The Oryzomys is a genus of semi-aquatic rodents that belong to the Oryzomyini tribe. These rodents live in southern North America to northern South America. There are 8 species of Oryzomys in the world, 2 of which are marsh rice rats which have various ranges, some of which overlap each other.

Oryzomys palustris in vegetation Oryzomys
An Oryzomys palustris in vegetation

The Oryzomys was first scientifically described by Spencer Fullerton Baird in 1857. However, Oryzomys was applied to 100+ species of rodents. Oryzomys became more narrowly defined in 2006.

All Oryzomys species are medium-sized rats that have long and coarse fur. Its upper parts are reddish to grey, and its underparts are buff to white. These rodents have broad feet with webbing between its toes to aid it in its semi-aquatic environments.

Oryzomys molestus Eliot Oryzomys
The Oryzomys albiventer

The habitat of the Oryzomys are in wetlands, such as rivers, marshes, and lakes. They swim well and are nocturnal creatures. They are omnivorous. Their woven nests are built from vegetation. Typically, their gestation period will last between 21 – 28 days and 4 young are born.

Two of the Oryzomys species have become extinct since the 19th century. It is thought that a 3rd species, Oryzomys peninsulae will become extinct soon. This may be due to habitat destruction and the introduction of species such as the brown rat, black rat, and the small Asian mongoose. The Oryzomys gorgasi is assessed by the IUCN Red List as being endangered. On the other hand, some species are quite common such as Oryzomys couesi and Oryzomys dimidiatus.

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