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Mastozoología neotropical

versión impresa ISSN 0327-9383versión On-line ISSN 1666-0536

Mastozool. neotrop. v.16 n.1 Mendoza ene./jun. 2009

 

ARTÍCULOS Y NOTAS

Observations on the natural history of Abrocoma sp. (Rodentia, Abrocomidae) in a Polylepis woodland in Bolivia

Teresa Tarifa1*, Carola Azurduy2**, Renzo R. Vargas2***, Noemí Huanca2, Jehizon Terán2, Greissy Arriaran2, Claudia Salazar2, and Lenny Terceros2

1 Colección Boliviana de Fauna, La Paz, Bolivia; Current address: 3407 Fairoaks Circle, Caldwell, Idaho 83605, U.S.A. .
2 Centro de Biodiversidad y Genética, Universidad Mayor de San Simón, Casilla 538, Cochabamba, Bolivia;
*[Corresponding author: <teresa_tarifa@yahoo.com>]
**Current addresses: Gothenburg Natural History Museum, 402 35 Gothenburg, Box 7283, Sweden and Sagogången 1 422 45 Hisings Backa, Sweden;
***Current address: Laboratorio de Ecología Terrestre, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago, Chile.

ABSTRACT: We report four opportunistic field observations of a species of Abrocoma in Polylepis besseri woodlands in Cochabamba Department, Bolivia. These observations suggest four significant aspects of Abrocoma sp. natural history: 1) they have arboreal activity, 2) they may be specialized herbivores that feed on Polylepis leaves, 3) they have diurnal activity, and 4) they have docile behavior. These observations represent the first descriptions of aspects of the behavior and ecology of an abrocomid in Bolivia, and also suggest that Polylepis woodlands, a threatened Andean habitat, may provide an important habitat for specialized mammal herbivores such as Abrocoma sp.

RESUMEN: Observaciones sobre la historia natural de Abrocoma sp. (Rodentia, Abrocomidae) en un bosque de Polylepis en Bolivia. Reportamos cuatro observaciones de campo ocasionales de una especie de Abrocoma en un bosque de Polylepis besseri en el Departamento de Cochabamba, Bolivia. Estas observaciones sugieren cuatro aspectos significativos sobre la historia natural de Abrocoma sp.: 1) tienen actividad arbórea 2) podrían ser herbívoros especializados que se alimentan de hojas de Polylepis, 3) tienen actividad diurna y 4) tienen un comportamiento dócil. Estas observaciones son las primeras sobre el comportamiento y la ecología de un abrocómido en Bolivia y sugieren que los bosques de Polylepis, un hábitat amenazado, constituirían un importante hábitat para mamíferos herbívoros especializados como Abrocoma sp.

Key words. Abrocoma; Bolivia; Natural history; Polylepis woodlands.

Palabras clave. Abrocoma; Bolivia; Bosques de Polylepis; Historia natural.

