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I've been a Canberran since moving here from Adelaide on the first day of 1980. I now live in suburban Duffy with my partner Louise Maher, ABC 666 radio and on-line journalist. Among my early memories is following Sleepy Lizards (Shinglebacks) around the paddocks north of Adelaide, guarded by the faithful bull terrier. I have always been passionate about the natural world, trying to understand how it works, how the nature of Australia came to be, and sharing those understandings. My especial passions are birds, orchids and mammals. For much of my life I have been a full-time naturalist, running bush tours, writing books etc, doing consultancies, presenting a regular radio slot on local ABC, chairing a government environment advisory committee and running adult education classes. Recently I have eased back somewhat, but am still writing, teaching, doing some radio work and running overseas tours - as part of my fascination with our Gondwanan origins I've been running tours to South America for the past decade. I was awarded the Australian Plants Society Award in 2001 and the Australian Natural History Medallion in 2006, both for services to education and conservation.

Wednesday, 12 September 2012

Carrion On

I hope that no-one is put off by this posting, dealing as it does with animals which make a living, in whole or in part, by eating other animals which have previously died. My interest in such things is never with the macabre per se (I have never had any interest in horror movies!), but I'm always fascinated by the way in which animals (and plants of course) go about their business. 

Pacific Gull with fish, Esperance.
Gulls' willingness to scavenge makes them very successful, and very willing to take whatever's on offer,
including chips (presumably to complement meals such as this).
Immature Black-breasted Buzzard, Argentinian Patagonia,
unwilling to relinquish its road-killed European Hare. While these introduced hares are abundant and adults certainly hunt them, youngsters doubtless benefit from the roadside takeaway supply.
Animals eat meat because it is a high source of protein, along with some fats (ie energy), nitrogen and some other nutrients. In contrast most vegetable food is more consistently abundant and easier to 'catch', but in the case of leaves in particular (which includes grass) is harder to digest. There is no a priori reason why the meat needs to be 'fresh', and in any case this is relative; meat starts to decompose from the time of death. The primary advantage of eating carrion is that is generally easier and safer to obtain; hunting is an energy-intensive process, with often a low success rate and in the case of larger prey - which gives a greater reward - attendant dangers. On the other hand it is an uncertain resource, in that while animals die all the time, many are not readily found and a large exposed carcase is likely to attract lots of competitors, some of which bring their own dangers. As a result most animals that eat carrion do so opportunistically, being perfectly competent hunters (or indeed omnivores, eating plant material too) as well. Most cats for instance (but not Cheetahs) won't pass up an already demised meal if it is presented.

Wedge-tailed Eagle on road-killed Red Kangaroo,
Sturt NP, far north-western New South Wales.
Southern Caracaras, specialised South American falcons,
on sheep carcase, Chilean Patagonia.
As decomposition proceeds, chemicals including cadaverine and putrescine are produced, which make carcases smell bad (and thus easy to find!) but are toxic in higher concentrations. As might be expected however, scavengers which concentrate more on carrion-eating as opposed to hunting are more immune to these chemicals, so that vultures (both Old- and New-World) and goannas or monitors (which include the famed Komodo Dragon) can and regularly do eat very rank food indeed. Perhaps in fact it is easier to digest; crocodiles will leave prey wedged underwater to decompose. However it also certainly expands your gastronomic horizons if you don't need to be too fastidious. 

White-backed Vultures on cow carcase, Ngaoundaba Ranch, central Cameroon.
Andean Condors on Guanaco carcase, probably killed by a Puma, Torres del Paine NP, southern Chile.
These magnificent birds are carrion specialists, and smaller scavengers rely on them
to open up carcases that they can't breach.
For some reason most of my photos of carrion-eaters are of birds (perhaps just because most of them, unlike many scavenging mammals, are daytime feeders) but many mammals and some reptiles indulge. And of course by far the majority of carcase-munchers are very small; uncountable billions of ants and flies and beetles in particular - both adults and larvae - work every day to return thousands of tonnes of animal nutrients to the soil. In turn, other animals come to the bodies to munch on them. I've seen White-faced Herons at road kills; while they're remarkably versatile, I suspect they're eating insects rather than the carrion itself, but as ever I could be wrong of course.

An extremely determined ant with grasshopper carcase, Blanquillo Lodge, Peruvian Amazonia.
After all that, I hope your next meal is of vegetables; or at least fresh...

2 comments:

Denis Wilson said...

Thanks Ian, Interesting post.
I have a certain fascination/revulsion for Carrion Beetles.
Not pretty, but necessary.
http://peonyden.blogspot.com.au/2011/10/carrion-beetle-ptomaphila-lacrymosa.html
Check out the next old, dry carcase you come to.
Cheers.
Denis

Ian Fraser said...

Hmm, that might well be mine... (carcase that is). Thanks for that Denis, I just read your Carrion Beetle blog with fascination; I'll certainly look more closely, visceral response notwithstanding, next time I'm in proximity to a dead roo. By one of those coincidences that make the world go round, I've just posted on beetles, before seeing this comment!