Monday, 27 April 2009

Land of the Dodo 9: Waterbirds

At first contact, there were many species of water bird have colonised the Mascarenes, of which seven are extinct and of the survivors, all are wide-ranging species which still survive in other parts of the world, and may yet recolonize naturally.

Of the ducks and geese, the Mascarene Teal Anas theodori survived on the islands until approximately 1700. This was closely related to the Madagascan Berniers Teal, itself now critically endangered and subject to a captive breeding programme. (Image of captive bird at Slimbridge)

Mauritius and Reunion each had an endemic species of sheldgoose, Alopochen, close to the Egyptian Goose which still is widespread in Africa, and for which there is a small feral population in the UK. Both species were extinct by 1700, probably as a result of rats.

Probably also exterminated by rats were the three species of Night Heron, Nycticorax, although habitat destruction may also have played a part. The Night Herons could fly, but were reluctant to do so, and probably preyed heavily on land crabs and baby tortoises. The destruction of the crabs by rats and House Shrews would have eliminated much of their food supply.

Reunion held a species of ibis, Threskiornis solitarius, which was close to the African Sacred Ibis. Like the night herons, it was reluctant to fly and probably became extinct (by 1720) for similar reasons.

The small population of Greater Flamingos on the islands was probably eliminated by hunting. Even before human contact, most of the birds would probably have been non breeders from Madagascar or mainland Africa.

The reason for the extinction of the widespread and successful Dimorphic Egret is unclear – probably introduced mongooses were responsible. The available habitat for water birds is limited on the islands, and colonies were probably restricted to only a few sites. The Reed Cormorant probably died out for similar reasons on the islands, despite being widespread in Africa.
Finally, at least one widespread species has colonised naturally since the arrival of humans on the island. The small Striated Heron (close to the American Green Heron) probably colonised in the early 19th Century and is now present on all the islands.

Saturday, 18 April 2009

Land of the Dodo 8: Birds of Prey

Prior to human contact the Mascarenes were home to six species of birds of prey, active by both day and night. Today only two species survive, the Reunion Harrier and the Mauritius Kestrel. The Mauritius Kestrel is particularly important as it is one of the best examples of what a coordinated approach to conservation can do with a highly endangered species.

Unfortunately extinct are all three of the three endemic species of owl, all placed in the genus Mascarenotus. Apparently most closely related to the widespread genus Otus, the Scops Owls (one of which reached the UK from Europe two years ago and actually held territory for a while), the Mascarene owls were larger, and had the long legs without feathers which usually indicate a specialist lizard feeder. Their distinctiveness is such that they may have originally evolved on the islands preceding the emergence of Mauritius. They were all gone by 1830 at the earliest. Shown here is a Madagascar Scops owl.

The image here is of a Reunion Harrier, Circus maillardi. These have a world population of fewer than 400 individuals and a low reproductive rate, although they are slowly increasing under protection. Unlike most harriers, they will hunt over woodland. Their original diet was probably birds, but today perhaps 50% of their diet comprises introduced mammals, including the ubiquitous tenrecs. Although now confined to Reunion, it formerly occurred on Mauritius and could potentially be reintroduced there at some point – there have been several successful reintroductions of birds of prey around the world (including the extremely successful reintroduction programmes for White-tailed Sea Eagle and Red Kite here in the UK) although as far as I am aware there have been no introductions of harriers so far.

Finally, we have two species of kestrel. The Reunion Dubois’ Kestrel is now extinct, but was similar in structure to the European Common kestrel Falco tinnunculus. Surviving reasonably well (and shown below) is the Mauritius kestrel, Falco punctatus, but it was a very close run with extinction.

The initial problem was deforestation, which by 1900 had reduced the population to about 200 pairs. The final disaster was DDT spraying for malaria, which eliminated all birds outside one small area, the Black River Gorges where it was not used. In 1974 the total wild population known was four birds, of which only one was a breeding female.

At this point an extensive support plan was put into effect. Wild eggs were harvested to create a captive population, and nestlings were supplementary fed. Removing eggs from an incomplete clutch of eggs often results in birds laying additional eggs, so boosting productivity. Nest sites were monitored and protected against raids by monkeys or rats. By 1994 nearly 350 had been released.

Today the Mauritius kestrel has a wild population of 800 – 1000 individuals, and has been downgraded from Critically Endangered to Vulnerable status.

