Poecile atricapillus x gambeli
Status: No accepted records (but see Comments).
Comments: Although Mountain and Black-capped Chickadee apparently hybridize “extensively in Rio Grande valley of central New Mexico” where neither species is common, hybridization is only occasional in the large area of overlap of the ranges of the two species where each species is common and they separate by habitat (McCallum et al 2020). Although Phillips (1986) was “aware of no authentic specimen” of hybrid Black-capped and Mountain Chickadees, and McCallum et al (2020) noted that a purported hybrid from Wyoming was thought to be a slightly aberrant Black-capped Chickadee and not a hybrid, evidence is accumulating that hybrids or at least introgressants do occur in eastern Colorado and southeastern Wyoming (eBird,org, accessed Feb 2021).
Hybrids were reported in the Laramie Mountains of eastern Wyoming in early Oct 2017 (Cody Porter, eBird.org), only about 75 miles from Nebraska, and, more significantly for Nebraska, at Wyoming Hereford Ranch at the east edge of Cheyenne, Wyoming. Ted Floyd determined that “many, if not most” of the chickadees in and around the ranch looked and sounded like intermediates (http://tinyurl.com/chickadee-2015-09-06a). Wyoming Hereford Ranch is about 35 miles from Pine Bluffs and the Nebraska border.
There are two records of phenotypic Black-capped Chickadees in Nebraska singing songs more akin to those of Mountain Chickadee, and a third likely record. Whether such birds are in fact hybrids or whether they learned incorrect songs as juveniles is unknown. If such birds are from the mixed populations in southeastern Wyoming described above, the latter explanation may be more accurate. An alternative explanation is suggested by studies carried out by Kroodsma et al (1999), who found that Black-capped Chickadees occupying various islands offshore from mainland Massachusetts sang discernibly different songs on different islands which were also different from the homogeneous mainland songs. The parallel in western Nebraska might be differing songs of chickadees occupying isolated geologic features, such as the Pine Ridge and Wildcat Hills in Nebraska and the nearby Laramie Mountains in Wyoming, from the contiguous population of Black-capped Chickadees in eastern and central Nebraska.
Recently, recordings were made by Steve Mlodinow in Gering Cemetery, Scotts Bluff Co 28 Apr 2019 of phenotypic Black-capped Chickadees that responded to songs of both species, but more strongly to those of Mountain Chickadee and sang more like Mountain Chickadees (ML154665171 Black-capped Chickadee Macaulay Library). A similar phenomenon was noted by Rosche (1974), who found two chickadees in the Wildcat Hills of southern Scotts Bluff Co 18 Jul 1974 which resembled Black-capped Chickadees morphologically but sang Mountain Chickadee songs. Rosche had not heard any Mountain Chickadee songs at the site until he played a tape, at which time the two singing birds appeared. The two birds did not respond to taped Black-capped Chickadee songs. A song “reminiscent” of Mountain Chickadee’s song was heard south of Redington, Morrill Co 27 Jun 2003, about 20 miles southeast of Rosche’s 1974 location.
Kroodsma, D.E., B.E. Byers, S.L. Halkin, C. Hill, D. Minis, J.R. Bolsinger, J. Dawson, E. Donelan, J. Farrington, F.B. Gill, P. Houlihan, D. Innes, G. Keller, L. Macaulay, C.A. Marantz, and J. Ort. 1999. Geographic variation in Black-capped Chickadee songs and singing behavior. Auk 116: 387-402.
McCallum, D.A., R. Grundel, and D.L. Dahlsten. 2020. Mountain Chickadee (Poecile gambeli), 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.mouchi.01.
Phillips, A.R. 1986. The known birds of North and Middle America. Part 1. Published by the author, Denver, Colorado, USA.
Rosche, R.C. 1974. Mixed-up chickadees. NBR 42: 80.
Silcock, W.R., and J.G. Jorgensen. 2021. Black-capped x Mountain Chickadee (hybrid) (Poecile atricapillus x gambeli). In Birds of Nebraska — Online. www.BirdsofNebraska.org
Updated 24 February 2021