Most folks think of spring as a time for birds to come back, and to nest.
The truth is many bird species that live in back yards do so year round. The birds that migrate are birds whose food is no longer available in winter. An obvious example would be Robins, who eat earthworms and fruit, both of which are scarce or gone in winter, so they must leave when it gets cold. Spring always makes me think of baby birds, partly because dozens of people will call me and ask what to do when they find a baby bird in their backyard. The old myth is that parents can smell your scent on the baby and abandon it.