Oregon

In July 2016, the AOU Checklist Committee announced their decision (Retter 2016) to recognize two species of Scrub-Jay: Woodhouse’s (Aphelocoma woodhouseii) and California (Aphelocoma californica).  Birders and ornithologists have long recognized the distinctions between these two species taxa.  While this historical knowledge provides some useful guidance in separating the two, it has also given rise to some misconceptions. The two species differ in geographic range, have differing population traits, and are somewhat difference in appearance.

Range and Distribution – In general, California Scrub-Jays are predominantly a west coast species, breeding primarily west of the Cascades and along the Columbia River.  In recent years they have expanded their range north to include the lowland valleys along much of Oregon’s outer coast and north through the interior western Washington lowlands and Puget Trough, almost to the Canadian border.  Woodhouse’s Scrub-Jays are a Great Basin species, with a range that lies almost entirely south of the Pacific Northwest.  The distribution of Woodhouse’s in Great Basin habitats, such as juniper woodlands, has apparently led many birders and ornithologists to presume that any Scrub-Jays found in this arid corner of the region are Woodhouse’s Scrub-Jay.  This has proven not to be the case in the Northwest.  Like several other coastal slope species such as Anna’s Hummingbird, Black Phoebe and Lesser Goldfinch, the range of California Scrub-Jays has expanded both north and east at a rapid rate in recent years.  Contrast the eBird range map of California Scrub-Jay through 1990 with their current range.  The range expansion east of the Cascades, as well as north, has been dramatic, and it continues.  As recently as 1990, there were no eBird records of California Scrub-Jay north of Seattle, only one in eastern Washington and three records of scrub-jays (unknown species) from southeast Oregon.

Population Dynamics – The dynamics of the two species differ presently in ways that are of interest to eBirders.  As noted above, California Scrub-Jays are currently demonstrating a significant range expansion, while the only sub-population of Woodhouse’s Scrub-Jays that appears to be expanding currently are the birds in Texas populations (Curry et al, 2002).  Although both species are considered to be non-migratory and generally sedentary, both species occasionally engage in irruptive dispersions.  Woodhouse’s populations exhibit periodic, long-distance, irruptive movements, often in association with other corvids such as Pinyon and Steller’s jays and Clark’s Nutcrackers (Alderfer 2006).  Irruptive movements by California populaitons are not as well documented, and may be shorter-range.  Out of range scrub-jays in the Pacific Northwest are more likely to be California than Woodhouse’s, except in a corvid irruption year in the Great Basin when the probability of a wandering Woodhouse’s likely increases in our area.

Behavioral differences between the two species are commonly described, with Woodhouse’s often described as reclusive and tending to avoid developed areas.  Northwest birders know that California Scrub-Jays are generally not shy (although finding one while they are nesting can be a challenge) and readily adapt to human landscapes.   However, there are many reports of conspicuous Woodhouse’s Scrub-Jays that appear at feeders in residential areas; single birds cannot be identified by behavior.  Conversely, the resident California Scrub-Jays in southern Lake County, Oregon, which are found away from human habitation, tend to be more wary of approaching humans than birds found in urban/suburban settings.  Single birds cannot be identified on the basis of behavior alone, as perceived differences in behavior may simply be a function of how frequently individuals come into contact with humans.

Identification – There are several consistent plumage differences between the two species, but birders must be aware of the complicating effects of feather wear, and that birds in Juvenal plumage are less distinct.  California Scrub-Jays are generally brighter (Figure 1), showing a stronger contrast between their blue upperparts and the brown back patch, and between whitish underparts and a sharp blue breastband.  They also show a wider, brighter white supercilium.  Woodhouse’s tend to be more dully colored overall, have a less defined back patch that is primarily gray, and a less conspicuous breast band that does not stand out as much against the adjoining grayish-white underparts.  Undertail coverts range from grayish-blue on Woodhouse’s to blueish in the northern California races.

California Scrub-Jays with worn plumage, prior to the completion of their Definitive Prebasic molt which can be as late as October, may look very drab and can strongly resemble Woodhouse’s Scrub-Jay.  Their back patches show little brown and are low contrast.  Breast bands can be obscured and their supercilium may be difficult to see well.  Summer and early fall reports of Woodhouse’s Scrub-Jay are problematic, unless the observer accounts for feather wear.  Juvenal California Scrub-Jays (Figure 2) are less sharply patterned than adults, with a dingier supercilium, a dull brown breast band, and drab back.  Juvenal feathers wear more quickly than adult feathers, making the effects of feather wear even more pronounced.

Some authorities describe vocal differences between the two species (Dunn and Garrett 2001).   Useful recordings for hearing these differences include:

Woodhouse’s:

http://www.xeno-canto.org/310670

http://www.xeno-canto.org/205390

California:

http://www.xeno-canto.org/92088

http://www.xeno-canto.org/269053

References:

Alderfer, J., ed.  2006. Complete Birds of North America.  National Geographic, Washington. D.C.

Curry, R.L., A.T. Peterson and T.A. Langen.  2002.  Western Scrub-Jay (Aphelocoma californica).  In The Birds of North America, No. 712 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.

Dunn, J.L. and K.L. Garrett. 2001. Parapatry in Woodhouse’s and California Scrub-Jays revisited.  Western Birds 32: 186-187.

Retter, M.P. 2016.  2016 AOU Supplement is Out!  ABA Blog, at: http://blog.aba.org/2016/07/2016-aou-supplement.html.

 

Figure 1:

 

Figure 2:

Article by: Bill Tweit