Integument is a word that many people don’t know. It comes from Latin for integumentum – a covering. So the integumentary system of an animal is skin and related structures like hair, feathers, horns or claws.
It’s an organ system, believe it or not, and it has many roles. It acts as a physical barrier to protect your insides from the outside. It helps regulate water, temperature, excretion of waste and senses of pain, pressure, touch and temperature.
There are specialised structures in different species. Hair, feathers, horns, claws and shells are all part of the same system and the one thing that they have in common is a protein called keratin. I bet you’ve heard of that one.
Keratin is a strong fibrous protein that creates filaments. It doesn’t easily dissolve in water or organic solvents, otherwise bathing would be impossible. The toughest layers of skin and nails is created through cornification – where keratin is produced and the cells are filled with it, losing their nuclei and organelles.
Keratin is combined with collagen and elastin to give it strength and flexibility. It’s amazing stuff, really. Birds and reptiles have even tougher skin layers made up of keratin called beta-keratins, that make up their feathers, beaks, claws and scales.
Even things like the horn of a rhinoceros are made of keratin. So it can serve purposes like defence and the ability to climb, run, swim and fly. So let’s see what the outside does and why it matters.
Fur/Hair
Almost all mammals grow hair or fur. It can be waterproof and the pigmentation provides camouflage but its main role is temperature regulation. There are different types of hair with different purposes.
Most fur coats have two kinds, guard hairs that are good at keeping water reaching the skin and the undercoat that acts like an insulating blanket. See huskies and wolves.
Wool is a thick, soft coat that often curls like sheep. Spines are a very stiff guard hair type that is used for protection like we see in porcupines and hedgehogs. They are very sharp.
Specialist Hairs
My cat Echo showing her whiskers.
One of the most interesting hair types is vibrissae. Most people know these as whiskers like what Miss Echo has on her face, eyebrows and behind her wrists. These are sensory hairs that give information about the environment and help in navigating through small spaces or darkness. Each whisker is connected to a nerve ending, which is why we don’t generally like cutting the whiskers.
Hair grows in a cycle and often it reaches a certain length then falls out. A certain amount of hair falling out is normal for most species and the hairs are usually replaced. This cycle is managed hormonally by the thyroid hormones and sex hormones especially. For some animals there is a seasonal component where the coat changes, like many arctic animals change from grey or brown to white in the winter.
Not all mammals have hair, or much hair. Naked mole-rats are weird little guys and they are naked, hence the name. They do have whiskers though. Elephants and rhinos are also hairless. Some mammals are born hairless and it grows in as they develop, while others are born haired. Humans of course typically have hair on their heads and a fine downy hair on the rest of the body. At puberty, hair grows in new places like the underarms and pubic region, as secondary sexual characteristics and this is driven by increased levels of the sex hormones.
Nails and Claws
Nails and claws are specialised keratin structures at the end of toes and fingers. True claws and nails grow from the very last bone in the digit. Claws are curved and hooked, while nails are flat like in humans.
Many predatory animals have retractable claws, particularly cats. This means they can hide the claws inside their paws and extend them for use. Their claws are used for traction and to help hold onto prey.
Nails that are big enough to bear weight on are hooves. Ungulates like horses, cows, sheep etc have these. They are still made of keratin but can be very tough. They keep growing and need regular trimming in domesticated ungulates.
Most reptiles have claws on their feet and they can be very sharp and strong. Snakes generally do not, as they lack limbs, but some of the ‘older’ boids in evolutionary terms possess single claws on either side of the vent scale as remnants of their lost limbs. Because snakes evolved to have limbs then evolved to lose them. Boa constrictors are a great example and they have these ‘spurs’ as well as little bits of vestigial pelvis bones.
Birds also have claws and use them for grip. In birds of prey, they are called talons and are their primary method of hunting. They need to use the talons to catch their prey. If you have to handle a bird of prey safely, you need to get control of the feet as they will do much more damage with their talons than with their beaks.
