Here we are, already mid-March. The Spring Equinox is a few days away and if we didn’t have calendars to remind us, the burgeoning choir of birdsong certainly does. This week, I thought we could explore our group’s lovely, evocative namesake – the dawn chorus.
One of the sweetest gifts of spring is the beautiful symphony of birdsong rising from the predawn darkness, growing in strength and complexity as morning breaks and sunlight fills the skies. This cacophony of birdsong is called the dawn chorus. It is prompted by increasing day length, which triggers a hormonal change in birds that stimulates the brain regions controlling song production.
It is a magical phenomenon to experience and the best time of day to hear birds.
At least once this spring, roust yourself from your warm, comfy bed at ~4:45 a.m., grab a cup of joe, and head outside to listen as morning light extinguishes the stars and the first birds start to sing.
Marine biologist, author, and conservationist Rachel Carson described the dawn chorus so splendidly in her 1956 essay Help Your Child to Wonder:
“No child should grow up unaware of the dawn chorus of the birds in the spring. He will never forget the experience of a specially planned early rising in the predawn darkness when the first voices are heard. Perhaps a few cardinals are uttering their clear, rising whistles, then comes the song of a white throat, pure and ethereal, with the dreamy quality of remembered joy. Off in some distant patch of woods a whippoorwill continues his monotonous night chant, rhythmic and insistent. Robins, thrushes, song sparrows, add their voices. In that dawn chorus one hears the throb of life itself.”
Why do birds engage in this early morning chorus? There are a number of theories, and they're not always mutually exclusive.
Advertising Fitness — Singing is an essential part of bird life, but it’s costly in terms of time and energy. Singing loud and proud early in the morning demonstrates to other birds within hearing distance that the singer is strong and healthy enough to survive the night. And the louder and livelier your song, and the more time you’re singing it, the better the territory you can claim and higher chance a female chooses to mate with you.
Less Atmospheric Turbulence — There is generally less heat and wind to create air turbulence in the morning, which means a bird’s dawn chorus song is clearer and more consistent in strength and quality. Any variability in the signal quality of a male’s song could lead to doubt as to the identity of the singer.
Low Light Levels — One theory is that early morning light levels are too low and insects too inactive for effective foraging. Since light levels don't affect social interactions as much, birds take the opportunity to sing instead.
A theory that’s been debunked by research is that there is less ambient noise at dawn, so less sound competition with buzzing insects or man-made noise such as traffic, construction, or those cursed leaf blowers. But birdsong travels just as far through the air at noon as at dawn; remember, it’s atmospheric turbulence that determines how clear and strong a bird’s song carries.
Yellow-rumped Warbler (Audubon’s) — an early dawn choruser
I ran three Breeding Bird Survey routes in Idaho, arriving at the first station by 4:50 a.m. when it was still dark. At start time, usually about 5:15 a.m., the dawn chorus was ‘a crescendo’ whether in forest or sagebrush. I couldn’t see a bird, but keyed in on the songs and number of singers of each species. There was a distinct order in which birds joined the chorus, with American Robins, Hammond’s Flycatchers, Western Tanagers, and Yellow-rumped Warblers singing the wake-up songs. Then the Chipping Sparrows, Spotted Towhees, and Hermit Thrushes would pipe in. By my first few stops, the forests and hillsides were a chorus in full sound.
“Summer birdsong concerts can sound like a beautiful cacophony, a jumble of tweets and twitters and trills and whistles. But to the trained ear, all that bird song is like a symphony orchestra. And if you can recognize the sound of each instrument, you’ll know which birds are making the music.” ~ Gustave Axelson, The Cornell Lab
Ornithologists who have studied the dawn chorus in both temperate and tropical ecosystems found that the order in which bird species start to sing each day is anything but random. They found that each species started singing at a specific time relative to first light. For songbirds, this time is related to the species’ typical foraging height and its eye size. Species that forage higher in tree canopies or with larger eyes sing earlier than others. Larger eyes gather more light than small eyes, and upper canopies brighten faster than shaded lower understories. Eventually, each species will have adequate light to see predators and rivals, and can safely join the dawn chorus.
In Idaho, American Robins sing early in the dawn chorus, in part due to comparatively large eyes.
Western Tanagers are also early chorusers; they are a high canopy species and have relatively large eyes.
An interesting side-note to birds singing at first light is the factor of light pollution. Studies are investigating the effects of light pollution on the phenology of dawn and dusk singing in songbirds. Some studies suggest light pollution leads to a longer daily singing period for songbirds, possibly increasing breeding success. Other studies suggest extended singing can reduce songbirds’ lifespans. It’s safe to say at present, the ecological consequences of light pollution on the dawn chorus and songbird fitness remain poorly understood.
The dawn chorus gradually subsides as the sun starts rising and there is ample light for birds to begin moving around to forage. Although singing still occurs throughout the day (and sometimes into dusk), its initial purpose to vigorously proclaim territory changes to courtship and the business of survival.
A Common Yellowthroat greets the sunrise with his charming witchity-witchity-witchity song.
No matter where you live, the amazing repertoire of the dawn chorus is there to welcome you to another sunrise. It’s something we can readily enjoy from our backyards while we’re self-quarantined during the Covid-19 pandemic (may as well be optimists!). Listening to the joyful sound of birds is a lovely way to get outside ourselves and engage in the lives of these compelling creatures.
UK International Dawn Chorus Day — Bless you, U.K., you are always a step ahead of us Americans.
‘Dawn Chorus’ by English visual artist, illustrator, and designer James Marsh
The forest canopy is now open for your birdy observations and musings!