There are two methods. The most common form is observation, since most species have what science calls sexual dimorphism – that is, distinct physical characteristics between males and females. This occurs in animals from different families and orders, such as chickens, ducks and sparrows. The evolutionary explanation for this dimorphism, according to a study published by American biologist Russell Lande, would be that most birds are monogamous. As they can only have a single partner to mate with, males would need to attract females through physical skills. However, there are species in which it is not possible to perceive visual differences, such as thrushes. In such cases, there are techniques for making the discovery.
SEXUAL DIMORPHISM
– (Bruno Rosal/)
“The males are generally more showy and have more exuberant plumage than the females”, says Luís Fábio Silveira, curator of the ornithological collections at the USP Museum of Zoology. Furthermore, in several species, one of the genera is larger than the other – female hawks and falcons are larger than males, for example.
OTHER CASES
– (Bruno Rosal/)
In birds without dimorphism, such as thrushes, herons and storks, sexing – that is, the technique used to determine sex – is done by laparoscopy or molecular analysis. The first consists of an incision made in the bird’s abdomen to identify the organs of the reproductive system (testicles or ovaries). Molecular analysis is the famous DNA test. Through blood, feather or eggshell samples, it is possible to detect whether or not there is a gene found exclusively in females.
Reader Question Vladimir Kowalsky, Bethlehem, PA
CONSULTANCY Luís Fábio Silveira, curator of the ornithological collections of the Zoology Museum of the University of São Paulo, and Giovanni Nachtigall Maurício, professor of the postgraduate program in Animal Biology at the Federal University of Pelotas (RS)
SOURCES Antarctica and the Arctic Circle: A Geographic Encyclopedia of the Earth’s Polar Regionsby Andrew Jon Hund