The next time you poke your one of your feet outside your nice warm bed in the morning and think it\u2019s too cold to get up, just imagine being a reindeer, stuck outside, in the snow and ice, desperately looking for food in temperatures as low as -30\u00b0C.\u00a0 There are a lot of people that don\u2019t believe reindeer can fly, but to be honest, I find it pretty amazing they survive at all.<\/p>\n
\nCold Comfort<\/h1>\n
There are two problems with being cold.\u00a0 Firstly, chemical reactions happen more slowly, and some even stop, at low temperatures.\u00a0 Secondly, when water crystallises into a solid (freezes), it expands.<\/p>\n
Because we humans are clever, and can paint, write poetry, even play the trombone (should the urge take us), we sometimes forget that when it comes down to it, all living things (including us) are, at the most basic level, chemical reactors.\u00a0 So, when the cold slows chemical reactions down, it slows life down!<\/p>\n
Living cells can\u2019t survive freezing.\u00a0 This is because they contain a lot of water, if that water freezes it rips the cell apart, killing it.\u00a0 Have you ever seen what happens to a lettuce if it freezes accidentally in your fridge and then defrosts? It just turns to mush.\u00a0 There are plenty of organisms that survive in temperatures where all the water around them is freezing, but they are only able to do this because they prevent ice-crystals forming within their cells in the first place.<\/p>\n
Anti-Freeze<\/h1>\n
Every winter, car owners add chemicals to the water in their car engines to lower the freezing point and prevent the water inside wrecking their engine.\u00a0 A number of animals use a similar trick: the arctic ice fish, Trematomus has glygoprotein antifreeze in its blood.\u00a0 The parasitic wasp, Brachon cephi is just one of a large number of insects, mites and other arthropods whose blood contains glycerol.\u00a0 The larvae of the midge Chironomus have a neat trick, its cells are surrounded by dilute fluid and the cytoplasm within its cells is packed with sugars and salts.\u00a0 This ensures that the water outside the cells freezes first, protecting the cells themselves.\u00a0 The fluid in their cells can stay liquid at temperatures as low as -32\u00b0C.\u00a0 Some animals, most notably deep living fjord fish are able to become \u201csuper-cooled\u201d without freezing.<\/p><\/blockquote>\n
Mammals and birds have an inbuilt central heating system that keeps their core body temperature at around 37\u00b0C (40\u00b0C for birds).\u00a0 To generate heat they break up chemicals obtained from their food or fat from their body\u2019s stores.\u00a0 The heat is generated in muscles by fast contractions (shivering), in the liver and in the fat cells themselves.\u00a0 It is then distributed around their bodies by their blood as it circulates.\u00a0 This extra heat frees them from the effects of cold weather, but it diverts both raw materials and energy from other essential life processes like growth, repair, muscle action, digestion etc.<\/p>\n
Keeping your body hotter than the environment requires a constant use of energy and mammals can use up to 80% of their food in this way.\u00a0 This is because heat always flows from hot to cold.\u00a0 The cup of tea that I made twenty minutes ago and forgot to drink has gone cold because its heat has flowed away.\u00a0 The room has become ever so slightly warmer as a result but sadly, the cup of tea was small compared to the room, so I haven\u2019t noticed the room get warmer, just the tea becoming undrinkable.\u00a0 Excuse me whilst I put the kettle on again.<\/p>\n
Right, I\u2019ve made not one, but two cups of tea.\u00a0 One is in a plastic cup; one is in an empty baked bean tin (more of them later).<\/p>\n
Trying to find the extra energy that heat generation requires, in winter, when food is at its most scarce presents huge problems.\u00a0 For this reason, rather than deal with the cold, many animals opt to hibernate through it.\u00a0 They allow their bodies to cool and slow down to the point where they are barely alive and remain inactive throughout the winter.\u00a0 This way, their fat reserves last a lot longer and is perfect for animals like hedgehogs and shrews that feed on insects, worms, and other critters that\u00a0 are either dead or dormant during winter.\u00a0 Reindeer are vegetarians so there is always food available if they can get to it.\u00a0 They have large hooves that are useful for kicking through the snow to find food.\u00a0 Polar bears actually hunt other cold weather animals (including humans) so their available food actually goes up during the winter, for them, the lean period when they have trouble getting enough food is the Summer.<\/p>\n
\nHappy Hibernators<\/h1>\n
