The convoluted nomenclature of the nightingale-thrushes (Aves: Turdidae: Catharus) began with a taxonomically composite species (Turdus minor J. F. Gmelin, 1789) that was a source of widespread confusion until the mid-19th century. In a recent paper, I reviewed the early history of T. minor and demonstrated that Alexander Wilson (1766–1813), who split the composite T. minor into two species that were also composites (T. solitarius and T. mustelinus; Wilson, 1812), did not correctly distinguish any of the five species now recognised as breeders in eastern North America (Halley 2018). Those species are: Hermit Thrush Catharus guttatus (Pallas, 1811), Veery C. fuscescens (Stephens, 1817; for neotypification see Halley 2018), Swainson's Thrush C. ustulatus (Nuttall, 1840), Grey-cheeked Thrush C. minimus (Lafresnaye, 1848) and Bicknell's Thrush C. bicknelli (Ridgway, 1882). The confusion of Wilson's composites had downstream effects on the understanding of Charles Lucien Bonaparte (1803–57) and John James Audubon (1785–1851), who likewise failed to distinguish the five eastern species (Halley 2018).¹ The number of species in eastern North America was gradually resolved by Giraud (1844), Brewer (1844), Baird et al. (1858) and Ridgway (1882).

Here, I disentangle the taxonomic history of Western Thrush T. ustulatus Nuttall, 1840, which has long been recognised as the first description of the western (coastal) subspecies of Swainson's Thrush C. u. ustulatus (AOU 1998: 505, Mack & Yong 2000, Ruegg 2007). The Swainson's Thrush complex is comprised of two genetic clades (recognised as species or subspecies) that were evidently geographically isolated (during the breeding season) in forested refugia during the Last Glacial Maximum (LGM). Following deglaciation, the populations expanded and came into secondary contact in the mountains of northern Washington and British Columbia, where they formed a narrow hybrid zone that persists to the present day (Ruegg & Smith 2002). Many recent authors (e.g., Mack & Yong 2000, Ruegg 2007) have classified the western (coastal) clade as C. u. ustulatus (Nuttall, 1840) and the eastern (inland) clade as C. u. swainsoni (Cabanis in Tschudi, 1845), although some authors have elevated the two clades to species rank (e.g, Piacentini et al. 2015, del Hoyo & Collar 2016). Speciation has occurred in Catharus multiple times despite periodic episodes of gene flow between incipient (and even non-sister) species (Bay & Ruegg 2017, Everson et al. 2019) and the taxa in question meet the criteria for species rank under nearly every species concept including ‘relaxed’ approaches to the biological species concept (BSC) that permit some gene flow between species (de Queiroz 2007). For these reasons, the two clades are herein classified as sister species: C. ustulatus (coastal) and C. swainsoni (inland). Their generalised breeding ranges are shown in Fig. 1.

Figure 1.

Map of the North American breeding ranges of Catharus swainsoni (Cabanis in Tschudi, 1845), C. u. ustulatus (Nuttall, 1840), C. u. oedicus (Oberholser, 1899) and C. u. phillipsi Ramos in Phillips, 1991. The contact zone of C. u. ustulatus and C. u. oedicus in northern California is poorly defined and requires further study (see Bond 1963: 378). Data provided by BirdLife International and Handbook of the birds of the world Alive (2018). Bird species distribution maps of the world. V. 2018.1. Available at  http://datazone.birdlife.org/species/requestdis.

History of Townsend's specimens of western thrushes

The original description of T. ustulatus was based on two specimens that John K. Townsend (1809–51) collected during the second Wyeth expedition (1834–37) while camped on the Columbia River near Vancouver, Washington. They were the first Catharus specimens from western North America to reach the eastern seaboard, and they arrived before the confusion surrounding the eastern species was resolved.

Thomas Nuttall (1786–1859), the seasoned botanist, explorer and author of Manual of the ornithology of the United States (1832, 1834; hereafter, Manual), was Townsend's companion and mentor on the first part of the expedition. However, the two naturalists parted ways in September 1835, which had consequences for the fate of Townsend's specimens. Nuttall sailed to the Sandwich Islands (Hawaii) and then ‘around the Horn’ of South America to eastern North America, where he landed in summer 1836 (Graustein 1967). Meanwhile, Townsend stayed in the Pacific Northwest for another year, and eventually returned to Philadelphia in November 1837 (Mearns & Mearns 2007).

A collection of specimens that Townsend shipped in September 1835, which included two study skins labelled ‘Turdus Wilsoni?' and one labelled ‘Turdus minor,' reached the Academy of Natural Sciences of Philadelphia (ANSP) in July 1836, shortly before Nuttall's return. The invoice from Townsend's 1835 shipment is preserved at the American Philosophical Society (APS) Library, Philadelphia, PA (Mss.B.M843). Nuttall and Audubon examined the three western specimens of Catharus from Townsend's consignment at ANSP in September 1836, but neither recognised them as new species. This was a consequence of their general confusion with respect to Wilson's composites (see Halley 2018). Audubon purchased duplicates with Nuttall's approval, including (presumably) one of the two ‘Turdus Wilsoni?’ specimens, which he took to London in July 1837. Audubon then remained in Europe until summer 1839, supervising the completion of The birds of America (1827–38) and writing the final two volumes of Ornithological biography (1838–39) (Fries 2006).

