Sloths: a Misunderstanding

19 Apr

Sloths are an oft-misunderstood species.  Despite moving slowly and appearing to sleep all day, the life of a sloth can be quite compelling.  Sloths are masters of camouflage; they hide in plain sight despite being hunted by the most vicious predators in the jungle.  And let’s face it – how many times have you been in a resort in Cahuita, Costa Rica and had a sloth just appear, as though out of thin air?  Not only are sloths masters of stealth, but they are quite intelligent.  Many of the sloths at the Sloth Rescue Center in Costa Rica spent their youths finding ways out of their containers.  Our visit to the rescue center explained – sometimes in song – the simple dignity of these animals, and the complexity behind their behavior.


There are currently six sloth species belonging to two different families: Bradypodidae (three-toed sloth) and the Megalonychidae (two-toed sloth).  However, the distinction between two and three toed sloths is inaccurate as all sloths have three toes.  The difference is only present on the species’ fingers.  Only the Hoffman’s Two-fingered sloth (Choloepus hoffmanni) and the Brown-throated sloth (Bradypus variegatus) are found in Costa Rica.  Neither is considered endangered, however two species not found in Costa Rica, Bradypus torquatus and B. pygmaeus, do receive protection.

Ground sloths have gone extinct relatively recently.  These sloths could grow up to 20 feet in length and would feed by pulling entire branches from the trees.  However, these sloths had none of the adaptions that allowed their modern counterparts success in their environments.

Sloths belong to the order Pilosa.  Therefore, they are most closely related to armadillos and anteaters.


Sloths are arboreal, and very rarely leave their tree.  They are indigenous to the rainforests of Central and South America.  They are either diurnal or nocturnal.  Sloths are also proficient swimmers, which is instrumental for survival during the rainy season.



Sloths each leaves, shoots, and buds.  However, sloths have been observed complementing their diet with insects and small birds.


The harpy eagle, jaguars, and humans pose the largest threat to sloths.  While harpy eagle and jaguar related fatalities are difficult to document in the jungle, most sloth deaths are believed to be human inflicted.  While sloths are tough in their natural environment, such as being able to withstand falls from the canopy, many succumb to the dangers provided by deforestation and human development.  Many sloths at the rescue center were victims of electrical burns from power lines or lacerations from barbed wire fences.  Sloths are natural climbers and are unable to differentiate between a human imposed danger and their own habitat.


The sloth has many adaptions suitable for living in a tropical climate.  Their claws are strong enough to support the weight of a hanging sloth even after its death.  The claws are also utilized for territorial disputes between the males.

Other adaptions allow the largely defenseless sloths to escape predation.  The bradypus has nine vertebrates that allow a full 180 degree range of motion of the head.  Therefore, this sloth can detect whether an aerial – harpy eagle – or ground – jaguar – threat is imminent.  The sloth has also formed a symbiotic relationship with cyanobacteria.  These algae assist in camouflage by forming green spots on the sloth’s fur.

Sloths also have an incredibly slow metabolism to complement their lifestyle and diets.  Leaves offer little nutritents and are difficult to digest.  Therefore, it can take a sloth upwards of one month to digest a single meal!  The sloth has a multichambered stomach and has formed a relationship with symbiotic bacteria to assist in the digestion of leaf material.  About once a week the sloth exits the tree to use the bathroom.  By going so infrequently, the sloth minimizes the time away from the tree, when they are most vulnerable.  Sloths also have a very low body temperature for mammals, diverting much of their energy to digestion.  While the term sloth is synonomous with being lazy, recent studies have determined that sloths in the wild only sleep about ten hours per day.

Other Fun Facts

Sloths are solitary animals.  Adult sloths only interact to mate or dispute over mating or territory.  However, in the sanctuary sloths can become social if paired with a single other companion from a young age.

It's just unnatural

Sloth reproductive organs are protected by the rib cage.  Therefore, determining the sex of a sloth in the wild is nearly impossible.  This led to problems in the sanctuary, as some sloths were misnamed or reproduced with their companion – all without their caretakers knowing it was possible!

Rescue Center Facts

The Sloth Rescue Center in Costa Rica originally began as a bed and breakfast.  A singular baby sloth was brought to the future rescue center over twenty years ago.  Now, the facility is home to over 130 sloths.  While the center attempts to reintroduce these sloths into the wild every year, there are many limitations that prevent their efforts.  Many sloths are too injured to climb trees.  Sloths that were brought in as babies cannot be reintroduced into the wild.  In the wild, infant sloths cling to their mother’s fur while she teaches the infant which plants are nontoxic.  Without such teaching, the sloths must remain in the sanctuary for the entirety of their lives.

The rescue center is nonprofit, and relies on tours and donations to cover its operating expenses.  There is no government agency that is responsible for the collection of injured sloths.  Therefore, a large local effort is required for this institution to survive.  Many of their refugees were passed along from concerned citizen to concerned citizen until they reached the sanctuary.  Unfortunately, many sloths do not survive this journey.

The sloth sanctuary is thriving.  The original sloth, Buttercup, still resides at the rescue and is now the oldest surviving sloth in capture in the entire world.  Wild sloths attempt to scale into the sanctuary to meet the resident female population protected there.  Ultimately, centers such as this one can mitigate some of the harm that development has inflicted on indigenous species.

Briggs, Helen (2008-05-13). “Article “Sloth’s Lazy Image ‘A Myth'””. BBC News. Retrieved 2010-05-21.


