When it rains, he sits by the french doors staring glumly out into the garden and sighs. Arnold hates the wet.

When it's fine and hot and the gentle breath of the summer's breeze whispers of more such days to come, he likes to lie on a chair on the deck and sleep and dream. This makes him happy.

He is, it has to be said, very particular about his food. Serve the wrong thing and he'll sulk. His best friend lives next door. They like to play. Well, sometimes. Occasionally, the best friend gets his ears boxed, just for the hell of it of course. This makes Arnold very happy indeed — and makes me so too.

All these things mean he has, without a doubt, a rich life, full of joys and sulks. And why shouldn't he, he's a cat.

That animals — even less obviously social animals, like cats — have emotional lives is something most appreciate, according to American scientist Marc Bekoff.

"I think common folk, lay people, know it. Pet owners know it."

However, Bekoff, a professor emeritis of ecology and evolutionary biology at the University of Colorado, has made it his life's work to scientifically prove that animals not only have emotions but have moral lives too — a finding he will discuss in Auckland this week at the 20th New Zealand Companion Animal Conference, staged by the New Zealand Companion Animal Council

"Basically, animals have the ability to make moral judgments, right or wrong judgments," Bekoff says by phone from his home in Boulder, Colorado.

"They know what they're supposed to do in a particular situation, like in play. When they're playing they will have an expectation that if 'I invite you to play, I won't bite you too hard, I won't knock you too hard and I will honour the rules of the game'. They make decisions about food sharing, about reciprocity — I scratch your back and you scratch mine, paying back favours. The evidence is really clear, as time goes on, that this is in fact what is happening. More and more animals are showing this kind of moral intelligence."

Bekoff, who has worked over the years with famed English biologist Jane Goodall, will give the Auckland conference's hour-long keynote address, "Inside Animal Minds", as well as taking part in a debate immediately afterwards with the moot "do animals possess the emotions and morality of humans?".

He will, of course, be speaking to the positive — and will, no doubt, receive a better hearing than when he first mooted such ideas 20 years ago.

"Scientists used to be prone to question whether we could even talk about animal emotions, let alone morality, in ways that related to the emotional lives of humans. But trends are changing quite a bit now. Thanks in part to my own research and that of others in the field, I think it's safe to say there are fewer and fewer sceptics."

Indeed, Bekoff says he is still invited to "a lot of high-end academic conferences and fewer and fewer people probably think I'm a loon. Well, they may think I'm a loon, but they still invite me ..."

The idea that animals have some sort of moral dimension is almost as old as Western thinking, he contends, with Aristotle making claims about moral behaviour spanning the animal kingdom. However, it wasn't until Charles Darwin's radical reshaping of our natural history in the late 19th century that the idea of emotion and morality in animals took a formal shape.

Indeed, Darwin wrote, in his The Descent of Man, that "any animal whatever, endowed with well-marked social instincts ... would inevitably acquire a moral sense of conscience, as soon as its intellectual powers had become as well-developed, or nearly, as in man".

Bekoff, who has a flutey giggle which comes easily, fell into researching the animal mind while at medical school in 1960s where he was studying in a PhD programme.

"I didn't want to kill animals [for research]. I decided I wanted to study them ... But my route was really studying play behaviour [of animals such as wolves and coyotes].

"I'm one of the people who really formalised [this field of studying] in terms of really saying that there was a strong adaptive significance to being moral and that there were consequences to animals showing moral intelligence."

The question is, of course, what exactly does Bekoff mean by moral intelligence? In his latest book, Wild Justice: The Moral Lives of Animals, published this year and co-authored by philosopher Jessica Pierce, Bekoff argues that many animals are adept social actors who form intricate networks of relationships and live by rules of conduct that maintain social balance.

He points to recent neurological findings underscoring his own field research, which included close observation and analysis of play by captive coyotes, wolves and free-ranging dogs. None of this is anthropomorphism — the word almost makes the jovial 64-year-old sound angry — it is, he asserts firmly, fact.

"I think [anthropomorphism] is a false fear. I don't entertain arguments about it any more. I'll say 'oh look, that elephant in the zoo isn't happy' and they'll say 'oh you're being anthropomorphic. Look at her, she's happy'. And I'll say 'wait a minute, isn't it as anthropomorphic to say that animals are happy as not happy?"'

Myriad examples of moral behaviour have been documented both in captive and wild animals groups, Bekoff says. For example, there is the story of the captive male Diana monkey who learned to insert a token into a slot to obtain food and who, when he realised a female couldn't work out this trick, inserted a token for her and let her eat the food reward.

One of the most compelling examples of animals having a sense of morality, according to Bekoff, is the story of a female Western Lowland gorilla named Binti Jua, who lived in the Brookfield Zoo in Illinois.

In 1996, a 3-year-old boy climbed the wall of the gorilla enclosure and fell six metres to the concrete floor below.

"As spectators gaped and the boy's mother screamed in terror," Bekoff has written, "Binti Jua approached the unconscious boy, reached down and gently lifted him, cradling him in her arms while her own infant, Koola, clung to her back.

"Growling warnings at the other gorillas who tried to get close, Binti Jua carried the boy safely to an access gate and the waiting zoo staff. Binti Jua was widely hailed as an animal hero. She was even awarded a medal from the American Legion."

It is, of course, inevitable that by accepting animals have both capacity for emotion and morality that humans must reassess their attitudes and treatment of them, Bekoff believes.

"I think among the things [animals] are telling us is that they are far more complex than we ever give them credit for, that they need to have rules of social conduct in order to survive. But they are also telling us — and this is where a lot of the work I do spills over — they're telling us we need to treat them better, they're telling us that they are complex, they have emotional and moral intelligence, they've got a point of view on the world and they don't like what is happening to them when we abuse them. That's the message."

It will come as no surprise that Bekoff is vegan. However, he is surprisingly non-judgmental — realistic is the word he uses — about meat-eaters. He's somewhat tougher on semi-vegetarians.

"People will say things like 'I'm a vegetarian but I eat fish' and I'm thinking 'shit, the last time I looked, fish were not vegetables'. People say 'I'm a vegetarian but sometimes I eat chicken' Well, then you're not a vegetarian. You don't have to apologise, I don't want people to feel defensive ... but I want them to live up to what they are claiming to be. Among the changes [I'd like to see] I would say 'walk the talk'."

It is interesting too — and a perhaps a measure of his self-declared realism — that although he is attending the Companion Animal Conference in Auckland, and has had dogs all his life, he believes that "in a certain world" humans would not keep pets.

"But what are we supposed to do with the billions we have?"

He feels the same about zoos (though he strongly disagrees with the keeping of elephants, such Auckland Zoo's Burma) and hopes they will eventually be phased out.

"But in my mature years I've just become a realist and [think] zoos are going to exist, people are going to eat meat, people are going to have pets, so what to do with the real world?" Bekoff remains what he calls a "hopeful monster", — an avowed optimist despite the real world.

"I'm an idealist. A lot of people think I'm whacked for being hopeful, including my partner. But I think there are just a lot of things happening that look to be promising. And if we give up hope, we're screwed. In all honesty, I can sometimes look around and go 'jeez, this just deplorable'. But if you give up hope, there is no future."

The 20th NZ Companion Animal Conference is at the Stamford Plaza, Auckland, on Monday and Tuesday.