Tuesday, May 23, 2017

Sanderlings: Arctic Swashbucklers


Sanderlings (Calidris alba) are smallish sandpipers of the swash zone, perhaps the "peeps" seen most commonly on the beaches of central California.  They stick together in flocks as they run up and down the beach, chasing the waves as they forage in the swash zone.  (The swash zone is the part of the beach that is covered with each incoming wave, and uncovered again to reveal potential tasty morsels beneath the sand.)


The rather cute, gentle appearance of Sanderlings belies their amazing life strategy.  These birds may not look it, but they are truly daring, swashbuckling adventurers, flying thousands of miles between overwintering grounds around the world and breeding grounds high above the Arctic Circle. 

Sanderlings are one of the most widespread shorebirds in the world, found during the winter on most temperate and tropical beaches.  For most of the year, they can be found in California, though numbers are lowest in June when they return to the Arctic to breed.  A few nonbreeding adults may stay behind during the summer, saving themselves the energy required to migrate. 


After incredible long-distance migrations, Sanderlings breed on the tundra far above the Arctic Circle.  They nest on dry tundra with low growing plants, such as lichens and mosses, building nests on the ground.  These nests are little more than shallow scrapes, perhaps lined with small leaves.


A favorite food of Sanderlings is sand crab (Emerita analoga), thumb-sized crustaceans that spend most of their time buried in the sand.  Sanderlings also eat other invertebrates, such as amphipods (shrimplike crustaceans with laterally compressed bodies, sometimes called beach fleas or sand hoppers) and isopods ("pillbug"-like crustaceans with dorso-ventrally compressed, or flattened, bodies), as well as marine worms and small mollusks. 

Aside: If you happen to be interested in the dazzling array of invertebrates that inhabit California's enchanting coastline, I highly recommend Ed Ricketts' classic book, Between Pacific Tides.  It has yet to be surpassed in breadth and depth in the nearly 80 years since its original publication in 1939, and I find it to be very readable and enlightening.

Sanderlings in May, beginning to show colorful breeding plumage

Sanderlings are pale most of the year, gray above with extensive pure white on chest and bellies.  Most commonly, this is how we see them during the winter months in California.  During the summer breeding season, Sanderlings' backs and heads become flecked or spangled with black, white and red.  The birds we saw at Moss Landing recently, during the second week in May, were beginning to show their brighter breeding plumage (see photo above).

Sanderling in March, much paler in color as they appear through the winter.
 
Though this is a common and widespread species, its future is not considered entirely certain.  According to Cornell's All About Birds website, between 1959 and 1988, the number of Sanderlings in California decreased by 3.7% each year.  This decrease is likely due to development of shoreline habitat as well as exposure to toxins.  Pesticide runoff from nearby agricultural fields, oil spills, municipal runoff (chemicals, oils, etc. from cities' storm drains) and ever-increasing plastic pollution on our beaches and in our oceans pose very real threats to shorebirds and the greater ecosystem.  Overwintering habitat is critical for migrant shorebirds like Sanderlings, and in California much of that habitat is protected by California's State Beaches.


Next time you visit the beach, pay special attention to the small shorebirds chasing the waves in the swash zone.  Learning to identify Sanderlings is the first step in decoding the sometimes mystifying group of sandpipers and other shorebirds.

Sunday, May 21, 2017

Caspian Terns at Moss Landing

Terns are a neat group of birds, and Caspian Terns (Hydroprogne caspia) are particularly eye-catching with their bright bills and dark caps.  They are in the same family as gulls, Laridae, though unlike gulls, terns seem to be generally free from the stigma that is usually attached to those ubiquitous birds of the coast.  While visiting Moss Landing recently, I spotted (and heard) quite a few terns swooping overhead; I was excited to see a few on the ground, within range of my camera!


The Caspian Tern is the largest species of tern in the world; it is as big as a large gull, and is frequently seen in mixed flocks with gulls.  They occur on every continent except Antarctica. 

