Tinamus resonans, Morais & Crozariol & Godoy & Plácido & Raposo, 2025

Morais, Luis A., Crozariol, Marco A., Godoy, Fernando I., Plácido, Ricardo A. A. & Raposo, Marcos A., 2025, A new species of Tinamus (Aves: Tinamiformes) from the western Amazon, Brazil, Zootaxa 5725 (2), pp. 279-291 : 282-285

Tinamus resonans sp. nov.

urn:lsid:zoobank.org:act:

Proposed Portuguese name: Sururina-da-serra

Proposed English name: Slaty-masked Tinamou

Type locality: Serra do Divisor , left bank of the Rio Moa, Mâncio Lima, Acre, Brazil ( 7°25'46.8"S / 73°40'08.7"W, 415 m a.s.l.) .

Holotype: MN 53848 ( Fig. 2 ), skin and an open wing, adult female, collected and prepared by Luis A. Morais and Marco A. Crozariol on 14 July 2025. Alcohol specimen (carcass) MHNCE 1289 . Tissue sample MNT ( MN) 5020, MHNCE 1289 and INPA A 34051 .

Description of holotype: Lores, crown, nape, and entire posterior portion of the neck dark slate-gray; cheeks, throat, anterior and lateral regions of the neck, and the upper chest vivid cinnamon-rufous, shifting to a slightly more ochraceous tone in the upper cheek area ( Fig. 2A ); when the bird adopts a calling posture, the throat assumes a noticeably whitish-cream hue (as can be seen in the individual photographed in Fig. 1D ); dark slate-gray post-ocular stripe extending from behind the eye across the auriculars, partially enclosed by the cinnamon-rufous cheeks and a distinct superciliary stripe of the same cinnamon-ochre coloration; this superciliary stripe is subtly interrupted by the slate coloration at the rear edge of the auriculars but continues into the post-auricular region, creating a masked facial impression ( Fig. 2B ); the slate-gray of the hindneck descends from the crown as a broad stripe that contrasts abruptly with the rufous tones of the neck and throat and then blends posteriorly into the mantle; entire upperparts, including the mantle, scapulars, upper back, and dorsal surface of the wings, uniformly taupe brownish-gray, lacking any transverse barring ( Fig. 2C ); remiges slightly darker dorsally ( Fig. 2E ) and light gray ventrally with a silvery sheen; underwing coverts pure white ( Fig. 2F ); abdomen sepia, with a well-defined whitish-cream area along the central posterior ventral line, extending from the level between the thighs to the cloacal opening, and also visible along the inner surfaces of the thighs; flanks with a darker shade of sepia, tending toward brown, and the feathers bear narrow whitish-cream margins, producing a subtly scaled pattern ( Fig. 2D ); undertail coverts with a central dark-brown triangular marking on each feather with contrasting whitish-cream edges; iris dark-brown; tarsi and toes dull olive-lead-gray; bill straight, dark-grey with a slate gloss, and with a slight dorsal curvature of the maxilla between the nostrils and the tip; proximal base of maxilla with a small ivory-white spot; mandible bicolored, proximal edges near the commissure dark-grey, similar to the maxilla, and entire ventral surface sharply contrasting ivory-white. Weight 342g, total length 296 mm, wingspan 517 mm, wing chord 149 mm, culmen length 28.8 mm, height of bill at nostrils 5.7 mm, tarsus length 49.1 mm, and tail length 40 mm. The ovary measured 12.1 × 7.7 mm, with the two largest follicles measuring 3.9 mm and 3.5 mm.

Paratypes: 1) MN 53847 , skin (shmoo) and an open wing, adult female, Serra do Divisor , left bank of the Rio Moa, Mâncio Lima, Acre, Brazil ( 7°24'58.2"S / 73°40'06.8"W, 351 m a.s.l.), collected by Luis A. Morais and Marco A. Crozariol on 11 July 2025. Weight 362g, total length 310 mm. The ovary measured 19.8 × 8.7 mm, with the largest follicle measuring 7.7 mm. Alcohol specimen (carcass with complete skull preserved) MHNCE 1282 . Tissue sample MNT (MN) 5019, MHNCE 1282 and INPA A 34049 . 2) MN 53849 , skin, adult female, Serra do Divisor , left bank of the Rio Moa, Mâncio Lima, Acre, Brazil ( 7°26'32.6"S / 73°40'14.5"W, 435 m a.s.l.), collected by Luis A. Morais and Marco A. Crozariol on 12 July 2025. Weight 360g, total length 320 mm, wingspan 508 mm, wing chord 153 mm, culmen length 29.7 mm, height of bill at nostrils 6.5 mm, tarsus length 51.1 mm, and tail length 42.4 mm. The ovary measured 16 × 11.5 mm, with the largest follicle measuring 6.8 mm. Alcohol specimen (carcass) MHNCE 1285 . Tissue sample MNT (MN) 5021, MHNCE 1285 and INPA A 34050 .

