The pioneering natural history studies of the Spanish military engineer Félix de Azara (1742–1821) in Paraguay and the La Plata Basin represented one of the first serious attempts to document the fauna of the southern cone of South America (Beddall 1983). Azara produced a remarkably detailed three-volume descriptive work on the region entitled Apuntamientos para la historia natural de los páxaros del Paraguay y Río de la Plata (Azara 1802–05), introducing many of its birds to a European audience for the first time. Azara had no formal biological training, but grouped birds into ‘families’ based on his own observations of similarities in structure, and his keen eye for detail enabled him to correctly identify taxonomic relationships with surprising success (though not of course without some mistakes). He did not apply scientific names to his descriptions, instead giving his species vernacular names alone. The unpublished Spanish original was translated into French by Charles-Nicolas-Sigisbert Sonnini de Manoncourt (Azara 1809), and subsequently Louis Jean-Pierre Vieillot attached scientific names to many of these descriptions. More than half of the 448 species that Azara described proved to be new to science. A detailed chronology of his travels, life and work was provided by Contreras (2010).

However, to date not all of Azara's descriptions have been conclusively associated with known species, and a series of authors have attempted to re-identify these descriptions and apply them to known taxa (Sonnini in Azara 1809, Hartlaub 1847, Berlepsch 1887, Bertoni 1901, Laubmann 1939, Pereyra 1945, Smith 2017, 2018a,b,c,d, in press, Smith et al. 2018). A brief paragraph of text dedicated to no. 243 ‘Trepador pico corto' is one of the descriptions that has never been satisfactorily associated with any known species. Azara (1805) used his text to distinguish this bird from his no. 242 ‘Trepador común’ which refers to Narrow-billed Woodcreeper Lepidocolaptes angustirostris (Fig. 1). The original description is reproduced below with original punctuation and my own translation follows it, including a conversion of measurements into modern units (unit conversion: 1 inch = 25.4 mm; 1 line = 2.21 mm).

‘No sé sino que le compré muerto en el Paraguay. Longitud 7 ½ pulgadas: cola 2 7/12: braza 10 5/6. Anteriormente había comprado otro idéntico que era cerca de una pulgada menor. Todas las tintas y su distribución son lo mismo que en el precedente, á quien tuve á la vista para el cotejo; sin mas diferencia que ser las blanquizcas no tan claras, y todas las demás mas vivas y fuertes. Las únicas diferencias que encontré en el resto se reducen, á que el pico del anterior es 5 líneas mas largo, aunque del mismo grueso, material y forma. La boca de aquel era blanquizca, y la del presente amarilla. La lengua del precedente poco más angosta y más aguda, y la cola algo menos vigorosa y cóncava. Estas diferencias me han parecido muy suficientes para creerlos de diversa especie; pues en esta familia, como en todas las abundantes en caractéres comunes, tiene mas peso qualquiera diferencia, que muchas identidades; y la que hay en la longitud del pico es aquí muy grande'.

Figure 1.

Narrow-billed Woodcreeper Lepidocolaptes angustirostris, Teniente Enciso National Park, Boquerón department, Paraguay, July 2006 (Paul Smith)

Figure 2.

Lesser Woodcreeper Xiphorhynchus fuscus, Hotel El Tirol, Itapúa department, Paraguay, June 2005 (Paul Smith)

‘I know nothing more than I bought it dead in Paraguay. Length 7½ inches: tail 2 7/12: wingspan 10 5/6. Previously I had bought another identical specimen that was almost an inch smaller. All of the colours and their distribution are the same as those of the previous species, which I had available for comparison; with no other differences than the whitish areas were not so clean, and the rest of the plumage was brighter and more strongly coloured. The only other differences I found can be summarised as the bill of the previous species being 5 lines longer, although of the same width, material and shape. The mouth lining of that individual was whitish; that of the present specimen yellow. The tongue of the previous a little narrower and sharper, the tail somewhat less vigorous and concave. These differences seem to me sufficient to consider it a distinct species, you see in this family, like all of those with many characters in common, any difference is of greater importance than many similarities; and the difference in the length of the bill is very great.'

