Creepers — Family Certhiidae
Brown Creeper Certhia americana
A bird of deep forest like the Brown Creeper finds little habitat in a region as arid as San Diego County, but the county’s higher mountains support a small population. Thick stands of big-cone Douglas fir and incense cedar on north-facing slopes and in deep canyons offer the best habitat. The local population is probably more or less resident, but a few winter visitors, perhaps from farther north, scatter to lower elevations.
Breeding distribution: Breeding Brown Creepers are confined to the coniferous forests of San Diego County’s higher mountains, occurring above about 4200 feet elevation in all five ranges: Palomar, Hot Springs, Volcan, Cuyamaca, and Laguna. They are more numerous on Palomar (up to 20 around Fry Creek Campground, D14, 18 July 1998, D. S. Cooper) and in the Cuyamaca Mountains, especially on Middle Peak (M20; up to 12 on 11 June and 2 July 2000, R. E. Webster). The steep slopes of these more humid ranges support more of the big-cone Douglas fir and incense cedar that favor creepers. Numbers in the dryer Laguna Mountains, dominated by open stands of pine, are considerably lower (maximum daily count 3 around Mount Laguna, O23, 29 July 2000 and 7 July 2001, J. R. Barth). The Laguna Mountains represent the southern tip of the Brown Creeper’s range along the Pacific coast, as there is no resident population in Baja California.
Nesting: The Brown Creeper typically builds its nest behind a loose slab of bark. In San Diego County the incense cedar, with its shaggy reddish bark, is the tree offering the most nest sites. The two nests described by atlas observers, both on Hot Springs Mountain (K. L. Weaver, C. R. Mahrdt), were in incense cedars.
Our records of creepers’ breeding activity imply incubation begun on dates ranging from mid April to late June. Thus the breeding season we observed was practically equivalent to the range of 33 California egg dates, 16 April–8 July, reported by Bent (1948).
Migration: Outside its breeding range, the Brown Creeper is a very rare migrant and winter visitor, visiting diverse trees. Dates of such dispersers range from 13 August (1970 and 1983, Point Loma, S7, AB 24:718, 1970 and 38:247, 1984) to 19 February (1978, Wilderness Gardens, D11, Unitt 1984), though there are only two records earlier than late September. The three records for the Anza–Borrego Desert range only from 19 October to 2 November (ABDSP database).
Winter: In the creeper’s breeding range, its numbers in winter seem little different from those in the breeding season (maximum count 9 in Palomar Mountain State Park, E14, 27 February 2000, P. Unitt). At that season creepers often associate with mixed flocks of other small arboreal birds. Away from coniferous woodland creepers are rare; we noted them at low elevations on only 13 occasions from 1997 to 2002. These records are scattered over the coastal slope south to Singing Hills golf course (Q14; one on 5 December 1999, N. Perretta), though in previous years the species had been recorded south occasionally to the Tijuana River valley (3 November 1963, G. McCaskie; 19 December 1987, P. Unitt). The Brown Creeper is recorded rarely on Escondido, Oceanside, Rancho Santa Fe, and San Diego Christmas bird counts, in frequencies ranging from 4 times in 17 years for Escondido to 3 times in 50 years for San Diego. Its occurrences are not as irregular as those of many other montane birds, but there was a larger incursion in 1987–88, when these four counts yielded a total of six individuals; their annual average is only 0.13. San Diego County represents the southern tip of the creeper’s winter range as well as its breeding range on the Pacific coast; only five sightings have been reported from northern Baja California (Erickson et al. 2001).
Conservation: With much of its habitat in state parks and the Cleveland National Forest, the Brown Creeper is under little threat of direct habitat loss in San Diego County. But as a less common coniferous forest species, clinging to the edge of its range, it is susceptible to climate change that could reduce or eliminate its habitat. Drought at the turn of the millennium has already stressed the trees on which the creeper depends. Fires sweeping the county’s mountain ranges could eat away at the creeper’s limited range.
Taxonomy: The subspecies of the Brown Creeper resident from San Diego County north to southern Oregon is C. a. zelotes Osgood, 1901, distinguished by its dark chestnut rump, whitish underparts, and whitish streaks on the upperparts. The white streaking of the upperparts is much reduced by plumage wear; the Brown Creeper is especially susceptible to wear because of its delicate plumage and constant contact with tree bark. It was the more extensive white streaking of fresh-plumaged birds that led me to misidentify a specimen of zelotes from the Laguna Mountains as a migrant of C. a. montana Ridgway, 1882, from the Rocky Mountain region (Unitt 1984). The color of the rump (paler tawny in montana, darker cinnamon in zelotes) is less affected by wear and a better diagnostic character (Unitt and Rea 1997). Nevertheless, migrants of more distant subspecies are possible in San Diego County, as montana has been collected at Hinkley and Yermo in the Mojave Desert and C. a. americana Bonaparte, 1838, has been collected in the Imperial Valley and at Cambria, San Luis Obispo County. C. a. zelotes is likely at low elevations as well, having been collected at Riverside, Rialto, and Yucaipa. No lowland specimens have been collected in San Diego County (Unitt and Rea 1997).