We present information on the occurrence of colubrid vine snakes (Oxybelis) and dipsadid sharpnose snakes (Xenoxybelis) from the lowlands of Bolivia. These genera have been poorly reported from Bolivia and information presented herein includes nine new record provincials from the departments of Beni, Cochabamba, La Paz, Pando, and Santa Cruz, Bolivia. Moreover, we present the first records of Oxybelis inkaterra Jadin, Jowers, Orlofske, Duellman, Blair & Murphy, 2021 from Bolivia and we extend the known range of this species by approximately 207 km (Río Sipia, La Paz) and 628 km (Campamento Guacharos, Cochabamba) southeast of the type locality (Puerto Maldonado, Peru) in South America. In addition, we present morphometric information, meristic characters, coloration pattern, ecological aspects and natural history for the three species of vine snakes (O. aeneus, O. fulgidus, O. inkaterra) and two species of sharpnose snakes (X. argenteus, X. boulengeri) from the Bolivian lowlands.

Arboreal, Oxybelis aeneus, Oxybelis fulgidus, Serpentes, Xenoxybelis argenteus, Xenoxybelis boulengeri

The genera Oxybelis Wagler, 1830 (Colubridae) and Xenoxybelis Machado, 1993 (Dipsadidae) comprise several widely distributed Neotropical colubrid species commonly known as vine snakes and sharpnose snakes, respectively (Arredondo et al. 2021; Uetz et al. 2023). Several species are sympatric in many regions of South America. However, Oxybelis has a much broader distribution that includes a northernmost distribution into the southern United States, whereas the northernmost distribution of Xenoxybelis occurs in southern Venezuela (Wallach et al. 2014; Nogueira et al. 2019; Uetz et al. 2023).

The nomenclatural history of the genus Oxybelis is long and convoluted (see Jadin et al. 2021). In addition, taxonomy within the genus has been unclear and disputed (Keiser 1974; Machado 1993; Jadin et al. 2019, 2020). Keiser (1974) maintained retaining Oxybelis aeneus (the type species for the genus) as a single species throughout its extensive range. However, Jadin et al. (2019, 2020) presented compelling data that supported multiple species and considerable diversity; moreover, they proposed an O. aeneus complex to include six species with the description of two new species for Central America and northern South America. Additionally, new species within the complex have also been described from Ecuador (Torres-Carvajal et al. 2021) and Peru (Jadin et al. 2021); among them Oxybelis inkaterra Jadin, Jowers, Orlofske, Duellman, Blair & Murphy, 2021.

The taxonomy of the genus Xenoxybelis has also been unclear and debated (see Melo-Sampaio et al. 2020). The genus was initially described by Machado (1993) and currently includes two species: Xenoxybelis argenteus (Daudin, 1803) and X. boulengeri (Procter, 1923) (Prudente et al. 2008; Melo-Sampaio et al. 2020; Uetz et al. 2023). Both species (X. argenteus and X. boulengeri) have been previously included in the genera Oxybelis (Peters and Orejas-Miranda 1970; Fugler et al. 1995) and Philodryas (Wallach et al. 2014; Nogueira et al. 2019). Oxybelis and Xenoxybelis, as reflected in their taxonomy, are not related but members of different colubrid families (Colubridae and Dipsadidae). However, they are a good example of convergence due to their arboreal lifestyle (e.g., morphology, coloration, diet, and habitat).

Vine snakes and sharpnose snakes are diurnal and predominately arboreal, although they are occasionally terrestrial (Duellman 1978; 2005; Dixon and Soini 1986; Martins and Oliveira 1998; Santos-Costa et al. 2015; Harrington et al. 2018). In general, species from these genera are quite cryptic, due to their coloration, elongated head, and attenuated slender bodies and long tail (authors’ pers. obs.). Prey items include a diversity of small vertebrates, including lizards, birds, amphibians and mammals (Cunha and Nascimento 1978; Henderson 1982; Nascimento et al. 1988; Martins and Oliveira 1998; Duellman 2005; Scartozzoni et al. 2009; Santos-Costa et al. 2015).

