Black-throated Blue Warbler Dendroica caerulescens
Flight call description A short, abruptly rising "stip". Nocturnal migrants often give a double call with the notes about a half-second apart.
Fig.1. Maryland September 30, 1994 (MO).
Bird in flight.
Similar species Distinctive. Dark-eyed Junco's flight call may be similar but is higher and is typically delivered in a quick rattle-like series of two or more notes. See Lark Sparrow and short rising seeps.
Behavior Primarily a nocturnal migrant but engages in redetermined migration. Gives flight call regularly while perched and in flight during the day as well as during nocturnal migration.
Spectrographic description Measured calls (N=10) were 18.4-30 (23.7) mS in duration and in the 6.3-10.7 (6.4-9.6) kHz frequency range. The frequency track was abruptly rising, often with a small squiggle in the middle. Occasionally, after the abrupt rise, a sharp descent followed.