Scales
Reptilian skin is a bit more complicated. They are covered in scales or scutes with different shapes and sizes. Their skin is a lot tougher than mammalian skin and the patterns and shapes vary significantly by species.
Lizard scales might have modifications like spikes or ridges on them for defense. A single species can have different kinds of scales on different parts of their body. Like iguanas.
Turtwig – my Hermanns tortoise.
Snakes are entirely covered in scales and they use them for movement as well. They lack eyelids and the eyes are covered with a transparent scale called a ‘spectacle’ which goes cloudy when they shed. Reptiles periodically shed their skin. Snakes do it in one piece, while lizards tend to flake off in bits.
Chelonians like tortoises and turtles have scutes, thicker pieces of armor plating. Crocodilians also have these and you can see similar things on bird’s feet. These plates really do act like armour, but it is important to note that tortoises can feel you touching their shell, it’s not dead tissue and it’s not detachable.
To Be continued
Next week we’ll continue in this topic by looking at more specialised features including feathers, horns and antlers and how they function. After that, we’ll be looking at skin wound and healing.
Camouflage is a big deal in the natural world. It’s employed by both predators and prey species for a variety of reasons. They employ many techniques to mask their presence to hide from other animals. So if you’ve ever wondered why zebras have stripes or how a chameleon can change colour, you’re in the right place. Let’s get into it!
Some Definitions
Crypsis: the ability of an organism to avoid observation or detection.
Disruptive colouration: a form of camouflage that works by breaking up the outlines with a strongly contrasting pattern. Military camouflage uses this.
Countershading: where the colouration is darker on top and lighter on the underside, which counters the effect of light coming from above on a 3D object, making it harder to detect.
Counterillumination: a related mechanism that uses illumination to match the brightness of a background, often employed by marine organisms like squid that have bioluminescence.
Mimicry: some animals have evolved to look like other things in order to hide from prey or predators, especially common in insects.
Background matching is what it sounds like, animals that have colouration and patterns that match the background of their natural environment. So animals that live in the desert are coloured in sand, buff, ochre and brownish grey colours. Lions, gerbils, fennec foxes and desert reptiles like skinks or horned vipers are great examples.
Disruptive Colouration
This method uses strongly contrasting, non-repeating markings to break up the outline of the animal to help it blend in. This is the same principle behind military camouflage, which uses irregular patches of contrasting colours to hide their presence, matched to the environment they are in.
Leopards use it to hide from prey while many prey species use it to hide from predators. So let’s play a little game, shall we? The image below is a ptarmigan and its chicks that are hiding in plain sight. Can you count how many chicks are in this photograph? (I’ll put the answer at the end!)
They’re very well hidden, aren’t they? It is incredibly effective. These features evolve due to natural selection. Animals that can evade predators better as babies will have a better chance to survive and pass on those traits to their own offspring.
This image demonstrates how countershading works. It’s a method that reduces the animal’s shadow and makes it look flatter. The light hitting a darker part will create the flat colour and we see this in gazelles, sharkes and dolphins among others. This is known as Thayer’s Law and he created the next image.
Thayer painted two model birds. The one the left is painted in the same colours as the background. The one on the right is there, I promise. You can make out an impression of the circular wire base to the right of the visible model, if you look closely. This model bird is counter shaded and makes it almost entirely invisible.
Abbot Thayer, Public domain, via Wikimedia CommonsA horned lizard flattening itself – Public Domain
Animals use other measures to eliminate their shadows. Horned lizards can flatten their bodies and their sides thin to an edge to blend in and avoid creating shadows at all. The horned lizards are found in North America. Bearded dragons also have this capability and they come from Australia. It’s obviously an effective technique for two species that have evolved so far apart.
Crypsis
This is a catch-all term for organisms that have methods of avoiding detection from other animals, such as camouflage, nocturnal living, underground living and mimicry. Concealment involves visual, olfactory or auditory concealment, or a combination of them.
A pair of Sponge Decorator Crabs (Hyastenus elatus) grappling. Pipeline, Port Stephens, NSW Richard Ling, CC BY-SA 2.0 https://creativecommons.org/licenses/by-sa/2.0, via Wikimedia Commons
Decorator crabs collect items from the local area and add them to their carapace (shell) in order to blend in.
