Pages

Saturday, 28 March 2009

Just gone on show in the flamingo aviary at Bristol are six Marbled Duck (sometimes called Marbled Teal), Marmaronetta angustirostis. Although very teal-like in size (they weigh only 500g) and indeed in bahaviour, they are in fact a diving duck, related to the pochards, tufted ducks and canvasbacks. They have a large range, extending from Spain through North Africa to Iran, and wintering south into sub-Saharan Africa and North West India

The habitat of the Marbled Duck is temporary wetlands, often brackish, and with large amounts of vegetation. Their diet is a mixture of small seeds, aquatic invertebrates, and anything else they can filter from the mud. They usually feed early in the mornings and in the evenings, resting during the hours of daylight. Like most ducks, the female alone incubates the eggs, which are usually in a clutch of 10 or so, and cares for the ducklings. The nest is usually concealed in reeds.

Unfortunately, the specialised habitat of the Marbled Duck has been severely restricted, more than 50% having been destroyed in the last 100 years. The world population today is estimated as being below 20,000 birds, and possibly below 10,000. Conservation efforts are aimed at protecting existing habitat, and possibly habitat restoration where possible.

The species breeds well in captivity, and there are currently over 470 listed on ISIS, with 70 bred in the last 12 months.

Saturday, 21 March 2009

At the time of discovery, the Mascarenes were home to five species of giant tortoise. Mauritius and Rodrigues each had two, a saddle backed form adapted for browsing at higher levels and a smaller (c 12kg) domed form better shaped for grazing (most the others were probably in the 60-100 kg range). Reunion only had a single species, which was domed but considerably larger than the forms on the other islands. A painting by Julian Hume, who has done several paintings of Mascarene wildlife, is shown at the top of this post.The various forms have all been placed in the endemic genus Cylindraspis, although they were formerly all placed in the widespread genus Geochelone, along with the Galapagos and many African tortoises. These have now all been split into separate genera. The closest living relative is probably the Madagascan Radiated tortoise Astrochelys radiata, which is about the size of the smallest domed form, the Rodrigues C.peltastes. (image from Cites website). Derived from the same ancestor is the Aldabra Giant Tortoise, Dipsochelys gigantea, which used to occur throughout the Seychelles.

The genus apparently first evolved on Mauritius, later spreading to Rodrigues and Reunion. One interesting feature is that their shells were extremely thin, as protection was not needed on the pristine islands from mammalian predators. As hatchlings, tortoises would have been preyed on by native birds, especially the endemic night heron, and land crabs would probably have also taken some.

The giant tortoises were the dominant herbivores on the island. Their grazing would have kept areas of grassland open, and their browsing strongly influenced the larger vegetation. Many Mascarene plants have vividly coloured juvenile foliage, designed to discourage browsing until the plants grow too tall to be eaten by tortoises, and many trees produce flowers and fruit at the base of the trunks, where tortoises could distribute the seeds.

The extinction of the tortoises was almost certainly caused by direct hunting pressure from humans. Vast numbers were taken from all the islands as a source of fresh meat on sailing voyages, and they were even killed for extraction of oil. The coup de grace was probably given by pigs (which ate eggs) and cats (which ate hatchlings).

What is especially tragic is that at least one species nearly made it. In 1844, a group of visitors on a scientific expedition to Round Island discovered survivors, and one member of the party “captured a female land tortoise in one of the caves on Round Island and brought it to Mauritius, where it produced numerous progeny, which distributed among his acquaintance”. Given the lifespan of giant tortoises, a hatchling in 1845 could even have lived to the present day.

Today, giant tortoises can once more be found living in at least semi-wild conditions on Mauritius. As part of the environmental reconstruction programme, Aldabra Giant Tortoises were released on Isle Aux Aigrettes, and have successfully bred in the wild. The effect on the vegetation has been highly beneficial, and plans are in development for their use on other offshore islands, possibly in conjunction with Radiated Tortoises.

At Bristol Zoo we have four Aldabra Tortoises, an adult male called Biggy who is at least 80 years old, and three females of which two are old enough to breed, although they have not so far shown signs of doing so. The latest arrival, “Matilda” , who at about 15 years is the smallest, is in the picture below.

Friday, 13 March 2009

At the close of the last ice age, about 10,000 years ago, deciduous oak woodland spread over most of the British isles, shading into forests of birch and pine in the north. Living in those woods were perhaps 1,000,000 wild boar, Sus scrofa, making a good living from eating anything they found, especially acorns. Although they were hunted by people, they were not it seems favoured game animals – red and roe deer were far more popular judging by Mesolithic sites, probably because deer were easier (and safer) to hunt.

