I see American Robins all winter so I would not say seeing one is a sign of spring. I see them eating things like crabapples an berries during the winter. When the ground warms up I see robins on the ground eating earthworms so I would say that is a sign of spring.
Red-tailed Hawks are seen all throughout the winter in Connecticut.
The Red-tailed Hawk's smaller, noisier cousin, the Red-shouldered Hawk, is also seen in Connecticut throughout the winter. That seems to be a changing trend as I remember they used to e a rare find during the Christmas counts.