By Sally Siko

One of the best things about birding is that there’s always a potential to be surprised by something unexpected out in the field.
Case in point, a possible bilateral gynandromorph variation of a Northern Cardinal which I photographed last week at Bynum Bridge in Pittsboro NC.

If you look closely at the photos you can see that it’s colors are split right down the middle with bright red, male plumage on one side and buff-brown, female plumage on the other.

So, how does a Northern Cardinal end up being dual-plumaged?
It involves a cocktail of chromosomes, which work slightly differently than the X and Y sex chromosomes that mammals carry.
Female birds carry both sex chromosomes — which in birds are labeled W and Z — while males carry two Zs.
Gynandromorphy is thought to occur when female egg cells develop with two nuclei — so that one nucleus contains a single Z chromosome and the other contains a single W.
When that egg is fertilized by sperm carrying two male Z chromosomes, the egg develops with both ZZ (male) and ZW (female) chromosomes.
The bird then develops with half of its body containing male ZZ cells while the other half contains female ZW cells.
If this chromosomal mix-up occurs early on in the animal’s development, before many of their cells begin to divide, it can result in the sort of perfect bilateral split which may be the case seen in this bird.

In addition another thing that fascinated me was that I managed to capture a photo of the Cardinal with it’s male mate during a food exchange. Then the bird flew down into a shrub and settled onto a nest!
As it turns out, gynandromorphic birds will sometimes have at least one functioning ovary which means that they can lay eggs and reproduce.
Pretty neat huh?

Photos by @sally_siko of @bestlife_birding on my beloved full frame 50MP beast, the mighty @canonusa #5Ds