The prohibition "do not feed the animals" reflects a policy forbidding the artificial feeding of wild or feral animals. Signs displaying this message are commonly found in zoos, circuses, animal theme parks, aquariums, national parks, parks, public spaces, farms, and other places where people come into contact with wildlife. In some cases there are laws to enforce such no-feeding policies. Feeding wild animals can significantly change their behavior. Feeding or leaving unattended food to large animals, such as bears, can lead them to aggressively seek out food from people, sometimes resulting in injury. Feeding can also alter animal behavior so that animals routinely travel in larger groups, which can make disease transmission between animals more likely. In public spaces, the congregation of animals caused by feeding can result in them being considered pests. In zoos, giving food to the animals is discouraged due to the strict dietary controls in place. More generally, artificial feeding can result in, for example, vitamin deficiencies and dietary mineral deficiencies. Outside zoos, a concern is that the increase in local concentrated wildlife population due to artificial feeding can promote the transfer of disease among animals or between animals and humans. Sign example gallery Zoos Zoos generally discourage visitors from giving any food to the animals. Some zoos, particularly petting zoos, do the opposite and actively encourage people to get involved with the feeding of the animals. This, however, is strictly monitored and usually involves set food available from the zookeepers or vending machines, as well as a careful choice of which animals to feed, and the provision of hand-washing facilities to avoid spreading disease. Domestic animals such as sheep and goats are often permitted to be fed, as are giraffes. National and state parks In national parks and state parks, feeding animals can result in malnourishment due to inappropriate diet and in disruption of natural hunting or food-gathering behavior. It can also be dangerous to the people doing the feeding. In the US, early 20th century park management actually encouraged animal feeding. For example, "the feeding of squirrels had been seen as a way to civilize the parks and rechannel the energies of young boys from aggression and vandalism toward compassion and charity." Park rangers once fed bears in front of crowds of tourists. However, with a greater awareness of ecological and other issues, such pro-feeding policies are now viewed as detrimental, and US national