Researchers and bird-lovers were in awe when they spotted a rare bird that had both male and female characteristics at a nature preserve in Barrington.The mysterious bird, a bobolink, was a bilateral gynandromorph: Its body was divided right down the middle, with one side having male characteristics , the other side female.Luke Dahlberg, a conservation seed program manager with Citizens for Conservation and a longtime birder, first spotted the bird May 10 at the organization’s Hill ’N Dale Preserve. He dubbed it “Black and Tan,” for its dual colors.“It was just straight down the middle,” Dahlberg said.Experts say its discovery can help provide a greater look into the condition.Dahlberg was photographing bobolinks returning for the summer when he noticed one bird that was different from the others. At first, he thought the unusual coloring might have been the result of molting.But when he came back weeks later to the same spot, he saw it again and immediately could tell the color divide was nature's doing. Male bobolinks have distinctive black-and-white breeding plumage. Females are more muted brown and golden. Black and Tan displayed both patterns, making the bird instantly recognizable.Dahlberg consulted other bird experts, including members of the Illinois Ornithological Society. They confirmed his suspicions.Brian Peer, a biology professor and ornithologist at Stephen F. Austin State University in Texas, told WBEZ that gynandromorphism is believed to result from an error during meiosis, the process that produces egg cells. With this mutation, the bird has male and female genetic characteristics displayed on separate parts of its body.Peer said the phenomenon is extremely rare. He said there have been only about 30 to 40 observations of gynandromorphic wild birds, though it can be hard to spot. It's most noticeable in species in which males and females have distinctly different appearances.Peer coauthored a study documenting a bilateral gynandromorphic northern cardinal observed in northwestern Illinois from 2008 through 2010. The bird was monitored over three winters, providing detailed information about its behavior.According to Dahlberg, Black and Tan had established a territory at Hill ’N Dale. That allowed other volunteers to observe the bird throughout the summer.Black and Tan behaved largely like a male bobolink, singing a song typical of males of the species.Observers also saw the bird interacting with a female and carrying insects to a location with apparent nesting activity.These observations could help researchers better understand how gynandromorphic birds behave and whether their behavior more closely resembles that of males, females or a combination.“Every time that we see one of these birds, it really contributes to our knowledge of that kind of phenomenon because it is so exceedingly rare,” Peer said.The bird is no longer at the preserve. Dahlberg's hoping it'll be back next spring.Bobolinks migrate thousands of miles between their breeding grounds in the northern United States and southern Canada and wintering grounds in southern Brazil and northern Argentina. ...read more read less