How do zoo's know how much to feed their animals? They might know how much an animal eats in the wild but animals eat less in captivity so how do zoos know how much to feed an animal without overfeeding or underfeeding it?
Just trial and error. Zoos usually know how much they approximately need to feed their animals, as they got information from their former owner. After that, the keepers or biologists just observe the animals. If the animals seem to be hungry all the time or lose weight, they increase the quantity. If the animals get fat or don't eat all of their food, the keeper gives less food next time. This is a never ending proces, as the animal's needs change over time. It becomes even more complicated when a group of animals is concerned. Species with a very fast metabolism on the other hand, usually need acces to food all the time (think of small rodents, hummingbirds, bats and a lot of insects). These species are usually given a little more food than they need, just in case.
It's not just a matter of quantity: quality matters too and so does variety. The obvious method of monitoring this is by weighing the animal concerned: this is particularly important with hand-reared young animals, as it is with human babies. Some exhibits have built-in scales or weighbridges or facilities to put scales under shift cages. A zoo may also have a policy of recording each animal's weight when it is caught up for micro-chipping, ear tagging, close ringing or for any veterinary procedure. There is an increasing amount of information on record about the care of individual species in the form of the International Zoo Yearbook, journals such as EAZA's Journal of Zoo and Aquarium Research and Best Practice Guidelines for individual species. But as MrZ has written, a great deal of the responsibility lies with the keepers who observe the animals every day and feed them. Just as a good gardener can sense when a plant is not thriving and take appropriate steps, a good animal keeper should be able to do the same, and suggest changes to management or diet, in consultation with senior keepers and vets if need be. Alan
The others have covered the details well; if you want a subject that might be easier to research from the outside of the zoo world you might look at how horses are fed or you could look at cattle or other farm species. In good conditions you will see the same core elements. The main difference being that captive raised animals will have a greater variety of resources open to them and a greater level of potential understanding; whilst rarer animals in zoos might have less understood about what best suits their health. What I find most interesting is how feed adjustments can affect not just health in a physical but also a mental sense. I've heard about this most in the horse world where alternative feeds are often suggested to help avoid problematic behaviour in horses. I've no idea but I would suspect that similar is done with captive zoo animals - where such information is understood. I know that for predators they also attempt to simulate some elements of wild feeding with random starvation days where they are left unfed. Of course feeding likely varies depending on: 1) The zoos overall focus - those more focused on rewildling/reintroduction and conservation will likely have feeds adjusted to be more "wild" in nature. Meanwhile zoos with less of a focus or with animals not intended for such projects there might be more relaxed ruling on food. 2) Zoo finances - some feeds will be more expensive than others and thus finances will play a major part in what can be offered. 3) The suppliers - some foods might be harder to source or absent from some areas entirely. Which of course puts up the costs to bring those foods in. Thus some might use alternative feeds. 4) The education and awareness of the staff - since many keepers will be telling the management what should be fed to the animals those keeprs who are more "on the ball" and motivated might well push for better feed for their charges; whilst keepers with a more relaxed or just less educated background (or less experienced) might well not push for changes or for higher quality/expense feeds.
What, how, and how much to feed zoo animals is not just trial and error. It is based on years of nutritional research and experience, and is constantly changing as new information becomes proven and available. As an example, 25 years ago gorillas were fed raw meat and high sugar and starch feed stuffs. Because of ongoing research, that process has changed to feeding high fiber plant material and low sugar fruits, and gorillas are living longer and are much healthier. Zoos have too much of a financial and political investment to be risking it even on educated guesses. Having fed and cared for several thousand head of cattle and horses over the years, I can assure you most of what you've heard in the horse world about alternative feeds and behaviors is rubbish. Feeding alternative feeds to horses does have an effect on the behavior and mental state of the horse owners, but not so much the horses. Most often they talk about changing the feed so the horse is not so active. What they are really doing is providing a diet that is nutritionally deficient in some manner that makes the horse feel bad and not want to do the things that reflect their personality. I guess that is modifying behavior through feeding, but not a very sound practice to give an animal an unbalanced, unhealthy diet because the person feeding it can't handle the horse. On a side note, I feel horse owners should be a separate sub-species of Homo Sapiens. Everyone is an expert, knows an expert, or knows someone who knows an expert.
