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.
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.