This from the Cornell Lab of Ornithology's subscriber website "Birds of North America" re: Ruby-throat spring migration.....
Males begin arriving along the Alabama Gulf Coast in late February, preceding females by 8�10days; birds still fairly common in Palo Verde, Costa Rica, as late as 14 March. Peak migration on the Gulf Coast (sw. Louisiana) in the second half of April, with males preceding females by about 3 days.
Males arrive at Powdermill Nature Reserve (Rector, PA) late April; females arrive about 2 weeks later. Males arrive in Vermont during first week of May. In Ohio, arrival dates range from 25 Apr to 2 May in s. Ohio and from 5 to 12 May along Lake Erie. Both sexes present in New Brunswick, Canada, by mid-May.
Peak northward movement (unlike in the fall) is not in synchrony with peak flowering of any particular plant species. Arrival on northern breeding grounds may depend on earlier arrival of Yellow-bellied Sapsucker to guarantee availability of sap in absence of reliable nectar production.
