California Partners in Flight Riparian Bird Conservation Plan
Blue Grosbeak (Guiraca caerulea)
Photo by James Gallagher, Sea and Sage Audubon
Prepared by: Jennifer White (firstname.lastname@example.org)
White, J. 1998. Blue Grosbeak (Guiraca caerulea). In The Riparian Bird Conservation Plan:a strategy for reversing the decline of riparian-associated birds in California. California Partners in Flight. http://www.prbo.org/calpif/htmldocs/riparian_v-2.html
Three of 7 described subspecies occur in the United States. Grinnell considered the Colorado River Valley, Imperial and Coachella valley populations to be the Arizona Blue Grosbeak G. c. interfusa, but these populations are now considered G. c. salicaria (Ingold 1993).
G. c. caerulea - se and s central U.S.
G. c. interfusa - sw U.S. and n Mexico
G. c. salicaria - Central Valley, CA and se deserts/valley floors, from Oasis, Mono and Owens Valley, Armagosa River, sw CA to nw Baja and east to the Virgin River in sw Utah and the Colorado River, AZ (Phillips et al. 1964).
MANAGEMENT STATUS: None.
HISTORICAL BREEDING DISTRIBUTION
Early 20th century breeding range more southerly than now (Am. On. Union 1931). G. c. caeraula Only breeding consistently in New Jersey and Ohio since 1970s. Coues (1874 in Ingold 1993) originally suggested range expansion of this species, possibly due to cutting of eastern forests. G. c. salicaria also possibly expanding north (Ingold 1993).
CURRENT BREEDING DISTRIBUTION
G. c. salicaria 150,000 km2; G. c. 2,000,000 km2 (USFWS) ECOLOGY: The greatest Blue Grosbeak densities are reported for G. c. caeraula in se U.S. (spot-mapping, Ingold 1993). Reported densities are 30 males/km2 in Florida (Baker 1989 in Ingold 1993), and 31 males/km2 in e TX (Dickson Segelquist 1979 in Ingold 1993). BBS data from map in Ingold indicates CA densities to be less than 5 birds per route per year. Along the Colorado River, densities are reported as 4 to 6 pairs/40 ha (Rosenberg 1991). In Orange Co., CA, 2 nests were located 15 m apart (Bleitz 1956).
AVERAGE TERRITORY SIZE
SC: 6.12 ha to 5.2 ha and 6.2 ha (Odum and Kuensler 1955 in Zeiner 1990); GA: 1.2 ha in tung-oil groves.
TIME OF OCCURRENCE AND SEASONAL MOVEMENTS
Arrival date on breeding grounds: Males arrive in southern California from 5 April to mid-April (Garrett and Dunn 1981). Males arrive from 18 to 22 April (Tyler 1913, Rosenberg et al. 1991 in USFWS). Few females arrive before 1 May (USFWS). Departure date from breeding grounds: Begins 8 Aug (Tyler 1913 in USFWS). All birds have usually left California by the end of September. Early SEFI record on 16 Aug (Pyle and Henderson 1991). Spring migration period: Mid-April to May and mid-May (Ingold 1993), slightly later on Colorado River, late spring migrant 18 June on SEFI. Fall migration period: Mid-August to mid-September in S. Dakota (S. Dakota Ornithol. Union 1991), late August to early September in Coastal CA (Garrett and Dunn 1981 in Ingold 1993), 8 Aug (Tyler 1913), 16 Aug (SEFI Pyle and Henderson 1991).
Extent of wintering in CA: Stragglers through mid-October (Rosenberg et al. 1991, Unitt 1984) and mid-November (Garrett and Dunn 1981). Late fall migrant recorded on 3 December 1988 at Oak Canyon Nature Center (OCNC) and one definite winter record at Irvine Regional Park, from 29 February to 9 March, 1992 (Hamilton and Willick 1996). Also, "one valid record of G. c. salicaria in AZ" on 18 February, 1951 (Parker in Phillips et al. 1964). G. c. salicaria winters in western Mexico from southern Sonora to Guerrero (USFWS).
MIGRATION STOPOVER CHARACTERISTICS
Stop-over period: no information. Habitat use: Fall migrants in U.S. gather in flocks in grasslands, rice fields and grain fields (Ingold 1993). Routes: no information on G. c. salicaria, G. c. caerulea migrates along Pacific slope and some may cross the Gulf of Mexico (Ingold 1993).
