The White-Breasted Nuthatches of North America

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uring 2013, the American Ornithologists’ Union (AOU) evaluated a proposal to “split” the White- Dbreasted Nuthatch (Sitta carolinensis) into any- where from two to four species. The proposal did not Cryptic pass (AOU 2013a). Members of the AOU’s Commit- tee on Classification and Nomenclature of North and Middle American Birds were, however, nearly unani- mous in their desire to revisit the question soon, after more data have been gathered (AOU 2013b). What does this mean for North American birders? Certainly more Species identification challenges, but also an opportunity to con- The White-breasted tribute to our understanding of the current and changing ranges of these birds. Nuthatches Background A key geological event was the formation, 14–2½ mil- lion years ago, of the “Basin and Range” district of western North America. This event promoted the splitting 4UFWFO(.MPEJOPX of forests of the U.S. and Canada into three distinct regions: Eastern (east of the Mountain West, and extend- -POHNPOU $PMPSBEP ing north to include much of the continent’s northern THNMPE!BPMDPN reaches); Interior West (from the Rocky Mountains west to the eastern slopes of the Sierra Nevada and the Cas- cades, south to the mountains of northern Mexico, and including the Davis and Chisos mountains of Texas); and Pacific (from the crests of the Sierra Nevada and the Cascades west to the Pacific Coast). A more complete summary is given by Graham (1999). These distinctions were reinforced by “recent” Quaternary Period glacial cycles (Van Devender 1990, Graham 1999) and sub-

This article presents an overview, based on recent scientific literature and the author’s field and museum work, of our present knowledge of the identification and geographic distribution of the White-breasted Nuthatches of North America. The bird currently classified as the White-breasted Nuthatch exhibits considerable geographic variation, and may well comprise multiple species. Three distinctive populations—the “Carolina,” “Rocky Mountain,” and “Slender-billed” nuthatches—occur in the ABA Area. Field identification is problematic where the ranges of these populations overlap (Carolina and Rocky Mountain, mid-continent; Rocky Mountain and Slender-billed, farther west). Additional challenges involve vagrancy, hybrids, and natural variation within each group. Fortunately, careful study in

In Brief the ﬁeld often permits a credible identiﬁcation, especially if a nuthatch is both seen and heard; photos and audio can be very helpful too.

26 #*3%*/(t.":+6/& sequently led to many of the tripartite groupings of species and subspecies encountered in North America north of Mexico (Yellow-bellied, Red- naped, and Red-breasted sapsuckers; Blue-headed, Plumbeous, and Cassin’s vireos; etc.). White-breasted Nuthatches divide nicely along these lines, with Eastern (S. c. carolinensis), Inte- rior West (S. c. nelsoni), and Pacific (S. c. aculeata) subspecies-groups (Grubb and Pravosudov 2008) UFSUJBMT represented. Spellman and Klicka (2007) analyzed a single mitochondrial DNA (mtDNA) gene and concluded that there are four major groupings (or “clades”) of White-breasted Nuthatches; they split the Interior West group further into Rocky Moun- tain and Sierra Nevada/Cascade groupings, S. c. nelsoni and S. c. tenuissima, respectively. Gene flow between these two Interior West groups is not triv- HSFBUFS ial. Another study, looking at one mtDNA gene and DPWFSUT 19 nuclear DNA genes, found the same four groups (Walstrom et al. 2012), although sampling near contact zones was limited. Issues with gene flow and sample size were major reasons why the AOU decided not to split the White-breasted Nuthatch into multiple species. Furthermore, checklist committee members seemed inclined to split the White-breasted Nuthatch into three species (keeping the Interior West group as one) rather than four (AOU 2013b). No common names were proposed for these possible new species. Therefore, I follow the AOU’s nBOLT (1910) nomenclature, using Carolina Nuthatch for the carolinensis group, Rocky Mountain Nuthatch for the nelsoni group, and Slender-billed Nuthatch for the aculeata group. Given current knowledge, the Rocky Mountain (nelsoni, in the strict sense) and Sierra Nevada/Cascade (tenuissima) taxa are not Fig. 1. *OUIJTQPTF BGFNBMF8IJUFCSFBTUFE /VUIBUDI TVCTQFDJFTcarolinensis i$BSPMJOB reliably separable in the field, so I will discuss them /VUIBUDIw TIPXTBMMPGUIFWJTVBMDIBSBD as a single entity, the Rocky Mountain Nuthatch UFSTEFTDSJCFEJOUIJTBSUJDMF'JFME (see Grubb and Pravosudov 2008). TFQBSBUJPOPGUIFUISFFNBJO8IJUF CSFBTUFE/VUIBUDIQPQVMBUJPOT Distribution of Proposed Species SFRVJSFTBOBQQSFDJBUJPOBOE Carolina Nuthatch VOEFSTUBOEJOHPGUIF This nuthatch is largely resident from the Peace FõFDUTPGGFBUIFSXFBS QPTUVSF MJHIUJOH River region of northeastern British Columbia east BOEOBUVSBM through central Alberta, Saskatchewan, and Mani- WBSJBUJPO toba to Prince Edward Island and south to eastern Photo by Texas, northern Louisiana, and Georgia, plus a © Garth small area of the Florida Panhandle (Dunn and Al- McElroy.