Murcielagos (Bats)

16 Apr


When people think about bats, they often think about frightening images: vampires, Halloween, Dracula… Even one positive popular image associated to bats – the superhero Batman – has a dark side.

Another popular, and scary, myth about bats is that of El Chupacabra – a Latin American legend of a batlike creature that killed livestock such as goats by sucking their blood. This is one of the most gruesome and also unrealistic ideas associated with bats.

First of all, the size and features of El Chupacabra are greatly exaggerated in comparison to what real vampire bats (the ones that suck blood) look like.  Vampire bats get their name because they suck animal blood in order to survive, but never enough to kill the animal.  All vampire bats, not just the El Chupacabra, are however considered pests to farmers though because they can spread diseases to their cattle by leaving open wounds which are prone to infection.  Unaware farmers may kill any type of bats in order to protect their livestock because they view all bats as threats due to a lack of education about bats.

These myths have ruined the reputation of bats.  Many people do not like them, without good reason. So the goal of programs like the Conservation Association of Monteverde, Costa RICA (ACMCR — is to educate people of all ages to the truth about bats and to show them the benefits that these mammals bring to our environment so that we can all see why they should be not only appreciated for what they are, but conserved as well.

The bats didnt always have such a bad rep: The ancient Mayans and Aztecs worshiped bats as gods! Clearly they saw some good in these animals.

Reality about Bats

Bats are mammals (they have fur and they produce milk) – just like us!  They are one of the most common species of mammals as well.  Of the 5416 species of mammals worldwide, 21% (1116 species) are bats.  In Costa Rica, there are 113 species of bats.


Though they have wings, bats still maintain five fingers.  This is one piece of evidence that humans and bats are still pretty closely related evolutionarily.

Another myth about bats is that they are blind. The reality is they actually can see, but they are colorblind and their vision is relatively poor.  Because their vision is not great, bats rely mostly on a different method to “see”.  Bats use echolocation, an ability quite like sonar.  They emit high frequency calls and then listen to the echos in order to locate objects around them (such as their prey).  Some bats use their mouths to transmit the sounds, while others use a unique body part called the nose leaf.  Most bats have large ears to help them receive the sounds that are bouncing back. Bats can form 100 images per minute using this echolocation.

Where they live

Bats make their homes in a variety of different places: in caves or mines, under fallen trees, in hollow trees, in abandoned termite nests, in rolled up leaves (these bats have suction disks on their limbs to keep them from falling out), and in “camping tents” — the leaves are folded over and chewed to form a tent-like shape.


Bats have a varied diet, and you can usually tell what they eat by looking at their facial structures.  There are general rules that can help identitfy them, although these rules that follow only apply in Costa Rica:

  • Bats that eat fruit have a big nose leaf
  • Bats that are carnivorous have large ears
  • Bats that eat flying insects have tiny eyes
  • Bats that eat fish look like bulldogs
  • Bats that eat nectar have a long snout and long tongues
  • Bats that suck the blood from cows and other large mammals have flat noses, sharp front teeth, and a split lower lip

Environmental Benefits of Bats

Bats eat insects that we consider pests.  A 10 gram bat eats 1000 mosquitoes per hour! This means people can save a lot of money on pesticides and not get bitten as often.

Bats also aid in seed dispersal for some species of plants.  For example, A 20 gram short-tailed bat eats Cecropia seeds and disperses 24,000 seedlings per night! Bats are well known for helping regenerate forest due to their seed dispersal.

Nectar eating bats pollinate flowers. Most importantly, bats are the pollinator of the agave plant – which we use to make tequila!!


Groups like ACMCR are working to conserve bats.  At the Tirimbina Biological Reserve in La Virgen de Sarapiquí, Heredia, Costa Rica they research the abundance and diversity of bats as well as educate people (starting with young children) to eliminate the bad reputation that bats hold.  In order to study the bats, they use nets to catch them. The main reason that the bats fall into the net traps is because they turn off their echolocation from time to time to save energy and they unknowingly fly into the nets. The two species that were caught the night we went to the reserve were the Little black myotis – Myotis nigricans:

bat pic 2

and the Central American yellow bat – Rhogeessa tumida:

We also saw some bats on a boat tour we took down the river; these bats were called the “long nosed” bat (Rhynchonocteris naso)



Mi Cafecito

16 Apr


Mi Cafecita is a coffee plantation located in the high zones of San Carlos and Sarapiqui. It is 900 meter above sea level in elevation. It is a cooperative consisting of 137 small coffee producers. The coffee production is focused on Fair Trade principles and sustainable agriculture. The cooperative produces coffee for both domestic and international sales. They also offer tours and sell coffee and food on sight to attract business. Our class visited the facility and took the tour guided by Walter. We learned about each step of the coffee making process and were able to sample some of the fine product.

This is our tour guide, Walter

History and Social Impact

The cooperative started with a group of 40 coffee farmers in 1969. They came together and pooled resources to ensure their success and promote “spirit of mutual help in economic, social and cultural matters”. They adopted the title of Coopesarapiqui and Mi Cafecita coffee tours soon followed. It has also stood for clean and sustainable environmental practices.

This mural depicts how coffee plantations began in the 1800's

In addition to being a business the cooperative ensures that its members are taken care of. They also participate in restructuring and other social good projects. These include activities related to the crops themselves, modernization of agriculture practices and advanced marketing techniques. The cooperative is also dedicated to promoting the highest quality of environmental efficiency and places high merit on pollution prevention and implementation of the cleanest technologies without sacrificing quality or the needs of its members.

