Bryant's Savannah Sparrow (Passerculus Sandwichensis
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II SPECIES ACCOUNTS Andy Birch PDF of Bryant’s Savannah Sparrow account from: Shuford, W. D., and Gardali, T., editors. 2008. California Bird Species of Special Concern: A ranked assessment of species, subspecies, and distinct populations of birds of immediate conservation concern in California. Studies of Western Birds 1. Western Field Ornithologists, Camarillo, California, and California Department of Fish and Game, Sacramento. Studies of Western Birds No. 1 BRYANT’S SAVANNAH SPARROW (Passerculus sandwichensis alaudinus) Sam D. Fitton Criteria Scores Population Trend 10 Range Trend 0 Population Size 5 Range Size 10 Endemism 10 Population Concentration 0 Threats 10 Year-round Range County Boundaries Water Bodies Kilometers 100 50 0 100 Year-round range of the Bryant’s Savannah Sparrow, a California endemic. Authorities differ on whether the subspe- cies’ range extends north of Humboldt Bay, Humboldt County, and south of Morro Bay, San Luis Obispo County; the range mapped here includes all areas considered by some to pertain to P. s. alaudinus. Regardless, the overall outline of the range is stable, but numbers of this sparrow have declined at least moderately; formerly bred in the Point Lobos area, Monterey County (not mapped). 382 Studies of Western Birds 1:382–387, 2008 Species Accounts California Bird Species of Special Concern SPECIAL CONCERN PRIORITY SEASONAL STATUS IN CALIFORNIA Currently considered a Bird Species of Special Year-round resident; breeds mainly from early Concern (year round), priority 3. Not included on April to early July (Gill 1977), very rarely to previous lists (Remsen 1978, CDFG 1992). mid-August (Hunter et al. 2005). Some local movement is suggested by withdrawal from higher elevation grasslands in Humboldt County during BREEDING BIRD SURVEY STATISTICS inclement winter weather. FOR CALIFORNIA Data inadequate for trend assessment (Sauer et HISTORIC RANGE AND ABUNDANCE al. 2005). IN CALIFORNIA Grinnell and Miller (1944) described the Bryant’s GENERAL RANGE AND ABUNDANCE Savannah Sparrow as a “common” resident, locally “abundant,” of tidal marshes and grasslands in The Savannah Sparrow (Passerculus sandwichensis) the coastal fog belt. Representative areas occupied breeds widely across northern and central North included Humboldt Bay and Kneeland Prairie America and winters primarily in the south- (up to 2800 ft [853 m]), Humboldt County; vari- ern United States, Baja California, and main- ous sites in the San Francisco Bay area (Sonoma, land Mexico south to Guatemala and northern Marin, Solano, Contra Costa, Alameda, San Honduras; resident populations occur mainly Francisco, San Mateo, Santa Clara counties); on the Pacific coast from central California to Santa Cruz and Watsonville, Santa Cruz County; Baja California and on the northwestern coast Point Lobos, Monterey County; and Cambria and and in the central highlands of mainland Mexico Morro Bay, San Luis Obispo County. (Wheelwright and Rising 1993, AOU 1998). Of 17 subspecies of the Savannah Sparrow RECENT RANGE AND ABUNDANCE generally recognized, 4 breed in California IN CALIFORNIA (AOU 1957, Wheelwright and Rising 1993). The Bryant’s Savannah Sparrow (P. s. alaudinus), The general outline of the breeding range today formerly referred to as P. s. bryanti (Grinnell and remains largely unchanged (see map). Still, the loss Miller 1944), is a California endemic restricted to or degradation of coastal marshes and grasslands a narrow coastal strip from Humboldt Bay south within this sparrow’s range has no doubt reduced to the Morro Bay area (AOU 1957); its center of available habitat, causing local extirpations. This abundance appears to be the San Francisco Bay sparrow’s habitat likely suffered disproportionately area. There is uncertainty regarding the ranges during salt marsh conversion in the San Francisco and differentiation of coastal Savannah Sparrows Bay system because of its tendency to use the in California. P. Unitt (pers. comm.) ascribes higher portions of marshes, the areas easiest for all Savannah Sparrows breeding in Humboldt humans to develop (Shuford 1993). County to P. s. alaudinus and those immediately Recent breeding bird atlas projects give some north in coastal Del Norte County to P. s. brooksi. idea of the relative distribution in some counties To the south, he extends the range of alaudinus within the subspecies’ range. Despite variation in slightly south to Point Conception to include observer coverage and the amount of appropriate breeding birds at the mouths of the Santa Maria habitat among the counties surveyed, a simple and Santa Ynez rivers, Santa Barbara County. This index, percent of atlas blocks with evidence of determination is based on data (M. Holmgren