Bird song has diminished significantly in recent weeks. In doing some field work for the Maine Breeding Bird Atlas, I was struck by how few veeries, yellow warblers, ovenbirds, black-throated green warblers and white-throated sparrows I heard at several central Maine sites. Males of these species filled the air with their songs in June.

Of course, the silence makes sense. Most of these birds have fledged young. The male no longer needs to sing to attract a mate or to warn other males to stay out of its territory.

However, there is one bird that sings vigorously well into August: the red-eyed vireo. This species nests broadly throughout the eastern two-thirds of the United States and Canada. They are tree-top birds, found in forests as well as parks and suburban yards.

During the breeding season, the males defend a territory about an acre in size. A forest can therefore hold many red-eyed vireos during the nesting season. Their modest territory sizes and broad continental distribution make red-eyed vireos one of the most abundant songbirds in North America. One source estimates their population at about 130 million birds, making it the 12th most common bird in North America.

As birds of the canopy, red-eyed vireos are not seen easily without some effort. However, it is a piece of cake to find one with your ears during the Maine summer. The red-eyed vireo gives a sing-song vocalization consisting of one to five slurred notes or syllables. Most of the songs consist of two- or three-note syllables. The male pauses briefly between songs.

Here’s a mnemonic device to represent a sequence of red-eyed vireo songs: “here I am” – “up here” – “in the tree” – “how are you.” Point your browser to the AllAboutBirds website to find recordings of red-eyed vireos.

The males are indefatigable singers. One equally persistent researcher counted all the songs given by a single male in a day. Over 14 hours, that vireo sang over 20,000 songs!

Though distinctive, the songs of a red-eyed vireo are rather dull and monotonous. However, a careful look uncovers lots of interesting patterns.

Don Borror, an ornithologist at Ohio State University, published a paper on red-eyed vireo songs in 1981. Although sometimes difficult to distinguish by ear, red-eyed vireo songs are quite varied. These differences are easily seen in spectrograms of the sound on a computer.

Borror analyzed 12,500 songs from 46 birds from nine different states. He found that song repertoires varied from 12 to 117 songs, averaging 40 songs per male.

A male almost never sings the same song twice in succession. Like a jukebox, some songs are played frequently and others are only rarely used.

A 2020 paper by Nicholas Acheson of McGill University considerably expands our knowledge of red-eyed vireo vocalizations. Although Borror analyzed 12,500 songs, Acheson’s work indicates that Borror’s sample sizes were too small. Most of Borror’s recordings were made on a single day.

Acheson recorded the songs of 46 vireos on multiple days and at different times of day. He found that song repertoires varied from 17 to 341 distinct song types. The average repertoire size for individuals with over 1,000 songs recorded was 154. Amazing diversity! Acheson’s results suggest that Borror and other red-eyed vireo researchers underestimated repertoire size by two- or three-fold.

Furthermore, Acheson found that birds sang different subsets of their repertoire at different times of the day.

Acheson analyzed over 65,000 songs in his study, a herculean effort.

Much remains to be learned about red-eyed vireo songs. What influences the variation of repertoire size in males? Do females use male repertoire size to pick a mate? What are males communicating by singing different subsets of their repertoire at different times of the day?

Herb Wilson taught ornithology and other biology courses at Colby College. He welcomes reader comments and questions at whwilson@colby.edu

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