Marsh Deer

Observations: Little is known about the longevity of these animals, but one captive specimen lived 13.7 years (Richard Weigl 2005).

Perception Channels: tactile ; chemical

Blastocerus dichotomus is the largest South American deer, recognizable in part by its large multitined antlers of eight to ten points when mature. Head-body length is usually just under two meters, with shoulder height from 1.0 to 1.2 meters. The pelage is reddish brown in the summer, turning a darker brown in the winter. The tail is reddish orange, bushy, and 10 to 15 cm in length. Marsh deer have large feet with an elastic membrane between the hooves, which may help to keep them from sinking in the mud of their preferred marshy habitat. The legs are black below the carpal/tarsal joints, and there is a black band on the muzzle. Marsh deer have white eye rings and borders of the ears (Mares et al. 1989, Pinder and Grosse 1991, Redford and Eisenberg 1992, Whitehead 1972).

Range mass: 89 to 125 kg.

Average mass: 109 kg.

Sexual Dimorphism: ornamentation

Other Physical Features: endothermic ; bilateral symmetry

Marsh deer prefer marshy, swampy ground with standing water and dense vegetation. They also utilize flooded savannas during the wet season, but stay close to dense stands of reeds or similar vegetation near permanent water during the dry season. Surrounding mountainous terrain may also be favorable, but this may be an artifact of human hunting pressure as access is probably most difficult in mountainous areas (Mares et al. 1989, Whitehead 1972, Redford and Eisenberg 1992).

Terrestrial Biomes: savanna or grassland

Aquatic Biomes: rivers and streams

The marsh deer occurs from savanna patches along the southern margins of Amazonian Peru and Brazil south through northeastern Argentina. While formerly known in Uruguay as well, it is probably now extinct there. The major distributional area is defined by the Paraguay and Parana river basins. Pleistocene fossil deposits indicate that the marsh deer once occurred through northeastern Brazil as well (Magalhães et al. 1992, Pinder and Grosse 1991, Redford and Eisenberg 1992, Whitehead 1972).

Biogeographic Regions: neotropical (Native )

Marsh deer are herbivorous with diets comparable to other species of deer, although marsh deer consume mainly aquatic and riparian vegetation. Stomach analyses found that water lily and other leaves, grass, and browse were consumed. One study found that grass comprises about 50% of their diet and legumes 31% (Redford and Eisenberg 1992).

Marsh deer are valuable game animals, hunted for meat and sport (Roig 1991).

No negative impacts of B. dichotomus on human activities are reported in the literature. Wild ungulates sometimes compete with livestock for forage, and can serve as disease reservoirs, but the marsh deer's preference for wetland habitat may limit contact with some types of domestic livestock. Roxo and Gaspirini (1996) tested 116 marsh deer in Brazil and found that these deer do not harbor brucellosis in the São Paulo State region. Current numbers of deer are so low that negative impacts are very unlikely.

Marsh deer have suffered from uncontrolled hunting and habitat destruction, resulting in small, greatly-fragmented populations. Current hydraulic projects such as the proposed Hidrovia project on the Paraguay and Parana rivers threaten much of what remains of the habitat. One area, threatened with inundation in 1996 by a planned hydroelectric plant on the Parana River, contained 950 individuals making it the second largest population in Brazil. Marsh deer populations have also been reduced by cattle diseases, to which they are quite susceptible. Once common in Argentina, only a few hundred individuals may remain. Blastocerus dichotomus has been apparently extirpated in Uruguay (Mares et al. 1989, Pinder 1996, Quintana et al. 1992, Redford and Eisenberg 1992, Roig 1991, Whitehead 1972).

CITES: appendix i

IUCN Red List of Threatened Species: vulnerable

Blastocerus is occasionally but erroneously spelled "/Blastoceros/", especially in the German literature.

Marsh deer have 66 chromosomes (Duarte and Giannoni 1995).

Fawns are born singly, with mature coloration (no spots). Males do not shed their antlers at any particular time of the year, and may retain them almost two years. Rut usually occurs, however, in October and November, but the breeding season may not be fixed, and males do not seem to be particularly aggressive to each other. Newborn fawns are reported from May to September, as well as from September to November. The gestation period may be as long as a year (Whitehead 1972, Pinder 1996, Redford and Eisenberg 1992, Mares et al. 1989).

Key Reproductive Features: gonochoric/gonochoristic/dioecious (sexes separate); sexual

Average birth mass: 4200 g.

Average gestation period: 270 days.

Average number of offspring: 1.

