June 6, 1999
Prepared by: Susan L. Guers, Point Reyes Bird Observatory, 4990 Shoreline Highway, Stinson Beach, CA 94970. (415) 663-1648. Email: wscrubjay@hotmail.com
SPECIES: Western Scrub-Jay (Aphelocoma californica)
SUBSPECIES STATUS: This has been a topic of debate over the years. The subspecies of the Western Scrub-Jay are divided into two categories: the Coastal Group (Aphelocoma californica californica) which inhabit areas west of the Cascades and Sierra Nevada from Washington to Baja California; and the Interior Group (A.c.woodhouseii) whose birds inhabit the Great Basin and the Rocky Mountains (DeBenedictis 1994). DNA evidence shows that the californica group was derived from the populations of the woodhouseii group (Peterson 1992). There can be intermediates between these two groups; most often occurring from the west side of the Owens Valley in eastern California, where the ranges of the two approach the closest, but are separated by a barrier of unsuitable desert habitat (DeBenedictis 1994).
Currently, there are four subspecies of the Western Scrub-Jay that live and breed in California (Pyle 1997and Phillips 1986). Roughly speaking, the characters distinguishing the California subspecies are size and color (Bent 1946).
Coastal (A.c.californica) Group: Bright blue in color, underparts whitish. The "californica" group is characterized by a contrasting plumage pattern and a heavy bill and short wings (Pitelka 1951).
MANAGEMENT STATUS: No special status.
I. Historical references:
Grinnell and Miller (1944) in their work, The Distribution of the Birds of CA, also noted 4 separate subspecies of Western Scrub-Jay living and breeding in California. The subspecies A.c. californica was a common to abundant resident of the central and southern coast district, almost entirely west of the San Joaquin Valley and western margins of southeastern deserts. It was said that with human settlement of open valley lands, this jay had probably come to occupy more territory than it had originally.
A.c. superciliosa was listed as a common, year-round resident in the northern and central part of the state. In maximum numbers, it occurred almost the entire circumference and parts of the floor of the Great Valley—Sacramento and San Joaquin—with spill-over northeastwardly and west. Lowland areas uninhabited before by jays were now prime habitats due to human settlement.
A.c. woodhouseii was a locally common resident of the Great Basin mountain ranges east of the Sierra from Mono County south through Inyo County to extreme eastern San Bernardino County. An important observation was that it was thought to interbreed with A.c. superciliosa along the eastern slopes of the Sierra Nevada in Inyo County.
The subspecies A.c. oocleptica was a common, to even abundant, resident in its range of the northwestern coast strip from Del Norte and Humboldt counties south through Marin County.
In his groundbreaking work, Speciation and Ecologic Distribution in American Jays of the Genus Aphelocoma, Pitelka (1951) found what he believed to be seven distinct subspecies living and breeding in California. His work was the foundation for further research on this topic, and the overall present phylogeny of the Western Scrub-Jay. Currently, his 7 species are now grouped into the above-mentioned 4 species. Pitelka did not have the advantage of using DNA analysis when determining the subspecies of Western Scrub-Jay, and used plumage and habitat characteristics alone.
II. Current breeding distribution: Attempt to obtain the most current information.
b. Point count (singing individual encountered on 2 or more different days of census-at least one week apart):
c. Mist netting (female with brood patch, female with eggs in oviduct, juvenile with no skull ossification before 1 August): Since Western Scrub-Jays are rarely caught in mist nets, I did not include this data.:
e. Spot mapping: N/A
f. Area search: N/A
g. Breeding Bird Atlas:
In Sonoma County, it is also recorded as a year-round resident, and was found in 85% of all Atlas blocks with data. One of the most prevalent birds found in the county (Burridge 1995).
The Western Scrub-Jay is a common resident and breeder in most habitats of Orange County (Hamilton and Willick).
ECOLOGY:
I. Average territory size: At the Palomarin Field Station (Marin Co.) color-banded individuals have been studied for almost twenty years. On a typical 8 ha. plot, the average territory size is 2.5 ha, or roughly 3 territories per plot. The habitat here varies from pristine to disturbed coastal scrub, to grazed land.
Atwood (1980) found that territory sizes of birds on the mainland and on Santa Cruz Island to be between 2 to 3 ha., consistent with the above-mentioned data.
More study is needed to determine home ranges during the nonbreeding months.
**The size of an average territory may vary according to number of individuals in the area, as well as condition of the habitat involved.