Bolivian vine snakes Oxybelis aeneus (Wagler, 1824) and Oxybelis fulgidus (Daudin, 1803), and sharpnose snakes Xenoxybelis argenteus (Daudin, 1803) and Xenoxybelis boulengeri (Procter, 1923) are distributed in the Amazonian forests, Yungas, and riparian forests of the floodplains of Bolivia (Fugler et al. 1995; Moravec and Aparicio 2005; Nogueira et al. 2019; Eversole et al. 2021). However, information on the distribution and natural history of these species in Bolivia is extremely limited (Procter 1923; Donoso-Barros 1967; Fugler 1983; Keiser 1989; Fugler et al. 1995; Cadle and Reichle 2000; Cadle et al. 2003; Moravec and Aparicio 2005; Eversole et al. 2021).

Herein we report information on the distribution and natural history for Bolivian vine snakes and sharpnose snakes, including the first confirmed records of Oxybelis inkaterra from Bolivia.

We examined specimens of vine snakes (Oxybelis aeneus, Oxybelis fulgidus, and Oxybelis inkaterra) and sharpnose snakes (Xenoxybelis argenteus and Xenoxybelis boulengeri) deposited in the four herpetological collections located in Bolivia: 1. Colección Boliviana de Fauna (CIRAH) of the Universidad Autónoma del Beni José Ballivián, Beni, 2. Colección Boliviana de Fauna (CBF) of the Museo Nacional de Historia Natural, La Paz, 3. Museo de Historia Natural Noel Kempff Mercado (MNKR), Santa Cruz, and 4. Museo de Historia Natural Alcide d’Orbigny (MHNC-R), Cochabamba (Tables 1–4).

Scale counts, scutellation, and terminology follow Dowling (1951) and Peters (1964). Measurements were taken using a flexible ruler to the nearest millimeter (snout-vent length, SVL; tail length, TL; in the case of CIRAH after euthanasia). Dorsal scale row counts were taken at three standardized locations; head length behind occiput, midbody, and head length anterior to cloaca and separated by a script (-). Paired subcaudals were counted on one side only, average number of subcaudal and ventral scales in parentheses. In addition to the number of supralabials, the scales that make contact with the orbit are identified in parentheses (right/left). In addition to the number of infralabials, the scales that make contact with the first pair of chin shields are identified in parentheses (right/left).

Specimen identification was determined by comparing and analyzing meristic data, morphometrics, coloration, figures, drawings, and photographs from description and taxonomic information by Daudin (1803), Boulenger (1896), Procter (1923), Peters and Orejas-Miranda (1970), Keiser (1974), Cunha and Nascimento (1978), Duellman (1978, 2005), Nascimento et al. (1988), Keiser (1989), Prudente et al. (2008), Jadin et al. (2020, 2021). We follow the taxonomic nomenclature proposed by Jadin et al. (2020, 2021) and Uetz et al. (2023).

For CIRAH specimens, we determined sex via cloacal probing and photographed each individual following the methodology outlined by Eversole et al. (2019). In addition, each specimen was weighed (g) with an electronic scale (Ohaus model HH 320).

We obtained geographic coordinates in decimal degrees using the Global Positioning System (Garmin eTrex, WGS84). We mapped the distribution of vine snakes and sharpnose snakes using Arc GIS software (ArcMap 10.2) including previous records cited in Tables 1, 3.

We examined nine specimens of Oxybelis aeneus, six Oxybelis fulgidus, three Oxybelis inkaterra, one Xenoxybelis argenteus and seven Xenoxybelis boulengeri deposited in the Bolivian herpetological collections (Tables 1–4). The O. inkaterra record represents the first for Bolivia. We increased new locations of occurrence of these snakes for Bolivia and contributed information on some aspects of their natural history.

We compiled localities, geographic coordinates, voucher number (this study) and references of the previous, additional and first records of Oxybelis and Xenoxybelis for Bolivia (Tables 1, 3), and examined the morphometric and meristic characters of specimens (Tables 2, 4).

 Oxybelis aeneus (Wagler, 1824)

Fig. 1A, B

Specimens examined

One subadult female (CIRAH-201) collected at 2307 h on 14 June 2015 from the community of Exaltación. One adult (CIRAH-290) collected at 0225 h on 26 June 2015 and one juvenile female (CIRAH-408) collected at 2312 h on 22 June 2016 from Totaizal community. One adult female (CBF-0948) collected at 1100 h on 07 August 1992 from El Trapiche, Estación Biológica del Beni (EBB). One adult (MNKR-302) collected on 14 April 1990 from Perseverancia. One adult (MNKR-1414) collected on 17 October 1997 from Reserva El Chore. One adult (MNKR-1579) collected on 11 July 1997 from Comunidad en Maque. One adult (MNKR-3396) collected on 07 August 2002 from Santa Rosa del Sara. One adult (MNKR-5682) collected on 05 February 2022 from Potrerillo de Guenda (Table 1, Fig. 3).

