According to our trusty National Audubon Society Field Guide, robins don't go south in the winter, as I grew up believing. They may actually stay in Iowa over the winter or fly even further north to Canada.
And, now I've been told the turkey vulture is a better gauge of when spring arrives. The turkey vulture will not eat frozen meat (they probably don't even know where it is if they can't smell it), so they don't arrive until the weather is warm enough to ensure sufficiently stinky carrion.
What an assault these facts are to my understanding of spring!
If robins do stay in Iowa over the winter, they are quite invisible. It's only when the snow has melted, only the day light hours begin to surpass the dark, only when the calendar moves toward late February that I see robins working our yard again. Only when spring is in sight.
Though I appreciate the vultures for their efforts to recycle carrion, they just aren't as lovable as a sign of spring. So, regardless of what the experts say, I say: Hello, robins! Welcome, spring!