Rather than merely identifying this species as among the earliest “fall migrants” within the wood-warbler family, it’s apt to state the Yellow Warbler is an early “summer migrant.”
Dispersal and/or migration begins by mid- to late July throughout the majority of its eastern USA breeding range.
Migration of Yellow Warbler on the West Coast is not as early, typically initiating in August and peaking later in the month and into early September.
In addition, note this species has protracted migration, as some tardy individuals have been noted in Pennsylvania as late as October 1st and into late October from sightings in South Carolina and Florida.
Earliest arriving transients from the north into Mexico have been detected by late July. Most individuals, however, arrive in non-breeding territory by August, with peak numbers returning in September and October.