Download Observing Rainforest Wildlife

Know Before You Go
Rainforest Wildlife - Acquiring a “New Set of Glasses”
In order to truly appreciate the beauty
and
complexity
of
Amazon
biodiversity, you need a special set of
glasses to observe wildlife – and we
don’t just mean binoculars!
As a first time visitor to the Amazon it
is easy to take for granted the way an
animal looks or behaves as you add
another species to your growing list of
spottings and quickly move on in
search of something new.
We encourage you to let your curiosity get the best of you and slow down. Take the time to observe
carefully and ponder how the wildlife of the rainforest are uniquely adapted to the rainforest ecosystem.
Below is a framework of probing questions to help you “acquire a new set of glasses” as you
observe rainforest biodiversity.
Structure: Why do animals look as they do? For example, why do capybaras have all of their facial
features (eyes, nostrils, ears) towards the top of their head, rather than spread out on their face like
people do? Why do toucans have such large beaks and how do they manage to fly with them when their
beaks look so heavy but their necks are so small?
Food Finding: What types of food do they eat? How do they locate and consume it? How do they
protect themselves from consuming something that may be harmful? Do they eat the same type of food
throughout the year? What would cause them to change their eating habits? What do parrots eat when
fruits are less readily available during the dry season?
Physiology: How are an animal's physiological functions such as digestion, metabolism, and control of
body temperature adapted for their environment? How do termites digest wood?
Social Grouping: In what types of social or family grouping do animals live? Do they live with several
others of their species? Do they live closely with others that are not within their species? Do they live a
solitary life? Are they a member of a caste system? How do rodents such as the pacas live together and
react to each other? How do they react to a perceived threat?
Communication: How do animals communicate with each other? The rainforest can be a noisy place,
particularly in the early morning Why are so many of the animals making noise? With whom are they
communicating and for what purpose? What benefit could howlers derive from having their voices travel
over a mile?
Migration: Do animals live in the same place all year? Why do some animals migrate? How do birds
migrate vast distances to return to the same place year after year?
Mating/nesting: How do animals choose their mates? What rituals do they follow? Why would male
manakins perform an elaborate dancing ritual for the females? Why do several species vocalize more
commonly than others? Why are these noises important for mating? What are their nesting and child
rearing habits?
These questions will help you build a framework for observing wildlife and forming your own
hypotheses; but don't be frustrated if your questions merely provoke more complex questions, rather than
giving you a great number of answers. Questioning is one of the most important components of the
learning process and refining questions is a fundamental process of science.
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As you make observations, you will realize that the answers don’t fall into any separate,
discrete categories. Each animal must be viewed as a whole organism in which all of these
categories interconnect. Scientists are involved in an ongoing quest to understand the why’s
and how’s of the animal world and still do not have definite answers to many of the
seemingly most obvious questions about animals.
Structure
What is the first thing you notice about an animal? Have you ever tried to figure
out why it looks as it does or how different living conditions may have created
different features or adaptations? When sizing up an animal's appearance,
consider its environment and its need to: 1) be mobile; 2) protect itself from predators; and 3) obtain food.
Most New World (North, Central and/or South American) primates are canopy specialists and rely on a
prehensile tails that wrap around tree branches and act as a fifth limb. They also use a method called
brachiation which means, quite simply, that they swing by their arms. Spider monkeys are particularly
adept at this because they have very long arms and slender, graceful bodies.
How do sloths, who have no prehensile tails, manage to live in trees? They have three claws on each
foot that serve as hooks to latch them onto the tree while they hang around for days at a time and to help
them climb down the tree for their once a week visit to the ground to defecate. These claws certainly do
not enable sloths to travel as quickly as primates but their lifestyle of hanging around in trees until they
grow moss in their fur doesn’t require very speedy locomotion.
Capybaras, the largest existing rodents known, spend a fair amount of time on land, but are adapted to
live in water. They have webbed hind toes to aid in swimming and all of their facial features are located
on the upper part of their heads, which enables them to keep track of their surroundings while they are
swimming.
Tree frogs would have an extremely slippery job hopping across the perpetually wet leaves of the forest
if not for their specialized feet, on which they have mini “suction cups” that help them adhere to any damp
plants, grasses or debris they may encounter.
Since every creature in the rainforest is at some time either predator or prey, self defense mechanisms
are crucial to survival. What structural adaptations for survival can you observe?
