Bioacoustics of Machaeropterus eckelberryi

Remarks. DFL’s observations of Machaeropterus eckelberryi suggest that its behavior is very similar to that of M. r. striolatus . Males and females of M. eckelberryi both tend to remain in the mid-story and canopy of shorterstature ( 5–20m canopy height) woodland, particularly around trees in the family Melastomaceae, the fruits of which are an important part of their diet (pers. obs.). A male’s persistent advertising song is given from one of several perches on a small territory in a dispersed or exploded lek ( Prum 1994 ; Kirwan & Green 2012), just below the canopy. The small size and relatively inactive behavior of these manakins can make them difficult to spot, even when their general position is revealed by persistent vocalization. Both sexes can also be observed as they forage at fruiting trees, from which they pluck small, berry-sized fruits while performing brief hovering maneuvers typical of most small piprids. Presumably, these manakins also eat some arthropods to supplement their largely frugivorous diet ( Snow 2004 ). We have no information on nesting habits of M. eckelberryi , but specimens collected in early July and early August appeared to be entering breeding condition (males with testes over 4x 2mm , females with ova over 1mm diameter), suggesting that breeding begins near the end of the dry season (August–October). Gonad data from female specimens which we suspect to be M. eckelberryi (from NE of Jirillo, San Martín dept.) from November did not indicate breeding condition. Within its range, M. eckelberryi does not appear to come into contact with any other member of the M. regulus group, although there is a population of M. r. striolatus only about 100 km to the northeast of the Mayo valley localities, where specimens (e.g., LSUMZ 173121) document M. r. striolatus in white-sand forest at Jeberos, Loreto dept., at 165m elevation ( Fig. 1 ). Machaeopterus r. striolatus is typically a species of lowland terra firme forest, where there are fruiting melastomes (pers. obs.), however, it reaches elevations of about 1100m locally in southern Ecuador ( Ridgely & Greenfield 2001 ). We suspect that the geologic formations of the Cordillera Azul/ Escalera and the Mayo valley act as a barrier separating M. eckelberryi from the nearby, lower-lying habitat of M. r. striolatus . Available records of M. r. aureopectus indicate that it is largely a species of ridges and higher elevations—the holotype of the taxon is from about 550m , and the two FMNH specimens are from 900m . Kevin Zimmer (in litt., Feb. 2016 ) noted that he had encountered M. r. aureopectus west of Santa Elena , Bolivar , Venezuela , at about 940m elevation. Hilty (2002) noted that Striped Manakin (referring to aureopectus , obscuriostriatus , and zulianus ) occurs in Venezuela at elevations from 100–1200m , with most records above 300m . In short-stature woodlands of the Mayo Valley, M. eckelberryi does occur in syntopy with the slightly smaller, congeneric Fiery-capped Manakin M. pyrocephalus , although the latter tends to be found in disturbed habitats and flatter terrain (DFL, pers. obs.). To date, fieldwork in the Cordillera Azul has only detected M. pyrocephalus at low elevations (below 400m ) on the Río Huallaga side, below the elevations preferred by M. eckelberryi there ( Schulenberg et al. 2001 ; Merkord et al. 2009 ). Despite the fairly limited distribution of M. eckelberryi , its presence within one of Peru’s largest national parks (Parque Nacional Cordillera Azul), and its preference for poor-soil environments unlikely to be converted to agriculture suggests that the taxon is probably not in any serious conservation danger. A review of satellite imagery of the region suggests that there has been minimal anthropogenic damage to the ridges that we suspect hold its preferred habitat on the eastern flanks of the cordilleras Escalera and Azul. Taxonomy within the Machaeropterus regulus complex. At present, there is some taxonomic turmoil regarding the Machaeropterus regulus complex, with some authorities considering it two species (e.g., Snow 2004 ; Ridgely & Tudor 2009 ; Gill & Donsker 2014), and others retaining all taxa as one species (e.g., Kirwan & Green 2012; Remsen et al. 2014). Our initial reluctance to describe M. eckelberryi , despite recognizing that it was likely a new