The Bay-breasted Warbler has a flight call that is part of the zeep complex, a collection of calls from around a dozen different birds that sound almost identical. Differentiating them is exceedingly difficult, and sometimes impossible for many of the species.
Evans and O'Brien (2002) puts stock on the sound quality for the new listener, describing the dseet as low and sweet, as well as noting the slowness of the call. However, for novices unused to hearing the different calls, there is another publication from Landsborough (2017), where he analyzed most of the birds in the zeep complex and differentiated the BBWA as being the only bird with a significantly long wavelength.
While there is some discussion as to how the BBWA sounds nocturnally versus diurnally, in general, this is one of the easier zeep calls to identify.
Bull and Farrand (1994) only mentions the song. Sibley (2016) notes:
Call a clear chip. Flight call a short buzz like other Setophaga warblers.
Pieplow (2017) notes of the dzit call:
Very short, high, burry. Likely all year, including by night migrants. Rather variable and plastic.
He also notes a downslurred version, which may match Evans and O'Brien (2002), who notes that Bay-breasted give descending NFCs:
A relatively low, sweet "dseet" with a muffled, buzzy quality. Nocturnal flight calls tend to be descending and more pure-toned than diurnal flight calls. ... Shorter and less buzzy than most other zeep calls. Blackburnian Warbler sounds equally short but is usually higher, sweeter, and less sibilant. Surprisingly similar in quality and pitch to American Redstart, though when heard well, clearly in the zeep category.
And:
Gives flight call regularly while perched and in flight during the day as well as during nocturnal migration.
Stephenson and Whittle (2013) note of this warbler's "rising dense buzz":
Buzzy; dense; initial downslur keeps from having smooth profile; gives this call during day; distinctive.
Dunne (2006) notes:
Flight call is a short, soft, high "che'e," given with a slight vibrancy, that sounds like Blackpoll but is thinner and less buzzy.
Dunn and Garrett (1997) note:
Flight Note is a buzzy zeet, also very similar to flight note of Blackpoll.
These are all quoted directly from Landsborough (2017)
Evans and O'Brien (2002) notes:
The frequency track had a variable slope and was single-banded or with a faint second band. It was modulated with 1-3 (2) humps with a spacing of 18.1-24.7 (21.8) mS and a depth of 840-1700 (1300) Hz.
Here is a good example of this particular call.
Other calls:
This section may not be helpful. The idea is to make it easier to rule out other species more easily without going through the whole list, which may not be possible.
When describing this call in comments on an NFC checklist, try and add as many salient notes as possible and refer to this page for justification. If there are any species which seem similar, please get in touch so we can add them here. The intent here is to have a full list of differences for each possible similar call.
Pieplow notes 20 different birds who give dzit calls, 11 of which are in the same category as the Bay-breasted. Evans and O'Brien give 11 similar species in his Zeep calls complex page. Interestingly, these aren't the same 11 - Pieplow notes the Blue- (BWWA) and Golden-winged Warblers (GWWA) and Dark-eyed Junco (DEJU), while he puts the two Waterthrushes and Kentucky Warbler in a different category, noting that they are "often slightly rising"). Part of this is because Pieplow isn't interested in just NFCs, but all calls. DEJU can be safely eliminated at night, as Evans and O'Brien (2002) notes, "Zeee call has not been documented in nocturnal migration."
Landsborough studies the calls of nine similar birds, but doesn't include Kentucky, BWWA and GWWA. This is important, because Landsborough found that BBWA is statistically different in their inter-peak distance. As this is the most salient feature, it is worth checking the interpeak distance of these three species he didn't check. The following are from Evans and O'Brien (2002):
There is more to be said about the nature of zeep calls. Not all calls with a wide-spacing as the only noted feature would be BBWA. But, in short, this mean that Bay-breasted Warbler can safely be considered the only bird with such a long spacing of waves.