Three days ago we had swarms of hummingbirds. We were refilling feeders every day. Suddenly, now, barely a bird. One or two here and there. There are still a few ruby-throated migrants, but not very many. As migrants, they might hang around for a few days, or even a week each, but eventually they move on. Even though they don’t flock, they don’t travel as a defined group, they might still arrive or leave together. That seems to be what happened. They all got the same idea at the same time, and poof.