Diving petrels (genus Pelecanoides) comprise five species of small Southern Ocean Procellariiformes, which show limited morphological differentiation, thus complicating their identification (Fischer et al. 2018). The circumpolar and widespread Common Diving Petrel P. urinatrix is considered to number six subspecies: P. u. urinatrix (J. F. Gmelin, 1789); P. u. berard (Gaimard, 1823); P. u. exsul Salvin, 1896; P. u. dacunhae Nicoll, 1906; P. u. copperingi Mathews, 1912; and P. u. chathamensis Murphy & Harper, 1916 (Marchant & Higgins 1990, Dickinson & Remsen 2013).

The original description of P. u. exsul by Salvin (1896: 438) in the Catalogue of the birds in the British Museum diagnosed the taxon as a species, primarily based on the greyness of the throat, flank and underwing feathers. Specifically, he stated: ‘Adult. Similar to P. urinatrix, but the feathers of the sides and middle of the throat with a distinct subterminal grey bar; flanks mottled with grey, each feather with a grey shaft; under wing-coverts also grey, with white edges and dark shafts. Sexes alike. Hab. Southern Indian Ocean, from the Crozette Islands to Kerguelen Land’. This description was followed by a list of the 23 specimens that constituted the type series. However, the original description contains ambiguities: the type series consists of specimens from several widespread locations and the morphological description is too vague to define any diagnostic characters of the taxon.

Salvin's (1896) descriptions of the various Pelecanoides species did not note any of the diagnostic bill-shape characters of P. urinatrix, including the posteriorly sited nostril septa later diagnosed by Murphy & Harper (1921). In addition, Salvin's description for P. u. exsul also failed to mention the relatively short wing compared to P. u. urinatrix (see Marchant & Higgins 1990; means of sexed birds from breeding colonies 119.6–123.9 mm for P. u. exsul, and 127.0–131.8 mm for P. u. urinatrix).

Murphy & Harper (1921: 544) fixed the type locality for P. u. exsul as the Kerguelen Islands and published an updated diagnosis for the taxon. They primarily noted minor differences between P. u. exsul and other subspecies of P. urinatrix in bill shape (i.e., more converging bill sides of P. u. exsul) and a greater amount of grey on the lower throat of P. u. exsul.

Warren (1966: 94) identified 15 of the 23 syntypes of P. u. exsul listed by Salvin, and provided details of an adult male from the Kerguelen Islands (Natural History Museum, Tring [NHMUK 1880.11.18.656]). She noted that the ‘locality’ for the taxon was originally defined as ‘southern Indian Ocean’ but had been ‘restricted to Kerguelen Island’ by Murphy & Harper (1921). NHMUK 1880.11.18.656 was subsequently placed in one of the type collection cabinets at Tring, and labelled ‘TYPE’. However, as it was not formally designated as a lectotype (Warren specifically referred to it as a syntype and mentioned ‘fourteen other syntypes’), it maintained the same nomenclatorial status as all of the other specimens in the type series of P. u. exsul (Arts. 72.4.7 and 74.5; ICZN 1999).

Both Salvin (1896) and Murphy & Harper (1921) considered P. exsul to be a species, separate from P. urinatrix. Today P. u. exsul is commonly recognised subspecifically, but its distinctiveness has been questioned (e.g., see Clancey 1981, Norman & Brown 1987). Marchant & Higgins (1990) concluded that the supposedly diagnostic features of P. u. exsul noted by Salvin (1896) and Murphy & Harper (1921) occurred in some individuals of other subspecies of P. urinatrix, which leaves no clear morphologically diagnosable features for P. u. exsul. However, DNA work (using the mitochondrial cytochrome b gene) provided support for the distinctiveness of P. u. exsul (Grosser et al. 2021). Yet, this research did not clearly support other commonly recognised subspecies of P. urinatrix. Hence, the taxonomy of P. urinatrix sensu lato remains unsettled and is in need of re-examination.

To clarify the identity of P. u. exsul and help resolve ongoing confusion concerning the validity of the various subspecies of P. urinatrix, we relocated and re-examined the syntypes of Pelecanoides u. exsul at NHMUK. Although Salvin (1896) did not provide registration numbers for any of the specimens that he listed, he did provide sufficient information (some collection data and a unique letter for each specimen) to identify almost all of the syntype series. Salvin's letters between ‘a’ and ‘w’ were located on labels of 15/23 of these specimens. Seven other specimens were identified using their collection data (Table 1). Additionally, an unattached, isolated label at NHMUK was subsequently linked to a further syntype that was received by the South Australian Museum, Adelaide (SAMA) in 1982 on exchange from NHMUK (P. Horton in litt. 2019). All of the specimens were measured to the nearest 0.1 mm using the methods described in Fischer et al. (2018): wing length; inner (RT1) and outer (RT6) tail feather length; culmen length; bill width at base; bill depth at base; arch length; head length; and tarsometatarsus length. In addition, we scored the position of the nostril septa (Fig. 1, see Fischer et al. 2018 and supporting materials) and the angle and shape of the mandibles (viewed dorsally and ventrally). We provide details of these specimens in Tables 1–3. Two of the 23 syntypes on Salvin’s list could not be identified with a high level of certainty.

