It is said that when you see a cardinal, it's a loved one that you lost coming back to visit. Whenever we see a red cardinal now, we say "There's dad" or "Hi dad!"
I don't know if it's true that the spirit of our father can come back in the form of a bird but I do know that whenever I see one, I think of him. And it happens a lot because we've got 9 cardinal couples living in or near our back yard. We've set up feeders and fill them religiously every day. Their favorites are the small colanders we've hung from trees which allow free and easy access to what's inside. The birds sit on the edge eating the seeds they like and casually tossing everything else to the ground. In with the cardinals are blue jays, junkos, sparrows, titmice, and the occasional squirrel or two. We've also seen passing swarms of migrating birds stop by for a quick bite before going on their way.
With our current weather, the birds show up brilliantly against the bare tree branches. It's not uncommon to hear "dad's in the bushes" so I guess, in some ways, he does come back.