The variances between the sexes of the European goldfinch are subtle and cannot be determined with a quick glance. This is particularly true before the bird reaches sexual maturation. Close study of three of the adult bird's physical characteristics will be necessary in determining the sex, as it is the intensity of shared colours and head shape where the main physical differences are most apparent. There are also two nonphysical characteristics which can be used to tell between the male and female of the species.
Observe several European goldfinches and you will see that they are all of approximately the same size and colour. They are 5 to 6 inches in length with red faces and black wings bearing broad yellow bands. Both sexes will share black and white feathers on their head, a white rump and will have black tail feathers. The bird's bill will be pointed with a broad base.
Look first at the red mask of the European goldfinch. The mask of the male will be an intense red covering the entire face of the bird and continuing above and behind the eyes on to the head. The female will have a red mask but it will appear faded as compared to the male and will not continue above or behind the eyes.
Examine next the wings of the bird. The wings of the male will be jet black in colour with a very bright, well defined yellow band. A female's wings, much like the mask, will be similar but will lack colour intensity. Her wings will be more of a dirty brown with the yellow band being far less bright than that of the male.
Observe now the head of the bird. The head of a male European goldfinch should appear somewhat flattened and less rounded than that of the female. The female's head will be black and far more round in shape than the male of the species.
Determine the nonphysical differences by first listening for the song of a European goldfinch. If the bird is singing, then it is without question the male of the species.
Locate the nest of a European goldfinch during the springtime mating season. It is the male which can be observed foraging for food while the female builds the nest in preparation for the coming eggs. Once the eggs are laid, the female remains in the nest and acts as an incubator to her offspring. A lone adult European goldfinch in its nest with eggs can be identified as a female of the species.
Telling males and females of the species apart will be easier if you can observe multiple birds at once. This will allow you to compare and determine which holds the more intense and defined colours in its plumage.