Terns are known for their aerial dives, and Caspians are no different.  They fly over bodies of water while looking down to spot fish.  When they see potential prey, they dive steeply and plunge into the water in hopes of nabbing a fish.  Earlier this spring, at Elkhorn Slough, I watched several smaller Forster's Terns (Sterna forsteri) dive into the water repeatedly after their quarry.  It's quite a sight to see!


Caspian Terns breed in colonies, which they defend fiercely.  Breeding colonies are found on island beaches in rivers, salt marshes, lakes and other protected bodies of water.  Nests are shallow scrapes in the ground, lined with vegetation, shells and other debris. 


During the winter months and migration, terns roost on islands and isolated spits of land.  Caspian Terns can be found along the coast of central California year round, though their numbers seem to be highest from spring through fall.  They prefer protected waters to the open ocean.

 
Look for Caspian Terns, and other terns, flying high over the water, head angled down searching for fish.  Their plunging dives are spectacular and unmistakable.  Also listen for terns; like their gull relatives, they can be boisterous and make rather grating calls.  You might hear them before you see them!
 
 

Friday, May 19, 2017

Western Snowy Plover: A Threatened Species

Western Snowy Plovers (Charadrius nivosus nivosus) are small, sparrow-sized shorebirds, found up and down the Pacific coast in decreasing numbers.  They are cryptically colored and easy to overlook, as they blend in perfectly with the sand and bits of driftwood and sea wrack of their beach habitat.  Like other plovers, Western Snowy Plovers belong to the family Charadridae, along with our more familiar and conspicuous Killdeer (Charadrius vociferous).  I personally think Snowy Plovers are one of the cutest birds around. 


Ranging from Washington to Baja California, Western Snowy Plovers forage on beaches and foredunes for very small crustaceans, invertebrates and insects.  The breeding season lasts from March through September, which unfortunately coincides with the period of heaviest use of beach habitat by tourists.  These diminutive shorebirds nest on sandy beaches and shores, at stream mouths and on coastal dunes, laying three very tiny, perfectly camouflaged eggs in small nests made of seaweed, driftwood pieces, pebbles and sea shells.  Chicks leave the nest a few short hours after hatching, and adults lead them to suitable feeding sites where they teach the young plovers to forage in the sand among washed-ashore kelp and dune vegetation. 

The sad irony is that the same defense that protects the nests from predators, cryptic coloring, makes them vulnerable to trampling and crushing by uninformed and unaware beach-goers.  Tourists, vacationers, equestrians and frolicking dogs pose a large threat to nesting snowy plovers; a child or adult can easily step on and destroy a whole nest and never know.

Each time a nesting adult is disturbed and frightened off of its nest, the parent bird loses precious energy in running or flying away.  The abandoned nest is left vulnerable to predators, burial by blowing sand, and cooling off or overheating (both of which kills the developing chicks inside the eggs after just a short time).  Human activity near nest sites can cause adults to remain away for long periods of time; a kite hovering above a plover nest is perceived as a predator (such as a hawk) causing distraught parents to abandon the nest.


In 1993, the federal government listed Western Snowy Plovers as a threatened species due to low population numbers caused by habitat loss and destruction, loss of nesting sites and increased predation.  Development and human activity along the coast has led to a precipitous decline in suitable coastal strand habitat.  Introduced species that become invasive, such as European Beachgrass and iceplant, further compound the problem by crowding out native vegetation on small fragments of remaining dune habitat.  Dunes choked with non-native vegetation lack the open spaces plovers need for nesting, and thick plant cover provides hiding places for plover predators.

Natural predators of the snowy plover include falcons and owls, along with opportunistic mammals like raccoons and foxes.  However, humans have increased the number of plover predators by intentionally introducing animals, such as red foxes, dogs and feral cats, and by unintentionally attracting animals that thrive alongside humans, like crows and ravens.  Ruthless nest predators, these corvids scavenge the wake of garbage that follows wherever humans tread, receiving an unnatural nutritional boost that leads to greater reproductive success.  More hungry corvids in the area means fewer eggs and young of threatened birds, like Western Snowy Plovers and Marbled Murrelets (Brachyramphus marmoratus )in the north, hatch and grow to maturity.


