by Janine Duffy
The hop! The most distinctive thing about kangaroos/wallabies. How does it work?
Part 1: the tail.
A kangaroo’s large, heavy tail moves up and down in time with the legs – can you see in this picture the different positions of the tail? The pumping motion of the tail helps oxygen move in and out of the lungs. The tail also acts as a counterbalance, keeping the animal stable.
It is possible for a kangaroo to hop without a tail, but they probably tire more easily.
The hop, part 2: The legs.
A kangaroo’s large back legs are very powerful and can propel them up to speeds of 64km/hour (40 miles/hr). As the legs bounce with each hop, energy is stored in the tendons making the next hop easier – so, once they’ve got started it’s easy for a kangaroo to keep hopping. At cruising speeds they use less energy than a four-legged animal running at the same speed.
Interesting diagram at this link: http://people.stfx.ca/bmarshal/201/kangarookinematics.html
The back legs have huge areas of muscle, and very large, long tendons. The Achilles tendon on a medium-sized animal is 1.5cm diameter and 35 cm long. Human achilles tendons are about 15cm long.
To increase speed a kangaroo increases stride length, so they don’t bounce more often, they just cover more ground with each hop. We’ve seen footprints 9metres apart – that animal would have been moving quite fast. Over 35km/hr they do increase both stride length and hopping frequency, which does use more energy, so they only do that in emergencies.
The Kangaroo Hop, part 3: The feet.
Kangaroos have very long feet – almost as long as their shins/lower legs. In fact their scientific name: Macropus means big foot. The length of the foot increases the length of their legs, and provides great leverage.
When hopping, only the lower part of the foot touches the ground – see picture. So a kangaroo is effectively running on the tips of their toes. You can see this in their footprints – click this link to see a photo: kangaroo footprints
We can’t find any scientific research to support this, but we think kangaroos move extremely quietly compared to other animals. Maybe because they are in contact with the ground so little, or because their feet are soft (like a dog or cat’s), or maybe because they have only two feet to worry about they can place their feet carefully. Whatever the reason, a large mob of kangaroos can move very quickly without much sound at all, even through Bush full of sticks and dry leaves.
The stride length of a kangaroo hopping at speed is long – 6 metres at 50km/hr. That means they are only touching the ground 2 times a second. In contrast, a galloping horse touches the ground four times in each stride, and has a foot in contact with the ground at all times creating a constant drumming sound. At the same speed a horse touches the ground 8 times a second.
The best way to understand the kangaroo hop is to watch it in action. Come to Melbourne, Australia and take the Great Ocean Road 3 day tour or Koalas & Kangaroos IN THE WILD day tour. You’ll learn all about kangaroos and koalas as well!
Kangaroos also have great agility due to their hopping style – read more here: Kangaroo Agility