Kannabateomys amblyonyx (Wagner, 1845)

Don E. Wilson, Thomas E. Lacher, Jr & Russell A. Mittermeier, 2016, Echimyidae, Handbook of the Mammals of the World – Volume 6 Lagomorphs and Rodents I, Barcelona: Lynx Edicions, pp. 552-604 : 587

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Atlantic Bamboo Rat

Kannabateomys amblyonyx

French: Rat-épineux des bambous / German: Bambus-Fingerratte / Spanish: Rata de bambu atléantica

Other common names: Southern Bamboo Rat

Taxonomy. Dactylomys amblyonyx Wagner, 1845 ,

“Ypanema.” Restricted by L. P. Costa and colleagues in 2003 to Floresta Nacional de Ipanema, 20 km NW Sorocaba, Sao Paulo, Brazil .

Two subspecies are recognized.

Subspecies and Distribution.

K. a. amblyonyx Wagner, 1845 — SE Brazil, from Rio de Janeiro to Santa Catarina states.

K. a. pallidior Thomas, 1903 — Parana Basin of E Paraguay, NE Argentina (Misiones Province), and adjacent Brazil.

Descriptive notes. Head-body 230-347 mm, tail 300-420 mm; weight up to 570 g. The Atlantic Bamboo Ratis large and arboreal, with coarse fur and predominantly rufous brown or buffy dorsum. Belly is pure white and contrasts sharply with dorsum. Blocky head is covered with more gray to buff hairs; nose and chin are white. Robusttail is c.120% of head-body length, furred along its length, and covered with long whitish or grayish hairs. Tail is bicolored, pale below and dark brown above at base and becomes dusky to white toward tip. Ears are relatively short. Black vibrissae are long and coarse, with mystacial ones reaching posteriorly to shoulders. Forefeet have four digits, with digit two and three nearly twice the length offirst or fourth digits; all toes have nails rather than claws. Hindfeet have five digits, with reduced hallux but similar medial digit proportions. Palmar and plantar surfaces are orange. Compared with the two other dactylomyine genera, the Atlantic Bamboo Rat has several unique craniodental features, including shortened muzzle, nearly parallel maxillary tooth rows, tetralophodont cheekteeth, large dP, tooth with a well-developed anteroconid, and labial and lingualflexi that remain separate or wear to U-shaped fold rather than Yor V-shaped folds. Chromosomal complement is 2n = 98 and FN = 126.

Habitat. Primary forest, especially along riparian corridors, and old secondary growth with diverse bamboo understory from sea level to elevations of ¢.900 m. Primary forest habitats include native bamboo such as Chusquea bambusoides, Guadua sp. , and Merostachys sp. (Poaceae) ; those in disturbed habitats are primarily introduced Phyllostachys sp. and Bambusa sp. (Poaceae) .

Food and Feeding. Most important food items of Atlantic Bamboo Rats include large terminal or small lateral shoots, dry bamboo stems or sheets and leaves, or small green branches. They can consume 100 g (fresh weight) of bamboo tissues per night—a food rich in water and cyanide toxins and low nutritive content. While feeding, individuals remove outer, hard, and spiny sheet from culms using their incisors while holding branches with specialized hands and feet, and subsequently consuming inner tissues of shoots by directed chewing. They also forage on dry, spineless sheets found at bases of lateral branches, holding them with their forefeet while chewing. Leaves are cut at petioles from bases of lateral branches with incisors, while holding the branch with one hand, and then held by the other forefoot during consumption. A large shoot can weight 1600 g (including sheet) and at least one-fourth of the inner part can be eaten in a single night. The Atlantic Bamboo Rat has a simple, acidic stomach to detoxify bamboo cyanides. These bamboo rats can be located at night from piles of partially consumed bamboo materials that have fallen on the ground and by grinding sounds made while an individual masticates hard materials.