The Wild Bird Rehabilitation program at Monterey Bay Aquarium is one of the main shorebird rehabilitation facilities in Northern California, and these dedicated wildlife workers have had success with Western Snowy Plovers.  The following is a quote from their website:
 
"We work with local and regional parks and avian conservation groups to rescue abandoned, threatened or damaged eggs, chicks and adults during the breeding season. These are incubated and reared for release. Since 2000 we've reared and released 123 plovers at Monterey Bay beaches, including 80 that hatched from eggs."

Prior to release, Snowy Plovers are banded by Monterey Bay Aquarium.  The tiny, colored bands allow the birds to be tracked over the course of their lives.  Snowy Plovers typically return to the same beaches every year to breed, and the bands are vital to the data collection process.  California State Parks works with the U.S. Fish and Wildlife Service and bands plovers as well.  If you do see a Snowy Plover on the beach, it will most likely be sporting several colored identification bands on its tiny legs.

California State Parks estimates that Snowy Plovers nest at just over 20 sites in California, a number that has been cut in half in the last several decades.  Less than 1,500 breeding plovers are left in California, and about 2,500 along the entire Pacific Coast.  To help ensure the survival of the species, California State Parks monitors Snowy Plover numbers and breeding efforts, and closes portions of beaches from spring through fall to protect nesting habitat.  Much of the remaining habitat suitable for Snowy Plovers is on California State Parks beaches.


By following a few basic rules, you too can help the Snowy Plovers this breeding season!

Never approach plovers, nests or eggs.  Even if you don't see the birds (which you probably won't), obey posted signs and stay away from designated areas.

When you see roped off sections of beach, please, please, please respect the plovers' habitat and stay out.  Snowy Plovers, as well as their nests, eggs and chicks, are all very small and well-hidden; you probably won't see any birds or nests in the roped off area, but that doesn't mean they aren't there.  Even well-meaning people can accidentally destroy nests by stepping on them and crushing the eggs.   

Please obey posted signs and keep your dogs leashed!!

Never, ever feed wildlife.  This includes cute, innocuous-looking squirrels, bold gulls and everything else that is wild.  Feeding wildlife causes myriad problems; in this case, it attracts nest predators, like gulls, crows and ravens, that eat plover eggs.

Please clean up after yourself!!  Clean up all of your trash - and while you're at it, pick up a few extra pieces of garbage on the beach.  Human trash invites plover nest predators, like ravens, crows, foxes and raccoons; it draws them to the area, then creates an artificial source of energy, allowing them to be more reproductively successful which compounds the problem each season.  Plastic and other refuse is also dangerous and deadly for all manner of sea life (including birds).

Do not remove pieces of driftwood, sea weed, rocks or shells from California beaches.  This "junk" on the beach is part of the ecosystem and provides cover and nesting materials for Snowy Plovers.  Feel free to remove garbage: plastic bags, balloons, Styrofoam, broken flip-flops.  Help yourself!

An informative brochure from California State Parks about sharing the beach with Snowy Plovers can be found here:
http://www.westernsnowyplover.org/pdfs/state_parks_sharing_beach_brochure.pdf

Share this with fellow beach-goers!


An important postscript:  These photos were taken with a zoom lens from behind a barrier a respectful distance away from the birds.  I stayed just a minute or two.  If you see Snowy Plovers this summer, take just a minute to get your fix of cuteness and maybe snap a couple of photos.  Don't hang around the birds or try to get closer.  And for goodness sakes, don't ever chase or pursue a plover for a better photo!  You may do more harm than you will ever know. 

Appreciate these little guys from a distance, then let them get back to the task at hand, which is, hopefully, raising a small brood of young: just one part in ensuring the survival of this species.

