Costa Rica Wildlife: Mexican Mouse Opossums Costa Rica is a country known for its incredible biodiversity, with a vast array of unique and fascinating wildlife. One particular creature that can be found in this Central American paradise is the Mexican Mouse Opossum. Despite its name, the Mexican Mouse Opossum (Marmosa mexicana) is not exclusive to Mexico but can also be found in various regions of Costa Rica. These small marsupials belong to the Didelphidae family and are closely related to other opossum species found in North and South America. The Mexican Mouse Opossum is known for its unique physical characteristics. Its body size ranges from 11 to 17 centimeters, with a tail that can measure up to 12 centimeters long. Its fur color varies from light brown to gray, which helps it blend into its surroundings and remain camouflaged from predators. These creatures are primarily nocturnal, meaning they are most active during the night. Their diet mainly consists of insects, fruits, small vertebrates, and nectar from flowers. With their excellent sense of smell and sharp teeth, they are well-equipped to find and consume their preferred food sources. Mexican Mouse Opossums are commonly found in forested areas, where they make use of their prehensile tails to navigate through the trees with ease. They also have excellent agility and balance, allowing them to traverse challenging terrain and escape potential threats. One interesting fact about the Mexican Mouse Opossum is its reproductive behavior. Like other marsupials, females of this species have a unique reproductive system. They have a pouch on their belly where they carry and nurse their young, called joeys. These joeys are born in a relatively undeveloped state and continue to grow and develop while attached to their mother’s teats. Spotting a Mexican Mouse Opossum in its natural habitat can be quite rare due to its small size and nocturnal habits. However, keen wildlife enthusiasts visiting Costa Rica may have the opportunity to observe these remarkable creatures. The Mexican Mouse Opossum is just one of the many captivating species that can be encountered when exploring the diverse wildlife of Costa Rica. Its presence in the country highlights the importance of preserving and protecting the natural habitats that enable such unique creatures to flourish.

Is it a mouse? Is it an opossum? Meet the adorable Mexican mouse opossum (Marmosa mexicana)! Also known as zorro ratón, zorricí, or zorillo in Costa Rica, this tiny creature is about 6 inches long and weighs around 3 ounces. With males being slightly larger than females, they have a reddish-brown mouse-like appearance with a black eye mask and a long prehensile tail.

These opossums use their tails to navigate trees, as they are mainly arboreal animals that live and hunt among the branches. Their diet includes fruits and insects, and they also eat lizards, birds, mice, and bird eggs. They have a knack for raiding nests of house wrens, parrots, and woodpeckers.

Being nocturnal, they do most of their tree climbing and hunting at night. During the day, they nest in abandoned bird nests, make their own leaf nests, or, less commonly, burrow in the ground.

Other species in Costa Rica’s wild ecosystem prey on these tiny creatures, with their bones found in owl pellets and in rattlesnake stomachs. Despite their size, Mexican mouse opossums can be aggressive when threatened.

One surprising fact about these opossums is the absence of pouches. Following a short gestation, the female gives birth to 1 to 14 larvae, which cling to her and nurse for the first month of life. As they grow, they begin accompanying their mother on excursions, then can reproduce at five or six months old. However, it’s believed few Mexican mouse opossums survive past two years.

You can catch glimpses of this fascinating little creature through camera traps in trees or on the forest floor. Brief yet charming videos show their quick, mouse-like movements before they vanish from sight.

Vincent Losasso, the founder of Guanacaste Wildlife Monitoring, is a biologist who works with camera traps throughout Costa Rica. Learn more about his projects on Facebook, Instagram, or by emailing vincent@guanacastewildlifemonitoring.com.

1. Look up and into the trees: Mexican mouse opossums are mostly arboreal, so keep an eye out for them among the branches.

2. Explore at night: Since Mexican mouse opossums are nocturnal, your chances of spotting one are higher during the nighttime.

3. Listen for rustling in abandoned bird nests: During the day, Mexican mouse opossums can be found nesting in abandoned bird nests, so listen for rustling sounds when exploring potential nesting spots.

4. Keep your distance: While Mexican mouse opossums may look adorable, they can act aggressively when trapped, so it’s best to observe them from a safe distance.

5. Stay quiet and patient: Mexican mouse opossums are known for their quick movements and tendency to disappear rapidly. To increase your chances of sighting one, stay quiet and patient, waiting for any movement or rustling sounds.

6. Consider using camera traps: If you want to increase your chances of capturing footage or images of Mexican mouse opossums, try using camera traps in trees or on the forest floor.