The only bird that size with a red breast, blue back, and a cheerful song on a farm in Pennsylvania in May is a male Eastern Bluebird.
Each bird species is unique, and often the sexes are different in appearance, which requires additional clues. However, it can be mastered easily, over time, with practice. The best place to start is in your own backyard.
Check out the Regional Birder for a monthly update on what to see in your region, including monthly top ten birds, their favorite foods, and a sightings list.