Alien Earthlings

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Class: Mammalia

Costa Rica is home to about 225 species of mammals, roughly six percent of the world's species. Seven of these are endemic to Costa Rica and exist nowhere else in the world. It is one of the few countries in America that retains the same number of mammal species today as it did when Spanish colonizers arrived five hundred years ago. Brown-throated Three-toed Sloth - Bradypus variegatus

Twenty-one of our mammal species reach the southern limit of their range in Costa Rica and twenty-seven others reach their northern limits here. Despite the rich diversity, mammal encounters are relatively rare and usually ephemeral events.

As Ken Miyata and Adrian Forsyth write in their wonderful publication Tropical Nature:

"A naturalist's first visit to a tropical rainforest can be both an exhilarating and disappointing experience; the richness of the vegetation may overwhelm the senses at first, but sooner or later the apparent scarcity of animal or insect life will begin to raise questions."

Even the richest rainforest may only have an average of 14 mammal species. One reason mammal diversity in Costa Rican forests may at times seem dismal is that 110 of Costa Rica's 225 mammals are bats.

Bats are solely nocturnal and are usually only observed making speedy flybys overhead or not observed at all. Even when seen up close, many bats can only Tentmaking Bat feeding

be identified by experts and then only by handling the animals.

Apart from bats, about three fourth of the remaining Costa Rican mammals are either partially or entirely nocturnal and rarely seen by travelers. Only about thirty Costa Rican mammals are active during the day and even these are sometimes elusive and shy.

About 142 mammal species have been observed on the Osa Peninsula. That amounts to about 63 percent of all Costa Rican mammal species.

Common mammal species we encounter on the Night Tour include: Northern Raccoons, Crab-eating Raccoons, Mexican Mouse Opossums, Gray Four-eyed Opossums, Nine-banded Armadillos, Spiny Rats, Vesper Rats, Pacas, Tamandua Anteaters, Three-toed Sloths, Two-toed Sloths, Common Opossums, Woolly Opossums, Kinkajous, Striped Hog-nosed Skunks, Mexican Hairy Porcupines as well as several Bat species.

More elusive, and incredibly lucky, mammal encounters we have had on The Night Tour include: Ocelots, Margay, Pumas, and Tapirs. This page and the links on the right feature several common nocturnal mammal species represented in Drake Bay. All animals featured are wild individuals and most were photographed while on the Night Tour.

 


Paca - Cuniculus paca

The Paca is Costa Rica's largest rodent and is a nocturnal denizen of Drake Bay. Regrettably, this is not the case throughout the country. Despite being rodents, their meat is highly prized by hunters and is considered the best bush meat in the country. They have been hunted to the brink of extinction and are no longer found in many areas. Over the last few years we have seen this species making a comeback in Drake Bay and we commonly see them on the Night Tour. Paca - Cuniculus paca

Pacas are closely related to Agoutis but are strictly nocturnal. They spend their days sleeping in burrows, which have one main entrance and one or more escape routes. The Pacas stuff their escape routes with leaves. If a predator enters the den, the Paca will burst through the leaves covering their escape route and flee to safety. Dens may be up 9 meters long and are usually dug into the side of a bank.

In areas where they are not persecuted, they are often quite tame and have no fear of people. On many occasions during the Night Tour we have had Pacas walk onto the trail from the bushes and head right towards the group! When startled, they run a short distance into the vegetation and stand perfectly still. Unfortunately, this strategy does not work well against hunters with dogs, lights, and guns.

Pacas mostly feed on seeds and fruit. They live in monogamous pairs throughout the year, but usually sleep in separate dens and forage solitarily. Breeding takes place year round and females normally give birth to a single offspring. Pacas have been known to live up to 16 years in captivity and range from southeastern Mexico to northern Paraguay.

 


Striped Hog-nosed Skunk - Conepatus semistriatus

Perhaps the most feared mammal to be found in Drake Bay's rainforests is the Striped Hog-nosed Skunk. An encounter with the wrong end of this animal is an unforgettable event. Hog-nosed Skunks, like other skunks, posses incredibly potent scent glands near their anus. If threatened they can spray an incredibly fowl smelling liquid at a perceived threat for a distance of about three meters.

The substance burns if it makes contact with the skin and may cause temporary blindness if it reaches the eyes. Striped Hog-nosed Skunk - Conepatus semistriatusEven if no contact is made, the stench is so overpowering it immediately causes teary eyes, runny nose, and nausea.

Hog-nosed Skunks are generally very docile, peaceful animals, though, and do not spray unless provoked. When angry, they will generally loudly stomp their foot on the ground as a warning.

Striped Hog-nosed Skunks differ from their cousins by their very long nose. They are often seen sniffing along the ground and digging with their long, sharp claws for insects, worms, and small vertebrates that make their home in the ground. They are also fond of different fruits and coconuts. 

