Loudsongs

All subspecies deliver a series of long, upslurred notes separated by shorter intervals, the series generally rising in pitch (Fig. 2). Individual variation of loudsong characteristics within populations was high. For example, of 37 loudsongs analyzed for poecilinotus, nine contained 3–5 notes, 11 contained 6–8 notes, 13 contained 9–11 notes, and four contained 12–15 notes. The unusually large variability could not be related to gender or age in our samples. No diagnosable differences in loudsongs were found between populations as a consequence of the large within-population variability with one exception. Notes of nigrigula and vidua were frequency-modulated in an even pattern, whereas such modulation was erratic or lacking in loudsong notes of the other subspecies (Fig. 2). Differences in note shape allowed perfect allocation of loudsong recordings to the two groups, and differences in quality were apparent in the field and laboratory to the human ear.

FIG. 2

Loudsongs of Willisornis populations. Nomenclature follows recommendations of this paper. Acronyms for recording archives in Appendix. (A) W. p. lepidonotus, Kapawi Lodge, Pastaza, Ecuador (ISL BMW 157:001). (B) W. v. nigrigula, km 209 on BR 230 south of Itaituba, Pará, Brazil (ISL BMW 226:002). (C) W. p. lepidonotus, Kapawi Lodge, Pastaza, Ecuador (ISL BMW 157:001). (D) W. v. vidua, Caxiuanã, Pará, Brazil (ISL BMW 109:022). Magnified notes are expanded 3× on frequency axis, 4× on time axis.

Differences in loudsong characteristics among other populations did not meet our criteria as diagnostic, but when values were plotted geographically, distributional patterns emerged that may prove relevant to future species-level analysis. For example, frequency measures of the first note of poecilinotus loudsongs (37 individuals) were higher pitched than those of duidae (18 individuals), and ranges barely overlapped. When these frequency characters were mapped geographically, the extreme examples of each population occurred at considerable geographic distance from the contact zone, and loudsongs recorded closest to the contact zone (although only 2 individuals of each taxon) differed substantially.

Similar differences were found between duidae and lepidonotus loudsongs with duidae notes delivered at lower frequencies and a slower pace. For example, the mean of the lowest frequency of the central note of duidae was 1,948 Hz (range  =  1,332–2,177, SD  =  242, n  =  18), whereas that of lepidonotus was 2,302 Hz (range  =  2,177–2,678, SD  =  128, n  =  24), but the difference did not meet our significance test. Plotting frequency and pace geographically did not suggest a tendency for duidae loudsongs either to diverge or converge clinally with lepidonotus, although recordings are needed from the region where these populations are likely to come into contact. No significant differences were found with regard to elevational differences within lepidonotus, even though a small sample of higher elevation loudsongs tended to be higher pitched and faster.

Initial notes of griseiventris loudsongs in general were lower-pitched than the equivalent lepidonotus notes, but loudsongs of the western-most population of griseiventris, nearest the range of lepidonotus, were highest in frequency and closest to notes of lepidonotus, suggesting clinality. We identified no differences in griseiventris loudsongs east and west of the Rio Madeira.

Contact Call

These calls consist of abrupt notes given when flying between perches as well as when perched. They differed diagnosably between what we termed a twitter, which is found only in the repertoires of nigrigula/vidua, and a psit, which is delivered only by the remaining populations (Fig. 3). The twitter is a short (2–16, typically 3–5), high-pitched series of clear, almost tinkling, musical notes (Fig. 3A) Each note bends slightly downward in frequency; the series descends slightly in frequency; and intervals between notes with rare exceptions lengthen slightly (typically from 60 to 75 millisec, extremes 34 and 112 millisec). Notes, especially the initial note, often start with a small hook (Fig. 3A). In contrast, the psit note was shaped like an inverted U or V, usually sounding lower-pitched and harsher to the human ear than the twitter. The psit was typically given singly (Fig. 3B and C), but occasionally in short series that usually decreased in frequency, sometimes dramatically so (Fig. 3D and E).

FIG. 3

Contact calls of Willisornis populations. Nomenclature follows recommendations of this paper. Acronyms for recording archives in Appendix. (A) W. v. nigrigula, Jacareacanga, Pará, Brazil (ISL BMW 219:065). (B) W. p. poecilinotus, Reserva Ducke, Amazonas, Brazil (ISL BMW 131:020). (C) W. p. griseiventris, Prainha Nova, Amazonas, Brazil (ISL BMW 196:028). (D) W. p. griseiventris, Explorer's Inn; Madre de Dios, Peru (ML 35547). (E) W. p. duidae, Parque Nacional Natural Chiribiquete, Caquetá, Colombia (ISL MAR 006:033).