Hedgehogs in Britain can be seen out and about as late as December if the winter is mild enough.\u00a0 Often, these will be young animals that didn\u2019t manage to get enough food during the summer.\u00a0 If you see a hedgehog at this time of year, it needs help.\u00a0 Put out tinned cat or dog food with added crunchy munchies (for their teeth), and water.\u00a0 Don\u2019t give hedgehogs bread and milk.\u00a0 To survive winter, a hedgehog has to weigh approximately 450g by November.<\/p>\n
Champion Hibernator<\/h1>\n
Hibernating animals normally burn just enough fuel to keep their bodies above freezing 0\u00b0C.\u00a0 Not so the Arctic Ground Squirrel.\u00a0 These super-cooled, snowbound, critters allow their temperature to drop as low as minus 2.9\u00b0C.<\/p><\/blockquote>\n
An animal can\u2019t afford to generate unlimited amounts of heat, so to survive, it needs to limit the amount of heat it loses to the environment.\u00a0 Remember, my two cups of tea?\u00a0 The one in the metal tin was almost too hot to touch when I first filled it, but the tea inside is already going cold.\u00a0 The one in the plastic cup was cool to the touch even when the water inside was boiling hot.\u00a0 It\u2019s warming up slightly now, but the tea inside is still beautifully hot and drinkable.\u00a0 This marked difference between the two \u201ccups\u201d is due to their different heat conducting properties.\u00a0 Plastic is a good thermal insulator; metal is a good thermal conductor.\u00a0 This is why mammals have fur and birds have feathers, both provide excellent thermal insulation.\u00a0 A good layer of fat or blubber is also helpful.\u00a0 More than a food source, it\u2019s also a great insulator.\u00a0 Heat can also be lost when air, warmed in the body, is breathed out again.\u00a0 Penguins, Reindeer, Polar bears and a number of other animals solve this problem by reclaiming heat and moisture from the air on its way out thanks to the rather special shape of their nasal passages.<\/p>\n
\nFurry-Nuff (Get Down)<\/h1>\n
Both polar bears and reindeer have incredibly dense, two layered, coats consisting of a dense under-fur combined with an outer layer of long, hollow guard hairs.\u00a0 The hairs are packed together extremely tightly; 100 guard hairs cm-2 and 200 woolly under-hairs cm-2.\u00a0\u00a0 The hairs trap air, which then insulates them so well that both reindeer and polar bears can lie on snow without melting it.\u00a0 When you stroke a polar bear (only to be done when they\u2019re anaesthetised or they\u2019ll eat you!), they aren\u2019t warm to the touch the way a dog or cat is.\u00a0 The hollow guard hairs also help provide buoyancy when swimming.\u00a0\u00a0 Some books and websites will tell you that Polar Bear fur helps to collect and conduct sunlight to the bears skin, this is one of those famously wrong \u201cfacts\u201d that has been around so long everyone believes it.\u00a0 The most amazing bird feathers for providing warmth are the down feathers of the Eider duck (which we use to make Eider-down sleeping bags) and the feathers of the emperor penguin, the only animal to spend winter on the Antarctic Ice shelf where the temperature regularly drops below -40\u00b0C.\u00a0 The funniest place you\u2019ll find feathers is on the feet of the Ptarmigan.\u00a0 This arctic relative of the grouse is the only bird in the world to have feathers growing on its feet.<\/p>\n
Loverly Blubbery<\/p>\n
Polar Bears have a layer of fat 11cm thick.\u00a0 That\u2019s a lot of blubber, but not as much as a right whale which can have a fat layer over 50cm thick making up around 45% of its body weight.\u00a0 Blubber is especially important to animals in water because heat is conducted through water 27 times faster than in air.\u00a0 Fur isn\u2019t much use in water because can\u2019t hold on to the air that allows it to insulate so well on land.\u00a0 Whales don\u2019t have fur but don\u2019t spend time on land if they can help it.<\/p><\/blockquote>\n
Having a large body can also help an animal retain heat.\u00a0 Guess what? You can illustrate how this works with a cup of tea as well.\u00a0 Make enough tea to fill a bucket, measure its temperature and then put it in the garden.\u00a0 Now fill a cup with tea from the bucket and leave it outside as well.\u00a0 Check the temperature of both every minute.\u00a0 The cup will cool down much faster than the bucket.\u00a0 To grasp what\u2019s going on you need to do a bit of maths: imagine a cube, where every side measures 2cm.\u00a0 It will have a surface area of 6*(2*2)=24cm2 \u00a0(because a cube has six sides), a volume of (2*2)*2=8cm3, and a surface area to volume ratio of 3:1.\u00a0 If you increase the length of the sides to 20cm (ten times bigger), the surface area becomes 2400cm2 and the volume becomes 8000cm3, a ratio of 0.3:1.\u00a0 An animal will lose heat across its surface to the cold outside, so, the less surface area it has relative to its volume, the less heat it will lose.\u00a0 Thanks to their small size, shrews needs to eat the equivalent of their half their own bodyweight each day or die \u2013 even in the summer.<\/p>\n
