Marsh deer (Blastocerus dichotomus)

Spanish: Ciervo De Los Pantanos, Ciervo Marismeño
KingdomAnimalia
PhylumChordata
ClassMammalia
OrderCetartiodactyla
FamilyCervidae
GenusBlastocerus (1)
SizeHead-body length: 145 - 200 cm (2)
Shoulder height: 100 - 115 cm (2)
Weight100 - 120 kg (2)

The marsh deer is classified as Vulnerable (VU) on the IUCN Red List (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).

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).

Extremely fragmented populations of marsh deer 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).

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).

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 in marsh deep 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).

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.

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).

For more information on the marsh deer see:

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
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  1. IUCN Red List (January, 2008)
    http://www.iucnredlist.org
  2. World Deer (January, 2008)
    http://www.worlddeer.org/marshdeer.html
  3. CITES (January, 2008)
    http://www.cites.org
  4. Ultimate Ungulate (January, 2008)
    http://www.ultimateungulate.com/Artiodactyla/Blastocerus_dichotomus.html
  5. Tomas, W.M. and Salis, S.M. (2000) Diet of the marsh deer (Blastocerus dichotomus) in the Pantanal wetland, Brazil. Studies of Neotropical Fauna and Environment, 35: 165 - 172.
  6. Harris, M.B., Tomas, W.M., Mourao, G., Da Silve, C.J., Guimaraes, E., Sonoda, F. and Fachim, E. (2005) Safeguarding the Pantanal Wetlands: Threats and Conservation Initiatives. Conservation Biology, 19(3): 714 - 720.
  7. Wemmer, C. (1998) Deer: Status Survey and Conservation Action Plan. IUCN/SSC Deer Specialist Group, IUCN, Gland, Switzerland. Available at:
    http://data.iucn.org/dbtw-wpd/edocs/1998-040.pdf