Females are usually a mixture of gray, light-brown and red. But the cardinal Ammann saw was male-colored on the left, but female-colored on the right. The bird also sported a crest on its head usually reserved for males.
Ammann, a statistics professor at the University of Texas in Dallas, spotted the bird at his backyard feeder one morning and was puzzled, because he only saw the gray side but also noted the bright red crest.
"Intrigued, I continued to watch until she turned around so I could see her other side. Suddenly, what originally seemed to be a female cardinal now looked just like a male!" said Ammann in his firsthand account.
He rushed to grab his camera to document the confusingly colored cardinal. The complete collection of photos, along with other avian art and brilliantly colored satellite imagery, can be seen at Remote Sensing Art.
After snapping a single shot, Ammann watched as the cardinal flew away. But that was all the evidence he needed to start solving this mystery of the two-tone cardinal.
"In just a few hours I learned, in a reply to one of my Web queries, that this bird is an extremely rare bilateral gynandromorph cardinal," Ammann said.
"Quite a mouthful to say, but this means a genetic mistake occurred during the first cell division of the fertilized ovum, causing one of the cells produced by this division to be male and the other to be female. As this egg developed, the entire right side remained female and the left side remained male," Ammann continued.
This condition isn't unheard of in other birds, but is particularly noticeable in cardinals.
"The obvious differences in coloration between male and female cardinals, referred to as sexual dimorphism, makes gynandromorphy very noticeable when it occurs in cardinals," he explained.