Morphometric and meristic characters

Snout-vent length 575–843 mm (adults > 500 mm, n = 7). Tail length 345–520 mm (n = 7). Smooth dorsal scales 17-17-13 rows (100%), without apical pits. Ventral scales 182–192 (x̅ = 187). Subcaudal scales 152–168 (x̅ = 158). Divided cloacal plate (100%). Loreal absent (100%). Preocular 1 (100%). Postoculars 2 (100%). Temporals 1+2 (100%). Supralabials 8–9 (9/9 in 66% of specimens, 8/9 in 22% and 8/8 in 11%); fourth and fifth contact the orbit (33%), fourth, fifth and sixth contact the orbit (56%), and fifth and sixth contact the orbit (11%). Infralabials 9–10 (9/10 in 56% of specimens and 10/10 in 44%); the first four in contact with the first pair of chin shields (89%) and the first five contact the first pair of chin shields (11%) (Table 2); and usually the fourth, fifth and sixth contact the second pair of chin shields.

Coloration pattern

Upper region of head golden brown to tan; supralabials and ventral surface of head uniform cream color, the color transition is separated by a dark brown preocular line that extends from the nasal scale, under the eye, and toward the anterior region of the body. Black bars or spots present in the anterior region of the body; dorsal and ventral surface of the rest of the body relatively uniform light brown with scattered small black spots (Fig. 1A, B).

Figure 1. 

Vine snakes from Bolivia. A, B. Dorsal (CIRAH-408) and ventral (CIRAH-290) view Oxybelis aeneus, Totaizal community, Yacuma, Beni; C, D. Dorsal and ventral view Oxybelis fulgidus (CIRAH-929), Buen Retiro community, Vaca Diez, Beni. Photos by Cord Eversole (A–D).

Ecological notes

The specimens (CIRAH-201, 290, 408) were found resting on herbaceous plants and tree branches at a height between 0–4 m from the ground during nocturnal searches between 2307–0225 h. The localities where they were found are best described as riparian forests (secondary and tertiary forests) of the Mamoré River sub-basin.

 Oxybelis inkaterra Jadin, Jowers, Orlofske, Duellman, Blair & Murphy, 2021

Fig. 2A–D

First record

Bolivia.

Specimens examined

One adult female (MNKR-3740) collected on March 2005 from Campamento Guacharos, El Palmar, Parque Nacional Carrasco (PNC). One adult male (CBF-4275) collected on 24 June 2015 from Río Sipia, PNyANMI Madidi. One adult (CBF-3780) date and location unknown (Table 1, Fig. 3).

Morphometric and meristic characters

Snout-vent length 580–810 mm (adults, n = 3). Tail length 385–544 mm (n = 3). Smooth dorsal scales 17-17-13 rows (100%), without apical pits. Ventral scales 181–200 (x̅ = 193). Subcaudal scales 160–170 (x̅ = 164). Divided cloacal plate (100%). Loreal absent (100%). Preocular 1 (100%). Postoculars 2 (100%). Temporals 1+2 (100%). Supralabials 8–9 (8/8 in 67% of specimens and 9/9 in 33%); fourth and fifth contact the orbit (33%) and fourth, fifth and sixth contact the orbit (67%). Infralabials 9–10; generally the first four contacting the first pair of chin shields (Table 2) and fourth, fifth and sixth contact the second pair chin shields. Supraocular and prefrontal of similar length; posterior border of internasals extends beyond posterior edge of first supralabial; and presence of small scales between the second pair of chin shields (Fig. 2C).

Figure 2. 

First record of Oxybelis inkaterra (CBF-4275), Río Sipia, Franz Tamayo, La Paz, Bolivia. A, B. Dorsal and ventral view (surface mottled with dense black spots); C. Bottom of the head black spots; D. Eyespot on ventrals scales. Photos by Mauricio Ocampo (A) and Gustavo Rey (B–D).

Figure 3. 

Distribution of the vine snakes in Bolivia. Oxybelis aeneus (points), Oxybelis fulgidus (triangles), and Oxybelis inkaterra (blue stars, first records). Red symbols correspond to additional records.