Meanwhile, Townsend returned to Philadelphia in November 1837 with an additional collection, approximately three times larger than the 1835 shipment (Mearns & Mearns 2007: 324). Edward Harris (1799–1863) purchased more duplicates for Audubon, and Townsend also sent many specimens directly to Audubon so that he could sell them to European collectors (see Derby List, in which one specimen of ‘T. Wilsonii’ is mentioned; Mearns & Mearns 2007: 330). Thus, Audubon had access to multiple specimens of western Catharus from the Townsend collection in 1838, when he wrote:

An annotation (*) by Townsend in the margin of the ANSP copy of Ornithological biography vol. 5 (Audubon 1839: 204, ANSP Library, QL674.A915) reads: ‘*mistake. The specimen was marked Turdus Wilsonii ? J.K.T.’ (Fig. 2). This annotation was later mistranscribed by Stone (1906: 312), who inadvertently replaced Townsend's question mark with a period. Townsend included question marks on his labels and specimen invoice because he was uncertain about the identifications of some specimens (‘ Turdus Wilsoni ?'), not because, as Audubon presumed, he thought they represented a new species (APS Library, Mss.B.M843).

Figure 2.

Annotation by John K. Townsend in the ANSP copy of Ornithological biography, vol. 5 (Audubon 1839: 204, ANSP Library: QL674.A915): ‘*mistake. The specimen was marked Turdus Wilsonii? J.K.T.’ The image contrast has been boosted to render Townsend's faint pencil markings more visible. (Matthew R. Halley)

Townsend's original data are missing from all extant specimens of Catharus attributed to him, except one (USNM 2040), which bears a label in Townsend's hand with the name Merula silens Swainson (in Swainson & Richardson 1831)—not T. Wilsoni. Therefore, the specific identity of the specimen mentioned by Audubon (1839: 203) cannot be verified. The year ‘1838' in Audubon's comment is a typographical error, because Townsend had already returned to Philadelphia by late 1837. Nevertheless, a handwritten ‘5' is easily mistaken for an ‘8,' and Townsend's 1835 specimen invoice included the same uncertain identification: ‘Turdus Wilsoni?' (APS Library, Mss.B.M843). For these reasons, it is plausible (but not certain) that the specimen referenced by Audubon (1839: 203–204) was the duplicate he purchased in 1836 (without Townsend's knowledge, despite Audubon's claim that Townsend ‘sent’ it to him), rather than one of the specimens he acquired in 1838.

Meanwhile, from 1838 to early 1840, Nuttall was in Philadelphia preparing his next major botanical work, a 200-page tome that would eventually be peer-reviewed and published by the APS (Nuttall 1841). Botany was Nuttall's primary focus and expertise; his ornithological work was not executed with the same breadth of experience or attention to detail (Graustein 1967). His Manual was a commercial venture that, unlike most of his botanical writings, was published without peer review and contained ‘long passages without acknowledgment and with but comparatively slight verbal changes from [Alexander] Wilson' ... ‘[Nuttall] probably knew less about birds than has been commonly supposed' (Brewster 1906: 79–80). George Ord (1781–1866), a capable ornithologist and editor of Wilson's final (posthumous) volumes, upon the publication of the Manual, wrote in private correspondence: ‘I know that [Nuttall] is ignorant of ornithology; and I further know that he is a sorry scoundrel’ (APS Library, Mss.B.Or2).

During his residency in Philadelphia in 1838–40, or perhaps earlier, Nuttall made a cursory study of the remnants of Townsend's collection of western birds. However, by that time, relatively few of Townsend's specimens remained at ANSP; most had been dispersed among private collectors (Mearns & Mearns 2007). Townsend had shipped dozens of specimens to Audubon, to be sold in Europe, and generously supplied the cabinets of his friends including Ezra Michener (1794–1887), with whom he stayed while preparing the manuscript of his travelogue, Narrative of a journey (Townsend 1839).

Audubon visited Philadelphia on 10–13 February 1840, according to a letter (‘I left New York on the 10^th Inst. spent a few days in Philadelphia…,' Corning 1969, 2: 231), but there is no evidence that he saw Nuttall during that short trip. Nor is there evidence that Audubon knew of Nuttall's intention to describe a new species of thrush from Townsend's collection. Audubon usually stayed at Harris' home in Moorestown, NJ, when he visited the Philadelphia region (see Corning 1969), and probably spent very little time in Philadelphia itself. Meanwhile, Nuttall was busy with preparations to relocate from Philadelphia to Cambridge, Massachusetts, because he had been hired to give a series of botanical lectures for the Lowell Institute in Boston. Nuttall departed in late February 1840, approximately two weeks after Audubon passed through Philadelphia (Graustein 1967).

