Blastocerus dichotomusmarsh deer

Geographic Range

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).


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).

  • Aquatic Biomes
  • rivers and streams

Physical Description

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
    196.04 to 275.33 lb
  • Average mass
    109 kg
    240.09 lb


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 number of offspring
  • Average gestation period
    270 days


Behavioral data for B. dichotomus are sparse, but the species is generally crepuscular. Some populations have been reported to be diurnal or nocturnal, depending on season and hunting pressure. Marsh deer are often solitary or in small groups of two to five, with larger groups occasionally observed. They are widely scattered during the wet season, with large home ranges, but concentrated near water during the dry season. Males have larger home ranges than females. Mean densities (dry and flood season) in the Parana River Basin were 0.50-0.54 deer/km2 in 1995 and 1996 (Mares et al. 1989, Mourao and Campos 1995, Pinder 1996, Pinder 1999, Redford and Eisenberg 1992, Whitehead 1972).

Communication and Perception

Food Habits

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).

Economic Importance for Humans: Positive

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

Economic Importance for Humans: Negative

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.

Conservation Status

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).

Other Comments

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

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


Clinton Epps (author), University of California, Berkeley, James Patton (editor), University of California, Berkeley.



living in the southern part of the New World. In other words, Central and South America.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


uses smells or other chemicals to communicate


animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.


having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.


reproduction that includes combining the genetic contribution of two individuals, a male and a female

sexual ornamentation

one of the sexes (usually males) has special physical structures used in courting the other sex or fighting the same sex. For example: antlers, elongated tails, special spurs.


uses touch to communicate

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.


A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.


CITES, July 16, 1999. "CITES fauna" (On-line). Accessed October 18, 1999 at

Duarte, J., M. Giannoni. 1992. Cytogenetic analysis of the marsh deer, Blastocerus dichotomus (Mammalia, Cervidae). Revista Brasileira de Genetica, 18: 245-248.

Magalhães, R., M. Mello, L. Bergqvist. 1992. Pleistocene cervids from the northeastern region of Brazil.. Anais da Academia Brasileira de Ciencias, 64: 149-168.

Mares, M., R. Ojeda, R. Barquez. 1989. Guide to the mammals of the Salta Province, Argentina. Norman, OK, USA: University of Oklahoma Press.

Mourão, G., Z. Campos. 1995. Survey of broad-snouted Caiman latirostris, marsh deer Blastocerus dichotomus and capybara Hydrochaeris hydrochaeris in the area to be inundated by Porto Primavera Dam, Brazil. Biological Conservation, 73: 27-31.

Pinder, L. 1999. Marsh deer (Blastocerus dichotomus) ranging patterns in the Parana River Valley, Brazil. Papeis Avulsos de Zoologia (Sao Paulo), 41: 39-48.

Pinder, L. 1996. Marsh deer Blastocerus dichotomus population estimate in the Parana River, Brazil. Biological Conservation, 75: 87-91.

Pinder, L., A. Grosse. 1991. Blastocerus dichotomus. Mammalian Species, 380: 1-4.

Quintana, R., R. Bo, J. Merler, P. Minotti, A. Malverez. 1992. Use and situation of wildlife in the lower delta of the Parana River. Iherinigia Serie Zoologia, 73: 13-33.

Redford, K., J. Eisenberg. 1992. Mammals of the neotropics (Vol. 2): the southern cone. Chicago, USA: The University of Chicago Press.

Roig, V. 1991. Desertification and distribution of mammals in the Southern Cone of South America. Pp. 239-279 in M Mares, D Schmidly, eds. Latin American mammalogy: history, biodiversity, conservation. Norman, Oklahoma, USA: University of Oklahoma Press.

Roxo, E., R. Gaspirini. 1996. Survey on incidence of brucellosis in Pantanal deer, in Brazil.. Arquivo Brasileiro de Medicina Veterinaria e Zootecnia, 48(1): 79-81.

Whitehead, K. 1972. Deer of the world. New York, USA: The Viking Press, Inc..