Image via WikipediaWell that's a very thoughtful question. Blackbirds, crows and ravens are known for washing their food before eating. You are lucky it was just a pizza crust! I've heard reports of birds dipping road kill and variety of other foods in bird baths and leaving very unpleasant surprises behind.
Anyway why are they doing that? That's a good question. It's been pretty hot recently and nesting crows need to keep their babies hydrated. Dipping "baby food" in water not only softens it but allows the babies to get sufficient water to meet their daily needs.
Water is very important to birds. Offering a dependable source of water is probably the simplest and most important step you can take to increase the variety of birds in your yard.
Birds must be ready to fly at all times, and bathing is a critical part of feather maintenance and staying in top-flight condition. Water is also vitally important when it's extremely hot and a bird’s ability to regulate its body temperature can become stressed. Birds do not sweat and must remove excess body heat through their respiratory system.
So when temperatures rise, a bird's respiration rate increases and dehydrates birds. If that bird still hasn't left the nest they are dependant on their parents to supply liquids. Some babies are brought nice juicy bugs or berries. Many seed-eating species of birds provide some regurgitated seed and water. While others like the crows dip their food in water.
Thank you for sending in your observation. I'm sure a lot of people were wondering.