The duration of the psit call varied among populations. The mean length in northern lowland populations (poecilinotus, duidae, and lowland lepidonotus) was 0.093 sec (range  =  0.071–0.118, SD  =  0.0120, n  =  20; Fig. 3B), whereas the mean for highland and southern populations (highland lepidonotus and griseiventris) was 0.054 sec (range  =  0.047–0.063, SD  =  0.0051, n  =  20; Fig. 3C). The difference was diagnosable under our criteria. However, when four examples for gutturalis were added to the highland and southern populations, the mean and variance were slightly larger 0.055 sec (range  =  0.047–0.069, SD  =  0.0066, n  =  24), narrowly failing our statistical test.

Chirrs

This call consisted of a short series (duration: x¯  =  0.596 ± 0.189 sec, range  =  0.248–1.020 sec, n  =  52) of abrupt (5–9 millisec) notes, vertical on a spectrogram, repeated rapidly (∼5 notes in 0.1 sec), and typically descending in pitch (e.g., apex of notes ∼ 5 mHz descending to ∼4 mHz) (Fig. 4A). Chirrs have been recorded for all populations. No diagnostic differences in chirrs were found among Willisornis populations, although the duration of chirrs of nigrigula and vidua overlapped only slightly. Average chirr duration in nigrigula recordings was 0.728 ± 0.209 sec, range  =  0.420–1.020, n  =  10), whereas that of vidua was 0.399 ± 0.053 sec, range  =  0.322–0.444, n  =  6). Difference in means met student's t-test at 99%. At times chirrs were combined with contact calls.

FIG. 4

Chirr and raspy calls of Willisornis populations. Nomenclature follows recommendations of this paper. Acronyms for recording archives in Appendix. (A) Chirr W. p. griseiventris, Humaitá, Amazonas, Brazil (ISL BMW 219:081). (B) Raspy call W. p. poecilinotus, Iwokrama Forest Reserve; Guyana (ISL BMW 158:003). (C) Raspy call W. p. griseiventris, right bank Rio Jiparaná opposite Palmeiras, Rondônia, Brazil (ISL BMW 208:020). (D) Raspy call W. v. vidua, Caxiuanã, Pará, Brazil (ISL BMW 180:048).

Raspy Series

Notes in raspy series were typically repeated 2–4 times but were sometimes given individually or in longer series. Typical poecilinotus calls had “U” shaped notes (Fig. 4B); the series descending slightly in pitch, sounding like “cheery, cheery, churry, churry.” The call of griseiventris typically had the initial part of the note truncated, making it look like a “J” in a spectrogram, and the base of the notes typically rose slightly in frequency (Fig. 4C). Few calls were available for duidae, lepidonotus, and gutturalis, but they suggested intermediacy between poecilinotus and griseiventris and, consequently, differences among these five subspecies were not considered diagnostic. We suspect that analysis of larger samples may detect diagnostic differences in raspy series among these populations. Note shapes in raspy series of vidua and nigrigula, in contrast, differed consistently from those of other populations. Notes delivered by nigrigula and vidua (Fig. 4D) lacked the down-pitched beginning of the note and had a flat or sometimes ascending, vibrant base of wider frequency range than notes of the other populations.

Other Calls

Calls other than contact calls, chirrs, and raspy series were relatively rarely recorded and, in most instances, the recordist did not clearly attribute the call to a Willisornis population. Four differently shaped calls have been recorded, including down-slurred, inverted U shaped, and upslurred notes. The most common type was down-slurred, ∼0.2–0.4 sec in duration, and descending generally in the range of 4.0 to 1.5 mHz (Fig. 5A). Calls of this type were found in recordings of griseiventris, nigrigula, vidua, and lepidonotus above 800 m. A longer (0.45–0.6 sec), higher pitched, down-slurred (6 to 4 mHz) “pseer” (Fig. 5B) has been recorded twice for poecilinotus. Short (∼0.25 sec), inverted U shaped notes sounding like an abrupt “wheet” were recorded for poecilinotus in the 2.6–3.4 mHz frequency range (Fig. 5C) and in the 1.9–2.3 mHz frequency range (Fig. 5D) for gutturalis in which the notes were doubled, for lepidonotus below 800 m in a short series (Fig. 5E), and for an uncertain population near the contact zone between gutturalis and griseiventris. An abrupt upscale note given in series was recorded for griseiventris (Fig. 5F) and for lepidonotus below 800 m. The meager data suggest differences in other calls between northern and southern populations may be identified with a larger number of recordings.