Diagnosis: This species differs from all other Tinamidae by presenting, at least in females (the three individuals whose sex could be determined were female), a distinctive dark slate-colored crown, which extends into a prominent stripe down the hindneck and into the post-ocular region, forming a conspicuous facial mask ( Fig. 1 and 2 ). The ferruginous coloration of the breast places it near the T. variegatus / brevirostris group, from which it is readily distinguished by its uniform brownish-gray dorsum lacking any barring, a condition otherwise shared only with T. soui . It can be further separated from T. soui by its ferruginous breast, neck, and cheeks and the presence of white on the lower belly. Its vocalization is unique and therefore diagnostic among the vocalizations attributed to other Tinamidae . As described below, it is distinguished by its overall structure and note modulation.

Variation: No significant variation in plumage was observed among the type series or the photographed and observed individuals. Only minor differences in body size were noted. Notably, the bifurcated pattern of the post-auricular mask was consistently present in all specimens.

Etymology: From Latin, resonans is the present participle of the verb resonare (“to resound,” “to echo”), used here in its adjectival sense meaning “resounding” or “echoing.” The verb is composed of the prefix re- (“again” or “back”) and the root sonare (“to sound”), which derives from the noun sonus (“sound”). The name refers to the striking echoing effect of the species’ song, which reverberates across the steep montane slopes of its habitat as a result of strong acoustic diffusion. The common name “sururina” is an onomatopoeic term used by local riverine people to refer to ground-dwelling tinamous with modulated songs and is commonly applied to several species in the region, including Tinamus soui and T. variegatus . The addition of “-da-serra” (“from the mountains”) highlights the distinct identity and montane habitat of this species, setting it apart from other sympatric taxa.

Song: We collected and analyzed a total of 52 audio recordings of T. resonans , which revealed three distinct vocal patterns, hereafter referred to as Pattern A, Pattern B, and Pattern C.

- Pattern A (25 recordings) is the most acoustically complex vocalization and was the only type spontaneously emitted without playback. In all encounters, it was consistently the first song pattern performed following playback stimulation. Pattern A can be divided into two distinct sections: prelude and climax ( Fig. 3A ). The prelude consists of five to seven pure-toned, flute-like notes with a smooth tonal quality, resembling T. cinereus . Each note lasts between 2.3 and 3 seconds, with duration gradually increasing throughout the sequence. Conversely, the intervals between notes progressively shorten, beginning at approximately 2.5 seconds and decreasing to just under 1 second between the last two notes. Spectrogram analysis shows that these notes exhibit an asymmetrical “U”-shaped frequency contour. They begin around 1530 Hz, descend to approximately 1480 Hz, and rise again to about 1560 Hz. Each successive note starts at a slightly higher frequency, with the final note reaching up to 1660 Hz, representing an upward tonal shift of roughly two semitones from the first. The climax follows immediately after the final prelude note and typically comprises four repeated cycles. Each cycle includes three or four short, descending whistles followed by a longer whistle that begins at the same pitch as the final short note. After approximately 0.5 seconds, this long note abruptly rises about one tone and acquires a pronounced modulated (tremolo-like) quality, resembling the climax phrase of T. soui . With each repetition, the pitch of the climax increases slightly, reaching up to 1960 Hz in the final iterations. The vocalization ends with four to six short, descending chirps that extend the rhythmic cadence of the climax and mark the end of the call. Across the full sequence, the total tonal rise may span up to five whole tones and can last more than 45 seconds. Examples: ML641279042; ML641278816; ML641278817; ML641278818.