Observations on the natural history of organisms are sometimes considered of little significance and a part of old-fashioned science. However, knowledge of natural history is at the core of science; it allows researchers in other branches of biology to develop novel and meaningful hypotheses, to design significant field experiments and observations, and to facilitate syntheses from organismal to ecosystem levels; it is also at the roots of modern evolutionary biology, ecology, wildlife management, conservation biology, and nature appreciation (Bartholomew, 1986; Wilson, 2000; Greene, 2005; Schmidly, 2005; Willson and Armesto, 2006).
    We report here four opportunistic field observations of a possible new species of Abrocoma in Polylepis besseri woodlands in Cochabamba Department, Bolivia. These observations represent the first descriptions of the behavior and ecology of an abrocomid in Bolivia, and they have four significant implications for the knowledge and understanding of the biology of this species and abrocomids in general: 1) arboreal activity, 2) specialized herbivory, 3) diurnal activity, and 4) docile behavior. These observations also suggest that Polylepis woodlands may provide an important habitat for specialized herbivorous mammals such as Abrocoma sp., adding to the importance of conserving this threatened habitat in Andean countries.
    Abrocomid rodents are endemic to South America. With the exception of a few studies of Abrocoma vaccarum from Argentina and Abrocoma bennetti from Chile (Braun and Mares, 1996), the natural history of abrocomids is poorly known. Abrocomids are considered trap-shy and apparently disinterested in all types of baits (Braun and Mares, 1996). As a consequence, they continue to be poorly represented in museum collections and their ecology and behavior remain largely unknown.
    Abrocomidae currently consists of two genera: Abrocoma, with eight recognized species (Braun and Mares, 2002; Woods and Kilpatrick, 2005), and the recently described Cuscomys, with two species: C. ashaninka (Emmons, 1999) and C. oblativus [= Abrocoma oblativa] long considered extinct (Eaton, 1916), but possibly still extant (Emmons, 1999). Abrocoma boliviensis was considered to be Cuscomys by Verzi and Quintana (2005); herein we have maintained it as A. boliviensis to be consistent with the current checklist (Woods and Kilpatrick, 2005). In Bolivia, Abrocomidae is currently represented by two species: Abrocoma cinerea and A. boliviensis (Anderson, 1997; Salazar- Bravo et al., 2003).
    Polylepis woodlands are one of the most endangered habitats in Bolivia and other Andean countries (Fjeldså, 2002; Ibisch et al., 2003; Kessler, 1995, 2002). Previous studies of mammals in Polylepis woodlands have reported that most species have wide distributions that are apparently not directly related to the presence of Polylepis trees (Yensen and Tarifa, 1993; Tarifa and Yensen, 2001; Vargas, 2001; Yensen and Tarifa, 2002; Moya, 2003; Vargas, 2005; Tarifa et al., 2007). However, some species appear to use the woodlands as a refuge (e.g., Hippocamelus antisensis: Tarifa and Yensen, 2004).
    Our observations occurred in P. besseri woodlands of Sach'a Loma [also spelled Sacha Loma] and Quturi [also spelled Cuturi] located ca. 12 km SW of Pocona, Mizque Province, Cochabamba Department, Bolivia (ca. 17º 44' S, 65º 34' W). Both sites were located between 3600 and 4000 m elevation in Polylepis woodlands on steep mountainsides in the Cordillera de Cochabamba. The average annual temperature at Sach'a Loma is ca. 8.7ºC, with an average minimum temperature of 1.7ºC and maximum of 19.3ºC. The average annual precipitation is 721 mm (Fernández et al., 2001).
    The woodland fragments where the observations occurred have abundant rocky outcrops of glacial origin locally called "salles." The woodlands have three clearly differentiated strata: trees from 2 to 6 m tall, shrubs 1 to 2 m high, and undergrowth up to 0.5 m. The latter consisted of forbs, ferns, and grasses. The arboreal stratum was completely dominated by P. besseri besseri (Fernández et al., 2001).
    The small mammals of Sach'a Loma have been studied by Vargas (2001) and Moya (2003), and in both studies Abrocoma sp. was collected and voucher specimens deposited in the mammal collection at the Centro de Biodiversidad y Genética (CBG) at the Universidad Mayor de San Simón. Abrocoma sp. was the largest of the 8 species of rodents reported from Sach'a Loma and was the only species of abrocomid. Voucher specimens of Abrocoma sp. from Sach'a Loma were compared to the holotype of C. ashaninka and specimens of A. boliviensis, A. cinerea, and A. bennetti and the descriptions of both genera in Emmons (1999), Glanz and Anderson (1990) and Verzi and Quintana (2005). The voucher specimens agreed with Abrocoma in 12 of 16 cranial characters compared.
