Didelphis aurita - Big-eared Opossum​

Physical Description:

 Didelphis aurita was long considered a subspecies of Didelphis marsupialis, however recent DNA evidence places Didelphis aurita as its own species. Qualitatively the differences between the two are lacking and indistinguishable. Didelphis aurita and Didelphis marsupialis have undergone divergence at both the DNA and morphometric levels, but qualitative aspects of their skull morphology appear unchanged. DNA sequence data has shown a divergence of 2.9% in kimura two-parameter distance at the mitochondrial cytochrome b gene of Didelphis aurita and Didelphis marsupialis specimens each taxon being monophyletic (Cerqueira and Lemos 2000). Didelphis marsupialis and Didelphis aurita are not known to overlap in geographic range, so the site of location can be used for preliminary identification (Emmons 1997).

            Didelphis aurita has a well-developed black centerline on its forehead. The underfur is described as a dirty yellow color with the overhairs being black or grey. The ears are black and the tail is furred at the base as long as the hind leg, with black and white parts nearly of equal length, or sometimes the black parts being longer (Emmons 1997). Average body mass of Didelphis aurita ranges from 670-1560 grams. The tail length typically is around 31.72 cm with and average claw length of 0.47 cm (Vieira 1997). Opossums usually have around 50 teeth with a dental formula I 5/4, C 1/1, P 3/3, M 4/4 = 50. They have five digits on each foot with a hind foot that has an opposable thumb. The rostrum is long, ears and tail are naked, with the tail being highly prehensile (Eisenberg and Redford 1999). 

 Distribution:

Didelphis aurita occurs in Brazil, Paraguay, and Argentina (Ventura etal 2002). Didelphis aurita occurs from coastal Brazil from Bahia to Rio Grande do Sul, west to the lower Rio Paraguay. They typically occur up to 1000 meters in elevation (Emmons 1997). 

Ontogeny and Reproduction:

Didelphis aurita is considered insectivorous-omnivorous marsupial and occasionally eats vertebrates and fruits depending on the availability and the season. Fossorial invertebrates such as Diplopoda, Opiliones, and Coleoptera are highly preyed upon. They will eat the fossorial snake Cobra-cega (Liotyphlops beui). The main fruits consumed where the Passion flower (Passiflora actinia) and Sanctaecatharine nightshade (Solanum sanctaecatharinae). Most fruits are consumed during the wet season since that is when the most are available. The ability of Didelphis aurita to climb may explain the high fruit occurrence in its diet (Santori etal 1996).The Rufous-bellied Thrush (Turdus rufiventris) is the highest consumed vertebrate in their diet, but the Parana Grass mouse (Akodon paranaensis) and Black-footed Pygmy rice rat (Oligoryzomys nigripes) are frequently consumed rodents (Caveres and Monteiro-Filho 2001). Santori etal (1996) found the Collared lizard (Tropidurus torquatus) to be their most frequent prey.

 Typically, Didelphis aurita will produce 2-3 litter per year (Eisenberg 1999). The average litter size in eastern Columbia is 6.5. Breeding season begins in January after 4 months of anestrous and first litters are weaned in April and replaced by the second, which are weaned at the close of the reproductive season in August. Males usually include at least 3 females in their home range (Tyndale-Bisoe and Mackenzie 1976). Didelphis aurita frequently nests in tree cavities (Miles etal 1981).

Gestation lasts 13-14 days for South American species. They have yolk-sac placentas. After the young are born, they climb unassisted to the nipple area, where the mother will transport the entire litter attached to her teats for the first 5 or 6 weeks of their development. Following this, the young detach and begin the nest phase where the mother will not continually transport them, but will come back to the nest to nurse (Eisenberg and Redford 1999).

Ecology and Behavior:

Opossums are opportunist feeders and will commonly shift their home range to adapt to fluctuating resources. They are typically found in moister habitats (Eisenberg and Redford 1999). Didelphis aurita inhabits humid tropical lowland forests (Emmons 1997). Female home range is around 0.2 ha in the dry season and even less during the wet season. Males have a typical home range of 3.0 ha in the wet season (Caveres and Monteiro-Filho 2001).

Didelphis aurita showed to have the greatest frequency of movements in the range of 0-20 meters. In a study done by Gentile and Cerqueira, (1995) 61% of their movements were less than 60 meters. They also did not see males as being more nomadic than females, as Caveres and Monteiro-Filho (2001) observed in a study in Southern Brazil, however some females did have longer residence time than males (Gentile and Cerqueira 1995).

Didelphis marsupials do not typically exhibit territoriality, however female Didelphis aurita are territorial during the wet season when they are reproductively active. There main activity period was the first hours of the night. Caveres and Monterio- Filho (2001) suggested opossums may direct some of their foraging activity to capture crepuscular living prey.

            Opossums are solitary and antisocial animals and usually avoid one another or act aggressively. When two males meet there is almost always extreme agonistic behavior. Two opposite sexes meeting during the breeding season will initially be aggressive, but usually turns into courtship, and the two animals may spend several days together. If a male is placed with a female that is not in estrous, she becomes aggressive, but the male does not return her attacks (Nowak 1991).

Literature Cited:

Caveres, N.C. and E.L.A. Monteiro-Filho. 2001. Food habitats, home range and activity of Didelphis aurita (Mammalia, Marsupialia) in a forest fragment of southern Brazil. Studies on Neotropical Fauna and Environment 36: 85-92.

Cerqueira, R. and B. Lemos. 2000. Morphometric differentiation between neotropical Black-eared opossums, Didelphis marsupialis and D. aurita (Didelphimorphia, Didelphidae). Mammalia 64:319-327.

Eisenberg, J.F. and K.H. Redford. Mammals of the Neotropics. Volume 3. 1999. The University of Chicago Press, Chicago, Illinois, USA.

Emmons, L.H. Neotropical Rainforest Mammals. 2nd Edition. 1997. The University of Chicago Press. 14-16.

Gentile, R. and R. Cerqueira. 1995. Movement patterns of five species of small mammals in a Brazilian restinga. Journal of Tropical Ecology 11:671-677.

Miles, M.A., A.A.DeSousa and M.M. Povoa. 1981. Mammal tracking and nest location in the Brazilian forest with and improved spool-and-line device. Journal of Zoology 195: 331-347.

Nowak, R.M. Walker’s Mammals of the World. 5th Edition, Volume 1.1991. John Hopkins University Press. 19-20.

Ventura, J. etal. 2002. Morphometrics of the genus Didelphis ( Didelphimorphia: Didelphidae) in Venezuela. Journal of Mammalogy 83:1087-1096.

Vieira, M.V. 1997. Body size and form in two neotropical marsupials, Didelphis aurita and Philander opossum (Marsupialia: Didelphidae). Mammalia 61: 245-254.

Santori, R.T. etal. 1996. Diet composition of Metachirus nudicaudatus and Didelphis aurita (Marsupialia, Didelphoidea) in southeastern Brazil. Mammalia 60:307-311.

Tyndale-Biscoe, H. and R.B. Mackenzie. 1976. Reduction in Didelphis marsupialis and D. albiventris in Colombia. Journal of Mammalogy 57:249-265.

Reference written by Scott Williams, Biology 378 (Mammalogy), University of Wisconsin - Stevens Point.  Edited by Christopher Yahnke. Page last updated August 3, 2005.