Seen carrying a caterpillar (?), so assumption is carrying food for young.
Birds I found flying about and perching on various trees. They were yellow on the face and breast, and brown on the back and wings. The birds were chasing each other around, making high-pitched, almost hissing calls.
The Blue-winged Warbler (Vermivora cyanoptera) is a fairly common New World warbler, 11.5 cm (4.5 in) long and weighing 8.5 g (0.30 oz). It breeds in eastern North America in southern Ontario and the eastern USA. Its range is extending northwards, where it is replacing the very closely related Golden-winged Warbler, Vermivora chrysoptera.