447.

Long-tailed Pygmy Rice Rat

Oligoryzomys longicaudatus

French: Colilargo du Chili / German: Langschwanz-Zwergreisratte / Spanish: Rata arrocera pigmea de cola larga

Other common names: Long-tailed Colilargo

Taxonomy. Mus longicaudatus Bennett, 1832, “ Chili.” Restricted by W. H. Osgood in 1943 to Valparaiso, Chile.

Current concept of O. longicaudatus includes numerous nominal forms, most of them very poorly known and named by R. A. Philippi in 1900, plus Hesperomys (Calomys) coppingeri, Oryzomys magellanicus mizurus, and Oryzomys longicaudatus pampanus. Here, Mus magellanicus, with type locality in Port Famine, Chile, is treated as a junior synonym of O. longicaudatus . Entire taxonomy of O. longicaudatus needs a new comprehensive approach that includes molecular markers and morphological data; this is particularly important because O. longicaudatus is the main reservoir of hantavirus in the Andes. Monotypic.

Distribution. Chile and W, SC & S Argentina .

Descriptive notes. Head-body 100 mm, tail 118 mm, ear 16 mm, hindfoot 28 mm, and weight 36 g (mean values for Neuquén Province); Head-body 103 mm, tail 109 mm, ear 18 mm, hindfoot 28 mm, and weight 41 g (means for Tierra del Fuego Province); Head-body 93 mm, tail 127 mm, ear 16 mm, hindfoot 28 mm, and weight 33 g (means for Chubut Province). The Long-tailed Pygmy Rice Rat is the largest species of Oligoryzomys . Males are larger and heavier than females; mean weights of Chilean specimens are 37 g for males vs. 31 g for females. Important geographical variation in external traits and measurements also occur. Fur is soft, smooth, and luxuriant; hairs are deep ashy gray at bases; those of upper surfaces are fawn or pale rufous, with tips frequently black; those of under surfaces are tipped with white, slightly tinged with fawn; face is covered with short hair of mingled fawn and black; lips are nearly white; vibrissae are extremely long, black at bases and silvery at tips; ears are rounded and of moderate size, covered on inside with short hair the same color as face and on outside with very short whitish hair, scarcely discernible on blackish skin; dorsum is mixed fawn and black, with black disappearing on almost purely fawn sides; front of forelegs and outside of hindlegs are fawn; tail is scaly, with numerous very short bristly hairs, brownish above and nearly white beneath; hairs of upper surface of tarsi are short, very pale fawn approaching white; those of toes are still more white; and lengthened bristles covering claws are almost silvery. Chromosomal complement is 2n = 56, FN = 70.

Habitat. Andean dry coastal shrublands through southern Andean forests (Valdivian, Nothofagus [ Nothofagaceae], and mixed), ecotonal ranges, grassy and shrubby steppes to Magellan tundra, from sea level to elevations of ¢.2000 m. The Long-tailed Pygmy Rice Rat also occurs in margins of rivers that dissect Patagonia independently of main habitats; it does not occur in steppe away from bushes. Blackberry and wild rose tangles are preferred habitats in north-western Patagonia. The Long-tailed Pygmy Rice Rat showed seasonal fluctuations and interannual differences in abundances between habitats; abundances were greatest in autumn/winter in shrubland and summer/autumn in forest.

Food and Feeding. The Long-tailed Pygmy Rice Rat in Chile is omnivorous, with a tendency to eat seeds and variable proportions of green plants, arthropods, fungi, and fruits (e.g. blackberries and rose hips). Diet changes latitudinally. In Mediterranean Chile, it reportedly granivorous-frugivorous, changing to herbivorous between Mediterranean and Temperate Forests ecoregions. During summer, it prefers fruits and seeds, changing almost exclusively to seeds as winter approaches. In Argentina, studies based on fecal pellets of individuals trapped in shrubland environments of steppeforest ecotones suggested frugivorous-granivorous diets.

Breeding. In north-western Patagonia, ¢.50% the population of Long-tailed Pygmy Rice Rats has reached breeding condition in early spring (late October), and almost every overwintered male is breeding in November-December. Autumn population of females consists of nulliparous and parous individuals born in spring/summer, plus a few pregnant individuals. Pregnancies begin about the first of November. By late November and December, the entire overwintered female population is breeding. Reproductive activity continues in summer. At Fray Jorge National Park (Chile), pregnant females were recorded in March, probably responding to seed production following unusual periods of rainfall. Overall, mean number of fetuses was five, reaching seven during population outbreaks. There was no relationship between age of mother and size of litter. Reproductive activity had seasonal, interannual, and habitat-specific differences. Survival was higher in autumn/winter than spring/summer. Differences in abundance among years can be explained by reproductive parameters and population structure.

Activity patterns. The Long-tailed Pygmy Rice Rat is mostly nocturnal and terrestial, although it climbs well and is sometimes found 3 m aboveground.

Movements, Home range and Social organization. Lineal distances moved were 53-75 m. Large-scale outbreaks (“ratadas”) of Long-tailed Pygmy Rice Rat have been recorded in Chile and Argentina, associated with cyclical masting of the mountain bamboo Chusquea (Poaceae) . Darwin's recorded one of the earliest ratada when Longtailed Pygmy Rice Rats “overran the wooded country south of Concepcion, in swarms of infinite numbers.”

Status and Conservation. Classified as Least Concern on The IUCN Red List.

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