Sunday, 30 August 2009

A spiky problem

On view in Twilight World here at Bristol we have a group of interesting small rodents, the Turkish Spiny Mice Acomys cilicicus. Several UK zoos hold this species – Bristol has 75 (at last count!) and there are over 600 in UK zoos in all. The reason there are so many being kept is that the species is believed to be rare and possibly endangered in its homeland – at present it is only known from the type locality.

Spiny mice are an interesting group of rodents, with 20 or more species, mainly in Africa but some extending to the Greek islands, and, of course, Turkey. They are chiefly desert, or savannah woodland animals, and get their name from the bristly coat. It is believed this helps with heat regulation – the bristles would certainly not be an effective defence against predators.

Although long believed to be related to the murine rodents (house mice, brown rats and their allies) it now seems that the spiny mice belong to a separate group more closely related to gerbils, along with a few other African genera of rodents. Their reproductive biology is certainly different – instead of large litters of naked young, spiny mice produce small litters (2 – 3 in the case of A.cilicicus) of young after a fairly long gestation period of 5 – 6 weeks. The young are precocial, being born fully furred and with eyes open, and leave the nest when only a few days old. The life span is fairly long – up to 5 years although 3 – 4 is more usual.

As with most small desert rodents, spiny mice are omnivorous, feeding on seeds, flowers, plus some insects. The natural enemies would be cats, weasels or other small mammalian carnivores, birds of prey, and reptiles, especially snakes, although they are extremely alert and fast moving animals and I suspect from their fairly low reproductive rate that mortality in the wild is less than for similar rodents. They are good climbers, and will frequent bushes and rocky slopes as well as feeding on the ground. They do not seem to make nests – in the hot climates they prefer insulation is not really needed, and their habit of sleeping in groups (they are very sociable) means that even a cold night will pose few threats.

In captivity they need to be kept in groups – given sufficient space even multiple male groups work – with plenty of opportunity to climb. They need to be kept at least at room temperature – lower temperatures (below 15C) can stress them severely. In captivity the diet is a standard rodent mix with some added animal protein in the form of mealworms.

Some species of spiny mice are in the pet trade. The one usually seen is the Egyptian Spiny Mouse A.cahirinus, although the Golden Spiny Mouse A.russatus is also sometimes seen. They do not make especially good children’s pets though – they are a little inclined to nip and they move like lightening, which makes catching one when they get out a bit tricky. They are also good at chewing through plastic hamster cages – a large glass aquarium design is best.

Aside from the Turkish spiny mice most species from the mainland are not considered endangered, but the situation is different on the Greek islands. The Cyprus spiny mouse A.nesiotes has not been seen for many years and is believed extinct, and the Cretan spiny mouse A.minous is considered threatened. The reasons for the decline is probably an increase bin the human population, and even more cats, plus changes in land use reducing suitable habitat. One issue yet to be resolved however is the status of these endemic species – they are very similar to the widespread A.cahirinus and in view of the known tendency for rodents to hitch hike on ships from the earliest times, their must be a possibility that they reached the islands quite recently, possibly as a result of Greek or Roman shipping.

(Picture from Wikipedia)

Sunday, 23 August 2009

Banana scoffers of Africa

Living in African rainforests, and with a few species in more open country, is a group of mostly highly colourful, fairly large, arboreal birds, the turacos. Despite their African origins, several species occur at fairly high altitudes, and they are less susceptible to cold in captivity than one might think. They appear to be alert and curious, and I have seen several used in flying displays.

They are fairly widespread in captivity, both in zoos and private breeders, and a few species, such as the White-Cheeked, are semi-domesticated, with a few colour mutations being bred. However, other species are far more difficult to breed and are rarely if ever seen. Most species are not threatened, although some forms are localised and may be at risk from deforestation.

Turacos are currently classified in over 38 distinct taxa, currently grouped into 22 species in 6 genera, with the majority in the large Green Turaco genus Tauraco. They are a fairly distinct group, but appear to be closest to a group of “near passerine” birds including the cuckoos.

There is a very odd feature of turaco colour – whereas in almost all birds green colour is a structural effect, resulting from the structure of the keratin in the feathers, in turacos the colour is due to a green pigment. This can be extracted from the feather with a weak alkali solution.

Most turacos are week fliers, preferring to run or hop through the branches with only short glides, although they are capable of powered flight. More open country species, such as the Go-Away birds Corythaixoides, are stronger fliers. As such, turacos are an interesting model for early birds, as these are also believed to have been week fliers with similar means of getting around in the trees, although turacos themselves are fairly advanced birds.

Turacos are mainly fruit eaters, although some species also eat surprising amounts of foliage, and a few species take at least some insects, especially when rearing chicks. They will also eat flowers. They seem to have a fondness for banana – in fact one genus, Musphaga, actually means “banana-eater”.

