Home  |  About BBBO  |  ResearchEducationConservationBandingPhotosNews ArchiveLinks 


Bilateral gynandromorphy in a Black-throated Blue Warbler

One weird warbler was banded at BBBO this past spring. The bird was a Black-throated Blue Warbler that left banders Kelly Dockery and Jon Dombrowski a bit confused. Their confusion was well warranted as the bird was gynandromorphic, meaning that it displayed both male and female characteristics.

The left side of the bird resembled a typical male, with a solid black throat, bright blue wing color, and a bright white breast. The right side of the bird, on the other hand, revealed more female characteristics. The right breast had a yellow cast. The facial markings were relatively indistinct and tinged with the olive green color that is more typical of female Black-throated Blue Warblers. A distinct line was apparent down the center of the breast dividing the male and female characteristics.

Gynandromorphy is very rare in birds and little information can be found in the scientific literature. The bilateral plumage differentiation in this warbler possibly indicates that the bird had both an ovary and a testis. A similar bird was photographed in California in 1987.* Our warbler was banded, labeled as an “unknown” sex, and released to continue on to the breeding grounds where attracting a mate was likely a challenge.

*Patten, M. 1993. A probable gynandromorphic Black-throated Blue Warbler. 1996. Wilson Bulletin vol. 108. 

Photos by Jon Dombrowski.  Braddock Bay Bird Observatory 2007.