Structure plays a very important role in the acquisition of certain foods. For instance, marmosets,
which are small, sap sucking primates, have unusually long, sharp incisors. Marmosets use their incisors
to gnaw holes in trees to get to the sap, which they then drink or “suck” out of the tree.
Without these specialized incisors, the marmoset would have to substantially change its diet or would
soon perish because it would be unable to extract sap from the trees. The only other likely option would
be the gradual development of another characteristic that might better aid in sap sucking, making the
incisors no longer necessary, but this would have to take place before the loss of the incisors for
marmosets to be able to survive.
Many birds rely on specialized beaks to acquire their food. The size and shape of their beaks frequently
indicate the birds’ main food source. Toucans have deceptively large beaks. Although they look
extremely heavy they are in fact quite lightweight. The beaks consist of a tough horn like exterior
covering honeycomb like networks of bony fibers. Their upper mandibles are sharply serrated and curve
downward, enabling them to snip fruit, their primary food source, from the tree / vine.
The large beak size allows toucans to merely flip their heads back and gulp the fruit.
Interestingly, beak length and shape will vary among hummingbird species.
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Beaks are often used to locate nectar secreted near the base of a flower.
Hermit hummingbirds are one such group that are noted for their association
with Heliconias. These plants have beautifully colored bracts which cover the
somewhat inconspicuous flowers. The sickle shaped bills of the hermits allow
them to successfully gain nectar and pollinate the flowers of the heliconia.
Food Finding Behavior
How do animals adapt to prevent over competition for food in the rainforest? Instead of
all
clamoring for one type of food, they target different types of food at different levels of the
forest and at different times of day. High levels of competition among species for food,
as well as other resources, have resulted in increased specialization. Each species becomes
a specialist focusing on a specific resource that it is best at procuring. This degree of specialization
reduces the intensity of competition with other species as each specializes to its exclusive pool of
resources.
Bats are a prime example when discussing feeding specialization because there is greater species
diversity amongst neotropical bats than in any other mammalian order. The hundreds of neotropical bat
species are specialized to feed on every different type of diet. While some species eat only fruit, others
will consume animal blood. Many are nectivorous (nectar-eating), while still others are carnivorous (meateating). Each species has special features to aid it in food acquisition. For instance, nectivorous bats
have a very long, thin tongue, quite like a hummingbird’s, designed to lap up the nectar contained deep
within flowers. So as not to compete with hummingbirds and other diurnal (active during the day),
nectivorous birds, bats feed at night. To avoid too much competition with each other, individuals of many
bat species will fly at different levels of the rainforest, restrained by others
from expanding their foraging niches.
Since bats forage at night, eyesight is of little or no use. Instead, they rely
on unique sensory abilities. Bats have a highly specialized sonar, or “echo
location” system that allows them to detect the location of objects around
them, especially their prey. Imagine the difficulty you had with precision the
last time you swatted a mosquito, then imagine being able to do so blindfolded
and with great accuracy!
Physiology
Digestion and metabolism are physiological functions that play an important role in the feeding process.
Bats not only specialize in their methods of obtaining food, but they also specialize in their methods of
digesting food. The three species of neotropical “vampire bats,” as we commonly refer to bats that
consume animal blood, have heat sensors that help them locate the vein they will attack. Their incisors
are so sharp that they often leave very little scarring where the bat pierces the animal’s flesh. Their saliva
contains special anticoagulant enzymes, which keep the blood flowing freely while the bat laps up his
meal. The bat’s digestive system also contains special enzymes to aid in the digestion of the protein rich
blood, by breaking down the proteins and enabling the bat’s system to get the most possible nutrients
from the blood. Contrary to what Hollywood has taught us over the years, “vampire bats” don’t prefer to
prey on humans, and have only started to do so rarely as their animal prey grows increasingly scarce due
to human encroachment.
Hummingbirds are another of the rainforest’s creatures whose functions have become highly
specialized. Hummingbirds prefer nectar because of its high energy content and easy digestibility. Most
rely on hovering high in air by the flower while consuming the nectar within. To hover, the hummingbird
must beat its wings eighty times per second. Their heart rates can reach 1260 beats per minute!
Consequently, their metabolism is so fast, they feed almost continually. At night, their metabolism slows
down so they may rest without burning all of their fuel and practically non-existent reserves which at their
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waking metabolic rate would cause them to literally starve themselves to death! This specialized state is
known as torpor.
