The dark secrets zoos don't want you to know about - People love to see wild animals up close, and spending a day at the zoo is a popular activity for all ages.

There are many behind-the-scenes goings-on that occur at zoos around the world. Learn some facts about animals in captivity and about zoo operations in the following images.

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Lifespan - Animals often live longer in the wild than they do in captivity.

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Lifespan - Captive elephants and orcas (killer whales) live just a fraction of their potential lifespans—elephants, for example, live 30-50 years less on average in captivity. Orcas can live up to 100 years of age in the wild but survive just 14 years on average in captivity.

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You could get sick - If your zoo offers a petting zoo, beware! Animals kept in these kind of facilities can transmit salmonella, E. coli, and other diseases.

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Panda - In order to house and display a panda, foreign zoos must rent the animal from the Chinese government for a decade. Yearly lease rates can be close to a US$1 million and if a panda dies due to human error, China imposes a hefty fine of roughly US$400,000, according to Mental Floss.

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Zoochosis - Many zoo animals suffer from zoochosis, defined as atypical behavior brought on by captivity.

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Zoochosis - Its presence is marked by many different symptoms, including repetitive behavior, excessive grooming, anxious tics, and even self-mutilation.

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Zoochosis - To combat some of the behavioral problems associated with zoochosis, animals are given drugs.

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Zoothanasia - When zoos face limited capacity and have a surplus of animals, they either give the animals contraception to prevent more births or euthanize them.

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Zoothanasia - In various zoo-breeding programs, animals are allowed to mate and breed. Once offspring reach a certain age, they are euthanized, sold, or fed to other zoo inhabitants.

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Offspring - Others can be given or sold to hunting ranches, pet stores, circuses, and research labs.

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Breaking free - Many animals attempt to escape their confinements, with primates often creating the most ingenious escapes—some have built ladders out of tree branches while others have been known to dismantle video cameras.

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Animal sanctuary - Organizations that call themselves sanctuaries or rehabilitation centers may be falsely advertising themselves. Any operation can call itself a sanctuary, as there are no regulations surrounding the word.

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Problematic visitors - Zoo staff inform each other about problematic visitors via radio communications. People who continuously break rules, such as throwing things into enclosures or tapping on glass, face being thrown out by security guards.

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Inbreeding - Inbreeding is a huge problem in many zoos. The practice can cause mental and physical handicaps, stillbirths, and deformities. For example, the white tiger is the result of inbreeding and many cubs are born malformed.

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Transfer hassle - Transferring animals between zoos involves mountains of paperwork. Many zoos get around this by confiscating them from Fish and Wildlife services.

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Quarantine - Most zoos insist new animals undergo quarantine of 30 to 60 days in order to monitor for any parasites and diseases.

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Feeding - Animals are often fed a diet of processed food. As a result, certain animals—tigers, for example—develop dental problems and suffer distress due to their not being able to hunt for food.

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Feeding expenses - Many larger animals require hundreds of kilos of food per day, a huge slice of any zoo's expenditure. The daily cost of feeding an elephant, for example, is around US$125,000 per year. Specialized diets, such as bamboo for pandas, can also rack up the bills as adults need to consume between 10 and 20 kg a day.

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Overweight animals - Most animals in zoos are overweight as they are fed frequently and do not fulfill proper activity requirements to keep body fat under control.

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BBC study - According to information posted on freedomforanimals.org a BBC investigation found 35% of animals were dying at UK-based SEA LIFE centres (the world's largest aquarium chains). Furthermore, freedomforanimals' own research showed just 2.5% of the species held captive in SEA LIFE aquariums are endangered.

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Conservation - It is often more expensive to house animals in zoos than to conserve and protect their natural habitat in the wild. Website safe.org points out that it is 50 times more expensive to keep an elephant in captivity than conserve their wild counterparts.

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Conservation myth - Most animals are never released back into the wild after being held in captivity. Lack of proper socialization and skill development (such as a hunting and escaping predators), means the animals are unable to survive in the wild.

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Animals kept off-display - Many animals are kept in behind-the-scenes exhibits or housing. These animals include infants, smaller animals such as reptiles and birds, and aquarium-based animals. One reason for this is to facilitate private presentations without pulling animals from public displays.

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Nocturnal animals - Nocturnal animals undergo an adjustment period to reverse their internal sleep cycle. They live in nocturnal houses where bright, artificial lights are turned on at night while during the day, the exhibits are kept dimly lit.

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Penguins - Penguins have a reputation for being one of the smelliest animals in the zoo. Their poop, known as guano, is notoriously stinky.

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Enrichment - In an attempt to keep animals stimulated, zoos often implement so-called "enrichment" programs. Zoo keepers will switch out toys located in the enclosures while also providing animals with a new obstacle or object to explore.

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Visit purpose - A study on visitor behavior in the United States revealed that 86% of visitors went to zoos for recreational purposes while 6% visited for educational purposes.

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