Mind-Blowing Animals That Swap Sexes

7. The Fascinating World of Gynandromorphic Cardinals: A Study in Avian Sexual Dimorphism

Long prized for their beauty and unique look, northern cardinals feature bright red plumage in males and more muted brown-gray feathers in females. But rarely, a rare and amazing occurrence within cardinal populations captivates both ornithologists and casual bird observers equally: bilateral gysandromorphosis. This amazing disorder produces a cardinal that is rather literally divided down the middle: one half of its body shows the vivid red feathers typical of males, while the other half shows the subdued brown-gray plumage typical of females. Though it seems almost impossible in nature, the visual impact of such a bird is quite amazing and reflects the complicated interaction of genes and development in avian species. Not only a surface anomaly, bilateral gyneandromorphism in cardinals is a trait that influences birds fundamentally biologically. The obvious visible difference between male and female traits reflects an underlying genetic mosaic in which cells on one side of the body have male chromosomes and those on the other side have female chromosomes. Early in embryonic development, this genetic break probably results from a mistake in cell division soon following fertilisation. The two genetically different cell populations create tissues and structures with either male or female traits as the embryo grows, therefore producing an adult bird that is exactly half-and-half between the sexes. Because gendered andromorphic cardinals are rare, any sighting in the field of ornithology is a major event. One especially interesting case was the focus of a thorough investigation carried out between 2008 and 2010, which gave insightful analysis of the social contacts and behaviour of these unusual people. Because of its divided look, the gendered andromorphic cardinal—also known as the "half-sider—exhibited behaviours that distinguished it from its wholly male or female counterparts, the researchers said. Most remarkably, the bird was never seen vocalising or displaying mating activities over the whole monitoring time. This absence of usual reproductive activity begs interesting issues regarding the physiological and neurological effects of gyneandromorphism on avian behaviour and reproductive capacity. One of the most encouraging features of the study, despite its odd look and behaviour, was the fact that the gendered cardinal seemed to be well-accepted by its conspecifics. Other cardinals in the vicinity did not seem to treat the half-sider differently or show any aggressive or excluding actions towards it, the researchers observed. This acceptance begs important issues regarding how birds view and react to individuals that stray from the norm and indicates a degree of social flexibility inside cardinal populations. The gendered andromorphic cardinal's ability to fit into its social group without seeming prejudice offers a moving illustration of natural world tolerance and promise for the survival and well-being of these unique individuals in wild populations.