A zoo that prides itself on conservation was widely condemned yesterday for destroying two rare monkeys because it could not find new homes for them.

Newquay Zoo in Cornwall had the Sulawesi crested black macaques put down by lethal injection because they kept fighting and could not be kept in the same cage. The zoo claims that it was impossible to rehouse the animals and it was fairer to have them destroyed as “the last resort” than keep them in isolation.

There is now one macaque, a ten-year-old male called Chicito, remaining at the zoo, which hopes to acquire a number of females to start a captive breeding programme.

The environmentalist David Bellamy described the decision to kill the animals as “bloody mad”, but Stewart Muir, director of the zoo, defended it. He said that the relationship between three male macaques had broken down and that the only option was to to remove the two weaker males and leave the dominant one.

“We have had a bachelor group of three macaques for several years,” he said. “Unfortunately all three became aggressive and were physically hurting each other. The relationship had irrecoverably broken down and the only option was to remove the two weaker macaques and leave the dominant male.

“It would not have been possible to rehouse them anywhere that could promise us they would not be placed in isolation,” he said. “No zoo would have taken them on and be able to introduce them to an existing group. Ultimately it is fairer to put the animals down.

“We would never consider selling them to a private collector as their welfare could not be guaranteed. The euthanasia came at the end of a lengthy consultation process with vets and our ethics committee.”

However, wildlife experts, conservations groups, other zoos and even Mr Muir’s own staff condemned the decision. One member of staff described him as a “murderer”. The man, who asked not to be identified, said: “Staff at Newquay Zoo were told not to tell anybody about the decision. If they do they might lose their jobs. I am disgusted, it is murder. Both monkeys were healthy.”

The two macaques that were destroyed were Venus, who was 10 and had been born at the zoo, and Ia, who was 11 and had been bred at Jersey Zoo. Macaques have a life expectancy in captivity of 20 to 25 years.

A spokeswoman for the charity Animal Aid described the decision as “horrific and unacceptable”. She said: “It is not an act of conservation – these animals have been treated as disposable commodities. [The zoo] clearly did not make the effort to find an alternative. There is a sanctuary very close by who were not even called for advice. The zoo took the easy way out, but it is a barbaric way to treat an animal, especially an endangered species.”

The Cornwall Monkey Sanctuary at Looe, Cornwall, said that it could have found homes for the monkeys had it been asked. Matt Thomas, the head keeper, said: “That’s quite awful and that would not happen here. It would never be an option that would be considered.”

David Bellamy said: “What were they thinking? We have a duty to protect endangered species. The first thing they should have done is ring London Zoo, where they have a breeding programme. If they couldn’t find another zoo they could have sold them to a private collector for thousands of pounds. They must be bloody mad. They should have followed every line of inquiry to find these macaques a new home.”

Newquay Zoo’s website boasts that it is an “education and scientific charity dedicated to conserving our global wildlife heritage and inspiring in its many visitors a lifelong respect for animals and the environment”.

Mr Muir said that 29 zoos across Europe were approached about the monkeys but were unable to offer them a home. His decision not to isolate them was supported by Dr Bengt Holst, chairman of the European Association of Zoos’ Conservation Committee and Conservation Breeding Specialist Group.

Dr Holst said: “These primates are social animals and to isolate them is a bad thing to do. We would rather euth-anise them than isolate or lock them up on their own. The first option would be to see if one or both of them could be sent somewhere else. If that’s an option that should be done.

“In general, euthanasia can be used as a management tool.”

A species under threat

— The black crested macaque is the most endangered of six species that live on the Indonesian island of Sulawesi

— There are esimated to be fewer than 100,000 left in the wild

— They are classified as endangered on the World Conservation Union’s red list and listed on Appendix II of CITES, the Convention on International Trade in Endangered Species

— They are under threat because of logging, which destroys their habitat and hunting for food

— They feed on leaves, roots, buds, fruit, insects and caterpillars. They are important seed-dispersers

— In the wild they congregate in social groups of up to 100

— After a gestation period of 162-186 days, females give birth to one baby

— They are entirely black apart from their rump, which is pink

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