Losing Ground: Mountain Plover in California's Central Valley

Christened the "Rocky Mountain Plover" in 1834 by John James Audubon, the Mountain Plover, as it is now called, is actually a bird of short grass prairies rather than true mountain habitats.  Named for its breeding range in the Rocky Mountain region of the United States, specifically in parts of Colorado, Wyoming and Montana, a large percentage of Mountain Plovers spend a significant portion of their lives in California, where they winter on remnants of grassland, alkali flats and, most notably, plowed and fallow agricultural fields.

The Mountain Plover is a habitat specialist, adapted to life on short grass prairies and other areas of bare ground and sparse coverings of very short vegetation.  

And in California, the bare ground that Mountain Plovers need to survive is rapidly dwindling.

Mountain Plover, Yolo County California, January

Almost exclusively insectivorous, Mountain Plovers spend their entire lives on the ground, scurrying along with a distinctive run-and-stop style as they scour cracks in the earth in search of their invertebrate prey, which includes beetles, crickets and grasshoppers.  When threatened by predators, flocks of wintering plovers may flush and fly away, or simply hunker down into a depression in the ground and let their soft earth-toned backs camouflage them as they seem to simply disappear into the substrate.

On the prairies of the Rocky Mountain states, Mountain Plover pairs nest on the ground, building not one but two nests, which are little more than shallow depressions in the ground lined with bits of vegetation.  The female divides her clutch of eggs between the two nests, usually laying two or three eggs in each nest.  The male and female of the pair each incubate one of the nests, which are usually placed within sight of each other.

Mountain Plovers arrive on their breeding grounds in April, and leave in July after the young birds have fledged.  Some research indicates that flocks of Mountain Plover move to post-breeding staging areas in late summer before continuing on to their wintering grounds, but much is still unknown about this season of their annual migratory journey.

A large proportion of Mountain Plovers breed on Pawnee National Grassland, protected shortgrass prairie habitat in northeastern Colorado.  However, when we visited last June, the birds were at the peak of their breeding season, and as far as I could tell were all hidden safely out of view on their nests.

In November, flocks of Mountain Plover begin to arrive on their wintering grounds, where they stay until late February or March.  In California, flocks of Mountain Plover winter in significant numbers in the southern Sacramento Valley (especially Yolo County), a few key valleys within the Coast Range west of the San Joaquin Valley (such as the Panoche Valley and Carrizo Plain), and the Imperial Valley.  Mountain Plovers winter in southern Texas as well, though the majority of the North American population of Mountain Plover (which is also the entire world population of this species) spends the winter months in California.  

In fact, up to 90% of the world population of Mountain Plovers, which is estimated to be some 20,000 individuals, winters in California.  

To put the Mountain Plover's small population in perspective, the population of North America's familiar and somewhat less fussy Killdeer, a related species of plover, is estimated to be over 1 million birds, more than fifty times that of the Mountain Plover!  Though they too are in decline.

Sadly, the number of wintering Mountain Plovers in the Central Valley has declined sharply in recent decades.  Habitat loss has contributed greatly to the decline of the Mountain Plover on its breeding grounds as well, as short grass prairie habitat has been destroyed, degraded and converted to agriculture or development.  Since 1968, the world population of Mountain Plovers has declined by a radical 80%.  

Only two out of every ten Mountain Plovers that once inhabited North American prairies in the middle of the 20th century remain today.

In 1944, authors and ornithologists Joseph Grinnell and Alden Miller published their seminal work, The Distribution of the Birds of California, in which they wrote that Mountain Plovers were considered abundant in California prior to 1880, and "by 1915 had become notably scarce."  They also noted that between 1915 and 1944, there had perhaps been a slight increase in their numbers.  One of the chief wintering locations of Mountain Plover described by Grinnell and Miller was Knights Landing, in Yolo County, and today, that is still one of the best places in Northern California to find this special bird.

When Eric and I arrived at "the plover spot," a gravel roadside within a mosaic of plowed and fallow fields a few miles northwest of historic Knights Landing, a flock of about forty Mountain Plovers greeted us in a bare field not too far from the road.  We watched in delight as the plovers scampered over the bare earth in characteristic plover fashion, pausing now and then to nab an insect from the ground.  Even from a distance, the white chests of the plovers shone in the morning sun; but when they turned their backs, they melted seamlessly into the bare landscape of soil and stubble they were designed to inhabit.