In captivity they are fed chopped fruit, an artificial diet for softbills (“softbill” is an avicultural term for non-seed-eating birds), plus some leafy vegetables such as broccoli and lettuce. Many keepers also provide seasonal wild fruits such as blackberries.

They are fairly territorial, although territory size in the wild is unknown, and in captivity are usually kept either singly or in pairs. Flock behaviour in the wild does not appear to occur.

Turacos make an open, cup-shaped nest with two eggs. In captivity they readily take to nesting baskets, which may mean that in the wild they also re-use other birds’ nests. The chicks hatch after approximately 22 days and grow rapidly, leaving the nest at two weeks, although at this point they cannot fly.

Bristol Zoo currently has one paid of Red-Crested Turacos (picture at top from Wikipedia) on show. Unfortunately the aviary is not a walk-through, as you need to see the birds in good light to appreciate their beauty. They are in the aviary just before you enter our Butterfly House – if a reader is visiting Bristol Zoo please check them out. There has recently been a stud book set up, managed by Cotswold Wildlife Park, which has several species of Turaco on show, including the largest species, the Great Blue Turaco, which is Toucan-sized.

For more information on turacos, see the International Turaco Society website

Sunday, 16 August 2009

Land of the Dodo 12: The White-eyes

Scattered on most of the islands of the Indian Ocean, Australasia, and the pacific, as well as the mainland of Africa, and Asia is a huge group of small passerine birds, the White-Eyes, Zosterops. There are currently over a hundred species, with more being described each year. One would think that such diversity is a sign of a long history, but in fact the genus seems to have originated only a few million years ago. This makes Zosterops one of the fastest evolving vertebrate groups, about as fast as the well known cichlids of the African Rift Valley.

The reason for this rapid expansion is not altogether clear – separate species have evolved even on islands separated by only a few kilometres. This would suggest a species that does not move far, which is contradicted by the rapid spread of the genus as a whole. It appears that part of the reason is the short generation time and the tendency of the species to move around in flocks, which means that either large numbers of colonists arrive at a new location, or none – there is no steady “drip” of genes travelling from the source to the founder population.

White-eyes are fairly generalist small passerines, behaving in many ways like the leaf warblers Phylloscopus found across temperate Asia. The plumage is usually yellow-green, with a distinctive white eye-ring, which is where the name comes from.The main diet is insects, supplemented by fruits and nectar. The nest is an open cup made of grasses and moss, and the clutch is usually 2- 4 eggs.

There are three or four species surviving on the Mascarenes, living on Mauritius and Reunion. None are known from Rodrigues, but this may mean that they died out before being recorded. It appears that they are closest to the Asian White-eyes, although other Indian ocean islands have been colonised from Africa.
The Grey White-Eye is found on both Reunion and Mauritius. Depending on the taxonomist, the two islands are either home to a species each (Zosterops borbonicus and Zosterops mauritianus), or they are united as subspecies of the Reunion Grey White-eye shown here. Both forms are fairly distinctive, having lost the yellow in their plumage and also the white eye-ring, but in their behaviour they are typical white eyes. Both species are still common, probably because they are adapted to disturbed habitats such as man-made clearings.

Far more distinctive, and in more trouble, are the two species of Olive White-Eye. The Reunion species, Z.olivaceus, is allegedly still common, at least at higher elevations, but the Mauritius Olive White Eye Z.chloronothus (shown at top) is critically endangered, and is restricted to only 25 square kilometres on the mainland, with perhaps only 100 pairs. With a species with such a short lifespan this means that only 2 bad breeding seasons could result in its extinction, so strenuous efforts are being made to enable its survival, in the form of regeneration of native forest and captive breeding attempts. Some have been released on isle Aux Aigrettes, but until recently there had been no successful nesting. However, in October 2008 for the first time 2 young were fledged on the island.

The problem the Olive White-Eyes have is that they have become specialists. Unlike their adaptable ancestors, they have become specialist nectivores, feeding mainly on the nectar of native plants. With the widespread habitat destruction this has resulted in a loss of their food source, with inevitable results. Experiments are being made with supplemental feeding – as many in America who feed hummingbirds know, nectar feeding birds will often take to artificial feeding stations. The main problem is that nectar feeders tend to be territorial around food sources, so any feeding stations have to be widely scattered, which takes a lot of upkeep in difficult terrain.

Images- Mauritius Olive white-eye from Durrell Wildlife Conservation Trust
Reunion Grey White-eye from Wikipedia

Monday, 10 August 2009

New Arrival!

A major event for me at the zoo yesterday – I finally got to see (briefly) our new Okapi calf. She was born only a few weeks ago and still spends most of her time lying down in her mothers stable, out of the view of the public, but does venture out occasionally.