Our investigation (see Table 3, Figs. 1–3) indicates that the syntype series of P. u. exsul includes three different taxa: P. u. urinatrix (J. F. Gmelin, 1789), P. u. exsul Salvin, 1896, and South Georgia Diving Petrel P. georgicus Murphy & Harper, 1916. A syntype series consisting of more than one taxon can cause taxonomic confusion, therefore to stabilise the name Pelecanoides urinatrix exsul Salvin, 1896, here we designate NHMUK 1876.4.26.13 (female, collected ‘Observatory Bay, Royal Sound’, ‘Kerguelen’s Land’ [= Baie de l’Observatoire, La Grande Terre, Kerguelen Islands] by A. E. Eaton, on 14 October 1874) as the lectotype of this taxon (Figs. 1A, 2) in accordance with the amended Art. 74.7.3 (ICZN 1999). No previous lectotypification has been made for this taxon.

We chose NHMUK 1876.4.26.13 as the lectotype because (a) it is from the Kerguelen archipelago, to which the type locality was restricted by Murphy & Harper (1921), and (b) it displays morphological features usually associated with P. u. exsul, i.e. posteriorly sited nostril septa, relatively short, converging mandible sides, and comparatively short wings (<125 mm). Selecting this lectotype aligns with Recommendation 74A of the Code (ICZN 1999). Whilst ten syntypes met the same basic selection criteria (Table 3), NHMUK 1876.4.26.13 is the only one that also has a collection date, a collector and its sex recorded, as well as an undamaged bill. This designation results in all of the other syntypes listed in Tables 1–3 becoming paralectotypes of P. u. exsul, irrespective as to their taxon they are recognised as.

TABLE 1

List of Pelecanoides urinatrix exsul Salvin, 1896, syntypes, including their NHMUK and SAMA registration numbers and other information from their specimen labels. The ‘Salvin letter’ is in bold and italics where it appears on a specimen’s label. Position of nostril septa from base / posterior end (posterior = 0%, anterior = 100%). Sex: M = male; F = female. ? = unclear. - = unknown. The designated lectotype is highlighted.

Continued

TABLE 2

Measurements of the Pelecanoides urinatrix exsul Salvin, 1896, type series. L = length; *dried open. Some comparative measurements could not be taken from the skeletal specimens due to their state of preservation. All measurements in mm, taken by A. J. D. Tennyson (or P. Horton for SAMA B36415). The designated lectotype is highlighted.

TABLE 3

Current taxon identity of specimens in the Pelecanoides urinatrix exsul Salvin, 1896, type series, based on this study. Mandible shape: SB = short and bowed, LP = long and parallel-sided. Wing length short: <125 mm. The designated lectotype is highlighted.

Figure 1.

Dorsal views of bills of specimens from the type series of Pelecanoides u. exsul, showing positions of the nostril septa. (A) Pelecanoides u. exsul, NHMUK 1876.4.26.13 (lectotype), showing posteriorly (30% score, see arrow) sited nostril septa; (B) South Georgia Diving Petrel P. georgicus juvenile, NHMUK 1880.11.18.661 (paralectotype of P. u. exsul), showing centrally sited (50% score, see arrow) nostril septa (A. J. D. Tennyson, © Trustees of the Natural History Museum, London)

Figure 2.

Lateral (A) and ventral (B) views of the lectotype of Pelecanoides u. exsul, NHMUK 1876.4.26.13 (A. J. D. Tennyson, © Trustees of the Natural History Museum, London)

Figure 3.

Lateral views of paralectotypes of Pelecanoides u. exsul. (A) South Georgia Diving Petrel P. georgicus juvenile, NHMUK 1880.11.18.661; (B) Pelecanoides u. urinatrix, NHMUK 1875.7.2.25 (A. J. D. Tennyson, © Trustees of the Natural History Museum, London)

These designations fix the identity of P. u. exsul and maintain stability of the names most commonly used for Pelecanoides taxa globally. They therefore fulfil a primary objective of the International Commission on Zoological Nomenclature to promote stability of scientific names (ICZN 1999).