An 'Extremely Rare' Half-Male, Half-Female Bird Temporarily Took Up Residence Outside of Chicago

A half-male, half-female bird has Chicago-area birdwatchers atwitter. Scientists say an eye-catching bobolink with both male and female characteristics temporarily took up residence at a nature preserve just west of Chicago, giving some lucky birders a rare chance to observe one of nature’s most intriguing biological phenomena up close. The bobolink is what’s known as a “bilateral gynandromorph.” Because of a genetic anomaly, the right side of its body is male while the left side is female, with a straight vertical line dividing the two halves.

It’s believed to be the first documented gynandromorphic bobolink. A post shared by Cameron Rutt (@cameronrutt) Luke Dahlberg, conservation seed program manager for the nonprofit Citizens for Conservation, first spotted the bird this spring at the group’s 246-acre Hill ‘N Dale Preserve in Barrington Hills, about 40 miles northwest of downtown Chicago. He spent a day in May photographing male bobolinks in their striking breeding plumage—black-and-white with a golden patch on the back of the head—as they returned from their wintering grounds in South America.

But when he got home and looked through his photos, he was surprised to spot a bird with a very different appearance: a full-body profile of tan-gold feathers. Dahlberg shrugged it off, thinking that perhaps the creature just had an unusual molt pattern. Outside of breeding season, males sport the same yellow-brown coloration as females, after all.

But a few weeks later, back at the preserve, he spotted the very same bird. That’s when he noticed it had male plumage on one side of its body and female plumage on the other. Ornithologists later confirmed the creature’s status as a bilateral gynandromorph.

Rutt had never seen a gynandromorph in person, so he was “thrilled,” he tells WTTW. And in the end, the creature succeeded: According to WTTW, it nested, reproduced and raised fledglings. The bird has since left the preserve, reports the Chicago Sun-Times’ Elijah James, but Dahlberg hopes it will return next spring.

Earlier this year, fishers caught a rare 1-in-50-million “split-color” lobster off Cape Cod. The creature was fully female—so not a gynandromorph—but it still had two sets of genetic information in its body, which caused one side to be orange and the other to be brown. In lobsters, split colorization is thought to result from one fertilized, unlaid egg absorbing another fertilized, unlaid egg.