BIRDWISE: The sound of silence
During the past week I was struck with the recognition that bird song, so palpable during the past couple of months, was tapering off rapidly.
It's hard to believe that most species of songbirds have already raised their young and will soon be going into a post-breeding molt phase that precedes migration back south. It is indeed a short nesting season here in the northwoods. I want to take advantage of this lull in bird song to reflect on the importance of song in the lives of breeding songbirds.
Sound is the most important means of communication in most species of birds because, if you're a bird, it lets others know precisely where you are even when vegetation is dense.
In the fall and winter months, short calls are used to maintain contact among individuals, especially those that travel in loose flocks while foraging.
Male songbirds begin to sing full songs when lengthening daylight triggers the release of hormones essential for reproduction. Full song typically begins during migration and culminates with arrival on the nesting grounds and subsequent breeding.
Song is in integral part of the reproductive process and serves a number of different functions. Because each species has a unique song, it identifies the singer as a particular species: "I am a Baltimore oriole," "I am a purple finch."
Song is also believed to establish one's individual identity. Experiments in a few species have shown that subtle components of song, generally undetectable by humans, enable specific individuals to be recognized by members of their own species. In monogamous species particularly, recognizing one's mate is obviously a crucial element of successful reproduction.
Given that song identifies the singer at both the species and the individual level, it enables the singer to simultaneously attract potential mates and to advertise his presence to other potentially competing males. A male may move around from one location to another until a mate is secured but then settles in a particular area, where his song, often accompanied by aggressive behavior, tells other males to keep their distance. This interaction among males spaces them out, the phenomenon known as territoriality, which is important not only to minimize the possibility of cuckoldry (if you're young and don't read Shakespeare, look it up!), but also to lower the density of birds over the landscape and thereby reduce competition for food resources.
Some of our species will go through a second nesting this summer and there will be a brief resurgence of song. But by this time the males already have a mate, and a reasonable density of nesting birds has already been established. So song becomes less important and we are well on our way into a very quiet time of summer, birdwise.