in-depth look at the California Sister, check out Kate Marianchild's beautiful book, "Secrets of the Oak Woodlands" (a favorite of mine!)

Tuesday, September 19, 2017

Belding's Ground Squirrels

Summer in the high Sierra is rapidly coming to an end.  Nighttime temperatures are already dipping below freezing, and daytime highs remain in the sixties (Fahrenheit) or lower.  The seasons are changing, grading gently from summer into autumn, and Sierra Nevadan wildlife are busily preparing for the long winter ahead.  On a recent visit to Yosemite's Tuolumne Meadows, the Belding's ground squirrels (Urocitellus beldingi, syn. of Spermophilus beldingi) were particularly busy.

Belding's ground squirrels live in high meadows between 6,500 and nearly 12,000 feet in elevation.  Other open areas favored by Belding's ground squirrels include sagebrush flats and areas of mixed shrubs and grasses.  In addition to the Sierra Nevada, Belding's ground squirrels can be found in eastern Oregon, southwestern Idaho, and parts of Nevada.  They typically remain fairly close to a source of water.

Belding's ground squirrels eat a variety of grasses, herbaceous meadow plants, seeds and occasionally insects or carrion.  The common sight of these squirrels standing or seated upright in open areas has earned them the nickname "picket pins," since their upright forms resemble the pins that were used to picket horses in meadows.  This posture serves as the squirrel's defense, giving them a better vantage point from which to watch for predators.  Their alarm call is a familiar sound to alpine hikers.  Natural predators of the Belding's ground squirrel include coyotes, badgers, weasels and raptors.

Belding's ground squirrels spend nearly three-fourths of their lives hibernating in underground burrows.  Hibernation begins in September at the end of the short, high-elevation summer, and continues through May or June.  Generally, juvenile squirrels remain active longer into the summer than adults, eating as much as they can in preparation for hibernation.  During their first winter, up to 60% of juveniles may starve.  Belding's ground squirrels do not store food for use during the winter.

Monday, September 18, 2017

Wetland Report: Merced National Wildlife Refuge

Late summer is a quiet time at our local Central Valley wildlife refuges, but anticipation hangs in the air.  The wetlands have been dry since the early part of summer, as they are drained after the departure of our migratory birds.  But in September, the dry marshes slowly return to life.  Soon, very soon, the birds will return!

Last week, we took a quick trip out to Merced NWR to see how the wetlands are looking.  The marshes closest to the parking area and main observation deck are still dry, but three separate marsh areas along the back leg of the auto loop are filling with water.  Right now, Black-necked Stilts, Killdeer, White-faced Ibis and Great Egrets abound!  I was surprised by the number of shorebirds we saw!  There are yellowlegs, dowitchers and a few Least Sandpipers as well.  The first of the Northern Shovelers have also arrived.

Sandhill Cranes will start showing up at San Joaquin Valley wetlands by the end of this month - maybe even by the end of this week!  According to a quick glance at ebird, a few cranes were spotted as far south as the Elk Grove area over the weekend.  The arrival of the cranes is an exciting time indeed!  By winter, upwards of 20,000 Sandhill Cranes will fill the wetlands and surrounding fields at Merced NWR.

Golden, late-summer tule reeds

For now, a trip to the wetlands will still reveal a surprising number of birds - especially shorebirds.  The tules are as lovely golden-brown as they are green, and sunflower and milkweed seed heads are picturesque in the late afternoon sun.  You might even spot a few hardy wildflowers still hanging on through the heat.

 Heliotrope  (Heliotropium curassavicum)

Late summer is also dragonfly season in California!  Never a dull moment for the naturalist!

Thursday, September 14, 2017

The Sign of the Beaver in the Great Central Valley

The North American Beaver (Castor canadensis) is unapologetically one of my favorite mammals.  Considered pests by some, this large rodent is a master ecosystem engineer and keystone species in its environment.

During the 19th century, the humble beaver was nearly eradicated from the western United States, including California, through habitat loss, hunting and trapping for fur, and deliberate extermination.  The beaver is sometimes considered a nuisance species, since their enthusiastic lumberjack work may cause trees to fall across roadways, and their dams, ponds and levee burrows can cause flooding.  But it turns out that the beaver provides a suite of unexpected ecosystem services, including increasing wildlife habitat and water storage potential in the arid, drought-prone west. 

Beaver lodge at San Luis National Wildlife Refuge, April 2017

Beavers are hydro-engineers and excel at altering the flow of water though the environment.  The familiar "beaver dams" these large rodents create form small reservoirs, pools of quiet water in otherwise rapidly flowing aquatic environments.  Without beaver and their log-and-stick dams, water rushes downstream, eroding stream channels and sweeping fish down the river.  In the quiet waters of beaver ponds, however, valuable fish such as juvenile salmon are able to thrive.  Some speculate that the decline of salmon in the west is due in part to the loss of beaver and the habitat they create. 

Beaver track in wet sand, San Joaquin River National Wildlife Refuge, January 2017

Beaver ponds are thriving ecosystems in themselves, creating habitat for a number of wildlife species.  The California Department of Fish and Game states,

          "Beaver dams create habitat for many other animals and plants of California. Deer and
          elk frequent beaver ponds to forage on shrubby plants that grow where beavers cut down
          trees for food or for use in constructing their dams and lodges. Weasels, raccoons, and
          herons hunt frogs and other prey along the marshy edges of beaver ponds. Sensitive
          species such as red-legged, yellow-legged and Cascade frogs all benefit from habitat
          created by beaver wetlands. Migratory water birds use beaver ponds as nesting areas and
          resting stops during migration. Ducks and geese often nest on top of beaver lodges since
          they offer warmth and protection, especially when lodges are formed in the middle of a
          pond. Willow flycatchers use the shrubby re-growth of chewed willow stumps to seek
          shelter and find food. The trees that die as a result of rising water levels attract insects,
          which in turn feed woodpeckers, whose holes later provide homes for other wildlife. In
          coastal rivers and streams, young coho salmon and steelhead may use beaver ponds to
          find food and protection from high flows and predators while waiting to grow big enough
          to go out to sea." 
          Source: California Department of Fish and Wildlife publication, Living With Beavers

Evidence of beaver activity along the Tuolumne River, Stanislaus county, March 2016

In addition to wildlife habitat, beavers and their ponds provide hydrologic benefits to arid, often drought-stricken regions.  Beaver ponds capture and hold water, preventing it from rushing quickly downstream and eventually being lost to the sea.  Water held in beaver ponds is able to slowly percolate into the ground, increasing groundwater storage and soil hydration.  This ability of the soil to recharge itself makes the land much more resilient in the face of drought.

Evidence of beaver activity along the Tuolumne River, Stanislaus county, March 2016

In California, beaver still occur in the Great Central Valley, parts of the Sierra Nevada and the Cascades, and most of the northern third of the state.  Historically, beaver occurred along the coast of California as well.  I have seen evidence of beaver activity in the Great Central Valley as well as in the Sierra in the form of fallen trees and tooth marks, tracks, and stick lodges.  A beaver sighting is always an exciting event!

Beaver track in wet sand, San Joaquin River National Wildlife Refuge, January 2017

After years of the systematic depredation of the beaver, interest in California's beaver population is growing.  In light of the potential benefits of beaver ponds to fish (specifically salmon) and other wildlife, as well as ponds' potential for surface water storage and ground water recharge, it seems that beavers and their activity benefit the entire watershed.

Beaver tooth marks on a cottonwood log along the Tuolumne River, March 2016