In South America, Hog-nosed Skunks are immune to Pit Viper venom, and these snakes may also make up part of Costa Rican skunk's diet.

Females normally give birth to four or five kits and they may live as long as six years. Striped Hog-nosed Skunks range from Mexico to western Perú and eastern Brazil.

 


Vesper Rat - Nyctomys sumichrasti

Vesper Rat, Nyctomys sumichrasti, photographed in Drake Bay, Costa Rica during the Night Tour

 

Vesper Rats are perhaps the loveliest rats found throughout Costa Rica's forests. They are almost completely arboreal and move quickly and gracefully through the vegetation. The first toe on their feet is thumb-like and highly adapted to gripping twigs as they climb.

Because they are nocturnal, we often encounter them on The Night Tour. These little rodents tend to freeze when caught in a flashlight's beam, as is evident in the picture on the right.

These rodents feed on seeds, fruits and insects and range from southern Mexico to Panama.  They may live more than five years in captivity.

Vesper Rats very are similar in appearance to Mexican Mouse Opossums, but are much more commonly seen than the Mouse Opossum.

 


Mexican Mouse Opossum - Marmosa mexicanaMexican Mouse Opossum, Marmosa mexicana, photographed in Drake Bay, Costa Rica during the Night Tour

Perhaps the only opossum in Costa Rica that rivals the Mexican Mouse Opossum's good looks is the Central American Woolly Opossum. This tiny marsupial is simply adorable.

Although similar to the Vesper Rat, Mexican Mouse Opossums have some distinctive identifying features. The easiest way to distinguish the two is by their tail. The Vesper Rat has a hairy tail, while the Mexican Mouse Opossum has a naked, fully prehensile tail. Mouse Opossums also have a dark mask around their eyes.

Mexican Mouse Opossums are quite rare to see in the wild, so our encounters are always prized ones. Their frequent presence in the stomach contents of Spectacled Owls (Pulsatrix perspicillata) at La Selva Biological Station suggests their numbers are greater than previously thought.

Adult Mexican Mouse Opossums are generally solitary and seldom seen together. Little is known about their social structure. Adults measure between 26 and 39 centimeters with a tail that is nearly as long as their body. They generally nest in trees, underneath logs, in dense bushes, tall grass, abandoned bird nests, or underground burrows.

Their diet is mostly made up of insects and fruit, but they may also eat lizards, bird eggs and small rodents. We found one individual inside our house feasting on a banana and they have been discovered stowed away in bunches of bananas as far away as New York City! Mexican Mouse Opossum - Marmosa mexicana

After mating, females are only pregnant for about two weeks. They may give birth to up to 13 larvae. Unlike many other marsupials, Mexican Mouse Opossums do not have pouches.

At birth, newborns crawl to the mother's mammary glands and attach themselves to one of the nipples. Should they fall off, the young opossums will cry out to their mother. She will pull the lost baby toward her belly until it reattaches to her teat. The young opossums travel on the mother's back or tail once they are old enough. If any of the young should die the mother will eat their remains.

Mexican Mouse Opossums range from southern Mexico to Panama.

 


Gray Four-eyed Opossum - Philander opossum

The Gray Four-eyed Opossum is one of our most commonly encountered mammals on the tour. They are called Four-eyed Opossums because of the conspicuous white spots which are positioned above each eye.

Gray Four-eyed Opossum, Philander opossum, photographed in Drake Bay, Costa Rica during the Night TourThese small marsupials frequent creeks, rivers and swamps where they feed on frogs and freshwater shrimp.

Other food items preferred by Four-eyed Opossums may include lizards, bird eggs, fruit, nuts and nectar. 

Female Gray Four-eyed Opossums have a well developed pouch where they carry their young for about two and a half months.

Litters may number between two and seven larvae. After the young opossums emerge from the pouch, they will remain in a nest created by their mother and continue nursing for another two weeks. 

Four-eyed Opossums reach sexual maturity at seven months of age and usually only live for about two years. Their range extends from southern Mexico to Paraguay and northern Argentina.

 


 White-nosed Coati - Nasua narica

Coatis are some of Costa Rica's most frequently observed mammals. Large groups, of up to 40 individuals, may  be observed making their way through the forest. Although they are active during the day, we often  see lone males at fruiting Malay Apple, Mango, and Breadfruit trees during The Night Tour.Coati, Nasua narica, photographed during the Night Tour in Drake Bay, Costa RicaA

Packs are made up of females and immature individuals. Male Coatis are solitary and are only allowed near the pack during their breeding season. At this time, the male is accepted by the females and will mate with each member of the group.

Soon afterwards he will be expelled from the group, possibly because males are known to kill the newborns.

Pregnant females will break away from the pack about three to four weeks before giving birth. They usually make a leafy nest in a palm tree or a tree crevice.