    In May 2000, a female Abrocoma was captured at Sach'a Loma in a Sherman trap baited with a mixture of oats, peanut butter, tuna, and vanilla scent. We kept the animal in captivity for three days before we liberated it. During the days in captivity the Abrocoma showed a very docile character. The first day the Abrocoma escaped from the bag where it was kept, and was standing up and looking around without fleeing. When we tried to catch the animal, it started to escape; however, the animal moved slowly, so it was easy to recapture by hand. The second day we took the Abrocoma out in order to clean the bag. The Abrocoma did not try to escape or bite us. The third day, because the animal had been in the bag for many hours, we decided to take it out for some sunlight. We put the Abrocoma on a big rock. It escaped but it did not go very fast, so we were able to catch it by hand again. We began to pet it, and the Abrocoma remained in CA's lap sunbathing and eating Brazil nuts and raisins for several minutes. Finally, we left the animal in the woodland where it remained for some minutes before taking refuge in a crevice in a pile of rocks nearby.
    On 6 October 2002, at Sach'a Loma at 17:15 we observed an Abrocoma sitting on a thin branch at a height of 1.75 m in a young P. besseri tree 2 m tall. We saw the animal at some distance, and we decided to approach the tree very slowly trying not to scare it. The Abrocoma remained calm while we approached the tree. When we were close to the branch where the Abrocoma was sitting, we realized that it was not afraid of our presence and it continued calmly collecting young shoots with its hind foot and eating them. The animal repeated the same action several times while balancing on a thin branch. It used its rear feet and tail to support itself on the branch.
    After 15 minutes of observation, we felt comfortable in offering young shoots to the Abrocoma. We placed the young shoots close to its muzzle. It smelled the shoots and grasped them with its forefeet, then ate them. We observed the Abrocoma foraging on Polylepis shoots for more than 30 minutes, after which one of us reached out and touched the Abrocoma on its hind feet, dorsum and belly. When one of us tried to grasp the animal, it escaped and sought refuge within a pile of rocks nearby.
    During October or November 2003, we observed an Abrocoma sp. at Quturi between 12:00 and 13:00. The animal was on a low branch in a small P. besseri tree ca. 1.5 m tall. The Abrocoma sp. was feeding on shoots and young leaves of Polylepis. It was rising up on two feet to reach its food. Moving slowly when it felt threatened, it just shrank and camouflaged itself in the foliage-making itself like a type of little ball-and it did not move until it was more tranquil.
    During the period of observation, the Abrocoma moved slowly along the branches on the lower part of the tree while eating shoots and young leaves. We tried to feed the animal with bits of bread, which it did not eat. We touched the animal and petted it. After 30 minutes of observation, we tried to grasp the animal, but it escaped by jumping into some nearby rocks where it took refuge.
    The last field observation occurred on 24 October 2004. At 14:00, an Abrocoma was observed in the interior of a P. besseri woodland fragment at Sach'a Loma. The individual emerged from a pasture of Festuca and Stipa, after which it jumped into a small cave in a nearby rock pile.
    The lack of behavioral and ecological information about abrocomids was noted by Braun and Mares (1996), who mentioned that a specimen of A. vaccarum that they collected in Mendoza, Argentina was the only individual of this species encountered during their 5-year study of the mammals of the region. As a result, the observations presented here contribute not only to the knowledge of Bolivian abrocomids but also to an understanding of this family.
    Anatomical characteristics such as a long tail, long hind feet, wide feet, well-developed abdominal musculature, well-developed plantar tubercles, and strong, hooked claws are considered to be adaptations of rodents for climbing (Dublin, 1903; Holbrook, 1979; Dewsbury et al., 1980; Packer and Layne, 1991; Rivas and Linares, 2006). The specimens of the putative undescribed species of Abrocoma from Cochabamba and A. boliviensis both have relatively long tails, long feet, and strong, curved claws. In describing the numerous small plantar tubercles of Abrocoma, Glanz and Anderson (1990) suggested they would function to increase traction on rocks or tree branches. We observed Abrocoma sp. use its long tail for balance, watched them climb, and saw them move easily but deliberately among the branches. Because of their similar anatomy, we suggest that both Abrocoma sp. and A. boliviensis may be suited for arboreal activity, although the degree of arboreality remains to be studied.
    In contrast, A. bennetti and A. cinerea were characterized by Glanz and Anderson (1990) and Emmons (1999) as specialized for terrestrial life in open habitats and living in burrows among rocks; they have a short tail, reduced hallux, and inflated auditory bullae. We suggest that among the Abrocomidae there are those species that can be considered arboreally- adapted, C. ashaninka and C. oblativa (Emmons, 1999); species that are suited for arboreal activity, Abrocoma sp. and possibly A. boliviensis; and terrestrial species such as A. vaccarum (Braun and Mares, 1996) and A. cinerea.
