I’ve had wrist problems for a few years now, and to help deal with the tendonitis I’ve developed, my doctor told me to get some capsaicin to rub on it. Capsaicin cream is basically a concentrated version of the ingredient in peppers that makes your mouth burn (or eyes, if you’re unlucky). When you put capsaicin on your skin, it starts to warm up, and it feels pretty good. Unfortunately if you don’t use the cream enough, the warmth progresses to a horrible burning that cannot be assuaged.

They’re pretty cute. Especially the little one.
Image by fir0002 flagstaffotos [at] gmail.com Canon 20D + Canon 70-200mm f/2.8 L, GFDL 1.2, via Wikimedia Commons

The point of telling you this is that when I’m rolling around in bed trying desperately to find a way of cooling my arms down, I always think of a scene form Planet Earth. I believe it was in the deserts episode, and showed a bunch of kangaroos hanging out in unbearably hot conditions in Australia. To cool themselves down, the kangaroos licked the insides of their forearms to make the most of evaporative cooling. I always wish I could do this when my arms are burning, but I know the consequences would be even more painful. But I have come to call the forearm burning sensation kangaroo arms, and while I was writhing about one night I realized I haven’t actually posted about kangaroos yet.

There are four species of kangaroo, all in the genus Macropus. Also belonging in Macropus are the wallabies and wallaroos, which are differentiated from kangaroos by size, with kangaroos being the largest, wallabies the smallest, and wallaroos somewhere in between. All species of kangaroo are found in Australia, in habitats ranging from arid deserts to sparse woodland areas.

The largest species of kangaroo is the red kangaroo, which can reach 2 m in in height, and weigh 90 kg. Their colours range from reddish brown to grey-brown. I’m sure most of you know what kangaroos look like: big funny ears, cute little ‘hands’, and giant back legs that propel the animals in their awesome hopping motions.

Kangaroos can move pretty fast, reaching top speeds of 70 km/h (though only for short periods). The usual loping speed of a kangaroo is around 20 km/h. When kangaroos are moving slowly, they balance themselves on their forelegs and tail mid-stride, which allows them to bring their back legs forward for another leap. So really, these funny creatures use a five-legged motion.

A typical boxing match between kangaroos. Image credit: Dellex via wikipedia
A typical boxing match between kangaroos.
Image by Dellex, CC BY-SA 3.0, via Wikimedia Commons

Kangaroos are very social creatures; they usually live in groups of ten or more individuals called mobs. When a female is in heat and ready to mate, she roams around, calling attention to herself. This attracts a number of males, who sometimes fight over her, in typical kangaroo kickboxing style. The winning male then woos the female by pawing, licking and scratching her.

After 33 days of gestation a little baby joey is born. At this stage the joey is hideously ugly, in only a couple of centimetres long, and is completely hairless. Once it’s born, the joey claws its way up into the mother’s pouch and starts sucking on a teat. It will stay there for the next 190 days, just hanging around and eating mom’s milk. It will go in and out of the pouch for a while, making its final departure from the safety of the pouch at around 235 days. Meanwhile, the sexual cycle of the mother is reactivated once the joey first latches on. She can rebreed at this point, and if an egg is fertilized she will keep it in suspension until the joey leaves the pouch for good.

A kangaroo hopping. The hopping motion of kangaroos is more efficient at higher speeds than quadrupedal running.
Image by Eva Rinaldi, CC BY-SA 2.0, via Wikimedia Commons

Kangaroos are grazers, and so have stomachs similar to that of cows and other ruminants. Also like cows, they regurgitate what they have eaten, rechew it, and swallow it again. Kangaroos teeth are replaced as they are worn down, something that, in mammals, only occurs in elephants and manatees. Though there are many differences between kangaroos and cows, one very interesting one is that kangaroos don’t release methane gas as a byproduct bacterial digestion, instead converting the excess hydrogen into acetate, which is absorbed for more energy.

With their large size and mobility, kangaroos have few natural predators. If a predator is encountered, kangaroos will flee into water if there is any around, as they are quite good swimmers. If the predator persists, kangaroos have been known to grab the offender and hold it under the water until it drowns. Or if there is no water nearby the ‘roo might grab the predator and kick it violently with its hind legs, killing it. The moral of this story is that you probably shouldn’t attack kangaroos, because they are fearsome creatures.

As a result of their adaptability and lack of predators, kangaroos continue to do rather well in Australia. Which is good, because they are both cute and funny looking, so I’m glad they’ll be sticking around for while.

Cover image by Bardrock, CC BY 3.0, via Wikimedia Commons