A bird skipping by the window recently is the weirdest Shirley and Jeffrey Caldwell have ever seen.

His left side is the taupe shade of female Cardinals; his right, the scarlet signature of the males.

Researchers believe that the Cardinal attending Caldwell's bird feeder in Erie, Pennsylvania, is a rare bilateral, half-male and half-female gynandromorph. The unusual phenomenon is poorly known, but this sexual fracture has been reported in birds, reptiles, butterflies and crustaceans.

No one can be sure that the bird is a gynandromorph without having analyzed its genes with a blood test or necroscopy, but the division of plumage in the middle is characteristic of this rare event, according to Daniel Hooper, biologist of evolution at Cornell University's ornithology laboratory.

He said that gynandromorphs could theoretically be created by the fusion of two separately fertilized developing embryos.

It is also possible for a female to produce an egg containing both copies of her sex chromosomes, Z and W, and is then fertilized by two spermatozoa, each with a Z chromosome. Human sex chromosomes are labeled XX for females and XY for males, female birds are ZW, and ZZ males.) Scientists do not know exactly how such an egg produces a chick with ZW and ZZ cells.

The division is done in the middle of the bird simply because vertebrates develop bilaterally and symmetrically. Although one side is largely composed of ZW and the other of ZZ, previous research suggests a mixture of cells in the body of the bird.

But essentially, each side of the bird would be largely the brother or sister of the other. Genes other than those conferring gender are also affected.

The determination of sex in mammals is controlled by a gene located on the Y chromosome that stimulates the development of the testes, whose hormones regulate the development of the rest of the body. That's why gynandromorphism is so rarely seen in mammals, said Dr. Hooper.

He sees no reason for cardinals to be more likely to be of mixed sex than other creatures, but their color contrast by sex is particularly remarkable.

The cardinal women are taupe in color and are quieter than their brightly colored companions. In addition to their red color, male cardinals sing more often and with more complicated tunes, both to declare their territory and to attract women.

In 2008, Brian Peer, professor of biology at Western Illinois University of Macomb, Ill., Began studying a cardinal with a similar division in the middle. Over the next two years, he visited the backyard of a retired high school biology teacher more than 40 times, whose bird feeder had drawn a male, half-right, male bird-unlike Cardinal of Caldwell.

[ Like the Science Times page on Facebook. | Sign up for the Science Times newsletter. ]

An expert on cowboy behavior, Dr. Peer, was hoping to see if the cardinal behaved more in this way. a woman or a man. Unfortunately, he has never seen the bird with others, although he does not agree with the idea that the cardinal was alone – many cardinals have never mated in nature, he said.

Dr. His companion observed the bird for two winters, but he was eventually pushed out of the instructor's yard by a cardinal who defended his territory aggressively. The gynandromorph was not seen again.

The gynandromorphs would be infertile, although the Cardinal of the Caldwell Court seems to have associated with a male bird. Dr. Hooper stated that it was too early to know if this male was the father or partner of a mixed bird and would stay for the mating season.

Although birds have a pair of ovaries, the only functional is on the left side – which in this cardinal is a female, so it is theoretically possible that it can lay eggs said Dr. Hooper. He expected that any offspring would be genetically conventional because his oocytes would have only one sex chromosome.

Dr. Hooper stated that he would like to be able to study the bird in depth, learn about its genetics and also understand how its brain works. In the gynandromorphs, half of the brain is also a woman and the other half.

Male songbirds have many more neuronal connections in their brains that allow them to sing complex tunes. He wonders how a half-half brain would affect the cardinal's ability to learn, evaluate and produce songs.

"I imagine," he said in an email, "there is simply no complete neural network to produce a song or the appropriate hormonal cocktail in the brain in circulation. " motivate the bird to sing one, even if it can.

Butterflies can also be gynandromorphs, said Josh Jahner, postdoctoral researcher at the University of Nevada at Reno, in half or even more varied ways.

During his research, Dr. Jahner discovered that the wings of gynandromorph butterflies were similar to those of typical butterflies – although male and female colorations appear on the same insect, but the genitals of each gynandromorph are different from those of the butterflies. of others, Dr. Jahner said Understanding why can help scientists understand the rules of development

For her part, Shirley Caldwell appreciates both the attention and the opportunity to look at the cardinal unusual and looking for patterns in her daily activities. "It's very rewarding to get to know the bird," she said. It's a unique thing in life, and it's fun. "