Most animals have evolved and adapted over time to survive in harsh environments, and one of the main reasons for adaptation is to conserve energy, especially for prey species. A tired animal is much more likely to be preyed upon than an active, alert animal.
The main reasons for movement are:
- Finding food
- Searching for a mate
- Avoiding predators
- Finding a nest/sleeping site
The act of movement uses energy. The faster an animal moves, the higher the energy requirement. So there must be a benefit that either balances or outweighs the need to conserve energy. So, with this in mind, why do animals move?
Why Animals Need To Move
For land animals, friction is the biggest problem. Friction is created when one surface rubs against another. This could be an animal’s foot or another part of its body that touches the ground.
Aquatic animals have buoyancy to contend with. The animal’s weight produces a downward force, and the pressure of the water, or upthrust, pushes upward. When an animal’s weight and the upthrust of the water are equal, or the animal’s weight is less, the animal will float. This means they have to exert more energy to submerge themselves.
Animals with a weight greater than the force of the water will sink. They do not have to exert any energy to remain submerged, but they have to use more power if they need to reach the water’s surface.
In the air, animals have to work against gravity. This is the force that pulls the animal to the earth. To remain in the air, an animal must be able to produce greater lift. When the lift is equal to or greater than the force of gravity, an animal can fly. If the lift is less than the force of gravity, the flight is not possible.
There are many different types of movement, and each species has adapted its unique mode of transportation.
Movement On Land
The most common form of movement on land is walking and running. Mammals such as coyotes, cats, mice, and deer use quadrupedalism (walking on four limbs). Walking movements use energy from tendons, muscles, and the spinal column, but this is a leisurely pace and can be maintained for long periods.
Jogging, sometimes called trotting or pacing, is a faster, more energy-driven pace. For most quadrupeds, running occurs with diagonal or opposing limbs, so front right and rear left together, followed by the front left and rear right together.
Running, sprinting, and galloping are the fastest gaits and require a lot of energy. Most animals can only maintain a full sprint in short bursts.
Crocodiles and alligators have a slightly different movement style to that of other land-based animals. They walk and run using the same movement; the front right and rear left move together, followed by the front left and rear right.
Walking is slow, as crocodiles have adapted to a life in water. Running occurs in short bursts. Crocodiles and alligators will often take breaks from walking by lying on their bellies. Their legs are short, so their muscles require a lot of energy to maintain movement and lift the animal’s body weight off the ground.
Hopping is a unique form of movement and is often used by prey animals like rabbits and hares. Hopping occurs when the animal uses a large amount of energy from its hind legs to create a burst of power. Rabbits and hares can also use a slower form that looks like walking, but they move their front legs together, and then their back legs follow on.
Frogs and toads also hop while on land. They can create bursts of energy from their strong hind legs like a loaded spring. American bullfrogs can travel as far as 10 feet in a single leap. Insects such as crickets, locusts, and grasshoppers also use hops and jumps.
They have a lot of predators, so using this type of movement is a great adaptation. Being able to jump upwards or sideways makes it much more difficult for a predator to predict the direction or pattern of movement their prey will take.
Snakes, worms, snails & slugs, seals, sea lions & walrus all slither and crawl to move forwards, or sometimes sidewards.
Traveling forwards is expected, but traveling upward also has its advantages. Many animals are arboreal or semi-arboreal, meaning they spend time in trees. Climbing is often the best way of avoiding predators, especially if that predator cannot climb. Squirrels and chipmunks spend most of their lives in trees, occasionally venturing to the ground to search for and bury food. If they sense danger, they will immediately dash for the nearest tree.
American black bears are also expert climbers. Although they spend a considerable amount of time on the ground, bears are very good at climbing, thanks to their strong legs and sharp claws. Bears climb trees to forage for nuts and fruit, break open a bee nest, or find a place to rest. It is common to see bears sleeping in trees. They prefer trees with thick branches as they can better support the bear’s weight.
Movement In Water
When it comes to movement in the water, there are two main types; active and passive. Most aquatic animals are active swimmers, using their bodies to create propulsion through the water.
Active swimming animals living in North America include:
- Sea lions
These animals convert energy in their bodies to create movement using their tendons, muscles, and spine. Most aquatic animals use their tail to make most of the propulsion, and fins are used for directional motion.
Some animals also have flippers which create additional forward propulsion. Seals, sea lions, and walruses use their flippers for short bursts of speeding during hunting. They also use their flippers and tail to move on land like a human toddler when they are learning to crawl.
Passive locomotion, or floating, is used by animals with neutral or positive buoyancy. This includes jellyfish and remora. Passive locomotion is when the environment moves the animal rather than the animal creating the movement. Jellyfish will float on the water surface, traveling wherever the water current or wind takes them.
This has the distinct advantage of requiring no physical effort or energy use. However, animals cannot control where they go. While this is an excellent way to travel short distances, most animals only use passive locomotion occasionally.
Remora, a group of fish belonging to the Echeneidae family, has evolved a sucker-like appendage that they use to attach themselves to other fish or sea turtles. This is a harmless mode of transport for the host animal, and remora are also capable of swimming freely.
Movement In Air
The ability to fly is something many people wish for, but it takes a lot of physical effort for flying animals to stay airborne.
Flight is possible because the surface area of an animal’s wings creates lift, which neutralizes the force of gravity that pulls objects to the ground. Most birds need to keep flapping their wings to remain in the air. However, those with larger wingspans can also soar.
Soaring is an excellent way for birds to conserve energy but remain in the air. This is seen most often in birds of prey such as eagles and hawks. They can use thermal air currents to stay aloft, and their wings act like a hang glider.
Some small bird species like hummingbirds can hover. This is a marvel to behold and quite an astonishing ability, as the bird must beat their wings hundreds of times per minute to keep its body hovering in the air. Hummingbirds use their hovering ability to get nectar from flowers and catch flying insects.
A unique form of airborne travel is ballooning or kiting. This is a behavior that spiders have adapted as a form of locomotion. It is most common in hatchlings and young spiders and is a good way of ensuring genetic diversity, as ballooning allows the spider to travel large distances quickly.
To be able to balloon, a spider must first create a strand of webbing from its silk gland. This forms a triangular shape, similar to a parachute. The air current then catches the webbing and carries the spider away.
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Bryan Harding is a member of the American Society of Mammalogists and a member of the American Birding Association. Bryan is especially fond of mammals and has studied and worked with them around the world. Bryan serves as owner, writer, and publisher of North American Nature.