Coffee Production

The coffee plantations are located around 800 to 1000 meters above sea level, as is standard in Central America. It is grown in a tradition of their ancestors

This a freshly husked bean in a warm and welcoming hand

and stresses low acidity in order to produce first quality coffee that does not harm human health. The seedlings are rooted under a canopy for a few months and then planted in the soil. After a few years the plants are ready for harvest. Once the berries are harvested, they can then be removed from their husk and then sorted using a water based technique. The first quality beans naturally make better coffee which can be sold at a higher premium. Next, the beans are dried either in a greenhouse or an oven. The second skin layer is then removed and the coffee beans are ready for export. They do not roast the beans on site because the coffee is better when the beans are more freshly roasted and they have a longer shelf life.

This is greenhouse where the coffee beans are dried


The view from the scenic overlook

In addition to being a coffee plantation, Coopesarapiqui offers tours of its land and facilities, and birdwatching. Each highlight the land’s natural beauty. Our guided tour not only took us to some coffee plants, but also to some spectacular views of the Sarapiqui and Maria Aguilar Rivers and their surroundings. We saw a breathtaking valley and walked through some of the hills near the plantation where we saw a beautiful waterfall and scenic overlook.

The picturesque waterfall we viewed on the Sarapiqui river

Jack with a machete

Why are there more species of coral and fish in tropical Indo-Pacific area than the Atlantic?

26 Mar

Historical reasons:

During the last ice age, sea levels and temperatures dropped, and previously underwater ledges were exposed to erosion, both by the wind and water currents.  This typically creates features that, once the Ice age ends and sea levels rise, are ideal settlement regions for warm water corals.  These corals become reefs that attract a large number of different marine life, creating simple but unique trophic interactions that ultimately result in speciation via geographic and ecological isolation. The longer it took for the Atlantic to warm, along with the smaller area and the shallower depths, led to the Indo-Pacific gaining a leg up on coral speciation and ultimately led to a greater biodiversity in that region. Even today, it remains warmer than the Atlantic, perhaps continuing to add to the speciation

Geographic location

The interconnection of the Malaysian, Indonesian, and Philippine archipelagos on the continental shelf provides a mechanism for the isolation and reconnection of Indo-Pacific populations as sea levels change.  Populations in Indo-Pacific oceanic archipelagos also undergo isolation and reconnection as current patterns change with changes in sea level.  In addition to increasing the rate of speciation, isolation can decrease the rate of extinction by protecting populations from disease and predation.  Therefore, the bigger size of the tropical Indo-Pacific, relative to the Atlantic, gives it an advantage for achieving high species richness. Geographic isolation prevents gene flow, so populations develop genetic differences.  This independent evolution leads to speciation.

Besides size, the Pacific Ocean is older than the Atlantic. The Pacific has many more islands than the Atlantic does – and these islands provide opportunities for isolation and speciation. Also, they provide for the development of more coral reefs in the shallow waters surrounding the islands.

Temperature and salinity are also huge factors in the diversity of corals and fish because with a higher salt content in the Atlantic, fish and coral have a tougher time adapting to such waters.

The East Indies Triangle appears to act as a center for the concentration of the majority of tropical marine families. This small triangle extends from the Philippines to Malay Peninsula to New Guinea.  The location of the East Indies triangle acts as a place of dynamic evolutionary radiation as well as a long-term net source of species diversity. This “center of origin” greatly contributes to the overall species diversity of the Pacific Ocean and makes the Indo-Pacific Ocean incredibly more diverse than the Atlantic Ocean.

The main reason that area within this triangle is more successful than other marine areas is because during the time period of the Ice Age, it remained a relatively decent place for marine organisms to live.  Native species were able to survive and continue to evolve, but more importantly, species from other areas migrated to this region. This could be because they had left their homes to find better areas to live in or just because they were brought by the currents and then were able to better survive in the optimal conditions that existed in this triangle.


The different water density causes water to rise and fall, creating the thermohaline system (or Conveyor belt).  There are several different types of upwelling; however, all types drive water circulation and allow nutrients and CO2 to reach different regions of the sea.  Upwelling allows oxygen to reach the deep abyssal plain, allowing organisms on the deep sea to survive.  When water evaporates in the cool air ice can form, which further increases the salinity of the water.  The surface water is then replaced by deep water that is rich in nutrients and CO2.  This causes high primary production and creates more phytoplankton, which creates an environment for fish to thrive.


ALL IMAGES FROM GOOGLE Invertebrate Zoology

Gladfelter, William B., Ogden, John C., Gladfelter, Elizabeth H. Similarity and Diversity Among Coral Reef Fish Communities: A Comparison between Tropical Western Atlantic (Virgin Islands) and Tropical Central Pacific (Marshall Islands) Patch Reefs. Ecology, Vol. 61, No. 5 (Oct., 1980), pp. 1156-1168
Birkeland C. 1990. Caribbean and Pacific coastal marine system: similarities and differences. Nature & Resouce 26: 9.
Briggs, John C. “Coincident Biogeographic Patterns: Indo-West Pacific Ocean” Evolution, Vol. 53 No. 2 April 1999.
Barber, P. H. and Bellwood, D.R. (2005). “Biodiversity Hotspots: evolutionary origins of biodiversity in wrasses in the Indo-Pacific and new world tropics. MPE 35: 235-253
World atlas of coral reefs (Mark Spalding, Corinna Ravilious, Edmund Peter Green, 2001)

Polly Wanna Adaptation?

8 Mar

Polly Wanna Adaptation?

