Oregon

In eBird terms, this is actually a Bushtit (Pacific) meets Bushtit (Interior) story. Three distinct populations are found north of Mexico; taxonomists describe the Pacific group as the minimus group, Interior birds as the plumbeus group, and the Black-eared populations as the melanotis group (Sloane 2020). The latter group is not found in the Northwest, although there is one record of an interior bird with well-marked black ears that is thought to be a rare genetic polymorphism (Fuller 2020). The two Northwest populations differ visually and apparently have relatively little contact, as they are largely separated by major ecological barriers to bushtit dispersal, such as the Sierra and the Cascades (Harrap and Quinn 1995). Even though Bushtits are considered relatively sedentary, both populations are expanding their range (Harrap and Quinn 1995; Marshall et al 2003). With range expansion comes the possibility of increased contact, particularly in areas where the barriers to dispersal are not as significant, such as the Klamath Basin, the lower passes in the Cascades and the Columbia Gorge. Tracking their changing distributions, and looking for evidence of overlap, will improve our understanding of this characteristic species of the west.

Field Identification

Separating the two types is generally straightforward (Harrop and Quinn 1995, Pyle 1997), although heavily worn birds can be inseparable, and intergrades, which are likely in areas where the two populations adjoin or contact, can be a source of confusion. Pacific birds have brown crowns and mostly gray cheeks (Figure 1), while Interior birds have gray crowns (sometimes with a touch of brown in the forecrown) and brown cheeks (Figure 2). One caution about juvenile Pacific Bushtits is that they are very pale and gray-headed and thus are superficially similar to Interior birds in appearance, except they lack brown in the cheek. The underpart colorations of the two populations differ slightly. On average, the flanks of Pacific birds are washed with warmer, browner tones while the flanks of Interior birds are more grayish with no warm tones, giving an overall appearance of a more grayish bird. An old name for the Interior birds is the Lead-colored Bushtit, a fitting description. There are no known vocal differences between populations, discrimination can only be visual.

Historic Distribution

As recently as 2005, Interior Bushtits were known from only one location in Washington, an isolated group at the north end of Potholes Reservoir, Grant County (Wahl et al 2005), even though Bushtits presumed to be plumbeus were known to occur in eastern Oregon north to Wasco, Sherman and Gilliam counties bordering the Columbia River (Marshall et al 2003) and there were two Bushtit records of unknown type from areas just across the river in Klickitat County, Washington (Wahl et al 2005). Populations of Pacific Bushtits have been documented east of the Cascades in the Klamath Basin, the Columbia Gorge, and the Yakima drainage (Stepniewski 1999) where their range is clearly expanding at present. It should not be particularly surprising that the Bushtits of the Klamath are Pacific, as biogeographically, the Klamath Basin is connected to the Pacific Slope and not the Great Basin/Columbia Basin and is primarily populated by coastal species such as California Scrub-Jay and Oak Titmouse, rather than their Great Basin congeners.

Current Distribution

Since 2005, photos of Interior Bushtits have been posted on eBird from Wasco, Sherman and Gilliam counties in Oregon, confirming the presumption in Marshall et al (2005). Interior Bushtits have also been photographed in eastern Klickitat County and the Horse Heaven Hills in Yakima County. Where does the dividing line appear to be at present? In Washington, based on a very small number of photos, it appears to be Hwy 97 and in Oregon, a larger number of documented records suggest that the dividing line is currently Hwy 197/97 north of Madras and the Cascade Crest south of there, down to the Klamath Basin where Pacific populations prevail. The eBird maps of Interior and Pacific distribution illustrate this division well.

In Washington, all of the eBird Bushtit records west of Hwy 97 with documentation are referable to the Pacific group. The only records east of there are in the Toppenish/Yakima valley and one record from the east end of the Ponderosa/Garry Oak woodlands in the Simcoe Range. The two Interior birds east of 97 were found in small drainages in shrub-steppe.

In Oregon, the eBird records do not sort out quite as neatly, but the Deschutes River drainage appears to be the western edge of Interior birds. There are only two photos of Bushtits from Hood River County, both appear to be Pacific birds as would be expected based on their distribution on the north side of the Columbia. The photos from Deschutes and Jefferson counties are Interior, although there are a couple that might be intermediate. None of the photos from Klamath County are Interior; all are either Pacific or indeterminate. Lake County birds are Interior with some intermediates present, for instance this great photo of an intermediate bird with brown crown and cheeks (https://macaulaylibrary.org/asset/107479301#_ga=2.206940244.698661550.1606410324-582076538.1467990332) from Cabin Lake in October 2015.

How can eBirders contribute?

The photo record in the Macaulay Library of eBird is useful but scanty. More photos are needed from areas where distribution is still poorly known and where there is likely overlap of the two subspecies. In these overlap areas, there are only six photos from Klickitat County, two from Hood River County, seven from Wasco County, and six from Lake County. Adding to the photo record from these and other eastside counties where the status of Bushtits is still unclear contributes much to our understanding of the Interior population, which remains less understood than the Pacific population.

Good field notes are also important, and are lacking in many areas. For instance, of the 21 eBird checklists from Rock Creek in Klickitat County, none of them have field notes that would help with documenting which population is present in an area of potential overlap and all are recorded as Bushtit with no population designation. There is one photograph, of a bird that appears to be Interior. Even without a photograph, eBirders can contribute significantly by attempting to determine which population of Bushtits they find, and documenting it with field notes in their eBird checklist. Field notes must include description of crown and cheek color, and if both are seen well, then eBirders should enter birds with brown crowns and gray cheeks as Pacific and birds with gray crowns and brown cheeks as Interior. Birds that are not seen clearly, or are heavily worn, should be entered without a population designation.

Documentation of intermediate birds, either with photographs or written descriptions is also valuable, even though they cannot be entered into eBird as such. It is important to understand where intermediate birds are found, and also to document their appearance. While intermediate birds are most likely in the east end of the Klamath Basin, at the east end of the Deschutes Basin, and east of the Klickitat River, observers should be alert for intermediates anywhere along the east slope of the Cascades. Potential intermediates, whether photographed or not, should be described and entered without a population designation.

The isolated population of Interior Bushtits at the north end of the Potholes Reservoir in Grant County, WA has not been reported since 2016. eBirders should continue to watch for them in the area, and get good documentation of any sightings.

Additional occurrences of birds with black feathers on their cheeks should also be documented with photos, as it would be interesting to learn more about the frequency of this likely polymorphism.

References

Fuller, H. 2020. One Oregon Bushtit is unique among the already unique. Oregon Birds 46:59-61.
Harrap, S. and D. Quinn. 1995. Chickadees, Tits, Nuthatches & Treecreepers. Princeton University Press, Princeton, NJ. 464 pp.

Marshall, D.B., M.G. Hunter and A.L. Contreras, Eds. 2003. Birds of Oregon: A General Reference. Oregon State University Press, Corvallis, OR. 768 pp.

Pyle, P. 1997. Identification Guide to North American Birds, Part I. Slate Creek Press, Bolinas, CA. 732 pp.

Sloane, S. A. (2020). Bushtit (Psaltriparus minimus), version 1.0. In Birds of the World (A. F. Poole and F. B. Gill, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.bushti.01

Stepniewski, A. 1999. The Birds of Yakima County, Washington. Yakima Valley Audubon Society, Yakima, WA. 278pp.

Wahl, T.R., B. Tweit and S.G. Mlodinow, Eds. 2005. Birds of Washington: Status and Distribution. Oregon State University Press, Corvallis, OR. 436 pp.