It is currently peak breeding season and we at the Lesser Slave Lake Bird Observatory (LSLBO) are hard at work capturing, banding and observing those birds breeding in the area. In the Boreal Forest alone, 325 bird species nest and raise their broods over the summer, and over half of those are small songbirds who are indeed singing. For every one of these songbirds, there are variations in what we might call their basic song. Regional dialects distinguish birds raised on opposite sides of the country – or even just the other side of a mountain range – with further variants within an individual’s repertoire for various communications.
Songbirds like American Redstarts and Yellow Warblers take song variation to the extreme. One study on Yellow Warblers isolated forty different notes, which combined into sixty observed song patterns, with the theoretical number of possible patterns being in the tens of thousands (Bankwitz et al. 1979). From among these theoretical thousands, however, a single male may have just over fifteen distinct songs in his ‘setlist’ (Spector 1991).
Spring males are brighter with red streaking. 
Spring females are duller yellow with little-to-no red streaking.
The song a male Yellow Warbler will sing when establishing his breeding territory is not the same as the song he sings when faced with another male Yellow Warbler, or a female investigating the area for a potential mate, or even in response to a male Chestnut-sided Warbler who has a similar basic song. The identifiable mnemonic for this species of “sweet sweet sweet, I’m so sweet” happens to be most common for attracting a female (Stephenson 2022).
During the dawn chorus, males will alternate between various songs to counter sing against their neighbours or to chase off intruders. As singing slows down later in the day, they switch to a song preferred by the individual. The aforementioned sweet sweet sweet I’m so sweet song, with the rising end note, is called an Accented Ending. This pattern is common for a male’s personal song, while relegating a collection of Unaccented Ending songs with downward end notes for early morning territorial displays. Some males, however, might prefer using an Unaccented Ending (descending) pattern for their personal song instead, although the preference between one pattern or the other is not yet fully understood. A male’s personal song is often used to communicate with their mates, who respond with a call note (Spector 1991). Therefore it is possible to distinguish individual Yellow Warblers by the song they sing outside of the dawn chorus, though it may be difficult to do so purely by ear.
While more commonly associated with tropical non-migratory subspecies, female Yellow Warblers of our migratory subspecies have also been observed singing their own distinct patterns on rare occasions. Among these possible situations include older females exhibiting more male-like behaviours in the early breeding season, and in areas of high population density where females are forced into close quarters with other females (Hobson et al. 1990).
The primary vocalizations of female Yellow Warblers are call notes also shared by males. These include migratory flight calls, chip notes for territorial defense and predator alerts, and even a note specific to the presence of Brown-headed Cowbirds, which will parasitize Yellow Warbler nests by laying their own eggs within (Lawson et al. 2021).
While not all songbirds may have the variety in notes and patterns that these little warblers do, there are still plenty of species singing right now with different notes and variations waiting to be heard.
By Bronwyn Robinson, LSLBO Assistant Banders
References:
Bankwitz K, Thompson W. 1979. Song characteristics of the Yellow Warbler. Wilson Bulletin. 91(4): 533–550.
Hobson KA, Sealy SG. 1990. Female song in the Yellow Warbler. The Condor. 92(1): 259–261.
Lawson SL, Enos JK, Mendes NC, Gill SA, Hauber ME. 2021. Responses of female Yellow Warblers to playbacks signaling brood parasitism or predation risk: A quasi-replication study. Animal Behavior and Cognition. 8(2): 216–230. https://doi.org/10.26451/abc.08.02.08.2021.Accessed 15 June 2025.
Spector DA. 1991. The singing behaviour of Yellow Warblers. Behaviour. 117(1/2): 29–52.
Stephenson T. 2022. How to tell apart sound-alike warblers. Audubon [Accessed 15 Jun 2025].