The publishers of Nuttall's Manual were based in Cambridge and they expressed interest in publishing an updated (second) edition (Nuttall 1840). Nuttall's new ornithological material included c.150 pages of information from his Wyeth expedition journals (now lost) and various notes concerning specimens he had examined during his residency in Philadelphia. There is no evidence that Nuttall took a collection of bird skins to Cambridge. The manuscript that contained the description of Western Thrush T. ustulatus Nuttall, 1840, was drafted rapidly, without specimens at hand, and published within four months of Nuttall's arrival in Cambridge (Graustein 1967: 350).

The material basis of Turdus ustulatus Nuttall, 1840

The scientific description of T. ustulatus was based on a female specimen collected by Townsend on ‘the 10th of June' (1835 or 1836) on the Columbia River, presumably near Vancouver, Washington. Nuttall (1840) also described vocalisations given by multiple birds that were apparently neither collected nor clearly observed (‘as soon as seen [it] flits rapidly through the thicket') and a nest found ‘about the close of July [1835]…in the prairies of Wahlamet' (=Willamette River valley, Oregon). However, there is no evidence that the nest or vocalising birds were collected. Nuttall (1840) also cited Audubon's (1839: 203–204) note about the ‘female specimen of a Thrush [collected]…on the 19th June [1835]' among the synonyms of T. ustulatus. As explained above, Audubon's specimen was likely the duplicate sold to him in 1836, which may explain Nuttall's comment that ‘now’ he had only one specimen for description:

Therefore, the description of T. ustulatus Nuttall, 1840, was based on two female syntypes: one mentioned by Audubon (1839: 203–204) and the other described directly by Nuttall himself. Two of Townsend's study skins of C. ustulatus are extant: USNM 2040 (Fig. 3) and ANSP 23644 (Fig. 4). Both have been promoted as ‘the only specimen' described by Nuttall (1840). However, paradoxically, neither specimen matches Nuttall's description of the dorsal plumage, which actually presents a closer match to C. guttatus than to C. ustulatus: ‘Above olive-brown, a little darker on the head; the tail strongly tinged with rufous.' Just a few pages prior to his description of T. ustulatus, Nuttall (1840: 394–395) used those exact words to describe the dorsal plumage (‘olive-brown') and tail (‘strongly tinged with rufous') of Hermit Thrush T. solitarius Wilson, 1812; and he considered the bird in Audubon's Pl. 58 (= C. g. faxoni Bangs & Penard, 1921) to be an ‘excellent’ representation of T. solitarius (see Nuttall 1840: 393, and Fig. 6 in Halley 2018).

Spencer F. Baird (1823–87), who acquired USNM 2040 from Audubon, assumed incorrectly that it was Nuttall's syntype (Baird et al. 1858: 215). A plate (81) depicting USNM 2040 was published by Baird et al. (1860: VII) and claimed as ‘Mr. Nuttall's type' in the introductory pages (Fig. 5). Baird also pencilled ‘Type of Nuttall?’ in the margin of his personal copy of Pl. 81, deposited in the Smithsonian Library (see Deignan 1961: 432). This claim was later repeated by Hellmayr (1934: 457, ‘type [of T. ustulatus] in U. S. National Museum') and Deignan (1961: 431, ‘it may be assumed that [USNM 2040] is indeed the type, and that it is a female collected on June 10, 1835, as stated in Nuttall's description').

However, one label attached to USNM 2040, written in Baird's own hand, records the sex of the bird as male (‘m,' see Fig. 3) and his description of that specimen (‘uniform reddish brown [dorsal plumage and tail], with a faint olivaceous tinge,' Baird et al. 1858) does not match Nuttall's (1840) description of the T. ustulatus type (‘above olive-brown, a little darker on the head; the tail strongly tinged with rufous'). The illustration of USNM 2040 in Pl. 81 matches Baird et al.'s (1858) description, showing a more or less uniform reddish-brown coloration and no contrast between the back and tail (Fig. 5). There is no colour contrast in the plumage of this specimen today, after 160 years (Fig. 3). Thus, the discrepancy between Nuttall's (1840) and Baird et al.'s (1858) descriptions cannot be explained as a by-product of post-mortem change.

Figure 3.

USNM 2040 and its two oldest labels. The top label was apparently written by John K. Townsend: ‘Silent Thrush.– / Merula silens. Swainson p. 186. / Columbia River. Townsend.' The bottom label was written by Spencer F. Baird: ‘Turdus wilsonii Sw. / 2040 / Columbia River / J. K. Townsend / m[ale]’ (Matthew R. Halley)

Figure 4.