The plovers were utterly charming, and I was thrilled to get to spend some time with these truly gorgeous birds.  But something troubled me.

Mountain Plover, against a troubling backdrop of almond trees.

The adjacent field to the north was converted to an orchard a couple of years ago, and ground that was very recently plover habitat now supported rows upon rows of young almond trees.  The field across the street looked like it had been planted with trees just this year, the young orchard still swathed in protective cartons.  

Along the edge of this new orchard, I caught site of another specialist of short grass prairies, a Burrowing Owl, perched on the edge of an irrigation box.  While Burrowing Owls can adapt to changing landscapes, nesting and roosting in irrigation culverts and the like, an orchard irrigated by drip lines, frequented by heavy equipment, devoid of rodents and treated regularly with herbicides and pesticides is no place for a small, ground-dwelling owl.

Burrowing Owl, with a newly-planted orchard behind.

Not long after I spotted the owl, two more quintessential grassland raptors flew in and landed in the field: Ferruginous Hawks, North America's largest hawk and birds of immensely wide open spaces.  These majestic predators range across North American grasslands, hunting for rodents on wings that span nearly five feet.  There is no place for them in an orchard.

Horned Larks and American Pipits called almost continually from high overhead, flocks occasionally swirling down to the ground where these shortgrass prairie birds also make their living foraging on the ground alongside Mountain Plover.  Again, there is no place for either of these grassland species in an orchard.

Ferruginous Hawk in the open space it requires.

Birds of short grass prairies and other bare ground habitats, like Mountain Plovers, have already adapted to a human-altered landscape at least once, if not twice in the last few centuries.  As cattle replaced herds of bison and pronghorn across prairies, the plovers found their place alongside them in overgrazed grassland habitat.  

Remarkably, as the plow broke up rich native grassland up and down California's Central Valley, Mountain Plover once again found suitable wintering habitat on the bare earth of freshly plowed fields, left fallow for the winter.  

As irrigated agriculture spread into the Imperial Valley, Mountain Plovers followed, finding there an unexpected boon.  But though cultivated land works well enough to support wintering plovers, it is clear that they are forced onto it only after facing the loss of their native grassland habitat. 

Mountain Plovers in their winter habitat in Yolo County, California.

Though the world's population of Mountain Plovers has decreased alarmingly, the species has shown that it can exist alongside certain types of agriculture.  But not all types of agriculture.  As more and more acres of Central Valley farmland are converted to orchards, plover habitat is lost forever beneath a leafy canopy.  

Many of the birds of North America's great prairies and grasslands, some of the most inspiring landscapes on the continent, have proven that they can eke out a living in some pretty marginal habitat.  But they simply cannot adapt to life in an orchard.

Like many birds, Mountain Plovers show high site fidelity, returning year after year to the same traditional breeding, staging and overwintering grounds.  Grinnell and Miller have shown that flocks of Mountain Plover have been visiting these fields in Yolo County since at least 1944, and probably for many decades, if not centuries, before that.  

But as I looked out over an encroaching tide of trees, I had to wonder: How much longer will this land support wintering plovers?  How long will it remain suitable, bare-ground habitat? 

That sustained habitat loss over the last century has contributed to the loss of 80% of the entire population of Mountain Plovers is undeniable.  Numbers of Mountain Plovers also seem to be affected by the health of populations of burrowing mammals, such as moles, gophers, prairie dogs and ground squirrels, since prey abundance has been shown to be higher in habitats shared with these animals.  Eradication of these mammals across prairie, grassland and even agricultural habitats appears to have a surprising effect on plover populations as well.  

It should be plain to see that further loss of suitable overwintering habitat in California over the coming decades will prove detrimental to the survival of Mountain Plovers as a species, which is listed as a Species of Special Concern in California and proposed for listing as a federally Threatened Species.  Protecting high quality wintering habitat on California's agricultural land by assuring that arable fields remain open, rather than converted to orchards, is imperative to the continued survival of Mountain Plovers, not just in California, but in the entire world.  

It is a terrible thing to so mismanage the land we have been given to steward that we lose any species at all; but it would be truly heartbreaking to lose a species as beautiful and charming as the Mountain Plover.