Monday, September 17, 2007

Western Grey Kangaroo, Macropus fuliginosus

Kangaroos are an Australian icon and our best-known marsupial.

The two legged hopping type ancestor of present day kangaroos evolved in Australia around 8 million years ago, prior to that all marsupials walked on all fours. However marsupials have a long evolutionary history with the earliest known fossil dated to around 125 millions years ago (long before the dinosaurs disappeared). Now you may think that these fossils were discovered in Australia, but you would be wrong; they were discovered in China. The Australian line of marsupials are relatively late with the earliest known fossils only 55 million years old. It is thought that they had moved down via South America, into Antarctica during the warmer Gondwana period and then into Australia.

Around 15 million years ago, maybe due to climate change or the rise of placental mammals (the ancestors of cats, dogs, horses, cows and even us), the marsupials in most other parts of the world went extinct, leaving the island continent of Australia their remaining stronghold. A few marsupial species still survive in North and South America, plus Paupa New Guinea but none compare with the diversity of our marsupial fauna.

Mum and joey of the Western Grey Kangaroo, Macropus fuliginosus. The female joey will often remain with her mother long after leaving the pouch (over 2 years), even giving birth to a joey herself.

The Western Grey Kangaroo (Macropus fuliginosus) is very similar to the Eastern Grey Kangaroo (Macropus giganteus) and was considered to be the same species for over 100 years. Of the differences between them, the most obvious is their fur color, the western greys being much darker and brown in color, whilst the eastern greys are in fact, more grey. The eastern grey is also slightly larger (reaching close to 2 metres in height), although not much larger than the westerns. Mature males of both species are noticeably bigger than the females.

The western grey's territory extends from the west coast of WA, right across the southern part of the continent into western NSW, Victoria and southwestern Queensland, preferring the more arid zones. Interestingly all the kangaroos on its namesake, Kangaroo Island in SA, are western greys. Eastern greys occupy parts of Tasmania to northeastern Queensland and just entering eastern SA, preferring the higher rainfall regions (above 250 mm a year).

The eastern and western grey kangaroo territories actually overlap in SA, NSW and Qld, but they are not known to interbreed (although in captivity they can). Other obvious differences is in their behaviour, with the western greys keeping to small family groups, whilst the easterns often collect in large mobs of both genders and different ancestry.

A small western grey kangaroo family group of mum, dad and junior.

Possibly due to habitat, these two kangaroo species have slightly different diets. The eastern greys preferring grass and soft herbaceous plants, whilst the westerns greys tend to consume more roughage gained from a variety of shrubs and even tree bark. The dietary requirements of the eastern greys has put them into more conflict with farmers, as their prime grazing areas have been taken over for agricultural purposes. Whereas the more arid living western roos can often cohabit with domestic stock on large rangelands. Also due to their drier habitat, the western greys have a lesser need of water, gaining most of their moisture from what they eat.

Interestingly, western grey kangaroos sexually mature (by several months) earlier than the eastern greys, allowing depleted populations to re-establish more quickly. The male of this species has the derogatory name of 'stinker' because unlike the eastern grey, it develops a strong unpleasant curry-like odor upon sexual maturity. Generally grey kangaroos in the wild live for around 10 years, but this time span can be doubled when kept in captivity, such are the high stress levels and other hardships of a large herbivore contending with drought, predators and human restrictions.

A pair of western greys getting their roughage from a heath habitat.

By hopping, rather than running on four legs, the kangaroos have actually developed a very efficient means of locomotion. To hop faster, the kangaroo simply maintains a similar number of hops per minute, but simply increases its stride, also it recycles up to 70% of the energy used, we on the other hand can only recycle around 20%, so they can maintain high speeds for lengthy periods. I have clocked grey roos effortlessly doing 45 kilometres per hour over several kilometres. Yet another advantage of hopping is it aids breathing; when landing air is expelled from the lungs and when jumping, air is automatically drawn into the mouth. So kangaroos are very well adapted to living in open semi-arid rangeland, grasslands or open woodlands.

From time to time there is speculation that the grey kangaroo is endangered; this is certainly not the case as both species occur in their multi-millions. However, the eastern grey kangaroo although still very numerous are probably less so due to their grazing areas being utilised for farming activities, but they are far from being a threatened species and can occur in plague proportions in favoured undisturbed habitats. Still, I think we are very fortunate to have such a large uniquely Australian animal that can survive in most bush habitats and often in close proximity to human occupation. These kangaroos are so common that many people have a very indifferent attitude toward them and often consider them vermin, nevertheless we and the world would be worse off without them and we should cherish and foster their well-being.

Mum and a very cute joey playing hide and seek.Western Grey Kangaroo, Macropus fuliginosus


Gaye from the Hunter said...

A most interesting and informative account of our kangaroos, Jack.

As you have mentioned, Eastern Greys can congregate in large mobs. It is not at all unusual to see them in the Hunter Valley, NSW, in mobs of about 30, although mobs of about 8 to 15 would be more common.

Unfortunately there are many road kills - my husband counted 7 fresh carcasses on his 60km trip to work this morning. Roos are commonly seen all year round in the Hunter Valley. During times of drought, roadsides provide green pick produced from run-off from light showers.

The country is starting to dry off, even after flooding winter rains, which brings the roos to the roadsides again - hence high fatalities.

It is always pleasant and heartening to see the roos resting and grazing early and late in the day.

I was expecting to see the same kangaroo numbers and habits when I visited Western Australia last year, but I saw very few, and observed none at length, which was disappointing. But, also, I did not see any road-killed roos, which was not surprising after I realised that roo numbers were far less than in the east, and I supposed their habits also differed.

Do you know how often Eastern Greys need to drink from a water source, rather than obtaining moisture from vegetation?

A most enjoyable blog entry, especially as I am so fond of seeing kangaroos in the 'wild'.


Esperance Blog said...

>>I was expecting to see the same kangaroo numbers and habits when I visited Western Australia last year, but I saw very few, and observed none at length, which was disappointing. But, also, I did not see any road-killed roos, which was not surprising after I realised that roo numbers were far less than in the east, and I supposed their habits also differed.<<

Hi Gaye, re your comment above; I am not sure they are less common, but they are certainly less congregated. The Western Greys are possibly more active at night and less so during the day, so unless you read their tracks, you would think few if any were in the area. Whereas in the Eastern States I have often encountered mobs of eastern grey kangaroos feeding together during the day. Maybe this relates to the generally dryer environmental conditions to the west of The Great Divide.

Perhaps your other comment relating to the higher moisture requirements of the Eastern Grey Kangaroo is related (at least in part) to the habits of these two species, with the western greys being more economical with their moisture requirements. The type of vegetation they eat may also be an influence, as often there are more succulent plants growing in arid regions than in better watered areas where water conservation/storage (of plants) is less of a problem. I dare say there are also genetic considerations, but I doubt if much research has been conducted in that area.