FIG. 5

Other calls of Willisornis populations. Nomenclature follows recommendations of this paper. Acronyms for recording archives in Appendix. (A–B) Down-slurred calls. (A) W. p. griseiventris, Rio Bararati, Amazonas, Brazil (ISL BMW 229:045). (B) W. p. poecilinotus, Iwokrama Forest Reserve, Guyana (ISL BMW 155:021). (C–E) Inverted U shaped calls. (C) W. p. poecilinotus, 25 km SE Maripa, Bolívar, Venezuela (ISL BMW 071:003). (D) W. p. poecilinotus, Iwokrama Forest Reserve, Guyana (ISL BMW 144:012). (E) W. p. lepidonotus, El Tigre, Loreto, Peru (ISL JA 01:050). (F) Upscale call W. p. griseiventris, Fazenda Rancho Grande, Rondônia, Brazil (ISL KJZ 016:034).

Little is known of the functions of vocalizations in the Willisornis complex. K. J. Zimmer observed and tape-recorded a display by a male nigrigula in the presence of a female-plumaged individual in August 1991 near the Rio Cristalino, Mato Grosso, Brazil. Perched on a slender diagonal branch ∼0.7 m above the ground, the male drooped his wings, stretched his neck up vertically, and extended his head up and down rapidly on a vertical axis, calling continuously all the while. The calls included raspy series and chirrs, and other calls, and are the only indication we had of the behavioral role of these vocalizations.

Contact Between W. p. poecilinotus and W. p. duidae

Females are distinguished by gray underparts in poecilinotus (brown in duidae) and buffy “scales” on the lower back of poecilinotus (white in duidae). Males differ only by a smaller interscapular patch in poecilinotus. Geographic ranges of poecilinotus and duidae are only partially delimited by rivers. The Río Orinoco may separate the subspecies at the northernmost end of their contact zone. The most proximate specimen locations are from Caño Usate (COP, poecilinotus) and Campamento Manaka (COP, duidae), Amazonas, Venezuela, ∼90 km apart. The Rio Orinoco lies between these locations as well as between Caño Usate and Colombian specimens from Vichada (Instituto Humboldt). Ranges of poecilinotus and duidae at the southern end of their contact zone in Amazonas, Brazil, extend to the left and right banks of the lower Rio Negro, respectively. Extensive fieldwork did not find either taxon on the many islands (Anavilhanas Archipelago) in this broad river (Cintra et al. 2007), although duidae occupies some islands in the upper Rio Negro near São Gabriel da Cachoeira. No barrier appears to prevent antbirds from coming into contact in the region between the upper Orinoco and the right bank of the Rio Branco; poecilinotus alone appears to occupy the area below the Rio Branco south to the Amazon. Apparent hybrids have been collected in the Valle de los Monos on the southern slope of Mt. Duida, Amazonas, Venezuela, where poecilinotus has been collected on the southeastern slope and duidae on the western slope. As described by Zimmer (1934) and corroborated by reexamination of the pertinent specimens by MLI, one (AMNH 273015) of five females collected closely resembles duidae, one (AMNH 273017) is indistinguishable from poecilinotus, and the remaining three (AMNH 273015, 273018, 273686) have a mixture of ventral and back scale coloration of the two populations. The most proximate locations to the southeast of Mt. Duida in Venezuela are Río Putaco (COP, poecilinotus) and Ocamo (AMNH, duidae), ∼100 km distant. Further southeast in Brazil, an even greater distance, ∼280 km, separates specimens from the Rio Dimiti in Amazonas and the vicinity of Caracaraí, Roraima, although the intervening region is poorly studied ornithologically. No hybrids other than those from Mt. Duida are known.