- Pattern B (22 recordings) resembles an excited response and was generally heard after a few minutes of interaction with playback, typically following several renditions of Pattern A. It consists of a sequence of 5 to 17 short, tremulous notes, beginning with notes approximately 2.5 seconds long, which gradually shorten to about 1 second toward the end of the sequence. The notes accelerate progressively throughout the sequence ( Fig. 3B ), with initial intervals of about 3 seconds decreasing to less than 0.5 seconds toward the end. The notes also gradually ascend in pitch, ranging from approximately 1400 Hz to 1900 Hz, occupying the same frequency band as Pattern A. This vocalization closely resembles the excited song of T. soui from southeastern Brazil’s Atlantic Forest (LAM pers. obs.). Unlike Pattern A, which is highly stereotyped, Pattern B exhibits substantial structural variability. Examples: ML641278867; ML641278868; ML641279131; ML641279132.

- Pattern C (5 recordings) is a short, single-note call heard only in contexts involving multiple simultaneously vocalizing individuals, suggesting a possible social or responsive function. This call has a slightly tremulous tonal quality and lasts approximately 1.5 seconds ( Fig. 3C ). It begins near 1500 Hz and descends slightly in frequency by approximately one semitone. Examples: ML641278898; ML641278899.

At least one individual was observed performing all three vocal types, ruling out the hypothesis of vocal sexual dimorphism. One individual produced a structurally typical Pattern B, but with atypical tonal modulation and abrupt shifts in pitch within and between notes, resulting in a yodel-like effect ( ML641277867 ). This irregularity is likely related to syringeal muscle control and has been previously observed in individuals of other Tinamus species ( LAM pers. obs.), though its physiological basis remains, to some degree, uncertain .

Distribution and habitat: Tinamus resonans was detected at eight sites across the mountainous region of the Serra do Divisor, occurring on both banks of the Moa River, but predominantly along its left bank, within the Serra da Jaquirana ( Fig. 4 ). All records are restricted to the municipality of Mâncio Lima, Acre, Brazil (see Discussion). The species was observed exclusively on the steep forest floor within a narrow transitional zone between 310 and 435 m a.s.l., representing a gradient between submontane and stunted forest. This habitat is characterized by an exceptionally dense and widespread mat of fine roots and leaf litter, forming a continuous network over nutrient-poor, quartzitic sandstone soil ( Mendonça et al. 2020, 2023), through which the tinamou moves and forages. At all surveyed sites, the species was found in sympatry with Thamnophilus divisorius , which in Brazil was previously known only from its type locality, Morro Queimado.

Population size estimate: Over the course of ten independent encounters at eight sites, we confidently identified at least 15 distinct individuals. The mean distance between recorded individuals was 673 meters. Circular buffers with this radius were generated and clipped to the available elevational habitat ( 310–435 m a.s.l.), resulting in a total area of 450.81 hectares occupied by the 15 individuals. This corresponds to an estimated population density of approximately one individual per 30 ha. Considering the total extent of suitable habitat within the defined elevational range (63,302 ha), we estimate a preliminary population size of approximately 2,106 individuals in the Serra do Divisor mountain complex ( Fig. 4 ).

Behavior: Tinamus resonans was recorded vocalizing spontaneously during the late afternoon and dusk, between 17:40 and 18:30 local time. Its song is loud and carries over long distances, but undergoes marked acoustic diffusion along the steep slopes of the Serra, which alters the temporal structure of the song due to echo. On one occasion, a vocalizing individual was detected from the camp at 23:00 h, at an estimated distance of approximately 900 m from the nearest slope. The species consistently responded to playback within its estimated home range, approaching the observer within a few minutes in all trials. When confronted directly, individuals showed no avoidance behavior and appeared remarkably tame, seemingly failing to recognize humans as potential predators. In addition, individuals were observed crossing open areas of understory slowly and without signs of vigilance, a behavior contrasting with the typically wary responses of other tinamous. Between vocal responses, birds were also observed foraging on the forest floor, probing and overturning leaf litter with the bill in search of food items.

