The song of several sparrows and warblers is a trill. To tell them apart note the length of the trill, if it is steady or accelerating, on one pitch or rising, and if there is a distinct final note.
Black and white warbler
Trill formed with couplets
Chipping sparrow
mechanical, 2-3 second trill
Field sparrow
Accelerating trill
Pine warbler
Musical 1.5-2 second trill at one frequency
Northern parula
Rising trill ending with a separate zip note
Prairie warbler
Rising trill sometimes ending in a buzz
Swamp sparrow
Irregular musical trill all on one pitch
Worm-eating warbler
Very fast unmusical trill lasting about 2 seconds
