Tag Archives: animals

Staying airborne: How bird wings are built for aerodynamic and efficient flight

Flight is a concept that has, until relatively recently in history, eluded humanity. However, birds have been successfully flying for approximately 130 million years, proving themselves to be a physical marvel of the natural world. And while our means of flight have historically been crude in design and performance, nature provides an elegant, efficient solution to get creatures off of the ground. Rüppell’s griffon vultures have been recorded flying as high as 37,000 ft, while some species of shorebirds have been recorded flying as far as from Alaska to New Zealand over eight days without stopping. But how exactly do birds seem to effortlessly overcome gravity so effectively? And perhaps more importantly, how might we apply these answers to improve manmade aircraft?

Morphology

Obviously, the exact aerodynamics and physical characteristics of birds will vary from species to species, but there are still underlying similarities that enable birds to fly. A bird’s wing consists of a shoulder, elbow, and wrist joint which establish the wing’s basic shape and allow a range of motion. Covering the wing are structures called primary, secondary, and coverts, which are all groups of feathers that provide lift and stabilize flight. Feathers consist of flexible fibers attached to a center shaft, called the rachis. Overtime, the rachis will become damaged from fatigue and large instances of stress. As a result, birds will molt and regrow their feathers on a regular basis. 

A diagram of the structure of a bird wing
Picture by marcosbseguren on Wikimedia Commons

Generally, a bird’s body will be adapted to either gliding flight, in which the wings flap very infrequently, or active flight, in which the wings flap nearly constantly. For gliding birds, such as the ocean dwelling albatross, the wings will extend far away from the body, and prioritize both wing and feather surface area over flexibility. Additionally, these wings will have a thick leading edge, and will be much straighter. However for fast, agile birds, such as falcons, the opposite is true. Consequently, agility is sacrificed for energy efficiency. In both cases, the rachis will change shape and rigidity, becoming larger and stiffer for gliding flight and smaller and more flexible for agile flight. 

Aerodynamics

One of the most unique aerodynamic characteristics of birds is that nearly all of their lift and thrust is exclusively generated by their wings, as opposed to aircraft that implement both wings and engines. This provides, among other things, near instantaneous control of both flight direction and speed. In other words, this gives birds an advantage when hunting, escaping from predators, and maneuvering through a landscape. 

To aid in the generation of thrust and lift during flight, birds will change their wing shape through a process called active morphing. During flight, the wing will be bent inwards and twisted up during the upstroke, and extended and straightened during the downstroke. As a result, this minimizes drag while maximizing thrust and, consequently, energy efficiency. This can aid in anything from traveling farther distances to hunting prey.

An osprey folding its wings in while catching a fish
Photo by Paul VanDerWerf on Wikimedia Commons

Applications

Initially, these principles may seem difficult to realistically utilize in aircraft. After all, we are limited by the materials available and the size that aircraft must reach. However, small steps could be taken to improve the energy efficiency and responsiveness of aircraft. For example, wing shape, material flexibility, surface finish, and moving joints could all be explored. In fact, research at MIT is currently being conducted on flexible wings made of scale-like modular structures. If experiments like this are successful, it could show that aircraft designs inspired by nature may be the future of the world of aeronautics.

Which is more stable, washing machines or birds? The answer might surprise you

What do birds and washing machines have in common? Shockingly, it’s not the ability to wash clothes. Rather, most birds and washing machines are great examples of vibration isolation systems.

Now that’s cool and all – but what is a vibration isolation system?

Better known as a mass-spring-damper system, vibration isolators are generally a mechanical or industrial mechanism that can reduce the amount of vibrational energy produced by a system. Vibration isolators are incredibly important; studies show “undesirable vibrations” can shorten a machine’s service life and even permanently damage the machine and those using it. Considering this, engineers are constantly improving upon current vibration control systems, and are now looking to birds for inspiration.

But why birds? Well, to understand this, let’s consider a bird as a simple mass-spring-damper system.

Avian vibration isolation system represented as mass-spring-damper-system
Simple approximation of avian vibration isolation system as mass-spring-damper system. Taken from the 2015 study: ‘The role of passive avian head stabilization in flapping flight.”

First, visualize vibrations as an oscillating force stemming from the bird’s body moving back-and-forth. Vibrational forces can be generated by the flapping of wings, unexpected gusts, and/or movement of legs. Now, if we continue up from the body to the neck, we can see where avian skeletal and muscular structure really begins to “show off its feathers.”

