Flavescent Colilargo

Fascinating facts about the Flavescent Colilargo

• A chromosome count that swings between 64 and 66 pairs (2n = 64-66) makes this little rodent a genetic chameleon, while its chromosome arms number 66-70 (FNa = 66-70), a detail that helps scientists untangle its evolutionary ties to other South American mice.
• Its head-and-body length averages 87 mm and its tail averages 110 mm.
• Its coat fades from bright orangish-brown on the back to yellow-grey underneath without a clear line.
• It lives from sea level up to about 1,800 m (≈5,900 ft) and occurs in habitats such as marshes and scrubland.
• As the main reservoir for certain hantaviruses, it carries viruses harmless to itself but dangerous to humans, a reminder that wildlife health can directly echo in public health concerns.

At a glance

About the Flavescent Colilargo

The flavescent colilargo, Oligoryzomys flavescens, dazzles with a coat of bright orangish-brown interspersed with blackish hairs on its back, while its flanks blaze uniformly orange and its belly fades to a muted yellow-grey. This seamless gradient masks a clear demarcation between dorsal and ventral surfaces, giving the tiny rodent a sun-kissed appearance that blends effortlessly into the grasses and reeds of its South-American homes. Measuring about 87 mm from nose to rump, its tail stretches to roughly 110 mm, a proportion that aids balance as it darts through the dense understory of pampas, scrubland, primary and secondary forests, marshes, and even cultivated fields. Its skull bears distinctive long incisive foramina that usually reach the first molar and a short mesopterygoid fossa that stops before the third molar, traits that taxonomists use to set it apart from its congeners. Beyond its striking looks, O. flavescens thrives from sea level to 1,800 m, favoring habitats near water. Remarkably, this modest rodent serves as the principal reservoir for certain hantaviruses, harmless to the mouse but capable of causing serious disease in humans, making it a silent sentinel in the epidemiology of rodent-borne illnesses. Its adaptability to both pristine and disturbed environments, including agricultural lands, underscores a resilience that keeps it abundant across eastern Brazil, Uruguay, eastern Paraguay, and northern to central Argentina, even as landscapes shift around it.

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