B. Departure date from breeding grounds:
C. Spring migration period: Not known.
D. Fall migration period: Many individuals will exhibit post-breeding vagrancy. In most of these cases, the vagrancy is due to jays gathering acorns and carrying them up-slope to cache them for future food supplies. This exhibits the reciprocol relationship between oaks and Western Scrub-Jays: the jays are provided with food, shelter and nursery sites by the oaks, while the oaks are supplied with agents of dispersal for its species (Grinnell, from the Condor, 1936, as quoted in the book Oaks of California).
IV. Migration stop-over needs/characteristics: The fall migration of the Western Scrub-Jay seems dependent upon the availability of oaks and their acorns.
VI. Foraging strategy:
The Western Scrub-Jay is omnivorous—consuming both vegetable and animal matter.
They spend most of their time foraging in the lower parts of trees and the scrub
canopy, and more time in open areas. Ground foraging is a conspicuous occupation,
but seems to be carried on most "comfortably" within a few yards of some sort
of cover, within which they can dive in a case of emergency (Grinnell and Miller
1944).
They use "anvil" sites to break open nuts. Like most Corvids, Western Scrub-Jays will "cache" or store acorns in the ground with a thrust into loose soil or by hammering them in with their beaks and then covering them with dirt clods, rocks or leaves. They also wedge them into cracks or crevices in trees, stumps and logs. ***In their habit of ground storage of acorns, Western Scrub-Jays are active agents of oak dispersal, particularly in an uphill direction***(Shuford 1993) (See postbreeding seasonal movements).
VII. Displays: An upward bobbing movement may accompany the rattling call, which may be an intention-movement of flying, or have self-assertive or sexual significance (Goodwin 1976). Territorial disputes involve brief chases, ‘br’r’r’r’ calls accompanied by the upward bobbing and the ‘flitting display’; in which the head is held erect, the contour feathers closely oppressed; the whole attitude is one of alertness and the bird hops vigorously about switching tail and body side to side (Hardy 1961). I believe the "br’r’r’r" is what I call the "rubberband" call— which sounds a lot like a rubberband being twanged.
Females will beg for food from the feeding male using a low "greer, greer" call and submissive pose (Goodwin 1976).
VIII. Social Organization:
2. Mating system: Monogamous; keeping the same mate for many years (PRBO data).
3. Delayed breeding (where are immature birds?): Some birds may delay breeding, and will not develop sexual characteristics (BP/CP) until after their second year (Pyle 1997).
4. Post fledging biology of offspring (where do they go and when?):
Young can remain with their parents for up to five months and then, during
their first fall or winter, begin to disperse. How far they disperse can be
a big question, probably depending heavily on availability of territories
in the nearby area. A Western Scrub-Jay that was color-banded at the Palomarin
Field Station in Marin County during its first winter was recaptured four
years later as a resident 11 km east-northeast of Palomarin (Isenhart and
DeSante 1985). In addition, three nestlings from the same nest that were banded
during the spring of 1971 were recaptured within 100 meters of the nest the
following October to December (Ritter 1983).
5. Post breeding social behavior (mixed species flocks, or simply migrate
away?):
May form loose family?? groups which remain together until the following year’s
breeding season. Groups of 3 or more birds were seen together during the winter
months and up to mid-April, when it seemed like adults were forcing first-year
birds out of their territory (Personal obs.). Ritter (1983) supports this
theory by stating that during autumn and winter, Western Scrub-Jays in Chico
sometimes formed loose aggregations of up to 10 birds, which may be familial.
First-year birds seemed to make up a large proportion of flock members.
IX. Incubating sex: By the female alone—she can be fed on the nest by the male (Baicich and Harrison 1997).
X. Incubation period: 15-17 days, can be as long as 18 days (Stewart et al. 1972). These dates may vary according to region. Ritter (1983) reports an 18-day incubation period for the Western Scrub-Jay on his study site near Chico, (Butte County) CA, while Verbeek (1973) found an incubation period of 17 to 18 days in Monterey County.
XI. Nestling period: 18-19 days?? This may vary according to region—PRBO data from the Palomarin Field Station in Marin County show fledging dates from 19-25 days—considerably different from the above dates. Ritter (1983) reports a mean fledging date of 20 days in Butte County, while Verbeek (1973) found fledging dates ranged from 20 to 24 days in Monterey County. This difference in fledging dates may be due to human disturbance —i.e. the birds were able to leave the nest at day 18, but would have stayed longer given the choice.
