Flight Lines: Morning, lengthening days lead to singing birds
"In the Spring a young man's fancy lightly turns to thoughts of love," wrote British poet Alfred Lord Tennyson in his work titled, Locksley Hall. Indeed there is something about the slightly warming weather, the ever longer days, and the slow greening of the landscape which stirs the hearts of not only young men, but young organisms of all types.
I couldn't help but be reminded of this particular line of prose over the course of the past few weeks. During the depths of winter, scarcely a bird vocalizes. An occasional boisterous chickadee, a distant calling crow, or the irregular tap-tap-tapping of a woodpecker can sometimes be heard. But beyond these few examples, winter can be eerily quiet.
Beginning a few weeks ago, however, a noticeable change occurred outside my home. House finches began to sing in earnest. Slowly and intermittently at first, the birds have now reached a point where I exit my home in the morning and inevitably hear the busy rambling warble of male house finches. This is a species which sings year round but not at the level I am currently hearing.
Other than humans and maybe cetaceans (whales, porpoises, dolphins), birds are unique in the animal world for their level of vocal complexity. Not all bird species "sing" though; really only those in the Order Passeriformes carry out what you and I would classify as singing. Not surprisingly, this group is known as the perching birds or, more commonly, the songbirds.
Producing the vocal sounds is something called a syrinx, an organ unique in the animal world. Many structural variations exist among the birds but it might be enough to simply consider the syrinx functionally similar to our larynx. Both organs produce sound but in somewhat different ways. One remarkable skill birds exhibit is the ability to sing with their mouths full or their bills closed.
Of the vocalizations given by songbirds, most experts separate them into two distinct groups: Songs and calls. Songs would be defined as the definitive sound performances by males (usually) to proclaim a territory to prospective females and rivals. This is usually a fairly defined piece of vocal talent with some individual and geographic variation, yet unique to each species. Songs can range from the simple two-note "che-bek" of the least flycatcher to the 10-second stream of melodious notes and trills of the winter wren, and then everything in between.
In some species, both sexes are endowed with similar vocal complexity although this is not usually the case. Locally northern cardinals, Baltimore orioles, and rose-breasted grosbeaks are three examples of this sexual singing equality.
The fact that time of day is important is not lost on early risers. In a couple of months, the first hour or so of daylight will represent a slice of time when potentially every breeding (and migratory) songbird species present can be heard singing. Wherever it's encountered, this dawn chorus can be a dizzying yet rich experience.
Calls, on the other hand, are typically shorter, less musical, but with much more variety, and are given for a host of reasons. As far as researchers can claim from observations and experiments, bird calls convey information about day-to-day activities such as defense, warning, distress, begging (by nestlings), flock cohesion, and even comfort. Unlike most songs, calls are not seasonally dependent.
Apart from vocalizations there are other techniques some birds employ in order to communicate. The familiar drumming of a woodpecker is but one example. Others include wing clapping among the pigeons, feather vibrations by Wilson's snipes, bill snapping by owls and others, and the well known wing drumming of ruffed grouse.
All this communication being produced must be important to the birds. Scientists might ask it another way, "What is the biological advantage to this behavior?" Why else would these organisms give their locations away to potential predators?
We know a lot from recent research but many questions remain to be answered regarding birds and their sounds. One thing we know with some certainty is that the longer days (biologists call this "photoperiod") are currently stimulating an increase in hormones among birds. In turn, this produces an urge to sing. At the moment, no less than four male house finches are actively announcing territory in my neighborhood. These will soon be joined by more finches and males of other species as the days grow ever longer.