Arboreal

Arboreal
adj.
[ɑɹˈbɔɹi.əl]
Definition: associated with or relating to a tree, as in arboreal life (a life in or among trees)

Table of Contents

Arboreal Definition

Arbor is a Latin word meaning “tree”. Thus, arboreal means “related to or pertaining to trees”. The other similar words (synonyms) include arborous, arboraceous, arborary. Arbiform is the word used for expressing the term “resembling a tree”

Arboreal (biology definition): (1) Of, relating to, or pertaining to, a tree, (2) Pertaining to moving about or living in, on, or among trees. In a biological context, arboreal is a descriptive term used to associate with trees. For instance, a form of locomotion wherein organisms move about in trees is called arboreal locomotion. Movements such as climbing, swinging, or gripping on trees are examples of arboreal locomotion, and animals that are adapted for this kind of locomotion are called arboreal animals. These animals spend most (some, all) of their time among trees. Arboreal animals are very well adapted to staying or hanging on to trees. Many of them have little bodies and clawed or sticky feet. Some of them have prehensile tails that they use to grasp tree branches. Etymology: Latin arboreus (“tree-like”). Compare: aquatic, terrestrial.

Arboreal Animals

Arboreal animals are those animals that spend most of their life on trees. They feed, travel, play, and sleep on trees. They prefer to grow their young ones on the trees, which is a difficult task because the newborns are always prone to fall on the ground from height. However, they have adapted themselves in such a manner that these animals can now easily live on such heights.

Examples of such animals include chameleons, lizards, green tree pythons, tree snails, koalas, squirrels, cats, monkeys, parrots, sloths, and a variety of insects. Leopards and goats are also considered arboreal because of their excellent ability to climb the trees. Leopards can carry their kills to the top of trees to avoid other predators and scavengers.

arboreal mammals - examples — Figure 1: Tree animals: arboreal mammals that have the ability to run, jump and climb trees. Source: A photo collage by Shoaib Zaheer of Biology Online.

goats on a tree — Figure 2: Tree-climbing goats. Goats have the ability to scale up trees. Source: Maria Victoria Gonzaga of Biology Online.

Arboreal animals have adapted tree-top living to protect themselves from ground predators by staying atop or by hiding in foliage and branches. Tree-top living has many challenges and one of them is falling down from great heights. However, these creatures have adapted in a specialized way that helps them survive on the trees.

Many arboreal animals can be found on a tree canopy (the topmost region of trees) peaking above the forest. Those that are rather constrained by their weight and size are found living somewhere in the mid part of the trees. Arboreal animals are found in almost every forest ecosystem, however, they are more concentrated in tropical forests.

Challenges for Arboreal Animals and Adaptations

Living on trees presents many challenges for arboreal animals. These challenges include finding food, playing, or protecting themselves while atop a tree. A single misstep could end up in injuries. Gathering and storing food on a tree is also a big challenge for such animals. Also, during extreme weather, taking shelter with the young can be difficult.

Other challenges include moving on inclined branches, moving on narrow branches, dealing with obstructions, crossing gaps, and balancing. Most of the challenges are solved by physical adaptations. The adaptations of these animals to survive on the trees are described below:

Gravitational balance

The animals living on the ground have a high center of gravity. For example, a cow moves forward by moving its legs in an alternative fashion that makes the center of mass swing side to side. Similarly, giraffes, elephants, dogs, buffalo, and other animals have comparatively long legs and have a high center of gravity. An appropriate push can unbalance them. But this is not the case with arboreal animals. Arboreal animals have a low center of gravity. This increases their balance stability and minimizes the chance to fall from the trees. These animals have short legs, which also help in lowering their center of gravity.

Membranes for gliding

Many arboreal animals use a special technique while moving between the gap of trees and branches. This technique is based on parachuting or gliding action. Arboreal animals that can glide have stretchable membranes between their legs called patagia (singular: patagium). When these animals want to move from one branch to another, they will jump and expand the membranes between their legs.

The membrane will stretch, thus, increasing the surface area without adding any additional weight. The movement will be based on the airlift provided under the stretchable membrane. So, instead of steeply falling down, the animal will glide. It is similar to the one used in extreme sports, i.e. wingsuit gliding. Flying squirrels, flying frogs, flying geckos, flying snakes, and flying mice take advantage of this membrane.

These animals, though, are not technically flying but gliding via a patagium. Another gliding animal, the flying mouse (also known as the pygmy scaly-tailed flying squirrel or pygmy anomalure) is named as the world’s smallest gliding animal. It is neither a true mouse nor a true squirrel.

It is a rodent characterized by possessing a gliding membrane between the elbows and the knees. When it jumps this membrane provides significant surface area for airlift underneath. The flying mouse uses its tail to steer as it glides from one branch to another.

Idiurus marcotis - gliding — Figure 3: A flying mouse with a gliding membrane between upper limbs and feet. Credit: Animal Diversity.

Body structure

The arboreal animals have adapted in such a way that their body parts help them swing from one tree to another and one branch to another by using their strong arms. This adaptation is extremely necessary for arboreal animals to survive and live easily on trees especially on the forest canopy.