XII. Development at hatching: Altricial and naked.
Vegetable matter is primarily acorns, nuts, seeds and to a lesser extent, wild and cultivated fruits, berries and grains. Acorns, during the late fall and winter months, may represent 50-75% of their total diet. The month of October shows the largest amount of 88.6% (Bent 1946).
Animal food includes: insects (especially beetles, bees, wasps, ants, grasshoppers, crickets, moths and caterpillars), spiders, eggs and nestlings of wild birds, eggs and chicks of domestic fowl, mice and shrews, lizards, snakes and frogs (Shuford 1993). In addition, Western Scrub-Jays have been seen picking ticks and possibly other ectoparasites from both the Columbian black-tailed deer (Odocoileus hemionus columbianus) and the California mule deer (O. h. californicus) (Isenhart and DeSante 1985).
This bird is a generalist, and will eat just about anything if the opportunity arises. Humans are helping all Corvids by providing year-round food supplies in the forms of birdfeeders, landfills, ranching and agriculture, and any areas providing easy access to food, usually picnic or recreation areas.
***Food for such an omnivorous animal as the Western Scrub-Jay, in a climate of tempered winters, does not seem to be the limiting factor for spatial spreading or for limiting the population size, that the factors of available cover and the right kind of nest site do.(Grinnell and Miller 1944)***
B. Drinking: Williams and Koenig (1980) reported regular drinking visits to a spring in oak woodland in coastal California. Drinking water probably essential (Zeiner et al. 1990).
BREEDING HABITAT AND NEST SITE CHARACTERISTICS:
I. Overview of breeding habitat: (e.g. oak woodland vs.
oak savannah, age of stand, dominant species, plant species diversity,
structural diversity/variability)
The Western Scrub-Jay builds its nest relatively low to the ground
in a small tree or shrub, usually in oak woodland when given the choice.
Jays seem to prefer early successional growth habitat—i.e. shrubby and
dense habitats within which to take cover if the need arises. However,
if this is not an option, jays will use a variety of habitats—be it riparian,
coastal scrub or urban settings.
II. Nest Site.
C. Patch size: Not known.
D. Disturbance (natural or managed): (e.g. floods, fires, logging)
SPECIAL FACTORS: Factors influencing a species occurrence and viability.
I. Brood parasitisim: No known documented cases of brood parasitism by the Brown-headed Cowbird on the nests of the Western Scrub-Jay.
II. Dietary: Because the Western Scrub-Jay relies heavily on acorns as a large component of their diet, oaks play an important role in the conservation of this species. Whenever you see a Western Scrub-Jay, no matter what the subspecies, you will usually see an oak in the area. You hardly ever see one without the other. These jays need oaks in order to be successful.
III. Sensitivity to human-induced disturbance: Western
Scrub-Jays adapt relatively well to human disturbance. For example, the
lowland areas of both the Sacramento and San Joaquin Valleys that were
once uninhabited by these jays, now carry good numbers due to the plantings
of trees by colonizers. (Grinnell and Miller 1944) In addition, jays respond
favorably to humans due to a constant food supply in the way of birdfeeders,
landfills, agriculture and recreational areas.
A mixture of oak trees, brush plants or thickets, and some bare ground, meets
best all of the requirements of the Western Scrub-Jay —open ground and plant
growths for foraging, thickets near the ground for emergency refuge and night
roosting, and close branch work and foliage of large bushes and trees for nest
sites—all of which can be found in an urban setting (Grinnell and Miller 1944).
IV. Pesticide use: Like most bird species, probably doesn’t respond well to pesticide use. No documented studies were found on this topic.
V. Predators: The predators on Western Scrub-Jays are not all that well-known. Avian predators include raptors (i.e. Red-tailed Hawk and Great-Horned Owl), Common Ravens, American Crows, and possibly other jays (including both Steller’s and Western Scrub-Jay). Mammalian predators as well as snakes may depredate both adults and nestlings. In addition, man used to (and might still) play a big role in the decline in Western Scrub-Jay populations. Until recently, jay shoots were a regular occurrence for many farmers and hunters. Jays were seen as pests by both farmers and fruit growers for damaging their crops. At one shoot held in the fall of 1938, 1368 jays were killed. These shoots were organized in California under the pretext of reducing the numbers of a destructive bird, but largely too, as a pleasant recreation and an interesting competition for the shooters (Bent 1946).
VI. Exotic species invasion/encroachment: Does not really compete with exotic species, such as European Starlings or House Sparrows, for nesting space since the Western Scrub-Jay is an open cup nester and not a cavity nester. It may compete with these two species for food, especially in urbanized areas. No studies on this phenomenon are known.