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Fig. 2.5IFTFQIPUPTEFQJDUUIFOBSSPXFSEBSLDSPXOPGUIF3PDLZ.PVOUBJO/VUIBUDI 'JHB DPNQBSFEUPUIFCSPBEFSDSPXOTPG$BSPMJOB 'JHC BOE4MFOEFSCJMMFE 'JHD OVUIBUDIFT5IFDPOUSBTUJOHUFSUJBMBOEHSFBUFSDPWFSUTPGUIF$BSPMJOB/VUIBUDIBSFBMTPFWJEFOU FWFO XJUIBEPSTBM iUPQEPXOw WJFX5IF3PDLZ.PVOUBJO/VUIBUDI 'JHB TIPXTEBSLFSUFSUJBMTUIBOBWFSBHFBOEOBSSPXMZEBSL CVUOPUCMBDL HSFBUFSDPWFSUDFOUFST JODPOUSBTUUPUIFCSPBECMBDLHSFBUFSDPWFSUDFOUFSTPGUIF$BSPMJOB/VUIBUDI 'JHC 5IF4MFOEFSCJMMFE/VUIBUDI 'JHD TIPXTBQMBJOXJOH OPUSBSFGPSUIBUUBYPOCVUQFSIBQTEVFJOQBSUUPXFBSPOUIJTJOEJWJEVBMFig. 2a. Rocky Mountain Nuthatch. Chico Basin Ranch, El Paso County, Colorado; 2 October 2013. Photo by © Steven G. Mlodinow. Fig. 2b. Carolina Nuthatch. 5IJTJTUIFTBNFCJSE BTJO'JHD Crow Valley Campground, Weld County, Colorado; 21 September 2012. Photo by © Steven G. Mlodinow. Fig. 2c. Slender-billed Nut- hatch. Ridgeﬁeld, Clark County, Washington; 12 January 2009. Photo by © Scott Carpenter. derfer 2011, eBird data accessed 26 March 2014). The Carolina then into the cordilleras of Mexico south to Oaxaca. The Rocky Nuthatch is at least partially migratory, with wintering birds Mountain Nuthatch also occurs east from the Rocky Mountains westward to the Front Range of Colorado (Mlodinow 2014), along the southernmost edge of Colorado east to westernmost southwest to central Texas (Phillips 1986, Lockwood and Oklahoma, plus there are isolated populations in the Sierra de Freeman 2014), and south to the Gulf Coast from Louisiana la Laguna of Baja California Sur, the Black Hills of South Da- to Florida (Stevenson and Anderson 1992, Turcotte and Watts kota (Spellman and Klicka 2007, Grubb and Pravosudov 2008, 1999, eBird data accessed 26 March 2014). Additionally, large Dunn and Alderfer 2011), and the Pine Ridge of Nebraska (R. numbers have been noted migrating past Cape May Point (T. Wright, personal communication). Leukering, personal communication). The Rocky Mountain Nuthatch is at least a partial migrant, A range shift appears to have occurred over the past century, with a few occurring regularly to the eastern border of Colo- with Carolina Nuthatches establishing themselves as breeders rado (Mlodinow 2014), into the Nebraska panhandle (eBird along the South Platte River in northeastern Colorado, starting data accessed 26 April 2013), and in the lowland areas of New approximately in the 1980s (Mlodinow 2014), and retreating Mexico (Dunn and Alderfer 2011). Vagrants have occurred in as breeders from central and most of northern Florida since at southwestern Kansas (Phillips 1986) and San Diego County, least the 1950s (Stevenson and Anderson 1992). California (Unitt 2004). Vagrants have been recorded on Sable Island, Nova Scotia (Phillips 1986), in easternmost New Mexico (Baumann et al. Slender-billed Nuthatch 2013), and in southern Florida (Stevenson and Anderson 1992). This nuthatch is largely resident from southwestern Washington through western Oregon, most of California, and into north- Rocky Mountain Nuthatch western Baja California; there also is an isolated population in This nuthatch is largely resident from south-central British Co- Sierra de San Pedro Mártir of Baja California (Spellman and lumbia and the Washington Cascades south into Nevada and Klicka 2007, Grubb and Pravosudov 2008, Dunn and Alder- easternmost southern California and southeastern Arizona. fer 2011). An isolated population in the southern Puget Sound The range extends east to southernmost Alberta, the south- area of Washington has been extirpated since at least the 1990s western half of Montana, Wyoming, and westernmost Texas, (Wahl et al. 2005). Vagrants have occurred in central Arizona

