ONCE-IN-A-LIFETIME BIRD: Biologists made a “once-in-a-lifetime” discovery of a bird that’s male on the right side and female on the left. The rose-breasted grosbeak (Pheucticus ludovicianus), was captured during regular banding operations at the Carnegie Museum of Natural History’s Powdermill Nature Reserve, an environmental research center in Rector, Pa.

This condition, in which an animal possesses male and female traits divided down the middle of its body, is called bilateral gynandromorphism. In birds, gynandromorphy is thought to stem from an error during egg formation.

Plumage colors usually signal if a grosbeak is male or female, but this bird has both sexes’ signature shades. Scientists who captured the bird saw male coloration — pink wing “pits,” a red breast splash and black wing feathers — on the right side of its body. But the bird’s left wing was browner and had yellow “pits,” a color combination found in females, museum representatives said in a statement.

“Every member of the banding crew expressed delighted surprise and joy in experiencing the banding of this rare bird,” said Annie Lindsay, Powdermill’s Avian Research Center (ARC) bird banding program manager. “The bird received an individually numbered band just like all birds we catch,” Lindsay told Live Science in an email.

The scientists recorded the grosbeak’s age, sex and body measurements. They then collected feathers for genetic analysis and took photos and video before releasing the bird.

The ARC has collected and banded birds since 1961, and its dataset holds more than 800,000 records. In that time, scientists have documented only five examples of bilateral gynandromorphs, Lindsay said.