Coloration pattern

Upper region of head is brown with dark brown to black mottling, black spots on posterior edge of nasal, and on preocular; black mottling on temporals forming an irregular postocular stripe that extends to second or third ventral; supralabials with mottling on borders, infralabials heavily mottled; mental, first pair of infralabials, and chin shields black with white spots (more intense in specimens CBF-3780 and MNKR-3740). Dorsal scales mottled with black and brown pigment in all rows; on anterior third of the body, some scales have heavy black pigment on their borders and irregular transverse bands; anterior ventrals heavily mottled becoming fine stippling posteriorly; some ventrals mottled with scattered black spots anteriorly; posteriorly, these spots encircled with white pigment to form eyespot markings; some of these markings also occur on the ventral and lateral portions of the tail (Fig. 2A–D).

Ecological notes

Specimen CBF-4275 was accidentally severed into two pieces by local guides while they were clearing work trails near the camp. The area has xeric and thorny vegetation, with representatives from the Bromeliaceae, Cactaceae, and Araceae families. This particular individual, feeling threatened, remained motionless, mimicking one of the branches of the shrub it was on. Unfortunately, this behavior caused it to go unnoticed by the guide, resulting in the unfortunate accident.

 Xenoxybelis argenteus (Daudin, 1803)

Fig. 4A, B

Specimen examined

One adult female (MNHC-R 442) collected at 2315 h on 17 August 2001 from Villa Fatima community, Territorio Indígena y Parque Nacional Isiboro Sécure (TIPNIS) (Table 3, Fig. 5).

Morphometric and meristic characters

Snout-vent length 691 mm. Tail length 411 mm. Smooth dorsal scales 17-17-15 rows, without apical pits. Ventral scales 209. Subcaudal scales 182. Undivided cloacal plate. Loreal absent. Preocular 1. Postoculars 2. Temporals 1+1+2/1+2+2. Supralabials 6; fourth contacting the orbit. Infralabials 7; the first four contacting the first pair of chin shields (Table 4) and fourth and fifth contact the second pair of chin shields.

Coloration pattern

Upper center region of head brown; dorsolateral region of the head and supralabials light brown green, separated by broad grayish-green band, from nasal, crosses the eye, and extends to the body; ventral surface of the head yellowish green with scattered black points. Dorsal surface of the body light-greenish brown with two thin greenish-brown lateral bands; ventral surface bright yellowish green anteriorly and light green posteriorly with two lateral green bands (Fig. 4A, B).

Figure 4. 

Sharpnose snake from Bolivia. A, B. Dorsal and ventral view Xenoxybelis argenteus (MHNC-R 442), Villa Fatima community, Moxos, Beni; C, D. Dorsal (CIRAH-670) and ventral (CIRAH-624) view Xenoxybelis boulengeri, Alta Gracia community, Munuripi, Pando. Photos by Gabriel Callapa (A, B) and Cord Eversole (C, D).

Figure 5. 

Distribution of the sharpnose snakes in Bolivia. Xenoxybelis argenteus (squares), and Xenoxybelis boulengeri (diamond). Red symbols correspond to additional records.

Ecological notes

The specimen was found during the night resting on a branch of Piperaceae at a height 1.9 m off the ground in a secondary forest close to a stream.

Previous records of vine snakes (O. aeneus and O. fulgidus) collected in Bolivia include the departments of Beni, La Paz, Pando, and Santa Cruz (Fugler 1983; Fugler et al. 1995; Cadle and Reichle 2000; Quintana and Padial 2003; Nogueira et al. 2019; Eversole et al. 2021). This study increases the museum voucher material collected in lowlands of Bolivia by 13 additional records of O. aeneus (n = 7) and O. fulgidus (n = 6) for the departments of Beni, Cochabamba, La Paz, Pando, and Santa Cruz (Table 1, Fig. 3). It is likely that some records presented in this study correspond to the southern distribution limit of both species.

Furthermore, we report the first records of O. inkaterra for Bolivia, with specimens from the department of Cochabamba and La Paz (one specimen does not have a specific locality) and it constitutes the eighth and ninth locality of the species across its range (Table 1, Fig. 3). Oxybelis inkaterra was recently described by Jadin et al. (2021) within the O. aeneus complex, with specimens from Peru. Jadin et al. (2021) indicated that this species probably also occurs in Bolivia, Colombia and Brazil. Additionally, Torres-Carvajal et al. (2021) reported O. inkaterra from Ecuador. The specimens reported herein confirm the presence of O. inkaterra in Bolivia and extend the known distribution by approximately 207 km (Río Sipia) and 628 km (Campamento Guacharos, both localities located in protected areas) southeast of the type locality (Puerto Maldonado, Peru).

