These actually look like juveniles so they probably can fend for themselves. However, if you think that they are still too young to take care of themselves, you might try to capture them and try to find them a new home. This is especially important for the duck with the beak problem because it may get to the point it cannot eat. If the birds cannot fly, they also cannot protect themselves from inclement weather (can't migrate) or predators ( escape). The birds could have been dumped with the despicable owner thinking that since it is a park, they will be fed by guests. Are you sure the park did not Introduce them to the area? Feed them cracked corn and poultry layer pellets. Give them lettuce to supplement their vegetation needs. A little bread can be used as a treat. The Regal Swan