ANSP 23644 and its label. See text for information concerning provenance. The text ‘♀ JKT’ was purportedly copied from the base of the mount on which the bird was displayed during the mid-19th century, but the sex is recorded as male (‘♂') in the ANSP specimen ledger (ANSP Archives, coll. 54, box 3). Furthermore, the red type label has been defaced and there are no data linking this specimen to Nuttall (Matthew R. Halley)

Figure 5.

Cropped lithographic image of USNM 2040 (‘Turdus ustulatus') from Pl. 81 in Baird et al. (1860), ostensibly depicting ‘Mr. Nuttall's type' (see Baird et al. 1860: VII). Produced by [J. T.] ‘Bowen & Co. lith & col.’ in Philadelphia, Pennsylvania. It is reproduced here courtesy of Smithsonian Libraries (QL681.B138). Portions of another image (T. aliciae) have been digitally removed from the upper right of this figure for clarity.

Figure 6.

Digital scan of the ANSP Ornithology specimen ledger No. 3 (ANSP Archives, coll. 54, box 3), in which the sex of ANSP 23644 is recorded as male (‘♂'). This contradicts the ‘original’ data on the defaced specimen label (see Fig. 4).

Stone (1899: 19) claimed that ANSP 23644, which is similarly coloured to USNM 2040, was Nuttall's study skin of T. ustulatus, but not because the skin bore a label indicating its type status or because it matched Nuttall's (1840) description. Stone merely assumed that the specimen was at ANSP because Nuttall had worked there after returning from the west, and it was the only specimen of C. ustulatus from Townsend's collection that could be located: ‘...[T. ustulatus was] based on a Townsend specimen in the ANSP collection which I have identified as…' (Stone 1899: 19). In an unpublished memorandum dated 1893 and entitled ‘Explanations in regard to the Cataloguing of the Collection’, Stone confided that ‘no numbers were placed on the specimens to fix their identity’ when he began his work on the ANSP bird collection in March 1888 (ANSP Archives, coll. 54, box 4). His determination of Nuttall's type of T. ustulatus was apparently not based on evidence, but guesswork.

The remnants of a wire armature are visible, evidence that ANSP 23644 was once mounted for display. However, there is no original label or stand, only a secondary label that bears the following information, purportedly copied from the base of the (now missing) stand: ‘♀ JKT.’ However, Stone unambiguously recorded the sex of the bird as male (‘♂') in the ANSP specimen ledger (Fig. 6, ANSP Archives, coll. 54, box 3) and some additional text was (later?) forcibly scratched off the red type label (Fig. 4). The ledger is the oldest available primary source. This begs the question whether the original sex data was scratched off the type label and replaced with false data that matched Nuttall's description. In any case, there is no provenance with ANSP 23644 that connects the specimen to Nuttall, nor does the plumage of the bird match Nuttall's (1840) description of the T. ustulatus syntype.

Specimen comparisons

More than a century after Nuttall's description of T. ustulatus, Bent (1949: 167) aptly summarised the field marks that distinguish C. ustulatus and C. guttatus in the region where Townsend collected Nuttall's type, though it appears that he too overlooked the paradox:

To further investigate the identity of T. ustulatus Nuttall, 1840, I prepared a fresh series of adult specimens of C. ustulatus (n = 10) and C. guttatus (n = 10) from coastal Washington, west of the Cascade Mountains, and directly compared them to ANSP 23644 (C. ustulatus) and ANSP 16091 (C. guttatus), two of the four Catharus specimens from Townsend's collection now extant. I also prepared a series of C. swainsoni adults (n = 5) from eastern North America, yielding a total sample of 27 specimens for direct colour comparison (Table 1; 25 fresh, two historical). I used the rectangular (card-stock) window provided in Color standards and color nomenclature (Ridgway 1912) to match the capitalised colour names to the plumage just below the nape, and to the anterior and posterior portions of the tail. Most of the fresh specimens were 1–6 years old when they were scored, about the same age as the T. ustulatus syntype when Nuttall examined it in 1838–39. I also examined USNM 2040 (C. ustulatus) and compared it to other historical specimens in the USNM bird collection, but, for logistical reasons, was unable to directly compare it to the ANSP specimens or Ridgway (1912).

TABLE 1

Specimens used for colour comparison of Catharus ustulatus (n = 10), C. swainsoni (n = 5) and C. guttatus (n = 10). All specimens were prepared by Matthew R. Halley and deposited in the ornithology collection at the Academy of Natural Sciences of Drexel University (ANSP). Sex categories are female (F), male (M) and unknown (U). Localities are given as state abbreviation (PA = Pennsylvania; WA = Washington): county: town or site. The table is organised by species and date.

