Brazilian Marsh Rat

Fascinating facts about the Brazilian Marsh Rat

• At just 167–211 mm long (about 6.6–8.3 in) and with a tail that can out-stretch its body up to 214 mm, this rodent fits comfortably in a child's hand yet still manages a life on both land and water. Its compact size lets it slip through dense swamp grasses where larger mammals cannot go.
• Living on the fringe of rivers in the Atlantic Forest, it pops up in swampy grasslands of Brazil, Uruguay, Paraguay and northeastern Argentina, turning any wet woodland into a potential home. This range shows how a single species can thrive across both coastal plains and deep inland forests.
• It is seldom caught in live traps but is frequently caught by barn owls and mammalian carnivores.
• When the rainy season kicks in during spring and summer, females give birth to three-to-six pups, timing their families with the burst of fresh shoots they love to eat. The seasonal boom links rainfall directly to their reproductive success.
• Even though the International Union for Conservation of Nature lists it as “least concern,” its ability to live in sugar-cane and rice fields means farmers often see it as a pest, reminding us that abundant wildlife can coexist, and sometimes clash, with human agriculture.

At a glance

About the Brazilian Marsh Rat

The Brazilian marsh rat, Holochilus brasiliensis, has a cinnamon-brown back, brighter orange flanks, a paler orange belly, and white on the throat, chest, and near the groin. Adults measure 167–211 mm from nose to rump, with a tail length of 183–214 mm. Its dense, luxuriant fur insulates it in its swampy habitat. Living in the Atlantic Forest ecoregion of eastern and southern Brazil, Uruguay, eastern Paraguay, and northeastern Argentina, these nocturnal foragers patrol river margins and flooded grasslands. They feed on tender shoots, often after spring and summer rains, are rarely caught in live traps but are preyed upon by barn owls and mammalian carnivores, and can raid sugar-cane and rice fields.

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