In the same way, one can find seasonal harbingers elsewhere in the natural world. One of them is this species, Summer Azure, which shows up around the same time that Blackpoll Warblers are leaving. Summer Azure is part of a species complex that used to be known as "Spring Azure." Thanks to careful study of phenology, genetics, and microscopic traits, what once was one species is now several species, with a succession of overlapping flight seasons, starting in early spring and continuing through summer. Summer Azure is the last to appear and has two broods. In New Jersey the first emerges in late May or early June, and the second emerges later in the summer.
I photographed this Summer Azure in the Rutgers Ecological Preserve last week.