Males of a number of warbler species sing only one song, so that individuals can be identified by ear or sonagram.
For example, this Kentucky Warbler was recorded in May, 2007 at Glassboro WMA in New Jersey, and (possibly the same bird) again in May, 2008.
Another Kentucky Warbler at the same location (May)
These Worm-eating Warblers were singing at the same location (Glassboro WMA, NJ) on the same day in May, showing the amount of variation between different males.
Slow versions are similar to Chipping Sparrow
Worm-eating warbler and Chipping Sparrow singing together (Pine Warbler in background at 16s, May, NJ)
The Worm-eating Warbler uncommonly gives a more extended song with a mixture of clear notes and trills, the so-called flight song. It may also be given during episodes of agitation or excitement, as this recording was made while observing a foraging family group (parents plus fledglings), with alarm chips, flight calls and twitters also being heard (June, NJ).
time scale reduced
A different bird, in flight and agitated near a recently depredated nest (June, NJ).
Individuals of the following species also sing only one song:
Kirtland's Warbler (May, MI).
Orange-crowned Warbler (June, AK)
Wilson's Warbler (June, AK)
Wilson's Warbler extended song (BNA states there is no evidence for an extended or flight song; this may be plastic song by a migrant, May, PA).
Palm Warbler (eastern), a trill, similar to Pine Warbler but slightly buzzy (with chip calls, migrant, Mar, PA).
note the alternate inverted chevrons and buzzy notes
(eastern race, migrant, April, PA)
Yellow-throated Warblers reportedly sing only one song (BNA), but the birds I listened to at Belleplain State Forest, NJ in mid-April, 2009 would on occasion add an accent to the end of the song (dominica ssp).
The birds on Bull's Island, NJ are of the albilora subspecies (May, NJ).
Individuals of the following species sing only one song during the day but in addition have a distinct extended or flight song, which is usually given in flight at dusk, but can also be heard from perched birds.
Common Yellowthroat (July, ME)
Common Yellowthroat males often rise into the air briefly and sing a complex flight song. This one has a least seven different components (July, PA).
reduced time scale
Ovenbird (Apr, NJ)
Ovenbird flight song (also termed attenuated song). In this case the so-called flight song of the Ovenbird was given by a walking bird that appeared to be under stress by my presence close to a nest (May, NJ).
reduced time scale
This is the second half of a true Ovenbird flight song, as the bird descended to the ground (10 minutes after sunset, June, NJ).
Northern Waterthrush (migrant, May, PA)
Louisiana Waterthrush (Apr, PA)
Prothonotary Warbler (May, NJ)
Mourning Warbler (migrant, May, PA)
(migrant, May, PA)