As you can see in the case of the hummingbird, being unnecessarily heavy could be detrimental to its
ability to fly. As a result, birds rarely specialize in folivary (leaf eating). Leaves are fibrous and take far
longer to digest than nectar or small insects and, therefore, require digestive storage that adds weight.
Such arboreal herbivory is, however, common among marsupials, edentates, rodents, and primates, who
may cling to a tree or stand firmly on the ground while eating.
Plants often protect themselves from predation by using chemical warfare (carrying toxins in their
leaves, seeds, etc. to make them unpalatable to most animals). How then do herbivores combat these
toxins so they may eat plant parts without poisoning themselves? Herbivores (plant eaters) often have
specialized digestive systems. They pretreat the plant by chewing it and mixing it with saliva, making it
easier for the digestive enzymes and microbial fermentation to destroy or limit the toxins. Although many
plants will remain poisonous throughout this process and, thus, be considered unpalatable, it does
increase the herbivores options for food by increasing the palatability of many plants and seeds.
Among many other plant parts, macaws eat a variety of seeds, which tend to be the most toxic part of the
plant. One theory discussed in National Geographic in January of 1994, is that this greater reliance on
seeds during the dry season explains the greater presence of macaws at clay licks, which are large cliffs
of clay deposits where macaws scrape off and eat the clay at this time. The likelihood is that the macaws
eat the clay which binds to the toxins and carries them more quickly through the body, preventing their
absorption and thereby protecting the macaw from being poisoned.
Termites have adapted to combine their digestive process with building their nests. They have
developed a symbiotic relationship, a relationship by which both participants benefit, with a type of
flagellate protozoan that lives inside them. The protozoa digest the cellulose that the termites eat, helping
them turn digested wood and fecal material into the glue out of which the termites build and repair their
nests. The protozoa profit by gaining nutrients from the food they digest and by having a place to live.
Thermoregulation, the self-management of body temperature and moisture, is both a physiological and
behavioral process. Important physical factors in controlling heat exchange are body size and insulation.
Smaller animals have a greater surface to volume ratio and lose heat more rapidly so they require a high
metabolic rate and high energy to produce enough heat. Birds commonly consume vast quantities of
food, often several times their body weight, in order to maintain a stable body temperature. Large
animals will tend to have a slower metabolism, enabling them to stay warmer in colder temperatures for
longer periods of time.
Reptiles and amphibians, however, rely heavily on behavioral adaptations. Reptiles control their body
temperature by sunning to warm themselves and resting in the water to cool themselves. Amphibians
rely on living close to water or in moist regions at all times, because they must spend much of their time in
water to regulate their body moisture. Without these behavioral adaptations, reptiles and amphibians
would be physiologically unequipped to control their bodies’ temperature or moisture so they would soon
perish with any minor climactic shift in their environment.
Social \ Family Grouping
How do animals determine the social order in which they live? As best we can tell, different species
have a group size in which they function most efficiently. The size of the social systems range from
solitary to large groups and the diversity of roles within the groups vary from loosely structured to
amazingly complex.
Many neotropical mammals such as capybaras, peccaries, agoutis and pacas are highly social and live
in herds. Peccaries have dorsal scent glands. To identify each other, they rub against each other’s scent
glands. Agoutis and pacas tend to live in the same area and share the same food sources but have
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lessened the competition between the two species by the agoutis being diurnal and the pacas being
nocturnal so they feed and move about in their habitat at different times
Termites are referred to as social insects and live according to a tri level caste system in which they have
a highly efficient division of labor. Most of the nest’s inhabitants are either workers or soldiers.
Workers build the nest and feed the queen. They are blind and follow chemical trails laid down by other
workers. Soldiers defend the nest and the queen by ejecting a sticky substance that irritates would be
predators. The queen (or, occasionally, queens) is located deep within the nest and is so enormous that
she is practically immobile and must be catered to by the workers. Her sole purpose is to produce all of
the eggs for the termite colony.
Some flocks of birds travel together within the same territory and are mixed. For instance, many
tanagers, euphonias and honeycreepers travel with antbirds, woodcreepers and other species in large
mixed flocks that forage for army ants and any prey the ants may lose. Mixed foraging flocks occupy
specific territories and, when another flock is encountered, the same species from each flock engage in
“singing bouts” and displays as boundary lines are established. Adult members tend to remain in the
flock at least two years. Nesting occurs in the general territory of the flock, the nesting pair commuting
back and forth from nest to flock.”