Okapis are of course the most distinctive living member of the giraffe family (readers who think there is only one species of long-necked giraffe are mistaken – there are several), and was only discovered by western science in the early 20th century. Before a specimen was obtained it was thought to be a surviving Hipparion (an extinct, 3-toed member of the horse family), but once research material was obtained it became clear it was a giraffid.

Live Okapis were first imported to Europe in 1918, but at first the stress of capture and transport by ship resulted in high mortality. Bristol Zoo received the first Okapis in 1961, and was the first zoo in the UK to breed them. Since the first arrival, we have bred over 30 Okapi, and both our current adults - Rubani the male and Lodja the female – are descendents of these first Bristol animals. The worldwide population in captivity outside Africa today is only 143, with 11 births in the last twelve months (including ours), plus some in captivity in the Republic of Congo.

Okapis our secretive and solitary in the wild, so they are hard to study. The diet comprises mainly leaves, with some fruits on occasion, grasses, or even fungi. As browsers, one might think that a tropical forest would provide abundant food, but in fact most rainforest plants protect themselves with powerful toxins, and a large animal has to travel far to get sufficient non-toxic plant food. To compensate to some extent for the poisons they consume, wild Okapis eat charcoal from lightning-struck trees and eat mineral-rich mud. Females are larger than males, and most of the time are dominant to them which means they get the best food. Even so, spare resources for growing a baby to term are in short supply, and Okapi pregnancies are consequently long – just under 15 months.

Newborn okapis spend a lot of time resting up in thickets. To avoid the smell of their faeces attracting predators such as leopards, okapi babies have an odd habit of waiting many days after giving birth before beginning to produce dung – as long as 41 days has been recorded at Bristol, although it has been as little as 8 days with other births.

The calves grow fairly fast, and after are full grown at three years.. The lifespan of an Okapi can be as long as 30 years in captivity, although 15 – 20 is more typical.

The main threat to the wild population is the bushmeat trade and deforestation. The current wild population has been estimated at about 20,000 animals, but the constant war in the Congo means that these figures may be very inaccurate.

(Photo from Bristol Zoo website)

Monday, 3 August 2009

The endangered pest

Recently added to the Wallace aviary birds here at Bristol is a small flock of a very pretty small songbird, the Java Sparrow. They are kept because they pose an interesting example of how species can be at the same time threatened in one area and a potential pest in another.

Originating, it is believed, in Java and Bali in Indonesia, their popularity as cage birds means that they have been taken throughout neighbouring islands and more recently all over the world – there is for example a well established feral population in Hawaii. They are also popular in aviculture – I have a few in my aviary in my back garden right now – as they are extremely easy to care for and always present an incredibly smart appearance (bar a few weeks a year during the moult).

Javas (Also know as Rice Birds), have the scientific name Padda oryzivora. Oryzivora means “Rice Eater”, which will give a clue as to why they were persecuted in their homeland. They are extremely prolific, and as a result were major crop pests.

Javas are an estrildid finch, in fact the largest living species, and as such belong to a group of small, mostly grass-seed eating birds, which include several other popular cage birds such as the Zebra finch, Bengalese, and Gouldian finch. The basic ecology of this group of birds is to subsist as adults mainly on ripe and ripening grass seeds, supplementing with some other vegetable matter, and feeding their young on insects and unripe seeds. They often have large broods of young and in the right circumstances can increase their numbers very quickly. The downside of this is that they tend to be short lived in the wild, so adverse situations can result in equally rapid declines. Their main natural predators are probably snakes and small mammals when nesting, and birds of prey once fledged.

In recent years the Java sparrow has faced such a decline – in fact it is classed as Vulnerable on the IUCN Red List – and a recent survey could only locate 109 individuals at 17 sites. In addition, persecution in those areas where it has been introduced has resulted in declines amongst feral populations. The most probable cause is persecution by farmers, capture for the cage bird trade (although this is completely unnecessary as they breed well in captivity), and possible competition form the Tree Sparrow Passer montanus, which is the common city sparrow in Asia.

Javas were at one time introduced to Mauritius, undoubtedly as cage birds, and were breeding in the wild by the 1750’s. However, later persecution and probably competition with House Sparrows resulted in their extinction in the early 20th century.

Closely related to the Java sparrow is the Timor sparrow Padda fuscata from, as you might guess, the island of Timor. Timor sparrows are much less common in aviculture, although also threatened, but are dark brown where a Java is grey. It is currently more common in the wild than the Java, although it faces the same threats and is consequently classed as Near Threatened by the IUCN.
The conclusion of all this is that even the commonest species can be much more threatened than it looks, especially if it relies on groups for survival. Most people will be aware of the catastrophic collapse and extinction of the Passenger Pigeon – it is important therefore to build up as wide a knowledge of all species, both in the wild and in captivity, as it is possible to arrange.

If you wish to learn more about these beautiful little birds, look at the Java Finch Society website