Different Adaptations of Birds in the Tropics

In this blog we are going to explore characteristics of tropical birds that have many unique adaptations that occur nowhere else in the world. We also included adaptations of specific species, such as the parrot, hoatzins and hummingbirds. Before talking about different adaptations it is important to know how birds have evolved to bring about unique adaptations throughout the tropics.

Keel-Billed Toucan


Specific habitats for specific species:

Tropical Birds are so incredibly diverse in the tropics for a number of reasons.  Since the tropics are so diverse to begin with, one can easily see why.  With so many niches, plants, and organisms to live and feed on, tropical birds will always flourish.  As long as resources are available, birds will be able to adapt and evolve that will allow them to survive.  The different landscapes and plants which can grow in the tropics and nowhere else provide a key reason why so many birds thrive.  An example of this is the toucan.  Toucans only reside in places where dense woodlands cover slopes at higher elevations.  This is key because it is where the humidity is high, the temperature low, and mosses and lichens cover branches and trunks just the way toucans like it.  This is just one example of many that show how slight variations of climate and resources can provide for unique birds.  It is very interesting to understand because it is not just one thing which provides for these birds.  The biodiversity of all living things in the tropics correlates causing so many variations.  Just as was seen with the toucan, the branches, mosses, climate, and elevation all coexist to provide for a unique creature in a unique area of the world.  With such a variety, the toucan can adapt in its own way using its giant colorful beak.  This beak is used for specific foods as well as for camouflage in the rain forest.  Almost every bird is different in its own way adapting to its environment.    Even environmental changes from human interference can cause speciation among tropical birds.

One would think that there would be much lower numbers of birds in the deforested areas, but there were some species of birds that were more likely to be found in deforested areas than non-deforested areas. Undergrowth insectivores such as Orthotomus artrogularis and Trichastoma rostratum were more likely to be found in recently deforested areas than non- deforested areas. Although, many insectivores that were canopy bark gleaning species were negatively affected by deforestation, especially the hornbills. Even though deforestation may support many species of birds the sensitivity of the hornbills will cause a decline in seed dispersal for trees they are associated with, into logged areas.


Deforested foothills of Monteverde and mountains in Costa Rica

Speciation due to Isolation of glaciers:

There are a number of reasons why tropical bird species are so numerous and diverse.  The main reason comes as a result of the general diversity of all species in that region.  All over the world, the tropics on the equatorial band are a hotbed of species diversity, and this characteristic provides plenty of opportunities and pressures for bird species to specialize to the point of divergent evolution.  Some more detailed theories specific to the neo-tropics highlight the geo-biological effects that receding glaciers had on bird species.  The theory holds that the changing geography created a number of distinct refuge areas that sectioned populations and enhanced speciation rates.  A competing theory argues that the relative climactic stability of the tropics created an environment where selective pressures favored speciation and specialization among bird species, a characteristic not found further from the equator.  Most likely it is a combination of the two that led to the phenomenally speciose phylogeny found in the tropics, and the neo-tropics in particular.

Speciation from Specific Diets:

One factor that can determine the types of adaptions of birds is based on what food they eat. Birds adapt their habitat location and some morphological features like beak size based on the type of food they eat. In the tropics, the food sources are so diverse that bird species can become very specialized in eating whatever food source they live off of.  Some birds that eat insects and the types of adaptive strategies that a bird could have to eat certain insects are caused by a number of reasons. First they can adapt in the way they gather their food: hunting upon the wing, digging deeply into wood, picking bugs off of leaves etc. Second they can adapt in how specific their diet is by being generalists or specialists. This will affect where they live, how social they are, and the beak morphology. Birds that are specialists will have to live very close to their food sources and possibly have a beak specialized to eat certain kinds of insects. Birds that are generalists will be able to live in a wider range of habitats and have a more generalized beak structure. By combining these two types of strategies, the possibilities of bird variation are almost endless.  Food is not the only thing that influences these adaptations, but is a key factor. The amazing amount of insect diversity allows for such a large amount of bird diversity and specialization that is apparent in the tropics.

General bird characteristics that show different adaptations among species:

Birds are a group of diverse and interesting animals.  They have developed several adaptations that have allowed them to inhabit a large range of land. 


Birds’ feathers can be used to keep them warm or to keep them dry.  Feather coloration and length play a large role in sexual selection for many species of birds.  Also feathers can be crucial in camouflage – in the tropics the vegetation is green year round, so green-feathered birds have an easy time blending in when they fly through the trees.


Wings are a defining feature of all birds.  Many birds use wings to fly, and the size and strength of the species’ wings may be correlated to how fast or how far a particular species flies.  On the other hand, some birds are flightless, and their wings may serve other purposes – for example, penguins’ wings have evolved to function in a similar manner to flippers.

Look at them Beauties


Birds’ feet come in many shapes and sizes.  Birds of prey will often have talons and feet that can grasp so that they are better at hunting.  Claws on birds’ feet may also be utilized to turn over leaf litter or soil in search of food.  Some birds’ feet are webbed and adapted for swimming and may be adapted to help birds climb or perch in trees.  Also feet and legs may be stronger and made for running.


Beaks have evolved in different ways for different bird species based on what thing or things they choose to eat. One of the most obvious adaptations that the birds of the tropics have is their beak size and strength. For example, the toucan has developed a long beak that allows it to reach fruit that is high up in the tree. Since the bird is somewhat heavy, it allows them to find food higher up in the tree where the braches could not hold their weight. The parrot has also developed a beak that allows them to feed in tropical rainforest conditions. The parrot feeds on mostly seeds, and their strong beak allows them to crack the shell of most seeds, grind up the seed, and then consume it. This adaptation comes with some risks however. Since the beak of the parrot is so strong, it is able to crack open any seed, even if it is poisonous. Therefore, groups of parrots fly down to a riverbank daily to lick the clay walls. The clay detoxifies their bodies of the poison so they are able to carry out their digestion.