There is one part of the reindeer\u2019s body that can\u2019t be bulky; it\u2019s legs.\u00a0 Legs have to be relatively thin or walking is difficult and running is impossible.\u00a0 This means that they have a relatively large surface area compared to their volume and can lose heat easily.\u00a0 Heat loss from legs is a problem not only for reindeer, but for all animals in the cold.\u00a0 Birds help cut down the heat lost through their legs and feet by tucking one leg at a time into their insulating feathers.\u00a0 This option isn\u2019t really practical for reindeer, polar bears or even penguins (if they\u2019re balancing chicks on their feet).<\/p>\n
Any blood circulating through an animal\u2019s the legs will lose its heat.\u00a0 When it returns to the core of the body, it will then take heat back in, lowering the animal\u2019s overall temperature.\u00a0 Cold weather birds and mammals avoid this by having a blood circulation that incorporates a \u201ccounter-current heat exchange system\u201d.\u00a0 Heat is taken away from the arterial (outgoing) blood before it goes into the legs and given back to the venal (returning) blood on its way into the body core.\u00a0 That\u2019s the heat exchange part, but what about the counter-current?\u00a0 Well, the blood is running in opposite directions, so the coldest blood returning from the legs meets blood coming from the body that has already lost a lot of its heat.\u00a0 This is the most efficient system because heat flows from hot to cold at a rate inversely proportional to the temperature difference, in other words, the bigger the temperature difference, the faster the rate of heat transfer.\u00a0 If you want to check this out, get yourself a thermometer and a fresh cup of tea.\u00a0 Now, stir the tea gently with the thermometer and note down the time and the temperature.\u00a0 Wait 30 seconds and do it again.\u00a0 You can draw a graph of the temperature (y-axis) against time from the first measurement (x-axis) to show the exact nature of the relationship.\u00a0 Thanks to their heat exchange system, reindeer can have feet that are up to 30\u00b0C colder than the rest of their body.\u00a0 If your feet got that cold you would be in quite a lot of discomfort.<\/p>\n
Are you horrified at what a spoilt life we humans live now?\u00a0 If you\u2019re reading this in bed, shame on you.\u00a0 Come on, get up, get some warm clothes on and go and feed some birds.\u00a0 Remember, fat is best, so stick out some nuts and lard.\u00a0 Oh, and don\u2019t forget water too.<\/p>\n
Have a great Christmas and I\u2019ll see you in the New Year.\u00a0 By the way, although I love Christmas cards of reindeer and can even believe they can fly (when I\u2019m in the right frame of mind), I firmly draw the line at those pictures of polar bears and penguins on the same iceberg.\u00a0 Like, that could really happen.\u00a0 Duh.<\/p>\n ","protected":false},"excerpt":{"rendered":"
The next time you poke your one of your feet outside your nice warm bed in the morning and think it\u2019s too cold to get up, just imagine being a reindeer, stuck outside, in the snow and ice, desperately looking for food in temperatures as low as -30\u00b0C.\u00a0 There are a lot of people that […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"spay_email":"","footnotes":"","jetpack_publicize_message":"","jetpack_is_tweetstorm":false},"categories":[3,4],"tags":[8,23,7,10],"class_list":["post-35","post","type-post","status-publish","format-standard","hentry","category-articles","category-scitec","tag-animals","tag-articles","tag-biology","tag-thermodynamics"],"jetpack_featured_media_url":"","jetpack_publicize_connections":[],"jetpack_shortlink":"https:\/\/wp.me\/p2VEjn-z","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.howiewatkins.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/35","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.howiewatkins.co.uk\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.howiewatkins.co.uk\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.howiewatkins.co.uk\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.howiewatkins.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=35"}],"version-history":[{"count":4,"href":"https:\/\/www.howiewatkins.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/35\/revisions"}],"predecessor-version":[{"id":80,"href":"https:\/\/www.howiewatkins.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/35\/revisions\/80"}],"wp:attachment":[{"href":"https:\/\/www.howiewatkins.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=35"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.howiewatkins.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=35"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.howiewatkins.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=35"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}