The sample of recent specimens from western North America comprises, in most cases, the victims of cats and / or window collisions, salvaged by volunteers during the spring and autumn migratory periods (2003–17) and preserved (frozen) by G. Shugart and D. Paulson at the Univ. of Puget Sound. The migratory flyway west of the Cascades is utilised by ‘pure’ C. ustulatus individuals and hybrid C. ustulatus × C. swainsoni (Delmore & Irwin 2014). Breeding populations of pure C. ustulatus occur near Vancouver, Washington, where Townsend presumably collected Nuttall's syntypes, and extend north into the Seattle area. Vancouver is c.275 km south-west of the southern periphery of the hybrid zone and Seattle is c.70 km west. For this reason, without genotyping the birds, I cannot be certain that the sample of C. ustulatus study skins, from the spring and autumn migratory periods, does not contain any individuals of hybrid origin.

In the fresh C. ustulatus series, examined in 2018, the dorsal plumage and tails were more or less uniform Olive-Brown (Fig. 7). The dorsal plumage of ANSP 23644 was also more or less uniform Olive-Brown, though some parts of the specimen have faded in the direction of Saccardo's Umber, presumably during the years when it was mounted for display. Like fresh specimens of C. ustulatus, there is no obvious contrast in colour between the back and tail of ANSP 23644, nor any suggestion that there ever was such a pattern. Neither is such a contrast evident in the fresh series of C. swainsoni, the backs and tails of which are more or less uniform Brownish Olive. The tails of some C. ustulatus specimens exhibit a subtle tendency toward Sepia, but this difference would not be well characterised by Nuttall's (1840) description of a ‘tail strongly tinged with rufous' (my italics), which was identical to his description of Hermit Thrush T. solitarius Wilson (see Nuttall 1840: 394–395). In conclusion, it appears that Nuttall (1840) actually described one of Townsend's fresh C. guttatus specimens from western Washington, as evidenced by fresh specimens from that region with Brownish Olive back plumage (below the nape) and tails that transition (anterior to posterior) from Prout's Brown to Mummy Brown (Fig. 8). However, Nuttall's (1840) and Audubon's (1839) syntypes are apparently no longer extant. Neither of the two extant specimens of C. guttatus (or C. ustulatus) from the Townsend collection are a female collected on the ‘10th of June' as described by Nuttall (1840), or a female collected on ‘19th June [1835]’ as described by Audubon (1839: 203–204): MCZ 16298 is a male and ANSP 16091 was collected in ‘May'.

Figure 7.

Plumage colour comparison of (A) ANSP 23644, collected and prepared by John K. Townsend near Vancouver, Washington, and claimed as the ‘type of Nuttall' by Stone (1899: 19), and (B–D) three relatively fresh specimens of Catharus ustulatus, prepared by M. R. Halley: (B) ANSP 204297, a female that died in a window collision on 1 September 2014, on Vashon Island, King County, Washington (prep. = MRH88); (C) ANSP 205167, a male that died in a window collision on 2 May 2017, also on Vashon Island (prep. = MRH146); (D) ANSP 205165, a bird of uncertain sex that died in a window collision on 28 September 2016, in Tacoma, Pierce County, Washington (prep. = MRH141). These birds died during migration in a pathway used by ‘pure’ individuals of C. ustulatus and hybrid C. ustulatus × C. swainsoni (see Delmore & Irwin 2014) (Matthew R. Halley)

Figure 8.

Plumage colour comparison of (A) a female C. guttatus (Pallas) collected and prepared by John K. Townsend in ‘May' (1835 or 1836) on the ‘Columbia River’ (ANSP 16090), and (B–D) three specimens prepared by Matthew R. Halley: (B) ANSP 204316, an unsexed specimen that died in a window collision on 6 November 2003, on Salmon Beach Road, Skagit County, Washington (prep. = MRH87); (C) ANSP 204318, a female that died in a window collision on 22 September 2015, in Twisp, Okanogan County, Washington (prep. = MRH91); and (D) ANSP 204519, a male that died in a window collision on 14 April 2015, in Anacortes, Skagit County, Washington (prep. = MRH134) (Matthew R. Halley)

Behavioural observations and nest description

The behavioural notes given by Nuttall (1840) in association with T. ustulatus, and his description of a nest purportedly made by that species, were not based on specimens but on Nuttall's vague recollections and (apparently) field notes from 1835. If anything, they cast more doubt on Nuttall's understanding of the species in question:

These vocalisations, at least the calls (‘wit ‘wit), seem to be a good match to C. ustulatus, but some calls of C. guttatus have been similarly described (‘quit quit’, Dellinger et al. 2012). The transliteration of the song (wit wit t'villia t'villia) is also vague and could apply also to C. guttatus. Wood Thrush Hylocichla mustelina (J. F. Gmelin, 1789), an eastern species, does not typically range west of the Rocky Mountains.