Thursday, May 18, 2017

Invasive Species: European Beachgrass

Visit a beach in California, particularly in the northern half of the state, and you are likely to come across stands of European Beachgrass (Arundo arenaria).  It looks so innocuous, picturesque even, waving in the Pacific breeze and blurring the line between land and sea.  But this grass, a plant you've probably never thought twice about, is much more than it seems.  Innocuous it is not.  European Beachgrass is one of California's most wanted offenders: an introduced, aggressive invasive species.

This picturesque photo of the California's Pacific Coast has a secret...  Most people won't notice that the grass seen
here is an imposter; it's not native to the area, but a species that doesn't belong in this ecosystem.

The main crime this grass is guilty of is being too good at its job.  In 1869, European Beachgrass was planted around Golden Gate Park in San Francisco, and since 1900, it has been introduced to other parts of California's coast in an effort to stabilize sand dunes.  But sand dunes are by nature fluid, ever-changing, ephemeral.  ("Shifting sands" is a saying for a reason.) 

Unfortunately, this unique quality of sand dunes and the distinct habitat that they create was recognized too late: the exotic grass had been introduced, and found California's climate more than suitable.  Where it has been introduced, European Beachgrass has spread vigorously, to the point that native vegetation is choked out and the dunes are cemented firmly in place by the tenacious clumps of grass.  Dunes are no longer able to shift, build and re-shape with the winds.  Dunes covered in European Beachgrass re-form to become parallel to the coast, rather than perpendicular, creating foredunes that are so high and steep, the sand supply to the rest of the dune system is effectually cut off.

European Beachgrass near Watsonville, California

European Beachgrass spreads by creeping rhizomes, underground stems that are capable of producing roots and shoots (just like the pesky Bermuda grass in your garden: every tiny piece will develop into a whole new plant).  Pieces of rhizomes that have been dislodged by crashing waves are easily carried to new sites, where they wash ashore and root.  The ability of rhizomes to sprout makes removal of European Beachgrass extremely difficult.

Threatened Western Snowy Plovers require the open spaces of beaches and dunes for breeding and for survival as a
species.

Beaches and dunes with extensive stands of European Beachgrass have lower biodiversity than those with native plant cover.  The thick growth of European Beachgrass excludes native plants, including dune wildflowers that provide a food source for native butterflies and other pollinators.  The lack of open spaces on dunes choked with the introduced grass severely reduces nesting habitat for threatened Western Snowy Plovers (Charadrius alexandrinus nivosus).  To make matters worse, thick beachgrass provides cover for plover predators, diminishing the success of breeding pairs nearby.  Our native perennial dune grass, American Dune Grass (Elymus mollis) grows with ample open space between clumps.  Other natives that are excluded by European Beachgrass include Yellow Sand Verbena (Abronia latifolia) and the endangered Menzie's Wallflowers (Erysimum menziesii).  Dune systems that have been extensively stabilized by European Beachgrass may then be colonized further by lupine and coyote bush, transforming the dune community entirely.

Endangered Menzie's Wallflower, one of many native species that is choked out by aggressive European Beachgrass

Wednesday, May 17, 2017

Ecology and Restoration of California's Coastal Dune Habitat

Much like California's deserts, a cursory glance at our coastal dune ecosystem - by the untrained eye - shows little more than a barren, windswept, lifeless place.  But the concept of coastal dunes as lifeless is far from the truth.  In fact, the unfortunate truth is that much like deserts, coastal dunes have been written off time and time again as areas in need of "improvement."  As a result, nearly all of California's coastal dune systems have been severely degraded. 

Restored dunes at Moss Landing State Beach

Highways cut through the dunes, housing developments and condominiums perch on top of them, mining operations remove sand entirely.  Invasive plants have been introduced to "stabilize" the soil: most notably, iceplants (Carpobrotus chilensis and Mesembryantheum crystallinum) and Eruopean Beachgrass (Ammophila arenaria).  These plants have been wildly successful, covering extensive dune systems to the exclusion of native species.  Invasive plants crowd out native plants, offer native wildlife very little in the way of food and shelter, and alter the structure of the entire dune system.  It is from these iceplant-covered slopes, dangerously low in biodiversity, that we have arrived at the mistaken conclusion that coastal dunes are inherently barren wastelands.

