Henry David Thoreau wrote that the Scarlet Tanager “flies through the green foliage as if it would ignite the leaves.” One of the common names for this species over the years has, in fact, been Firebird. Of course, this refers to the male Scarlet Tanager and in breeding plumage at that, when he is bright scarlet in color with black wings and tail.
It is the male tanagers that return before the females in April and May. Traveling by night, singly or in small groups, they have molted along the way from South America where they overwintered looking like the females (yellow beneath, olive-green above with brown wings and tails).
The breeding range of the Scarlet Tanager covers most of the eastern United States between Canada, Oklahoma, and the Carolinas. Most of the males return to their previously established territories. These territories consist of from two to eight acres of mature deciduous forest.
Once on territory (either its old one or one it wishes to establish), the male climbs to a high perch and begins to sing. This alerts the other males to stay out and will attract a female when one arrives a few days later. It is unlikely that females return to mate with the same male.
The song of the scarlet tanager has been compared to that of a robin with a sore throat. Both males and females sing as well as making a number of other calls. Chances are, you will hear a tanager calling before you see one. The fact that they spend so much of their time high up in the forest canopy doesn’t help. The female is particularly difficult to see. Donald and Lillian Stokes in their Guide to Bird Behavior, point out that “she is exactly the same color as the sunlit leaves within which she feeds and nests.”
Once pairs are formed and mating takes place, it is the female who does all the work building the nest itself. This is usually placed about halfway out on a horizontal branch about twenty feet up. The male may accompany her back and forth to collect nest material, but this is just to make sure that no other male sneaks in and takes his place. Not that the nest is anything to brag about. Most of the time, it ends up being so flimsy that if you look up you can see the eggs through the bottom of it.
An average of four eggs are laid. These are pale blue-green in color with irregular brown dots. Incubation takes around two weeks. The female is also responsible for this, however, the male does bring her food when she is sitting on the eggs. Once the eggs hatch, they both set about feeding the hungry new arrivals.
In spite of taking aggressive measures to prevent it, Scarlet Tanager nests are parasitized by Brown-headed Cowbirds. In some cases, the percentage of nests having at least one cowbird in them has been recorded as high as 60%. The young tanagers, however, seem to be particularly well adapted to compete for the food that is delivered.
During the breeding season, tanagers are mostly insectivorous. One birding app factoid claimed that Scarlet Tanagers were recorded eating over 2,000 gypsy moths caterpillars in an hour. Unfortunately, it did not say how many tanagers were involved in this activity. Still, the birds probably do make a dent in all caterpillar populations.
They may also glean adult insects from leaves or pluck them from the air on the wing like flycatchers. Later in the summer, the diet may include more berries. Mulberries, elderberries, blackberries, and sumac berries are all possibilities.
The young fledge in only nine to ten days. After that, the young birds hang around the nest area for a couple of weeks making a lot of racket and still being fed by both parents. Juvenal birds aren’t much to look at compared to mom and dad. They are more brownish and streaky. Come late July or August, however, after their first molt, they look more like mom. Adults molt again before migrating back to South America. Females do not change that much. Males, however, lose their brilliant scarlet color and now also look more like the females. Naturalist Emma B. Parker has observed that partway through the process, the male’s red, green, and yellow feathers may resemble autumn foliage.
Throughout September, Scarlet Tanagers migrate south again at night in small flocks. Crossing the Gulf of Mexico, they eventually end up back in South America where they spend the winter months.
Scarlet Tanagers have the same predators as most other passerines. The biggest threat, however, comes from man. This species needs large, continuous areas of mature forest to breed. If there is too much fragmentation, the likelihood of success is considerably less. The longevity record for the Scarlet Tanager is ten years, however, most birds are probably lucky if they live to be half that old.