Researchers at a nature reserve in Pennsylvania discovered a truly odd bird - one with both male and female feather coloring.
Rose-breasted grosbeaks are sexually dimorphic, meaning males and females have different color plumage.
Males have black wing feathers, pink wing pits and breast spots that give it its name, while females have brown wings, yellow wing pits and no patches on their chest.
But a grosbeak observed at Powdermill Nature Reserve was split right down the middle - pink on the right side, yellow on the left.
The condition, called bilateral gynandromorphism, means the bird is both male and female, with one ovary and one testis.
This occurs when two sperm fertilize an egg that has two nuclei instead of one, which results in the egg to develop a chromosome from each sex
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Conservationists at Powdermill Nature Reserve described finding a rose-breasted grosbeak with bilateral gynandromorphism like 'seeing a unicorn.' The bird was born with male and female plumage colors split down the center of its body
The phenomenon has been observed in less than ten birds since Powdermill's Avian Research Center began bird banding 64 years ago.
'The entire banding team was very excited to see such a rarity up close, and are riding the high of this once-in-a-lifetime experience,' said Annie Lindsay, bird banding program manager. 'One of them described it as 'seeing a unicorn.'
A large, seed-eating member of the cardinal family, the rose-breasted grosbeak (Pheucticus ludovicianus) is commonly found across eastern North America until this time of year when it migrates to Mexico and South America.
Since usually only the left ovary is functional in birds, and the left side of this bird is the female side, Lindsay says the bird could still theoretically lay eggs and reproduce.
Male red-breasted grosbeaks have larger black feathers, with pink wing pits and a pink splotch on their chest. Females have brown feather, with yellow wing pits and a thick white line above their eyes
The grosbeak's bilateral asymmetry is visible on its back, as well. The feathers on the right (male) side of the bird are black and larger than the brown (female) ones on the bird's left
Usually only the left ovary is functional in birds, so this bird