A Little Dirty Is Natural and Better for Birds Birds actually prefer birdbaths with leaf tannins those golden-brown stains from fallen leaves. Tannins have natural antifungal and antibacterial properties that help keep feathers healthy. Over-cleaning or using bleach removes beneficial microorganisms birds rely on. Just change the water weekly and scrub lightly with a brush no chemicals needed. Only use a mild vinegar rinse if algae takes over. A little wild is healthier. Let your birdbath look like nature thats exactly how birds like it.