Didelphis aurita, Wied-Neuwied, 1826

Astúa, D., 2015, Didelphidae, Handbook of the Mammals of the World – Volume 5 Monotremes and Marsupials, Barcelona: Lynx Edicions, pp. 129-186 : 162-163

56.

Southern Black-eared Opossum

Didelphis aurita

French: Opossum oreillard / German: GroRohrOpossum / Spanish: Zarigleya de orejas negras meridional

Other common names: Azara's Opossum, Big-eared Opossum, Brazilian Common Opossum

Taxonomy. Didelphis aurita Wied-Neuwied, 1826 ,

“ Villa Vicoza am Flusse Peruhype ,” Bahia, Brazil.

Taxonomic status of the disjunct population of D. aurita in north-eastern Brazil needs to be properly assessed. Monotypic.

Distribution. E Brazil, from Pernambuco S to SE Paraguay and NE Argentina (Misiones).

Descriptive notes. Head-body 31-39 cm, tail 31-37 cm; weight 0.7-1.5 kg. Male Southern Black-eared Opossums are larger than females, and skull shape is sexually dimorphic. Dorsal fur is black or gray, with two distinct layers: dirty yellow underfur more or less visible underneath long, coarse, black, or gray guard hairs. Head is dirty yellow, with eye mask from behind whiskers through bases of ears; cheeks are yellow, pale orange, or dirty white, and there is a black line on center of forehead. Tail length is about the same as head-body length, tail is basally furred, and naked rest oftail is black on proximal one-half or more and white on rest. Ventral fur is similar to dorsal fur, but paler or orange, and shorter, and yellowish on chin and throat. Feet are black, and ears are large, naked, and black. Females have a pouch with eleven or 13 mammae, five or six on each side and a medial mamma. The Southern Black-eared Opossum has a 2n = 22, FN = 20 karyotype, with all acrocentric autosomes, and acrocentric X-chromosome and Y-chromosome.

Habitat. Atlantic rainforest, both coastal and inland in both primary and secondary forests and associated vegetation types, such as coastal restinga, and into the Araucarias forest in southern Brazil. The Southern Black-eared Opossum is highly tolerant of habitat disturbance and coexists with humans, with no habitat restriction within its distribution.

Food and Feeding. The Southern Black-eared Opossum is considered a highly generalist opossum with an opportunistic feeding behavior. Its diet includes a great variety of arthropods, supplemented with small vertebrates and fruits, apparently consumed according to their availability. In a restinga area in south-eastern Brazil, it fed on a high diversity of invertebrates, including Blattodea, Hymenoptera (ants), Orthoptera, Diplopoda, Chilopoda, Arachnida, Coleoptera, Isoptera (termites), and mollusks; it also ate rodents such as the Cursorial Akodont (Akodon cursor), skinks (Mabuya), ground lizards (Tropidurus), birds, snakes, frogs, and fruits of Araceae , Bromeliaceae , Cactaceae , Sapindaceae , and Passifloraceae . Based on presence of Diptera pupae in feces, it also consumes carrion. In this restinga area, arthropods consumed are mainly from the litter. In the Atlantic Forest, the Southern Black-eared Opossum feeds on arthropods and fruits in about the same proportions as in the restinga area, although arthropod remains are sometimes more frequently found in feces. In Atlantic Forest fragments in south-eastern Brazil, diets included Coleoptera, Hymenoptera, Arachnida, Orthoptera, and Diptera , along with seeds of Piperaceae , Urticaceae , Moraceae , and Cucurbitaceae , with species of Piper and Cecropia being the most frequent ones. In the Atlantic Forest of southern Brazil, diets also included Coleoptera, Orthoptera, Hymenoptera (ants), Arachnida, Lepidoptera, Diptera larvae, mollusks, Chilopoda, Decapoda, and unidentified mammals, birds, and reptiles; they also ate fruits, including Araceae and Urticaceae . In Araucaria Forest fragments in southern Brazil, diets of Southern Black-eared Opossums included invertebrates (mostly Coleoptera, Diplopoda, Opiliones, Decapoda, Blattodea, Hymenoptera, and mollusks); birds such as the rufous-bellied thrush (7Turdus rufiventris), unidentified rodents, and blind snakes (Liotyphlops); and 21 fruit species, mostly Passiflora (Passifloraceae) , Piper (Piperaceae) , Solanum (Solanaceae) , and Melothria (Cucurbitaceae) . Predation on snakes as inferred from fecal analyses is confirmed by observations of captive Southern Black-eared Opossums that successfully attacked and consumed pit vipers (Crotalus durissus and Bothrops). Young and small Southern Black-eared Opossums were seen attacking a snake simultaneously. Nutritional contents of preferred diets, determined with cafeteria experiments in captivity where individuals were free to choose food items according to their needs, resulted in 16-3 g of proteins, 26-7 g of carbohydrates, 5-1 g of lipids, and 3-2% of fibers per 100 g of dry matter. The Southern Black-eared Opossum seems to be an important disperser of seeds of several families of plants, including Araceae , Cactaceae , Moraceae , Myrtaceae , Rosaceae , and Solanaceae , and it acts as a pollinator of Mabea fistulifera ( Euphorbiaceae ) in south-eastern Brazil.

