The Living Museum vol. 68, no. 02,03; Summer, Fall 2006

              Illinois SightingsIllinois Sightings  
of Bilateralof Bilateral  
Gynandromorphismomorphism  
in Birdsds  
H. David Bohlen, ISM Assistant Curator of Zoology  
On March 15, 2006, while searching Sangchris Lake State Park near Rochester,  
Illinois, for new spring bird arrivals, I observed an odd-looking bird. I noted  
that it was a Northern Cardinal (Cardinalis cardinalis), but saw that when  
I viewed the bird on its right side, it had the plumage of a male and when I  
viewed on its left, it appeared to be a female. From either the front or back, the cardinal  
showed both plumages fairly evenly divided down the middle. The bird was singing, but  
this would not be unusual, since both male and female cardinals sing. I went back for my  
digital camera and telescope, then had difficulty relocating the cardinal in the brush, but I  
eventually got some photographs. Later, on April 10, the same bird was in the same place,  
and I took more photographs.  
I had seen a similar cardinal on December 6, 2002, just south of Springfield, though it  
was even more dramatically marked—the division line being sharper. It was generally the  
same, however: the right side was male, and the left side was female. I did not get photo- 
graphs on that occasion, nor could I find the bird on subsequent visits.  
With these sightings, I was aware that these were cases of a rare condition called bilateral  
gynandromorphism. This abnormal condition occurs when part of the body is genetically  
female and the other part is genetically male. This condition was responsible for the odd-  
looking cardinals.  
Still earlier, on March 19, 1986, I had salvaged a road-killed Eurasian Tree Sparrow (Passer  
montanus) three-and-a-half miles southwest of Springfield. I made a study skin of this bird,  
and as standard procedure, was internally examining the gonads when I noticed that it had  
a testis on the right and an ovary on the left (see photograph at right). The testis measured  
3.5 millimeters, and the ovary, 7 millimeters. Thus, this bird had both male and female  
sexual organs—but the abnormality did not show in the plumage, because Eurasian Tree  
Sparrows are not sexually dimorphic (that is, the males and females look the same). Some- 
times sexual dimorphism is apparent in external measurements, such as length of wings, tail,  
and tarsi, but this was not the case either in this specimen. Because the cardinals are visually  
sexually dimorphic, the plumage is strikingly obvious when gynandromorphism occurs (see  
photographs).  
In normal birds, the male has paired testes internally, and females have the ovary inter- 
nally on the left side (a few species, such as Northern Goshawk, sometimes have paired  
ovaries). Gynandromorphism is rare, but when it occurs, usually the male is on the right and  
the female on the left. Even more rare is the occasion when the plumage occurs the other way  
around, in which the female is on the right and the male on the left (this represents only  
about 15% of the total occurrences).  
Top: The female and male sides are apparent in  
the bilateral gynadromorphic Northern  
Cardinal. Photograph by H. David Bohlen.  
Directly above: A dissected ventral view of a  
bilateral gynandromorphic Eurasian Tree  
Sparrow showing a testis on the bird’s right and  
an ovary on the bird’s left side. Photograph by  
E. D. Cashatt.