A Parkersburg, West Virginia reader writes that, “Mockingbirds woke me up several times last night. Why are they singing at night?”
Birds vocalize throughout the year, but the purpose of the sounds varies. It may be tempting to assign human explanations to bird behavior, but such logic misleads. Contrary to folk wisdom and popular music, birds do not sing for joy. They sing to communicate.
Short, nonmusical chips, chirps, and whistles uttered year round convey information about location, food sources, and social position. Other calls rally broods and indicate alarm, danger, aggression, and annoyance. These “calls” are the sounds of daily conversation.
Calls may seem a dangerous way to communicate because sounds can lead hungry predators to tasty song birds. But part of the beauty of a call is its brevity. Once uttered, calls vanish into thin air, so predators can’t use sound to locate the callers. When danger threatens, birds simply stop talking until the threat passes.
True bird songs are longer, more musical, and usually limited to the breeding season. And songs are usually sung by males, though some females sing a softer, more subtle song.
Males sing to call attention to themselves. The message depends upon who hears the song.
Male birds sing to establish and defend a territory from other males of the same species. In this sense, song is a keep-out signal. Other males know that if they violate a territory’s boundary, they will be attacked. So they respect territory holders.
Furthermore, a single male can create the illusion that a territory is overrun with competing males, and therefore undesirable, by singing from multiple perches within the territory.
Mockingbirds, for example, which have an extensive repertoire of songs, often sing a different song when they move to a new perch.
To outsiders, it may sound as if many males occupy the area, so they look for places where there might be fewer competitors. Thus, a territory holder can defend his space by deceiving potential rivals. Why battle many males, when unoccupied and undefended habitat may be over the next hill?
Mockingbirds sometimes take this deception to extremes by singing all night long. If you hear a bird singing between dusk and dawn and it’s clearly not an owl or a whip-poor-will, it’s likely a mockingbird.
During the nesting season, male mockers can be heard any time of day or night. It may seem like overkill, but wandering males cannot mistake the keep-out signal, and potential mates may perceive it as an expression of the singer’s quality.
On the other hand, male song is also an invitation to females. It says, “I’m available. I can provide for you. Check out my territory. Be my mate.” It’s tempting to call it a love song, but biologists prefer to keep human emotion out of the discussion. Song is simply the crux of the pair-bonding process.
Another piece of the bird song puzzle is why they sing so early in the morning. Most people know that bird song begins early, but why so early? I hear the first robins and cardinals shortly after 4:30 a.m., well before dawn. And at 5:30, house wrens sing their explosive song with alarm clock regularity.
One of the triggers of early morning bird song is increasing light intensity. As dawn breaks, light triggers hormonal activity resulting in song. The brighter it gets, the louder and more enthusiastically birds sing.
For example, as soon as one male robin begins to sing, others follow. Those that fail to join the chorus may be seen as weak or inferior by other male and female robins. So they sing to demonstrate their ecological fitness, and a chorus builds.
Another powerful reason to join the morning chorus is to confuse predators. A single singing bird might be easy for a screech-owl to find. Locating an individual bird in a group of many is more difficult. This makes life difficult for birders, too. It’s difficult to pick out one bird from a chorus of many.
As you listen to the spring chorus with your morning coffee for the next few weeks, understand its biological basis and enjoy what many call the music of birds.