Olfactory concealment involves hiding scents to avoid detection by prey or predators, or even trick other species. The large blue butterfly caterpillar can mimic ants to trick them into feeding the caterpillar. Puff adders make use of this type of crypsis as well.
The reason most mammals lick their new-borns clean and eat the placenta is to mask the scenes. The idea is to make it less obvious that there are new-born animals around. So if anyone tells you that they eat the placenta for nutrients, that’s not quite correct. It has nutrients in it, of course, but it’s not essential. Humans have no natural predators so you do not have to eat your own baby’s placenta, unless you really want to.
Can you see the mantis in this image? It is on top of the flowers closes to the camera. Stick insects, flower mantises like the orchid mantis, and even cuckoos employ mimicry.
Cuckoos lay their eggs in the nests of other, smaller bird species. The egg looks similar so it won’t be rejected by the nest owner. Then the chick hatches and kicks out the other babies from the nest, so only it survives and is fed by the parent. Cuckoos are the real deadbeats of nature.
Motion Dazzle
Most of the camouflage methods we’ve discussed are broken by movement. Bold, contrasting markings help them hide by making it difficult to estimate their speed and direction when they move. The stripy horses, zebras, use this. They are striking to see as an individual but with an entire herd huddled together, it’s incredibly difficult to pick out one prison pony from the crowd. You have to really focus your eyes, even when they are moving. Nature invented optical illusions first.
Colour Changing
Panther Chameleon – Sapporo Maruyama Zoo (Public Domain)
Some animals can change colour. They have specialised chromatophore cells in their skin that can alter the wavelength of light they absorb, which creates the change in colour. This might be used to blend in to the environment, a trick octopuses use a lot.
However, it can also be a form of signalling and communication. Meet nature’s mood ring: the chameleon. They usually change colour to show their mood. The change is very quick, before your eyes.
There are some mammals that change colour but it’s far slower and generally seasonal. Arctic animals are brown or grey in the summer but they turn white in winter, via a seasonal moult that responds to changing temperatures and daylengths. Arctic foxes, arctic hares and stoats are great examples.
Hiding
Many animals burrow or hide their nests in remote spots. Maybe even using objects around them to disguise it’s presence. They might be more active at night when it’s easier to hide. Or they can disguise themselves underwater to ambush prey like alligators and crocodiles do. That’s why they don’t tend to chase you, they lunge at prey as it stops next to the water. If they miss, they give up quickly and wait for the next possible lunch to come along.
Just to give ostriches some credit here. The whole ‘burying their head in the sand’ thing is not an indication that they’re so stupid they think they’re invisible when they do this. Yes, their brains are smaller than their eyeballs but they’re not that stupid. They dig in the sand to build their nests for their gigantic eggs.
Ostriches don’t need to hide. They can run up to 45mph/72kmph. Even better, they can sustain 30mph/48kmph for a long time. They are faster than lions and they are faster than Usain Bolt. Why hide when you can run faster than basically anything else? Except maybe cheetahs. So let’s stop laughing at ostriches because they don’t deserve it.
Aposematism – The Opposite of Camouflage
Now for something completely different. Aposematism is the opposite of camouflage. There are some creatures that want you to see them. They want you to know they are there. And they want you to leave them the heck alone!
Aposematism is defined by bold, bright colouration to serve as a warning. It means ‘I am dangerous. Go away. Get lost. I will destroy you.’ It is a warning you absolutely need to take seriously. In most cases.
The danger could be a number of things. They might be poisonous – you die if you eat them. They might be venomous – you die if they bite or sting you. Or they might taste bad. Or they might just be very aggressive and want to give you a fair warning in rainbow hues. It’s nature’s way of saying FAFO. You shouldn’t want to find out.