Song Calls:

Birds have adapted different song calls capable of traveling through different environments and capable of being distinguished from the surrounding ambient sounds. A study demonstrated that climates with higher temperatures correlated to the higher song frequency of insects, such as crickets and katydids stridulate. Birds have developed songs with lower frequencies so they can be heard through the competing insect sounds. The high vegetation density in the tropics also interferes with the song travel.  Slabbekoorn studied bird song calls of the little Greenbul in different environments, and found that little Greenbuls populated in dense habitats transmitted their songs at a lower frequency than greenbuls populated in open areas. Another study found that birds that reside in the tropics have developed calls with frequencies between 2 kHz to 5 kHz. If male birds change their calls to be heard, they could earn an advantage when it comes to attracting female mates.  Eventually, over time, this adaptation could force evolutionary changes, splitting populations of birds into localized species with specialized reactions to the sounds in their vicinity.


Mating Call (Roaming Charges May Apply)

Metabolic Rate:

Birds that live in the tropics have to deal with a variety of constraints that their temperate counterparts do not have to face.  Thus, they have to develop certain adaptations to survive.  One of the most prevalent challenges facing these birds is the relatively low abundance of nutrients compared to density of animals competing for them.  Coupled with the heat and humidity, tropical birds can spend a lot of energy just foraging for food and water.  To compensate for this, tropical birds typically have a lower basal metabolic rate than temperate birds.  This means they require less oxygen on average than other birds, allowing them to survive, forage, and reproduce on less nutrition, and in turn increasing their diversity and abundance in the competitive tropics.  Tropical bird species also have slower growth rates and give birth to less young than birds in other environments.  Having less offspring means that the parents can focus more on feeding and protecting those they have to ensure that they reach maturity, and the slow growth rates allow juveniles to adapt to the environment that they must survive in.  Tropical birds can typically survive on less due to these biomechanics adaptations, which suits them well considering the dense biodiversity in the tropics.

Considering metabolic rate, tropical species of songbird were shown to have larger eggs than that of ones in the temperate regions. Researchers hypothesize that this could be due to the length of time spent at the nest. This papers shows and references other papers (tried to find) that find that the increase in egg size is an adaptation that helps to control the embryo’s temperature drop because of the parents time away from the nest and allows the embryo to grow productively with the greater nutrients in the egg. This idea follows along with the idea that in the tropics, it’s important to have strong young who can survive in the environment.

Unique adaptations of specific species:


In the tropics there is a wide diversity of hummingbird species. Many hummingbirds have actually co-evolved to form a specific beak length and nectar retrieving technique for one specific flower that it mainly feeds from. One example is the hermit hummingbird and the Heliconia. Hermit hummingbirds have long de-curved bills that specifically fit directly down the floral tube of the Heliconia plant. The white-tipped sicklebill hummingbird species has a shorter, but more hook like beak that it utilizes to get nectar from certain orchids. These specialized beaks provide a reason for the hummingbirds to stay close to certain flowers. In the tropics there is a wider variety of plants and thus the hummingbirds are drawn to stay within the area closest to the plants they know they can retrieve food from.
However, hummingbirds are the best suited to feed out of these tube shaped flowers because they also have a very unique flying pattern. The way they have adapted to beat their wings so rapidly and in the helicopter motion that they do allows them to steady themselves in the air. This steadiness allows them to hover over these tubular flowers and have the ability to spend more time to correctly place their beaks down the tubes to collect the nectar.
They also have very unique coloration that sometimes matches the coloration in the main flower they feed from. The coloration can sometimes help with camouflage, it can distinguish the difference between species, and it can also ward of unwanted predators. Some studies have been done that show that coloration is based on sexual selection. The brighter more vibrant the colors attracts more females. Overall hummingbirds are just one species of birds that have unique adaptive traits that allow it to survive and specialize in the tropical rain forest.


Young Hoatzins have clawed wings, which enable them to literally climb up branches. This is thought to be a vestigial trait from dinosaur precursors. What is incredible is that it was retained, and there is a clear reason for it; Hoatzin build their nests low to the ground, usually over or immediately near water (they feed on marsh reeds and swamp plants). The young are also good swimmers. They frequently fall out of the nest, and when they do, they swim to shore and are able to climb back up the tree into their nest – a truly remarkable thing to see a bird doing. This living fossil has retained ancient traits to help it survive in its rainforest environment.


Swallow-tailed gull (Creagrus fircatus):

The swallow-tailed gull (Creagrus fircatus) is one example of a tropical bird species that has unique adaptations to its environment.  Found primarily on the Galápagos Islands, the swallow-tailed gull is the world’s only nocturnal seabird.  Its nocturnal behavior has several advantages.  Diurnal gulls compete for food with a number of other fish-eating species and scavengers, including albatrosses, boobies, and terns; in contrast, the swallow-tailed gull feeds unopposed at night.  Some aggressive birds, such as hawks and man-o-wars, feed on young gulls.  By staying at their nests during the day, swallow-tailed gulls can protect their young from predators.  These birds are well-suited for nocturnal activity.  They have white areas on their wings and heads, which make them more visible when feeding their chicks or displaying for mates at night.  They have exceptionally large eyes with distinctive reflecting structures, which enhance sight in low light.  They have a unique diet of primarily squid, which only swim to the sea’s surface at night.  Finally, the swallow-tailed gull has unusual calls that resemble the clicking sounds made by bats and porpoises; these sounds have been hypothesized to be a form of echolocation.

