In early May Ruby-throated Hummingbirds and Baltimore Orioles return
Flycatchers such as Eastern Phoebe Great Crested Flycatcher and Eastern Wood-Pewees return early thru early to mid May
Sedge and Marsh Wrens, Rose-breasted Grosbeaks, Thrush (Hermit, Swainson's, Wood and Veery's) and Chimney Swifts return return from winter their habitats.
In early to mid-May, vireos and cuckoos return from their winter habitats.
Nighthawks return. They are not hawks, but members of the nightjar family. They are common in cities and around streetlights 'hawking' for insects.
Lilacs reach full bloom.
Peak of warbler migration varies between May 6 to 18.
Adult Purple Martins return to establish colonies early in month.
Peak of bird courtship. Listen for the morning chorus..
The year's first fireflies can be seen.
Chickadees and titmice become scarce at feeders as they nest and raise their young.
Eta Aquarids meteor shower starts in early-May. The peak viewing in Toronto is May 5 but continues through May 27