Nuthatches — Family Sittidae
Red-breasted Nuthatch Sitta canadensis
The Red-breasted Nuthatch is one of those mountain birds whose elevational range is barely touched by the tops of San Diego County’s highest peaks. It is a rare resident in deep forest on the north slopes of the Palomar, Hot Springs, Volcan, and Cuyamaca mountains. The Red-breasted is by far the most dispersive of California’s nuthatches, occurring widely outside its breeding range as an irregular winter visitor. These visitors seek conifers, being seen in other trees only if no conifers are near. Invasions may plant new isolated breeding populations at low elevations, such as the one on Point Loma.
Breeding distribution: From 1997 to 2002, we found the Red-breasted Nuthatch regularly and most numerously on Palomar Mountain. Its habitat there is forest dominated by the big-cone Douglas fir between 4500 and 5700 feet elevation, from Pauma Creek (D14) southeast to Dyche Valley (F15), mainly on the north-facing slopes of the southwestern of the mountain’s two parallel ridges. In this area the species is uncommon, with maximum daily counts of five or fewer, except for 11 (including fledglings) along Highway S6 near Fry Creek 31 May 2000 (E15, E. C. Hall, C. R. Mahrdt). It is regular on Middle Peak and the northeast slope of Cuyamaca Peak (M20) above 5200 feet elevation. During the atlas period the high count in the Cuyamaca Mountains was nine on Middle Peak (M20) 19 May 1998 (R. E. Webster); previously, as many as 20 were noted in the same area 19 July 1987 (AB 41:1488, 1987). There is one report from North Peak (L20), of two about 5200 feet elevation on the northwest slope 14 July 2000 (J. R. Barth).
On Hot Springs Mountain the Red-breasted Nuthatch has been known since the peak’s avifauna was first explored in 1980 (Unitt 1981), with a maximum of six 19 July 1986 (R. E. Webster, AB 40:1256, 1986). During the atlas period, however, K. L. Weaver and C. R. Mahrdt found it in the breeding season only twice, single individuals in square E20 on 9 June 2001 and in E21 on 19 June 1999. Atlas observers found it during the breeding season on Volcan Mountain for the first time, with two on Oak Ridge (I20) 22 July 1999 (L. J. Hargrove), a pair near Catfish Spring (I20) 16 June 2000 (A. P. and T. E. Keenan), and three at 5100 feet elevation 0.35 mile south of Simmons Flat (J20) 16 July 2001 (J. R. Barth).
On Point Loma (S7), mainly on and near the campus of Point Loma Nazarene University, the Red-breasted Nuthatch has been an uncommon resident since it colonized after the invasion of 1963. It may have died out in the mid 1990s, only to recolonize again after the invasion of 1996. Virginia P. Johnson netted a female with a brood patch on 10 March 1997.
Nesting: Like the other nuthatches, the Red-breasted nests in tree cavities. It may use a preexisting cavity or may excavate or enlarge its own. It is famous for smearing the nest entrance with pitch, deterring predators. Nesting in San Diego County, however, is still little known. One nest at Point Loma was in a hole in the sawed-off leaf base of a Canary Island date palm 2 June 1978 (Unitt 1984). Nesting confirmations in the mountains were of nest building on Cuyamaca Peak 23 May 1998 (G. L. Rogers) and of fledglings on Palomar 31 May 2000 (E. C. Hall) and 23 July 2000 (J. R. Barth). Nesting in the coastal colony at Point Loma may begin considerably earlier, as implied by the female with a brood patch on 10 March.
Migration: Red-breasted Nuthatch incursions are notoriously irregular. In San Diego County the species has been recorded away from breeding locations from 27 August (1998, one at O’Neill Lake, E6, P. A. Ginsburg) to 4 May (1997, three in Greenwood Cemetery, S10, P. Unitt). The largest numbers are seen in October and November, some invasions petering out as the winter wears on. Red-breasted Nuthatches have occurred in all regions of San Diego County, but records for the Anza–Borrego Desert are few, with one in “San Felipe Canyon” 2 October 1908 (F. Stephens, MVZ 3880; Grinnell and Miller [1944] reported this specimen as from Vallecito Creek), one at Tamarisk Grove Campground (I24) 4 November 1973 (P. Unitt), one in planted pines in Borrego Springs (F24) 30–31 October 1996 (P. D. Jorgensen), one on Villager Peak (C27) 19 October 1998 (P. D. Jorgensen), and one in Nolina Wash, Pinyon Mountains (K25) 15 October 1999 (D. C. Seals, S. Peters).