28 #*3%*/(t.":+6/& and on Vancouver Island, British Columbia (Phillips 1986). Identification Call notes Identification criteria for White-breasted Nuthatch taxa typically emphasize the differences in the call notes, which is reasonable, as these birds’ calls are generally distinct from one another. The most distinctive is the Rocky Mountain Nuthatch, which usually utters a rapid, stuttering, polysyllabic di-di-di-di-di burst that carries with it a sense of urgency. Carolina and Slender-billed 3a nuthatches both give calls that recall the Red-breasted Nuthatch, being somewhat nasal and usually emitted at a more leisurely pace than the calls of the Rocky Mountain Nuthatch: a throaty, emphatic yarnk...yarnk... for the Carolina, and a shriller, more wavering yurrr...yurrr... for the Slender-billed. With both Caroli- na and Slender-billed nuthatches, these notes are typically given one at a time, monosyllabically. Excited Carolina and Slender-billed nuthatches are prone to speeding up the rate of their calling, thus approaching the Rocky Mountain Nuthatch, and occasional Rocky Mountain Nuthatches will call in a more leisurely fashion, thus sounding more like the other two taxa. Indeed, recorded calls attributed to one taxon in the 3b field have proven to be of another via subsequent analysis of sound spectrograms of the calls (T. Floyd, personal communication). The songs of White-breasted Nuthatches—soft, whistled sequences, sounding like a distant Northern Flicker—are less variable among the three main groups, and are not discussed here.

