Two long-time bird feeders got a surprise when they spotted a little bird, half-red and half-yellow, sitting in a tree outside their home.
The cardinal was a bilateral gynandromorph. In a nutshell, half its body is male, while the other half is female.
‘This remarkable bird is a genuine male/female chimera,’ Daniel Hooper, a postdoctoral fellow at the Cornell Lab of Ornithology, told National Geographic.
The bird’s two-colored nature was the first giveaway. It was red on one side and yellow the other, the split coming right down the middle of its body.
‘Cardinals are one of the most well-known sexually dimorphic birds in North America—their bright red plumage in males is iconic—so people easily notice when they look different,’ Hooper says.
The bird was spotted by Jeffery and Shirley Caldwell in Erie, Pennsylvania. The couple has been feeding birds for 25 years.
‘Never did we ever think we would see something like this in all the years we’ve been feeding,’ Shirley said.
Cardinals display a range of 18+ rare color variations. The yellow one is striking but there is also the (likewise very rare) red/white gynandromorphic cardinal. h/t a.q.effro https://t.co/VCjTYIjK5h ~ @CryptoLoren pic.twitter.com/iOrkyFM1WO
— Loren Coleman (@CryptoLoren) 27 February 2018
Different sex determination from mammals
Birds have different sex determination from mammals, where females have two X chromosomes and males have both the X and Y chromosome.
However, with birds the opposite is true.
In birds’ Z and W chromosomes, Hooper says, the females have one of each chromosome (ZW), while males have two of the same (ZZ).
Male birds produce on Z-carrying sperm, while females produce either Z- or W-carrying eggs. The sex of the bird is thus determined by the egg that is fertilized.
Gynandromorphy occurs when a female egg develops with two nuclei, with both a Z and a W chromosome. This makes it ‘double fertilized’ by two Z-carrying sperm.
The bird then develops with one half of its body being male, the other half being female.
— Andrew McAfee (@amcafee) 7 January 2015
‘This one may actually be fertile’
‘Most gynandromorph individuals are infertile, but this one may actually be fertile as the left side is female, and only the left ovary in birds in functional,’ Hooper says.
Gynandromorphy is common in certain species, such as crabs and butterflies.
In July last year, trans rights activists adopted lobsters – which are also gynandromorphs – as a surrogate symbol of trans rights, and as a way to have the trans rights flag added as a messaging emoji.
— カモノハシ (@roso1954) 24 September 2015