See wasps, poison dart frogs and nature’s own most fearless animal. The honey badger. Yes, really, this large mustelid will destroy you with prejudice. It is found across Africa, Southwest Asia and the Indian subcontinent. They are so feared that the people of Somalia believe one bite will make a man infertile! I’m sure the honey badger wants to make sure you know this is true, as well.
The colours involved are often yellow, red and black in high contrast patterns but there’s a whole rainbow of danger out there. Here’s one of my favourite examples, the blue-ringed octopus. One of the deadliest sea creatures out there. He’s just a little guy but do not touch! No matter how small and cute it is. Blue means death. Like an old PC.
I know the name’s not the most creative but it’s accurate and that makes it easily identifiable. Blue rings on an octopus means potential death. If in doubt, no matter how small, cute or colourful, just leave them be. Or call in an expert if there’s immediate danger.
Another example is the milk snake and the coral snake. These snake species can resemble each other very closely. One is venomous and the other isn’t. Coral snake venom is rarely deadly to humans but it’s still useful to learn the difference if you live where they live.
This is the milk snake. The yellow bands are surrounded by black bands, with the red ones in between them.
The next image is of a coral snake, and this is the venomous version. It also has red, yellow and black bands but the pattern is different. However, I would always advise caution if you cannot confidently identify a snake species and leave them alone. Snakes rarely attack unprovoked.
A Coral Snake – Public Domain
Copying the Aposematism
Some species have caught on to the aposematism and use it to their advantage. They mimic similar species that have aposematism to share in the ‘back off’ message even though they are actually harmless. The hoverfly mimics wasps to deceive potential predators and be left alone. This is what’s known as Batesian mimicry.
There is also Müllerian (note the u should have an umlaut) mimicry where harmful species have evolved to resemble each other. Many bee and wasp species do this and it is honest because both of them can sting. The yellow and black striping is common to many bee and wasp species. Batesian mimicry is deceptive, in contrast.
Evolution of Camouflage
It’s all pretty amazing stuff. Animals evolve in response to environmental pressures, in order to keep surviving. Many of these traits came about as random chance, mutations that were beneficial to survival. That allowed them to be genetically passed down and eventually shaped the species’ appearance or behaviour. Remember that evolution is a very slow process. It takes many, many generations to happen.
It’s faster in simpler organisms like bacteria, because their reproductive generation takes hours. They’re single cells, mitosis is fast. Bacterial growth is exponential, their numbers double at regular intervals, depending on the kind of bacteria but it’s a matter of minutes. If you get a swab done for bacteria, entire colonies can grow within 24 hours on a petri dish. A colony is millions of bacteria.
Larger organisms produce a new generation more slowly. In humans it’s around twenty years, give or take. So my grandmother is part of the Silent Generation (1928-1945ish), my parents are Boomers (1946-1964ish) and I’m an elder Millennial (1981-1996). That’s not a lot of generations for evolution to occur. It’s about 70 years for three generations to exist. But what will humanity look like in 10,000 years? Will we still have appendices (probably because it turns out they do have a function)? What about in 500,000 years? A million? We’ll not be around to see it, but maybe we can leave our mark on the world for future generations to learn from.
Answer to the Ptarmigan Chick Question
I didn’t forget, don’t worry. There are five chicks hidden in plain sight. Let me show you where they are. I have placed blue circles around the adult ptarmigan and the five chicks so you can see where they are. How many did you find?
Just like Goldilocks and the Three Bears taught us, for life to exist things need to be just right. Temperature regulation in animals is essential. Bodily functions and physiological processes require specific temperatures to work properly. Too hot or too cold, and these functions will fail.
Our planet is at the perfect distance from the sun to have temperatures capable of sustaining life. We have liquid water and an oxygen rich atmosphere which only exists because the temperature is perfect, more or less. There is a temperature gradient where it is hottest around the equator and coldest at the poles. Climate change is also creating a shift in the average temperatures.
Living things function due to a whole range of biochemical reactions which need specific temperatures to be effective and efficient. The specific temperatures needed depend on species and the function in question. For example, many mammals have external testicles because sperm generation is more efficient at temperatures a couple of degrees below the normal body temperature.