POPULATION TREND: http://www.mbr.nbs.gov/bbs/bbs.html
The overall trend for populations of Western Scrub-Jays in California during the years 1966-1996 show a growth of 1.2% per year, a significant value (P=0.00), with a relative abundance of 10.38 individuals per route. Furthermore, in the Sierra Foothills of California, the trend appears to be a growth of 1.06% per year, again a significant value (P=.01283), with an average of 28 individuals per route.
DEMOGRAPHICS:
I. Age and sex ratios: NA
II. Productivity measure(s):
III. Survivorship: The longevity record for a banded Western
Scrub-Jay is 15 years, 9 months. (data from http://www.pwrc.nbs.gov/BBL/homepage)
IV. Dispersal:
MANAGEMENT ISSUES:
ASSOCIATED SPECIES: A list of other species that would benefit from management of the target species.
*** Any species that utilizes oaks be it for food, shelter or nest sites, would benefit from their conservation.
MONITORING METHODS AND RESEARCH NEEDS: Recommend methods that will address immediate needs as well as those most appropriate to monitor how effective the proposed management recommendations will be.
Even though the Western Scrub-Jay is a fairly common and abundant year-round resident, little is known about its basic breeding biology in the state of California—esp. when compared to its cousins the Island Scrub-Jay and the Florida Scrub-Jay. And, while it’s true that many specimens have been collected and studied, this does nothing when trying to answer ecological questions concerning this bird species and its environment.
Section 2: Action plan summary. Summarize the above information into concise statements under each section.
STATUS (from subspecies, trend, local extirpations, state and federal lists, etc.)
The Western Scrub-Jay is not doing poorly in any region, as a matter of fact, its populations are increasing, especially in areas where historically it hadn’t occured before ( i.e. the Modoc Region). See trend.
HABITAT NEEDS (e.g., elevation, patch size, breeding habitat characteristics, disturbance) There is a strong correlation between the occurrence of the Western Scrub-Jay and oaks, no matter what region of California is discussed. The loss of oak habitat may be detrimental to Western Scrub-Jays, but probably not to the same extent as it would to other species, since these birds have adapted so well to human urbanization and activities. However, jays are one, if not the best, avian oak dispersers we have in California. Jays will select acorns which are likely to grow into seedlings and are responsible for providing a valuable means for dispersing and planting oaks (Scott 1990).
CONCERNS (e.g., productivity, brood parasitism, habitat loss, lack of information, wintering distribution, pesticide use) Lack of information is my main concern. Even though this is a common and abundant species, little research has been done on the basic breeding biology of all the subspecies. The continued expansion of ranching in California destroys much of the oak woodland habitat, be it for cattle or vineyards. The loss of their primary habitat may drive the Western Scrub-Jay into areas not seen before—especially into more urbanized areas. This could mean declines in songbird populations.
OBJECTIVES (e.g., increase distribution, identify healthy breeding populations, increase available habitat, guide restoration efforts to benefit species)
The conservation of oak woodland habitat in California would not only benefit the Western Scrub-Jay, it would also benefit those that also highly depend upon this habitat for survival, i.e. Oak Titmouse or Acorn Woodpecker.
ACTION (e.g., acquire and restore habitat, specific management and restoration recommendations, specific research and monitoring needs, specific land protection recommendations) Gather more research on oak-wildlife relationships and present them as evidence to land managers for proof of the oak’s worth to the environment and they need to be conserved. Continue to conserve and preserve the existing oak woodland habitat, and try to plant more. Continue to monitor the populations of the Western Scrub-Jay, in order to determine such things as their nesting success and the extent of their wintering ranges.
SCIENTIFIC REFERENCES:
Atwood, J.L. 1980. Breeding Biology of the Santa Cruz Island Scrub-Jay. Pgs. 675-688 in D.M. Power, ed., The California Islands; Proceedings of a Multidisciplinary Symposium. Santa Barbara Natural History Museum. Santa Barbara, CA.
Baicich, Paul J. & Harrison, Colin J.O. 1997. A Guide to the Nests, Eggs, and Nestlings of North American Birds, Second Edition. Pg. 231. Academic Press. San Diego, CA.
Beal, F.E.L. 1910. Birds of California in Relation to the Fruit Industry (Part I). US Dept. of Agriculture Biological Survey Bulletin 30.
