Extraordinary Bird Found in US, which is half male and half female

Pennsylvania: Powdermill Avian Research Center banded the rare bird named Rose-Breasted Grosbeak. The bird found in the US at Powdermill Nature Reserve in southwestern Pennsylvania on Thursday is a bilateral gynandromorph which means it is half female and  half male . This bird was aged as an after-hatching-year, meaning it hatched last year at the earliest. Male Rose – Breasted Grosbeaks have black wing feathers and pink wing pits, females have brown wings and yellow wing pits. The grosbeak spotted at the reserve was split right down the middle — pink on the right side, yellow on the left.

So far, the Powdermill Bird Banding project in 60 years of history has caught ten of these extraordinary birds, the most recent of which was a Rose-breasted Grosbeak. Another type of bilateral gynandromorph form is Northern Cardinal, an Evening Grosbeak, and an Eastern Towhee.  Although this unusual RBGR would be an even more amazing sight to see in its breeding plumage next spring as per the blog on the Powdermill blog.

A bilateral gynandromorph, as stated in John Terres’ Encyclopedia of North American Birds, is a term used for an animal in which part of the body is genetically female and part is genetically male.  This phenomenon is better known in butterflies and once thought to not occur in higher vertebrates because of the overriding influence of sex hormones on secondary sexual characteristics, but this bird is actually the fourth example of this rare genetic anomaly observed at Powdermill.

The bird body aesthetics showed subtle but clear signs of bilateral gynandromorphism, with the male half on right side showing dark pink edging on the lesser wing coverts, compared to the olive edging on the left hand female side. The male side showed replacement of one Juvenal tertial with a blackish first basic feather.   The wing length on the male side was 100.5 mm, while that on the female side was just 97.5 mm.  This same bird was recaptured on Sunday, September 18, in a more advanced stage of first pre basic molt, and weighing 42.2 grams, or 1.4 g more than at its original capture.

Powdermill Nature Reserve is the field biological station of Carnegie Museum of Natural History; the Reserve is located in the Laurel Highlands region of southwestern Pennsylvania.  The Powdermill  has initiated a land bird banding program since 1961. Birds are identified to species, banded i.e. – information about their age, sex, wing length, fat deposits, and body mass is recorded.