Their gizzard grinds up the food, but this gritty material is needed to get the job done. You can provide grit in several ways. When there is no snow cover, a simple scrape in dry soil becomes a source of grit. During the winter you can mix a small amount of grit in with your bird seed. If you place grit on its own tray, be sure to keep it away from your feeders so it won't become contaminated.
Chlorine kills living creatures, and can be harmful to birds.
If you need to use chlorine bleach in your bird bath, use a very diluted but effective solution of about 1 tablespoon of bleach in 3 gallons of tepid water. The more diverse the habitat, the better the chance of attracting nesting birds to your property. The placement of various kinds of man-made nest boxes can attract many tree hollow nesting species. Even setting out bits of string for birds to use in their nest building, while not really necessary from the bird's standpoint, can assist birds that are building nests in the area. While it is in the egg, a hummingbird has a very short, stubby beak.