Bent, A.C. 1964. Life Histories of North American Jays, Crows and Titmice, in Two Parts, Part One. Pgs.88-114. Dover Publications, Inc. New York, NY.
Burridge, Betty. Ed. 1995. Sonoma County Breeding Bird Atlas. Madrone Audobon Society, Inc. Santa Rosa, CA.
DeBenedictis, Paul A. 1994. Aphelocoma Jays. Birding 3:195-198.
Erlich, Paul R., Dobkin, David S., & Wheye, Darryl. 1988. The Birder’s Handbook. Pg. 404. Simon & Schuster. New York, NY.
Goodwin, Derek. 1976. Crows of the World. Pgs. 274-277. Cornell University Press. Ithaca, NY.
Grinnell, J. & Miller, A.H. 1944. The Distribution of Birds of California. Pacific Coast Avifauna Number 27: 287-291.
Harris, Stanley W. PhD. 1991. Northwestern California Birds. Humboldt State University Press. Arcata, CA.
Hamilton, R.A. & D.R. Willick. 1996. The Birds of Orange County: Status and Distribution. Sea and Sage Press, Sea and Sage Audobon Society. Irvine, CA.
Isenhart, Frank R. & DeSante, David F. 1985. Observations of Scrub Jays Cleaning Ectoparasites From Black-tailed Deer. The Condor 87: 145-147.
Lehman, Paul E. 1994. The Birds of Santa Barbara County, California. Vertebrate Museum, University of California, Santa Barbara, CA.
Orr, Robert T. & Moffitt, James. 1971. The Birds of the Lake Tahoe Region. California Academy of Sciences. San Francisco, CA.
Pavlik, Bruce M., Pamela C. Muick, Sharon G. Johnson,& Marjorie Popper. 1991. Oaks of California. Pgs. 78-79. Cachuma Press. Los Olivos, CA.
Peterson, A. Townsend. 1992. Phylogeny and Rates of Molecular Evolution in the Aphelocoma Jays (Corvidae). The Auk 109(1): 133-147.
Phillips, Allan R. 1986. The Known Birds of North and Middle America. Part I. Pgs. 46-49. Denver, CO.
Pitelka, Frank A. 1951. Speciation and Ecologic Distribution in American Jays of the Genus Aphelocoma. Vol 50(3): 195-464. University of California Publications in Zoology, University of California Press. Berkeley, CA.
Pyle, Peter. 1997. Identification Guide to North American Birds, Part One. Pgs 302-303. Slate Creek Press. Bolinas, CA.
Ritter, Lyman V. 1972. The Breeding Biology of Scrub Jays. M.A. Thesis, California State University. Chico, CA.
Ritter, Lyman V. 1983. Nesting Ecology of Scrub Jays in Chico, California. Western Birds: 14: 147-158.
Ritter, Lyman V. 1984. Growth of Nestling Scrub Jays in California. Journal of Field Ornithology. 55(1) 48-53.
Roberson, Don. 1985. Monterey Birds: The Status and Distribution of Birds in Monterey County. Monterey Peninsula Audobon Society. Monterey, CA.
Sauer, J.R., J.E. Hines, G. Gough, I. Thomas, & B.G Peterjohn. 1997. The North American Breeding Bird Survey Results and Analysis. Version 96.4 Patuxent Wildlife Research Center. Laurel, MD.
Scott, T. 1990. Jays Plant Acorns. Oaks ‘n Folks. 5(2).
Shuford, W. D. 1993. The Marin County Breeding Bird Atlas: A Distributional and Natural History of Coastal California Birds :282-283. Bushtit Books.
Small, Arnold. 1994. California Birds, Their Status and Distribution. Pg. 174. Ibis Publishing Company.
Stewart, Robert M., Stephen Long, Meryl Stewart. 1972. Observations on the Nest Behavior of the California Scrub Jay. California Birds 3: 93-95.
Verbeek, N.A.M. 1973. The Exploitation System of the Yellow-billed Magpie. Unversity of California Publications in Zoology. 99:1-58.
Weathers, Wesley W. 1983. The Birds of Southern California’s Deep Canyon. University of California Press. Berkeley, CA.
Williams, P.L. & W.D. Koenig; 1980. Water Dependence of Birds in a Temperate Oak Woodland. The Auk 97: 339-350.
Zeiner, D.C., W. Laudenslayer jr., K. Mayer & M. White, eds. 1990.
California’s Wildlife, Vol.2, CA Dept. Fish & Game, Sacramento, CA.
732 pps.