Bird Behaviour: Bird Song
Bird song is a difficult phrase to interpret. Some people argue that it is the wrong term to use in relation to birds, because song is a human art form and, therefore, implies a form of music. Although we may think that many of the sounds that birds make when they are singing are musical – birds themselves do not and cannot appreciate that they are making music. Some specialists talk about the bird vocalizations – even this term produces complications because not all the sounds are vocal. Others use the term ‘sound pattern’, which is useful because of the difficulty in drawing a line between bird song and bird calls – a difference which is functional rather than musical. In some species, the song is made up of a rapid repetition of its call notes. Song can best be defined as a series of notes or sounds consistently repeated according to some specific pattern. It is produced mainly by the male, and usually during the breeding season. Call notes are usually short sequences of up to four or five notes, often much less musical. They are generally rather brief sounds with a relatively simple acoustic structure.
Both songs and calls convey messages over longer distances than do the postures that a bird adopts when displaying, although the effect of song is sometimes reinforced by displays. Song is not a language in the sense that we understand it – it cannot convey precise instructions but it can convey a feeling.
Whilst song serves a number of functions, some sexual, some social and some individual, the most important function of all is to proclaim the identity and sex of the singer. It also maintains an emotional relationship between the singer and his mate. Some songs and calls are linked with the presence of the young and will convey that information to other species. It has been claimed that certain types of budgerigar song actually induce the female to lay eggs. Finally, song will identify the individual, itself, to its mate and to its offspring because each bird song differs slightly from that of its neighbour.
For the individual bird, song helps to discharge nervous energy and, in spite of implying that everything about song is mechanical, a bird does manage to perfect song through practice and the possibility that some birds sing for the joy of it should not be arbitrarily ruled out.
Birds have a varied vocabulary of calls; some may be, like song, declarations of territorial rights, and be used when the motivation to defend is low. Calls also indicate needs, other than territorial or sexual; for example, the need for company may be one of the functions of the calls of young birds, which are still dependent on their parents. Alarm calls, especially those indicating certain dangers, such as the near approach of a predator, trigger an immediate reaction which may not only affect birds of the same species but others as well. The ‘pinking’ of a Blackbird when a Tawny Owl is discovered, gives a particularly obvious example of this type of call. Some of the more extreme alarm calls, which give warnings of predators, apparently also indicate fear and tend to be high-pitched with a relatively narrow frequency range and indefinite endings. This gives them an almost ventriloquial effect, making them extremely difficult to locate.
Anybody who has watched tits feeding in woodland areas will know that it is possible to locate the flock by following the contact notes. These contact notes tell each bird where the others are, and warn them off if they are getting too close. At the same time they attract back to the flock birds which have been wandering off. The utterances of some birds communicate not only the location but also the presence of some other object.
A type of song which is much quieter than the normal song of a species is the ‘subsong’. One of its characteristics is that the fundamental frequencies are generally lower than in the normal song. It also has a different pattern and is said to be characteristic of lower sexual motivation; some experts say it has no communicative function. I am not certain that we can accept this as the whole truth. In my studies of the Wheatear, for instance, ‘subsong’ was only used by unmated birds holding a territory, apparently as advertising song. The full song was only used by the unmated bird when it became extremely excited, for example, in a territorial battle. Once the Wheatear was mated it sang the full song and used the song flight. The warbling subsong was then used less often and then only in sexual circumstances. Subsong is also used by females under certain circumstances. In the autumn subsong is often used by young birds of many species and then it is thought to be in the nature of practice. As I have mentioned before, some birds such as Robins, use their full song until they are mated and then more or less stop singing. So we have enormous variations.
Most of the songs I have been writing about so far consist of vocal sounds. However, many advertising sounds made by birds are non-vocal. One of the best known examples is the drumming of the Great and Lesser Spotted Woodpeckers. These sounds are made by a very rapid tattoo of blows by the bill on a dead branch usually near its end. The sound can carry up to 400 metres or more through a wood. This drumming equates with the advertising song in songbirds. The bill clattering of White Storks, which is a greeting display, when one adult throws back its head in recognition of and greeting to its mate, is often shown in bird films.
The use of the wings to produce sounds are well known to the average birdwatcher. They vary from the wing-clapping of the Woodpigeon to the fast tumbling flight of the Lapwing, whose hard-beating wings are able to produce a ‘buzzing’ sound on the downstroke. Nightjars and some owls also clap their wings noisily as pan of their sexual and territorial displays. The ‘drumming’ or ‘bleating’ of the Snipe is perhaps the best example of producing sound from the tail feathers. To produce this the Snipe, while flying over its marshland territory, dives at a gentle angle and fans its tail. The outer pair of tail feathers are separated from the remaining six pairs and the sound, which lasts about two seconds, is the result of the air rushing past these feathers and causing them to vibrate.
Few birds sing all the year round and most song is correlated to the breeding season, being partly linked with the increasing length of the day. It usually parallels the growth of the testes. At the turn of the year, many species may resume singing, provided the weather is not too hard. Robins reach their maximum song-output as early as February but most species apparently do not reach it until April or May. The frequency of song falls off when the young hatch. In August, when many birds are moulting, there is little song but later in the autumn singing starts again from Chiffchaffs, Willow Warblers, Wheatears and others and they may even be signs of nesting activities. This may be accounted for, in part, by the autumnal recrudescence of the gonads.
Bird song has often moved the hearts and souls of poets and musicians as well as naturalists. To be out early at sunrise and hear the dawn chorus in spring, or to just sit and listen to the bird song in your garden on a summer’s evening, can be a thrilling experience, or simply relaxing if you are in a contemplative mood. The birdwatcher may want to go beyond contemplation and ask himself a whole range of questions. What are the times and seasons during which birds sing, and from where do they sing? How does the weather affect song? Does the range of song perches change throughout the season and depend on the amount of foliage? Are they exposed when in song, or hidden? How many different types of song does a male have and what are the occasions on which he uses them? Having started to answer these questions, others will follow. The tape-recordist, too, can capture the different varieties of song and calls and, perhaps, build up, by cutting, editing and resplicing, a sound picture of a typical bird from your garden or favourite habitat.
- Bird Identification using Song and Calls (birdwatchtips.info)
- Birdwatching: The Lives of Birds (birdwatchtips.info)