Although no one is sure as to the exact reasons for living in a mixed flock, one popular hypothesis follows
the safety in numbers theory. Basically, the more eyes you have to watch for predators, the less likely
you are to get caught off guard. Other possibilities are that having birds of several different species in the
flock make territory negotiations easier by having flock members from the same species as members of
other competing flocks. Perhaps there is less competition between flock members for food when the
flock is mixed because many members specialize in different types of food at various levels within the
canopy. Any one of these reasons may be correct or they may all be, in part, correct. Perhaps none of
them hit the mark and the explanation is still a complete mystery to humans.
In contrast to these other species, tinamous are solitary and elusive ground dwellers that bare a slight
resemblance to a chicken. Although they choose to live separately, they do communicate with each other
in a chorus of flutelike whistles at the beginning and end of each day. Quite likely, they partake in this
chorus to alert each other as to their whereabouts. What benefit might they derive from communicating
with their peers, from whom they appear to want to keep their distance?
As you explore the rainforest, look for variations on these social systems and consider why these systems
have evolved. What makes a certain social system, its size and the role of its participants, particularly
well-suited to a certain species?
Communication
Tinamous are only one out of a great number of rainforest creatures that call
to each other in warning or in greeting. Birds are extremely vocal
communicators and sing at all hours in the rainforest, but especially at
dawn and dusk. Why would they choose these times to be more vocal?
In many cases one bird will have a variety of songs that it uses at different times
and in different combinations. What might be the purpose of all these songs?
How would this gift of song improve a bird’s chances of survival and reproduction in the
neotropical rainforest?
Parrots are among the most gregarious bird species. They are almost always
found in large flocks and may shock unsuspecting observers who, thinking they
have found only a few parrots in the tree tops, are inundated with numerous
colorful, shrieking birds. With such an onslaught, most predators would be intimidated and
go elsewhere.
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Howler monkeys are, perhaps, the best vocal communicators in the rainforest. The male howler monkey
possesses a throat sac that acts as a resonator, producing a voice that carries nearly a mile. This is an
extremely useful method for determining territorial rights since the howls travel so far that the monkeys
may agree on territorial boundaries without ever meeting.
Many insects make sounds, usually by rubbing certain body parts together as does the cricket.
Interestingly, numerous insect species also use chemical trails. Consider the blind termite workers
mentioned in the last section and the trail they leave for the workers following behind them. Most ants
leave a trail that you can see if they walk over a smooth surface such as a leaf or rock. In addition, many
insect species release pheromones that attract the opposite sex.
What other types of communication have you noticed in your observations? What purpose does this
communication seem to have? One of the aspects of animal life in which communication may be most
useful is mating.
Migration
Most of the birds that migrate between breeding grounds in North America and wintering grounds in the
tropics are insect-eating land birds such as swallows, swifts, orioles, and warblers. Birds migrate
primarily to find food. Migration allows birds to take advantage of the abundant food supply of the
temperate-zone summer, and avoid the lean fare during the winter. Avoiding cold temperatures is a less
important reason for wintering in the tropics, than the scarcity of food (mainly insect prey) and the lack of
foraging time (due to short day length).
An important thing to remember about the rainforest is that the stability of its climate allows for a fairly
steady availability of resources. This does not mean, however, that there are absolutely no seasons in
the neotropical rainforest and no need for seasonal shifts in food acquisition. For instance, throughout
most of the year macaws rely on a variety of foods and often “migrate” to different areas of the forest in
search of seasonal foods. They explore mahogany trees, kapoks, coral bean trees, rubber trees and
many others. They eat fruits, flowers and seeds. They seem to rely more on flowers during May and
June, the start of the dry season and the time when flowers are most abundant. However, in August and
September, the driest part of the year, they rely more heavily on seeds, which are readily available .
Mating/Nesting
Contrary to what many humans may believe, we are not the only animals that go through a great deal of
effort finding a mate. Males of nearly every species go through a wide variety of mating rituals in their
attempt to entice the females to choose them over their peers.
