Considering Kangaroos

I hear so many stories of people coming to Australia and expecting to see kangaroos in the main streets that I suspect that some of them must be true. And here in Canberra it's pretty close to the way things are! In suburbs near the numerous hill reserves which are scattered through the urban area it's common to see roos grazing the lawn or drinking from garden ponds in dry spells. And driving anywhere in Canberra can be potentially hazardous when the roos are on the move. I could meet you at the airport and pretty much guarantee to find you Eastern Grey Kangaroos within about 10 minutes. 

Eastern Grey Kangaroos Macropus giganteus, just a few minutes from my Canberra suburban home.

These animals are showing the classic kangaroo characteristics of powerful hind legs, short forelimbs with grasping paws and a long heavy counter-balancing tail. Lounging about stretched out on the ground is typical daytime behaviour too.

The long hind legs are an adaptation to hopping, a form of locomotion which seems to have arisen in the ancestral kangaroos at least 30 million years ago. While members of a few rodent families, and a member of one other family of small marsupials (the carnivorous Kultarr) have independently evolved hopping, the kangaroos are the only large vertebrates ever to have developed the trick. (Tales of hopping dinosaurs seem to be no more than tales.)

Eastern Grey Kangaroos on the move.

It's not an efficient mode of locomotion at low speeds; at less than 12km an hour a trotting dog for instance uses less energy. As speed increases however the hopping kangaroo begins to pull ahead energetically, and increases its relative efficiency further as its speed increases. At 22km per hour, the highest speed that I'm aware that energy expenditure has been measured, a hopping kangaroo uses less than 75% of the energy a similarly sized dog would. At speeds of 40kph - which a kangaroo can readily achieve - it would be expected to be twice as efficient. 

The reason for this has been tentatively suggested in terms of the muscles and tendons acting like springs, storing kinetic energy which is used in the next leap. Doubtless this occurs, but we now know that galloping animals also utilise this 'bouncing ball' strategy, so a roo's advantage can't be attributed solely to this. It seems that the explanation lies in the much longer stride a hopping kangaroo can achieve. An animal can increase speed either by taking longer strides, or by taking more steps or hops per minute; it is the latter which uses much more energy. A kangaroo's gait allows it to simply to take longer and longer hops as it accelerates, to more than four metres per bound. At very high speeds it will also start to put in extra hops, which presumably uses more energy.

At very low speeds however, such as when feeding, a kangaroo 'caterpillars' along, using five limbs, the tail being co-opted for this purpose. 

Red-necked Wallaby Macropus rufogriseus, Namadgi National Park near Canberra.
To get to the next patch of desirable grass, the animal swings its back legs forward together, while balancing
on its forelegs and tail.
(Curiously, when swimming, a kangaroo suddenly learns how to move its hind legs independently of each other, the only time it does so.)

Now you've probably been distracted because I've suddenly switched to talking about a wallaby! Let's get that one out of the way. In vernacular, we tend to use 'kangaroo' for the larger members of the family Macropodidae (which has some 60 members), and 'wallaby' for smaller ones, but it's not taxonomically meaningful. It's even less so for today's purpose, as I'm going to be talking about only the members of one genus, Macropus (ie 'big foot'). I use 'kangaroo' loosely to refer any member of the family, but better still is the word macropod, which I'll use from now on. 

It was only by accident - literally - that we use the word kangaroo, that being the name for Eastern Grey Kangaroo in the Guugu Yimithirr language of north Queensland. It came to our attention very early on in the history of British involvement with eastern Australia, when James Cook's Endeavour struck a reef in 1770 near where Cooktown now stands, necessitating an extended stay, during which naturalist Joseph Banks learnt the word for the animal his greyhounds caught. I like to muse that had Cook sailed on by, as he'd intended, we'd almost certainly be calling them something like Patagarang or Badagarang, that being the word in the language of the people who lived in the area where the first settlement intruded on them, in 1788 where Sydney now stands. 'Wallaby' also comes from the language of the Sydney people (often referred to as Dharug, though that seems open to considerable doubt), apparently being the word for what we call Black-tailed or Swamp Wallaby Wallabia bicolor. 