Ecosystem Adaptations
The various ecosystems in the world are well adapted to their native environment. Species have evolved all kinds of ways to maintain their optimum temperature. That’s why a polar bear couldn’t survive in the Sahara Desert. Climate change is impacting this, as global temperatures rise. We have many species under threat of extinction, if not extinct already.
For other species, the climate shift might be beneficial. A current example is two different species that live in the Atlantic Ocean. The Atlantic Horseshoe Crab is declining in number as the ocean warms. In contrast, Atlantic Blue Crabs are thriving and their numbers are actually increasing.
So what does this mean? One of my goals with these articles is to help fellow writers understand various factors in the natural world. That way when you are including animals in your writing, whether they are real, mythological or original, they can fit into the right ecological niche. Let’s start with some definitions.
Definitions
Thermoregulation: physiological or behavioural methods for regulating the body temperature.
Endotherm: organisms that can generate their own body heat through their metabolism – colloquially referred to as ‘warm-blooded.’
Ectotherm: organisms that rely on external heat sources to keep their body temperature where it should be and regulate it through behaviours – colloquially ‘cold-blooded.’ It can be used interchangeably with poikilotherm but there are distinctions. Ectotherms generally want to stay at a constant temperature and use the environment to maintain it.
Poikilothermic: this is another term used to describe ectothermic organisms. It comes from the Greek word poikilos which means ‘various’ or ‘spotted.’ There is some crossover with ectotherms but poikilotherms are species that seek to vary their temperature dependent on physiological needs. Most reptiles, amphibians and fish fit this category. Mammals that are poikilothermic include the naked mole-rat and sloths.
Hyperthermia: A physiological state where the body temperature is too high from external means like an abnormally high environmental temperature or failure of the body’s cooling mechanisms. Heat stress or heat stroke are clear examples. Hyperthermia is dangerous as many enzyme reactions fail above a certain temperature and it can result in damage, especially to the brain.
Hypothermia: the opposite, the body is too cold and eventually the normal physiology that attempts to maintain core temperature high enough will fail and this leads to physical damage. It is equally serious and potentially fatal.
Fever/Pyrexia: both words mean the same thing. Fever is different from hyperthermia. The body raises its temperature in response to an infection, which can hinder the infectious agents while boosting the function of the immune system. Fever is unpleasant but it doesn’t always need treatment.
How Endotherms Regulate Their Temperatures
The simplest answer is that endotherms generate heat via their metabolism to maintain their body temperature. It does come with an energy cost, but they are less vulnerable to external temperature changes.
They employ mechanisms that help maintain the right temperature. In cold climates shivering and using up brown adipose tissue (brown fat.) Brown fat can be metabolised much faster than white fat. Many new-born mammals have this fat to keep them warm until they have dried off and had their first feed. For hot climates, things like sweating and panting can help keep the body cool. The circulation system can alter blood flow to lose or retain heat as well.
Endotherms are less vulnerable to external temperature fluctuations such as the day and night cycle. Many deserts get very cold at night, despite being very hot in the daytime.
The downside is having a higher metabolic rate and increased energy demands. This requires more food intake. Endotherms can’t last as long in periods of starvation, in general. Some endotherms will bask in the sun and rest a lot to reduce energy demand. This is why cats enjoy snoozing in sunny spots!
Only birds and mammals are true endotherms but there are some species can become endothermic during their reproductive season. Some endotherms will enter temporary hypothermia, a controlled physiological state that can be part of the normal circadian rhythm.
Hibernation
Hibernation is a longer seasonal cycle, usually to survive over winter when food is less available. It involves lowered metabolic rate, low body temp, slowed breathing and heart rate. Some species will eat a lot of food before winter to store the energy as fat. Smaller animals will use food caching, hiding stores of food nearby. Some of them carry a pregnancy through their hibernation period, such as black bears. They give birth shortly before or after they wake up.
The exact changes differ between species but hibernation is a way of surviving harsh winter weather and prevents a period of starvation. Especially since energy is required to maintain body temperature and if food is less available, it would be difficult to maintain the caloric intake required.