Fig. 3.5IFTFQIPUPTTIPXEJõFSFODFTJOUIFTJEFBOEnBOLQBUUFSOT PGUIFUISFFHSPVQTPG8IJUFCSFBTUFE/VUIBUDIFT/PUFUIFNFEJ VNEBSLHSBZPGUIF3PDLZ.PVOUBJO/VUIBUDI 'JHB WTUIFXIJUF TJEFTPGUIF$BSPMJOB/VUIBUDI 'JHC "OPUIFS$BSPMJOB/VUIBUDI 'JHD IBTEBSLFSnBOLT CVUSBUIFSQBMFTJEFTXJUIPSBOHFoCVõ 3c GFBUIFSTNJYFEJO5IF4MFOEFSCJMMFE/VUIBUDI 'JHE TIPXTQBMF HSBZnBOLTXJUIBUPVDIPGPSBOHFoCVõ"MTPXPSUIOPUJOHJTIPX DMPTFMZUIFCMBDLDSPXOPGCPUI$BSPMJOB/VUIBUDIFT 'JHTCoD 3d BQQSPBDIUIFFZF BTXFMMBTUIFUIJOCMBDLMJOFFYUFOEJOHCBDL GSPNUIFFZFPOUIJTUBYPO5IFIFBENBSLJOHTPGUIF4MFOEFSCJMMFE /VUIBUDI 'JHE BSFTJNJMBSUPUIPTFPGUIF$BSPMJOB 'JHTCoD JODMVEJOHBEBTIPGCMBDLCFIJOEUIFFZF/PUFUIBUUIFCJMMPGPOFPG UIF$BSPMJOB/VUIBUDIFT 'JHC TFFNTUPNBUDIUIFMFOHUIPGUIF CJMMPGUIF3PDLZ.PVOUBJO/VUIBUDI 'JHB Fig. 3a. Rocky Moun- tain Nuthatch. 5IJTJTUIFTBNFCJSEBTJO'JHB Conifer, Jeﬀerson County, Colorado; 28 December 2012. Photo by © Steven G. Mlodinow. Fig. 3b. Carolina Nuthatch. Wray, Yuma County, Colorado; 1 Septem- ber 2013. Photo by © Steven G. Mlodinow. Fig. 3c. Carolina Nuthatch. Ovid, Sedgwick County, Colorado; 3 November 2013. Photo by © Steven G. Mlodinow. Fig. 3d. Slender-billed Nuthatch. 5IJTJTUIFTBNF CJSEBTJO'JHE Portland, Multnomah County, Oregon; 10 May 2013. Photo by © Scott Carpenter.

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Table 1%JTUJOHVJTIJOH$IBSBDUFSTPG8IJUFCSFBTUFE/VUIBUDI(SPVQT Carolina Rocky Mountain Slender-billed Greater Coverts Pattern Prominent black or blackish centers with Dusky to gray centers with broad grayish edging; Typically gray centers, sometimes dusky, with little contrasting grayish edging little or no contrast to no contrast; plainest of all three Outermost Tertial Pattern Black on inner and outer webs Black to dusky on inner webs, dusky on outer webs Black to dusky on inner webs, dusky on outer webs; averages paler than Rocky Mountain Upperparts Coloration Paler gray Darker gray Medium gray Dark Crown Width Broad Narrow Broad Facial Pattern Black of crown approaches eye more closely than Black of crown farther from eye, typically forming arc Black of crown approaches eye fairly closely; Rocky Mountain; many birds have small black dash over face; no black mark behind eye occasionally small black dash back from eye or line extending back from eye Side/Flanks Coloration Pale gray to white, sometimes suffused with buff Medium blue-gray, rarely with buff wash Pale gray to white, sometimes suffused with buff Bill Length Averages shorter and stouter Averages longer and more slender Averages shorter and more slender