Females give birth to two to six young and they will remain in the nest until they are about four weeks old. Once they reach about six weeks of age, the pups and their mother will rejoin the pack.

We encountered the pregnant female pictured above several nights on the Night Tour as she prepared her nest in a tree.

Coatis are omnivores and have a varied diet consisting of insects, frogs, lizards, small vertebrates, crabs, and fruit.

Their range spans from the southern United States, through Mexico, Central America and into western Colombia and Ecuador. Life expectancy for Coatis is about 14 years.

 


Crab-eating Raccoon - Procyon cancrivorus and

 Northern Raccoon - Procyon lotor

There are two species of Raccoon in Costa Rica and they both make their home in Drake Bay. The Northern Raccoon ranges into North America while the Crab-eating Raccoon ranges into South America.

Both Raccoon species look very similar and are difficult to distinguish from a distance. The Crab-eating Raccoon is larger than the Northern Raccoon. Raccoon photographed in Drake Bay, Costa Rica during the Night Tour

Crab-eating Raccoons differ from Northern Raccoons because the fur on their necks points towards the head, instead of towards the tail like the fur on rest of the animal's back.

Also, the bands on their tails tend to be orange instead of white and they tend not to have under fur.

Costa Rica and Panamá are the only two countries where the two species coexist.

The word Raccoon is derived from the North American indigenous word "arakun" meaning scratching hands.

Both species are very good climbers, but often forage on the ground. They feed on crabs, mollusks, fish, frogs, small vertebrates, insects, fruit and other food they may scavenge.

Raccoons are mainly solitary and nocturnal, but they are sometimes active during the day.  

Little is known about the natural history of Crab-eating Raccoons but Northern Raccoons have been widely studied. With this species, a female Raccoon will typically receive one male when in heat and she allows him to mate and to accompany her for a few weeks. The female will eventually drive the male away in order to protect their her litter, since males are known to kill the young.

Gestation last 2 months and litters range from 1 to 7 cubs. The cub siblings leave their mother at about 9 months old and they may run together as a pack for a few months after leaving. 

 


Nine-banded Armadillo - Dasypus novemcinctus

There are two species of armadillo in Drake Bay: the Northern Naked-tailed Armadillo (Cabassous centralis) and the Nine-banded Long-nosed Armadillo (Dasypus novemcintus).  The latter is pictured here.

Nine-banded long-nosed Armadillos are common and often encountered in Drake Bay.  They can be active at night or during the day and usually forage slowly, with their snout pressed right to the ground.  Their keen sense of smell aids them in detecting prey items living in the leaf litter or underground.  In the tropics, Armadillos feed mostly on ants and termites, as well as fallen fruit.Nine-banded Armadillo, Dasypus novemcintus, photographed on the Night Tour in Drake Bay, Costa Rica

These animals have very poor eyesight and it is not uncommon for them to walk right into a bewildered hiker’s feet. When startled, Nine-banded long-nosed Armadillos will often jump straight up into the air and rush to safety.

The reproductive cycle of Nine-banded Long-nosed Armadillos is nothing short of amazing.  After mating, females are able to control the start of pregnancy by delaying the implantation of the fertilized egg on the uterus wall.

Although this animal's gestation period only lasts about 2 months, female Armadillos have stunned researchers by giving birth up to 32 months after mating! When they do give birth, it is exclusively to same sex identical quadruplets.

 


Hoffmann's Two-toed Sloth - Choloepus hoffmanni

In Costa Rica's lowland rainforests Hoffmann's Two-toed Sloths, Choloepus hoffmanni, are not so common to see. These animals are mainly nocturnal and they forage high in the canopy. They are active about 8 hours per day.Hoffmann's Two-toed Sloth, Choloepus hoffmannni, photographed in Drake Bay, Costa Rica during the Night Tour

Although they are active for shorter periods than Three-toed Sloths, Two-toed Sloths are more mobile. They change trees frequently and are rarely found in the same tree on consecutive days.

Two-toed Sloths feed mainly on leaves but they supplement their leafy diet with fruit, buds, flowers, insects, and even bird eggs and small vertebrates.

Two-toed Sloths have an incredibly long gestation period, about 11.5 months. Baby sloths cling to their mother during the first 6 months of their lives, never leaving her side.

Even after they are weaned, young sloths may remain close to their mother for up to two years.  They have been known to live up to 32 years in captivity.

A close inspection of the Two-toed Sloths in the two photographs featured here will reveal a distinctive green tint on the fur. Sloths have slits on each one of their hairs that serve as compartments where algae grows.

It has long been thought that the green tint afforded by the algae helps sloths better blend into their canopy habitat. This theory makes sense; after all having a green tint should help canopy dwelling sloths conceal themselves in the treetops.