Previous records of sharpnose snakes (X. argenteus and X. boulengeri) collected in Bolivia include the departments of Beni, Cochabamba, and Pando (Procter 1923; Donoso-Barros 1967; Keiser 1989; Fugler et al. 1995; Cadle et al. 2003; Moravec and Aparicio 2005). Our report adds eight new records for X. argenteus (n = 1) and X. boulengeri (n = 7), all from the Amazonian forests of the department of Beni and Pando respectively (Table 3, Fig. 5), considering that the type locality of X. boulengeri is located to the south in the riparian forests of the Mamoré River, Trinidad, Beni (Procter 1923). Xenoxybelis boulengeri is considered rare and poorly represented in scientific collections (Prudente et al. 2008).

The meristic and morphological variation of O. aeneus has been well supported by Jadin et al. (2020) in its distribution range of the Amazon basin. The characters of the examined specimens of Bolivian O. aeneus (Table 2, Fig. 1A, B) are congruent with the description of the species by Jadin et al. (2020), and the color pattern (in life) matches the description of the species by Keiser (1989) and Jadin et al. (2020).

The meristic characters and color pattern (in life) of the examined specimens of O. fulgidus (Table 2, Fig. 1C, D) are congruent with the description of the species by Daudin (1803) and Boulenger (1896), and other related publications (Peters and Orejas-Miranda 1970; Nascimento et al. 1988; Cole et al. 2013; Fraga et al. 2013; Curlis et al. 2020). In addition, we contribute meristic data of the examined specimens, information scarcely available in the available literature. It is likely that the reduced number of subcaudals (128 scales) in the specimen CIRAH-929 is the result of the specimen having lost part of its tail at some point during its life.

Specific meristic characters and coloration of O. inkaterra specimens reported in our study (Table 2, Fig. 2A–D) are congruent with the original description of the species by Jadin et al. (2021). However, specimen CBF-4275 has few eyespots in the posterior ventral and subcaudal region of the body; this is less evident in specimen MNKR-3740. Furthermore, this last specimen presents two supralabials that contact the orbit (fourth and fifth), unlike the other two specimens examined (fourth, fifth and sixth contact the orbit).

Our examined specimen of X. argenteus (Table 4, Fig. 4A, B) is consistent with the description and identification of the species by Daudin (1803) and Duellman (1978) respectively. In addition, we contribute with meristic data of the examined specimen. The absent loreal scale and undivided cloacal scale are specific characters of the species.

The meristic characters and color pattern (in life) of the examined specimens of X. boulengeri (Table 4, Fig. 4C, D) are congruent with the description of the species (Procter 1923; Keiser 1989; Duellman 2005; Prudente et al. 2008). However, our data on ventral scales (196–205) and divided subcaudal scales (132–186) of male specimens are slightly lower than those reported by Prudente et al. (2008). It is likely that the reduced number of subcaudals (132) counted in this study is the result of a specimen also having lost part of its tail at some point in its life. Furthermore, unlike Prudente et al. (2008) who described one preocular, we counted two preoculars in 29% (n=2) of the specimens examined.

The mimicry of Oxybelis and Xenoxybelis with their environment is characteristic of this group of snakes, which is why it is very difficult to observe and capture them during the day. As a result, 91% of the specimens examined (CIRAH) were collected during the night, generally resting on branches or leaves of bushes at a height between 0–4 m from the ground. Only one specimen was found at ground level.

These new and first additional reports of Oxybelis and Xenoxybelis represent contributions that can be used to improve the understanding of their distribution (Figs 3, 5) and aspects of their natural history in Bolivia and throughout their range in South America. In addition, they constitute valuable voucher specimens for Bolivian herpetological collections.

We thank the local guides of the different communities of Beni, Cochabamba, La Paz, Pando, and Santa Cruz for their collaboration during the active searches for snakes. We acknowledge the management and staff of the herpetological collections of the Museo Nacional de Historia Natural - La Paz, Museo de Historia Natural Noel Kempff Mercado - Santa Cruz, and Museo de Historia Natural Alcide d’Orbigny - Cochabamba. To the Director and protection team of the Reserva Nacional de Vida Silvestre Amazónica Manuripi. To the Dirección General de Biodiversidad y Áreas Protegidas for the collection permits for scientific samples. Lastly, we thank Dr. Robert Jadin for the suggestions and confirmation of the O. inkaterra specimens from Bolivia.