Also, all White-breasted Nuthatches give weak, mumbling, na- this taxon’s range seem to show the plainest greater coverts, sal notes when foraging: plink, pleek, etc. Audio recordings and whereas birds from Arizona and New Mexico average darker- sound spectrograms of typical calling sequences are available centered greater coverts. Some Rocky Mountain Nuthatches on the Birding magazine website: aba.org/birding have almost blackish centers to their greater coverts, but these are never as dark as those of Carolina Nuthatches, and when Visual characters present, the dark center is narrower. Slender-billed Nuthatches The standard identification literature has given short shrift to usually have plain greater coverts, with little or no contrast. visual identification cues, but I have found that these are sur- These differences would seem to make the identification of prisingly useful. The discussion in Wood (2006) provides a Carolina Nuthatches straightforward. However, feather posi- good starting point. To help clarify the usefulness of various vi- tioning can confound interpretation, as the scapulars or side sual characters, I studied approximately 150 specimens each of feathers sometimes partly veil the greater coverts, making the Carolina and Rocky Mountain nuthatches and 50 Slender-billed dark centers less apparent. Also, the centers of the greater co- Nuthatch at The Field Museum of Natural History in Chicago verts are less evident if these feathers are crowded together and and at the University of Puget Sound’s Slater Museum of Natu- more evident if they are spread apart. ral History. Also reviewed were more than 100 photos of each taxon online from locations at which only one is likely—for ex- Tertials ample, Illinois for Carolina Nuthatch. I found the three most use- On all three taxa, only the inner web of the smallest (innermost) ful characters to be the following: (1) the pattern of the greater two tertials is black or dusky. On the largest (outermost) tertial, secondary coverts (hereafter, greater coverts), (2) the outermost Carolina Nuthatches are black on the inner and outer webs, tertial pattern, and (3) the width of the dark crown. Two other Rocky Mountain Nutatches are dusky (occasionally black, es- characters were useful: (4) the side/flank coloration and (5) the pecially on southern birds) on the inner web and dusky on the facial pattern. I was able to find no consistent difference in vent outer web, and Slender-billed Nuthatches are gray to dusky (between the legs) pattern, and I believe that the differences in (rarely blackish) on both the inner and outer webs. Again, back color are probably of little value in the field. Fig. 1 provides feather positioning can make this character difficult to assess. an overview of terminology (greater coverts, tertials, flanks), and Table 1 summarizes useful and proposed differences. Crown and Face Carolina Nuthatches have a rather broad dark crown when Greater Coverts viewed from above. In Rocky Mountain Nuthatches, the crown Carolina Nuthatches have blackish centers to their greater co- stripe is relatively narrow. Slender-billed Nuthatches have a verts that contrast markedly with the feathers’ edges. Rocky crown width similar to that of Carolina Nuthatches, but may Mountain Nuthatches are variable in this character, ranging average a bit narrower. When viewed from the side, the broader from rather uniformly marked greater coverts to coverts with crown of Carolina and Slender-billed nuthatches tends to bring dusky (but not black) centers. In my museum and photograph- the crown edge closer to the eye than in Rocky Mountain Nut- ic studies, I found that birds from the northwestern portion of hatches. Be advised that the posture of a bird can affect the ap-

30 #*3%*/(t.":+6/& pearance of crown width, particularly The H-word with side views. Where the ranges of different White- Many, perhaps most, Carolina Nut- breasted Nuthatch populations inter- hatches have a narrow black line ex- sect, it is quite possible, if not likely, tending backward from the eye, some- that some hybridization occurs. One times short, sometimes rather long. should always be open to the possibil- This mark is seemingly never present ity of hybridization when confronted on Rocky Mountain Nuthatches. Some with potential vagrants or in regions Slender-billed Nuthatches appear to where the ranges of two taxa approach 4a show a very brief dark mark behind or overlap one another. the eye. Acknowledgments 4b Sides/Flanks I owe a debt of gratitude to The Field The sides of Carolina and Slender-billed Museum of Natural History and the nuthatches are whitish or pale blue–gray, University of Puget Sound’s Slater Mu- sometimes washed in orange–buff. The seum of Natural History for their gen- sides of Rocky Mountain Nuthatches are erosity in allowing me to ponder their pale to medium blue–gray, sometimes specimens ad nauseam. Additionally, nearly as dark as the back, rarely washed Scott Carpenter and David Irons are to in orange–buff. be thanked for making so many images of Slender-billed Nuthatch available to Bill me. Finally, but not least, many thanks There is extensive overlap in bill size, to Tony Leukering, Mark Lockwood, with bill length ranging from 15.4 to and Michael O’Brien for helpful com- 4c 19.5 mm in Carolina Nuthatch, from ments on an earlier version of this man- 16.9 to 21.7 mm in Rocky Moun- uscript. tain Nuthatch, and from 16.3 to 19.2 mm in Slender-billed Nuthatch (Pyle Literature Cited 1997). In Colorado, where Carolina "NFSJDBO0SOJUIPMPHJTUT6OJPO<"06> and Rocky Mountain nuthatches occur, The AOU Check-list of North American Birds I have found bill length to be of little SE FE "NFSJDBO 0SOJUIPMPHJTUT 6OJPO use in the field. Slender-billed Nut- /FX:PSL hatches do, however, appear to have a "NFSJDBO 0SOJUIPMPHJTUT 6OJPO <"06> shorter and, in particular, slimmer bill; B 'JGUZGPVSUI TVQQMFNFOU UP UIF bill shape of this taxon may well be AOU Check-list of North American Birds. Auk useful for field identification. o

