492.

Gorgas’s Marsh Rice Rat

Oryzomys gorgasi

French: Oryzomys de Gorgas / German: Gorgas-Sumpfreisratte / Spanish: Rata arrocera de marisma de Gorgas

Other common names: Gorgas's Oryzomys, Gorgas's Rice Rat

Taxonomy. Oryzomys gorgasi Hershkovitz, 1971, “Loma Teguerre (7°64 N, 77° W), Departamento Antioquia, northwestern Colombia.

Oryzomys gorgas: includes curasoae named by D. A. McFarlane and A. O. Debrot in 2001, an extinct subfossil from continental shelf Curacao Island off northern Venezuela. Monotypic.

Distribution. Known only from two localities in trans-Andean N South America, one each in coastal NW Colombia and NW Venezuela; perhaps expected to be found at other coastal areas between these two sites.

Descriptive notes. Head—body 94-152 mm,tail 116-138 mm, ear 15-17 mm, hindfoot 30-32 mm. No specific data are available for body weight. Gorgas’s Marsh Rice Rat closely resembles other species of Oryzomys in external appearance, with small ears and dense mystacial vibrissae recurved along oral margins. Tail is distinctly bicolored at base, with visible epidermal scales and ventral caudal hairs longer than those on caudal dorsum, terminating in a short (c.6 mm) pencil of hairs. Hindfeet are distinctly modified for semi-aquatic locomotion, with thin fringes ofsilvery hairs along metatarsal margins; plantar surfaces are hairless and smooth, but distal to thenar pad, plantar epithelium is densely tubercular; small webs occur between second, third, and fourth digits extending less than one-half the length of first phalange on any digit; and bases of claws lack prominent ungual tufts. Cranially, Gorgas’s Marsh Rice Rat differs from other species of Oryzomys by its short and blunt rostrum, posteriorly tapering incisive foramina, absence of sphenopalatine vacuities, and broad hamular process of squamosal that reduces subsquamosal fenestra to a small opening. Karyotype is unknown.

Habitat. Coastal environments of mangroves, freshwater-inundated grasslands, and salt marshes. The single known Colombian specimen of Gorgas’s Marsh Rice Rat was trapped in a freshwater swamp in an area of high annual rainfall; Venezuelan specimens were trapped in mangroves along a swampy lagoon margin surrounded by xerophytic vegetation.

Food and Feeding. Gorgas’s Marsh Rice Rat is omnivorous. Stomach contents from the single known Venezuelan locality contained crustaceans, insects, grass and other plant seeds, and other plant parts. Adult and larval parasitic nematodes were present in stomachs, suggesting that insects that serve as intermediate hosts for these parasites are a regular part of the diet of Gorgas’s Marsh Rice Rat.

Breeding. No information.

Activity patterns. Gorgas’s Marsh Rice Ratis terrestrial and semi-aquatic.

Movements, Home range and Social organization. No information.

Status and Conservation. Classified as Endangered on The IUCN Red List. Gorgas’s Marsh Rice Rat occupies a small range, its distribution is highly fragmented, it is known from very few localities, and its coastal wetland habitat is declining in extent. The single Venezuelan locality is in a protected area (Ciénaga de Los Olivitos).

Bibliography. Hershkovitz (1971), McFarlane & Debrot (2001), Ochoa, Gémez-Laverde et al. (2008), Percequillo (2015i), Sanchez et al. (2001), Voss & Weksler (2009).