Most wildlife biologists would tell you that they discourage the public from feeding wildlife. Wildlife are experts at finding their own food. And feeding them just increases the risk of of possible injury or disease transmission. That being said, people love to feed birds. And ducks are no exception. As long as the ducks do not become accustomed to taking the handouts, there isn't much problem with them getting the occasional "free lunch". It helps people feel connected to nature to have such an experience. And that is a good thing. It is only illegal to feed deer in Illinois, due to concerns about Chronic Wasting Disease. It is not illegal to feed birds. However, the feeding area should be kept clean to help reduce the potential of spreading disease. And of course, if the park or other natural area has signs requesting that the public not feed the wildlife then that request should be followed.