taxon, was because of the lack of crucial information about the morphologically very similar M. r. aureopectus . Their similarity suggested a sister relationship to us, but convergence in plumage characters could not be ruled out without genetic analyses. Further, the presence of an isolated population of several “Guianan” or “Tepui” taxa in the Cordillera Azul and nearby San Martín region of Peru provided a pattern to which Machaeropterus could conceivably conform. These include Cnemotriccus fuscatus duidae Zimmer ; Cotinga cotinga (Linnaeus); Tachyphonus phoenicius Swainson ; Tangara cayana (Linnaeus) ; Tangara varia (Statius Müller) ; and Euphonia plumbea Du Bus de Gisignies. Unfortunately, M. r. aureopectus remains a poorly known and understudied taxon; even its distribution is poorly known, as exemplified by the fact that the first probable specimen (a female) of this taxon from Guyana was not published until 1998 ( Agro & Ridgely 1998 ). More information on the life history and voice, and additional specimens, including tissue samples, of M. r. aureopectus would be very useful for a more in-depth study of the taxonomic and systematics of the M. regulus complex. In lieu of genetic data, however, we use voice as a proxy to indicate genetic similarity, as differing vocalizations among most suboscine passerines have been shown to correlate strongly with genetic differentiation (e.g., Kirwan and Green 2011 :26). The strong distinction in note structure in the advertising songs between M. eckelberryi and the striolatus group has led us to the conclusion that M. eckelberryi is most appropriately considered a biological species apart from the rest of the striolatus group. In addition to the remarkable vocal differentiation of advertising songs of the striolatus group and nominate M. regulus ( Fig. 4 ) cited above, their differences are further augmented by the distinctive, attenuated outer two primaries of M. r. regulus ( Fig. 5 ). This character is unique within the M. regulus complex, and noteworthy in not having been mentioned in the literature previously. Taken together, these characters point to the presence of two biological species within the existing M. regulus ( sensu lato ), in addition to the new M. eckelberryi . Thus, we suggest a systematic reorganization to recognize a monotypic M. regulus (Eastern Striped Manakin), a polytypic M. striolatus (including M. s. antioquiae , M. s. aureopectus , M. s. obscurostriatus , and M. s. zulianus ; Western Striped Manakin), and a monotypic M. eckelberryi (Painted Manakin) .

Variation in the type series. We designate all specimens of M. eckelberryi that we examined (listed above) as paratypes, and all were compared alongside the holotype. Among adult males of M. eckelberryi , there is little plumage variation, but most are whiter-throated than the holotype, with only a few (e.g., LSUMZ 161894, 161899, MUSM 17726) approaching it in its dingy grayness. On some female M. eckelberryi (LSUMZ 85046, 161896, 161898, MUSM 17721), there is an indistinct whitish inner edge to rectrices (visible from underneath), but this is not apparent in all specimens (and is lacking in M. r. striolatus and the only M. r. aureopectus female available to us, FMNH 344154). Females lack the modified, thickened shafts on the inner secondaries and stiffened shafts of the rectrices. The plumage of immature males (skull 100% ossified in MUSM 22693; 99% ossified and bursa of Fabricius 4x 2 mm in LSUMZ 171009 ) is female-like overall, but there is already a suggestion of a pure yellow breast band, and LSUMZ 171009 has one crimson crown feather. Males in immature plumage also lack the modified inner secondaries of adult males. The feather modifications exhibited by adult male M. eckelberryi are shared by M. r. striolatus , M. r. zulianus , M. r. antioquiae , M. r. aureopectus , and M. r. regulus . By comparison, the holotype of M. r. obscurostriatus seems to have secondaries 5–8 modified. Furthermore, it is noteworthy that the outer two primaries of M. r. regulus are distally attenuated and slightly curved ( Fig. 5 ). Based on label data, irides tend to be chestnut or brick red on adult male M. eckelberryi , but dark brown on most females and immature males. Tarsi and toes vary from dark brown to pinkish-gray and have yellow soles. Specimen preparators described maxilla color as blackish, often