Characterized as a multi-layered structure, the avian neck contains many sections of “hollow” bones, connected by surrounding muscles. The structural units (muscles and bones) of the avian neck have properties of both springs and dampers, optimizing them for vibration isolation.

Simplified representation of multi-layered neck as spring-damper structure

For starters, we see the muscles largely act as springs. Springs have the unique ability to move a body with its vibrations. This behavior is present in the muscles connected to the bone segments, in that they are capable of instantaneously compressing, elongating and twisting in response to rapid changes in the body’s movement. This elastic response prevents not only the head, but the whole bird, from shaking when bombarded when vibrations from any form of movement.

Simplified visualization of multi-layered spring-damper structure. The transparent grey portion represents the hollow bone, which is connected by the black lines, or strong spring-like muscles. The empty space between each unit would consist of the softer, damper-like muscle. Taken from the 2021 study: “A novel dynamics stabilization and vibration isolation structure inspired by the role of avian neck.”

Alternatively, the muscles, primarily those not connected to bone, can act as dampers. Effective dampers are similarly identified by the ability to move with vibrations; however, they can dissipate some of the vibrational energy as heat, or store energy until relaxed. The interior muscles are capable of slowly deforming (changing shape) if exposed to steady vibrations, allowing for dissipation of excessive vibrational energy.

But hey, what about those bones?

The avian neck has nearly three times the number of bone sections than most mammals, on top of muscles entirely surrounding the neck. This drastically increases the bird’s flexibility, helping it maneuver through sharp positional changes, thereby further limiting the effect of vibrational forces.

Finally, what makes the avian vibration isolator truly superior is its passive activation. As engineers at Shanghai Jiao Tong University point out, manmade passive vibration isolators fall short because they require sensors and input energy to adjust for “shocks and random vibrations.” As previously explained, the multi-layered neck is well equipped to handle random oscillations, yet, more importantly, the bird’s neck muscles can passively change position to brace for incoming vibrations.

A recent study from Stanford University proved this concept by recording a whooper swan’s reaction to different strength gusts. They found that swan’s neck adjusted to protect the head, and that even when the flapping doubled, the movement of the head reduced by a quarter. Finally, it is important to note that passive activation is not limited to the sky; researchers have found that mainly terrestrial birds like chickens and pigeons have a similar neck structure and system for maintaining stability and clear vision.

Overall, continuing to study the avian vibration isolation system could prove very beneficial for many different applications. For a more in-depth look at the current work out, check-out the studies referenced throughout the article. Otherwise, enjoy watching this chicken work its body control magic!

Mercedes-Benz “Chicken” Magic Body Control Advertisement, highlighting the chicken’s amazing head stabilization ability.

Nine Brains Are Better Than One: An Octopus’ Nervous System

Picture this: Earth has made its first contact with an extraterrestrial species, and, as to be expected, their anatomy and nervous system are entirely different from our own. Rather than having a single brain where all sensory information and motor controls are processed, they have nine brains. Rather than having a rigid skeleton, they have compact arrays of muscle tissue that stiffen and soften when they move, and their many limbs have an infinite number of degrees of freedom. Oh, and they can only breath underwater, too.

What was just described isn’t an alien at all, but actually the complex anatomy belonging to a common octopus, otherwise known as Octopus Vulgaris, and there is a lot we can learn from it. So how does an octopus fully control all eight of its flexible limbs? The answer lies in its partially de-centralized nervous system. When most people think of a nervous system, they think of a single brain sending out messages to move our arms and legs, then gathering information back to process everything we touch, see or hear. For an octopus, though, this process is much more complicated.

Independent Thinkers

Each arm of an octopus is able to control itself semi-independently from the central brain. An octopus has about 500 million neurons in its body, two-thirds of which are distributed amongst its limbs. This means that there are about 40 million neurons in each tentacle. That’s more than two times the number of neurons the average frog has in its entire body! An experiment conducted by German Sumbre et al. showed that even when a disconnected arm was electrically stimulated, it would still move in the same basic patterns of a tentacle being controlled naturally by an octopus. The arm even adapted its movement patterns the same way a still-connected tentacle did when the arm’s environment and initial posture were changed.

There are two columns of images. The left shows an octopus outstretching its arm over the course of 920 seconds. An arrow tracks the movement of a bend in the arm that travels along the arm until it is fully stretched out. The right column shows a single, detached octopus arm outstretching over a similar time frame. The single tentacle follows a similar movement pattern as the original octopus' arm. Another arrow also follows a similar bend that travels along the single arm as it stretches out.
An experiment shows that an electrically stimulated octopus arm (right), when detached from its central nervous system , will still move in the same basic patterns as an arm naturally controlled by an octopus (left). Image modified from G. Sumbre, Science Magazine.

