Man has long been fascinated by living creatures, and there is a long
history of appreciation of birds for their beautiful plumage, their bright
joie de vivre, and their song. In fact song and birds are inextricably linked,
celebrated by poets and composers the world over. Certainly, other groups of
animals sing (whales, crickets and some monkeys, for example), but for most of
us none of them can compete with birds for the loveliness of their song. Song
is surely linked in our minds with birds, as much as their ability to fly and
their possession of feathers.
Singing is most characteristic of birds in the order passeriformes, this
group comprising about 5000 of the world’s
9000 or so bird species. The oscine passerines include most of our familiar
small birds, from crows to cardinals and including warblers, sparrows and
Carolina wrens. Some non-passerines sing, including hummingbirds, but their
songs are generally less developed and attractive (to our ears, at least).
Birds sing for two main reasons :
1. To attract a mate and
2. To establish and hold a territory.
As might be expected from these functions, singing is mostly a male
activity. Under the influence of a seasonal increase in hormones, the male is
ready to breed. To raise a family, he first needs to establish a home or
territory. Most larger animals defend a territory, a certain area which the
individual claims for his own use (and that of his family) and from which he
excludes all other individuals of his species. When a male sings, he is laying
claim to his territory and sending a message to other males "this
is my property, keep out".
The territory may be an acre or less, or several square miles depending on the
species. The bird may be able to establish and maintain his territory by song
alone. If another male tries to invade his territory, he is likely to respond
with increasingly vigorous song, display flight, or if necessary physical
confrontation. However, song often enables the bird to repel its rival without
physical contact.
Once the bird has established its territory, it needs to find a mate.
Once again - for many species - song is the key. The song used to attract
females may be different from the one used to establish a territory. If the
bird successfully attracts a mate, and once eggs are laid, he may reduce the
frequency of the female attracting song, but still keep up the territorial
song. He must keep the food and cover on his territory for himself and his
family.
Birds produce sounds in various ways. Not considered further here are
sounds made by knocking on trees (woodpeckers) and noises made by wind passing
through feathers (e.g. nighthawks and snipe), although they may serve a
similar function to song in other species.
The avian equivalent of the mammal’s
larynx is the syrinx, a hollow structure situated where the trachea splits to
form the two bronchi. This location on the two bronchi enables the bird to
produce different sounds from each bronchus simultaneously (or to breathe
through one while singing with the other!), and makes possible a very complex
song. The name Syrinx will be familiar to classical scholars, Syrinx was a
nymph who was pursued by the god Pan. Running to escape his embrace, she was
cornered when her way was blocked by a stream. By her wish, and to escape her
pursuer, she was transformed to a hollow-stemmed reed. When the wind blew over
the opening, a soft musical sound was produced. Pan tied several of these
reeds together, and thereby invented the pipes that bear his name.
Singing is a potentially a risky business to a bird. The song that
attracts a wife, can also attract a predator! Even a bird like a painted
bunting, which usually stays well hidden in dense cover, can often be easily
seen when perched high and singing. To the bird it is worth the risk. Breeding
is the only chance he has to transfer his DNA to a new generation.
It has been shown that there are advantages and disadvantages to
different song characteristics. For example, low frequency (pitch) sounds
travel further (in part by reflection from the ground), but require more
energy to produce, and may not be anatomically possible for small birds.
Higher frequency sounds are more easily distorted by vegetation, but are
common in birds which live in open areas. Many birds sing from the top of a
tree to enhance sound propagation. Some open country birds sing while in
flight to gain extra height.
As you might expect, song is most noticeable in the breeding period
(roughly February to July here in Central Florida). We often hear the first
northern parula song around Valentine’s
Day, and then increasing amounts from various birds up to the peak around the
end of May. However there is some singing all year round (especially this far
south). You will also notice some wintering birds singing, I have noticed this
in American robins later in the winter. You can buy recordings of bird sounds
to help you learn their songs.
Hopefully, when our birds start their breeding cycle this spring you
will be able to enjoy their song with a bit more understanding of what is
going on, and why. Instead of throwing the alarm clock at that wren, you’ll
react more like Sir Joseph Banks, naturalist with James Cook, who, while at
anchor off the coast of New Zealand in 1770, wrote "This
morn I was awakd by the singing of birds...their voices were the most
melodious wild musick I have ever heard, almost imitating small bells...".