with grayish-black tomia, and mandibles as pinkish-gray or gray. Morphometrics. DFL made standard measurements of the museum skins listed in the “specimens examined” section (above): culmen (measured from distal edge of nares to maxilla tip); bill depth (at nares); maxilla width (at nares); flat wing; primary extension (measured from tip of longest secondary to tip of longest primary); tail length (from insertion point to tip of longest rectrices); and tarsus length (measured from joint of tarsometatarsus to the underside of the hallux at its base). Bret Whitney took measurements (not including primary extension) of the larger series of M. r. regulus available at the Museo Zoologia da Universidade de Sao Paulo (MZUSP) to augment our sample size of that taxon. Whitney measured the following MZUSP specimens: MZUSP 33495, 33497, 91013, 91472, 91473 (females); 33494, 91011, 91474, 91475, 94423, 94425–94427 (males). The means and standard deviations of these measurements were calculated and are presented in Table 1 . We present a PCA of the measurements (minus those from MZUSP due to the missing primary extension measurement) in Fig. 3 to illustrate the overlap in morphospace among the various taxa in the M. regulus complex. In this PCA, we see no overlap in the plotting of M. eckelberryi and M. r. aureopectus , indicative of apparent morphological distinctiveness, particularly in primary extension and tail length, but note that sample size for M. r. aureopectus is very small. Vocalizations. Members of Machaeropterus are generally quiet and unobtrusive unless a male is giving an advertising song from a perch. This song can be vocally produced, as by M. eckelberryi , M. r. regulus , M. r. striolatus , M. r. aureopectus , M. r. antioquiae , and the Fiery-capped Manakin M. pyrocephalus (Sclater) , or mechanically produced using modified secondaries, as by the Club-winged Manakin M. deliciosus (Sclater) . In all members of the genus, the advertising song is short, fairly simple in structure, and strongly stereotyped. When a female is present, the singing male may become more active and perform a courtship display (e.g., as described for M. r. regulus in Sick 1993 : 500 ), but these displays have not been fully described for several members of Machaeropterus ( Bostwick 2000 ; Schulenberg et al. 2010 ; Kirwan & Green 2012), and we have not observed any such display by M. eckelberryi (although the thickened secondary shafts and stiffened rectrices suggest it must have a display involving mechanical sound production), so we will not consider the courtship display further. The advertising song of M. eckelberryi is noticeable and persistent, and often is the best means of detecting the bird; it may be delivered as rapidly as 30 songs/min, at shorter intervals than is typical of any other taxon in the M. regulus complex on average. It is a simple, unmodulated, rising “ chiWEE? ” ( Fig. 4A, B ), which is quite distinct from the homologous monosyllabic “ DJEW! ” of M. r. regulus ( Fig. 4G ), and the two-noted “ cli-CHEW! ” vocalizations of M. r. striolatus ( Fig. 4C, D ), M. r. aureopectus ( Fig. 4E ), and M. r. antioquiae ( Fig. 4F ). In addition, the advertising song of these latter three taxa also has a lower-frequency hollow, whistled component. After considering that this undertone may be produced by mechanical means, much in the same way as Bostwick (2000) described for M. deliciosus , DFL discovered that this undertone is also given by M. r. striolatus when vocalizing in the hand (when their wings are immobilized), and thus we can discard this hypothesis. There is no such audible undertone associated with the advertising song of M. eckelberryi . Taxon Sex (n) Flat wing Primary Tail Tarsus Culmen extension M. eckelberryi F (7) 52.8 (+1.6) 12.5 (+1.4) 19.8 (+1.6) 14.3 (+0.5) 6.4 (+0.3) M. eckelberryi M (12) 54.7 (+1.1) 13.8 (+1.1) 19.5 (+1.4) 14.8 (+0.8) 6.2 (+0.3) M. r. aureopectus F (1) 52.9 9.3 23.7 15.3 6.6 M. r. aureopectus M. r. striolatus M (2) F (3) 48, 52 49.5 (+0.9) 10, 12 11 (+1.2) 16, 21 20.5 (+2.4) 15, 15.4 14.4 (+0.5) 6.4 * 6.9 (+0.1) M. r. striolatus M. r. antioquiae M. r. antioquiae M (11) F (2) M (8) 50.7 (+1.1) 48, 49 50.2 (+2.0) 12.2 (+1.1) 8.4, 9.6 11.3 (+01.9) 20.1 (+1.2) 17.1, 20.7 18.2 (+1.9) 14.3 (+0.5) 13.9, 14 14.1 (+0.5) 6.3 (+0.4) 6.4, 7 6.3 (+0.4)) M. r. obscurostriatus M (1) 50 10 15 13 - *