400.

Franciscos’ Arboreal Rice Rat

Oecomys franciscorum

French: Oecomys des Francisco / German: Francisco-Baumreisratte / Spanish: Rata arrocera arboricola los Franciscos

Other common names: Franciscos’ Oecomys

Taxonomy. Oecomys franciscorum Pardinas et al., 2016, 0-4 km NW of the junction between Ruta Nacional 11 and Riacho Pilaga, Estacion de Animales Silvestres Guaycolec, Formosa, Argentina.

Morphological and molecular variation of O. franciscorum was detected along its distribution, suggesting the need for additional taxonomic research. Monotypic.

Distribution. SC Brazil (Mato Grosso do Sul State) and NE Argentina (Formosa and Chaco provinces); probably in E Paraguay.

Descriptive notes. Head—body 139-151 mm, tail 166-176 mm, ear 20-22 mm, hindfoot 28-5-30 mm; weight 60-80 g. Franciscos’ Arboreal Rice Ratis sligthly larger than the Mamore Arboreal Rice Rat ( O. mamorae). Its pelage is soft, abundant, and deep (individual hairs are 16 mm long over mid-rump). Dorsal hairs have dark gray bases and terminal yellowish tips (c¢.3 mm long); they are finely intermixed with longer black guard hairs projecting c.5 mm beyond fur over mid-dorsum. General tones are bright on dorsum and paler on flanks. Dorsal and ventral colors are moderately demarcated, and countershading is conspicuous. Venter is generally yellowish; hairs of throat and chest are tinged whitish; and perianal and genital areas, abdomen, and internal surfaces of hindlimbs are washed reddish. Pheomelanin pigments are paler toward rostrum, giving face a yellowish appearance. Short whitish hairs are present around lips and rhinarium, and sides of rostrum are bordered by small reddish hairs. Mystacial vibrissae are abundant and black, the longest surpassing external borders of pinnae. Tail is pale brown, slightly darker on dorsum, with its dorsal and ventral surfaces finely covered with short rigid hairs that do not conceal fine-scale pattern below. A rudimentary tuft (3 mm) is present at tip oftail. Ears are comparatively large, oval, and covered by short, delicate reddish hairs, giving a general cinnamon tone and naked appearance. Manus and pes are covered dorsally with dark brown hairs; sides of manus and pes and toes are covered with tawny to whitish hairs. Hindfeet are relatively short and broad; ungual tufts are bright white and well-developed on second through fourth digits. Four mammary pairs are present. Chromosomal complement is unknown in Argentine populations, but itis 2n = 72, FN = 90 in Brazilian Pantanal populations.

Habitat. Humid Chaco gallery forests along rivers and streams with dense Bromelia serra ( Bromeliaceae) understories and interior of Chaco biome along riparian corridors in gallery forests.

Food and Feeding. Stomach of one Franciscos’ Arboreal Rice Rat contained a mass of green matter, probably plant remains.

Breeding. Holotype was a scrotal male collected in August, suggesting at least reproductive activity in late winter.

Activity patterns. Franciscos’ Arboreal Rice Rats are nocturnal, according to three individuals trapped and several retrieved from owl pellets. They are arboreal or semiarboreal and have been trapped on the ground and up to 2 m high in vegetation.

Movements, Home range and Social organization. No information.

Status and Conservation. Not assessed on The IUCN Red List. Distribution encompasses close to 20,000 km?®. Its restriction to forested riparian habitats, combined with the fact that its Chacoan environments, especially those of the Humid Chaco, are being extensively converted to agroecosystems, suggests that it could be classified as Vulnerable.

Bibliography. Andrade & Bonvicino (2003), Carleton et al. (2009), Massoia & Fornes (1965¢c), Myers (1982), Myers & Wetzel (1979), Orozco et al. (2014), Pardinas & Ramirez-Llorens (2005), Pardinas, Teta et al. (2016).