Audubon has an article by Kenn Kaufman explaining how birds know when to migrate
Back in February, unseasonably warm temperatures swept over much of North America, buds began opening on trees, and flowers began to bloom weeks early. Naturally, birders began to ask: Will our migratory birds come back earlier, too?
That question doesn’t have a simple yes or no answer because the timing of bird migration is . . . complicated. Every species is slightly different; short-term changes in weather do have an impact, but so do a variety of other innate and environmental factors.
Read this quick primer on how North American avians schedule their spring journeys at How Different Spring Migrants Decide When to Head North | Audubon