" Dottie Warner Do hummingbirds migrate based on day length, or does it vary with weather? It is unusually warm in Indiana this year (no frost yet in most areas)."
Don't know but looked it up and this is what I found. I am thinking day length, but don't know for sure.
Ruby-throats aren't well adapted to cold temperatures; they have a tough time below the mid-20s (F), and don't enter torpor as regularly as their western cousins to conserve energy. To avoid the cold, and the scarcity of food when flowers stop blooming and insects stop flying, they go south. Some adult males start migrating south as early as mid-July, but the peak of southward migration for this species is late August and early September. By mid-September, essentially all of the Ruby-throated at feeders are migrating through from farther north, and not the same individuals seen in the summer.
So reading the article for this question What do you think how to answer this question?
If there are blooming flowers around, the hummingbirds will be there, but if not they will migrate. Great question and gives us some food for thought. Till next time, this is Becky Litterer from Becky's Greenhouse, Dougherty Iowa