California Partners in Flight Coastal Scrub and Chaparral Bird Conservation Plan
Wrentit (Chamaea fasciata)
Photo by Eric Preston
Prepared by: Geoffrey R. Geupel (email@example.com), Grant Ballard (firstname.lastname@example.org), and Mary K. Chase
PRBO Conservation Science
4990 Shoreline Highway
Stinson Beach, CA 94970
Geupel, G.R., G. Ballard, M.K. Chase. 2002. Wrentit (Chamaea fasciata). In The Coastal Scrub and Chaparral Bird Conservation Plan: a strategy for protecting and managing coastal scrub and chaparral habitats and associated birds in California. California Partners in Flight. http://www.prbo.org/calpif/htmldocs/scrub.html
action plan summary
Seven subspecies have been described: C.f. phaea, the darkest of the 7 subspecies, ranges from Columbia River south along the humid coastal belt of Oregon to the California border; C.f. marga, interior s. Oregon; C.f. rufula, nw. California coast from Oregon border to Marin County; C.f, intemedia, San Francisco Bay region except Marin County; C.f. fasiata, central coast of California from w. Monterey County to c. San Luis Obispo County; C.f. henshawi, palest and grayest subspecies from interior and s. California coast, local in Central Valley and east side of the Sierra and desert divide; C. f. canicauda, nw. Baja California, Mexico, south to latitude 30 degrees north. There has been some debate over subspecies of the Wrentit (see Geupel and Ballard 2002).
No official management status. One of a few species that has fallen outside the criteria for listing under the Migratory Bird Treaty Act (MTBA) because the unique family name was never listed in the Mexican Convention of 1918 and 1936.
Common resident west of deserts, along coast and coast ranges, and in western foothills of Sierra Nevada (Grinnell 1915). See also Grinnell and Miller 1944. Recorded as a rare resident in Golden Gate Park, San Francisco (Mailliard 1930).
CURRENT BREEDING DISTRIBUTION:
Limited to the west coast of North America; bounded to the north by the Columbia River, south by the deserts of Baja California, and inland by the Sierra Nevada and Cascade mountain ranges. Within California, generally found west of the Cascades and Sierra crest and east of deserts, but not in much of the Central Valley (Small 1994). Not found on Channel Islands or on Palos Verdes Peninsula, Los Angeles County (Small 1994). In Santa Barbara county, found commonly in dense brush everywhere but the Cuyama Valley (Lehman 1994). Common to very common in brushy habitat throughout Monterey County (Roberson 1985).
Breeding Bird Atlases:
San Diego County - common in sage scrub and chaparral, ranges east to edge of Anza - Borrego Desert, where occurs in mesquite thickets (San Diego County Bird Atlas, (http://www.sdnhm.org/research/birdatlas/).
Contra Coast County - confirmed or probable breeder in much of central and western portions of the county (Contra Costa County Bird Atlas, (http://www.flyingemu.com/ccosta/sgsp.html).
Marin County - confirmed or probably breeder in most of Marin County (Shuford 1993).
Sonoma County - breeding confirmed in 15 blocks and probable in 46 blocks in Sonoma County (Burridge 1995).
BBS route: http://www.mbr-pwrc.usgs.gov/bbs/
AVERAGE TERRITORY SIZE:
The territories of 105 pairs in coastal California in 1988, 1990, and 1997 averaged 0.62 hectares, range 0.24 to 2.15 (PRBO). Territories generally smaller in denser scrub than in sparse scrub (Erickson 1938, PRBO).
TIME OF OCCURRENCE AND SEASONAL MOVEMENTS:
Non-migratory. Resident throughout range. Garret and Dunn (1981) suggest that limited upslope movement may occur in mountains of southern CA after nesting.
Gleaning: most insect items are located within "peck range," seized by the bill and swallowed whole. On occasion will hover at sticky monkey flowers (Mimulus sp.) or flycatch insects. Fruits and seeds also consumed.
Insects, spiders, caterpillars, fruit, and seeds with more emphasis on seeds in winter. Seeds of poison oak (Toxicodendron diversilobium) are especially important, providing a 7 month food supply through winter.
Will use standing water for drinking if available. More often will use drops of moisture collected on leaves from fog, mist and rain.
Prefers coastal sage scrub, northern coastal scrub, lowland hard and montane chaparral (Grinnell and Miller 1944, Small 1994). Known to breed in almost any habitat that includes a somewhat dense shrub understory including mature riparian, valley oak (Quercus lobata), Douglas fir (Pseudotsuga menziesii), and redwood (Sequoia sempervirens) forests, early successional forests, riparian (Salix sp.) scrub, Coyote bush (Baccahris sp.), poison oak, and blackberry (Rubus sp.) thickets, suburban parks and larger gardens. Avoids introduced Eucalyptus (Eucalyptus sp.) and broom (Genista sp.) fields (PRBO).
