Sunday, 27 February 2011

A good start to our 175th anniversary year

Finally, after many disappointing years, Bristol has two lion cubs. The proud parents are two (a male and a female) of the around three hundred Asiatic Lion, Panthera leo persica, in captivity. The wild population as of April 2010, comprised 411 individuals, including 150 cubs, all located in the Gir forest and a few neighbouring areas in Gujarat, India.

In prehistory, lions were the most widely distributed of large mammals, with a range extending from South Africa to Peru, and as far north as Britain. In that range various subspecies have been recognised, with the American form sometimes being treated as a separate species P.atrox, but aside from being unusually large the American lion was a typical lion.

One feature of the extinct cold-climate lions, at least as shown on cave paintings, is that the males were maneless or nearly so. This makes sense considering the conditions they survived in – a mane would rapidly weigh the animal down with ice crystals in the winter and make hunting impossible. As they seem to have derived from these cold-adapted forms, the American lion was probably also maneless, although no paintings survive from that period as confirmation.

The collapse of the lion population began about 10,000 years ago with the mass extinction of the Americas, where lions probably succumbed to loss of their main prey species. By around 2,500 years ago, they had gone from most of Europe but still survived in the Balkans and throughout the Middle East. Wherever large concentrations of people, especially livestock farmers, developed, lions were wiped out as a direct or indirect threat to humans. The last known Asiatic lion seen alive outside India was in Iran in 1941.

The Gir forest reserve is now the only place lions survive outside Sub-Saharan Africa. The reserve itself is 1412 km² of dry teak forest and some surrounding grassland, and is probably at maximum carrying capacity for lions. The reserve needs to be large enough to maintain viable populations of the lions prey – chiefly wild boar and deer although they will also take wild cattle and gazelles.

Clearly, the population in both the wild and captivity is far too small. The calculations are complicated, and depend among other things on reproductive rates and lifespan, but in general for a mammalian species to have reasonable long-term survival prospects without human intervention there needs to be around 5,000 breeding adults in a continuous population. Below this number, natural disasters, inbreeding, and diseases increase the risk of extinction dramatically.

This brings us back to our cubs. The Asiatic lions in Europe’s zoos are managed centrally, as with most of the species that can be seen in zoos today. There is a separate studbook for those in American zoos for reasons of ease of management, and currently the Asiatic lion studbook is managed from Twycross Zoo. Our male, Kamal, came from Twycross while our female, Siva, came to us from Besancon in France. The cubs were born on 24th December and their existence has been kept under wraps until we were sure they were going to be Ok (first litters in lions and other animals often do not survive due to maternal inexperience) and also they could not be put on show until the cubs had been vaccinated – lions are vulnerable to many diseases spread by domestic cats such as Feline Immunodeficiency Virus (FIV). Canine distemper, present in Bristol’s extensive urban fox population, is also a risk.

The cubs will remain with the mother until they are at least 2 years old, when in the wild the male at least would disperse to find a pride of his own. Where the cubs go to will be determined by the studbook holder, depending on where new pairs are to be created to maintain genetic diversity in the captive population.

At present reintroducing zoo-bred lions to the wild is a very distant prospect - although given their prehistoric range there are plenty of possible areas. Reintroducing carnivores, especially ones capable of attacking humans, is universally difficult or impossible. The creation of some large fenced areas where they could live at least a semi-natural existence is a far more likely scenario, but given the state of conservation awareness and political will in possible countries (including South East Europe) there is very unlikely to be any such attempt for several decades at least.
For more on the lions of the Gir forest, see here:

For a video of the birth of our cubs, see here:

Next week; hornbills

(images from Bristol Zoo website, Asiatic

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