Nuttall's (1840) narrative was written as if he and Townsend distinguished T. ustulatus from Wilson's composite T. mustelinus in the field: ‘...we heard their notes...easily recognizable from the notes of that Atlantic species.' However, neither man recognised that there was a new species until years later. Remember that, in 1836, Nuttall did not think that either of the two specimens of ‘T. Wilsonii?' were a new species when he and Audubon examined Townsend's collection in Philadelphia, and Townsend wrote (after Nuttall's departure) on 11 April 1836: ‘The Wilson's Thrush (Turdus wilsonii)…breeds here [near Vancouver] & is consequently, for a part of the year in full song' (see Mearns & Mearns 2007: 359). Nuttall even sanctioned the sale of one of the specimens to Audubon after coming to the ‘hasty conclusion that it was no other than the well known Wilson's Thrush’ (Nuttall, 1840). Furthermore, the vocalisations that Nuttall apparently transcribed in his field journal (now lost) were not uttered by the same individuals that Townsend collected, nor is there evidence that they were heard by Nuttall on the same day Townsend collected the specimens. Thus, it seems that the extent of Nuttall's first-hand knowledge of the behaviour of these secretive birds was overstated by later authors who were not personally acquainted with him:

The nest described by Nuttall (1840) seems unlikely to have been made by C. guttatus or C. ustulatus, or indeed any Catharus species. Mud has often been mentioned as a structural material in historical literature of C. ustulatus, but has not been observed in C. ustulatus nests by modern researchers (Mack & Yong 2000). Published references to mud are probably a consequence of Nuttall's (1840) original composite description of T. ustulatus: ‘lined with dry leaves and some mud, externally of coarse grass.’ Heckscher et al. (2014), by dissecting a sample of nests of C. fuscescens, recently debunked similar claims about the ostensible use of mud in nest construction; the natural desiccation process of wet leaves stabilises nest structures in lieu of mud. There is no evidence that Nuttall (1840) collected or dissected the nest he described.

Green moss typically replaces grass as a structural material in C. ustulatus nests (Mack & Yong 2000), but Nuttall (1840), an expert botanist, made no mention of moss in his description. Furthermore, the location of the nest on the ‘prairies of Wahlamet' (= meadows in Willamette River valley, Oregon) is peculiar breeding habitat for C. ustulatus. Rathbun in Bent (1949) reported that in western Washington, ‘[C. ustulatus] nests from June 10 up to the middle of July…well within the forest, and a favorite location is among the low growth along the forest's edge, particularly in the proximity of water.’ In short, the nest described by Nuttall was probably not made by any Catharus species.

Nomenclatural consequences

The name ustulatus (Nuttall, 1840) has been in universal use in global ornithological literature for more than 150 years. However, the original description of T. ustulatus Nuttall, 1840, was likely based on a (syntype) specimen of Hermit Thrush C. guttatus (Pallas, 1811), a different species than that to which the name ustulatus has traditionally been applied. The identity of a second syntype, mentioned by Audubon (1839: 203–204) and cited by Nuttall (1840: 400) among the synonyms of T. ustulatus, is not identifiable (see above). The two extant specimens of C. ustulatus attributed to the Townsend collection (USNM 2040, ANSP 23644) have both been claimed as types, but this status can be ruled out on the basis of collection dates and sex data that conflict with the accounts of Nuttall (1840) and Audubon (1839). Furthermore, they do not match Nuttall's (1840) description of the colours of the dorsal plumage and tail.

Neotypification is reserved for circumstances in which ‘an author considers that a name-bearing type is necessary to define the nominal taxon objectively' (Art. 75.1). However, this is not a straightforward case because the only syntype for which an adequate description exists (in Nuttall 1840) is a closer match to C. guttatus than C. ustulatus, and a neotype must be ‘consistent with what is known of the former name-bearing type from the original description and from other sources’ (Art. 75.3.5). Accordingly, traditional nomenclature can be preserved and stabilised via neotypification only if the ICZN uses its plenary power to set aside Art. 75.3.5. A petition of this kind will soon be submitted to the Bulletin of Zoological Nomenclature for consideration by the Commission.

The material basis of T. swainsoni Cabanis in Tschudi, 1845

As a replacement name, T. swainsoni Cabanis in Tschudi, 1845, is typified by the original material in Swainson & Richardson's (1831) circumscription of Merula Wilsonii (i.e., not including the type material of the synonyms, see ICZN 1999, Art. 72.7). Their original material included several ‘northern specimens' of unspecified provenance, a male collected in May 1827 at Carlton House National Historic Site of Canada, Saskatchewan, and ‘no less than five others, killed last year in New Jersey, and now in our museum’ (Swainson & Richardson 1831: 183). Therefore, T. swainsoni Cabanis in Tschudi, 1845, was based on a series of syntypes (Art. 72.1.1) collected at geographically distant localities, and of unknown breeding origin because they were collected during the migratory period.

