California Partners In Flight
Oak Woodland Conservation Plan
For The
Western Scrub-Jay

June 6, 1999

Prepared by: Susan L. Guers, Point Reyes Bird Observatory, 4990 Shoreline Highway, Stinson Beach, CA 94970. (415) 663-1648. Email:

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).

Interior (A.c.woodhouseii) Group: Dull blue in color, underparts grayish. The "woodhouseii" group lacks the contrast of plumage and is characterized by a longer bill, but not so heavily basally, and longer wings. (Pitelka 1951)  

MANAGEMENT STATUS: No special status.

range map:

I.  Historical references: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.

  1. UTM or lat long coordinates of sites known to contain breeding populations:
1. Type of method used in determining breeding status (by site and year).
            a.  Expert opinion:

            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.:

    d. Nest searching:

                 f. Area search: N/A

                 g.  Breeding Bird Atlas:

In Marin County, the Western Scrub-Jay is a year-round resident, with a very large overall breeding population. It was recorded in 214 of 221 blocks (96.8%) (Shuford 1993).

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).

In Monterey County, the Western Scrub-Jay is a common and widespread resident, occurring in virtually all wooded areas and absent only in areas lacking trees. Was found in 88% of the Atlas blocks. Population estimates for the county may exceed 20,000 pairs (Roberson 1985). A common permanent resident of Santa Barbara County; most numerous in oak and riparian woodland, residential areas, and urban parks; less abundant in oak savanna, Chaparral, and in oak-conifer woodland (Lehman 1994).

The Western Scrub-Jay is a common resident and breeder in most habitats of Orange County (Hamilton and Willick).

The Western Scrub-Jay is a permanent resident of the Deep Canyon Region of the Santa Rosa Mountains, located in Riverside County. Their distribution coincides with that of the Scrub Oak (Quercus berberidifolia) (Weathers 1983). Common resident and breeder in scrub and open mixed woodland, containing oaks. Most common inland and in the southern portions of the region (Harris 1991). Listed as a casual spring and late fall transient (Orr and Moffitt 1971).                 h. BBS route: See attached map.
                i. Other/Local opinion: N/A


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.

    Ritter (1983) found that the approximate territory size of Western Scrub-Jays in Chico, CA to be 2.2 ha. However, considerable extension of their movements occurred during the nonbreeding season. Then, the home ranges covered between 4.9 ha to 5.4ha.

    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.

II.  Time of occurrence and seasonal movements.
Some post-breeding vagrancy may occur---individuals moving upslope with the intent of caching the fall’s bounty of acorns. Winter fluctuations in populations has been shown, with many groups being found along rivers (Phillips 1986). Dispersal of juveniles may occur during the months before breeding season—possibly January or February????(Ritter 1983, personal obs.). III.  Extent of wintering in CA: All subspecies will winter in California, although some individuals can spread in fluctuating numbers and chiefly along rivers, to areas where they do not breed, i.e. east to Kansas and Nebraska (Phillips 1986).

IV.  Migration stop-over needs/characteristics: The fall migration of the Western Scrub-Jay seems dependent upon the availability of oaks and their acorns.

V.  Nest type: Open cup.
The nest is usually a structure composed of sticks or twigs intertwined into a large, bulky cup. Moss and dry grass may be woven amongst the sticks or twigs. The nest can be lined with finer twigs, rootlets, plant and bark fibers, grass and/or horsehair (Shuford 1993, Baicich and Harrison 1997). Both sexes will participate in the building of the nest. In addition, Western Scrub-Jays in the Sacramento Valley built false nests in late February and early March prior to building complete, functional nests (Ritter 1972).

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:

VIII. Clutch size: 3-4 (2-7) (Erlich et al. 1988). Clutch size may be smaller in arid regions (Baicich and Harrison 1997).

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.

XIII.   Major food items (by season): XVI. Wintering ground needs and distribution:
Phillips (1986) reports that wintering populations of Western Scrub-Jays may reside near rivers.



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.

    A.  Substrate (species):
Ritter (1983) states that four plant species, California Wild Grape, Blue Elderberry, Interior Live Oak (Quercus wislizenii) and Coffeeberry, provided cover for 84% of his 127 nests. Concealment of the nest was the primary factor in the selection of plant species for nest placement.
    B.  Height of nest:
Ritter(1983) states that over 50% of his nests were placed 2-4m above the ground, and that variation among nest sites was great—nests were placed in terminal branches, the forks of branches, the forks of tree trunks, on lateral branches and in vines. Mean=3.4m, SD=1.94m, range=.6m-15.2m, n=119. He found that these heights did not vary greatly from the nest heights of the Island Scrub-Jay, but were higher than those of the Western Scrub-Jays in Monterey County and the Florida Scrub-Jay.
    C.  Height of plant:
III. Vegetation surrounding the nest (Importance of each category may differ by species) NOTE:: Even though PRBO has been taking vegetation measurements on nests for over 15 years, I will only use vegetation measurements which adhere to the BBIRD protocol (Martin et al. 1996).
    B.  Dominant plant species in canopy:
    C.  Average shrub cover:
    D.  Dominant shrub species:
    E.  Average forb cover: Not a factor for Western Scrub-Jay nest sites?
    F.  Dominant forb species: Not a factor for Western Scrub-Jay nest sites???
    G.  Ground cover: Not a factor for Western Scrub-Jay nest sites??
    H.  Slope:
    I.  Aspect:
    J.  Tree DBH:
    K. Snags: Not a factor.
    L.  Distance to water: Not measured.
IV. Landscape factors
    A.  Elevation: (varies according to subspecies; Grinnell and Miller, 1944). All subspecies are typically found in the Upper Sonoran Zone, but can also be found in both the Lower Sonoran Zone and Transition Zone. B.  Fragmentation: Fragmentation of closed canopy forests may actually benefit the Western Scrub-Jay as they may use the newly created "edges" as opportunities to penetrate areas they would not have ventured before. (Personal hypothesis)

    C.  Patch size: Not known.

    D.  Disturbance (natural or managed): (e.g. floods, fires, logging)

    E.  Adjacent land use: Urbanization does not seem detrimental to the populations of Western Scrub-Jays, quite the contrary it seems to be almost beneficial in supplying favorable habitat and feeding conditions. Unfortunately, with the increase in jay populations, there may be a decrease in other songbird populations, as jays are a well-known predator on many other nesting songbird species.
V. Other:

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.


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.


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
IV.  Dispersal:


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.



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