San Diego Natural History Museum--Your Nature Connection[San Diego County Bird Atlas Project]

Reports from the Field
Spring 1998

News from Square V12, Otay Mesa West
Bountiful Boden Canyon

News from Square V12, Otay Mesa West

It's not pleasant watching a Northern Harrier flying low over the bulldozers, earthmovers, and huge water trucks that are methodically scraping the coastal sage scrub off hundreds of acres on Otay Mesa. The chaparral that supported the birds and small mammals, mice, voles, and gophers, which in turn were the livelihood of the hawks and harriers, is being scraped off, piled up, and burned. Otay Mesa, from Otay Valley Road south to Interstate 905, is the latest major housing development of Pardee Homes, as reported in the San Diego Union-Tribune, 4 January: "Ultimately, over the next decade, 3000 homes will take shape on the Pardee site over 1000 acres." The site extends roughly from Interstate 805 on the west to the new Whitewater Canyon Water Park and Brown Field on the east. The development entails the removal of the only bush of Rosa minutifolia, the exquisitely spiny wild rose of Baja California, growing in the U.S.

Fortunately, one major canyon has been left untouched, at Del Sol Blvd., near the 805. The canyon extends east from the 805 about one mile and appears to be about a half mile wide. It still rings with the songs of the native scrub-dwelling birds and is home to many small mammals. But it is now an island, surrounded by freeways and construction. Last summer, the water park opened, and now a 20,000-seat amphitheater is under construction next to it. These two developments, plus the Pardee site and Brown Field, coincide neatly with atlas square V12. Will my efforts in this square document the disappearance of many of its birds?

--Pat Walsh

Bountiful Boden Canyon

For years, Boden Canyon was nothing more than a geographic name with a mysterious flora and fauna. Because most of the canyon is in private ownership, legal access to the public is highly restricted, and all roads and trails entering the canyon end at locked gates. Until 1994, a survey and adequate inventory of the canyon's biological resources was not possible. In May and June of that year, the landowners engaged a consulting firm, Lettieri-McIntyre and Associates, to appraise the biology of Boden Canyon. In late June, after intense negotiations between Dick Barber and the owners, the Palomar Audubon Society was invited to continue the census of the birds, as well as to inventory the amphibians, reptiles, and mammals. In addition, the owners agreed to permit access to their land for the Escondido Christmas Bird Count, opening rich habitat excluded from previous counts. Then an understanding with the owners led to permission to conduct Bird Atlas surveys in Boden Canyon. We have taken squares I14 and J14, which include all of Boden and Tim's canyons and much adjacent public and private land.

Recently, the Joint Powers Authority of the San Dieguito River Open Space Park informed us of the sale of Boden Canyon to the state of California. With escrow to close sometime in March, the people of California will have acquired habitat that will serve future generations as a natural park.

Located east of Rancho Guejito and west of Orosco Ridge and Pamo Valley near Ramona, Boden Canyon is 4.5 miles long, oriented north-south, and covers about 2100 acres of high-quality wildlife habitat. The elevation ranges from 800 to 1800 feet. Water includes a 1-acre pond at 1600 feet elevation and a 3-acre pond at 1060 feet, as well as a seasonal creek that ultimately reaches Santa Ysabel Creek to the south. The canyon supports nine major vegetation types, in order of decreasing extent, mixed chaparral, mixed coast live oak/riparian woodland, coast live oak woodland, coastal sage scrub, nonnative grasslands, willow riparian woodland, Engelmann Oak woodland, freshwater marsh, and eucalyptus woodland. Massive rock outcroppings and boulders dot the hillsides. The Rancho Guejito fire of 1993 burned nearly all of the western portion of the canyon, including several hundred acres of dense chaparral and, to a lesser degree, oak woodland. Currently, these areas are in stages of succession, and revegetation is well in progress.

A summer morning's hike from the lower to the upper pond is strenuous but not without rewards. Here, the habitat is predominantly post-fire chaparral, yielding Turkey Vultures, White-tailed Kites, Grasshopper, Sage, Black-chinned, Lark, and Rufous-crowned Sparrows, Rock Wrens, Lazuli Buntings, and Blue Grosbeaks. At the upper pond, Nuttall's and Acorn Woodpeckers, flickers, Western Wood Pewees, and Pacific-slope (Western) Flycatchers greet us. In the oak and riparian woodland, the White-breasted Nuthatch, Ash-throated Flycatcher, Oak (Plain) Titmouse, Anna's Hummingbird, House Wren, Acorn Woodpecker, Western Bluebird, and Phainopepla all nest.

Our surveys, plus those of Lettieri-McIntyre, have revealed 128 species of birds in Boden Canyon. Some 20 species of waterfowl and shorebirds have been observed on the lower pond, including the winter appearance of Canada Geese, Canvasbacks, Ring-necked Ducks, Lesser Scaups, American Wigeons, and, most recently, three female Hooded Mergansers. The American Coot, Ruddy Duck, Mallard, Killdeer, and Great Blue Heron are also frequent at the lower pond. Occasionally, we inadvertently flush a Common Snipe or hear the distant call of a Sora. Mountain Bluebirds made a spectacular appearance this year with a flock of four males and five females seen throughout January. During summer, the chattering of a Yellow-breasted Chat is clearly audible in the nearby riparian woodland.

To date, we have recorded 14 raptor species, of which the Cooper's, Red-shouldered, and Red-tailed are the most frequent. The Ferruginous Hawk, Sharp-shinned Hawk, Prairie Falcon, and Merlin are uncommon to rare visitors. Only the Red-tailed Hawk has so far been confirmed as nesting. At night, the calls of a Western Screech Owl and Great Horned Owl animate the oak woodland, the whistles of the Poor-will the chaparral-covered western slope of Orosco Ridge.

In May 1994, Bob Faught reported a nesting pair of Bell's Vireo in the riparian woodland of Santa Ysabel Creek near the southern entrance to the canyon. In August of that year, we heard the song of one Bell's Vireo in Boden Canyon, 1.5 miles north of the other site. The canyon may support additional breeding pairs, given the large population nearby to the west in the San Pasqual Valley.

Remarkably, Boden Canyon supports some species typical of higher elevations. The Mountain Chickadee, a winter visitor in oak woodland, is occasionally seen in large numbers. The Dark-eyed Junco has been regular in summer for several years and has nested. Least expected were Western Gray Squirrels, in San Diego County typically associated with coniferous and oak woodlands above 3500 feet. In March 1996 we discovered them in the northern reaches of the canyon in square I14, in the canopy of dense live oaks. So far, we have seen eight individuals, presumably adults.

On a behavioral note, while conducting our routine breeding census on 13 May 1997, we were captivated by the intense, agitated behavior and calls of Bewick's and House Wrens, Spotted Towhees, and a Western Bluebird in a densely wooded area of I14. Our curiosity drew us to a large Engelmann Oak. Here, at the end of a dead branch 15 feet above ground, was a cavity where a pair of House Wrens were frantically defending their nest from a formidable intruder„a large adult California Striped Racer. We looked on realizing the wrens could not defend themselves from such an onslaught. A 30-minute visit to the site on 30 May revealed no signs of House Wren activity. We are looking ahead to a second breeding season with the atlas and another productive year in Boden Canyon.

--Clark R. Mahrdt and Richard L. Barber

Spring 1998 Wrenderings | Wrenderings Archive | Bird Atlas Introduction