Includes California sage (Artemisia californica), coyote bush (Baccharis pilularis), California blackberry (Rubus ursinus), poison oak (Toxicodendron diversilobum), chamise (Adenostoma fasciculatum), coffeeberry (Rhamnus californica), Douglas fir (Pseudotsuga menziesii), monkeyflower (Mimulus guttatus), bracken fern (Pteridium aquitinum), vetch (Vicia sp.), bush lupine (Lupinus arboreus), California hazlenut (Corylus cornuta), live oak (Quercus agrifolia), alder (Alnus sp.), valley oak (Q. lobata), and wild grape (Vitis californica) (Erickson 1938, Geupel and Ballard, in press, PRBO).
HEIGHT OF NEST:
Nest heights ranged from 17 to 280 cm at Palomarin (mean = 75, SD = 29, n = 1020 - PRBO).
HEIGHT OF PLANT:
Heights of nest shrubs and trees ranged from 40 - 600 cm (mean = 146 cm, SD
= 88, n = 517).
Vegetative cover above the nest ranged from 0 - 100% (mean = 78%, SD = 24, n = 562) (PRBO).
TYPICAL BREEDING DENSITIES:
Densities at Palomarin ranged between 1.80 and 3.34 territorial individuals per ha (1980 - 1996; PRBO).
Voice is used to announce presence and boundary infractions. When intruders are detected, territory-holders quickly fly to the vicinity or to a territory boundary and sing. Head feathers may be erected as individuals fly towards each other and sing or scold. Tail is usually held straight up.
Monogamous; no reports of polygamy or polyandry.
3 (58%) or 4 (37%), rarely 1, 2 or 5. Mean = 3.57, n = 733 nests) at Palomarin (PRBO).
Mean incubation period = 14.9 d for Wrentits at Palomarin (range = 11-18, mode = 15, SD = 0.81, n = 192).
DEVELOPMENT AT HATCHING:
Altricial and naked, eyes closed.
Mean nestling period from 242 nests at Palomarin was 14.6 d, mode 15, range 11-19, SD=1.5 (PRBO).
POST FLEDGING BIOLOGY OF OFFSPRING:
Both parents feed fledglings, and some young are fed by parents at least up to 41 d post fledging (Geupel and DeSante 1990). Spends average of 30 d on or near natal territory. Young birds from different broods often observed moving together in groups of 2 and rarely up to 5, 10 or more weeks after fledging (Erickson 1938).
POST BREEDING SOCIAL BEHAVIOR:
Generally stay within territories defended all winter, although some short (< 500 m) off-territory movements may occur in non-breeding season.
Most young birds pair and breed by their second year; a few individuals delay pairing and "float," usually no more than one breeding season.
NUMBER OF BROODS:
Usually 1. About 20% of breeders attempt second broods, and about 16% are successful at fledging two broods (Geupel and DeSante 1990).
Rare or uncommon host throughout range. If cowbird egg(s) laid early enough, all Wrentit eggs or young are lost.
Breeds from sea level to near 2300 m.
Fragmentation and isolation of shrublands may cause local extirpation. In one study, Wrentits persisted longer in habitat fragments than other scrub-requiring birds, probably because they occurred at higher densities before fragmentation took place (Soulé et al. 1988). However, when these fragments were re-surveyed in 1997, Wrentits had disappeared from many fragments where they had been present in 1987, and these local extinctions were more common in small (<10 ha) fragments and relatively old fragments (32-86 years; Crooks et al. 2001). Wrentits did not recolonize any fragments in this study, as might be expected due to their low dispersal ability. Wrentits breeding in chaparral habitat of Southern California were negatively associated with the amount of surrounding urbanization (Stralberg and Bao 1999).
Wrentits occurred in 100% of chaparral fragments over 7 ha in size in urban San Diego County, but their occurrence dropped off sharply in smaller habitat patches (Soulé et al 1988).
DISTURBANCE (natural or managed):
Positively influenced by the extensive clear cutting that has occurred in the
Coast Range, Sierra Nevada, and Siskiyous. Populations are increasing and expanding
as forests are replaced with shrubby cover (Browning 1992). Fire suppression
also probably favors Wrentits as shrub and low woody cover increases. Catastrophic
fire seems to decrease Wrentit abundance if shrub cover is lost.
