On one night in May, there were 700 million birds in the air over the U.S.

Birding friends have told me that spring migration was disappointing this year. In particular, they said, the warbler flight was very small. As with so many things, it depended on timing. Migration flights are tracked by radar these days. Estimates of the number of migrants show that the flight was concentrated into two groups of nights. May 1-2 and May 2-3 were prime. Two weeks later flights again were good — the nights of May 13-14, May 14-15, and May 15-16. The days following those night flights would/could/should have been good for migrating birds. For the night of May 14-15 it was estimated that 700 million birds were in the air somewhere over the continental U.S. The best day, then, was May 15, depending, of course, on local conditions.