Sunday, August 18

The Least Bittern nocturnal call

The Least Bittern is likely to call frequently during nocturnal migration, as the American Bittern and other herons do. Identification of the presumed nocturnal call has been based on its similarity to an infrequently heard diurnal call, and to nocturnal flight calls of the Eurasian Little Bittern. However, documentation of this call by terrestrial Least Bitterns has been almost completely lacking. In fact, Nathan Pieplow, who terms it a "squeak", states in the Peterson Guide to Bird Sounds that there are no such recordings of it.
Recently I was able to obtain two recordings of single squeak calls on different mornings by a bird in a local marsh. These were spontaneous calls made by a bird hidden in vegetation. The tone of these terrestrial calls is a little different from the nocturnal calls, but there is a definite similarity on the spectrograms. This seems to confirm that the presumed nocturnal calls are indeed made by migrating Least Bitterns. There is also one xeno-canto recording, by Paul Marvin, of a bird seen making this call in a flight over a marsh.
Nocturnal calls:
(early Aug, PA)

(early October, PA)

(mid-Sept, PA)

Calls by terrestrial birds:
(July, PA)

first call (Aug, PA)

The Xeno Canto recording (July, Fl)

The call is fairly distinctive, but note that some of the many varied nocturnal flight calls of the Rose-breasted Grosbeak can sound similar. Sonagram analysis can be very helpful in these cases.

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