Recently, though, researchers have proposed that perhaps the algae is providing sloths with an added benefit.

Scientists think that perhaps the Sloths are acquiring nitrogen from the algae, which is something they do not obtain from their primarily leafy diet.  It is thought that the nitrogen is then passed on to the Sloths through ingestion or by absorption through the skin. Hoffmann's Two-toed Sloth photographed during the Night Tour in Drake Bay, Costa Rica

The moths, which can be observed on the photo on the left, play a role in this as well. It appears that the amount of algae growing on the fur is directly correlated to the number of moths living on the sloth. The algae thrives on the feces and decaying remains of the moths, so the bigger the moth population, the more the algae grows.

This leads researchers to think that the Sloth's peculiar habit of coming down to the ground to urinate and defecate could be linked to this chain.

When the sloth defecates on the ground, moths and beetles living on the sloth crawl down and lay their eggs on the feces. The larvae develop there and eventually fly back into the treetops as adults in search for another Sloth host.

The Sloths put themselves at considerable risk by travelling all the way down to the ground to defecate, but in doing so they provide these insects with a suitable place to lay their eggs and a great place for their larvae to develop.

The insects insure the propagation of the algae on the Sloth's fur and the algae provides the Sloth with an important nutritional supplement. The complicated relationship between these completely different creatures is so intertwined that Sloth Moths, Cryptoses choloepis, have evolved to live exclusively in the fur of Sloths and do not exist anywhere else in nature.

 


Mexican Hairy Porcupine - Sphiggurus mexicanus

The Mexican Hairy Porcupine is one of the most elusive mammals in Drake Bay. So much so, that it is not listed as being on the Osa Peninsula in many of the guide books. It took us many years before we saw our first one and they are always a rare find around here. Mexican Hairy Porcupine, Sphiggurus mexicanus, photographed in Drake Bay, Costa Rica during the Night Tour

They tend to be nocturnal and solitary and very little is known about their natural history.

Technically Porcupines are rodents and they are the only rodents in Costa Rica to have a prehensile tail. Porcupine's tails are different from any other new world mammal in that the gripping pad is located on top of the tail, rather than on the bottom.

When they grip with their tail it curls upward, as can be observed in the photograph featured here.

The Porcupine's quills are this animals most prominent and distinguishing feature.

Although Porcupines cannot throw their quills, the quills do provide Porcupines with protection from predators by breaking off very easily and lodging into a would  be predator's skin.

Each quill has a very sharp point and is covered with tiny backward pointing scales. This makes them very difficult to remove once they are lodged in the skin.

It is thought that the yellow quills also serve as aposematic coloration, warning colors, to deter predators. Also, when Porcupines are startled the quills stand vertically making them look much larger than they actually are.

Despite their spiny armor, felines feed on porcupines by flipping them onto their back where they lack quills.

Mexican Hairy Porcupines feed mainly on seeds, fruit, leaves, flowers and flower buds. They enjoy Ficus spp., Cecropia spp., and we often encounter them feeding on the fruit of Cojoba arborea.

Below is a video of a Mexican Hairy Porcupine we recorded during a Night Tour

 

 


Enjoy our individual mammal pages by following the links located at top of the page on the right hand side!

 

References:

Alonso-Mejia, A. & Medellin R.  1992  "Marmosa mexicana"  The American Society of Mammologists

Beletsky, L.  2005  Travellers' Wildlife Guides Costa Rica  Interlink Publishing

Emmons, L.  1990  Neotropical Rainforest Mammals  University of Chicago Press

Fogden, M. & P.  2001  Vida Silvestre de los Parques Nacionales y Reservas de Costa Rica  Editorial Heliconia, Fundacion Neotropica

Forsyth, A. & Miyata K.  1984  Tropical Nature  Touchstone / Simon & Schuster

Henderson, C.  2002  Field Guide to the Wildlife of Costa Rica  University of Texas Press

Janzen, D.  1983  Costa Rican Natural History  University of Chicago Press

Marceau, J. 2001. "Nasua narica" (On-line), Animal Diversity Web. Accessed January 08, 2009 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Nasua_narica.html 

Wainwright, M.  2002  The Natural History of Costa Rican Mammals  Zona Tropical

http://www.nhptv.org/NATUREWORKS/coati.htm

Weinstein, B. 1999. "Marmosa mexicana" (On-line), Animal Diversity Web. Accessed May 08, 2009 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Marmosa_mexicana.html

 

Mammal Files

Mammals Home Page

Bats Home Page

Brazilian Long-nosed Bats

Greater Bulldog Fishing Bats

Tent-making Bats

White-lined Bats

Brown-throated Three-toed Sloth

Kinkajous - Potos flavus

Common Opossums - Didelphis marsupialis

Northern Tamandua - Tamandua mexicana

Central American Woolly Opossum - Caluromys derbianus

 

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