Bread is bad for any animal and I’m fairly certain their are studies that correlate bread in developing water fowl = poor nutrition / malnourishment = bone deformities i.e angel wing. Doesn’t mean ever offspring will develop this but in a population where poor diet is introduced by people there’s more prevalence. Frankly any study can prove that a poor diet in a developing being will cause problems later in life.

Even if there wasn’t a strong enough case animals should not be given people food period. Feed them veggies and greens if you’d like to feed the local water fowl. Bird seeds can also be ok even if it’s just ends up getting eaten by the other avian locals.