Blastocerus dichotomus (Illiger, 1815)

Don E. Wilson & Russell A. Mittermeier, 2011, Cervidae, Handbook of the Mammals of the World – Volume 2 Hoofed Mammals, Barcelona: Lynx Edicions, pp. 350-443 : 436-437

38.

Marsh Deer

Blastocerus dichotomus

French: Cerf des marais / German: Sumpfhirsch / Spanish: Ciervo de los pantanos

Taxonomy. Cervus dichotomus Illiger, 1815 ,

Lake Ipoa, Paraguay.

This species is monotypic.

Distribution. E Peru, Bolivia, Brazil (S of Amazonia), Paraguay, and N Argentina.

Descriptive notes. Head-body 180 cm (males) and 165 cm (females), tail 13-15 cm, shoulder height 115-130 cm (males) and 100-115 cm (females); weight 110-130 kg (males) and 70-100 kg (females). Bucks are on average 30-50% heavier than does. Relatively large-sized deer, with a narrow face and long, thin legs; bushy tail. Legs black up to the radius. Muzzle black, white ring around eyes. Yellowish tail with black tip. Fawns unspotted. Permanent dentition of 32 teeth. Preorbital, nasal, rear interdigital, and tarsal glands are present. Antlers of adult males are typically fourto five-tined, 40-45 cm long, with radial branching; the main beam bifurcates not far from the base and each tine tends to bifurcate. Yearling males have simple spikes; two-year-old subadults have forked beams. Antler casting occurs in almost every month of the year, with a peak in September. Hooves are elongated; the pads of the hoof are connected by a strong membrane and can be spread up to 10 cm apart.

Habitat. It occurs in several kinds of wetlands, including marshy habitats and seasonally flooded areas. It avoids forests and selects areas with a water depth of 30-60 cm.

Food and Feeding. It is an intermediate feeder with a tendency to browse easily-digestible food. The diet consists mainly of semi-aquatic and aquatic plants.

Breeding. It is not yet known at what age females attain puberty. They have an estrous cycle of 24 days. The mean length of gestation is 271 days. In captivity there is no clear seasonality in reproduction. In the Pantanal of Brazil, the main fawning season is in April-August, with a higher frequency of births in May-July, when the water level is declining. In Argentina births are mainly in December—March. Does give birth to a singleton, weighing on average 4-5 kg. The fawn is relatively precocious and at five days of age it begins to follow its mother. Jaguars (Panthera onca), Pumas (Puma concolor), caimans and anacondas may prey on full-grown Marsh Deer; Maned Wolves (Chrysocyon brachyurus) may prey on fawns.

Activity patterns. It is mostly diurnal, but it may become nocturnal when persecuted. It avoids eating during the hottest hours of the day.

Movements, Home range and Social organization. Its large haunches and long limbs make it a saltatorial deer. Its movements follow the advance and recession of the water level. Males have home ranges of 800-5000 ha, females of 300-2400 ha. It is quite adept at swimming. It is a weakly gregarious species. Females form small family groups and males are mostly solitary.

Status and Conservation. CITES Appendix I. Classified as Vulnerable on The IUCN Red List and decreasing. Overhunting and habitat loss have drastically decreased the original distribution, creating small isolated populations. It was extinct in Uruguay by the late 1950s. The largest population lives in the Pantanal wetland, in Brazil, where in 1991-1992 a large scale survey estimated it at around 44,000 animals. In Argentina, estimates for Ibera marshes are around 1100-2000 animals, and other important populations are known from Formosa Natural Reserve and the Parana River Delta. In Bolivia, several populations are known from the Beni savannas and Noel Kempff Mercado National Park, and in Pampas del Heath, north of Madidi National Park, a recent survey gives an estimate of around 700 Marsh Deer. The main population in Paraguayis in the Yacyreta region where density is low. Hydroelectric dams and drainage for agriculture continue to reduce its range. Poaching and diseases transmitted by introduced livestock contribute to its decline. Pollution of water associated with gold mining is an additional threat in Pantanal, Brazil.

Bibliography. Duarte et al. (2008), Pinder & Grosse (1991), Piovezan et al. (2010), Schaller & Vasconcelos (1978), Tomas & Salis (2000).

Figures

36. White-tailed Deer (Odocoileus virginianus), 37. Mule Deer (Odocoileus hemionus), 38. Marsh Deer (Blastocerus dichotomus), 39. Pampas Deer (Ozotoceros bezoarticus), 41. South Andean Huemul (Hippocamelus bisulcus), 42. Northern Pudu (Pudu mephistophiles), 43. Southern Pudu (Pudu puda)

Distribution. E Peru , Bolivia , Brazil (S of Amazonia), Paraguay , and N Argentina .