Macaws (Parrots):

Parrots have a few unusual adaptations. Some use not only their feet to climb trees, but also their beaks. One particular parrot species, the Southeast Asian hanging parrot, sleeps upside down like a bat. Parrots mate with one partner their whole life. If one partner dies the other one either lives out its life in solitude or joins another pair to make a triplet. Macaws gather on clay cliffs of the Amazon River to ingest minerals that bind to the seed toxins that they eat rendering them harmless. Swifts are a quasi-rainforest species because they spend most of their lives in flight. However, when these birds land they need to land in emergent trees because their wings are so specialized for prolonged flight that they do not facilitate a traditional take off.

The ability for parrots to talk is based around the similarities they have to human larynx. Firstly, talking birds do not have vocal cords; rather they vibrate the sound they produce in their throats. The syrinx is situated between the lungs and trachea and consists of the branching bronchi of the bird. It is similar to the voice box of humans. Either side or both sides together of the branched syrinx are used to produce sounds. Because of the branched shaped of the syrinx, the bird can produce two different pitches at one. It uses almost all of its air to produce sounds in comparison to humans that only use 2%. Each individual uses different techniques to produce sound within this complex.
The words parrots speak are not considered part of their language, but the African Grey Parrot is said to have the ability to understand the meanings of words to produce sentences. As said the birds are largely mimickers which could be to their advantage to protect against predators or invaders to their territories. Their varying sounds are also used to attract mates. While the parrot and other talking birds are deemed intelligent birds it could be a result of the specialized use of their feet and beaks. The combination of fine motor skills, may have aided in the development of their brains, seeing as their frontal cortex shows similar features found in humans. As their brains developed so did their ability to produce sounds and see the meaning in their ability to produce a variety of sounds.


Kevin Likes Chocolate



Tattersall, G.J., et al. Heat exchange from the toucan bill reveals a controllable vascular thermal radiator.Science. 2009 Jul 24 ;325(5939):468-70.

Hailman, J. 1964. The Galápagos Swallow-tailed gull is nocturnal. The Wilson Bulletin 76: 347-354.

Nelson Giogio Kirschel, Alex. How ecology shapes bird song in tropical rainforest. Los Angeles: ProQuest LLC, 2009. 62-63. ; adaptations; bird calls in tropical


Strover, dawn. “Not So Silent Spring.” Conservation Magazine . (Vol. 10, No. 1), January-March 2009: Web. 4 Mar. 2012.

Martin, Thomas E. Egg Size variation among Tropical and Temperate Songbirds: An Embryonic Temperature Hypothesis. Proceedings of the National Academy of Sciences of the United States of America. Vol 105 (27): 9268-9271. 2008

Bird Species and Traits Associated with Logged and Unlogged Forest in Borneo; Daniel F. R. Cleary, Timothy J. B. Boyle, Titiek Setyawati, Celina D. Anggraeni, E. Emiel Van Loon and Steph B. J. Menken; Ecological Applications , Vol. 17, No. 4 (Jun., 2007), pp. 1184-1197

The Structure of the Tropical Rainforest

20 Feb

The structure of the tropical rainforest is very different from the temperate forests we’ve got up here in Rhode Island. There is a reason why people compare cities to jungles; the rainforest is every bit as architecturally diverse and lively as any city (but jungles are prettier and they smell better…) The structure of the rainforest is both vertical and horizontal, a three-dimensional panoply of microenvironments and niches. Here we are going to explore the nature of this structural diversity, and how niches make it possible. Animal species found in the same layer are said to feed in similar fashions as other animal species also found within the same layer. Plant species also follow a similar pattern of species convergence within the each layer. Many factors are responsible for the characteristics of the TRF. Those responsible include: the overall climate, sunlight, gaps, moisture, and nutrient. While not one factor  has been considered the limiting factor, many have commented on the availability of nutrients leading to the complexity of the TRF.

The structure of the rainforest is one of great complexity. The dense nature of the TRF illustrates evolution at its greatest challenge. With then number of plants and creatures encompassing these lands, much organization was done over time.

The TRF shows clear layers found in both its animal and plant grouping. According to P.W. Richards (1952), the vegetation of the TRF is divided into:

1)    Emergent Layers

2)    Main Story Canopy

3)    Understory

4)    Shrub Layer

5)    Herb Layer/ Forest Floor

These layers provide different microhabitats for animal and insect species which was defined by J.L. Harrison (1962) into six categories which are:

1)    Upper

2)    Canopy

3)    Middle- Flying animals

4)    Middle –Climbing animals

5)    Large Ground Animals

6)    Small Ground Animals

The strata of a TRF

Tropical rainforests are characterized by high temperatures, heavy rainfall and low seasonality. This creates a perfect greenhouse-like environment in which plants can grow, but also presents a large amount of competition between different plants struggling for limited light in the event of a tree-fall.

Less than a quarter of the sun rays reach the forest floor. All plants desire sunlight, it is especially apparent when a gap forms in the forest. The gap can be caused by fallen tree, storm damage, and the effects of humans clearing the forest. Once a gap is formed, competition for sunlight begins. The gap provides the opportunity for plants that have been dormant waiting for sunlight to become revitalized and create change. Beside the gaps formed by fallen trees, we must also include the gaps found within the canopy leading to the emergence of epiphytes.