Breeding. Young Atlantic Bamboo Rats are born precocial and large-sized. One 600g female was found with two near-term embryos weighting 60 g and 62 g in February. Juveniles have delayed dispersal, staying in parents’ home ranges until near or at adult size. Individuals usually build large nests in bamboo thickets, although no such nests are apparently constructed with any introduced bamboo species in Brazil.

Activity patterns. Atlantic Bamboo Rats are arboreal and mainly active at night, but they have been observed feeding and calling at sunset.

Movements, Home range and Social organization. Atlantic Bamboo Rats are agile and rapid climbers, moving through complex bamboo by grasping stems and shoots with their specialized hands and feet. Mean distance traveled per night was 259 m using radio-telemetry. Large bamboo nests may serve as diurnal restsites, but individuals have also been observed perched and resting on horizontal branches. Some rare radiotracked individuals were observed at bases of bamboo clumps well below their normal rest sites, possibly to avoid predators (e.g. capuchin monkeys, Cebus sp.). In the Biological Reserve of Poco das Antas, Rio de Janeiro State (south-eastern Brazil), home ranges are 0-09 ha for males and 0-06 ha for females. Densities reached 1-5 ind/km?, Only one radio-tracked male had a home range of 0-16 ha. Males and females used an average of 3-5 restsites, with two sites used less than 50% of the time. These rest sites were usually located at extreme perimeters of home ranges. Some radio-tracked Atlantic Bamboo Rats opportunistically expanded their home ranges when individuals in adjoining home ranges were removed. In Rio Grande do Sul State of southern Brazil, density was estimated at 4-3 ind/km?. Individuals are usually difficult to locate in the canopy and are rarely seen below 3 m. Most reported sightings result from vocalizations or noise generated by feeding individuals. Usually individual callers sat at culms and produced sounds, while throwing muzzles forward at each note. Calling is most common during the night but sometimes begins at sunset. Calls are characterized by series of similar notes produced over similar time intervals. Frequency of these calls is 4 kHz, each note is 0-2 seconds long, and vocalizations might last from less than a second to several minutes. Role of vocalizations is not clearly understood, but it is likely related to predator presence or space and resource defense. Atlantic Bamboo Rats mainly rely on slowly renewed and sparsely dispersed large bamboo shoots, and males and females are likely territorial, particularly females during pregnancy and lactation. Atlantic Bamboo Rats are thought to be socially monogamous, expressed in part by reduced sexual polymorphism, bi-parental care, and delayedjuvenile dispersal. After weaning, both sexes show parental care including food provisioning, grooming, and huddling. Monogamy, however, might be flexible depending on availabilities of food resources because females have reduced home ranges and are confined to widely spaced bamboo patches—two attributes that decrease possible male defense and might promote polygamy. Extensive bi-parental care might also reduce risk of inexperienced young falling from trees and increase availability of low-energy bamboo food.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The Atlantic Bamboo Rat is rarely seen, difficult to locate, and even more difficult to trap. It has been reported to colonize new areas with introduced bamboo species and where little natural vegetation persists, but most museum specimens come from primary or secondary forests in highland areas. In view of a highly specialized bamboo-related ecology, this endemic Atlantic Forest species requires additional surveys and research to document possible conservation needs.

Bibliography. Costa et al. (2003), Crespo (1982), Eisenberg & Redford (1999), Emmons (1990, 1997a, 2005), Franceschi et al. (2008), Hensel (1872a), Jentink (1891), Kierulff et al. (1991), Leite & Patton (2002), Olmos (1992), Olmos et al. (1993), Patton et al. (2015), da Silva, FA. (2014), da Silva, FA. et al. (2012), Silva, L.EB.M. (1993), Silva, R.B. et al. (2008), Stallings et al. (1994), Tate (1935), Thomas (1903b), Wagner (1845), Woods (1993), Woods & Kilpatrick (2005).

Figures

Subspecies and Distribution. K. a. amblyonyx Wagner, 1845 — SE Brazil, from Rio de Janeiro to Santa Catarina states. K. a. pallidior Thomas, 1903 — Parana Basin of E Paraguay, NE Argentina (Misiones Province), and adjacent Brazil.