514.

Uruguay Swamp Rat

Scapteromys tumidus

French: Akodon bouffi / German: Uruguay-Sumpflandratte / Spanish: Rata de ciénaga de Uruguay

Taxonomy. Mus tumidus Waterhouse, 1837, “ Maldonado,” Maldonado Department, Uruguay .

Scapteromys tumidus is the type species of the genus. Monotypic.

Distribution. Extreme S Brazil (Rio Grande do Sul State) and most of Uruguay.

Descriptive notes. Head-body 150-195 mm, tail 133-176 mm, ear 20-29 mm, hindfoot 36-45 mm; weight 50-165 g. The Uruguay Swamp Ratis slightly larger and heavier than the Argentinean Swamp Rat (S. aquaticus). Tail is ¢.86% and earis c.14% of head-body length. Dorsum is brownish to ocherous brown, and venter is ivory white. Subtle cranial differences exist between the Uruguay Swamp Rat and the Argentinean Swamp Rat. Chromosomal complement is 2n = 24, FN = 40.

Habitat. Typically Atlantic coastal swamps, lakes, and lagoons and floodplains of the Uruguay River. The Uruguay Swamp Rat is usually trapped in marshy or low places near freshwater with high vegetative cover.

Food and Feeding. The Uruguay Swamp Rat is mainly insectivorous; stomach contents of eleven individuals trapped in April-May were 85% invertebrate, mostly coleopterans and particularly scarabaeid beetles.

Breeding. Male Uruguay Swamp Rats were reproductively active every month of the year except January, June, and July, with peak testis size in April-May; pregnant females were caught in spring and summer. Litters typically have two embryos.

Activity patterns. Most Uruguay Swamp Rats have been trapped at dusk or during the night; diurnal activity is limited to juveniles and subadults and may be correlated with high population levels. Charles Darwin collected the holotype ofthis species and wrote, “This rat was caught in so wet a place amongst the flags bordering a lake, that it must certainly be partly aquatic in its habits.” Although claws of the Uruguay Swamp Rat are adapted to burrowing (a fact reflected in the etymology of the genus name), it seems not to make runways of its own but frequently uses runways constructed by other rodents.

Movements, Home range and Social organization. No information.

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

Bibliography. Barlow (1969), Bonvicino et al. (2013), Brum-Zorrilla, Lafuente & Kiblisky (1972), Brum-Zorrilla, Oliver et al. (1986), D’Elia & Pardinas (2004, 2015), Gonzalez (1994), Hershkovitz (1966a), Queirolo et al. (2016), Quintela, Fornel & Freitas (2016), Quintela, Goncalves et al. (2014), Waterhouse (1837 1839).