Marsh deer tend to live in pairs or small family groups of less than six individuals and are more widely distributed during the wet season when there is more suitable habitat available (2). Marsh deer remain hidden during the day and emerge at dusk and graze until early morning on a number of grasses and plants that are soft, protein rich and highly digestible (4) (5). Breeding generally occurs through the year, although further south, mating seems to take place between October and November. Gestation lasts for about eight months, with the females normally giving birth to a single fawn. The young are weaned at six months but remain with their mother for about a year. A female marsh deer is ready to mate again as soon as she has given birth and therefore may be pregnant throughout her breeding years (2) (4).

Although there are protected areas within the range of the marsh deer, they are poorly managed. The Pantanal wetland is a Biosphere Reserve and is considered as a “wetland of international importance”; despite this only a tiny percentage is formally protected (6). A number of conservation proposals have been drafted and initiated including a reintroduction project in Río Pilcomayo National Park, Argentina in 1994, although the results of these are unknown (7). The World Conservation Union (IUCN) suggest future initiatives should include a review of the population status, the creation of new protected areas in suitable habitat and strengthening the management of existing protected areas, including measures to control hunting and exclude livestock (7). One potentially positive aspect for the survival of the marsh deer is that the private sector is increasingly establishing reserves in the area. Despite this, the future of the marsh deer is far from optimistic and a balance needs to be reached between conservation and human land use in the region (6).

This surprisingly shy and secretive deer is actually the largest native deer species in South America. Marsh deer have large, primarily ornamental antlers, which are usually impressively forked, growing to about 60 centimetres in length and weighing, on average, about two kilograms. They are shed irregularly and may be retained for up to two years. Marsh deer also have well-developed hindquarters, making them good at jumping, which is the fastest way to move in water (2). The marsh deer has a shaggy, reddish chestnut coloured coat, with paler undersides of the neck and belly. The muzzle and lips are black, as are the lower legs. The eye is surrounded by a faint white ring and the large ears are lined with white hair. Marsh deer have long, broad hooves that are particularly adapted to the marshy environment, as they are joined by a special membrane and can spread out, giving the hooves a greater surface area, to prevent the deer from sinking into swampy ground (2) (4).

Marsh deer are found in marshy habitats such as floodplains, grasslands and moist forests (4), preferring areas with a good amount of cover for protection, such as reed beds or where grass stands are high (2). This species is predominantly found close to permanent sources of water, favouring areas where the water level is about 50 centimetres, but do wade in areas where the water level reaches over a metre. When the water level gets too high the deer move to higher, dryer locations (2).

Extremely fragmented populations are found south of the Amazon River into northern Argentina, Brazil, Peru, Bolivia and Paraguay. It also used to occur in Uruguay, but is now believed to be extinct there (1). Recognised subpopulations are restricted to the Delta de Paraná in Argentina, the Iberá wetlands (Corrientes Province) in Argentina and the Paraná basin in Brazil (1).

Classified as Vulnerable (VU) on the IUCN Red List 2007 (1) and listed on Appendix I of CITES (3). The Paraná Brazilian Basin subpopulation is classified as Critically Endangered (CR), the Delta del Paraná subpopulation is classified as Endangered (EN) and the Iberá subpopulation is classified as Vulnerable (VU) on the IUCN Red List 2007 (1).

The marsh deer has disappeared from much of its former range as a result of hunting and the expansion of agriculture in central South America. From the early 19th century grasslands have been used to keep cattle on ranches with the exclusion of native deer (2) (4). Presently, the ongoing decline in marsh deer population numbers is predominantly due to habitat loss and fragmentation, caused by agriculture and the construction of hydroelectric dams destroying the floodplain habitat. Competition from domestic livestock also plays an important part, with more than 40 percent of the forest and savanna habitats in this region altered for cattle ranching through the introduction of exotic grasses (6). Marsh deer also suffer from poaching, pollution of waterways from gold mining and disease caught from domestic livestock (1) (7). The remaining populations of marsh deer are dangerously small and highly fragmented, and as a result, are more vulnerable to extinction.

The marsh deer (Blastocerus dichotomus) is the largest deer species from South America reaching a length of 2 m (6.6 ft) and a shoulder height of 1.2 m (3.9 ft). It is found in Argentina, Bolivia, Peru, Brazil, Uruguay and Paraguay. Formerly found in much of tropical and subtropical South America, it ranged east of the Andes, south from the Amazon rainforest, west of the Brazilian Atlantic rainforest and north of the Argentinian Pampa. Today it is largely reduced to isolated populations at marsh and lagoon zones in the Paraná, Paraguay, Araguaia and Guapore river basins. Small populations also occur in the southern Amazon, including Peru where protected in Bahuaja-Sonene National Park. It is listed as a vulnerable species by the IUCN and is protected under CITES Appendix I. Ths is the only species in the genus Blastocerus.

The latter half of its scientific name refers to the forked antlers. Marsh deer resemble the North American mule deer or blacktail deer.