The next few years look like they will be especially interesting for antpitta (Grallariidae) enthusiasts. Most major checklists have been moderately stable at near 50 species of antpitta for some time (SACC currently recognises 51). However, the next decade may see this number jump closer to 70 species with forthcoming taxonomic work, much of it dependent on vocal analyses. A multinational team headed by the indefatigable Mort Isler is currently undertaking a full revision of the Rufous Antpitta group, which will probably recognise about half-a-dozen species from within the current one. Research on several other taxa will likely elucidate other long-suspected splits, with Grallaria gigantea/G. excelsa, G. andicolus, G. nuchalis, G. quitensis, Myrmothera campanisona, and several Grallaricula species being particularly fertile areas for study. (Plus there must still be a couple of undiscovered species lurking out there!).
Spotted Antpitta Hylopezus macularius was always a great candidate for such analysis, occurring over a wide Amazonian range with populations separated by many of the regions great rivers. A new study by a Brazilian team (Carneiro et al. 2012) has teased apart the systematics of this group, with some fascinating conclusions (and still plenty of room for work by XC recordists!).
It has long been known among birders that the population in south-central Amazonia - encountered by most observers near Alta Floresta, Mato Grosso, Brazil - has an obviously different song compared to other populations of Spotted Antpitta. Unfortunately this difference was not consistent across the subspecies to which these birds were thought to belong, H. m. paraensis, confusing recognition. Compare these two songs, currently on XC as paraensis:
Carneiro et al. found that songs of the population represented by the first of these recordings average fewer notes, only four or (more often) five, and less often six notes as in the remaining populations of Spotted Antpitta, while the pace of songs (number of notes/duration) was shorter than in any other population. The interval between the second and third notes was longer than in other populations and also longer than those between the other notes of the song. Calls of this population also differed most conspicuously from those of other populations by the smaller number of notes (five or six) and their shorter duration (unfortunately XC has too few recordings of Spotted Antpitta calls to demonstrate this).
Genetic analysis of available material for all populations of Spotted Antpitta by Carneiro et al. found not just two but four diagnosable populations, two on each side of the Amazon. These results were then combined with morphological and vocal data, which produced some supporting evidence for four groupings within the current Spotted Antpitta, which did not fit with the current subspecies taxonomy.
Of course to fully understand the details of this study it is best to consult the original paper. In summary, Carneiro et al. conclude that the four genetically distinct populations probably represent biological species, and name these as:
Hylopezus macularius Spotted Antpitta* - north of the Amazon, in Brazil from Amapa west to the Branco and Negro rivers, and north to easternmost Venezuela, including all of the Guianas. (*See final paragraph for a comment on this English name.)
H. paraensis Snethlage’s Antpitta - south of the Amazon in Brazil from the Xingu River eastward through Pará state to westernmost Maranhão.
H. dilutus Zimmer’s Antpitta - north of the Amazon from the western banks of the Negro and Branco rivers in the Brazilian state of Amazonas through southern Venezuela (Amazonas), southern Colombia (Amazonas), easternmost Ecuador, and north-east Peru west of the Ucayali River.
H. whittakeri Alta Floresta Antpitta – between the Madeira and Xingu rivers in Brazilian south-central Amazonia.
Although the genetic distance between the two groups that formerly comprised the subspecies paraensis was the smallest of that between any two of the four new taxa, its vocal differences were by far the greatest. Carneiro et al. concluded that this population (with the obviously different song above), is a new and distinct species which they name Hylopezus whittakeri, after well-known Manaus-based birder Andy Whittaker who drew attention to the distinctness of this form.
The remaining three genetically distinct populations are all quite similar vocally. There are some subtle differences in note structure between the taxa, and dilutus (into which the former subspecies diversa is synonomised) averages shorter song phrases, typically about 2.0s, rather than 2.3-2.6s in the other taxa. Compare these songs of dilutus, macularius, and paraensis:
Frankly, some conclusions of this study would be more satisfying if the vocal, morphological, and genetic data all pointed in the same direction and separated out into four clearly defined groups, but biology is rarely so neat and tidy. Indeed such situations are not unusual among the antpittas: some long-recognized species are extremely similar vocally and yet are morphologically obviously distinct (e.g., Grallaria dignissima and G. eludens) while others are very similar morphologically but completely distinct vocally (e.g., many of the Rufous Antpitta taxa).
The westernmost taxon dilutus has the most obvious morphological differences from the other taxa, with significantly shorter tarsi, greater bill depth and width, obvious brownish rather than greenish upperparts with little or no pale shaft streaking, and a darker, denser band of breast spotting. Morphologically only minor differences exist between the other three taxa, although macularius averages darker buff flanks than all other taxa.
Despite its morphological distinctness, and some suggestive vocal differences, sample sizes for dilutus were very small, especially of recordings (only four), and Carneiro et al. have wisely declined to recommend that macularius and dilutus be considered separate species at this time. Further vocal and morphological data are needed to confirm the genetic evidence that these two groups are separate species.
This study highlights some important gaps that XC recordists could help fill. There are too few recordings to really be confident exactly what the song of the dilutus taxon sounds like, and there is apparently no recording of its call whatsoever. Although it is not going to be the highest priority for those visiting the quite heavily birded area of Iquitos in north-east Peru, this may be the easiest region to see “Zimmer’s Antpitta”, and more (natural) recordings would be invaluable. This same taxon occurs in Amazonas in southernmost Venezuela, and no recordings seem to exist of this population (in XC or anywhere else). Genetically and morphologically it appears to be dilutus, but its voice is unknown. It is also unknown how connected the dilutus populations of Venezuela and Peru are, so anyone visiting south-east Colombia should really be listening for this species (one recording purporting to be Spotted Antpitta from Colombia sounds like Myrmothera campanisoma). Finally, for all of these “Spotted Antpitta” taxa, XC is desperately short of recordings of calls (indeed this is true for most antpittas on XC).
A brief comment on one of the English names proposed by Carneiro et al. If separated from dilutus, the new monotypic taxon macularius would be confined to the Guianan Shield, for which the authors suggest the name Spotted Antpitta. Although this English name matches its scientific name, using the old group name for one of the newly split taxa always invites confusion (e.g., does “Spotted Antpitta” mean macularius alone, macularius + dilutus, or the old species group as a whole?). The name Guianan Antpitta fits its distribution very well, and would avoid this problem. (Donegan  suggested “Guianan Antpitta” for Grallaricula kukenamensis if that taxon is split from G. nana, but the name Roraiman Antpitta would be much more suitable for that species given its very restricted tepui distribution.)
Many thanks to Alex Aleixo and Mort Isler for correspondence that assisted with this article.
Carneiro, L.S., L.P. Gonzaga, P.S. Rêgo, I. Sampaio, H. Schneider, and A. Aleixo. 2012. Systematic revision of the Spotted Antpitta (Grallariidae: Hylopezus macularius), with description of a cryptic new species from Brazilian Amazonia. Auk 129: 338-351.
Donegan, T. 2008. Geographical variation in Slate- crowned Antpitta Grallaricula nana, with two new subspecies, from Colombia and Venezuela. Bull. B. O. C. 128: 150-178.