Anyone who has spent time in parks, forests or protected areas would have noticed very distinct 'DO NOT FEED WILDLIFE' signs. While it may be fun to get close to a wild animal, feeding is not always as innocent as it seems.
When you feed native animals, you're giving them the wildlife version of junk food. Instead of eating a wide range of natural foods that they either hunt or forage for, they become dependent on processed seeds, bread and other foods that are not part of their natural diet. This can make them very sick and lead to imbalances in their diet. These dietary imbalances such as calcium deficiencies prevent the development of strong bones, beaks and immune systems in young birds, which can also lead to malnutrition, disease and death.
Animals that expect to be fed by people can become aggressive when they are hungry. A perfect example of this is the dingoes in Australia, that have lost their fear of humans due to tourists feeding them for the chance of an up close and personal selfie. This has lead to aggression, threatened tourists and ultimately the euthanasia of many dingoes. Once animals know that humans are a reliable source of food, they may converge on your home or campsite, potentially disrupting their migratory patterns and displacing other species. This is seen in Cebu, Phillipines where locals feed the Whale Sharks to ensure tourism flourishes all year round. The problem here is that even though the whale sharks are becoming more friendly, they are not migrating north to mate and reproduce. This population of very critically endangered sharks will most likely disappear by the end of the century.
When food is openly available, wildlife will gather in unusually large numbers. This can also be seen in private or territorial species. Many wild animals do not interact with others of their own species except during mating season and when raising their young. This is one way nature minimises the spread of disease. However, when animals gather and fight over food, disease and virus can spread not only among the species but into human populations as well.
So even though feeding animals can be quick and easy way for them to interact with you and become a friend, you are really just making an enemy.