551.

Kemp's Grass Mouse

Deltamys kempi

French: Akodon de Kemp / German: Kemp-Grasmaus / Spanish: Raton campestre de Kemp

Other common names: Delta Mouse, Kemp's Akodont, Kemp's Mouse

Taxonomy. Deltamys kempi Thomas, 1917, “Isla Ella, in the delta of the Rio Parana, at the top of the La Plata Estuary,” Buenos Aires, Argentina. Tentatively, U. F. J. Pardinas and colleagues located Isla Ella at 34°22’S, 58°38’W, Delta del Parana, Buenos Aires, Argentina.

Deltamys kempi is the type species of the genus. Uruguayan populations initially were distinguished based on morphological grounds under the subspecies langguthi, a proposition not corroborated by studies of molecular markers. Conversely, these studies suggest existence of two different reciprocally monophyletic clades roughly north and south of Lagoa dos Patos (Brazil). An undescribed species (or a new genus closely related to Deltamys ?) was highlighted as present in southern Brazil based on a few specimens from Santa Catarina and northern Rio Grande do Sul states, and very recently a new species was described, D. araucanria, based on animals from Araucaria forest in Rio Grande do Sul State, Brazil. Alpha-taxonomy in Deltamys is still open to research, particularly based on morphology. Monotypic.

Distribution. S Brazil, Uruguay, and extreme CE Argentina .

Descriptive notes. Head—body 100 mm (mean value for males), tail 83-5 mm, ear 12 mm, hindfoot 23 mm; weight 22 g. Males are slightly larger and heavier than females. Kemp's Grass Mouse is small akodont-like sigmodontine, with conspicuously small eyes and dark-colored velvety pelage. Dorsum is shiny blackish brown, and venter is dull brownish gray. Tail, only faintly bicolored, is slightly shorter than head-body length and finely haired throughout. Hindfeet are narrow and have six plantar pads and moderately long claws (c.2-5 mm in adults); ungual tufts are whitish or brown and are typically shorter than claws. Chromosomal complement has 2n = 37 or 38, FN = 38.

Habitat. Marshy environments, particularly borders of wetlands, swamps dominated by sedges ( Scirpus giganteus and Schoenoplectus californicus, both Cyperaceae), flooded grassland, relatively pure stands of pampas grass ( Cortaderia selloana, Poaceae), areas of dense grassy cover and with reeds and grasses usually without trees; and more rarely in woodland with high diversity of trees and shrubs.

Food and Feeding. Stomachs of Kemp's Grass Mice contained insects, a few pieces of seeds, and limited remains of green plants. Individuals captured in winter had mainly arthropod remains, mostly insects, and insect larvae in their stomachs.

Breeding. Kemp's Grass Mice with reproductive signals are recorded in late winter (August), spring, and summer (September—March). Weights of reproductive individuals were 19-29 g for males and 17-28 g for females. Spherical nest is made of plant fibers and sometimes placed in hollow logs. In Uruguay, one nest with three young was found in a fallen palm ( Syagrus capitata, Arecaceae), with cavity entrance 30 cm aboveground. Population structure suggests significant early spring recruitment to late spring—summer population. Individuals weighing 18-26 g are dominant in autumn and winter populations. Very old individuals (weighing more than 26 g) were found mostly in spring and summer. Life span reached a maximum of 18 months.

Activity patterns. Kemp's Grass Mouse is terrestial, and trapping data indicate that it is nocturnal. Despite predilection for wet environments, they exhibit no special external adaptations for aquatic life. Its long rostrum, morphologies of manus and pes, and claw length have been associated with digging habits, and some degree of fossoriality apparently is suggested by body proportions. Captive individuals sometimes dug but usually foraged and looked for resting sites on the ground.

Movements, Home range and Social organization. No information.

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

Bibliography. Bianchini & Delupi (1994), Castro et al. (1991), D’Elia et al. (2003), Gentile de Fronza et al. (1979, 1981), Gonzalez & Martinez (2010), Gonzalez & Massoia (1995), Gonzalez & Pardinas (2002), Montes et al. (2008), Pardinas & Teta (2015a), Pardinas et al. (2007), Quintela (2014), Sbalqueiro et al. (1984), Suarez & Bonaventura (2001), Teta, Cueto & Suarez (2007), Teta, D'Elia et al. (2016), Thomas (1917a), Udrizar et al. (2005), Ventura et al. (2011).