The ongoing threats are introduced predators such as monkeys, and potentially introduced avian diseases. The small population that the birds were reduced to means that the birds have lost a lot of genetic diversity and this makes the population more vulnerable to new diseases.

Wednesday, 15 April 2009

Whats this?

On Monday I had a day out at Kew Gardens up in London, I will do a full post about it next week, but in the meantime how many people reading this blog can identify this flower? (answer next time)

Saturday, 11 April 2009

Gorillas part 3 - diet

Ask a member of the public what gorillas eat, and they will say bananas. As with most things you everyone knows however, this is not the whole truth. As two species occupying a vast area and many different habitats, the diet of gorillas is in fact highly varied.

The bulk of a gorillas diet comprises not fruits, but the leaves and stems of herbaceous plants. One might think that these are easy to obtain, but in fact eating leaves is often the riskiest way to make a living. The problem is that plants protect themselves with a variety of defences, both physical (thorns, stinging hairs and so on) and also chemical defenses in the form of poisons or highly distasteful compounds such as resins or tannin. Investigators who have tried tasting the leaves and plant parts eaten by gorillas usually report that they are extremely bitter or resinous to the taste.

As a result, gorillas (and other forest leaf eaters) often have to travel long distances to locate plants they can eat. Many of these may taste best only at certain times of the year, and as a result gorillas eat a huge variety of plant species – up to 180 species have been reported as being eaten by one population of Western Lowland Gorillas. Popular food items are bedstraw (Galium), wild celery, nettles and bark.

Mountain Gorillas in Virunga live at altitudes where the variety of plants is much reduced, and as a result the list of plant species is shorter. The bulk of their diet in fact consists of bamboo shoots, which they are strong enough to break of the plant even though the stems are as thick as my wrist.

Fruit is eaten by gorillas when they can get it, especially by Western gorillas which live in more productive forests, but the percentage is always less than for chimps. The large size of gorillas, especially the silverbacks, limits their ability to reach the outer branches where most of the fruit is.

As with chimps, gorillas are fond of insects, especially some species of ants. The preferred species appear to be rich in iron, and it has been suggested that this may help in the detoxifying of plant poisons in their livers. Mountain gorillas do not have access to these, but instead eat iron-rich mud at various traditional sites. Earth eating is common among many vegetarian rainforest animals, and even birds such as macaws will eat earth to help them with toxins in their diet. The microscopic structure of the clay also absorbs plant toxins before they are taken up by the gorillas’ digestive system.

As well as food, plants also provide gorillas with medicine. Both chimpanzees and gorillas specifically seek out certain plants they otherwise avoid when feeling unwell, and have a highly standardised way of selecting and consuming the pharmacologically active part of the plant. Gorillas in the wild often carry a high load of intestinal parasites, and certain leaves may be carefully prepared and then swallowed whole – the hairs on the leaves tarp the worms and take them out of the body.

All of this has implications for the diet of captive gorillas. Most gorillas are fed a variety of commercially grown fruit and other produce, in many cases supplemented by a commercially produced biscuit. The problem is that commercial fruit is nothing like the wild fruits eaten by gorillas. Just compare a bite from a crab apple with an apple from a supermarket, and you can see what domestication can do to a plant. Humans have a sweet tooth, and we have bred our fruit over thousands of years to be high in sugar and water, and low in protein and fibre – the exact reverse of a wild fruit. Feeding commercial fruits to fruit eating rainforest animals is probably a main reason why captive primates of all sizes are prone to obesity and tooth decay.

As a result, most zoos are re-thinking their diets for gorillas, reducing the amount of fruit and increasing the amount of leafy vegetables and browse. Here at Bristol for example, gorillas get celery, leeks (of which they are very fond), leafy greens and cut branches among other things. They are also fond of herbal tea!

Friday, 10 April 2009

Land of the Dodo 7:Going Batty

When first colonised, the Mascarenes were home to three species of fruit bat and at least three – possibly more – species of microbat. One of the fruit bats, and at least one of the microbats, is now extinct. The other microbats are doing well, but the two surviving fruit bats are both much reduced in numbers and range.

Traditionally, bats have been divided into two groups, the fruit bats or megabats, confined to the Old World, and the microbats, which have a worldwide distribution. The main reason for this is that the old world fruit bats do not use echolocation in the same way as microbats do, and it was believed that this may even have been because they were not closely related to microbats, possible having developed flight independently. It now appears that this distinction is inaccurate, and the most basic division in the bats is between a group containing the megabats, horseshoe bats and their relatives, and all other bats. Interestingly, horseshoe bats wrap their wings around themselves when at rest as do megabats, whereas in other species the wings usually are held at the sides. In the Americas, many species of microbats also eat fruit.

