This Northern Cardinal (Cardinalis cardinalis) has female plumage on its right, and male plumage on its left, a condition known as bilateral gynandromorph.

Bilateral gynandromorphy is a condition in which one half of a bird’s body appears as a female and the opposite half appears as a male. Often, the left side is female and the right side is male.

This condition occurs in a variety of bird species, with the most frequently reported species being the Evening Grosbeak (Coccothraustes vespertinus).

To date, almost all observations of wild ‘halfsiders’ have been brief, single observations, or descriptions of collected birds without detailed or prolonged observations of their behaviors.

In a paper published in the Wilson Journal of Ornithology, Prof Brian Peer of Western Illinois University and his colleague Robert Motz report the most extensive observations of a gynandromorph bird in the wild – a rare Northern Cardinal with the brownish-gray feathered appearance of a female cardinal on its right side and that of a male’s red feathers on its left side that was spotted several years ago in Rock Island, IL and was observed from December 2008 to March 2010.

The scientists documented how the cardinal interacted with other birds on more than 40 occasions during that time period and how the bird responded to calls.

They never observed the bird singing and never saw it paired with another cardinal.

“We never knowingly heard the gynandromorph cardinal vocalize nor was it obviously paired with another individual, whereas other cardinals in the area vocalized and were paired, especially as the breeding season approached,” the scientists wrote in the paper.

“Based on our observations, it was unclear whether the bird was ever mated or whether it was capable of vocalizing.”

The bird was never subjected to unusual aggressive attacks from other cardinals.

“The gynandromorph we observed fed amongst conspecifics in addition to other species such as Black-capped Chickadees (Poecile atricapillus), Dark-eyed Juncos (Junco hyemalis), Song Sparrows (Melospiza melodia), and Mourning Doves (Zenaida macroura).”

“At times the bird appeared somewhat less likely to feed when others were present; however, on one occasion it drove a conspecific from the feed as is typical of normal cardinals.”

The scientists said: “these observations increase our limited knowledge of the behavior of wild bilateral gynandromorph birds that are rare and difficult to observe.”

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Brian D. Peer & Robert W. Motz. 2014. Observations of a Bilateral Gynandromorph Northern Cardinal (Cardinalis cardinalis). Wilson Journal of Ornithology 126 (4): 778-781; doi: 10.1676/14-025.1