As a kid visiting the beach, my abiding memories are of iceplant: rolling dunes covered in nothing but iceplant.  Even as a curious, observant young naturalist, I could not have told you anything about native dune plants and wildflowers!  All I knew was iceplant.  I assume the experience of many California beach-goers has been the same.


Non-native Sea Rocket (Cakile maritima) blooms on restored dunes at Moss Landing State Beach, where the battle 
to eradicate introduced, invasive plants continues.

In their natural, undisturbed state, coastal dunes are fluid, moving entities that support a diverse and unique assemblage of plants and animals.  The introduction of non-native plants not only excludes native species, but also stops the development of dunes.  The thick cover of non-native plants differs from the widely-spaced growth pattern of native plants.  The dunes become immobilized, and sand builds up along the foredunes to create tall, steep slopes that effectually cut off the supply of sand to the rest of the dune field.  This eventually starves the dune field, leading to the degradation of the entire ecosystem.  As the shape and structure of the dune field changes, it becomes unsuitable for native wildlife.

Western Snowy Plover (Charadrius alexandrinus nivosus)

While coastal dune ecosystems are relatively food-poor habitats, they still support a surprising variety of life.  Insects are the most numerous group, and several rare butterflies rely on dune habitat.  Rare members of the genus Euphilotes, or Buckwheat Blue butterflies, feed exclusively on Buckwheat plants of the dunes.  Federally threatened Western Snowy Plovers (Charadrius nivosus nivosus) and endangered California Least Terns (Sternula antillarum browni) breed in California's coastal dune habitats.  Black Legless Lizards (Anniella pulchra nigra), an endangered subspecies of the California Legless Lizard, live below ground in the sand of the dunes on the southern coast of Monterey Bay and the Monterey Peninsula.  Federally endangered plants of the coastal strand habitat include Tidestrom's lupine (Lupinus tidestromii) beach layia (Layia carnosa) and Menzie's wallflower (Erysimum menziesii).

Menzie's wallflower (Erysimum menziesii)

Ecologically, there are similarities between coastal strand (coastal dune and beach habitats, collectively) and desert plant communities.  Both have sandy soils, and one of the main properties of sand is that it is porous, lacking the ability to hold a significant amount of water.  In response, both plants of the desert and coastal strand plants may exhibit long tap roots and succulent leaves. 

Like desert plants, plants of the coastal strand must adapt to survive in harsh conditions.  Challenges include excess salts in the soil (from evaporation in the desert and salt-laden sea air on the coast), high winds and abrasive sand, shifting sand and occasional burial, and lack of freshwater.  Prostrate growth forms are common in plants of the coastal strand, as this protects plants from excessive winds.  Beach Sagewort (Artemisia phycnocephala) is covered in soft, protective hairs, a natural barrier against windblown sand; Beach Bur (Ambrosia chamissonis) grows new, upright stems after it has been buried by shifting sand. 

Restored dunes with silvery Beach Sagewort and Beach Bur

Perhaps not surprisingly, quite a few genera of plants have representative species in both desert and coastal strand communities.  Beach Sagewort belongs to the same genus (Artemisia) as our familiar sagebrushes, and the genus Ambrosia, to which Beach Bur belongs, has several desert members as well.  The buckwheats, Eriogonum spp., have members in alpine, desert, and coastal strand communities.  Wildflowers such as Beach Primrose (Camissonia cheiranthifolia), Red Sand Verbena and Yellow Sand Verbena (Abronia maritima and A. latifolia, respectively) will all look very familiar to any desert wildflower aficionado. 

Beach Primrose (Camissonia cheiranthifolia)

Like the cryptogamic or cryptobiotic crusts of desert soils, a thin soil crust also forms on the surface of undisturbed coastal dunes.  This crust is caused by the moist, salty air and is critical to the development of dune vegetation.  It is imperative that this crustal layer remains intact, as it holds in place just enough moisture and substrate to create a seedbed suitable for the germination and establishment of new plants.  Just like in deserts, trampling obviously disturbs this important layer; careless activities such as off highway vehicle use severely damages the soil crust, and in turn the entire ecosystem.

