747.

Southern Big-eared Mouse

Loxodontomys micropus

French: Phyllotis austral / German: Sidliche GroRohrmaus / Spanish: Raton orejudo meridional

Other common names: Southern Pericote

Taxonomy. Mus micropus Waterhouse, 1837, “ Santa Cruz,” Argentina . Restricted by G. R. Waterhouse in 1839 to “caught in the interior plains of Patagonia in lat. 50°, near banks of the Santa Cruz.”

The holotype of L. micropus was secured by Darwin at an indeterminate point along the Santa Cruz River during a single trip to the interior of the southern Patagonia made by Captain R. FitzRoy and his crew in April-May 1834. According to Darwin’s notes, this animal probably was captured in the vicinities of the present Estancia Los Guindos. Mus micropus is the type species of the genus Loxodontomys . The taxon pikumche with type locality near Santiago, Chile, was distinguished from micropus mostly on karyological grounds, but it was demonstrated that the holotype of pikumche was a composite. Although the skin belongsto a specimen of Loxodontomys, skull and mandibles belong to a subadult from the genus Phyllotis . P. Teta and colleagues in 2011 restricted the name pikumche to the skin, an act that maintains the linkage of the name to Loxodontomys . Nevertheless, status of pikumche—whether a valid species or a subjective synonym—cannot be addressed until the genusis properly revised. Similarly, Phyllotis (Auliscomys) micropus fumipes was coined to distinguish animals from Chiloé Island, Chile; its status requires further study. Monotypic.

Distribution. S Chile and SW Argentina .

Descriptive notes. Head—body 99-144 mm (mean 126 mm), tail 830-112 mm (mean 97 mm), ear 15-23 mm (mean 19 mm), hindfoot 25-32 mm (mean 29 mm); weight 30-64 g (mean 47 g). The Southern Big-eared Mouse is medium-sized and robust, with thick, lax, and lusterless pelage. Dorsum is generally gray to brownish, grizzled with brownish yellow and intermixed with dusky black; venter is paler, often washed with white or yellow. Ears are proportionately small and densely covered with short brown hair. Tail is about as long as head-body length. Post-auricular patches are reduced or absent. Soles of hindfeet are naked and lightly scutellated, with six small tubercles. Claws are well-developed, especially those of hidfeet, reaching 3 mm in length. Females have four pairs of mammary glands. Specimens from northern populations have distinctly countershaded body pelage, and tails are more distinctly bicolored. Chromosomal complement is 2n = 34, FN = 36 in southern Chilean populations and 2n = 32, FN = 34 in northernmost Chilean and Argentinean populations.

Habitat. Nothofagus (Nothofagaceae) forests, precordilleran shrubby steppes, humid dense grasslands, and open habitats of spiny shrubs and dry grasslands on hard soil pavements. The Southern Big-eared Mouse is particularly abundant in ecotones between Nothofagus forests and Patagonian steppes. In precordilleran shrubby steppes of north-western Argentinean Patagonia, it has been caught in humid, dense grasslands or among bushes such as Berberis (Berberidaceae) or thorny Colletia spinossissima ( Rhamnaceae). In Chile, it is found in bushy forests of Nothofagus pumilio and N. antarctica and of N. dombeyi and Araucaria araucana (Araucariaceae), with dense, low vegetation of mountain bamboos Chusquea (Poaceae) . Along an elevational transect through temperate rain forests in Valle de La Picada (Osorno, Chile), the Southern Big-eared Mouse was caught more commonly in shrubby habitats of N. dombeyi and Drimys winter: ( Winteraceae) at higher elevations.

Food and Feeding. Fecal pellets from live-trapped Southern Big-eared Mice in shrubland habitats in Argentinean Patagonia typified the diet as herbivorous-graminivorous, with an important proportion of Poa (Poaceae) but also other herbs. Stomachs can be filled with up to 10 g of chewed green leaves and fungi. Stomachs from Chile contained mainly seeds (17%), fruits (28%), flowers (20%), other plant tissues (23%), and fungi (6%). In humid, dense grasslands of north-western Patagonia, stomachs contained mainly grasses, sedges, and rushes (e.g. Carex, Festuca argentina, Juncus, Poa pratensis, and Stipa). Captive individuals ate fungi of several kinds, including Cyttaria (Cyttariaceae); leaves of Vicia (Fabaceae), Oenothera (Onagraceae), and Mulinum spinosum ( Apiaceae); and blossoms of dandelion ( Taraxacum officinale, Asteraceae), Colletia spinossissima ( Rhamnaceae), and M. spinosum. They ate stems of Calceolaria (Calceolariaceae) but not blossoms. Individuals from Bariloche in Argentina ate nine taxa of fungi.

Breeding. Reproductive season of the Southern Big-eared Mouse starts at the beginning of spring and lasts until the end of summer or early autumn. All overwintered adults are in breeding condition by spring, and by the end of November, a few youngof-the-year have large testes and vesicular glands. Breeding males had testes of 8 mm or longer and vesicular glands of 10 mm or longer. All overwintered females were pregnant or parous in spring. In north-western Argentinean Patagonia, pregnant females were caught early in November, and lactating females in mid-November. In Chile, nine of 13 parous females and 14 of 18 pregnant females were caught in November-December; 13 postpartum females were collected in April. By mid-February and March, few individuals remain reproductively active, and in April, most females were nulliparous or lactating. Litters had 4-5 young. There was no relationship between number of fetuses and age of female.

Activity patterns. The Southern Big-eared Mouse is terrestrial, mostly nocturnal, but sometimes diurnal.

Movements, Home range and Social organization. In humid dense grasslands of northwestern Patagonia, the Southern Big-eared Mouse excavates tunnel systems, with numerous entrances and food chambers. Densities in a uniform forest of N. antarctica varied from 5-1 ind/ha in May to 1:7-4-2 ind/ha in November. In a mixed forest of N. dombeyi and N. pumilio, 0-9 ind/ha, 1-1 ind/ha, and 4-1 ind/ha were recorded in May, November, and April, respectively. In Patagonia, sex ratio of 151 individuals of all ages was biased toward females (55%). Spring sex ratio was equal, but autumn sex ratio was only 35% male, based on 37 captures. Two females that weighed 60 g and 65 g when captured and released in May were recaptured 5-5 months later and had gained 14 g and 13 g, respectively. In captivity, numerous adults can live amicably in the same cage.

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

Bibliography. Canén et al. (2010), Cantoni et al. (2001), Hershkovitz (1962), Kelt (1994, 1996), Mann (1978), Meserve et al. (1988), Monjeau (1989), Novillo et al. (2009), Osgood (1943a, 1947), Pardinas, D'Elia, Patterson & Teta (2016b), Patterson et al. (1989, 1990), Pearson (1958, 1983, 1995), Pearson & Pearson (1982), Perez et al. (1989), Pine et al. (1979), Polop et al. (2015), Reise & Venegas (1987), Simonetti & Spotorno (1980), Spotorno, Cofré et al. (1998), Teta, Pardinas & D’Elia (2011), Teta, Pardinas, Salazar-Bravo & D'Elia (2015), Teta, Pardifas, Udrizar & D’Elia (2009), Thomas (1916a, 1919a), Udrizar et al. (2008), Venegas (1974), Waterhouse (1837, 1839).