For the Birds Radio Program: Red-eyed Vireo
The bird that once was the most abundant songbird of eastern forests has problems up here, but faces worse problems in South America.
In late July and August, when most birds have long ago quit singing, Red-eyed Vireos are still going strong. These endearing birds, only slightly larger than warblers, sing an endless string of short, simple phrases, reminding some of a preacher droning on and on, pausing for dramatic emphasis, never quitting. One ornithologist actually counted the number of songs a single Red-eyed Vireo sang throughout a single day–22,197 during a I0-hour period. I trust the ornithologist used a clicker rather than keeping count in his head.
The Red-eyed Vireo’s greatest gift in the singing arena is sheer persistence. Its plumage isn’t much more distinctive than its song, a drab olive upperside and plain white underside set off by nothing more than a dark cap and eye line. But perhaps vireos think they’re more colorful than they actually are, since they look at one another through brilliant red eyes, their vision being too acute to require rose-colored glasses.
Oddly, no one has a better explanation than that of why Red-eyed Vireos have red eyes. But we do know that they are among the most observant songbirds in the forest. I used to take my education Blue Jay Sneakers along with me when I taught an Elderhostel up at the St. Paul YMCA camp on Bumtside Lake near the Boundary Waters. lf l left her out in her cage on the porch of my cabin, within minutes one or two Red-eyed Vireos would be scolding her, often actually lighting on the cage. I don’t think I’ve ever seen a Gray Jay in summer without at least one or two Red-eyed Vireos harassing it. And when I take Archimedes, my education screech-owl, out for a walk, the first birds to spot her and start scolding are invariably Red-eyed Vireos.
It would be wiser if Red-eyed Vireos paid less attention to jays and owls and more to cowbirds. Vireos are the commonest hosts of this nest parasite. More nests of Red-eyed Vireos than any other species been recorded hosting cowbirds in both raw numbers and as a percentage of all their nests. Red-eyed Vireos were one of the most abundant species in all of North America when deciduous forest covered the eastern half of the continent. When cowbirds spread out of the prairie states, they didn’t hurt Red-eyed Vireos as badly as they hurt less common species, but still took a toll. Fortunately, Red-eyed Vireos are still common enough to bring their endless song to otherwise-quiet mid-summer woods.
By the time vireos stop singing in September, they’ll be headed for the lowland tropical forests of South America and their hardest time of year. Cowbirds and forest fragmentation are problems here, but are nothing compared to deforestation in South America. When I flew over Mexico and Central America on my way to Costa Rica this spring, I saw dozens of fires large enough to be visible from the plane. Squandering so much tropical habitat for cattle production is almost enough to make a person become a vegetarian–and apparently IS enough to turn Red-eyed Vireos into vegetarians. As soon as they reach the tropics their diet switches from insects to fruits. Of course, even in summer they don’t eat beef–they feed on insects. In summer they’re on an avian version of the Atkins diet, concentrating on proteins and fats. In the tropics they’ll change to high carbs. This annual meal plan could be hyped as the Vireo Diet.
Combined with flying four or five thousand miles on their own power twice a year, it’s an effective way to keep slim and trim. Perhaps that’s what they’re doing all that singing about.