Master Delegaters

So how does this partially de-centralized nervous system work? The octopus does, in fact, have a central brain located between its eyes containing about 180 million neurons. This is the part of the nervous system that determines what the octopus wants or needs, such as if it needs to search for food. These are sent as messages through groupings of neurons. Commands like “search for food” are then received by each of the tentacles, who all have their own smaller, independent brains. With these commands in mind, each tentacle gathers its own sensory and position data, processes it, and then issues its own commands on how to move by stiffening or relaxing different parts of the arm, all without consulting the central brain upstairs. As the tentacle moves, it keeps collecting and processing sensory information, and any relevant information, such as the location of food, gets sent back to the central brain to make larger decisions.

Beyond the Octopus

There is still a lot left unknown about how exactly an octopus’ nervous system functions. However, new and upcoming fields such as soft robotics and artificial intelligence are starting to look towards the opportunity for innovation that octopuses present. Learn more about how the anatomy of an octopus is being applied to science and technology here and here!

Further Reading

Sources

Sumbre, G. “Control of Octopus Arm Extension by a Peripheral Motor Program.” Science, vol. 293, no. 5536, Sept. 2001, pp. 1845–48. DOI.org (Crossref), doi:10.1126/science.1060976.

Zullo, L., Eichenstein, H., Maiole, F. et al. Motor control pathways in the nervous system of Octopus vulgaris arm. J Comp Physiol A 205, 271–279 (2019). https://doi.org/10.1007/s00359-019-01332-6

Levy, Guy, et al. “Arm Coordination in Octopus Crawling Involves Unique Motor Control Strategies.” Current Biology, vol. 25, no. 9, May 2015, pp. 1195–200. DOI.org (Crossref), doi:10.1016/j.cub.2015.02.064.

Do Hammer-Shaped Heads Help Sharks Swim?

With their sandpaper skin, cartilage skeleton, electroreceptive sensors, and rows of dangerous teeth, sharks fascinate many people. However, even within this distinctive group the hammerhead sharks that make up the Sphyrnidae family have attracted a special attention due to the unusual shapes of their namesake heads, called cephalofoils. Several evolutionary benefits of the cephalofoil have been proposed by researchers. The wide hammer-shaped head may allow the shark to house more sensory receptors in its snout, to bludgeon prey, and to move and maneuver through the water more easily. Here we will address the question posed by the third theory: Does the cephalofoil found on hammerhead sharks provide an advantage in moving and maneuvering underwater?

Great Hammerhead Shark
Image of “Great Hammerhead Shark” by Wendell Reed showing a close-up of the cephalofoil. https://search.creativecommons.org/photos/3fa18a9b-9085-4867-93e1-15a88b01389b

Many advancements in the aviation and nautical industries have been developed from the study of sea creatures. There is certainly some potential that research into the mobility of sharks could someday be used as inspiration to advance locomotion technologies. In addition, a deeper understanding of the physiology and behavior of hammerhead sharks could help us to better preserve their habitat and species from endangerment – a crisis which some of them are already facing.

The theory that the cephalofoil provides advantages in forward swimming to hammerhead sharks relies on it supplying some hydrodynamic lift similar to the wing of an aircraft. Aircraft wings provide lift partly by creating a pressure difference between the top and bottom wing surfaces. An area of higher pressure on the bottom surface of a wing will generate upward lift. One study by Matthew Gaylord, Eric Blades, and Glenn Parsons applied a derivation of the Navier-Stokes equations – a set of partial differential equations for analyzing fluid flow – to water flow around digitized models of the heads of the eight most common species of hammerhead. It was found that in level, forward swimming there was some pressure differential that developed between the dorsal (top) and ventral (bottom) surfaces of the cephalofoil, but for each species it was very small and often in the direction to produce negative lift. The drag coefficients of the cephalofoil of each hammerhead species were then calculated and shown to increase as the size of the cephalofoil increased. The drag created by a cephalofoil was always much greater than the drags caused by the heads of a control group of non-hammerhead Carcharhinidae sharks.

Images of the pressure contours at zero angle of attack on the dorsal (top image) and ventral (bottom image) sides of the cephalofoil. The eight leftmost sharks are the hammerheads. Taken from Gaylord, Blades, Parsons.

