white-throated sparrow

white-throated sparrow

Thursday, May 1, 2014

Colorado River Migration Spectacular

I stand and watch as waves of songbirds appear in a nearby mesquite, pause briefly for a snack, and then flit on northward.  A Blue Grosbeak perches high in a branch, brilliant blue in the early morning light, its metallic “chink” call and delightful mellow warbling song reminding me of dense willows along rivers coursing through hot deserts.  Now there is a handsome male Black-throated Gray Warbler, heading north to grace montane oak forests with its cheery buzzing song.  A Townsend’s Warbler appears next, a stunning orange and black gem that will soon adorn the magnificent Douglas fir trees in the Pacific Northwest.  Spritely Wilson’s Warblers, drab greenish Orange-crowned Warblers, Nashville Warblers, Pacific-slope Flycatchers, Western Tanagers, Black-headed Grosbeaks; all passing by on their way to various points in western North America.  Above, an endless river of swallows, swifts, and blackbirds cruise by, and shorebirds forage furiously in pools of water, fueling up for their journey to the tundra.  Four species of rails skulk amongst the marsh vegetation, their presence revealed only by their strange and evocative calls: Yuma Clapper Rail, Virginia Rail, Sora, and Black Rail.

This is El Doctór, and this is the most amazing migration spectacle I have ever seen.

El Doctór is a nature reserve that protects 1850 acres of wetland within the Colorado River Delta in Mexico, providing critical habitat for marshbirds (including the threatened Yuma Clapper Rail) and stopover habitat for migrating shorebirds and songbirds.  It is an oasis within the vast Sonoran Desert, and one of the last remnants of what was once a vast network of wetlands within the Colorado River Delta.  I visited this area as part of a larger team effort to investigate the effects of a large water release (“pulse flow”) into the Colorado River channel.  Scientists from both Mexico and the US were out in force, measuring water flow, seed dispersal, and seedling sprouting - I was there to observe the foraging behavior of birds.  While it is too soon to speculate on how well the birds are responding to the pulse flow, I can share my experiences with the area's birds.

Birding the Lower Colorado River

Most of the study areas were public lands that could be visited by anybody, although they were generally not well-signed (except Cienega Santa Clara) and interested birders should contact a local guide for directions or assistance getting to the sites (see http://mexicobirdingtrail.org/plan-a-trip/colorado-river-delta/).  I had no trouble getting around in my car; then again, I've taken my Saturn on some crazy roads before and know how to drive it through the myriad sand patches that characterize the dirt roads in this region.  There are hotels in the border town of San Luis Rio Colorado, and all sites can be reached within an hour and a half.  Gas and delicious tacos are available in the small town of Luis B. Sanchez.  I can’t attest to any of lodging options - I was hosted by Juan Butrón at his house in a tiny community near Cienega de Santa Clara.

El Doctór

El Doctór is a wetland is one of the first places with trees and water that northbound migrants encounter after crossing the Sea of Cortez or large stretches of surrounding Sonoran Desert- and as you can see from the map, the desert around here is VERY sparse and dry, quite unlike the relatively lush saguaro-palo verde-mesquite desert scrub around Tucson.  Hence I saw the largest concentrations of migrants during my visits to this site.  Of course my brief visit provided only a snapshot of migration - for instance, it was too early for many Empidonax flycatchers other than Pacific-slope - but this spot had the highest diversity of migrant warblers (10 species) and was the one place at which I heard all four rail species.  Year-round residents included Crissal Thrasher, Verdin, Northern Mockingbird, and Abert’s Towhee.

Cienega de Santa Clara

This is an even larger area of wetland a bit north of El Doctór - 14,000 acres of cattail marsh, critically important for the Yuma Clapper Rail.  Another literal oasis in the desert, the last few kilometers of the road to the cienega pass through bare sand completely devoid of vegetation, bringing to mind the Sahara or another planet entirely!  Juan treated me and a trio of Canadian journalists to a long boat ride through the cienega on my first full evening in Mexico.  American Coots bobbed on the water throughout and handsome male Cinnamon Teal caught the evening sunlight.  After an hour of gliding quietly through the dense cattails, we reached a shallow area on which hundreds of shorebirds had gathered.  Black-necked Stilts, American Avocets, and Long-billed Dowitchers dominated the scene, and the sound of a hundred American Coots running on the water’s surface as they fled our boat sounded like a thunderous ocean wave.  During a second visit to the cienega another evening, I explored the shoreline, mostly short pickleweed and a few scraggly tamarisks.  Migrant warblers were using this area, especially Yellow-rumped Warblers (Audubon’s race), many of which were sallying and tumbling after invisible flying insects.  A large flight of Tree Swallows came by, a stream of them that lasted a good forty minutes.  Song Sparrows sang from the edge of the pools, and a few shorebirds stopped by now and then, a Least Sandpiper obligingly foraging in the late evening sunlight mere meters from me.  I tried to make a third visit the next week, but I unwisely chose a windy day, and the blowing dust was so thick as I approached the cienega that visibility abruptly reduced to ten feet and soft sand was piling up on the road - I decided to turn around!

Rio Colorado Restoration Sites

I made numerous visits to many places along the Rio Colorado, but Pronatura Noroeste has some nice restoration areas along the river not far outside Luis B. Sanchez.  Workers have removed large stands of invasive tamarisk and have replaced them with native mesquite, cottonwood, and willow.  The plots are in various stages of development - there are bare fields with Horned Larks singing their tinkling songs from the sky, plots with cottonwoods no taller than me, and dense thickets with mature willow and mesquite (these were favored by the warblers).  The sound of Ring-necked Pheasants from the surrounding wheat fields brought incongruous memories of a summer working in Iowa - apparently this species is expected here, but it had not been on my radar!  The larger trees and open spaces provided habitat for Bullock’s Orioles and many flycatchers - Vermillion Flycatchers, brilliant red balls of fluff performing their fluttering flight songs; pugnacious Western Kingbirds; Ash-throated Flycatchers investigating nest holes.  Lesser Nighthawks coursed by in broad daylight, and Burrowing Owls frequently flushed from the dirt levees.  Remaining areas of tamarisk housed rasping families of Black-tailed Gnatcatchers, skulking Crissal Thrashers, and Greater Roadrunners.  The river itself held plenty of slow-moving water and dense marsh vegetation, with rails, Marsh Wrens, Caspian Terns, and Pied-billed Grebes.

It was a very successful trip, the sheer number of migrants provided me with a wealth of foraging data, and the sight of cottonwood seedlings sprouting provided new hope for the region.  I was impressed by the dedication to nature shown by many of the Mexicans I met, and with seven more years of pulse flows planned, perhaps some of this amazing riparian habitat can expand across the salt flat currently separating the river from the Sea of Cortez and revitalize the farthest reaches of the delta.