By the 14th Century however, wild boar were extinct as wild animals in the UK. There are references to them being hunted as late as the 17th century, but these seem to have been imported especially for hunting.

The reason for their disappearance was not in itself habitat destruction or hunting for food – they are prolific and adaptable creatures, and were in any case classed as protected by Norman landowners. The real reason was that they were simply a major agricultural pets. Not only did they eat crops (and in the Middle Ages losing your crop meant starvation), but they competed with domestic pigs. It was customary for peasants to have the right of “pannage”, which meant they could drive their pigs into otherwise protected forests, to feed on wild foods, especially acorns to fatten them up for the winter. As competitors, wild boar were a menace, and whatever the rules said were hunted to extinction.

And there the matter stood, until the late 1980’s and 90’s, when people realised that they actually tasted pretty good…

Soon, there were wild boar farms in several places, especially in the south of England. It was at this point, that people discovered something important about boar: they are really good at escaping.

Soon, there were reports in several places of wild boar living, and breeding, in the wild for the first time in 500 years. The closest population to Bristol, in the Forest of Dean, and there are other well established populations in Kent and on Dartmoor, plus other here and there. The official number in the Forest of Dean is “at least 50”, but given the size of the known founder population, it may be well over 900 or even higher, depending on the number killed by poachers.

As you can imagine, this has caused a good deal of controversy. On the one hand, they are an authentic part of our native fauna, and at least at present the numbers are more or less manageable. On the other, they are prolific, can carry serious animal diseases such as swine fever or foot and mouth, and could easily kill a dog. A sow defending her piglets is quite a formidable animal, and might even attack a human being. More likely is a car accident – several have already been killed on roads and running into an animal the size of an adult boar could easily write of a car (and possibly the driver) – although deer collisions are far commoner and more likely to occur, deer being prone to panic.

No final decision has yet been made about what to do about them – in the meantime, if you go out to the woods today you may get a big surprise…

Friday, 6 March 2009

When first discovered, Mauritius and the other Mascarene islands were home to seven different species of parrot. Today, only a single species, the critically endangered Echo Parakeet, survives, and another, the Indian Ring necked Parakeet, has been introduced to Mauritius The chief causes of the decline of the other species are not always clear, but hunting, habitat destruction, and introduced species, especially rats, are probably the main causes.

As far as is known, the endemic parrots all belonged to a group of Asian and African parrots called the psittaculines. Four species belonged to the genus Psittacula, like the Indian Ring-Necked Parakeet (see earlier post “An Interesting Evening”. The others belonged to unique endemic genera, probably closer to the living Eclectus Parrot of South East Asia.

First to go was the largest, The Broad Billed or Raven Parrot of Mauritius, Lophopsittacus mauritianus. Often described as flightless, it actually could fly but was reluctant to do so, probably because it was so tame. No live animals made it back to Europe, and given the fondness of early mariners for parrots, this probably means it was a dietary specialist like the Hyacinthine Macaw or Kakapo, dependent on only one or two species of palm tree for successful breeding. The rats which arrived early would have been the main cause of its demise by competing for the palm nuts. Males were much larger than females, which suggest there may have been something odd about its breeding biology, but what that was can never be known. It was last reported in 1674.

At about the same time Dubois’ parrot, Psittacula borbonicus, on Reunion vanished. There are few descriptions of this bird, but it is described as having a brightly coloured head, so it may have been similar to the Plum-head parakeet of India (shown here)

In the 1750’s two further species vanished. On Mauritius, Thirioux’s Grey Parrot, Psittacula bensoni, and on Rodrigues Leguat’s Parrot, Necropsittacus rodericanus both died out, followed by the Mascarin Parrot Mascarinus mascarinus on Reunion. The Mascarin had a body form similar to a living Eclectus Parrot, and live specimens did reach Europe. These species had survived rats, but the ongoing deforestation of the islands, especially removal of tall trees which provided nest sites, were probably the main cause of their demise.

Finally, in 1874, Newton's Parakeet Psittacula exsul died out. This was probably also a consequence of deforestation.

Still surviving however (just) is the Echo Parakeet Psittacula eques. Until the 1750’s it also occurred on Reunion, but twenty years ago it was down to perhaps 20 birds in the wild. With intensive care, captive breeding, and close attention to all nests, it is now up to perhaps 350 in total, which is still a critically low number, although its threat status has just been lowered from Critically Endangered to Endangered . It now also has to cope with its close relative, the introduced Indian Ring Neck. Although Echo parakeets probably originate from a colonisation of the islands by Indian Ring necks, they now eat different foods and do not hybridise. Unfortunately, they do compete for nest sites and Indian Ring Necks are a potential reservoir for disease. For a brilliant update on the state of the Echo, look at http://10000birds.com/its-all-about-the-echospart-one.htm