Fruit bats are important pollinators (despite their name, they are fond of nectar) and also dispersers of seeds. A lack of these is a major cause of delays in regeneration of cleared tropical forests world wide, and it has been shown that encouraging fruit bat population helps considerable in restoration of forest cover.

Unfortunately, fruit bats and people have very similar tastes, and as a result in many parts of their range they are persecuted as crop pests. Recently the Mauritius government authorised a cull of one of the surviving species, the Mauritius Fruit bat, despite the estimated population being only 20,000. This has now been halted pending further investigation of the status of the species.

On Rodrigues, there were at least two species, the Mauritius Fruit Bat and the Golden Bat (Photo of Golden Bat at head of this post – image from Lubee Bat Conservancy). Only the Golden Bat survives, although it formerly bred on Mauritius as well. It is seriously endangered, with a world population estimated at 5,500, which is still a great improvement on the case in the 1970’s, when it was down to 150.

Sadly extinct is the smallest and most widespread of the three fruit bats of the Mascarenes, the Rougette. Possibly most closely related to the surviving Seychelles Fruit bat, it lived in large groups in hollow trees. This is unusual for fruit bats – most species roost on open branches of tall trees. It was this habit that may have caused its extinction – they were easy to capture both by people and introduced monkeys, and deforestation would have removed roost sites.

The insectivorous microbats on the islands seem to have survived better, with the exception of one species on Reunion, the Pale House bat. This may have gone extinct for the same reason as the Rougette – it seemed to have had similar habitat preferences. Most of them have close relatives in Madagascar, Africa or India. People tend not to think of bats as migrants, but many can travel long distances over water – there is a record of a Little Red Flying Fox which managed to reach New Zealand from Australia.

There are several institutions which hold Golden Bats. Bristol formerly held a non-breeding group, but these have gone to other collections. They are often quite active by day, especially in the afternoon. Bristol currently holds a breeding group of Livingstone’s Fruit Bat, which I will blog about another time.

Monday, 6 April 2009

Year of the Gorilla 2 - Bristol Zoo efforts

Since 1997, Bristol Zoo has been working with the Cameroon Wildlife Aid Foundation (now renamed Ape Action Africa) which has a base at Mvog-Betsi zoo in Yaounde, and now also administers a sanctuary at Mefou National Park. Working with the Cameroon government, Bristol supports the activities of AAA by advising local members and providing veterinary support and training. Bristol has always majored on education for local children, and we are supporting educational activities out in Cameroon.

AAA currently cares for several chimpanzees and gorillas orphaned by the bush meat trade. This is unfortunately widespread, and contrary to what may be thought it is not a subsistence level trade – gorilla meat is very expensive and poorly paid drivers of logging companies find bushmeat an easy way to earn cash.

As a result of this, AAA received numerous orphan primates. At Mefou and at Yaounde these are cared for and hopefully rehabilitated. The problem however with releasing any of the apes in particular is that they are not afraid of people and so are at grave risk of being killed if released outside a protected area. In addition, they have all been exposed to, and are potentially carriers of, human diseases that could prove very dangerous to wild gorilla or chimpanzee populations. The best strategy therefore for orphans is therefore a semi-natural situation as at Mefou.

AAA has a volunteer scheme as part of its fund raising activities. Volunteers can work out at Mefou or Yaounde provided they fund themselves and are prepared to spend sufficient time there. Details are on the AAA link on this blog.

(Images from CWAF/AAA website)

Friday, 3 April 2009

Land of the Dodo 6: Lizards by night and day

Before contact, the Mascarenes were home to at least 24 species of lizard in six genera, and they occupied all habitats from rock crevices to the canopy. They can be divided into two groups – the mostly terrestrial and insectivorous skinks and the climbing (on trees or rock surfaces) geckos.

There were seven different species of skink on the various islands, of which four still survive. Extinct before even being described was the largest lizard on Mauritius, the 60cm long “Didosaurus” which is only known from subfossil remains and was probably wiped out by rats.