However, the same study showed that the pressure difference between either surface of the cephalofoil did significantly increase in some species if the shark raised or lowered its head. This extra hydrodynamic force caused by the pressure differential at nonzero angles of attack would help the shark to turn its head up or down very quickly. This more explosive maneuverability was particularly present in the hammerheads that commonly feed on fish and less present in the species that feed predominantly on slower bottom dwellers. Another study by Stephen Kajiura, Jesica Forni, and Adam Summers theorized that the unbalanced, front-heavy cephalofoil may provide extra stability during tight turns by preventing banking. The unbalanced head would create a moment – or torque – to counteract the force from the tail that causes most sharks to roll into their turns. Not banking around turns could be important to some hammerhead sharks that often swim so close to the seafloor that banking into a turn could cause their head or fins to bump into the floor. It is likely that hammerhead sharks evolved the cephalofoil at least in part to provide more explosive and stable maneuvering.

Featured image “Hammerhead Shark” by bocagrandelasvegas.

Dolphin Magic or Dolphin Muscle?

Because of the film Bee Movie, many people at one point were intrigued by the idea that bumblebees should not physically be able to fly due to their large bodies and tiny wings. But, they fly anyway. Technology is advanced enough to study bee wing movement and determine that they produce enough lift to allow them to fly, disproving the previous notion. Similarly, Gray’s Paradox for a long time inferred that dolphins should not be able to swim nearly as fast as they do. But, they still consistently swim at speeds over twenty miles per hour. It was not until recent history that advancements allowed researchers to determine why they are able to reach such high speeds.

Gray’s Paradox

All the way back in 1936, Sir James Gray observed the high speeds dolphins could reach in the ocean. He calculated an approximation of the amount of power the dolphins would need to produce to sustain these speeds, based on the drag force on the dolphin as it travels through the water. Gray compared this to the amount of power he expected the dolphin to be able to produce. In order to compute this, Gray used muscle power data from oarsmen. When he compared the muscle mass of these oarsmen compared to dolphins, he determined that the power dolphins could produce was only about one seventh what was needed to travel at the high speeds of which they are capable.

Force Diagram, showing that the same forces that the swimming mammal applies to water are applied back on it. Allows observation of max speed to determine these forces.
This diagram shows that the drag force, D, thrust force, T, and net axial force, Fx, must be equal for the swimmer and the fluid. The lateral velocity, u, can be used to determine the resulting drag force, allowing researchers to estimate how much thrust is needed. Credit: [2]

And now we have arrived at Gray’s Paradox. What allows dolphins to move so quickly? To Gray and other researchers for most of a century, this was a mystery. If the assumptions they had made were correct, that would mean dolphins have some way of travelling through water more efficiently than was thought to be possible. This sparked a large amount of speculation into how dolphin skin could reduce the drag force of the water, which was originally believed to be the way Gray’s Paradox would be resolved.

Answering Questions while Creating More

Finally in 2008, Timothy Wei’s research team was able to definitively disprove Gray’s Paradox. He set up an experiment that would allow the force that dolphins exert to be measured. This mainly consisted of having dolphins swim through a curtain of bubbles in a tank. By recording at high resolution the movement of these bubbles as the dolphins swam by, the researchers determined the speed of the water around the dolphin as it traveled. With this information, Wei’s team showed that dolphins are able to produce over 300 pounds of force at one moment, and over longer periods of time 200 pounds of force. This is approximately ten times more force than Gray estimated.

Wei’s findings resolve Gray’s paradox by showing that dolphins have the ability to produce sufficient power from their tail movement to overcome the strong drag force of the water as they move at high speeds. However, this does not explain how dolphins produce so much power with their amount of muscle mass, which is still being examined. One idea is that this is caused by anaerobic muscle fibers that behave in different ways than in humans, and allow more power to be generated than Gray expected.

Future Plans: Investigating Force Generation

Timothy Wei plans to continue examining force generation in the swimming of other marine animals. This has the potential to provide more understanding of how marine animals evolved in their swimming aptitude. On the level of microbiology, this research could improve understanding of how dolphin and other animal muscles can perform such high levels of power generation over sustained periods of time.

Additional Reading and Sources

How Mice Could Help You Regenerate a Lost Limb

If you have ever experienced a nasty scrape or burn, you know the process of healing is not very fun. Human skin can take several weeks to regenerate after an injury and that often comes with a fair amount of pain. For a bigger injury that involves tissue damage, there is often little the human body can do to regenerate larger parts. However, thanks to a small rodent – the African spiny mouse – regenerative medicine for humans could be making huge advances in the near future.

