distal (far) end of the humerus (upper arm bone). Ecology and behavior The distribution of Oryzomys couesi extends from southern Texas and central Sonora, but not the central plateau of Mexico, through Central America south and east to northwestern Colombia; see under "Taxonomy" for details. The species has also been found in late Pleistocene cave deposits in Mexico and Honduras. It is common in watery habitats, such as marshes and small streams, but also occurs in forests and shrublands with sufficient cover. In addition, it is found in sugarcane and rice fields. In Texas, it occurs in marsh vegetation along resacas (oxbow lakes) and in Veracruz, it has even been found on the dry coastal plain among shrubs. It occurs from altitude down to sea level. On Cozumel, the proportion of juveniles and females is higher near roads that function as habitat edges. Cozumel rice rats rarely cross roads, which may isolate subpopulations on the island. Oryzomys couesi lives on the ground and is semiaquatic, spending much time in the water, as Alston in his original description already recognized, but is also a good climber. A study in Costa Rica found that O. couesi is an excellent swimmer, diving well and using its tail to propel itself. It is probably able to forage underwater, which may help differentiate its niche from that of the ecologically similar cotton rat Sigmodon hirsutus, which also swims well, but does not dive. When disturbed, O. couesi will enter the water and swim away. It is primarily active during the night. Oryzomys couesi builds globular nests of woven vegetation suspended among reeds, about above the water or the ground; in Texas, larger individuals make larger nests. It does not usually make its own runways in vegetation, but may use those of other rodents, such as cotton rats. Population densities range from 5 to 30 per ha (2 to 12 per acre). On Cozumel, density is around 14.5 to 16.5 per ha (5.9 to 6.7 per acre), but shows large seasonal variation. In western Mexico, one study found densities of 3 per ha (1.2 per acre) in cloud forest and 1 per ha (0.4 per acre) in a disturbed area. In 24 hours, male Texas O. couesi move up to and females up to . The diet includes both plant material, including seeds and green parts, and animals, including small fish, crustaceans, snails, insects like ants