Contact Between W. p. duidae and W. p. lepidonotus

Chapman (1923) described the duidae male as paler gray below, the female as more reddish and brighter throughout compared to lepidonotus. In addition, the interscapular patch was found to be smaller in duidae (Zimmer 1934). Chapman's original description and Zimmer's (1934) analysis were based on specimens from near the extremes of their ranges: Venezuela and northwestern Brazil for duidae and Peru and Ecuador for lepidonotus. Later Colombian specimens from along the base of the Andes in Meta were identified as duidae and those from western Caquetá and Putumayo as lepidonotus (Meyer de Schauensee 1964). Most recently, the population in the Sierra de Chiribiquete, Caquetá, Colombia, was identified as duidae (Stiles et al. 1995) which, along with the population in Tonantins, Amazonas, Brazil (CM), closes the gap between their ranges. However, a sufficient series of specimens from the intermediate region in Colombia has not yet been procured to examine possible clinality in morphological characters.

Contact Between W. p. lepidonotus and W. p. griseiventris

Females are distinguished by brown underparts in lepidonotus (gray in griseiventris) and white “scales” on the lower back of lepidonotus (absent in griseiventris). Males do not differ diagnosably. The Río Ucayali separates the ranges of lepidonotus and griseiventris in central Peru. However, further south towards the headwaters of the Río Ucayali, no river appears to perform this function. The closest confirmed locations are Kiteni; Cuzco (LSUMZ) for lepidonotus and the east slope of Cordillera de Pantiacolla, Madre de Dios (FMNH), for griseiventris. These locations are ∼190 km apart and are separated by mountainous terrain with elevations >2,000 m. There are more proximate locations to the north in intervening terrain of lower elevation cited in the literature with unidentified subspecies.

Contact Between W. p. gutturalis and W. p. griseiventris

Females are distinguished by brown underparts in gutturalis (gray in griseiventris) and white “scales” on the lower back of gutturalis (absent in griseiventris). Females of gutturalis also typically have crown redder than back (concolor in other populations). Males of gutturalis have black throat patches (absent in griseiventris). The geographic range of gutturalis is the smallest of any subspecies, restricted in Peru and Brazil to the region immediately south of the Amazon and east of the lower Río Ucayali (Fig. 1). The extent of its range to the east and south is unclear. The likelihood that the Rio Juruá provides a barrier in a section of their contact zone is supported by specimens of female gutturalis from Eirunepé (formerly João Pessôa) on the left bank of the Juruá and by male griseiventris from Santa Cruz on the Rio Eiru, a right bank tributary (Pinto 1942, 1978; specimens examined at MZUSP). However, sight records from both banks of the Rio Juruá at the Reserva Uakarai were identified as griseiventris (Andrew Whittaker, pers. comm.). To the southwest, in the Juruá–Ucayali interfluvium, griseiventris has been found at Divisor, Loreto, Peru, and at two other locations west of the Sierra del Divisor (Vriesendorp et al. 2006:195). Consequently, known ranges of gutturalis and griseiventris are separated by ∼280 km of probably suitable habitat in this region with no river barriers.

Contact Between W. p. griseiventris and W. p. nigrigula

The extension of the gray of the underparts to the sides of the head (ear coverts and lores) distinguishes female nigrigula from griseiventris. Males of nigrigula have a black throat, while throats of male griseiventris are plain gray. The Rio Canumã and, continuing further upstream, the Rio Sucunduri, separates their ranges (regions of locations 22 and 24; Fig. 1). However, the range of griseiventris passes the headwaters of the Rio Sucunduri to reach the Rio Tapajós above Jacareacanga, where it overlaps nigrigula and may hybridize with it locally (BMW observations and recordings of both taxa). Beyond this point, to the south, only griseiventris has been found on the left (west) bank of the Rio Tapajós and its major tributary, the Rio Teles Pires, whereas nigrigula occurs on the right (east) bank of these rivers.

Contact Between W. p. nigrigula and W. p. vidua

Males of nigrigula have discreet black throat patches which are absent in vidua, the throat of which tends to be more whitish than its gray underparts. Females of vidua differ from nigrigula by having flanks suffused reddish-yellow-brown (slightly tinged in nigrigula) and wing edgings grayish-brown (reddish-yellow-brown in nigrigula). Interscapular patches are larger in nigrigula (15–20 mm) than in vidua (0–10 mm). The known geographic ranges of nigrigula and vidua with one exception are separated by a wide geographic gap west of the Rio Xingu (Fig. 1), although much of the region between the known ranges of these populations is unexplored ornithologically. The only known convergence of nigrigula and vidua is based on sight records by BMW in September 1994 of males within ∼1 km of each other at Riozinho, Area Indigena Kayapó, Pará; it cannot be considered definitive, but does serve to suggest the possibility of parapatry of these forms in this poorly studied region.