    Previous studies of small mammals in Polylepis woodlands at Sach'a Loma and other places in Bolivia were based on collecting efforts using traps placed at ground level (e.g., Yensen and Tarifa, 1993; Vargas, 2001; Yensen and Tarifa, 2002; Moya, 2003; Maradiegue 2006). Although for species lists there may not be much difference in the number of species captured in arboreal vs. ground level traps, for ecological studies the differences in habitat, available food resources, patterns of vertical stratification, and canopy utilization are among the most critical parameters that affect community composition of small mammals (Meserve, 1977; Laakkonen, 2003; Vieira and Monteiro-Fihlo, 2003; Wells et al., 2004). Therefore in ecological studies in Polylepis woodlands, it is important to consider species with arboreal activity, which uses vertical structure. Trapping only at ground level will underestimate the abundance of species with arboreal activity and also misrepresent the composition of small mammal communities.
    Diurnal activity in Abrocoma sp. at Sach'a Loma and Quturi was surprising, but almost nothing is known about the activity patterns of Bolivian abrocomids. Whether Abrocoma sp. is also active at night is not known, but these observations suggest that classical trapping techniques may have been unsuccessful for that reason. As a specialist herbivore, it may not be attracted to conventional baits, as is the case with other abrocomids (Glanz and Anderson, 1990; Braun and Mares, 1996).
    It is also noteworthy that Abrocoma sp. was observed eating young shoots of P. besseri. Braun and Mares (1996) cited observations by Oliver Pearson in which he saw A. cinerea eating leaves of Polylepis, among other plants, in Peru. Taken together, these observations suggest that Polylepis woodlands may provide an important habitat for abrocomids.
    Yensen and Tarifa (2002) noted a deficit of specialized herbivores in the small mammal guild in Polylepis woodlands, suggesting that a segment of the community has been lost at many sites, perhaps due to the degradation of those woodlands by human activity. The woodland fragments at Sach'a Loma and Quturi were well preserved. Consequently, these woodlands may give us insights into the original small mammal composition of Polylepis communities and serve as a useful baseline.
    Abrocoma sp. was observed in the densest portions of the woodlands. This leads us to suspect that their docile behaviors of 1) shrinking the body into a ball and remaining still when threatened, and 2) relying on their grayish- brown color for camouflage among the P. besseri leaves was a cryptic antipredator behavior. Similar behavior was observed in Ochrotomys nuttalli, a rodent with arboreal activity (Layne 1960, cited in Packer and Layne, 1991) and an arboreal specialist, Dactylomys dactylinus (Emmons, 1981). This cryptic antipredator behavior was considered an adaptation to arboreal life (Layne 1960, cited in Packer and Layne, 1991; Eisenberg 1978). This behavior also suggests that Abrocoma sp. is a species with regular arboreal activity.
    The behavior that we observed in Abrocoma sp. of relying on its motionless behavior and grayish-brown color for camouflage in the vegetation could imply that a reduction in vegetation cover accompanying fragmentation would more readily expose them to view by predators. This might explain their apparent rarity because most remaining Polylepis woodlands are highly fragmented and disturbed.
    The docile behavior of Abrocoma sp. may also make them vulnerable to invaders like Rattus rattus that are becoming increasingly common in Polylepis woodlands as human use increases. R. rattus has been observed preying on A. bennetti in Chile (Eduardo Valladares, pers. comm. 2006) and have been found in Polylepis woodlands adjacent to pine plantations in Tunari National Park, Cochabamba Department (Maradiegue, 2006). Finally, the docile character observed in Abrocoma sp. may have also been present in C. oblativus [= A. oblativa] and helps to understand why the Incas could keep them as pets, as suggested by evidence that these animals were buried with their owners in Inca burial caves (Eaton 1916).

ACKNOWLEDGEMENTS

We are grateful to Eileen Lacey and Eric Yensen for their comments on a previous version of the manuscript and Eduardo Valladares for providing information on Abrocoma bennetti from Chile. RV's study was funded by the Centro de Biodiversidad y Genética (CBG), Idea Wild, and Wildlife Conservation Society; and NH, GA, CS, and LT's studies were funded by the Cooperación Inter-Universitaria Belga (VLIR-IUC) through the CBG. Marlene Gast provided help with English usage on a previous version of the manuscript. We are especially grateful to Eric Yensen for his help with English usage on a later version of the manuscript. Martin Ubilla, Diego Verzi, and an anonymous reviewer provided helpful comments on the manuscript.

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Recibido 27 noviembre 2006.
Aceptado 5 marzo 2008.

Editor asociado: D Verzi

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