Charles Darwin believed that female choice of mating partners was the dominant factor behind the
evolution of male appearance and courtship behaviors. Males have to be good looking or give impressive
song or dance performances quite simply because it improves their chances of attracting a willing female.
In addition, males must compete with each other and establish dominance. Some males will even
interrupt other males while they are mating. Oddly enough, these aggressive males often stand a better
chance in their later attempts to mate.
Sexual dimorphism, a difference in body size, coloration, patterning, or even structure between males
and females, is very common. In most primates the males have a larger build than the females just as
most men are, on average, taller than most women. Birds tend to differentiate by coloration, with the
males having brighter, more colorful plumage in order to attract the females, who are usually much more
drab. There are, however, many exceptions to this rule. Parrots have little or no apparent sexual
dimorphism and some members of the diverse sixty five species continga family are sexually
monomorphic (all look the same), while others are extremely sexually dimorphic.
Perhaps one of the more common examples of sexual selection that you will encounter while walking
forest trails is that exhibited by the screaming piha. Unlike many other species of birds, there is no
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dimorphism exhibited in the plumage between males and females. Instead, this drably colored bird uses
its call as a means of attracting a mate. Unlike many of its brightly colored relatives, pihas have one of
the more noticeable calls that you will hear. The characteristic "pi-pi-yo" can be heard for great distances
and is an affective lure with which to attract the opposite sex. It is actually the male who vocalizes in his
attempt to attract a female.
One of the most interesting features of many neotropical bird mating rituals is their system of leks. A
lek is a group of amorous male birds that stake out an area, wait for a fertile female, and perform their
mating ritual, whether it’s a series of songs, dances or otherwise, then one of the group gets to mate with
her.
Some, as in the case of manakins, even have what appears to be a system of apprenticeship within the
lek. Male manakins perform their courtship dance for one female as a team but only one dancer actually
gets to mate with the female. Usually it is the same manakin of the team that gets to mate, leading one to
question why the others would put their energy into participating if they are never rewarded. One
possibility is that they are related and, in helping their relative to mate, they are promoting their genetic
material but, more likely, they are subordinate to the leader that gets to mate and, as he ages and dies,
they will replace him as the one who gets to copulate.
Oropendulas have developed a fascinating nesting system to protect their young from predation. These
birds nest in colonies making long, hanging basketlike nests. They choose trees that are out in the open
to dissuade monkeys from attacking the nests, because monkeys much prefer staying in the canopy to
crossing areas of open ground. Oropendulas have been known to drive caciques (who build similar
nests) from their nests, destroying their eggs and killing their young. Scott K. Robinson, who studied the
yellow rumped cacique in the Peruvian Amazon, hypothesized that the oropendulas did not attack the
caciques to lessen competition for food (since they rely on different food sources) but more likely because
the creation of a “maze” of empty cacique nests may confuse potential predators and keep them away
from nearby oropendula nests.
Tamarins are small monogamous primates that mate for life and spend a great deal of time rearing their
young. Males participate in child rearing perhaps because the females typically give birth to twins that
total approximately twenty percent of the mother’s body weight. It would be impossible for the female to
care for, feed and transport her heavy young all on her own. Instead, the job is shared by the older
siblings and the father, who help carry the young on their backs. It is unlikely that the male’s increased
participation is because tamarin males have decided that they would prefer to be included in the rearing
of their young, but is more likely because they have invested their time, energy, and genetic material in
producing the offspring, all of which would be for naught if the offspring perished.
Crocodilians build nest mounds and lay up to sixty eggs and may spend a number of weeks with them,
helping them move from the nest to the water. This is less time than a tamarin, for example would take
with her twins and, with sixty eggs per clutch, the crocodilian can better afford to lose a few. Amphibians
generally lay masses of gelatinous eggs in ponds and streams either floating or attached to rocks where
they will hatch and go through their developmental stages. Once again, this reproductive strategy allows
for a significant loss of eggs or offspring without threatening the overall existence of the species.
Interdependence of Wildlife Characteristics
As you can see, there are no clear delineations between the categories of structure, physiology, feeding,
communication, social grouping and mating. They are all interconnected.
By slowing down, looking carefully, fascinating interactions are revealed. Each new discovery
leads to more questions. Once you feel sufficiently swamped with your hypotheses on the why’s and
how’s, you may further aggravate and fascinate yourself with the ongoing, as of yet unsolved, question of
“when?” When did these characteristics appear and in what order?
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