And to head off another oft-asked question, 'Wallaroo' is not a kangaroo-wallaby hybrid, but any of three species of mostly stocky muscular hill kangaroos. This is yet another Sydney language word. This term is used for M. robustus along the Great Dividing Range along the east coast, while the word Euro (from the Adnyamadhanha language of the Flinders Ranges in South Australia) is used throughout the inland for the same species.

As marsupials, embryos develop externally, but in the pouch (ie the marsupium). In the case of the big kangaroos time in the pouch varies with species from 200 to 300 days.

Agile Wallaby Macropus agilis with joey, Cape Hillsborough NP, tropical Queensland.
This one is starting to explore the world, but retreats to safety when it feels the need.

Eastern Grey Kangaroo, Canberra. The joey dives in head-first, then reorganises itself while inside.

More seasonal climate species, such as the Eastern and Western Grey Kangaroos M. fuliginosus, breed seasonally, but the extended pouch life means that the female is usually caring for a pouch young and a still dependent joey 'at foot', who follows her around and feeds from her. Arid land species, such as Red Kangaroos and Euros, tend to breed continuously. In either case the female produces quite different types of milk from the two teats (protected in the pouch), with one of them elongated to assist the youngster leaning in from outside to feed. Furthermore Red Kangaroo females will at any one time be not only caring for a pouch young and dependent joey, but will also be carrying a blastocyst (an embryo 'frozen' in development at only a few cells, some 0.25mm in diameter). This is released to grow when either the mother loses the pouch young, or it leaves the pouch as it grows.

There is of course a lot more to say, but you've probably had enough for now. Let's finish with a partial gallery of Macropus, though I fear I can only offer you about half of the thirteeen species.

Big male Eastern Kangaroo, Canberra.
Like most of the big kangaroos (though not many smaller macropods), Eastern Greys have benefited
greatly from agriculture, which supplies pastures and water points. They are expanding well out of their
traditional range into the semi-arid zone, utilising farm dams.

Western Grey Kangaroos:
female, Cape Le Grande NP, Western Australia (above);
big male, Silverton, far western New South Wales, below.

Western Greys are really brown. They evolved in Western Australia when the south-west
was isolated from the east by arid conditions, and later spread east. It was only recognised
as a separate species from the Eastern Grey in recent decades.

Red Kangaroos M. rufus; Western Australia (above), south-west Queensland (below).
This beautiful animal is found throughout the arid inland.
Theoretically males are red and females blue-grey, but a substantial proportion of animals (varying
between populations) has the 'other' colour, or a blend.

Wallaroo, Nangar NP, New South Wales.
Wallaroos (mostly from the Great Dividing Range) are blue-grey, while Euros (from the drier inland)
are reddish grey, despite being the same species.
Note the shaggy coat and big ears.

Euros, Broken Hill, far western New South Wales (above)
and Idalia NP, south-western Queensland, (below).
Both habitats are typical, in rocky ranges.

 

Kangaroo cave painting, Nourlangie Rock, Kakadu National Park, Northern Territory.
In this sandstone habitat, the painting probably represents a Euro.

Antilopine Wallaroos (or Kangaroos) M. antilopinus, Kakadu NP.
This is the kangaroo of the tropical savannahs.

Agile Wallaby, Kakadu National Park.
Also a tropical macropod, though one that goes into the brushes more than the Antilopine does.

Red-necked Wallabies, Namadgi NP, near Canberra, above and below.

The origin of the species name, rufogriseus, 'red and grey', is obvious.

In Tasmania (here Ben Lomond NP) the same species is known as Bennett's Wallaby.

Tammar (or Dama) Wallaby M. eugenii, Kangaroo Island, South Australia.
This engaging little animal is still common here, but scarce on the adjacent mainland
and in south-western Western Australia.

Whiptail (or Prettyface) Wallaby M. parryi, Undara NP, north Queensland.
This elegant wallaby is found throughout coastal and hinterland
tropical  and subtropical eastern Australia.

 I hope you've enjoyed this brief introduction to a genus that many of us here take for granted; in the not-too-distant future I'll talk about some of the other small macropods in other genera.

MEANTIME, BACK ON WEDNESDAY