Winter: The Red-breasted Nuthatch is one of the more frequent montane invaders, with a few recorded in San Diego County in most winters, including every year from 1997 to 2002. But the larger incursions, during which the species would be rated as uncommon rather than rare, are sporadic. The falls and early winters of 1963, 1969, 1972, 1975, 1983, and 1996 saw the largest. San Diego County Christmas bird counts in December 1996 and January 1997 yielded a total of 26, more than in any previous year. Thus the five-year atlas period began with the winding down of a major invasion, accounting for several records of stragglers remaining into spring 1997. Numbers over the next five winters were small, with the maximum daily count of six near the San Luis Rey Picnic Area (G16) 22 January 2001 (W. E. Haas).
Conservation: The magnitude of Red-breasted Nuthatch invasions is controlled by factors outside San Diego County (Koenig 2001, Koenig and Knops 2001), but the planting of ornamental conifers has made conditions more amenable to them when they arrive. Certainly the species never would have colonized Point Loma if the area had not been heavily planted with pines. Its colonization of San Diego County’s mountains, however, may also be fairly recent, as it was not reported there in the breeding season until 1970. And its population may be increasing gradually; numbers reported from Palomar Mountain 1997–2001 were greater than known there previously, though coverage was much more thorough. Nevertheless, the areas of forest suitable for breeding Red-breasted Nuthatches are so small that a fire could eliminate these isolated populations.
White-breasted Nuthatch Sitta carolinensis
The White-breasted Nuthatch is the most widespread of San Diego County’s three nuthatches. It is a common year-round resident in mountain forests and a familiar patron of bird feeders near this habitat. It is uncommon in oak woodland in the foothills. At low elevations it is a rare and irregular wanderer, apparently most frequent when stressed in its normal range by drought.
Breeding distribution: The White-breasted Nuthatch is one of the common birds of the conifer-dominated woodlands of San Diego County’s mountains. Daily counts range as high as 52 on Hot Springs Mountain (E21) 24 July 1999 (K. L. Weaver), 40 on North Peak, Cuyamaca Mountains (L20), 14 July 2000 (E. C. Hall), and 40 at Mount Laguna (O23) 9 June 2001 (C. G. Edwards). The species is locally common as well in oak woodland at lower elevations (up to 15 in Camp Pendleton 1.5 miles south of Margarita Peak, C5, 25 May 1997, J. M. Wells, and in Boden Canyon, I14, 27 June 1997, R. L. Barber). The White-breasted Nuthatch’s distribution in San Diego resembles that of other oak woodland birds like the Acorn Woodpecker and Oak Titmouse. The nuthatch, however, does not approach the coast as closely as those species; the western margin of its range is shifted a few miles to the east. If the nuthatch requires larger patches of woodland than the other species, then that requirement could account for the difference in distribution. In northwestern San Diego County, in Camp Pendleton, it ranges to about 8 miles from the coast, at about 600 feet elevation in Las Pulgas Canyon (D5; up to six on 28 May 2001, P. Unitt). Near the Mexican border, the site nearest the coast is Dulzura, 19 miles inland and about 1200 feet elevation (U17; up to four, including a male feeding a fledging, 19 June 1998, D. Povey). Single birds were at low elevations in isolated oak groves in Gopher Canyon (F8) 27 June 2000 (P. A. Ginsburg) and near the east end of Lake Hodges (K11) 9 June 1997 (E. C. Hall). One was in riparian woodland lacking oaks along the San Diego River in Santee (P12) 26 June 2001 (M. B. Mulrooney), but this may already have been a postbreeding disperser.
Along the eastern side of its range, however, the White-breasted Nuthatch follows the limits of the oaks almost exactly. It descends to about 4400 feet elevation in the middle fork of Borrego Palm Canyon (F22; up to 10 on 18 July 2001, J. R. Barth) and ranges east to Boulevard (T26) near the Mexican border (nest with nestlings on 20 May 1999, J. K. Wilson). The White-breasted Nuthatch may be a rare resident along San Felipe Creek or only a postbreeding visitor: one was near Paroli Spring (I21) 16 June 2000 (J. O. Zimmer), another near Scissors Crossing (J22) 13 July 2001 (P. Unitt). In 2002, when J. R. Barth monitored the Scissors Crossing area intensively, the first individual showed up 16 June and numbers reached their maximum of 10 on 14 July. High elevation is no limit to the White-breasted Nuthatch in San Diego County, as it breeds near the summit of Hot Springs Mountain (E20; up to 14 on 19 May 2001, K. L. Weaver, C. R. Mahrdt).
