528 PROCEEDINGS OF THE NATIONAL MUSEUM V0L.no 



of food and water. At least the larger species, Oryzomys concolor, 

 never lives far from water. I have often shined individuals at night 

 running along the maze of tree trunks, vines, logs and even fences 

 that connect their arboreal nests with the water's edge. The smaller 

 species is the one most commonly found in houses where arboreal 

 habitats are simulated by the palm-thatched roofs and natural timber 

 frameworks. A lone mouse or one or two families of either species 

 may be permanent residents in the thatched roof or attic of a house. 

 On the other hand, manj^ individuals merely visit buildings for feeding 

 on insects or man's food stores. Marauding mice are obliged to cross 

 the cleared ground between the forest-edge and the building. 



Oryzomys concolor frequently nests near the ground. It is commonly 

 taken in traps placed on logs, along fences and on the banks of streams 

 sheltered by shrubs and overhanging vines. 0. concolor has managed 

 to survive in a number of localities (e.g. Vilianueva, Colombia) 

 where the primitive forest cover has been reduced to small isolated 

 stands, scattered trees, shrubs and thinly wooded stream banks. 

 It also thrives in plantations of coffee, bananas and other fruits. 

 Where living conditions are optimum, Oryzomys concolor tends to form 

 colonies and can become excessively numerous. The collector Sala- 

 m6n Briceno notes (MS.) that the species does considerable damage 

 in coffee plantations in the district of Merida, Venezuela. 



The smaller species, Oryzomys bicolor, is strictly arboreal and prefers 

 to nest high above ground. Although one of the most common native 

 house mice in tropical South America, it is not found in areas where 

 forests have lost their dominance. It lives in pairs or in single family 

 groups and is nowhere known to be abundant. 



Males of Oryzomys concolor exude a musky odor. The females of 

 either species of Oecomys produce two to four young in a litter. The 

 condition of the mammae in dry skins suggests that young are born 

 the year round. 



The name Oecomys (oikos— house -\-mus) was given in allusion to 

 the mice's predilection for houses. In eastern Ecuador where ar- 

 boreal rice rats are common, the local Quechua name for 0. concolor 

 is "polanda ucucha" (banana rat) and for 0. bicolor, "jahua uchucha." 

 The meaning of "jahua" is obscure. 



Oryzomys bicolor Tomes 



Distribution (fig. 1): Tropical zones of Panama, Venezuela (ex- 

 clusive of the Maracaibo basin), Ecuador, the Guianas, the Amazonian 

 and upper Rio Paraguaj^ basins of Brazil, and the Amazonian regions 

 of Bolivia, Peru, and Colombia; altitudinal range, from near sea level 

 to about 2,000 meters above. The apparent disbributional hiatus in 