Savannah Sparrows breeding, is illustrative of unpubl.) that suggest, with statistical significance, the generally restricted distribution of this spe- a split at Point Conception: P. s. alaudinus to the cies. Starting from the north: Humboldt County, north, P. s. beldingi to the south (M. Holmgren 11% of atlas blocks (Hunter et al. 2005); Sonoma and P. Unitt pers. comm.). Beadle and Rising County, 11% (Burridge 1995); Marin County, (2003) differ somewhat in recommending that 52% (Shuford 1993); Napa County, 11% (Berner birds from Morro Bay south are P. s. beldingi and et al. 2003); San Francisco County, 20% (unpubl. all north to Humboldt Bay are P. s. alaudinus. data); Alameda County, 11% (unpubl. data); San Regardless of the taxonomic treatment, these birds Mateo County, 59% (Sequoia Audubon Society occupy a very narrow geographic and ecological 2001); Contra Costa County, 11% (unpubl. data); range in coastal California. Santa Clara County, 14% (unpubl. data); and Bryant’s Savannah Sparrow 383 Studies of Western Birds No. 1 Monterey County, 11% (Roberson and Tenney Little is known about the abundance of this 1993). sparrow. It generally tends to occur at higher den- Within its narrow coastal range (see map), the sities in coastal marshes than in other habitats (Gill distance inland this sparrow is found from the 1972, Wheelwright and Rising 1993), though, for coastline or bay shore generally ranges from 13km Marin County, Shuford (1993) reported that to 16 km, but it has been located in Humboldt it was distributed in coastal and bay marshes County as far as 40 km inland, near Willow Creek, at apparently lower densities than in fog-belt and has been confirmed breeding at about 24 km grasslands. In Monterey County, Roberson and inland (Hunter et al. 2005). During fieldwork for Tenney (1993) estimated 80–100 pairs, and in other atlas projects, observers have reported pos- Napa County, Berner et al. (2003) reported cat- sible and even probable breeding even farther than egorical estimates of abundance in three southern 40 km inland, such as near Lake Berryessa, Napa blocks (representing the center of abundance for County (Berner et al. 2003). Without definitive the county) of 10–100 individuals in two blocks evidence of breeding, atlas compilers can have dif- and 100–1000 in one. Gill (1972) estimated ficulty interpreting such records, given lingering 800–1000 breeding pairs of Savannah Sparrows wintering birds or migrants can occur inland in in the southern San Francisco Bay. It is difficult to coastal counties through late May (Roberson and estimate overall abundance given these few local Tenney 1993), well into the breeding season of estimates, but the total number of breeding pairs alaudinus on the immediate coast. probably exceeds 10,000 within the entire coastal Likely reflecting increased observer coverage, breeding range. more breeding locales above or inland from the fog belt have been documented in recent times. ECOLOGICAL REQUIREMENTS Among these are the Bald Hills in Humboldt County (Hunter et al. 2005) and east of Salinas in This sparrow occupies low tidally influenced habi- Monterey County (Roberson and Tenney 1993), tats, adjacent ruderal areas, moist grasslands within where individuals apparently use habitats somewhat and just above the fog belt, and, infrequently, drier than those originally described by Grinnell drier grasslands. Bay-shore habitats are composed and Miller (1944). At the southern extreme, breed- primarily of broad expanses of higher parts of ing Savannah Sparrows are now known from the Pickleweed marsh, 1.5 to 3 m above mean sea lower reaches of the Santa Maria and Santa Ynez level, above cord grass stands, and where the rivers (M. Holmgren pers. comm.). Pickleweed community merges into grassland (Gill Conversely, Bryant’s Savannah Sparrows no 1972, Shuford 1993, Wheelwright and Rising longer occupy some historic sites and likely have 1993). Plants typical of this habitat are Pickleweed declined greatly in the core of their range because and Saltgrass (Distichlis spicata). Adjacent to salt of habitat loss. The San Francisco Bay area has marshes this sparrow also occupies weedy spoil experienced salt marsh habitat loss possibly in areas, canal banks, and bottomland pastures (Gill excess of 90% (Larson 2001). This area likely 1972, S. Harris pers. comm.). In south San had the most breeding Savannah Sparrows and Francisco Bay, it nests mainly on levee tops grown perhaps as many as all coastal areas combined. to grasses and in areas of high Pickleweed on levee Here, habitat was converted to urban, industrial, banks (Gill 1977). Around Humboldt Bay, it or flooded areas (Larson 2001), with little suitable breeds in extensive dairy pastures, especially in the habitat remaining and little additional created. taller grasses and rushes along