Oryzomys - Distribution, Ecology, and Behavior

Distribution, Ecology, and Behavior

The range of Oryzomys extends from New Jersey in the eastern United States through Mexico and Central America south to northwestern Colombia and east to northwestern Venezuela and Curaçao. Species of Oryzomys usually live in wet habitats such as marshes, streams, and mangroves, but both the marsh rice rat and O. couesi are also occasionally encountered in drier habitats. They occur or occurred on many continental-shelf islands and one oceanic island, Jamaica; their adeptness at colonizing islands may be caused by their close association with water and frequent occurrence in coastal wetlands. The oldest fossils date to the Rancholabrean of the United States, about 300,000 years ago; although there have been some earlier North American records, those are not in fact referable to Oryzomys or even Oryzomyini. Oryzomyines likely evolved in South America east of the Andes; the presence of Oryzomys in Central America and other trans-Andean regions is thought to be the result of one of several independent invasions of this region by oryzomyines. Alternatively, Oryzomys may have evolved from the Pliocene North American Jacobsomys. O. antillarum may have reached Jamaica during the last glacial period while sea levels were low.

Behavior is known mainly from the marsh rice rat and O. couesi, with some scattered data from the other species. Oryzomys are semiaquatic, spending much time in the water, and otherwise mainly live on the ground; both the marsh rice rat and O. couesi are known to be excellent swimmers and will flee into the water when disturbed. Both are also active during the night and build nests of interwoven vegetation, which may be suspended above the water. Breeding may occur throughout the year in both species, but is known to be seasonally variable in the marsh rice rat. In both, gestation takes about 21 to 28 days and litter size is usually one to seven, averaging three to five. Young marsh rice rats and O. couesi become reproductively active when about 50 days old.

The marsh rice rat, O. couesi, and O. gorgasi are known to be omnivores, eating both plant and animal material. They eat both seeds and green plant parts and consume a variety of animals, including insects, crustaceans, and many others. The barn owl (Tyto alba) is a major predator on the marsh rice rat and remains of O. antillarum, O. couesi, and O. gorgasi have been found in owl pellet deposits. Several other animals are known to prey on Oryzomys. A variety of parasites are known from O. couesi and the marsh rice rat and two parasitic nematodes have been found in O. gorgasi.