SENSITIVITY TO HUMAN-INDUCED DISTURBANCE:
Prescribed fires probably causes mortality. Fairly resistant to impacts caused
Known nest predators (eggs or nestlings) include Western Scrub-jay (Aphelocoma californica), garter snake (Thamnophis sp.) and gopher snake (Pituophis sp.). Predators of adults unknown.
EXOTIC SPECIES INVASION/ENCROACHMENT:
May be negatively affected by introduced Eucalyptus (Eucalyptus sp.)
and broom (Genista sp.). Possibly affected by introduced nest predators.
DEMOGRAPHICS AND POPULATION TRENDS:
AGE AND SEX RATIOS:
From PRBO: The mean annual probability that a nest fledged = 1 natal young using the Mayfield method was 45.5% (range 25.8-78.7, SD = 13.7, n = 18 yr, 840 nests) at Palomarin. Mean lifetime reproductive success (LRS) measured in terms of the total number of young fledged was 4.34 (range 0-31, SD = 5.45, n = 226).
Average lifespan for 231 color-banded individuals banded as nestlings or hatch-year birds at Palomarin was 2.7 yr (range 1-11, SD = 2.16). Juvenile survival to recruitment was estimated at 21.9% (Baker et al. 1995). Annual adult survival for known breeders was 59% (females) and 64% (males) and did not vary annually during an 11-yr study at Palomarin (1980-1991, Nur and Geupel 1993).
Highly philopatric. Distance from natal nest-site to first breeding attempt averages less than 400 m (Baker et al. 1995).
Breeding Bird Survey Trends are non-significant and show slight declines in some areas and slight increases in other areas (Sauer et al. 1999).
Habitat loss is an issue in much of the coastal California range of the Wrentit, due to human development and conversion of shrublands to grasslands.
Habitat fragmentation and isolation of habitat patches are likely to limit dispersal and re-colonization, increase predation, and reduce gene flow in this sedentary species. Isolated populations in Golden Gate Park (San Francisco Co.) and San Diego County appear to be extirpated or disappearing.
Introduced or human-subsidized predators, especially corvids, may significantly
increase nest predation
In southern CA: Cactus Wren, Spotted Towhee, Orange-crowned warbler, Black-chinned sparrow, Song Sparrow (Chase et al. 2000).
MONITORING METHODS AND RESEARCH NEEDS:
Population trend monitoring: Wrentits are relatively well-represented on BBS monitoring routes in California overall, but data is lacking for the Sierra Nevada, southern CA grasslands and Los Angeles ranges regions within CA (Sauer 2001).
Adult survivorship can be well-monitored through constant-effort mist netting, providing that transients and non-transients individuals can be distinguished (Nur et al. 2000), however more netting stations are needed in coastal scrub and chaparral habitats. Constant-effort mist netting is less reliable for monitoring local reproductive success than is nest monitoring (Nur and Geupel 1993).
Need more understanding of the mechanisms by which landscape fragmentation and urban proximity reduce Wrentit populations. Wrentits may be a good model species for this type of research, due to their relatively sedentary nature and high abundance.
Wrentit populations are denser in undisturbed coastal scrub than in disturbed coastal scrub (PRBO). Need more understanding of the specific habitat characteristics that promote higher density populations (e.g., higher shrub species diversity or more cover, or both?) and whether these populations are also more productive.
ACTION PLAN SUMMARY
SPECIES:Wrentit (Chamaea fasciata)
No special management status, but has restricted range, with most of the world's population within California. Breeding Bird Survey Trends are non-significant and show slight declines in some areas and slight increases in other areas (Sauer et al. 2001).
Strongly associated with shrubland habitats, including coastal sage scrub, northern coastal scrub, lowland hard and montane chaparral, or other habitats with a dense, diverse native understory. Probably requires high degree of connectivity between habitat patches. Due to the high year-round territoriality of adults, juveniles likely need nearby un-occupied habitat that containsa suitable forage in order survive the winter and recruit back into a population.
Habitat loss is an issue in much of the coastal California range of the Wrentit, due to human development, encroachment, and conversion of shrublands to grasslands.
Habitat fragmentation is likely to limit dispersal, re-colonization and gene flow in this sedentary species.
Introduced or human-subsidized predators may harm productivity.
Wrentit population density in coastal scrub habitats may be reduced by habitat
degradation and physical disturbances that alter shrub cover or diversity.
Identify and preserve high quality habitat, particularly in Southern California regions that are undergoing rapid rates of habitat loss and degradation.
Increase number of demographic monitoring stations in California.
Study effects of habitat fragmentation on Wrentit primary population parameters. Determine negative effects of urbanization on local populations.