Breeding. Female Southern Black-eared Opossums make nests in tree cavities and burrows, and they also make open nests in tree forks and on woven lianas and epiphytes. They reach sexual maturity at ¢.170 days, and gestation is 14-15 days. Littersize is c.7 young. Mean litter sizes of 7-3 young (5-9), 6-8 young, seven young, 7-2 young, 7-4 (4-11), 6-5 (4-9), and 7-4 (6-11) were observed at different sites in south-eastern Brazil. Mean litters of 8-1 young (4-12) were observed in southern Brazil, and up to twelve young in one litter have been reported in captive specimens. Breeding season lasts from July or August until March or April in south-eastern Brazil, and two litters can occur during the same breeding season. In southern Brazil (27° 29’ S), however, females with pouch young were only found in October—January.

Activity patterns. The Southern Black-eared Opossum is mainly nocturnal, usually active during the first hours of the night in southern Brazil. Its activity period is sometimes partially synchronized with activity peaks of rodents, suggesting that it is maximizing prey capture. In south-eastern Brazil, Southern Black-eared Opossums were mostly nocturnal, with two peaks of activity: the first around sunset (declining during the following 4-5 hours) and the second about eight hours after sunset. During this second peak, juveniles and subadults were less active than adults. Daytime activity was also recorded, representing c.10% of total activity, and occurred during three hours preceding sunset. Activity pattern showed no influence of reproductive or climatic season.

Movements, Home range and Social organization. Southern Black-eared Opossums usually explore the ground, understory, and canopy with equal frequency, thus being considered generalists in vertical space use, although at some studysites a preference for the ground seems to occur. They are good climbers, using even thin branches with ease, and they have been observed reaching heights of 20 m in the canopy. Unlike smaller species of opossums, the Southern Black-eared Opossum is able to climb using its claws, which are relatively large, and as a consequence, it uses vertical supports more frequently. It is also able tojump across gaps. In a restinga forest in south-eastern Brazil, most frequent movements recorded were less than 60 m, although occasional movements of up to 300 m were observed. Given size of the study grid, however, along with the body size of the Southern Black-eared Opossum, and comparing distances moved by other species of the same genus, 300 m is likely an underestimate. Estimates using spool-and-line devices in the Atlantic Forest of south-eastern Brazil yielded similar estimates, with distance between successive captures of 20-83 m; maximum recorded distances traveled were 290 m. Home ranges estimates also vary considerably. Estimated home ranges at several sites in southern and south-eastern Brazil were 0-2-3 ha, 0-6-2-7 ha, 1-1 ha (on average, range of 0-4-1-6 ha), 2-6 ha, and 1-4 ha; however, larger values of 1-5-9-5 ha, based on spool-and-line tracking, have been observed. Home ranges of females do not overlap, and they do not vary from season to season (although older and larger females tend to have larger home ranges). In contrast, males’ home ranges overlap with those of up to three females. Females maintain their home ranges throughout the year, but males are more transient. Movements of females did not differ between breeding and non-breeding seasons in an Atlantic Forestsite in south-eastern Brazil, but they used larger areas less intensively during the drier season. In contrast, movements of males increased during the breeding season, suggesting that movements of females are driven by resource availability, whereas those of males are affected by their search for mates. Perceptual range of Southern Black-eared Opossums, or the maximum distance at which a landscape element can be detected, is 200 m, based on abilities of individuals released in a grass matrix to detect and head for forest fragments from where they had been removed; however,this distance depends on vegetation obstruction and decreases to 30 m or less if the grass is tall (c¢.50 cm) and 50 m in plantations. Orientation is dependent on wind direction, especially at longer distances when visual orientation may be hampered. Estimated densities of the Southern Black-eared Opossum were 240 ind/km? in southern Brazil and 20-150 ind/km? in south-eastern Brazil.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The Southern Black-eared Opossum has a wide distribution, large populations, and high tolerance for habitat modification. Although it is mainly an Atlantic Forest species and the Atlantic Forest is highly threatened by deforestation and fragmentation, its generalist habits, including its capacity to coexist with humans, indicate that loss of any specific habitat or vegetation would not directly affect conservation status of the Southern Black-eared Opossum.

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Figures

65. Pygmy Opossum (Chacodelphys formosa), 66. Agricola’s Opossum (Cryptonanus agricola), 67. Chacoan Mouse Opossum (Cryptonanus chacoensis), 68. Guaiba Mouse Opossum (Cryptonanus guahybae), 69. Unduavi Mouse Opossum (Cryptonanus unduaviensis), 70. . Emilie’s. 9 Opossum.. Gracilinanus. (null), 71. Aceramarca Opossum (Gracilinanus aceramarcae), 72. Agile Opossum (Gracilinanus agilis), 73. Wood Sprite Opossum (Gracilinanus dryas), 74. Northern Gracile Opossum (Gracilinanus marica), 75. Brazilian Gracile Opossum (Gracilinanus microtarsus)

Distribution. E Brazil, from Pernambuco S to SE Paraguay and NE Argentina (Misiones).