Sloths
Sloths are mammals that behave more like ectotherms. Their body temperature fluctuates according to their environment. This means they are capable of starving to death with a full stomach of food. If the temperature drops too low, they can’t digest their food and it can then rot and produce toxins. This can happen in reptiles too.
Polar animals have specialised structures that help them maintain their temperature in cold conditions. Features like insulating fur, waterproof feathers or blubber under their skin help them stay warm.
Penguins have specialised blood vessels that act as heat exchangers where the veins sit next to the arteries where the blood is warmer, so heat is exchanged to warm the blood returning to the heart.
Hot Climates
Animals that are native to hot climates have peripheral blood vessels that allow them to lose heat – elephants have these in their ears. It’s also why fennec foxes have such large ears compared to their body size. Panting is a common way of losing heat as well, especially in canine species. Some species like humans and horses sweat to lose heat with evaporation. Dogs are at risk of hyperthermia because they don’t really sweat, they only have sweat glands on their paw-pads so panting is their main way of losing heat.
Ectothermic species don’t produce much internal heat from their metabolism and so they rely on the environment to keep their body at the right temperature. Reptiles, amphibians and fish are generally all ectotherms. Most insects are too.
Most deep sea aquatic species are adapted for the temperature of where they live, such as in the abyss level of the ocean. Water temperature is stable and constant so they rarely need to do anything.
Reptiles especially keep warm by basking in the sun to raise their temperature or seeking shade to cool down. They also employ reduced metabolism in the cold to maintain their body and minimise energy usage when food is more scarce. Most reptiles do have body fat stores, usually within the coelomic cavity (abdominal cavity in essence) or sometimes in extremities like the tail. Leopard geckos store a lot of fat in their tails, for example.
Due to this, many ectothermic species are slower at night or early in the morning. They need to warm up before going about their day! They tend to be more active in the daytime although nocturnal species exist. Geckos are usually nocturnal and they wait for food to pass by rather than searching for it as this uses less energy.
Ectotherms can last much longer without food because they are capable of slowing down their metabolism when it is cold. However, if they are unable to find a suitable basking spot and heat, they can starve to death even if food is plentiful. They need to warm themselves to digest and metabolise their food – kind of like the sloths we mentioned earlier. Sadly I have seen this happen in captive reptiles – such as a snake whose basking lamp and heating system broke down after it had been fed and the prey began to rot and made the snake sick. Very sad.
This is the reason that reptiles are not found in the polar areas. Many that live in temperate regions will hibernate or ‘brumate’ over winter. Species that live in the equatorial areas like most of Africa, do not hibernate as there’s no need for it. It never gets cold enough.
Antifreeze
There are naturally occurring anti-freeze proteins. Yes, really. Some species of fish, amphibians and reptiles can freeze in the winter and wake up in the spring. They survive with the help of antifreeze proteins that prevent ice crystals forming in the body. These crystals would damage the organs and kill the animal without these proteins. Just like the radiator of a car!
Some plants also have this capability. Many of the cabbage related vegetables can do this like kale, spinach, brussels sprouts. Hellebores, pansies, cornflowers, poppies and lavender produce antifreeze proteins.
Interestingly the sacred lotus, an aquatic plant that grows in ponds and deltas, or in flood plains. It is the national flower of India and has the ability to regulate the temperature of its flowers just like an endothermic animal. This seems to be a way of attracting insect pollinators by promising a cosy environment, I suppose!
Species have adaptations to suit their native environments and make sure they can survive the conditions they live in. This is why introducing non-native species can be difficult and detrimental to the local ecosystem. Animals that live in colder climates will struggle when it is hot, and vice versa. That’s why huskies love being outside in the snow and ice, while a greyhound will hate it and usually require a coat of some kind to go outside in winter. Just like us, we don’t have much body hair to insulate us, which is one reason we wear clothes.
Hyperthermia
This is defined as overheating, where body temperature is elevated above normal. It is due to a failure in thermoregulation or temperature extremes beyond what the body can cope with. This is not the same as a fever, or pyrexia, which we’ll get to.