Yellow Sand Verbena (Abronia latifolia)

The main difference between plants of the desert and those of the coastal strand is life strategy.  While annuals prevail in deserts, where they are able to grow very quickly, set seed and die in one short rainy season, plants of the coastal strand are largely perennial.  Cloudy days and year round fog creates a different environment from the intense sun of the desert, preventing the high photosynthetic rates required for the rapid growth of annuals.  The foggy climate of the coastal strand is far more moderate than the extremes of the desert, so even though freshwater can be in short supply, the absence of an intensely hot, dry season allows perennial plants to persist here throughout the year. 

 Beach Pea (Lathyrus littoralis)

As I mentioned earlier, as a kid I noticed little else at our favorite beaches beside iceplant (and Eucalyptus, but that's another story entirely!)  But when we began visiting a different beach, Asilomar State Beach in Pacific Grove, I noticed something different.  The dunes looked different.  There were different plants growing on them, and a neat boardwalk to walk on. 

White-crowned Sparrows (Zonotrichia leucophrys) not only breed but also can spend most of their lives in
coastal strand habitat.

I didn't know it at the time, but the Asilomar Dunes are one of the best places in Central California to see an example of dune restoration.  Development, sand mining and unrestricted use by enthusiastic beach-goers completely destroyed most of the dune system by the early to mid-1900's, and what was left was badly trampled and eroded.  Seeing how the natural state of the dunes had been so degraded, groups of people stepped in to fix the problem they had created. 

Unfortunately, these early efforts to fix the problem only compounded it.  By introducing non-native, invasive plants to stabilize the dunes, the ecosystem was drastically altered.  In the area of Asilomar State Beach, this began in the 1960's with the introduction of iceplant.  But iceplant doesn't provide food or shelter for wildlife, and by the 1970's, the iceplant had excluded virtually all native plantlife and the dunes were considered a wasteland - an idea that has persisted in many uninformed minds. 

In 1984, efforts to restore the Asilomar Dunes began with the goal of returning them to their natural "pre-European" state.  Nearby isolated remnants of native vegetation served as a guide; seeds were collected and plants were raised in a specially built nursery.  Non-native plants were removed and the dunes were dramatically reshaped, as non-native "stabilizing" plants had reshaped the entire dune system by not allowing the wind to work on the dunes in a natural way.  Native plants were planted, and a boardwalk was built to allow restricted visitor access to the area.  Today, the restoration work is on-going and showing great signs of success. 

Endangered Menzie's Wallflower, replanted at Asilomar State Beach. 
Each plant is protected from herbivory by a small wire cage.

Most people are probably as unfamiliar with our native dune habitat as I was.  The boardwalk across the Asilomar Dunes allows visitors to experience the dunes, offering an up-close close look without causing damage to the plants.  Today, 35 native plant species grow in the restored dunes, each specially adapted to the unique environment and playing a distinct role in the ecosystem.  (Many of these plants were mentioned above, including Beach Sagewort, Beach Bur, Beach Buckwheat and the sand verbenas.)

Red Sand Verbena (Abronia maritima)

In addition to being threatened habitat for an assemblage of unique species, coastal dunes offer an ecosystem service to the general population as well.  Coastal dunes provide a buffer against extreme high tides and storm waves.  But to be effective, the dunes need to be able to move freely as wind and waves dictate.  When they are over-stabilized by non-native and invasive plants, the dunes become immobile and much more susceptible to erosion.

Clearly, it behooves us all to protect and restore California's coastal strand, its beautiful stretches of beaches and dunes, preserving the integrity of the coast and its native habitats.  If you remain unconvinced, I invite you to pay a visit to one of California's coastal dune systems.  In central California, try the restored dunes at Asilomar State Beach, Moss Landing State Beach, or the Marina Dunes Preserve, all near Monterey.  Visitors to these special places are able to experience the dunes without trampling the vegetation; they are able to walk among the plants, butterflies and birds, to hopefully gain a deeper understanding and appreciation for coastal dunes.