Nesting: The White-breasted Nuthatch is a secondary cavity nester, using natural holes in trees or those excavated by woodpeckers. Earlier literature summarized by Pravosudov and Grubb (1993) reported no nests lower than 13 feet, but all the nests whose heights atlas observers described were lower: about 8 feet (in a coast live oak east of Rainbow, C10, P. Unitt), 6 feet (in an ornamental broad-leafed tree at Cameron Corners, U23, M. McIntosh), 4 feet (in a coast live oak in along San Vicente Creek, L15, A. Mauro), and just 1 foot off the ground (southeast of Lake Cuyamaca, N21, P. D. Jorgensen). Our observations suggest that in San Diego County White-breasted Nuthatches lay at least from early April through mid May, well within the range of 21 March–9 June for 56 California egg dates given by Bent (1948).
Migration: The White-breasted Nuthatch does not engage in regular migration, but small numbers disperse occasionally outside the breeding range. This dispersal begins possibly as early as mid June, as suggested by the records from San Felipe Valley, certainly by mid July. Most dispersers are seen on the coastal slope, but one was at Borrego Springs (G24) 31 July 1999 (M. C. Jorgensen), another at Tamarisk Grove (I24) 3 August–2 September 1990 (B. Knaak). White-breasted Nuthatches have been noted at least as late as 22 March at locations where they do not breed (1997, one at Blue Sky Ecological Reserve, L12, M. and. B. McIntosh). The end of such dispersal is uncertain because scattered individuals occur through the breeding season at such locations on the margin of the breeding range.
Winter: In winter most White-breasted Nuthatches remain in their breeding range. The species is still most abundant at higher elevations; our maximum daily count was 50 around Mount Laguna (O23) 21 January 2002 (E. C. Hall, J. O. Zimmer). Winter visitors outside the breeding range decrease rapidly with distance from the edge of that range, suggesting they result largely from short-distance local dispersal, not long-distance migration. The only desert records are of one at Ellis Farms, Borrego Springs (F25), 17 December 2000 (L. J. Hargrove, P. Unitt) and two at Butterfield Ranch, Mason Valley (M23), 13 January 2000 (H. and K. Williams). The highest count outside the breeding range during the atlas period was of five at Lake Hodges (K10) 22 December 2000 (R. L. Barber et al.), but the few winter wanderers 1997–2002 were eclipsed the following fall and winter by the largest incursion ever recorded in San Diego County. For example, from 1953 to 2001 the White-breasted Nuthatch was noted on only 13 of 49 San Diego Christmas bird counts, maximum seven on 31 December 1961, whereas the count on 14 December 2002 yielded 20.
Conservation: No trend in White-breasted Nuthatch numbers in San Diego County is clear. The species depends on mature trees for foraging and nest sites, so it depends on the maintenance and regeneration of oak and coniferous woodland. The nuthatch may benefit from the spread of Nuttall’s Woodpecker, a primary cavity excavator whose old holes the nuthatch uses. The two largest invasions outside the breeding range, in 1961 and 2002, followed the two driest years in San Diego County history, so some birds may have been driven out of their normal range by drought-induced lack of food.
Taxonomy: Sitta c. aculeata Cassin, 1857, is the subspecies of White-breasted Nuthatch resident in San Diego County and the only one collected here. It inhabits the Pacific coast region from Washington to northern Baja California and is characterized by a comparatively short bill and brown-tinged female. The subspecies breeding in the Great Basin/Rocky Mountain region, S. c. nelsoni Mearns, 1902, and S. c. tenuissima Grinnell, 1918, differ in call as well as bill length and plumage. A bird giving calls characteristic of these subspecies has been heard once at Point Loma (4 October–November 2000, R. E. Webster), as well as once in the Imperial Valley (Patten et al. 2003). Other White-breasted Nuthatches recorded in the latter area called like aculeata, as did the one in Borrego Springs 17 December 2000.
Pygmy Nuthatch Sitta pygmaea
The Pygmy Nuthatch is a bird of montane coniferous forests, where it prefers open stands of pines. As a result, it is most common in the Laguna Mountains, where such habitat is widespread, less common in the Cuyamaca, Volcan, and Hot Springs mountains, and rare and localized on Palomar Mountain. The Pygmy Nuthatch is highly social, flock members calling to each other constantly, roosting, and even breeding communally. Invasions of Pygmy Nuthatches out of their normal range are rare.
Breeding distribution: The Pygmy Nuthatch is one of the commonest birds in the Laguna Mountains, where daily counts run as high as 75 between Burned Rancheria Campground and Horse Meadow (P23) 23 June 2000 (E. C. Hall, J. O. Zimmer). The large pines surrounding the meadows on the mountains’ plateau offer ideal habitat. The Pygmy Nuthatch is also common in the Cuyamaca Mountains (up to 25 on Middle Peak, M20, 2 July 2000, R. E. Webster) and in the Volcan Mountains down to Julian (up to 20 north of Julian, J20, 17 August 2000, M. B. Stowe), but there is a short gap between these populations: during the breeding season we noted only a single individual on one occasion between Julian and William Heise County Park (K20). Another population is isolated on Hot Springs Mountain, where it is concentrated near the summit (E20; up to 14 on 17 June 2000, K. L. Weaver, C. R. Mahrdt). On Palomar Mountain, forested largely in big-cone Douglas fir rather than pine, the Pygmy Nuthatch has been found during the breeding season only in Lower Doane Valley (D14; seven on 17 July 1999, J. R. Barth; six, including a juvenile, on 4 August 2000, P. D. Jorgensen). Elevationally, the Pygmy Nuthatch ranges in San Diego County from about 4000 feet in Green Valley, Cuyamaca Mountains (N20; three on 26 June 1999, B. Siegel) to 6533 feet at the summit of Hot Springs Mountain.
