Monday, 25 May 2009

Return of the Crane

Back in 1981, I was on a bird watching holiday in Norfolk in the east of England. It was the last day, and we had gone into the Norfolk Broads to see what we could add to our list for the week. It was a very foggy day, but we stopped to see what we could find in a field, soon locating a few Golden Plover. At this point, we heard an unfamiliar trumpeting sound coming from the low clouds, and Brian Bland, who was leading the group, immediately said “Those are cranes!” Naturally, we were surprised by this, as Eurasian Cranes are scarce passage migrants in the UK, but we looked towards the approaching sound and made out three cranes which came and landed only a few hundred metres from us. They were not adults however, but a pair with a just fledged chick – the first to be bred in the UK since the 17th century.

It still remains the greatest birding experiences of my life.

Eurasian (they are usually called Common) Cranes are indeed one of the worlds commonest species, with an estimated world population of perhaps 275,000 birds and a range from western Europe to eastern Siberia, but in Britain a combination of drainage of wetlands for farmland and hunting for food (they were a centrepiece of medieval banquets) resulted in their extinction as breeding birds, only showing up when migrants wintering in France and Spain passed through on their way north to Scandinavia and Siberia. A few years before my sighting, a young pair had taken to hanging round Norfolk, and when they apparently vanished in the spring there was much speculation – which happily proved to be correct.

Unfortunately, there is comparatively little breeding habitat available at the original site, and the population since then has grown very slowly, now numbering perhaps 20 or so individuals, despite other wild birds having been attracted to the site to join the founders. For that reason, it has been decided to attempt to establish another population using captive raised birds from wild laid eggs. The first site for the attempt has now been announced as the Somerset levels not far from Bristol.

The project is being coordinated by the Wildfowl and Wetlands Trust at Slimbridge, and when I went there today some of the previous year’s juveniles and subadults were on show. Some of these, plus ones raised in the next year or two, will be transferred to a predator free soft release pen on the levels, in which it is hoped they will eventually breed and establish themselves in the area. Roger Tippett, the president of the Severn Counties Foreign & British Bird Society (see link), gave a very interesting talk on his work as a volunteer at Slimbridge in the Crane School they run each year. Roger will be at the SCFBBS stand at the Royal Bath & West Show this Saturday (as will I) – come and have a chat if you are visiting!

For more information on Cranes, see the WWT trust release here:

Friday, 15 May 2009

Gorilla society

“Gorillas live in family groups of several females and offspring led by an adult male, known as a silverback from his distinctive hair” – that, at any rate, is the standard description you will see outside any gorilla enclosure in any zoo in the world. In reality, the actual situation is rather more complex.

For one thing, as I described in my previous post, gorillas are actually two species, the Western and the Eastern (including Mountain) gorillas. Unfortunately, until recently practically all knowledge came from studies of Mountain gorillas, and it is becoming clear that the Western Lowland gorillas do things differently.

Firstly, although it is true that all gorillas are born in a group, males often do not stay there. On reaching maturity, males will leave and live by themselves until they manage to acquire females to start a new group. Unsuccessful males will live their entire lives as solitary as orang-utans.

In some cases multiple male groups have been seen in both species, but this seems mainly to occur when a silverback dies and there are several sub-adult males among the survivors. Silverback gorillas are such powerful animals that for an adult male there are essentially no natural predators other than humans, so there is no need to band together for mutual defence.

In Mountain gorillas at least 40% of males do not leave, instead remaining with the silverback and joining a small core group of silverbacks in a much larger band. The largest of these groups so far observed had no less than seven silverbacks and the group was over 60 strong.

In a few cases groups with more than one silverback have been seen in Western gorillas, but these are very rare and in most cases seem to involve a father and son situation.

Females usually leave their birth group at around nine years of age, when they reach reproductive age. They may join a lone silverback to start a new group, or they may join an existing group. Even when they join a new group, they may not remain there, especially if they lose an infant.

Recent work on habituated Western gorillas shows an interesting difference between them and Mountain gorillas. Whereas Mountain gorillas are fiercely protective of their females and invariably attack any unknown males they encounter (sometimes with fatal results), Western gorillas seem to associate much more peacefully, even allowing females to sit next to a silverback from another band and then return to their own family. Examination of DNA shows a possible reason – it appears that the silverbacks in these cases are closely related and probably grew up in the same band. It appears that the dispersal of males from Western Gorilla bands may be an illusion – they remain close to the birth groups and in touch with their erstwhile companions. This raises an interesting possibility – that the true nature of Western gorilla society is not the single band but a network of family groups – a sort of “suburbia” if you like,
If this is the case it has implications for how Western Gorillas are looked after in zoos. Although the focus of all management is on creating a single breeding group, it might be better to aim for much larger facilities holding several groups (preferably led by related silverbacks) with facilities for holding non-breeding males either by themselves or in bachelor groups in at least visual contact with their former families

Friday, 8 May 2009

Land of the Dodo 9: Rails

One of the most successful groups of birds to colonise oceanic islands are the Rails, the group of birds which includes coots, moorhens, and gallinules. Invariably terrestrial, and usually secretive, they do not look like good long distance flyers, but they are surprisingly good at finding and settling down on remote atolls.
Unfortunately, having done so, they frequently (and often rapidly) tend to become flightless, which means that extinct rails are a major feature of the history of human colonisation of the worlds’ islands.

