Rare Half-Male, Half-Female Bobolink Spotted Near Chicago

At Hill 'N Dale Preserve in Barrington Hills, Illinois, roughly 40 miles northwest of Chicago, a unique bilateral gynandromorphic bobolink was spotted, showcasing male feathers on its right side and female feathers on its left. Luke Dahlberg, who manages the conservation seed program for Citizens for Conservation, first captured images of the bird in May 2025. Initially believing it was experiencing an unusual molt, he soon recognized its distinctive split-sex characteristics. Ornithologists later verified it as the first known gynandromorphic bobolink. Dubbed 'Black and Tan,' the bird was also photographed extensively by Cameron Rutt, a conservation ecologist at the Field Museum, who took around 1,000 pictures. This bird exhibited typical male behavior, singing and establishing a breeding territory, successfully raising fledglings before departing the preserve. Gynandromorphism has been documented in fewer than 100 birds across approximately 45 species, possibly resulting from errors during female meiosis, as noted by ecologist Brian Peer from Stephen F. Austin State University. Previous instances include a gynandromorphic northern cardinal in Illinois (2008-2010), a split-sex cardinal in Pennsylvania (2019 and 2021), and a green honeycreeper in Colombia (2023). Dahlberg remarked on the bird's rarity, stating, "I had a better chance of photographing a unicorn."