Swainson's collection was sold to the Univ. of Cambridge (UK) in 1840, but there is no trace of the specimens mentioned in his M. Wilsonii account (Swainson & Richardson 1831: 183, Parkinson 1988). Three specimens of C. swainsoni are extant in the collection, but none have collection dates (UMZC No 27/Tur/6/j/5–7) and two were collected by Ward in ‘Pennsylvania.’ Because no other extant material from Swainson's collection is known, the type material of T. swainsoni Cabanis in Tschudi, 1845, is presumed to be lost or destroyed. Therefore, the text description of the Carlton House specimen is the only available evidence for determination of the identity of T. swainsoni:

The above description is insufficient to distinguish between C. swainsoni (Cabanis in Tschudi, 1845) and C. minimus aliciae (Baird et al., 1858), which both occur during the spring migration in Saskatchewan. The latter species was not yet known when Swainson & Richardson (1831) made their description, nor when Cabanis (in Tschudi, 1845) published the replacement name T. swainsoni. Morphometric values given by Swainson & Richardson (1831) are insufficient to distinguish between these two closely related taxa. The coloration of the dorsal plumage of C. swainsoni and C. m. aliciae is practically identical and approximately one-quarter of C. m. aliciae males have ‘medium buff' on the throat (Ouellet 1993) that may extend onto the cheeks and lores like C. swainsoni (e.g., ANSP 203886, 204425). The bird described by Swainson & Richardson (1831) had ‘pale yellowish brown' lores (my italics), which does not exclude C. m. aliciae from consideration. Coues (1878: 36), who distinguished T. aliciae from T. swainsoni on the basis of ‘the distinct yellowish orbital ring and lores [my italics] of swainsoni not being seen’, conceded that these characters are ‘faintly indicated' in some specimens of C. m. aliciae. No mention of the eye-ring was made in Swainson and Richardson's (1831) description. Furthermore, Richardson's remark that the eggs of M. Wilsonii are ‘without spots’ matches C. m. aliciae but not C. swainsoni, adding further uncertainty (Bent 1949).

Neotypification of T. swainsoni Cabanis in Tschudi, 1845

The name T. swainsoni Cabanis in Tschudi, 1845, has been in universal use for the eastern (inland) taxon for more than 150 years. However, it is not unambiguously identifiable because none of its syntypes are extant and the attributes of the specimens described by Swainson & Richardson (1831), to which Cabanis (in Tschudi 1845) applied the replacement name T. swainsoni, are shared by more than one species.

To fix the taxonomic identity of Merula Wilsonii Swainson & Richardson, 1831 (excluding synonyms), and its replacement names including T. swainsoni Cabanis in Tschudi, 1845, an adult male (ANSP 207077) in the collection of the Academy of Natural Sciences of Drexel University, Philadelphia, PA, is hereby designated as its neotype (Fig. 9). This action stabilises traditional nomenclature and prevents destabilising confusion arising from alternative identifications. It fulfills the requirements for neotype designation in the Code (ICZN 1999) by clarifying the taxonomic application (status) of the name, as explained above (Art. 75.3.1), describing, illustrating and referencing the defining characters of C. swainsoni and its neotype (Art. 75.3.2), providing data sufficient to ensure recognition of the specimen designated (Art. 75.3.3), providing grounds for believing that all original type material has been lost and is untraceable (Art. 75.3.4), showing that traits of the neotype are included in the original description (Art. 75.3.5), choosing a neotype collected in the Mid-Atlantic region of North America, where some of Swainson & Richardson's (1831) syntypes originated (Art. 75.3.6), and recording that the neotype is preserved as the property of a recognised scientific institution (Art. 75.3.7). The choice of a specimen from its breeding grounds provides more stability than selecting a migrant individual with an unknown breeding locality.

ANSP 207077 is an adult male collected by M. R. Halley on 17 July 2019 on the west branch of Tionesta Creek, Allegheny National Forest, Warren County, Pennsylvania (41^°69′03.79″N, 79^°23′98.00″W, 550 m elevation). The bird was on its breeding territory near Heart's Content, an old-growth stand of eastern hemlock Tsuga canadensis and eastern white pine Pinus strobus. For more detail concerning the vegetative history of the area see Lutz (1930) and Rooney & Dress (1996). An audio recording was made of the singing bird with a Sennheiser ME66/K6 condenser microphone and Sony Zoom H1 recorder (.wav format, 24 bit, 96 kHz). Speaker playback of the recording was used to lure the bird into a mist-net. A compressed audio file (.mp3) was uploaded to xeno-canto.org (XC 489007) and an uncompressed file (.wav) was deposited in the Macaulay Library of Natural Sounds (Cornell University, Ithaca, NY) (ML 170463711, eBird checklist S58570739).

Figure 9.

