You just cleaned the bird bath, and an hour later there is a soggy piece of bread, kibble, or another food item floating in it. Crows and grackles are known to dunk dry food in water, and the best-supported explanation is simple: moistening hard or dry food can make it easier and faster to eat.
Mosquitoes can use a neglected bird bath as a breeding site, but you do not need harsh sprays or a dry bowl all summer to prevent that. The most reliable approach is simple: keep the water fresh, empty and scrub the basin regularly, and treat water movement as an extra layer rather than a guarantee.
A bird bath can turn cloudy or develop algae surprisingly quickly in warm weather, especially when leaves, droppings, and other debris collect in shallow water. The safest low-maintenance approach is not a magic additive. It is frequent water changes, regular scrubbing, sensible shade, and a simple vinegar solution when you need extra cleaning power. I