The genus Oxymycterus Waterhouse, 1837: Comprises approximately 25 species endemic to South America, distributed mainly across Brazil, Paraguay, Uruguay, Bolivia, and Argentina. They inhabit a wide variety of environments with abundant vegetation cover, including grasslands, tall grasslands, wetlands, savannas, and open forests. The genus name derives from the Greek oxys = sharp and mykter = snout, referring to its most distinctive characteristic: a long, pointed snout adapted for probing the ground in search of food.
Morphological description: The red hocicudo Oxymycterus rufus Fisher, 1814 is one of the largest representatives of the small sigmodontine rodents found in Argentina. It has a robust, compact body; the head-and-body length ranges from 13 to 16 cm, while the tail measures between 7 and 12 cm, always shorter than the body.
Its most distinctive feature is its long, narrow, highly mobile snout, reminiscent of that of a shrew. It possesses long, highly sensitive whiskers that allow it to explore vegetation and the ground while searching for food. The forelimbs bear strong claws adapted for turning over soil, leaf litter, and plant debris.
The fur is relatively dense and somewhat coarse. The dorsal region varies from cinnamon-brown to reddish-brown and cinnamon, generally crossed by a darker mid-dorsal stripe extending from the head to the rump. The flanks are ochre-colored, while the underparts are grayish or yellowish. The ears are small and partially concealed by the fur, and the eyes are relatively small.
Its robust appearance, short tail, and characteristic elongated snout readily distinguish it from most other field mice occurring in Argentina.
Natural history: This is a primarily solitary species with semifossorial habits. Although it carries out much of its activity above ground, it uses natural shelters among vegetation, small ground cavities, and shallow burrows where it rests and protects itself from predators.
It is active both during the day and at night, moving mainly through dense grasslands and other habitats with abundant herbaceous cover. It rarely remains exposed in open areas, making it an infrequently observed species in the wild.
Its elongated snout, together with the well-developed claws of the forelimbs, represents a remarkable adaptation for locating small invertebrates hidden among leaf litter and within the upper few centimeters of the soil. During this activity, it continuously displaces plant debris and small amounts of substrate using rapid movements of its forefeet.
Populations may undergo marked fluctuations in abundance from year to year, mainly associated with variations in rainfall, vegetation productivity, and food availability.
Distribution and habitat: The species is widely distributed across eastern and central Argentina, Uruguay, southern Brazil, and parts of Paraguay.
In Argentina, it occurs primarily in the Pampas and Espinal regions, also reaching parts of the Chaco and several mountain ranges in the central part of the country. It mainly inhabits natural grasslands, tall grasslands, wetlands, stream margins, seasonally flooded lowlands, and other habitats with abundant herbaceous vegetation. It also occurs along the edges of forest patches and in mountainous areas with native grasslands.
Over recent decades, several studies have documented an increase in its abundance within agricultural landscapes of the Pampas region. It is now commonly found along roadsides, railway embankments, road margins, drainage canals, and crop edges, habitats that serve as important dispersal corridors and refuges within agricultural landscapes.
Diet: Unlike most small South American rodents, whose diets are dominated by seeds and other plant resources, the red hocicudo shows a marked specialization in feeding on invertebrates.
It is estimated that at least 70% of its diet consists of insects and other small soil invertebrates, including beetles, larvae, ants, spiders, and earthworms, which it locates using its elongated snout and highly sensitive whiskers. The remainder of its diet consists of leaves, seeds, fruits, and other plant resources, whose importance varies according to seasonal availability.
Reproduction: Reproduction occurs mainly during spring and summer, coinciding with the period of greatest food availability. As in most small rodents, females may produce several litters during the breeding season, allowing populations to recover rapidly when environmental conditions are favorable.
Predators: The red hocicudo is a common prey item for numerous birds of prey and carnivorous mammals. It has been recorded in the diet of nocturnal species such as the Great Horned Owl (Bubo virginianus) and the American Barn Owl (Tyto furcata), as well as diurnal raptors including the White-tailed Kite (Elanus leucurus), the Variable Hawk (Geranoaetus polyosoma), and other species of hawks and eagles.
Among carnivorous mammals, predation has been documented by the Pampas Fox (Lycalopex gymnocercus), while in mountain grasslands it also forms part of the diet of the Córdoba Red Fox (Lycalopex culpaeus smithersi).
Importance and threats: The red hocicudo plays an important ecological role as a consumer of terrestrial invertebrates, contributing to the natural control of numerous insect and other arthropod populations. At the same time, it serves as a food resource for a wide variety of birds of prey, carnivorous mammals, and snakes, forming an integral part of the food webs of grasslands, wetlands, and agricultural ecosystems.
In Argentina, it is classified as a species of Least Concern (LC) due to its wide distribution and because many of its populations appear to remain stable or have even increased over recent decades.
Nevertheless, the loss and fragmentation of natural grasslands, wetland drainage, agricultural intensification, and the use of agrochemicals continue to represent potential threats to some populations. Despite this, the species has demonstrated a remarkable ability to persist in modified landscapes where natural vegetation corridors, such as roadsides, railway embankments, and stream margins, provide food, shelter, and dispersal routes.
Bibliography:
Calfayan, L. M., Cavia, R., Fraschina, J., Guidobono, J. S., Gorosito, I. & Busch, M. (2023). Environmental drivers of long-term variations in the abundance of the red hocicudo mouse (Oxymycterus rufus) in Pampas agroecosystems. Integrative Zoology, 18:330–343.
De Oliveira, J. A. & Gonçalves, P. R. (2015). Genus Oxymycterus. En: Patton, J. L., Pardiñas, U. F. J. & D´Elía, G. (Eds.). Mammals of South America. Volume 2. Rodents. University of Chicago Press.
Fraschina, J., León, V. & Busch, M. (2014). Role of landscape scale in rodent distribution and abundance in Pampean agroecosystems. Journal of Agricultural Science, 6:22–33.
Gómez, M. D., Coda, J., Simone, I., Martínez, J., Bonatto, F., Steinmann, A. & Priotto, J. (2015). Agricultural land-use intensity effects on small mammal communities in the Central Pampas of Argentina. Mammal Research, 60:415–423.
Gómez Villafañe, I. E. et al. (2005). Guía de roedores de la provincia de Buenos Aires. LOLA.
Gómez Villafañe, I. et al. (2019). Oxymycterus rufus. En: Categorización 2019 de los mamíferos de Argentina según su riesgo de extinción. SAyDS–SAREM.
Torres, R. 2018. Orden Rodentia. Pp. 44–75, in: Mamíferos de Córdoba. R. Torres & D. Tamburini, eds. Universidad Nacional de Córdoba, Córdoba.
Author of this compilation: Enzo Rossi – 12/07/2025