A tree-fall lets light into the lower strata.

Each layer is home to millions of its own distinct species, in a vast cobweb of symbiotic relationships and other interactions.  Although there is a huge variety of trees in the forest, there is a “typical” rainforest tree structure; most trees have little branching, and wide roots to capitalize on as much of the poor soil as they can. They often have smooth bark to try to prevent epiphyte colonization. Buttress roots are common, too. Because some trees can have extremely widespread root systems (up to 3 acres in some paleotropical forests), most emergent trees are not that close to one another. The tallest and broadest trees are not found in the rainforest. The trees have their branches concentrated near the canopy, so as to not waste energy on leaves that are never going to see the sunlight. Most trees do not have large canopies or branches because of the lack of light in the undergrowth. Plants in the lower strata have “drip-tips” to prevent accumulation of water on their leaves, which would otherwise rot quickly.

Emergent trees exhibit the "typical" rainforest tree structure

       Drip-tips keep the leaf surface dry

Epiphytes are one of the elements of the rainforest’s architecture that is especially different from what we usually see in temperate forests. They are plants that grow on other plants. They usually do not parasitize the tree but simply use it as a “ledge to stand on” to get better access to sunlight. Epiphytes in the lower strata obtain their nutrients in other ways, by feeding on decaying matter, animal feces, and rainwater leftovers. Epiphytes have been found to live in greater abundance on trees with rougher bark. In the event of a tree-fall, the epiphyte population in that particular area will usually decrease.  They also receive nutrients from shallow roots and the vessel they have formed in their host plant.  Their location on the host plant occurs in gaps of leaves and branches found on the host. The emergence of epiphytes are one of the many adaptations plants have created to overcome competition further leading to the complexity of the TRF.

The soil of the TRF has often been called the “wet-desert” because of the lack of nutrients found within it. The nutrient cycle found within the tropical rain forest is very efficient but also in high demand. The majority of carbon is found from leaf litter, living vegetation, and dying wood trees. With the aide of fungi as recycling support any material that can be reused is converted to usable material and quickly taken in by neighboring plants. While nutrient necessary for plant growth, but so is the need for energy from sunlight.

Lianas help support tall rainforest trees

Liana plants are very characteristic of the structure of the rainforest; they are woody long-stemmed vines that grow in the soil and climb up trees to the top of the canopy for sunlight. They bridge many different trees together to help them withstand strong winds. The way the ubiquitous lianas function is a good metaphor for the rainforest as a whole, I think; if a liana is dragged down, it usually pulls several tall trees with it. In the same way,  the species of the rainforest are so intertwined that there’s no such thing as a solitary extinction, really; what would happen to Darwin’s magnificent orchid if its moth were gone?


Perhaps the most critical factor enabling the spectacular structural and biological diversity of the rainforest is the plethora of biological niches in which the species establish themselves. Niches allow a vast number of organisms to thrive in a relatively small area by minimizing the competition between species. The niches are established by microclimates that are created throughout the forest’s vertical column. The upper layers, for example, are dry and extremely hot; water is scarcer up here. The lower regions are much cooler and wetter. Species segregate according to what microclimate they’ve adapted to thrive in.

The adaptations that many plants are created often revolve around the competition for nutrients or sunlight. Those that revolve around nutrients include the formation of shallow roots, stilts, buttresses, and pneumatophores, just to name a few. Each allows the plant to quickly gather nutrients upon their availability in the poor soils of the TRF. Other adaptions can also include the emergence of carnivorous plants as a way to gather nutrients outside the normal plant nutrient cycle. Sunlight adaptations include brood leaves and buttresses to provide the plant with support to reach maximum sunlight available.

Tropical rainforests have an intricate structure that makes them truly unique among biomes. Popular culture makes us think of rainforests as being some Indiana Jones-esque jungle that is impermeable to all who don’t come slinging machetes. The reality is that the rainforest’s structure is extremely varied and the underbrush is not all that thick due to lack of light. If you want to stray from the established trail, you’re more than capable of doing so.

just don't step on me.



“The Distribution of Feeding Habits Among Animals in a Tropical Rain Forest”. J. L. Harrison Journal of Animal Ecology , Vol. 31, No. 1 (Feb., 1962), pp. 53-63

Richards, P. W. (1952). The Tropical Rain-forest, an Ecological Study. Cambridge.

Kricher John, Tropical Ecology. 1st edition, Princton university Press 2011

Schnitzer S.A., Bongers F. (2002) The ecology of lianas and their role in forests. Trends in Ecology and Evolution, 17 (5):223-230.

Addo-Fordjour P, Anning A, Addo M, Osei M. Composition and distribution of vascular epiphytes in a tropical semideciduous forest, Ghana. African Journal Of Ecology [serial online]. December 2009;47(4):767-773.

Kricher, John. Tropical Ecology. First Edition. Princeton University Press 2011. Pg 103-105.

Biodiversity in the Tropics

9 Feb

There are multiple factors coming into play when discussing why the tropics are so rich with biodiversity.  Most ecologists would agree that it is a combination of these factors acting together that allow for such a high number of different species in such a relatively small region of the world.  We summarized the four major causes of tropical biodiversity and detailed how each play a role in the unique ecological make up of the tropics, specifically Costa Rica



The position of the sun over the equator, the location of the tropics, creates consistent warm temperatures in tropical regions. Warm temperatures in the tropics have a significant effect on biodiversity.  An article posted by the  Smithsonian Institution claimed that during the period of rapidly warming climate change known as the ‘Paleocene-Eocene Thermal Maximum’ a significant amount of species evolved and extinctions were minimal. The world warmed by 3-5 degrees C and carbon dioxide levels doubled in only 10,000 years[1]. The main focus of this article was to show that increasing temperatures in the tropics might be beneficial for speciation to occur in the tropics.