No detailed information, may hover and glean, fly-catch, walk or hop on the ground (Ingold 1993). Large bill allows for manipulation of large grains such as corn (zea mays), and insects such as grasshoppers and mantids (Ingold 1993).
Insects are eaten during the breeding season. Primarily, grasshoppers and crickets, secondarily, seeds of wild and cultivated grains, in the winter often in rice fields. Snails and other invertebrates, fruits.
The Blue Grosbeak has been described as a habitat generalist as it will readily nest in the exotic salt cedar (Tamarix chinensis), in orchard trees, or in native willow/cottonwood habitat (Rosenberg et al. 1991 in USFWS). Miller (1951 in Bent 1968) found grosbeaks in California to occur mainly in "riparian woodland and fresh-water marshes." Blue Grosbeaks are riparian edge species, occurring at forest/field edges or at forest/gravel-bar interfaces (Gains 1974). Blue Grosbeaks prefer herbaceous annuals and young, shrubby willows and cottonwoods, such as those regenerating after a flood (Grinnell and Miller 1944, Rosenberg et al. in USFWS). Plant growth form is likely more important than plant species, Blue Grosbeaks prefer upright growing herbs for nest placement. Tall plants, shrubs and trees may be important in providing singing perches and shade for nest sites.
Canopy cover (averaged densiometer readings): Densiometer readings at the nest, mean =11.61 (n=36, SE=4.11, median=0) (PRBO unpubl. data, Cosumnes and Lower Sacramento Rivers, Central Valley, CA).
Distance to water:
Tyler (1913 in Bent 1968) thought it important, but P. Unitt (1992) found them nesting in dry washes in San Diego Co. and Pequegnat (1951) found them to be "common along dry Baccharis dominated arroyos on the Pacific drainage below 1,500 ft." Orange Co.
Substrate (species): At Central Valley, CA sites Cosumnes River and Lower Sacramento River: Milk Thistle (Silybum marianum), Smartweed (Polygonum spp), Pale Smartweed (Polygonum lapathifolium), Sunflower (Helianthus annuus), Himalayan Blackberry (Rubus discolor), Mustard (Brassica spp), Sandbar Willow (Salicacaea sessilifolia), Beggar ticks (Bidens frondosa), Daisy, Cockle Bur (Xanthium canadense), Dock (Rumex spp), Goosefoot (Chenopodium spp), Prickly Lettuce (Lactuca serriola) (PRBO, unpubl. data). Rosenberg et al. (in Ingold 1993) document a positive effect on nesting Blue Grosbeaks from planting of natural habitat in residential areas and from the spread of salt cedar (Tamarix) in the lower Colorado River valley.
Height of nest:
Range from 15 cm to 7.8 m (Stabler 1959 and Bent 1968 in Ingold 1993), and from 0.15 to 6m but most often 0.6 to 3m (Zeiner 1990). Nest height, mean=55.47cm (n=38, SE=3.37, median =55) (PRBO unpubl. data, Cosumnes and Lower Sacramento Rivers, Central Valley, CA).
Height of nest plant:
Mean=131.32cm (n=38, SE=7.23, median =110) (PRBO unpubl. data, Cosumnes and Lower Sacramento Rivers, Central Valley, CA).
Percent of nest cover:
SE=4.34, median=96) (PRBO unpubl. data, Cosumnes and Lower Sacramento Rivers,
Central Valley, CA). NEST TYPE
Open cup, made
of stems, thin twigs, bark strips, rootlets, dead leaves, corn husks, cardboard,
cotton, paper, plastic/cellophane, shed snakeskin, lined with fine rootlets,
tendrils, hair, fine grasses. Shed snakeskin is reportedly a common component
in nests. Tyler (1913 in Bent 1968) reports that in his experience there
was always a piece of paper or a paper-like leaf woven into the nest. Two nests
from Cosumnes contained clear plastic (PRBO unpubl. data). CA nests fastened
to 2-3 upright shoots (Tyler in Bent 1968).
Open cup, made of stems, thin twigs, bark strips, rootlets, dead leaves, corn husks, cardboard, cotton, paper, plastic/cellophane, shed snakeskin, lined with fine rootlets, tendrils, hair, fine grasses. Shed snakeskin is reportedly a common component in nests. Tyler (1913 in Bent 1968) reports that in his experience there was always a piece of paper or a paper-like leaf woven into the nest. Two nests from Cosumnes contained clear plastic (PRBO unpubl. data). CA nests fastened to 2-3 upright shoots (Tyler in Bent 1968).
TYPICAL BREEDING DENSITIES
AZ: 4 to 6/ 40 ha (Rosenberg 1991).
