Strange bird behavior?

I just saw a grown bird (I'm pretty sure it was a mockingbird) sitting outside my windowsill and another bird flew up and fed it a berry. This happened at least 5 times, and the sitting bird kept chirping and cleaning its feathers it looked like. Is this some kind of recognized mating ritual? Because both of the birds looked to be adults. It was just bizarre to me since they were both fully grown and the one being fed wasn't in a nest, but sitting on my window. Thanks for any insight!