A composite image of the bobolink nicknamed Black and Tan, showing its male and female sides split down the middle. | Luke Dahlberg / Citizens for Conservation
By Patty Wetli | WTTW News
Back in early spring, Luke Dahlberg, conservation seed program manager with the nonprofit Citizens for Conservation, was spending his Sunday at the office.
His “office,” to be fair, is the 200-plus acre Hill ‘N Dale nature preserve near Barrington Hills, and Dahlberg wanted to take advantage of the lighting to photograph birds, specifically male bobolinks arriving on their breeding grounds after wintering in the pampas of South America.
“That’s when they’re just singing like crazy, they’re showing themselves,” Dahlberg said. “And usually the female bobolinks will come back a couple weeks afterwards.”
After snapping pictures of every bobolink in sight, Dahlberg went home and began scrolling through his camera roll. One bird stood out.
Male bobolinks, as with many bird species, have far more striking breeding plumage than their female counterparts. Dahlberg described the fellas’ white back and black undersides as looking like a tuxedo worn backwards, with a blonde patch on their heads lending a Dennis Rodman-circa-mid-‘90s vibe.
The bird in question didn’t quite fit the profile.
“It turned its face and it was in non-breeding plumage,” Dahlberg said, which struck him as odd but he chalked it up to a strange molt pattern.
A couple weeks later, Dahlberg pointed out this same unusual bobolink to some visitors from Illinois Audubon Society and that’s when he learned he had stumbled onto something extraordinary.
The bobolink was what’s called a bilateral gynandromorph — half female, half male, split down the middle — as the result of a genetic anomaly.
On its right side, the bird presented as male; on its left, it sported the duller plumage of a bobolink female.
“I had a better chance of photographing a unicorn,” Dahlberg said. “It’s extremely rare in nature.”
So rare that Abigail Derby Lewis, executive director of Citizens for Conservation, reached out to former colleagues at the Field Museum to confirm the ID.
“I’ve never seen one of these gynandromorphs in real life and so I was thrilled. I would definitely say the vast majority of birders will never see a gynandromorph in their life,” said Cameron Rutt, ornithologist and conservation ecologist at the Field. “Your chances of running into one, by yourself, in the wild are vanishingly slim.”
A 100% female bobolink on the left and a 100% male bobolink on the right. | hstiver / iStock; U.S. Fish and Wildlife Service
Of the approximately 11,000 species of birds on the planet, only 45 are mentioned in the scientific literature as exhibiting gynandromorphism, totaling fewer than 100 individuals, according to Rutt.
The bird at Hill ‘N Dale is the first-ever record of a bobolink gynandromorph.
Read on here.
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