Sunday, 9 January 2011

Food tips for vultures

An iconic image of the Mata Atlantica is a flock of vultures* circling high in the sky, soaring lazily on thermals as they peer down looking for carrion. That's all very well, but frankly they could be up there all day without seeing anything, especially if the dead meat is under a forest canopy. What a hungry vulture needs is a short cut. There are several.

As I mentioned in a previous blog, some carrion hunters can detect the ethyl mercaptan from rotting bodies and so fly low over the forest until a whiff catches their attention. Black vultures simply use their superb vision to keep track of these birds, follow them in and nick it. There are not many creatures who will stand up to a determined gang of black hissing vultures** with a 5ft wingspan, not least when they use vomit as a defensive manoeuvre.

Black vultures roost together, setting off around sunrise on their daily hunt for corpses. Now, if there was a dead cow around yesterday there is a fair chance that something will still be left today. But maybe not much, and certainly not enough for everybody. It's been shown that Black vultures returning to a meal head off earlier in the morning, flapping energetically to get there beaks in the feeding trough first. Unfortunately, it has also been shown that the smarter vultures know this, and so follow any birds trying to sneak away surreptitiously before dawn, so there is invariably a crowd for breakfast. Still, as it might be you doing the following tomorrow, this seems to be generally accepted without too much rancour.

And lastly, one can just wait for food to drop dead in front of you. A common sight along many highways are vultures perched on the street lights - roads might be a bane for many animals, but they're a boon for vultures. High perches with a clear view are exactly what they need - life is after all a balance between energy spent and energy gained, spend none and you are half way there. Roads are also noisy, chaotic places, which is nothing new to a vulture, but tends to keep larger solitary raptors at bay. And lastly of course a steady diet of road kill, though not as much as you might think. Surveys show about 0.1 to 0.5 mammals per km per month, mostly possums and not enough for a growing vulture. So, unfortunately, the vulture does have to go and search for food the traditional way, but every little helps.

* a "kettle" apparently, though a "kettle of vultures" conjures up all sorts of unpleasant images
** a "venue" - this I can understand

Saturday, 1 January 2011

Hello possum

The is the black eared possum (Didelphis aurita), also known as the Gambá-de-orelha-preta or Saruê, a species of opossum found in Brazil, Argentina and Paraguay. A bit bigger than other possums in South America (60 to 90 inches long and up to 1.6 kg), but with a relatively shorter tail as it's not in the trees quite so much. They do climb of courrse, just not so fast or dexterously. On the other hand, on the ground they are faster than other possums and it's been shown they can see quite a lot further.

Photos courtesy of Heliana Soneghet Pacheco

Although possums do look a little like rats, in fact they are marsupials. The mother gives birth after about 13 days to 8 tiny possums which crawl into a pouch and then suckle for about 100 more days. By the end they are quite a weight to carry around! Babies born at the end of one breeding season are able to reproduce at the start of the next , which can lead to a lot of possums. Actually, possums tend to spread out as they are quite territorial, especially the females, with about 0.5 to 1.5ha depending on how good the territory is.

So what do possums eat? Well, pretty much everything. Insects, fruit and lots of small mammals, they have actually been recommended for keeping down levels of mice. Rather more impressively, they also go for snakes! Somehow they manage partial or even complete immunity to the venom of many species including the fer-de-lance, Bothrops asper, whose bite can be fatal to humans.

When they meet something too big to eat, and too fast to run from, they "play possum", ie. play dead. This can be surprisingly convincing, even including a smelly secretion to suggest that they've started to "go off". As many predators prefer live food this is worth a try as a last resort, but it doesn't work terribly well against oncoming traffic. Nonetheless the Saruê is a success story, and has otherwise adapted well to the modern Mata Atlantica.