Fig. 4.5IFTFQIPUPTTIPXEJõFSFODFTJOHSFBUFSDPWFSUQBUUFSOTBOEUFSUJBMQBUUFSOTBNPOH UIFUISFFHSPVQTPG8IJUFCSFBTUFE/VUIBUDIFT0OFPGUIF3PDLZ.PVOUBJO/VUIBUDIFT 4d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õVTFEJOUPUIFEBSL CMVFoHSBZTJEFTPGPOFPGUIF3PDLZ.PVOUBJO/VUIBUDIFT 'JHB BOJOGSFRVFOUCVUOPU PWFSMZSBSFUSBJUFig. 4a. Rocky Mountain Nuthatch. 5IJTJTUIFTBNFCJSEBTJO'JHB Conifer, Jeﬀerson County, Colorado; 28 December 2012. Photo by © Steven G. Mlodinow. Fig. 4b. Rocky Mountain Nuthatch. Patagonia, Santa Cruz County, Arizona; 23 February 2013. Photo by © Steven G. Mlodinow. Fig. 4c. Carolina Nuthatch. 5IJTJTUIFTBNFCJSEBTJO'JHC Crow Valley Campground, Weld County, Colo- rado; 21 September 2012. Photo by © Steven G. Mlodinow. Fig. 4d. Slender-billed Nuthatch. 5IJTJTUIFTBNFCJSEBTJO'JHE Portland, Multnomah County, Oregon; 10 May 2013. Photo by © Scott Carpenter.

ABA.ORG/BIRDING 31 WHITE!BREASTED NUTHATCHES

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Recent evidence suggests that three or four species are represented by what we currently label the White-breasted Nuthatch. Most individuals of these “new” species are identifiable with careful study of calls and plumage. Correct identification requires that observers understand the effects of posture, plumage wear, and lighting—as well as the somewhat subjective nature of human hearing and seeing. As always, an appreciation for variation in field characters—aural and visual—is essential. Photos and audio recordings may be necessary for establishing the identity of birds well out of range. Many such “cryptic” species have been recognized over the past decade or two, mainly in the tropics, but also right here in the ABA Area. Perhaps the most famous is the Gunnison Sage-Grouse, described to science only in 2000. A very recent example is that of the erstwhile Sage Sparrow, now considered to comprise two species, the Bell’s and Sagebrush sparrows; conceivably, a third species is involved. Genetic data are certainly part of the elucidation of cryptic species, but phenotypic characters play a role, too. For example, the differences between what we today know as the Bell’s and Sagebrush sparrows were well understood by the ornithologists of the 19th century. And the recent discovery of the Gunnison Sage-Grouse was based on a broad suite of evidence: behavioral, vocal, physiological, and of course genetic. By being more aware of birds at the subspecies—or apparent subspecies—level, rather than simply at the species level, savvy birders can contribute to our under- Final Thoughts standing of biogeography as well as identification criteria.

32 #*3%*/(t.":+6/&