Saturday, 17 December 2011

In the pink

Greater Flamingos, India
The first aviary a visitor encounters at Bristol is the Camargue aviary opposite the entrance. Although it contains several species, the most instantly recognised are our flock of Greater Flamingos, Phoenicopterus roseus, one of two living species found in the Old World, along with the Lesser Flamingo, Phoeniconais minor. There are another four species found in the Americas, of which the only one found naturally in North America is the American Flamingo Phoenicopterus ruber. The American Flamingo was formerly classed as a subspecies of Greater Flamingo but has now been split into a separate species. There other three species live in the Andes at high altitudes, and comprise the Chilean, Andean, and Puna or James’ Flamingoes. Very few Andean or Puna flamingos are in animal collections, but some can be seen at the Wildfowl and Wetland Trust collection at Slimbridge.The vast majority of flamingos to be seen in zoos or wildfowl collections are Greater, Chilean, or American flamingos.

Chilean flamingos

American flamingos
Today, flamingos can only be found naturally in the Old World in the Mediterranean, Africa, and North West India, but in the past they were more widespread. They were reported by early visitors to Mauritius, where they were probably wiped out with other endemic birds such as the Dodo, and further in the past they are known as fossils from Australia, where they were probably driven to extinction by increasing aridity during the Pleistocene. In the Americas they also occurred further north in the past – some fossil flamingos have been recorded from Oregon for example, though I am not sure of their date. The key feature controlling their distribution is not so much temperature as habitat – they need shallow, saline lakes with a fairly simplified ecosystem based on blue-green algae and brine shrimps, which provide their diet.

Lesser flamingo

Puna flamingo

Andean flamingo
Flamingos are filter feeders, extracting food particles from the water by using their thick, fleshy tongue as a piston to force water through fine plates on the roof of the mouth which trap the food particles. Depending on the gaps between the plates food items may be single-celled blue-green bacteria, or larger shrimps, baby fish, and small molluscs. Different species have different target food items, which is why two species of flamingo can often be found side by side. The Phoenicopterus species feed on larger prey items than the Phoeniconais forms.

Whatever there food preferences, the diet of flamingos will contain carotenoid pigments derived from blue-green algae, which are the source of the pink or red in their feathers and skin. Different species have different levels of pigment, and deposit them differently in their feathers, which is why different species may vary from almost white to deep red. Young flamingos have feathers which are white or brown, and take at least ay year for the feathers to turn fully pink. The bare parts, especially the legs, can take several years to colour up.

Flamingos are very long lived birds – they have been recorded as living in to their 50’s in captivity and probably often reach at least 30 in the wild. They need a long lifespan as they are not very productive – they only lay a single egg at a time and probably in the wild only raise a youngster to independence perhaps one year in three. They are of course famously social – colonies can reach many tens of thousands of birds in the Rift Valley. Even these vast flocks however may only be a shadow of the numbers that once existed – for example during the Messenian Crisis around 6 million years ago the temporary closure of the Straits of Gibraltar essentially caused the entire Mediterranean to dry out into one giant salt pan, which would have been prime flamingo habitat. The numbers living then must have been truly astronomical. We know that flamingos very similar if not identical to the modern forms were around then from fossils – modern-type flamingos go back at least 30 million years.

As a result of their specialised habitat, flamingos are at risk of human interference. Disturbance, drainage of lakes, and industrial pollution are probably the main threats. Having said that, around the Mediterranean flamingos will often breed and feed close to human activities, especially salt pans. There are major colonies in Spain and the Camargue, and they also winter on Cyprus.

Chilean flamingos, Norfolk, UK 2010
Flamingos have been kept in waterfowl collections for many years, and it is not unknown for them to escape. They may survive in the wild for many years, but a group of escaped Chilean flamingos in Germany some years ago actually began breeding in the wild, and still probably survive. These birds may have been the source of two birds which showed up at Cley in Norfolk in 2010. Some years ago a pair stayed with the swans at Abbotsbury in the South West UK, and even built a nest as I recall being told, but did not succeed in raising a chick. Given the number of other water birds which have colonised the UK in recent years, I wonder if flamingos will join the avocets of Norfolk? – flamingos and avocets after all favour very similar habitats. The main obstacle would be that they need to be in a large flock to encourage breeding, but it is not impossible.

At Bristol we had a good breeding season this year, raising seven chicks. This takes our flock to 38 birds, close to the minimum size for regular annual breeding. The youngster can be told by their white plumage and grey legs. Adult males are much taller than females. The captive diet is a specially prepared artificial diet which contains an artificial colour compound to replace the carotene in the wild diet. Flamingos are quite hardy birds, but in severe weather they are shut inside their house.

Well, that’s about all for this week. Next week part one of the review of the year, which has been a significant one for Bristol Zoo and for me.

(Images from wikipedia, Norfolk Wildlife trust website)

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