Thousands of people protested in Valencia last weekend against what they see as government efforts to stop an important tradition in Spain: bullfighting. For centuries, crowds have watched matadors baiting bulls. But opponents say it is cruel and stressful for the animals. Pro-bullfighting groups are calling for the sport to be added to the Unesco list of intangible cultural heritage.

Elephants, and lions - these animals are used in circuses worldwide. They are subjugated into performing demanding tricks. According to the animal protection organization Peta, the animals are often removed from their mothers when they are far too young. After much public pressure, the Ringling Brothers Circus in the US will stop using elephants. But the practice will continue in other shows.

It's been more than 10 years since fox hunting was banned in the UK. And yet, the controversial activity continues in a different form. Trail hunting has replaced the traditional hunt - but satisfies neither hunters nor opponents. Pro-hunting lobbyists are campaigning to get the law repealed, while animal rights activists argue trail hunts allow illegal hunting with dogs to continue to take place.

A trip to the zoo may sound like fun - but for some animals, the bars and fences mean misery. Despite rules put in place by the World Association of Zoos and Aquariums to ensure welfare of the animals, the organization has been accused of overlooking cruelty in Thailand, Kazakhstan and Sri Lanka.

No animals were harmed in the making of this picture gallery - but can the same be said about Hollywood films? Peta says that like in circuses, many creatures are removed from their mothers when they are too young, and subjected to abuse. But there are protective measures in place - the American Humane Association works with the film and television industry to insure the safety of animal actors.

The gates are up, and they're off - greyhounds chasing down a mechanical rabbit. That's what they were born to do, right? Running is actually just a small part of the dogs' lives. The League Against Cruel Sports estimates for 95 percent of the time, race dogs are shut in kennels. "Cruelty, drug abuse, injury, neglect and killing" - just a day in the life for these dogs, according to the league.

One animal pitted against another - dog fighting is entertainment based on suffering. And while it's illegal in many countries, dog fighting continues to take place in back alleys and behind closed doors, with people gambling on the outcome. The dogs are commonly kept on chains, and are bred to be aggressive. If you see this "sport" taking place, best report it.

Chimpanzees have had a knack for dealing with tools for a long time. Researchers from the Max Planck Institute for Evolutionary Anthropology in Leipzig have found evidence in West Africa proving that chimpanzees have been cracking nuts with stone tools for the last 4,300 years.

British scientists have shown that bottlenose dolphins call their mates using individual whistling patterns. In other words, dolphins use something that is comparable to our names. Apparently, they develop their individual series of whistles as a signature at a very young age.

New Caledonian crows (not pictured) seem to have the ability to invent tools. In 2002, the magazine Science reported on a crow bending a straight wire into a hook to fish food from a vessel.

Pigs can learn certain behavior by observing their relatives. That's what scientists from Vienna found while working with Kune Kune pigs. The animals were also able to repeat what they learned half a year later, thus proving a long-lasting memory.

Ants keep plant lice as farm animals to harvest a sweet nectar that the lice secrete. To make sure they do as their masters want, the ants use a chemical substance, with which they force the lice to move slower, thus make it impossible for them to escape.

Pigeons can do something that humans must develop over a couple of years: they are among the few animals that recognize themselves in a mirror. This self-awareness is an important piece of evidence in distinguishing intelligent animals from instinctively acting ones.

Two orca populations near Canada's west coast are apparently maintaining a 700,000-year-old culture. The so-called "Residents" and "Transients" share the same habitat temporarily. However, they do not mate and rely on different food. Transients traditionally eat mammals; the Residents eat fish. Surprisingly they do not deviate from their habits even in times of need.