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 )
Argentina, Uruguay, Paraguay, Bolivia, Brazil
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
Habitat and Ecology
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).
Life History and Behavior
Perception Channels: tactile ; chemical
Lifespan, longevity, and ageing
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.
Molecular Biology and Genetics
Barcode data: Blastocerus dichotomus
Below is the sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen.
Other sequences that do not yet meet barcode criteria may also be available.
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Download FASTA File
Statistics of barcoding coverage: Blastocerus dichotomus
Public Records: 1
Specimens with Barcodes: 1
Species With Barcodes: 1
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
IUCN Red List Assessment
Red List Category
Red List Criteria
- 1994Vulnerable(Groombridge 1994)
- 1990Vulnerable(IUCN 1990)
- 1988Vulnerable(IUCN Conservation Monitoring Centre 1988)
- 1986Vulnerable(IUCN Conservation Monitoring Centre 1986)
- 1982Vulnerable(Thornback and Jenkins 1982)
Date Listed: 06/02/1970
Lead Region: Foreign (Region 10)
Where Listed: Columbia River (Clark, Cowlitz, Pacific, Skamania, and Wahkiakum Counties, WA, and Clatsop, Columbia, and Multnomah Counties, OR)
Population location: Columbia River (Clark, Cowlitz, Pacific, Skamania, and Wahkiakum Counties, WA, and Clatsop, Columbia, and Multnomah Counties, OR)
Listing status: E
For most current information and documents related to the conservation status and management of Blastocerus dichotomus , see its USFWS Species Profile
The principal population in Paraguay is in the Yacyretá region where density is low. Most populations in Paraguay were reported to be declining in the 1970s (Jungius 1974, 1976). In Peru the species occurred in small numbers in Pampas del Heath (Hofmann et al. 1976, Montanbault 2002, Escamilo pers. comm.). The last record of the species in Uruguay dates back to 1958 (Ximenez et al. 1972, González 1994).
Relevance to Humans and Ecosystems
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 are valuable game animals, hunted for meat and sport (Roig 1991).
The marsh deer (Blastocerus dichotomus) is the largest deer species from South America reaching a length of 2 m (6.6 ft) and a height of 1.2 m (3.9 ft) at the rump. It is found in Argentina, Bolivia, Peru, Brazil, Uruguay and Paraguay. Formerly found through all of tropical South America today it is reduced to small isolated populations at marsh and lagoon zones in the basins of the rivers Paraná and Paraguay as in the Amazonian region of Peru where it is protected in Bahuaja-Sonene National Park. Current distribution of this species is east of the Andes, south of the Amazon rainforest, west of the Brazilian Atlantic rainforest and north of the Argentinian Pampa. Small population reside in the Amazon River basin but the largest population occur in the flood plains of the Paraguay, Guapore, Araguaia and Parana Rivers. There are some isolated populations The latter half of its scientific name refers to the forked antlers that they carry. They resemble Mule Deer or Blacktail Deer.
It is listed as a vulnerable species, according to CITES, appendix I.
The marsh deer lives only in marsh areas, pantanal and chaco, in which the level of water is less than 70 cm deep. They are swift swimmers. The marshes with their high vegetation density protect them from predators and provide them with food. These deer also have a small migratory pattern, they follow the water levels between the dry season and flooding season. With the fluctuation in water levels, they are able to find new food sources that the water uncovers during the dry season. Some freshwater ponds on the Pantanal Wetland, Brazil reported low densities of individuals dictating that those ponds are not able to support large populations of Marsh Deer. 
Since Marsh Deer live near aquatic habitats, they eat a majority of their diet in aquatic plants. A study was conducted and they found 40 different species of plants in which they ate. The main food component was Graminae which took up 22% of their diet, Pontederiaceae took up 12%, Leguminosae was about 11%, and the rest was filled in with Nymphaeaceae, Alismataceae, Marantaceae, Onagraceae, and Cyperaceae. They also enjoy eating aquatic flowers and shrubs that grow in the swamps and the floating mats. They can be best classed as a grazer-browser for food. Their diet also changes between the dry season and the flood season.
They possess very large ears lined with white hairs, reddish brown colored body and long dark legs. The hair turns darker during winter. There are also white marks on the hips and around the eyes. The legs are black below the tarsal as is the muzzle. The tail is of a paler reddish tone than the rest of the body on its upper part and black on the under part. The head-and-body length is 153 to 200 cm (5.02 to 6.56 ft), while the tail adds a further 12–16 cm (4.7–6.3 in). The height at the shoulder can range from 100 to 127 cm (3.28 to 4.17 ft).
The claw, which is large in relation to the body, has elastic interdigital membranes which are useful for swimming and walking on marshy surfaces. Only the males possess antlers which are ramified and reach a length of 60 cm (23 inches). An adult typically grows to a weight of 80 to 125 kg (176 to 276 lb), although an occasional big male can weigh up to 150 kg (330 lb).
Usually the rutting season coincides with the dry season but can change from animal to animal. They may use this to their advantage for breeding or finding mates because the densities of marsh deer are significantly higher on the Negro River marshland boundary during the dry season compared to the less dense, more distributed population during the flooded season.  Gestation lasts approximately 271 days. The offspring (normally one per female, though occasionally twins are born) are born between October and November. The infant deer are whitish which becomes more adult-like after a year.
The natural predators of the marsh deer – the jaguar (locally called onça or yaguaraté) (Panthera onca) and the puma (Puma concolor)— have almost completely disappeared from its habitat. The former major threat was poaching for its antlers, but this is somewhat under control. Destruction of its habitat presents nowadays the major threat to marsh deer. The dam at Yacyretá altered an area in which several hundred individuals lived and the draining of marshes for farmland and cattle threaten hundreds of hectares every year in Argentina and Brazil. Contagious diseases from cattle are also a problem, though it has been shown that the deer is not affected by brucellosis.
- Duarte, J.M.B., Varela, D., Piovezan, U., Beccaceci, M.D. & Garcia, J.E. (2008). Blastocerus dichotomus. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 10 April 2009. Database entry includes a brief justification of why this species is of vulnerable.
- (Cabrera 1961; Thornback & Jenkins 1982; Tomas et al. 1997)
- (Tomas et al. 1997)
- (Tomas et al. 2001)
- (Tomas & Salis. 2000)
-  (2011).
-  (2011).
- (Tomas et al. 2001)
- (Duarte & Garcia, 1995)
- Tomas, W.M., and S.M. Salis. 2000. Diet of the marsh deer (Blastocerus dichotomus) in the Pantanal wetland, Brazil. Studies on Neotropical Fauna & Environment. 35:165–172.
- Tomas, W.M., S.M. Salis, M.P. Silva, and G.M. Mourao. 2001. Marsh deer (Blastocerus dichotomus) distribution as a function of floods in the Pantanal Wetland, Brazil. Studies on Neotropical Fauna & Environment. 56:9-13.
- Tomas, W.M., M. Beccaceci, and L. Pinder. 1997. Cervo-do-pantanal (Blastocerus dichotomus). Biologia e Conservacao de Cervideos Sul Americanos. 24-38.
- Cabrera, A. 1961. Catalogo de los mamiferos de America del Sur. Rev Mus Argentino Cien Nat Bernardino Rivadavia. 4:1-732.
- Thornback, J., and M. Jenkins. 1982. The IUCN mammal red data book, Part 1: Threatened mammalian taxa of the Americas and the Australian zoogeographic region (excluding Cetacea). IUCN. 516 pp.
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