A neotropical migrant bird is a bird that spends the summer in its breeding range in North America, but migrates to Central or South America for its non-breeding range in winter. The Scarlet Tanager (Piranga olivace) is a neotropical migrant and a regular visitor to the Atlanta metro area during spring and fall migration. The Scarlet Tanager is quite recognizable to most bird watchers, but it can be tricky to identify, especially during fall migration. The problem lies with understanding a couple of things about bird plumage. First, male and female birds do not always have the same plumage. Second, there are seasonal differences in the plumage of some birds as they molt their feathers. The replacement of all or part of the feathers is called a molt. Molts produce feathers that match the age and sex of the bird, and sometimes the season.
Look at the pictures above…notice any differences? In the breeding season (summer) the male (left) is gaudy scarlet red with distinctive black wings and black tail. The female (middle) has a less dramatic olive-yellow coloration. The male also has a drab olive coloration during the winter months (right) as the birds migrate to South America. In science we refer to this difference in appearances as sexual dimorphism and seasonal dimorphism. Dimorphism (di= two, morph = “appearance”) translates as “two appearances.” Therefore, sexual dimorphism means two appearances between the sexes (just like humans) and seasonal dimorphism means two appearances between seasons (breeding vs. non-breeding).