Male and female Marsh Wrens look alike, but when I find one singing along Portage Bay, it’s undoubtedly a male.

Despite knowing it happens annually, I’m always surprised when I hear birds begin to sing every year. I spend most of my days outside and I wake up early, so I notice subtle changes in the seasons acutely, and my ears are always pricked for avian voices. That’s how I detect many of the birds I watch. As a result, I noted that within the last week, more birds have been singing than a week earlier.

As days lengthen in the temperate world most organisms have physiological reactions, and birds are no different. One result is that male birds’ testes swell, and increased testosterone expands song volume and frequency. Many resident birds sing year round; I hear Song Sparrows and Pacific Wrens regularly throughout winter. But, when the daylength broadens, birds ramp up the energy they put into singing. The other morning in the vicinity of 17th and Roy I counted six species singing, not an impressive number. However, four out of the six I hadn’t heard since last summer.

Why do birds sing? Overall it’s a pretty simple answer. Birds generally sing either to impress the opposite sex or defend a territory. In the vast majority of cases, if you hear birdsong the vocalist is going to be a male bird.   

Don’t confuse “singing” as a term for all bird vocalizations. You can break down vocalizations into two broad categories, songs and calls. Songs tend to be multi-syllabic performances by male birds to attract mates and defend territory. Calls aren’t necessarily single notes, but often they are merely a chirp, and they may communicate any number of things to their own kind, or even other species. An American Robin in Interlaken Park might come across a Barred Owl and begin an incessant high pitched chirp that will actually alert other nearby birds, from chickadees to crows, of the presence of a predator. Start paying attention to things like that and you’ll have some cool encounters (I have actually found Barred Owls in Interlaken because of bird alarm calls).

So birds sing, and they call, but how do they do it? Unlike people, who have single chambered larynxes for speech, birds have a dual chambered vocal system called a syrinx. The two chambers can be manipulated to produce two notes at once, or even flow a note from one side to the other without taking a break to breath. A very small bird, the Pacific Wren will regularly sit and sing for 10 seconds without breathing, uttering a dazzling array of phrases that the human ear can’t even break down without a recording to slow it down. This is one of the most complex bird songs in North America and you can hear it on the Hill.

All birds have syrinxes, but not all birds technically “sing.” Passerines, the largest order of birds , also also called songbirds, because they have the most complex vocalizations. Sure, a Bald Eagle may whistle away overhead, or a gull may holler earsplitting cries, both potentially related to defending territories, but neither are considered to have “songs.” The distinction is made mostly because neither bird learns these vocalizations. If you raised a Bewick’s Wren and a Red-tailed Hawk in tandem, never exposing either to their “native language,” the Red-tailed Hawk would make the same sounds as a wild hawk, but the Bewick’s Wren would never be able to sing like its wild brethren. Such a wren will have the urge to sing, and it’s calls will be similar, but without a wild singing role model to listen to, it will never learn to sing the song of a Bewick’s Wren.

Interestingly, learning can mean that songbirds develop regional dialects. A favorite example is of  our local White-crowned Sparrows. The Hill’s breeding population is a subspecies called pugetensis, which is the one we regularly hear singing in spring. In the non-breeding, another subspecies gambelii, which breeds in the Western Arctic also shows up. At certain times of the year on the Hill, a tuned ear might catch the song dialect of a gambelii White-crowned Sparrow who just can’t help himself, despite not being on territory where the singing really counts, mixed in with the songs of the local pugetensis songs. Call me a bird nerd, but I think that’s magical.

A singing Hermit Thrush, an example of a bird that breeds in the mountains nearby but is almost entirely silent when wintering in Seattle.

The best time of day to bird song is early morning. I know it’s really spring when I have half awake memories of American Robin song drifting in the window well before dawn. In the bird world, there’s a thing called the dawn chorus, when the birds are the loudest, and everyone seems to chime in. We don’t really know why birds sing more in the morning. Possibly it’s just to let everyone nearby know that the owner of a territory is still kicking. Either way, if you want to hear bird song at peak volume (and with less traffic noise to contend with), get up at dawn and listen. It doesn’t really matter why they do it, nor who is talking, mostly, it’s just a beautiful display of biodiversity that we can enjoy through one of our less emphasized senses.