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.