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:
                                                                                               light
carbon dioxide (6CO2) + water (6H2O) --------> glucose (C6H12O6) + oxygen (6O2) 
                                                                                         chlorophyll

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!

video
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. 

Source: http://www.seaotters.org/otterspot/World-Range.gif

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: https://www.seaotterweek.org/