The concept of regeneration is not something new in the animal world – we have seen creatures like salamanders regenerate lost tails and starfish regrow lost limbs. However, the African spiny mouse is the only mammal ever observed to be able to completely regenerate tissue such as skin, fur, hair follicles, sweat glands, and even cartilage. Being able to quickly shed skin caught in the mouths of large predators comes in handy for the mouse to be able to escape, but they must also be able to quickly heal those wounds.

African spiny mice in a research lab have spiny hair shown in (a) and (b). A skin wound was administered to a mouse in (c). Scabbing has occurred over the full injury as seen in (d) by Day 3. By Day 30, the original wound has healed and new hair follicles have been regenerated as seen in (e) and (f).
Figure 1. African spiny mice in a research lab have spiny hair shown in (a) and (b). A skin wound was administered to a mouse in (c). Scabbing has occurred over the full injury as seen in (d) by Day 3. By Day 30, the original wound has healed and new hair follicles have been regenerated as seen in (e) and (f). Source: Seifert, A., Kiama, S., Seifert, M. et al. Skin shedding and tissue regeneration in African spiny mice (Acomys). Nature 489, 561–565 (2012). https://doi.org/10.1038/nature11499.

How exactly does this happen? Researchers have found that the skin of the spiny mice is much weaker than that of most other mammals – think 20 times weaker than the skin of your regular old house mouse. Upon being handled, the skin is quick to shed leaving gaping wounds across the backs of these mice. This is due to the density of hair follicles found in their skin – a greater proportion of follicles means there is much less connective tissue to hold the skin leading to very easy tears. The weakness of the skin is contrasted by the rapidity by which it heals – the wounds can shrink to two thirds of their original size in a single day!

To understand a little bit more about the biomechanics of this process, we must look at how exactly the skin heals. As it turns out, collagen, the structural protein found in tissues which is responsible for skin elasticity among other things, is partly responsible for this phenomenon. Whereas mammals like you and I heal injuries through the generation of dense layers of collagen fibers aligned in parallel layers, these mice produce collagen fibers in crisscross networks that resemble the original makeup of tissue. This leaves the healed skin completely scar-free.

In addition, researchers have noted that ear wounds in the mice heal in a way similar to salamander tail regeneration. When a mouse’s ear gets injured, a ball of cells forms at the site of the wound that resembles cells in the embryonic state. This cell clump, called a blastema, is what allows the lost tissue to regrow on the ear. Scientists hope to use this information to study regeneration of tissue in humans.

An experiment was performed on both an African spiny mouse (Acomys) and another genus of rodents comparable to a house mouse (Mus) by making 4mm punctures in each species' ears. The size of the puncture was then observed over the following days showing that Acomys completely healed the ear puncture after 56 days while the size of the ear puncture in Mus remained relatively the same size showing no regeneration.
Figure 2. An experiment was performed on both an African spiny mouse (Acomys) and another genus of rodents comparable to a house mouse (Mus) by making 4mm punctures in each species’ ears. The size of the puncture was then observed over the following days showing that Acomys completely healed the ear puncture after 56 days while the size of the ear puncture in Mus remained relatively the same size showing no regeneration. Source: Matias Santos D, Rita AM, Casanellas I, et al. Ear wound regeneration in the African spiny mouse Acomys cahirinus. Regeneration (Oxf). 2016;3(1):52-61. Published 2016 Mar 9. doi:10.1002/reg2.50.

While there is still more research to do on the healing mechanism of the spiny mice tissue, the research done on these little mammals provides an excellent foundation for regenerative medicine for humans – something that studying regeneration in other animal species has not been able to accomplish. Being able to regenerate a lost limb was something once found only in science-fiction but could be a real possibility in the future.

Read More:

Insights into the regeneration of skin from Acomys, the spiny mouse

Optimal skin regeneration after full thickness thermal burn injury in the spiny mouse, Acomys cahirinus

Unique behavior of dermal cells from regenerative mammal, the African Spiny Mouse, in response to substrate stiffness

African spiny mice can regrow lost skin

Swimming Fast and Slow: What We Know About the Sailfish’s Iconic Fin

Indo-Pacific Sailfish
Indo-Pacific Sailfish. Credit: D. Corson/Shostal Associates

Sailfish, or Istiophorus platypterus, are one of the most recognizable fishes in the ocean due to their large sail-like dorsal fin. But, did you know that they are also iconic because they are one of the fastest swimmers in the ocean? Sailfish top speeds have been recorded to be up to 30 m/s, which roughly translates to 67 miles per hour. When researchers examined the sailfish swimming out in the ocean, they discovered that they have the unique ability to retract and deploy their sail and other fins. Furthermore, they saw that when swimming at top speeds, swordfish retract their sail, and when the fish are hunting prey, they deploy it. How does retracting the sail help them swim fast, and how does deploying the sail help them hunt? 

