Laura Erickson's For the Birds

Wednesday, February 16, 2022

Winter Bird Song, Part II

Great Reed-Warbler 

Mid-February chickadees, cardinals, and White-breasted Nuthatches are singing. These non-migratory species spend winter on or near the territories they’ll claim come spring, near the mates they’ll nest with come spring. Migratory birds wintering up here who will breed farther north don’t normally sing at all in winter. Some do begin during migration before they reach their destination, even while it’s still wintry. There is nothing more beautiful than juncos and Fox Sparrows singing away during an April blizzard. But neither species is singing right now. 

Winter Wrens and Hermit Thrushes, species with two of the most gorgeous songs on the planet, seldom jump the gun to thrill migration watchers. They wait until they’re on territory to sing.

Oddly enough, some birds that migrate long distances do sing their territorial songs in the dead of winter while they are hundreds or thousands of miles from where they’ll nest. Alert listener Don Watson called my attention to a February 2016 article in The Atlantic by Joshua Sokol, “The Birds That Spend All Winter Practicing Love Songs,” subtitled “Some species work on their beach body. Others work on their pipes.” 

The article, about European birds singing in sub-Saharan Africa in winter, focused on the work of Claire Spottiswoode. She’s been an avid birdwatcher since her childhood in South Africa, where she loved listening to Great Reed-Warblers, which sounded to her like “deep-throated jazz musicians.” These birds don’t breed in Africa, but in Europe, and as Spottiswoode became a researcher, she started wondering why they were singing at all so far from their breeding grounds. Singing is energy intensive and attracts predators, plus reed-warblers don’t associate with mates in winter and obviously aren’t defending a nesting territory. So why on earth are they such active singers in winter?

One of Spottiswoode’s former grad students, Marjorie Sorensen, conducted a study in Zambia testing the possibilities. She found that when playing recordings of their songs, Great Reed-Warblers neither reacted aggressively nor avoided the recordings, so the winter songs apparently had no territorial function. And the singing individuals had no higher testosterone levels than non-singers. Breeding reed-warblers have two song-types—quick ones to warn away intruders and longer ones communicating with potential mates. The winter songs were just as complex as the breeding songs but in a slower tempo. Sorensen explained that “They don’t really have breaks between their songs. They’re just singing, singing, singing.” The songs also seem to meander mid-verse, with the birds switching more rapidly from sound to sound. Females choosing a mate seem to prefer more complex notes, so males apparently use their low-stakes winter rehearsals to try a variety of tones and perfect the best ones. 

There will need to be more research on how these songs change from winter through migration and on the breeding grounds to test whether the purpose of winter singing really is to practice. But this new explanation is inspiring more ornithologists to study the issue. Examining the songs of 57 species that sing in winter, researchers noticed that these species tend to be ones with complex songs and/or drab plumage, making their songs very important in attracting mates. It’ll be fun watching how research teases out what exactly is going on. Here in America, the change in White-throated Sparrow songs from their traditional Old Sam Peabody, Peabody, Peabody to a slightly different version (which doesn’t appear to be as universal as scientists originally proclaimed a couple of years ago) apparently sprung up as males from different parts of the country were listening to one another’s songs on their wintering grounds. 

This is why I so love ornithology—one could study birds every day during a long lifetime and never even scratch the surface. The more we know about birds, the more we realize how much we don’t know.