Another reason why the tropics are so diverse is because of the high degree of geographical and climate variability within them.  The Tropics are continuously expanding, which provides more chance for evolution and diversification. As the Tropics grow and expand, habitat variation also increases. Habitat variation allows speciation as organisms evolve to survive in their specialized habitat.   There are a tremendous amount of “microclimates” in tropical regions.  One example of such variation can be from the giant buttress trees growing throughout the forests.  These trees create different “sections” around it, allowing for different organisms to make their own homes.  In one crevice a tarantula can make its nest, while on the other side, a snake can make a different home.   Mountains might separate lowland rainforests, or sections of the rainforest might be cleared out for agricultural use. This isolates segments of the population from one another, and allows them to become evolutionarily divergent.  In addition within a microclimate, plants, animals, and insects reach their peak amounts of variations, and as resources deplete, species begin to compete for these resources, and only those with dominant adaptations survive.

Evolutionary and Ecological Theories

 A different view is held by ecologists, who have suggested that the tropics could act as a cradle and/or a museum.  The cradle view holds that the tropics are uniquely suited to speciation:  species generation is high, and species tend to accumulate in tropical ecosystems far more than outside the tropics. This view reflects the ideas of Dobzhansky, who hypothesized that the equitable tropical climate—offering abundant rainfall, no frost or cessation of plant growth, warm and relatively constant temperatures, and few severe meteorological fluctuations overall—allows speciation to exceed extinction to a greater degree in the tropics than at higher latitudes.  In contrast to the cradle perspective, the museum view holds that speciation rates are not higher in the tropics, but that extinction rates are exceptionally low instead.  Consequently, the tropics maintain their older species while adding new ones through evolution, which leads to a high species richness[2].  Therefore, more diversity comes about when the rate of speciation is higher than that of extinction.  The tropics have the most favorable climate for survival with prime temperatures and constant rainfall.  This, along with the high number of niches, decreases the rate of extinction.

Another theory is the Janzen Connell hypothesis, which holds that disease prevents certain species from dominating an entire region, allowing multiple species to live in close vicinity.  Since specific pathogens kill certain species that are localized in certain regions, if the pathogens kill off dominating species, then the less aggressive species living in that area would be able to survive[3]. In 2005, researchers developed yet another theory to explain how different species share limited space.  According to this theory, variations in birth rates and mortality rates of different species determine community membership.  Because more abundant species have lower birth rates and higher death rates, while uncommon species have higher birth rates and lower death rates, the species regulate themselves.  Don’t be quick to confuse “diverse” with “abundant.” While the tropics are extremely diverse, some species are plentiful while others are rare[4].

Environmental Policy

The rainforest at one point took up approximately 12% of the world’s land, but has regressed today to approximately 5.6%.  While the amounts may seem small, 5.6% is around 2.6 million square miles[5].  One suggestion is that Costa Rica’s high biodiversity and species density has a lot to do with the country’s policies on conservation.


Education is key in conservation, and the government of Costa Rica promotes environmental education to both its citizens and tourists.
More than 26% of Costa Rica’s land is protected, and policies continue to be made in an effort to end deforestation and protect the beauty that is Costa Rica.  “Loss of area directly translates to loss of species.[6]”  When we allow deforestation and pollution to destroy ecosystems, species go extinct.  The high value that Costa Rica places on nature has helped shaped its national and international policies and has kept the number of species living in the small country of Costa Rica high.

Plant/Primary Production

 Costa Rica, because of its location is able to support the perfect environment for tropical rainforests.  Because of the high amount of sunlight, photosynthetic organisms can consistently find energy to grow, and because of the unique relationship between primary producers and decomposers, the tropics provide secondary consumers with plenty of resources. Fungi called mycorrhizae form a mutualistic relationship with the roots of the tree, allowing for more efficient nutrient exchange. However, in the tropics, this relationship is extremely prevalent, creating a much more effective cycle of nutrient flow from the soil into the roots of the plant.  Thus, though the total amount of nutrients within the soil of a tropical region is low compared to a temperate one, the amount of nutrient recycling within a tropical region is extremely high.  In other words, high biodiversity in the tropics is a result of efficient usage of available nutrients, not necessarily a large amount of nutrients[7].

This all contributes to the very high rate of nutrient flow from one organism to another which characterizes tropical environments, all making for a ton of organisms looking for constantly shifting nutrients.  Therefore, energy productivity is high all year round, and organisms are active all year as well so organisms can specialize in one food source with the expectation that it will be there all year.

[1] Dymala, Susan et al. (2009). Floral indicators of late Paleocene-Eocene thermal maximum climate change in the Bighorn Basin, Whyoming. GEOL 393/394.

[2] Kricher, John. Tropical Ecology. First Edition. Princeton University Press 2011

[5] Darwin, Origin of Species, 1859.

[6] Kricher, John. Tropical Ecology. First Edition. Princeton University Press 2011

[7] Vitousek, P.M. and Sanford Jr., J.R.  (1986). Nutrient cycling in moist tropical rainforest.  Ann. Rev. Ecol. Syst 17: 137-167