Model habitat requirements for high density vs. low density populations so
that restoration, protection, and preservation of appropriate coastal scrub
types can be more effectively promoted.
REFERENCES: All data is from Geupel and Ballard (2002) unless otherwise cited.
Baker, M., N. Nur, and G. R. Geupel. 1995. Correcting biased estimates of dispersal and survival due to limited study area: theory and an application using Wrentits. Condor 97: 663-674.
Burridge, B. 1995. Sonoma County breeding bird atlas: detailed maps and accounts for our nesting birds. Madrone Audubon Society, Santa Rosa, CA.
Chase, M. K., W. B. Kristan, A. J. Lynam, M. V. Price, and J. T. Rotenberry. 2000. Single species as indicators of species richness and composition in California coastal sage scrub birds and small mammals. Conservation Biology 14:474-487.
Crooks, K. R., A. V. Suarez, D. T. Bolger, and M. E. Soulé. 2001. Extinction and colonization of birds on habitat islands. Conservation Biology 15:159-172.
DeSante, D. F., and G. R. Geupel. 1987. Landbird productivity in central coastal California: the relationship to annual rainfall, and a reproductive failure in 1986. Condor 89: 636-653.
Erickson, M. M. 1938. Territory, annual cycle, and numbers in a population of wren-tits (Chamaea fasciata). Univ. California Publ. Zool. 42: 247-334.
Garrett, K., and J. Dunn. 1981. Birds of Southern California: status and distribution. Los Angeles Audubon Society, Los Angeles, CA.
Geupel, G. R., and G. Ballard. 2002. Wrentit (Chamaea fasciata). In The Birds of North America (A. Poole and F. Gill, eds.). No. 654. The Birds of North America, Inc. Philadelphia, PA.
Geupel, G. R., and D. F. DeSante. 1990. Incidence and determinants of double brooding in Wrentits. Condor 92: 67-75.
Grinnell, J. 1915. A distributional list of the birds of California. Cooper Ornithological Club, Hollywood, CA.
Grinnell, J. and A. H. Miller. 1944. The distribution of the birds of California. Pacific Coast Avifauna 27: 325-327.
Johnson, N. K. 1972. Origin and differentiation of the avifauna of the Channel Islands, California. Condor 74: 295-315.
Lehman, P. E. 1994. The birds of Santa Barbara County, California. Vertebrate Museum, U. of California., Santa Barbara, CA.
Mailliard, J. 1930. Handbook of birds of Golden Gate Park, San Francisco. California Academy of Sciences, San Francisco.
McMonagle, P. T. 1992. Wrentit (Chamaea fasciata) use of valley oak-riparian forest. Master's thesis, California State University, Northridge.
Mirsky, E. N. 1976. Ecology of coexistance in a wren-Wrentit-warbler guild. PhD. Dissertation. University of California, Los Angeles.
Nur, N., and G. R. Geupel. 1993. Evaluation of mist-netting, nest-searching, and other methods for monitoring demographic processes in landbird populations, p. 237-244. In D. M. Finch and P. W. Stangel [eds.], Status and management of Neotropical migratory birds. Gen. Tech. Rep. RM-229, Fort Collins, CO. U. S. Dept. of Agric., For. Serv., Rocky Mt. Range Exp. Sta.
Roberson, D. 1985. Monterey Birds: status and distribution of birds in Monterey County, CA. Monterey Peninsula Audubon Society, Carmel, CA.
Sauer, J. R., J. E. Hines, and J. Fallon. 2001. The North American Breeding Bird Survey, Results and Analysis 1966 - 2000. Version 2001.2, USGS Patuxent Wildlife Research Center, Laurel, MD (http://www.mbr-pwrc.usgs.gov/bbs/)
Shuford, W. D. 1993. The Marin County breeding bird atlas: a distributional and natural history of coastal California birds. Bushtit Books, Bolinas, CA.
Sibley, C.G., and J.E. Ahlquist. 1982. The relationships of the Wrentit (Chamaea fasciata) as indicated by DNA-DNA hybridization. Oiseau 51: 189-199.
Small, A. 1994. California birds: Their status and distribution. Ibis Publishing Co., Vista, Ca. Pg. 197.
Soulé, M. E., D. T. Bolger, A. C. Alberts, J. Wright, M. Sorice, and S. Hill. 1988. Reconstructed dynamics of rapid extinctions of chaparral-requiring birds in urban habitat islands. Conservation Biology 2: 75-92.
Stralberg, D., and S. Bao. 1999. Identifying the spatial structure in error terms with spatial covariance models: A case study on urbanization influence in chaparral bird species. 1999. Geographic Information Sciences 5: 106-120.