Hyperthermia is a medical emergency in both humans and animals as it can result in death and significant damage, particularly brain damage. Heat stroke where the body temperature is elevated from excessive heat exposure that overwhelms the body’s temperature regulation. Severe cases will result in blood pressure drops, confusion, dehydration and even seizures. Organ failure and death will result if not attended to.
Heat stroke is very serious, especially in young or elderly people. Dogs are also very vulnerable to it, especially the brachycephalic (flat faced breeds) like bulldogs. They struggle to pant enough to cool down because of their restricted airways and I have seen dogs die from heat stroke, or suffer permanent damage from it. PSA – do not leave dogs, young children or animals in a hot car in summer. Exertion in hot weather is also a risk for both people and animals so avoid long walks, running about or doing anything strenuous when it is excessively hot.
Hypothermia
The opposite – remember your prefixes. Hyper- means too high, while hypo- means too low. Hypothermia occurs when the body temperature drops too low and the body cannot maintain internal heat generation to sustain it. It can be serious and risks death in some cases too.
Mild cases will show confusion and shivering – this is muscle contractions to try and generate some heat. Once hypothermia progresses the shivering stops. Severe cases can result in hallucinations and a risk of death. People will often show paradoxical undressing in severe hypothermia. This is likely due to the blood flow. In cold temperatures, the peripheral vessels (arms and legs) contract to keep blood pressure and heat in the core of the body. They become exhausted and relax, allowing blood to flow and make the person feel warm, so they start stripping off. Which makes the whole thing worse. Very scary.
Hypothermia can be caused by exposure to cold weather, especially cold water immersion like falling through the ice of a frozen lake. Being wet increases heat loss from the skin. There are other factors that can impact temperature regulation. Low body fat, old age and low blood sugar increase the risk of hypothermia. So does alcohol intoxication – it’s not uncommon in winter for people to present with hypothermia after a night out where they have overindulged. Alcohol can make you feel warmer and thus not notice the cold.
It should be noted that the heart rate drops and respiratory rate also slows down. If you’ve watched Grey’s Anatomy, you will have heard the phrase: “They’re not dead until they’re warm and dead.” That is true, as even if there’s no detectable pulse, with aggressive rewarming and medical care, people can be revived. The same applies to some small animals where they can appear to be dead when cold but recover when warm – hamsters are notorious for this one! So you should always attempt to warm them up in case they can recover.
Fever
Finally, fevers are a different thing altogether. The body has it’s internal regulation system that keeps the temperature at a ‘set point’ in endothermic animals. The hypothalamus is responsible for this. In case of infection and an immune response, this set point is increased to raise the body temperature. Fever is thought to improve effectiveness of white blood cells and hinder the reproduction of pathogens like bacteria.
It’s a common symptom of illnesses, particularly infections. This can range from the common cold, where recovery will happen in a few days, and sepsis which is much more serious and requires intensive intervention. It is important to distinguish a fever from hyperthermia, as hyperthermia is much more life threatening.
Treating a fever may not always be necessary or recommended but there isn’t much evidence that treating the fever with antipyretics like paracetamol improves or affects outcomes in sepsis. Fever is uncomfortable and unpleasant to experience but it is rarely life threatening in itself, even if the cause is serious. Rarely young children can experience ‘febrile seizures’. Fever makes you miserable and can affect cognition. It is not the same as hyperthermia, though, and fevers do seem to be beneficial in aiding the body fighting off pathogens.
Regarding animals, normal temperatures vary by species. So the threshold for a fever is different in dogs to chickens. Normal human body temperature is accepted to be around 37°C or 98.6°F. Fever would be above 38°C or 100.4°F. In dogs the normal temperature is between 38.3°C to 39.2°C or 101°F to 102.5°F. Fever is above 39.4°C or 103°F. In chickens normal temperature is 40.6°C to 41.7°C (105°F to 107°F). Anything above 43°C or 110°F is a fever in this species.