Sailfish swimming with both the sail retracted (0:24) and extended (0:40). Disregard the silliness of the video. Credit: Pew

Speeding Up

When it comes to swimming fast, the answer may have to do with drag. Due to their hydrodynamic characteristics, sailfish have a very low drag coefficient, which is the quantity used to describe the resistance of an object moving through fluid. Sailfish have a drag coefficient of 0.0075, which is similar to smaller fish such as pike, dogfish, and small trout. Additionally, due to their size, sailfish are able a generate much more force with each swimming motion than their smaller peers. The combination of these two factors allows them to move at such high speeds. The thing that truly sets sailfish apart, though, is this ability to retract their sail and pectoral fins. Studies show that when the sail and other fins were retracted, sailfish are able to reduce their drag by about 18%. With less drag to worry about, the fish can be more efficient in generating thrust from its swimming motion, which allows it to speed ahead of the competition. To get a sense of just how fast these fish move, watch the end of the video above, where they only get up to 40 mph!

Slowing Down

Sailfish usually feed on smaller fish that swim in schools, like sardines. These small fish “exhibit higher performance than large fish in unsteady swimming,” which is to say making quick lateral movements. So, if a sardine senses a sailfish coming at it at full speed, it will likely have no problems avoiding it. With the sail dorsal-fin raised, the increase in drag slows the fish down dramatically and steadies its swimming path.

In the figure below, sub-figures C and D show how much the tail oscillates (in grey) and the direction in which the fish is moving (in black) when the sail is retracted and deployed, respectively. Zero on the Y-axis represents the tail being directly in line with the rest of the body and the fish is moving straight forward. While the sail is up, the tail moves far less aggressively and the fish more consistently moves in a straight line.

Side by Side comparison of Sailfish swimming with and without sail
Affect of Sail on stability while swimming. Credit: Stefano Marras

This allows the sailfish to become more controlled in its movements and help pursue a sardine performing evasive maneuvers. When it gets within striking distance, the sail helps counterbalance the fish’s swift lunge at its prey, which provides much-needed accuracy. Biologists have also theorized that the large size of the sail helps herd the school closer together, but no official research has been done on this.

Take-Aways

The sailfish’s ability to retract and deploy its sail dorsal-fin gives it unique advantages in both long-distance swimming and hunting. Minimizing drag is one of the most important concepts for travel through any fluid (air or water), so understanding how the sailfish is able to reduce drag could provide a new perspective on things. The sail’s ability to provide stability at lower speeds has potential use in any sort of water travel, whether it be with cargo ships (like the Evergreen in the Suez), boats, or submarines.  

If you are interested in another unique feature of the Sailfish, its bill has been a popular topic as of late, especially with its feeding habits. The bill is often used like a sword, either spearing or stunning prey, and also has been thought to have helpful drag-reducing qualities. Click here for more information.

Sources

Woong Sagong, “Hydrodynamic Characteristics of the Sailfish (Istiophorus platypterus) and Swordfish (Xiphias gladius) in Gliding Postures at Their Cruise Speeds,” Plos One, https://doi.org/10.1371/journal.pone.0081323

Stefano Marras, “Not So Fast: Swimming Behavior of Sailfish during Predator–Prey Interactions using High-Speed Video and Accelerometry,” Integrative and Comparative Biology,” https://doi.org/10.1093/icb/icv017

P. Domenici, “How sailfish use their bills to capture schooling prey,” The Royal Society Publishing, https://doi.org/10.1098/rspb.2014.0444


How the Largest Land Animal Stays Cool – And What We Can Learn From It

African Elephant raising tusk
African Elephant. Credit: Wolfgang Schlaifer

African Elephants have the largest volume to surface-area ratio of any living land mammal; it’s not a surprise then that they have to dissipate a tremendous amount of heat. You and me eat 2,500 calories a day – an adult male elephant might consume over 70,000 calories each day! This means these gigantic beasts need to remove several kilowatts of heat. So how do they do it? And can we learn anything from these biological marvels?