The Mascarenes had at least six extinct species, which roamed the thickets and grasslands of the islands feeding on invertebrates, especially snails (snail shells show the distinct signs of being broken open by powerful beaks), crabs, and in the case of the largest species possibly even baby tortoises. This did not help them against rats, cats, and mongooses – all were gone by 1720 at the latest.

The picture at the top of this post is of a Purple Swamp hen, Porphyrio, which is the probable ancestor of a bird, the "oiseau bleu" formerly found in the hills of Reunion. Unfortunately no bones have yet been found, but the description fits very well and this species is very widespread in Africa and southern Europe (it has also been introduced to the Everglades). Birds of this type also colonised New Zealand, evolving into the highly endangered flightless Takahe.

The most specialised (and probably oldest endemic species) was the Red Hen, Aphanapteryx. This has caused some confusion, as after the extinction of the Dodo the name was transferred to the Red Hen, and consequently people believed the Dodo survived longer than was in fact the case. The Red Hen had silky feathers, similar to a Kiwi, although in no way related.

Three endemic species of Wood Rail, Dryolimnas, inhabited the three main islands. These were local forms of the Madagascan White-Throated Rail, which has a flightless race still inhabiting Aldabra.

The Mascarene Coot, Fulica newtoni, was close to the Crested Coot of Africa and Spain. The reason for its extinction is unclear – Coots are usually well able to take care of themselves. However the available habitat for water birds is limited on the islands, so habitat destruction by early colonists was probably a major factor.

Finally, a new arrival reached the islands in the late 18th Century, probably from Africa. Common Moorhens, Gallinula, the same species that is found in Europe and the USA, have now become widespread in the islands. There have been reports in the past of White-throated Rails reaching the islands from Madagascar, so it is still possible that new rails may yet colonise the islands.

Friday, 1 May 2009

New arrivals 2 - lorikeets

Opening this weekend is Bristol Zoo’s newest exhibit, a walk through aviary for 30 Rainbow lorikeets (Trichoglossus haematodus moluccanus). These colourful and acrobatic members of the parrot family belong to the group of parrots known as the lories. There is no scientific distinction, but “Lory” is generally used for short tailed members of the group and “Lorikeet” for the longer tailed species.

The Rainbow lorikeet (sometimes called the Green-Naped Lorikeet) is a widespread species with at least 20 subspecies, some of which are probably full species. The range is throughout Indonesia, New Guinea and northern Australia, and it has also been introduced to Western Australia and New Zealand, where it has been classed as a pest because the birds not only feed on orchard crops but also compete with native species of lorikeet. The wild population is estimated as at least 5,000,000 birds, although some subspecies are threatened, for example the Bali lorikeet T. haematodus mitchellii.

It is an adaptable species, freely using coconut plantations or settlements as well as rainforest. Lories and lorikeets are, to various degrees, specialists in feeding on pollen and nectar, although they also take plant buds and fruit, especially wild figs. In order to track down flowering trees, lorikeets are nomadic, which probably accounts for their wide distribution.

As with almost all parrots, lorikeets nest in holes in trees where the female lays two or three eggs. The young fledge at about 60 days.

In captivity, lorikeets are fed an artificial nectar mixture which needs to be supplied fresh several times a day. In addition they receive fresh fruits such as apple and grapes, and must always have access to clean water as they are extremely fond of bathing. Lorikeets lack the muscular gizzard to grind up seeds, so although they will take them it is not good for them.

Although lories and lorikeets of various species are widely kept and bred by private individuals, their specialised diet means that they require much more intensive care and specialised knowledge than the more commonly kept seed eating species of similar size such as cockatiels. In addition, they are quite noisy birds so a keeper needs sympathetic, or preferably distant, neighbours!

In our exhibit, visitors will be able to buy a small cup with a dab of artificial nectar and on entering the aviary the birds will come down to feed from their hands. I went on a practise run for this last week and after a wait (they had just gone into the aviary so they were still getting used to the new surroundings) they came down to feed. Visitors beware however – they will also land on your head!