Tail flicking and spreading (Phillips et al. 1964, Mayr and Short 1970, Stiles and Skutch 1989 in Ingold 1993), may erect crown feathers (Ingold 1993).
Assumed monogamous, 2 successive nesting attempts observed by same pair (Stabler 1959). No known color band studies.
Range from 2 to 5, usually 4.
11-12 days (Stabler 1959).
DEVELOPMENT AT HATCHING
Altricial and nidicolous, natal down mouse gray, no information on hatching weight or vocalizations (Ingold 1993). Approximately 2 days to hatch (Stabler 1959). Bill (gray lower mandible), legs and feet dull brownish pink, gape flanges yellow (Baicich and Harrison 1997). Post fledging biology of offspring: mixed age, mixed sex feeding flocks (Bent 1968 in Ingold 1993).
Range from 9-19 days (Stabler 1959), 9-13 days (Baicich and Harrison 1997).
Altricial young attended by both male and female, females re-nest while males attend fledglings (Baicich and Harrison 1997).No information on female attentiveness during incubation, female fed by male (Ingold 1993). First eggs in California from 18 April to 12 July (Taber in Bent 1968), first eggs in Coastal southern California from 10 April (Willett 1933) to 7 July (Unitt 1984). First egg at Cosumnes CA (5/16/97) last egg (8/6/95) (PRBO unbupl. data). Breeding in the southwest may coincide with monsoon rains in July (Short 1974).
POST-BREEDING SOCIAL BEHAVIOR
Mixed age, mixed sex feeding flocks (Bent 1968 in Ingold 1993).
NUMBER OF BROODS
Reportedly heavy parasitism by brown headed cowbirds, and a known host to Bronzed cowbird (Ingold 1993). Friedmen studied museum nest collections and found a rate of 10.8% brood parasitism for G. c. salicaria (1977). Nests may be built over a cowbird egg (1992). Blue Grosbeaks can raise both host and parasites (Sutton 1967).
In western Sierra foothills there are few records above 1,000 ft. There is one nest record at 1,700 ft. in Maraposa Co., and nest records from above Lake Isabella (Verner and Boss 1980). Nests below 1,500 ft. Orange Co. to valley floors, to -200 ft at Salton Sea.
Does well along road sides and near open areas or fields, young willow riparian/weedy field edge. Ordination study results give the Blue Grosbeak low ordination values (1.80 (range: 1.8 to 9.57) Whitmore 1975, and 8.1 (range: 3.2 to 43.3) James 1971) which indicates that Blue Grosbeaks prefer open areas with higher ground cover. May have increased in ne U.S. due to forest fragmentation there.
At Cosumnes nested on roadsides with only thin strips of vegetation between road and agricultural field.
Benefits from floods which increase annuals and young willow/cottonwood habitat.
ADJACENT LAND USE
Forages in agricultural fields and nests along roadsides and cultivated fields.
DEMOGRAPHY AND POPULATION TRENDS
Apparently, not recorded recently from the inland valleys of the Coast Ranges of central California, USFWS. Expansion northward, two nest records in Idaho (Powers 1969, Rich and Trentlage 1981 in USFWS report).
Zeiner et. al (1990) reported that the breeding population declined in California in recent decades because of habitat degradation, destruction and cowbird parasitism. The Blue Grosbeak is generally acknowledged to have declined in some parts of it's California range, including coastal southern California (Willett 1912) and the San Joaquin Valley (Remsen 1978). Gains (1974) considered the Blue Grosbeak to be uncommon in the Sacramento Valley, occupying only 20 to 40% of suitable habitat (in USFWS report). BBS data from 42 California sites, 1969 to 1989, suggest a non-significant annual rate of increase of 2.5% (USFWS report).
MANAGEMENT ISSUES AND OPTIONS
EXOTIC SPECIES INVASION/ENCROACHMENT
Readily nests in exotic plant species (e.g., Tamarix).
There is limited biological information on the distribution, nest success, Brown-headed Cowbird parasitism rates, and possible effects of pesticide use on Blue Grosbeak. Blue Grosbeaks benefit from the conservation and management for early successional riparian habitat and adjacent open areas.
HABITAT AND POPULATION OBJECTIVES
MONITORING METHODS AND RESEARCH NEEDS
Determine current breeding distribution throughout California.
Locate and increase amount of high quality breeding habitat.
Gather natural history information for California Blue Grosbeak in valley/riparian habitat and in dry washes/arroyos of Coastal California.