Physical Features

Close up of an elephant's ears. Details on blood vessels going through ear flap.
Close up of elephant’s ear, credit: Magda Ehlers

In order to combat the heat, elephants have developed several unique features. First is the large, flapping ears. Phillips and Heath have studied the heat exchange by the ears extensively, finding remarkable advantages. It may not look like it, but those ears make up 20% of an elephants surface area – this essentially transforms them into large heat sinks. But that’s not the end of their ears’ advantages. Elephants are able to regulate heat transfer through vasomotion; this is an oscillation of blood vessels that is unrelated to heart beat. Thus, elephants are able to store heat in their ears by expanding the blood vessels, then releasing this heat during the nighttime when it is more efficient. Modeling has shown that nearly 100% of heat loss requirements can be met through the movement of the ear.

Close up of African Elephant hair. The hair is not very dense and very thin.
Close up of African Elephant hair on head. Credit: Conor L. Myhrvold in the Woodland Park Zoo, Seattle, Washington.

Elephant ears aren’t the only heat-reducing mechanism. Myhrvold et al. propose that a low density of hair could also be a method to remove heat. As humans we often think of hair as a mechanism to keep us warm – this is true as it will serve as insulation against our skin. Low density hair, however, provides a larger surface area (they act as small little heat fins) that offsets any increased insulation they may cause. Researchers found the break-even point to be 0.3 million hairs/m2 – elephants only have 1500 hairs/m2.

Internal Control

A thermal image of elephants; the animals are much brighter compared to their environment.
Thermal image of elephants, credit: Endangered Wildlife Trust/LJMU

Us humans are homeotherms – this means our internal body temperature is kept stable regardless of outside temperatures. Most other mammals follow homeothermic tendencies, but there is recent evidence that elephants are actually heterotherms – their bodies are both self-regulating and adaptive to the environment. In fact, elephant body regulation is very similar to desert mammals like camels. During the day elephants will increase their body temperatures, and during the night they will lower them (this also helps for when the night is very cold and the animal wishes to conserve instead of dissipate heat). Weissenböck et al. discovered that elephants can have a body temperature range from 35.0°C – 37.5°C (95°F – 99.5°F), a range that is about twice as large compared to humans.

What We Can Learn

African Elephants present a unique natural problem: how do you cool something so large that produces so much heat? This problem is also present in our own human world from cooling down skyscrapers to making sure your computer CPU doesn’t overheat. One of the more promising developments is thermal energy storage and how it can heat, cool, and provide electricity for the modern world. Elephants’ physiological adaptations can serve as the blueprints for future innovation in heat transfer and dissipation.

Sources and Additional Readings

Polly K Phillips &James Edward Heath. “Heat exchange by the pinna of the african elephant (Loxodonta africana)”, Comparative Biochemistry and Physiology Part A: Physiology, Volume 101, Issue 4, 1992.

P.G. Wright & C.P. Luck. “Do elephants need to sweat”, South African Journal of Zoology, Volume 19, Issue 4, 1984.

Myhrvold et al. “What is the Use of Elephant Hair?” PLOS One. 2012.

Alex Fowler & Adrian Bejan. “Forced convection from a surface covered with flexible fibers”, International Journal of Heat and Mass Transfer, Volume 38, Isssue 5, 1995.

Weissenbock et al. “Taking the heat: thermoregulation in Asian elephants under different climatic conditions”, Journal of Comparative Physiology B, Issue 182, 2011.

Down to the Bear Bones: How Polar Bears evolved from Grizzlies to hunt in the Arctic

Katmai National Park in Alaska holds an annual “Fat Bear Week”, in which Twitter followers are asked to vote for the fattest bear in the park. This year’s winner was Holly, somewhere in the range of 500 to 700 lbs. That’s a big bear. However, in 1960, a male polar bear in Kotzebue Sound, Alaska, weighed in at 2,209 lbs. In fact, on average, polar bears weight up to 60% more than Grizzly bears, their closest animal relative. 

A very fat grizzly bear standing on rocks.
Holly, aka Bear 435, the 2019 winner of the Fat Bear Contest. From Katmai National Park via Twitter.

So just how did Polar Bears get so big? Well, as anyone in the Midwest knows, a harsh winter requires a good winter coat. The advantage of thick skin and fur, as well as a higher capacity to put on weight made heavier polar bears more adept to survive. However, bigger bears that could survive the cold were more likely to fall through the ice, so these adaptations required better foot mechanics.

Consequently, polar bears developed a distinctive gait. A rotary gait is a “double suspension” gait, meaning the animal bounces both off the hind limbs and then the fore limbs . This is contrasted from the grizzly bear’s transverse gallop, which involves only one “bounce,” — this loads each limb for a longer time and more vertically. The rotary gait improves stability, giving the polar bear the ability to travel quickly and smoothly on icy surfaces. 