The most obvious of the lizards were the various species of day gecko, Phelsuma, of which there were at least nine. Four of these survive, and are important to the native plants as they are fond of nectar and are important pollinators. . One of the surviving species, the Blue-Tailed Day Gecko of Mauritius, is at the head of this post (picture from MWF website). At Bristol we have two species, both from Madagascar where the genus probably originated and which has most of the world’s species. Unfortunately, the survivors do not include the most spectacular gecko of them all, the 1 metre long Newton’s Day Gecko of Rodrigues, which was a vivid emerald green

Much less obvious were the night geckos, Nactus, of which at least two species survive. These seem to have had a small radiation of species in the Mascarenes, after managing to colonise the islands from Australasia, where a few other species are still found.

All these lizards were important as food sources for many of the birds, especially the Mauritius Kestrel and the various endemic owls. They also dispersed seeds and pollinated plants as noted above.

Unfortunately, as well as the native wildlife these days the lizards have to cope with introduced competitors. House geckos (Hemidactylus) are widespread and compete with the native Night Geckos, and even introduced honeybees are competitors for nectar with the Phelsuma geckos.

Relocation efforts and reintroduction to offshore islets has been a great success, and for example the Telfairs skink Leiolopisma telfairii, which was restricted to Round Island, can now be found on Isle Aux Aigrettes and Gunners Quoin, where it is breeding well. This is important, since the larger skinks are omnivorous and are probably significant dispersers of the seeds of native plants

For further information (and some great pictures) look at the MWF website in the links section.

Thursday, 2 April 2009

Year of the Gorilla Part 1 - How many apes?

As 2009 is the Year of the Gorilla, I thought it would be a good idea to run some posts during the year on gorillas, their conservation, and interesting features of their biology. To start with, we need to define what we are talking about, so I will commence with a brief post on their classification:

Ask the average member of the public to name the different apes and most people will list the gorilla, chimpanzee, and orang-utan. A few will add the bonobo, and some will add gibbons to the list. If you ask a taxonomist the same question, the answer you will get is “at least 20”.

So why the difference?

First of all, there is no such animal as “the” gibbon. The gibbons are a widespread and quite diverse group of at least 14 species, many with several subspecies, ranging across Southeast Asia and Indonesia. Aside from differences in size and coat colour, gibbons are all very similar in their means of locomotion, which conceals a considerable genetic diversity.

Also in South East Asia, we have the two (yes two) species of orang-utan. The Bornean Orangutan, Pongo pygmaeus, and the Sumatran Orangutan, Pongo abelii, are actually quite different from each other – the estimated date of their separation is 1.5 million years ago. There was once at least one other species, the Mainland Orangutan, which ranged across Asian rainforests as far as southern China. It certainly survived up to the end of the last Ice Age, possibly more recently than that, and has been suggested as a source for the legends of the Yeti.

Moving to Africa, we have our closest living relatives, the Chimpanzee Pan troglodytes, and the Bonobo Pan paniscus. Bonobos in particular are highly threatened in the wild, and Chimpanzees are declining fast.

Finally, we are up to the two species of gorilla. Traditionally, all gorillas were classed in a single species, with the Mountain gorillas in Virunga national park in Ruanda placed in a separate subspecies to the lowland gorillas. However, with more study it has become clear that this taxonomy is out of date, and gorillas are two species, with considerable differences in their diet and social behaviour.

First, with a range centred on the Eastern Congo and Ruanda, we have the Eastern Gorilla, Gorilla beringei. This has at least two subspecies, Grauer's gorilla, G,beringei graueri shown here;

And the Mountain gorilla, G,beringei beringei shown here;

Not currently treated as distinct is the Bwindi Gorilla, which is regarded as the same subspecies as the Mountain Gorilla but which looks quite different, howver this may be because it lives at lower altitudes and so does not grow the distinctive long hair of the Mountain Gorilla.

Moving westward, we have the other species of gorilla, the Western Gorilla. Most threatened of all great ape taxa is the Cross River gorilla, Gorilla gorilla diehlii, with a population of under 250 which is split into several patches of fragmented habitat surrounded by famland. Bpth subspecies of Western Gorilla can be distinguished by the brown hair on their heads - Eastern Gorillas are black headed. This can be easily seen on this female Cross River Gorilla:

Finally, we have the Western Lowland Gorilla, Gorilla gorilla gorilla. Thanks to recent discoveries, it appears that there are far more of these than was thought – the world population may be over 200,000. These are the gorillas that are seen in zoos – the ones shown here are two of Bristol zoos gorillas, Salome and Komale.

Next time, conservation actions and news from Africa - the Bristol connection