Nesting: The Pygmy Nuthatch nests in tree cavities, which it often excavates itself. Unmated males often serve their relatives as nest helpers (Kingery and Ghalambor 2001). In San Diego County the birds commonly nest in pine snags but also use big-cone Douglas fir or oak if these trees are mixed among the pines. Our observations from 1997 to 2001 indicate that Pygmy Nuthatches lay from about 4 May to about 5 June, slightly extending the 14 May–1 June range of seven egg sets collected in San Diego County 1920–35 but well within the 17 April–27 June range of 89 egg sets from throughout California (Bent 1948).
Migration: Dispersal of Pygmy Nuthatches outside their breeding range is very rare, concentrated into a few recorded invasions. None of these took place during the five-year atlas period. Large-scale irruptions are known only in 1966–67, 1972–73, and 1987–88. Wanderers have been recorded in San Diego County from 29 August (1987, 16 at Point Loma, S7, R. E. Webster, AB 42:137, 1988) to 30 May (1966, one at Point Loma, AFN 30:546, 1966). The pines planted on Point Loma have served as an attraction for dispersing Pygmy as well as Red-breasted Nuthatches.
Winter: The Pygmy Nuthatch, as a resident species, is seen in winter in much the same numbers as in summer (maximum daily count 100 around Laguna Meadow, O23, 21 January 2002, E. C. Hall, J. O. Zimmer). During exceptionally cold or stormy weather numbers seen may be depressed because the nuthatches may go a whole day without emerging from their roost holes (Kingery and Ghalambor 2001). Occasional birds are seen at sites, still in pine woods, where they are not known in the breeding season (up to six at Pine Hills, K19, 6 February 2002, M. B. Stowe). On Palomar Mountain, winter records are still largely from Lower Doane Valley, but the species has been noted also at nearby Doane Pond (E14; 24 December 2000, G. C. Hazard) and at the Palomar Observatory (D15; 13 on 28 December 2000, K. L. Weaver).
In invasion years Pygmy Nuthatches have dispersed over much of San Diego County’s coastal slope but are unrecorded in the Anza–Borrego Desert. The most recent irruption was in 1987–88, which yielded 17 on the Oceanside Christmas bird count and four on the Rancho Santa Fe count—the only records of the Pygmy Nuthatch on either of these counts.
Conservation: Like other birds of coniferous forest, the Pygmy Nuthatch is threatened more by fire, prolonged drought, and climate change than by habitat loss to development. When stressed by drought, the pines on which the nuthatch depends are susceptible to attack by a bark beetle. Many pines died during the drought beginning in 1999. The effect of the death of these on birds is unknown, but the Pygmy Nuthatch, which forages in pines almost exclusively, is more likely to be affected than other species.
Taxonomy: The Pygmy Nuthatches resident in San Diego County are S. p. leuconucha Anthony, 1889, which occurs also in the sierras Juárez and San Pedro Mártir of Baja California. This subspecies has been defined primarily by its larger size, especially of the bill, although the measurements tabulated by Norris (1958) reveal that no single linear measurement suffices to distinguish leuconucha from S. p. melanotis van Rossem, 1929, which inhabits mountain forests over the rest of western the United States. Though leuconucha does average significantly larger, it fails the test for extent of overlap (Patten and Unitt 2002) on the basis of any single measurement. Nevertheless, colorimetry of a small sample of fresh-plumaged specimens suggests that the paler back and especially paler crown of leuconucha might, perhaps combined with measurements in a multivariate function, distinguish the subspecies adequately. On the crown, seven August–November specimens of melanotis from northeastern California, Oregon, Nebraska, Colorado, and Arizona read L = 28.1–33.3, whereas six September–December specimens of leuconucha from the Laguna Mountains and Sierra Juárez read L = 33.3–36.2
The one lowland specimen (Point Loma, 3 September 1985, SDNHM 35442) is S. p. melanotis on the basis of both its short bill (9.9 mm from nostril) and comparatively dark crown (L = 32.9). Thus it originated from north of San Diego County, a pattern likely typical of montane invaders.