A series of drawings depicting the gait of a galloping polar bear.
A series of drawings depicting the gait of a polar bear. Modified from S. Renous, J.P. Gasc, and A. Abourachid, Netherlands Journal of Zoology (1998).

Another significant difference between the species are their skulls, which, while similar in size, vary greatly in bite force and bone strength. The polar bear has a stronger bite, but a weaker skull. Polar bears are one of the most rapid instances of evolution in surviving species of animals, having evolved from the grizzly bear within the last five hundred thousand years. So why are their skulls weaker if their bite is stronger? 

Simply put: seals are easy to chew. Grizzlies are omnivores, as most bear species. Their diet subsists of salmon, elk, and small game, but includes a hefty amount of vegetation. Polar Bears, in the ice and cold, were forced to eat seals (as well as penguins, fish, even belugas). Seals are largely blubber, providing the caloric intake necessary to sustain these large beasts, but offering little resistance in the chewing process. 

Two line drawings of skulls, one of a polar bear and a grizzly bear
Skulls of the polar (left) and grizzly bear (right). Modified from P. Christiansen, Journal of Zoology (2006).

The polar bear’s skull morphed quickly, elongating to allow it to hunt for seals and fish through small holes in the ice. This weakened and lowered the density of the skull; however, because the seal-heavy diet required less effort to chew than vegetation, there was no selective advantage to a skull reinforcing. So, with a more efficient gait and a stronger bite, the polar bear developed into a killing machine in the icy north.

Interested in more of the polar bear’s hunt? Learn about how they can swim for hundreds of miles, or to see these arctic advantages in action, check out this video of a polar bear hunting a seal.

Canine Hip Dysplasia: What You Should Know

Canine hip dysplasia (CHD) is a degenerative hip disease that tends to develop in large breed dogs, such as the Bernese Mountain Dog, affectionately referred to as Berners. CHD significantly decreases the quality of life of a dog and often leads to complete immobility if left untreated. Experts estimate that about 28% of Berners are affected by dysplastic hips, making them the 8th most susceptible dog breed.

Bernese mountain dog with superimposed image of hip ball and socket joint.
Image from Packerland Veterinary Clinic.

At birth, puppy skeletal structures are largely composed of cartilage that is much softer than bone. This softer cartilage is able to adapt much more easily to the rapid growth that occurs during the early months of a dog’s life. In their first few months, Berners will typically gain 2-4 pounds per week, which adds increasingly large stresses to their developing bones and joints. While genetics play a large role in the susceptibility of a dog to develop CHD, the loading cycles and forces on the cartilage greatly shape the development of the dog’s hip.

Correctly formed hip versus a deformed femur head and shallow hip socket.
Image from Dog Breed Health.

The hip is a ball and socket joint, where the head of the femur, the very top of the dog’s leg, should fit perfectly into a socket in the pelvis. If the ligaments that hold the femur in the hip socket are too weak or damaged at all, the positioning of the

Evenly distributed forces on a correctly developed hip joint versus force concentration acting on a dysplastic hip joint.
Modified from The Institute of Canine Biology.

hip joint will be off and the hip will be subjected to unbalanced forces and stresses over the course of the dog’s life. The distribution of forces experienced by the hip joint in normal hips is evenly spread, while dysplastic hips are subjected to a stress concentration on the tip of the femur. These unnatural forces will cause laxity in the hip joint, leading to instability, pain, and often times the development of osteoarthritis.

 

There are also a number of environmental factors, many of which are inherent to large dog breeds, that dramatically increase a dog’s susceptibility to CHD. A study by Dr. Wayne Riser concluded that factors such as oversized head and feet, stocky body type with thick, loose skin, early rapid growth, poor gait coordination, and tendency of indulgent appetite all contributed to the development of CHD. All of these features are generally inherent to large breed dogs, such as Berners, so great care must be taken in order to mitigate their effects on the quality of life for these dogs.

Multiple studies have shown that treatment that is implemented early in the dog’s life is much more effective than late-in-life treatments. CHD warning signs can be seen in puppies as young as 4 months old, and most veterinary professionals agree that if scans occur at 2 years of age, the most optimal time for treatment has passed. Since larger stresses will be put on the hip joint as the dog grows, surgical repairs, or changes in diet and exercise, are most effective if implemented before the dog’s skeletal frame is completely developed.

 

timeline of canine hip dysplasia development
Modified from The Institute of Canine Biology

Additional information regarding this topic can be found at The US National Library of Medicine or The Journal of Veterinary Pathology.