They also believe keeping animals in zoos and aquariums where there are high death rates is permissible.
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It said Pattycake surpassed the median life span for gorillas in zoos, which is 37 years old.
And he believes that if wild polar bears die out there is no point keeping some alive in zoos.
The report says unless the animals' health and psychological suffering can be addressed, the ethics of keeping elephants in zoos must be questioned.
Whereas more than 300 Western Lowlands mountain gorillas are in captivity in America, perhaps as few as three of these beautiful but endangered primates are sheltering in zoos on their home continent.
Canada will not take the wolves back, there is little room in zoos, and there is no appropriate wild space in the United States that could handle a population of wolves such as the one in Yellowstone.
"In my opinion, given the correct housing and care it would be ethically acceptable to keep a few elephants in a few zoos, but certainly not the numbers we have in all the zoos we have now, " Dr Sherwin added.
The long-term plan is for the tragopans to live in special aviaries in several Indian zoos in the Himalayas.
Woburn Safari Park in Bedfordshire joined city zoos in announcing it would temporarily shut its doors to the public to protect its rare animals.
Researchers from Bristol University studied 77 animals in 13 zoos and found that almost half of the elephants displayed abnormal behaviour.
"Some of the animals were born in the zoos and must have developed it there, " said Chris Sherwin, from Bristol University's Department of Veterinary Science.
The stud-book keeper for the snow leopard, for example, is in Helsinki Zoo, and works closely with zoos in Russia, China, India and America.
File this in the quirky Super Bowl wager department: Zoos in Baltimore and San Francisco are gambling with the homes of two ravens and a rhino.
Two of them remain at the zoo, while the other three have departed to zoos in France.
The Wildlife Conservation Society said Pattycake was the 31st oldest gorilla of 338 living in North American zoos.
Mainly because funds are scarce, they do less to preserve endangered species than do zoos in America or Europe.
Negotiations are also under way with zoos in Moscow and Quito.
When word of their release into the Sanctuary started to spread, we immediately began receiving emails from around the world, asking if we would accept Asian elephants rescued from zoos in Argentina, Korea and Romania.
Conservation partnership BirdLife International established the Bali Starling Project, with the cooperation of the Indonesian government and US and British zoos, in an attempt to save the species from extinction.
Primatologists have spent years observing them, either in African forests or at zoos.
Given the age profile of the London males and the failure to find a mate in the world's zoos, Mr Zimmerman is not very confident for the future of the species.
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Travellers can also search for particular zoos via regional chapters of the group, such as the Association of Zoos and Aquariums in the United States, which has issued 224 accreditations.
Where African zoos are weakest is in research and conservation.
Evans said the Columbus Zoo in Ohio has been a global pioneer in taking gorilla babies in need of surrogates from other zoos, but this is a first for Cincinnati.
Sick animals often have higher white-cell counts as their bodies churn out more ammunition to fight the infection, but those in the Virginian study all came from zoos, and were believed to be hale and hearty.
Conscious of the speed at which habitat is being lost, zoos are trying to avert dangers in advance.
Staff at the two Devon zoos are making sure animals are comfortable in sub-zero temperatures.
With the animals coming from zoos - some, reportedly, kept in poor conditions - the immediate outlook for the lemurs themselves was clearly positive, as they'd have forest to roam through rather than a cage to stare through.
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