In an insight into whether zoos have a place in the modern age, Liz Bonnin investigated culling practices in captivity, behaviour exhibited by zoo animals not seen in the wild, and different species that have struggled in captivity.
BBC's Horizon: Should we close our zoos? Had viewers heartbroken, angry and fascinated. But these issues in particular were the most shocking...
1. The practice of culling "surplus" animals in zoos.
Footage of a zoo in Copenhagen killing a giraffe and feeding it to other animals trigged a huge backlash. But while the practice is openly carried out there, to avoid inbreeding and for zoos to ensure genetic diversity, it's estimated that 300 to 500 healthy animals are culled throughout Europe. It's not usually done so publicly though.
2. The fact that 90% of animals in zoos are not endangered in the wild and 70% were born in captivity.
3. When animals have been moved from small zoo enclosures the response within the zoo industry hasn't always been positive.
Breaking with a 150-year tradition, Detroit Zoo moved its Asian elephants to a sanctuary because they didn't have enough space, and it apparently caused outrage among people in the industry. Some thought they should have been moved to a different zoo, others were annoyed it had been done so publicly. Research shows elephants are dying a lot earlier in zoos than in the wild, and often suffer from stress, painful foot problems and obesity.
4. The scary stereotypical behaviour by some zoo animals that isn't seen in the wild.
Animals have been seen to exhibit stereotypical behaviour in zoos not seen in wild animals. Species that are "wide raging carnivores" pace a lot in captivity for example.
Detroit zoo moved polar beers to a large £16 million enclosure and say they exhibit less stereotypical behaviour. But polar bears born in captivity would be unlikely to survive in the wild.
5. An interview at Sea World about orcas.
Trainer Dawn Brancheau was killed by orca Tilikum in 2010, which was the focus of the documentary Blackfish. On Horizon, Chris Dold from Sea World explained Brancheau's death as a tragic accident. Since filming Sea World have given in to public pressure, and said the current orcas will be the last they keep.
6. The tragedy of the Northern White Rhino
Persecution by humans in the 70s means the species is now extinct in the wild. There are now just three left (five at the time of filming) on Earth - but in captivity. Despite immense efforts by zoos all over the world trying to breed them and save the species, it hasn't been successful.
7. Science can only do so much if human practices in the wild don't change.
As a result of human impact, some animals are going rapidly extinct. Zoos say they are conservation centres and part of the solution. And that's true in some cases, the California Condor is a good example of a species saved by zoo interaction.
But even if zoos try to breed endangered animals, as long as animal habitats are still being destroyed in the wild, no amount of work by zoos to save species will help.