Also beware grass clippings, which can sometimes cause an impacted crop. If they're cut very finely it shouldn't be a problem--grass is good for them, after all. But when they eat it on their own, they nip off tiny pieces so it's easier for then to digest. When it's pre-cut (from the lawnmower, for example) the fibers/pieces can be too long to get past the crop, and can turn into a tangled mass that keep the poor birdies from getting the nutrition they need. Some birds don't seem to have a problem with grass clippings, but it's something to keep in mind.