Conservation: The Serra do Divisor is protected as national parks in both Brazil and Peru, forming a continuous conservation corridor of nearly two million hectares ( Koga et al. 2022; Vriesendorp et al. 2006 b). On the Brazilian side, the Serra do Divisor National Park (SDNP) was established in 1989, covers 843,012 ha and overlaps two Indigenous Lands as per the Decreto Federal n° 97.839, of June, 16th 1989 (available from: ttp://www.planalto. gov.br/ccivil_03/decreto/antigos/d97839.htm and https://uc.socioambiental.org/pt-br/arp/598, both accessed 15 September 2025). Although approximately 400 people live in the northern sector, where the park’s mountainous terrain lies and where T. resonans is found, anthropogenic disturbances remain minimal, with less than 1% of primary forest altered since the park’s creation ( Koga et al. 2022). These alterations are concentrated mainly in the foothills of the Serra do Divisor, particularly along the banks of the Moa River. In areas where T. resonans has been recorded, there are no signs of human disturbance, and access trails had to be opened by us during field surveys. The only site within the range where human presence occurs is at Morro Queimado, which hosts the Mirante Trail leading to its summit, a popular viewpoint for sunrise and sunset. The summit clearing formed naturally in 1995, following a small fire triggered by a lightning strike ( Whitney et al. 2004). This trail appears to have no measurable impact on the local avifauna: it is narrow, experiences low annual visitation, is the sole site where tourists can reliably observe Thamnophilus divisorius , and is also where T. resonans was first documented, confirming its occurrence even at this location. Aside from this localized visitation, other human activities in the montane zone are scarce, particularly hunting. We conducted interviews with local residents, which indicated that they do not ascend the mountains for this purpose, preferring to hunt larger-bodied animals inhabiting the lowlands, as also reported by Lemos et al. (2018). These authors further noted that the second most preferred vertebrate for hunting is the Whitethroated Tinamou Pezus guttatus ( Pelzeln, 1863) , targeted primarily at night while roosting a few meters above ground, a behavior distinct from that of Tinamus species, likely including T. resonans . The most immediate threat to the conservation of T. resonans , and to the biodiversity of the SDNP as a whole, is a proposal to downgrade the park’s legal status from National Park to Environmental Protection Area ( Área de Proteção Ambiental), enabling the construction of a highway crossing the park as part of the planned extension of BR-364, linking the Brazilian municipality of Cruzeiro do Sul to Pucallpa, in Peru ( Brazil 2019). This anti-ecological proposal also includes mineral exploitation in the mountainous area of the Serra do Divisor, the only known habitat for T. resonans , placing the species at direct risk. Furthermore, there is an additional proposal for a transcontinental railway connecting the Atlantic to the Pacific, also crossing the SDNP ( Farrell & Silva-Macher 2017). The implementation of these projects, driven primarily by economic interests, would trigger well-documented negative environmental and social impacts associated with road building in the Amazon, including displacement of Indigenous peoples and loss of Indigenous languages ( Krokoszyński et al. 2007, Farrell & Silva-Macher 2017, Short 2018, Rojas et al. 2021, Koga et al. 2022, Ruaro & Laurance 2022, Frisbie et al. 2025), significantly undermining conservation efforts in one of the planet’s most pristine and biodiverse regions. Moreover, species restricted to specific microhabitats within narrow elevational ranges, such as T. resonans and Thamnophilus divisorius , are particularly vulnerable to climate change. Even minor shifts in temperature or precipitation can cause significant changes in vegetation structure and resource availability, thereby increasing extinction risk for highly specialized, range-restricted taxa ( Neate-Clegg & Tingley 2023). Furthermore, due to the extremely shallow soils in the area where T. resonans occurs ( Mendonça et al. 2020, 2023), the habitat is prone to landslides in years of intense rainfall, as has already been documented in the SDNP ( Silva et al. 2022), another factor that should be considered in the context of climate change. Currently, Thamnophilus divisorius is classified as Least Concern (BirdLife International 2018), however, with the proposed downgrading of the SDNP, mining and the construction of roads, both species would certainly face elevated extinction risk.

Figures

FIGURE 1. Photos of an individual of the new Tinamus described in the present study at Morro Queimado, Serra do Divisor National Park, Mâncio Lima, Acre, Brazil, by Luis A. Morais.

FIGURE 2. Holotype of Tinamus resonans sp. nov. (MN 53848). Ventral view (A), lateral view (B), dorsal view (C), flanks (D), dorsal surface of the wing (E), ventral surface of the wing (F).

FIGURE 3. Spectrograms of the vocal patterns recorded from Tinamus resonans sp. nov. Song pattern A (A), song pattern B (B), song pattern C (C). Time and frequency scales are standardized across spectrograms.

FIGURE 4. Elevation map of western Amazonia showing the distribution of rivers and mountain ranges. The yellow symbols indicate localities whereTinamusresonanssp.nov. was recorded.Blue dotsrepresent currentknownoccurrences ofThamnophilus divisorius, according to Gonzalez & Acuy (2017). The dashed red line represents the border between Peru and Brazil.