Saturday, May 13, 2017

Bullock's Orioles

A fiery flash darts through the riparian canopy of oaks, pouring forth a beautiful song.  For a moment you are stunned.  You grab your binoculars and search for this flaming apparition.  After following the song and scanning the trees, your eyes are drawn to a patch of bright sunshine in the canopy.  Your binoculars come to rest on a brilliant, almost tropical-looking bird: a male Bullock's Oriole (Icterus bullockii).  If you're relatively new to birding in California, particularly the Central Valley, you might be very surprised to learn that a bird this bright and beautiful spends the warm months with us!
 
A bright and flashy male Bullock's Oriole

Bullock's Orioles breed across much of the western United States, migrating to Central America for the winter.  In the Great Central Valley of California, they seem to favor Valley Oaks (Quercus lobata) in riparian areas.  Cottonwood trees are also favorite nesting and foraging sites, and especially in the arid West, they usually stick close to water. 

Male Bullock's Oriole; notice the prominent black line through the eye.

Bullock's Orioles feed by gleaning insects and small spiders from the canopy.  They also eat caterpillars, fruit and nectar.

Male Bullock's Oriole, showing off his white wing patch

For quite a while, Bullocks and Baltimore Orioles (Icterus galbula) were lumped together as Northern Orioles.  The two species do hybridize in the Great Plains where their regions overlap, but researchers don't believe they are closely related genetically.


Bullocks Orioles may spend up to two weeks building intricate hanging nests, the male and female of the pair working together to weave grasses, twine and other fibrous materials into the structure.  The nest is then lined with soft material, like feathers or the downy "cotton" of cottonwoods and willows (which is really part of the seed structure of those trees; the fluff encloses the seed and aids in wind dispersal).  The nests are typically suspended high above the ground from flexible branches.  This nest placement discourages predators, though on windy days as I watch oriole nests bounce in the breeze, I wonder that the young orioles don't get motion sickness!

A Bullock's Oriole pair's woven hanging nest in a Valley Oak

Female Bullock's Orioles are more drab in color than males, but can still be distinguished from other species by their long, thin bills and faint eye line.  Like many other species, orioles are affected by habitat loss.  Since they are insect eaters, pesticide use may have a detrimental effect as well.

Female Bullock's Oriole

Friday, May 12, 2017

Tree Swallows: Iridescence on the Wing

Swallows of all species are beautiful, graceful birds, swooping acrobatically through the air as they catch insects on the wing.  Tree Swallows (Tachycineta bicolor) are one of our most flashy birds, with their iridescent plumage contrasting with clean white fronts.  In most places, swallows migrate south for the winter, only returning to breed in the summer; but here in California's Great Central Valley, Tree Swallows and similar Violet Green Swallows (Tachycineta thalassina) stick around all year.  Still, they are probably most visible in the warmer months.  I enjoy watching swallows every chance I get, and have been happy to see quite a few Tree Swallows out and about recently. 


Tree Swallows nest in tree cavities, as well as nest boxes.  Because they take so readily to nest boxes, researchers have been able to study the ecology of Tree Swallows in detail.  Like other swallows, Tree Swallows feed primarily on flying insects, which they snatch out of the air with great agility.  Swallows are one of nature's great pest control agents!  They will also consume plant matter, especially in the winter when insects are scarce.  Because of the large amount of insects they consume, Swallows are exposed to high levels of pesticides that bioaccumulate in the ecosystem; these harmful chemicals become concentrated in the bodies of the birds. 


Nests of grass and other soft plant material are placed in cavities, usually excavated by woodpeckers in trees.  Introduced species like the aggressive European Starling compete with our native cavity nesters for suitable nesting sites, and typically succeed in driving out the native species.  Standing dead trees, or snags, provide valuable habitat for Tree Swallows.