Scarlet tanagers

An adult male scarlet tanager.- Ken Magnuson

For many of our songbirds, striking plumage coloration in a male may attract an interested female. But it’s a liability the rest of the time, when the goal is to eat as much as possible while not being noticed by predators. As a result, even our most garish birds are surprisingly deft at concealment.
Exhibit A is surely the scarlet tanager. Females and young of this midsize songbird are dull olive with slightly darker wings — a fine color scheme for concealment in trees. But adult males are brilliantly, flamboyantly, eye-jabbingly red, a red really without comparison, and made to seem all the brighter through contrast with black wings.
Yet a cautious nature and treetop habits can make these birds infuriatingly difficult to spot. Oh, you can hear them singing easily enough, a long song comprising short phrases like an American robin’s, only with a peculiar burry quality. But to spot one as it moves deliberately about a tree canopy can require both patience and luck.
Though not a common nester on the Vineyard, the scarlet tanager breeds here reliably, generally in the large tracts of woodland along the moraine from Lambert’s Cove west to Aquinnah. Here as everywhere else, these birds prefer and maybe require relatively large tracts of forest. They nest much less regularly, if at all, in the stunted woodlands of the sandplain and the south shore.
Scarlet tanagers defend large breeding territories, and won’t attempt to breed in plots they deem too small. And the species is vulnerable to nest parasitism by brown-headed cowbirds, which find host nests much more readily in fragmented woods than in expansive forests. Tanagers often nest in the same area for many years running, likely reflecting members of one lineage returning year after year. My breeding-bird survey stop at the intersection of Tea Lane and North Road, for example, has produced a scarlet tanager in practically all of the 15 years or so I’ve been covering this route.
Given the stealth coloration of the female and the bashfulness of the gaudier male, the vocalizations of this species are often the best clue to its presence. The song, as I’ve noted, resembles a robin’s in structure and pitch; perhaps more distinctive is the characteristic call note, a brisk, two-syllable “chip-BURR.” Tanagers are quite vocal, so even with a sparse population like the Vineyard’s, this is not usually a difficult species to find if you know what to listen for. The Land Bank’s Waskosim’s Rock preserve and the Trustees of Reservations’ Menemsha Hills reservation typically have a few breeding pairs.
Seen up close, the bill of a tanager is an impressive little weapon, tipped with a nasty hook, robust in structure, and powered by equally robust jaw muscles. It’s an ideal tool for foraging on a wide range of arthropods, which normally make up the vast majority of a tanager’s diet (they also eat seeds and berries). In particular, scarlet tanagers seem fond of bees and wasps, which they often bash senseless on a branch before swallowing, and of beetles, which the bill can crush readily.
They also prey heavily on moths, both adult and larval, and are said to be one of few species of birds that eat bristly gypsy moth caterpillars in large numbers. It is not by accident that the great Massachusetts ornithologist E.H. Forbush called this bird “the guardian of oaks.” The many kinds of caterpillars that feed on oaks surely make up a large portion of this bird’s diet.
Tanagers typically forage high in the tree canopy; there are accounts of them feeding on the ground, but I can’t recall seeing this behavior myself. Likewise, while I’ve read of tanagers hawking insects in flight, this is a behavior that seems most untanager-like to me. Mostly, tanagers bring a methodical approach to their hunting, moving slowly along branches and seeming to search carefully in every possible insect hiding place.
In addition to our breeding population, the scarlet tanager is well represented on the Vineyard by migrants, which come through in the autumn during a long window lasting from late August into November. These birds are true long-distance migrants, wintering for the most part in South America. They’re trans-Gulf migrants in the spring, often hitting the shore of Texas or Louisiana in large numbers before working their way north.
Breeding widely across the eastern United States, scarlet tanagers are at their most common along the spine of the Appalachians. Being woodland dwellers, this is a species that has profited from the regrowth of forest of former farmland in the Northeast.
Overall, though, while its nesting distribution may be broadening, numbers of this species appear to be declining, suggesting that they may be experiencing high mortality on their wintering grounds or during migration. So the presence of this excellent bird on the Vineyard in the future is far from guaranteed.