TABLE 1

Comparative measurements between Azara's nos. 242 and 243, and Paraguayan individuals of Narrow-billed Woodcreeper Lepidocolaptes angustirostris (trapped in Parque Nacional Teniente Enciso, dpto. Boquerón) and Lesser Woodcreeper Xiphorhynchus fuscus (Hotel El Tirol and Estancia Nueva Gambach, dpto. Itapúa). Comparative measurements of another confusion species, Scalloped Woodcreeper Lepidocolaptes falcinellus are based on Brazilian specimens from the literature. Measurements (in mm) were taken from live birds by PS, or are referenced to source. Bill length was measured along the culmen from the bill tip to the feathers by both PS and Azara, with Silva & Straube (1996) measuring bill from the tip to the anterior edge of the nares (resulting in a slightly shorter comparative measurement). Bill depth was measured at the anterior edge of the nares by PS, and at the bare area adjacent to the feathers of the bill base by Azara. Tail length was measured along the underside of the tail from the base to the tip of the longest feathers by all sources (described by Azara as ‘from the coccyx to the tip of the tail').

Ever since Lichtenstein (1818) tentatively associated the ‘Trepador pico corto’ with Straight-billed Woodcreeper Dendroplex picus (J. F. Gmelin, 1788), a species distributed well north of Paraguay, from Panama south to Amazonian Bolivia and the northern Pantanal of Brazil (Marantz et al. 2019a), there has been little effort to improve on that identification. In fact, it was repeated by Hartlaub (1847), Sclater (1890), Laubmann (1939) and Pereyra (1945) despite there being no records of D. picus from Paraguay. The only doubting voice had been Sonnini's (Azara 1809) premature dismissal of the validity of the description with the following statement:

‘Je ne sais si les légères différences que M. d'Azara a fait remarquer entre cet oiseau et le précédent, suffisent pour constituer deux espèces distinctes; et mon doute est d'autant plus fondé, que des deux seuls pics - grimpereaux à bec court, observés par ce voyageur, l'un avait un pouce de longueur totale de moins que l'autre; d'où l'on peut conclue que les dimensions de ces oiseaux sont sujettes à varier. Il ne serait donc pas étonnant que leurs becs ne fussent pas de la même grandeur. Quant aux teintes plus ou moins fortes des couleurs qui, du reste, ont la même distribution, l'on sait qu'un caractère aussi faible n'a jamais indiqué une distinction d'espèces. (S.)'

‘I do not know whether the slight differences which Monsieur d'Azara has remarked upon between this bird and the preceding, suffice to constitute two distinct species; and my doubt is all the more founded on the fact that of the only two Trepador pico cortos observed by this traveller, one had a total length of an inch less than the other, from which it can be concluded that the dimensions of these birds are subject to variation. It would not be surprising that their beaks were not of the same size. As for the more or less strong hues of colours which, moreover, have the same distribution, we know that such a feeble character has never indicated a distinction of species.'

Sonnini's misplaced certainty was repeated by Vieillot (1818), who took the unusual step of electing not to give the description a formal scientific name. However Sonnini erred, and Azara was correct that his description does indeed represent a distinct species. No. 243 can be conclusively identified as Lesser Woodcreeper Xiphorhynchus fuscus (Fig. 2), based on the diagnostic characters highlighted by Azara (1805) and the comparative measurements he provided (Table 1).

Lesser Woodcreeper is a common species in the Paraguayan Atlantic Forest region. It is distinguished from Narrow-billed Woodcreeper Lepidocolaptes angustirostris by its shorter bill, buffy tinge to those parts of the plumage that are white in L. angustirostris, and the richer coloration of the upperparts. One other potential confusion species also occurs in Paraguay's forests, Scalloped Woodcreeper Lepidocolaptes falcinellus. However, that species is characterised by the pure white throat and base colour to the underparts, and possesses body and bill measurements that closely resemble the congeneric L. angustirostris (Table 1).