This ability of movement from one branch to another is termed brachiation and is found in primates (any mammal of a family of lemurs, apes, monkeys, lorises, etc).

Long Arms: The particular feature that helps primates move is their long arms which help them cross the gaps between branches. The top speed of spider monkeys can reach up to 35 miles per hour.

long arms of arboreal animal — Figure 4: Long arms of arboreal animals.

Wrist: The wrist of these animals can freely rotate to accommodate the turning motion of their hands while jumping, grabbing, and swinging.
Prehensile Tails: Prehensile tail animals can use their tails to grab something or support them while climbing trees. Monkeys are the best example of animals that have prehensile tails. Other animals that have prehensile tails are tree pangolins, harvest mice, and spider monkeys. These animals have specially adapted tails that help them climb, swing and move on trees.

Feet with strong grip: The animals living on the tree have high chances of falling and get injured. To mitigate such a lethal risk, they have adapted to have feet that have a strong grip equivalent to their hands or more. The feet of such animals can grab the branches tightly. The joints in their ankle are also very flexible which helps them maneuver easily. Squirrel’s ankle joints are so flexible that they can turn backward or forward. The fingertips of arboreal animals don’t have hairs which help maintain good friction between their hands and branches. If there are hairs on their fingers there are chances of slipping.

Other features: Primates that move and live on trees have specialized body structure such as shorter spines, long curved fingers, short fingernails instead of claws, long forelimbs, and shorter thumbs. Some animals have adhesive feet that work best on smooth surfaces. The adhesion works on the principle of suction. The common examples of animals using this technique are arboreal salamanders and tree frogs. Small size is another feature that is advantageous for arboreal animals. Small size increases stability, lower center of mass, and lower the weight both for swinging and gliding animals. The only exception to size are orangutans that can weigh up to 300 pounds and live on tropical rainforest canopy in Sumatra and Borneo.

Arboreal Locomotion

Arboreal locomotion means the movement or travel of animals on the trees. In the areas where dense forests are present, animals have evolved to live and move on them. Some animals climb or stay on trees for a short period of time while others are exclusively arboreal. The movement of animals on trees has many challenges overcome by changes in anatomical and behavioral features.

These animals use their strong upper limbs and feet while jumping and swinging from one branch to another. In case they miss a branch while traveling, they grab the nearest branch within no time. They have become experts in locomotion. Sometimes they furiously fight or play on the trees but do not fall while running due to their quick senses and adapted body structure.

The other species that live on trees such as snakes and snails use limbless climbing techniques. For example, snakes use concertina locomotion and lateral undulation.

Arboreal Examples

There are about 2500 different arboreal species living in tropical, equatorial, and subtropical areas of the world. A few examples of arboreal animals are as follows:

Orangutan

Starting with the orangutan, they are uniquely arboreal living their lives on a forest canopy. They occasionally come down but most of the time they are sitting quietly on the treetops, eating or observing. The orangutan has legs but they are usually counted as hands because the legs and feet are equally capable in terms of movement and grabbing.

Tree kangaroo

Tree kangaroos have adapted for arboreal locomotion mostly found in tropical rainforests of New Guinea. The special thing about tree kangaroos is that they are the only true arboreal macropods (family of kangaroos). Tree kangaroos thrive on treetops and seldom walk on the ground.

When on the ground they have speed equivalent to a human, however in trees they are agile. They can jump from one tree to another and researchers found that they can downward jump 30 feet on another tree. They have powerful hind legs and forelimbs.

Sunda flying lemur

Sunda flying lemur, also known as Sunda colugo or Malayan colugo, is a strictly arboreal animal. They use all of their four feet to grip the tree trunks. They use hoping movement while climbing by stretching their front legs and then bringing two back legs. They sleep during day time on treetops or holes in the tree trunks.

They are more active at night. They have an uncanny ability to glide without losing altitude. The gliding is possible due to their gliding membrane that is connected from their neck to upper limbs to toes and nails. This creature is helpless on the ground but very active on trees.

Try to answer the quiz below to check what you have learned so far about arboreal.

References

ADW. (2020). Idiurus macrotis long-eared scaly-tailed flying squirrel. Retrieved March 15, 2021, from https://animaldiversity.org/accounts/Idiurus_macrotis/
Dewan, A. (2013). Sumatran orangutans’ rainforest home faces new threat. Retrieved March 15, 2021, from https://phys.org/news/2013-05-sumatran-orangutans-rainforest-home-threat.html
E-Warrior. (2016). The Sunda Flying Lemur Or Malayan Colugo.
Pinterest. (2019). Saving Indigenous Lands in the Amazon. Retrieved February 15, 2021, from https://www.pinterest.com/pin/32862272268001998/
Weebly. (2020). Tropical rainforest- Flora and fauna. Retrieved March 15, 2021, from https://helpthetropicalrainforests.weebly.com/flora-and-fauna.html
WWF. (2018). Tree Kangaroo. Retrieved March 15, 2021, from https://www.worldwildlife.org/species/tree-kangaroo