ANSP 207077, the neotype of M. Wilsonii Swainson & Richardson, 1831, and its replacement names including T. swainsoni Cabanis in Tschudi, 1845; see text for detail of the specimen's provenance (Matthew R. Halley)

Approximately 50 µL of blood was drawn via brachial venipuncture into a microhematocrit capillary tube. Fresh blood was applied to a FTA card, and smeared onto a glass slide which was immediately fixed in pure methanol. The bird was euthanised in the field via cardiac compression, then transported on dry ice to ANSP, where it was prepared as a study skin and spread wing (Fig. 9, prep. = MRH214). The wingspan of the fresh (pliable) specimen measured 293 mm before removing the skin. An immature (unscleratised) feather louse with sternal asters (Myrsidea sp., identified by J. Gausas) was removed from ANSP 207077 and preserved in 95% EtOH. Samples of the heart, liver and muscle tissue of ANSP 207077 were frozen (-80° F) and archived (ANSP tissue = 35982). The syrinx was excised and initially preserved in 95% EtOH, then transferred to 10% neutral buffer formalin. Prior to preparation, the bird weighed 29.8 g with a stomach full of black insect parts and some seeds. It had enlarged, cream-coloured testes (10 × 6 and 9 × 6 mm) and enlarged seminal vesicles. No fat or moult was noted. There was no bursa and the skull was 100% pneumatised.

Diagnosis .—C. swainsoni is distinguished from other Catharus species by the combination of a buffy eye-ring, which is bold and spectacle-like, and uniform brownish-olive dorsal plumage and tail. In contrast to the similar C. m. aliciae (Baird et al., 1858), which also has Brownish Olive dorsal plumage and tail, the eye-ring of C. swainsoni is ‘full and distinct,' the breast spots are ‘larger and less distinct' and there is a ‘lack of emargination on p6’ (Pyle 1997: 397).

Through neotypification, the name C. swainsoni (Cabanis in Tschudi, 1845) is now restricted to the inland species to which the names C. u. swainsoni and C. swainsoni have been formerly applied (e.g., Ruegg 2007, del Hoyo & Collar 2016). For clarity of reference, the synonyms, nomenclatural combinations and principal citations of C. swainsoni (Cabanis in Tschudi, 1845), C. u. ustulatus (Nuttall, 1840), C. u. oedicus (Oberholser, 1899) and C. guttatus (Pallas, 1811) are provided in the Appendix.

English common names

Molecular phylogenetic studies have unanimously demonstrated that the resident (nonmigratory) Catharus species, which have been traditionally called ‘nightingale-thrushes,' do not form a monophyletic group (Outlaw et al. 2003, Klicka et al. 2005, Winker & Pruett 2006, Voelker et al. 2013, Everson et al. 2019). Therefore, the common name ‘nightingale-thrush' is appropriately applied to all species in Catharus and continued use of ‘thrush’ for the migratory species alone perpetuates historical misconceptions about phylogenetic relationships.

Recently, the American Ornithological Society North American Classification Committee addressed a similar problem in hummingbirds by voting to ‘standardize the English group name of all species of Lampornis to Mountain-gem and reduce the prevalence of the English group name ‘hummingbird' across the family, thereby strengthening the association of these species with other species of Lampornis and emphasizing their distinctness relative to other species in the Trochilidae' (Chesser et al. 2019: 7). Following that example, I propose that the common names of the migratory species of Catharus be revised to ‘strengthen the association' of these species with the other (non-migratory) species in the genus. This action will highlight the distinctness of Catharus relative to other genera in the Turdidae and ‘reduce the prevalence' of the vague English group name ‘thrush’ across the family. Proposed names are listed in Table 2 and discussed below.

TABLE 2

Scientific and English common names of species in the genus Catharus, known collectively as nightingale-thrushes. Current names follow Clement (2000) with updates by Halley et al. (2017). The ordering of species according to phylogenetic clades (A–C) follows Voelker et al. (2013) and Everson et al. (2019). Novel proposed names are shown in bold.

The common names Boreal Nightingale-Thrush (C. swainsoni) and Pacific Nightingale-Thrush (C. ustulatus) are ecologically and geographically appropriate and will reduce confusion with past uses of ‘Swainson's Thrush’, which was formerly applied to both species. Use of the adjective ‘Russet-backed' for C. ustulatus is problematic because the similarly named Russet Nightingale-Thrush C. occidentalis occurs sympatrically with C. ustulatus in southern Mexico for most of the year. The fact that two other Catharus species have widespread breeding ranges that include boreal forest (C. guttatus, C. minimus) should not raise objection to the use of ‘Boreal Nightingale-Thrush’ for C. swainsoni alone; consider the similar case of Boreal Chickadee Poecile hudsonicus and Black-capped Chickadee Poecile atricapillus, which breed sympatrically in boreal habitats.

In phylogenetic analyses, C. guttatus has been reconstructed as the sister species of C. occidentalis, and this pair is more closely related to Ruddy-capped Nightingale-Thrush C. frantzii and Black-billed Nightingale-Thrush C. gracilirostris (also sister species) than to any of the long-distance migratory species (Voelker et al. 2013, Everson et al. 2019). The common name Hermit Nightingale-Thrush C. guttatus (Pallas) will strengthen the association of these closely related species (Table 2). For the same reasons, I propose the common names Veery Nightingale-Thrush C. fuscescens (Stephens), Grey-cheeked Nightingale-Thrush C. minimus (Lafresnaye) and Bicknell's Nightingale-Thrush C. bicknelli (Ridgway).