I was struck, one early spring morning, by the sheer volume and variety of birdsong all around, hinting at the beginning of breeding activity now that the coldest weather seems finally to have left us. It prompted me to clear out nest boxes, applying an appropriate parasite treatment to ensure they are ready to receive prospecting occupants. The sooner birds can begin reproductive activities in a safe environment, the longer fledged young will have to mature before next winter.
Among our smaller songbirds, nest-building and egg production are preceded by several weeks of hormone-induced preparation, the result of the lengthening days and slowly rising temperature. Among the passerine (or perching) birds, the males are starting to sing, which is a signal to advertise their breeding status and readiness to compete for mates.
A Singing Competition
Competition in nature leads to the proliferation of individuals best suited (fitted) for occupation of the environment in which they must survive. Such competition is a fundamental driver and developer of birdsong, just as it is of the development of bright plumages or complex courtship behaviours. Competitive birdsong is multifunctional, designed to signal ownership of territory and repel rivals, or to attract a mate with information about the songster’s fitness. It is an unambiguous signal across distance to often unseen members of the same species in potentially dense habitats. Each species has its own distinct song type, within which variations exist.
Vocal communication requires a great deal of energy supported by locally abundant food reserves. If an individual is vocalising impressively, then he clearly thrives within his territory and this information is of great importance both to potential mates as well as potential rivals. The degree to which a female is impressed will tell her about the suitability of the male to pass on his genes to the next generation. The degree to which a rival male is impressed will signal whether or not a fight for dominance is likely or can be avoided. There are many examples of vocal breeding behaviour in nature: lions and deer that roar, frogs and toads that call, whales and birds that sing, to name but a few.
Since singing is costly in terms of energy use, once a mate has been secured the males of many species sing less often. This is no act of complacence on the part of the male, who may need to redirect his energy reserves towards parenting activities. Birds also stop singing during the post breeding moult, as this might attract predators at a time when flight efficiency is reduced.
On the whole, only male birds sing, with occasional exception. This is because it is usually the female who makes the mate choice and the male who must stand up to her considered scrutiny. For this reason the repertoire, or sheer variety of song, can be a significant factor in expressing the resourcefulness of the male to a female. Birds expand their repertoire by listening to others around them. Some readily mimic other species and inspiring environmental sounds. Great tits and especially starlings are known for this ability. On the cirl bunting project here in the Roseland we have known one of our males to mimic the call of a chaffinch.
Identifying birds by their songs and calls is a useful skill in conservation work. Moreover, birdsong is also an important yet still developing scientific study. Analysis of digital recordings of individual birds can tell us a great deal of information and help to explain particular behaviours associated with vocalisation. For example, birdsong is known to reveal the personality of an often unseen individual. Studies have shown that birdsknow not only who their neighbours are but also what kind of personality each one possesses through its song. Individuals may change the character of their song depending on the intended receiver. A male great tit may, for example, sing one kind of song towards a female neighbour but another to a rival male. Rival males can discern dominance between themselves. Song interruption, for example, is a competitive behaviour that can be attractive to females deciding on mate choice. Thus dominant males in some species will aggressively interrupt the singing of rivals, rather than listen and wait, in order to assert their dominance but avoid an actual fight.
Humans with an experienced ear can also sometimes tell the difference between individual birds. On the cirl bunting project it is possible to learn the difference, for example, between experienced adult songsters and the newest juveniles, whose songs lack refinement. This can be a useful skill to develop for the survey work that we carry out here in the Roseland.
The Dawn Chorus
Birdsong activity naturally reaches its peak during the main part of the breeding season. However, within the annual cycle occurs that daily songburst which many of you know as the Dawn Chorus. It follows a regular pattern:
Early rising species start singing about an hour before sunrise. As other species join in, the chorus reaches full volume about a half hour before sunrise, lasting for around an hour. It then gradually fades in the hour after the sun has risen. There are a number of theories for the occurrence of the Dawn Chorus phenomenon, some or all of which may be relevant to a greater or lesser degree, depending on the species and habitat. Some examples of these are that:
In the pre-dawn darkness food resources are difficult to locate, especially live prey, therefore energy is better spent declaring ownership of territory, physical fitness and advertising for mates. The earliest risers are usually robins, thrushes and blackbirds that typically feed on organisms constantly active at or near the surface of the soil. Species that join in the chorus later – starlings, warblers such as chiffchaffs and others – may do so because their prey becomes more easily detected later in the day
Singing may attract unwanted attention from predators and the darkness helps to conceal the songster
At this time, unclaimed territories may be more easily detected if no-one else is singing in them
Air turbulence tends to be minimised in the darker hours, which permits song soundwaves to travel many times further without distortion, reaching those potential mates and territorial rivals.
The best time of the year to hear the full range of Dawn Chorus species in the UK is during May and June, when the migrants have returned to join in the singing with our permanent residents.
Many bird species will in fact sing at different times throughout the day and some even prefer to sing towards dusk, rather than in early morning.
If you want to listen out for the songs of different species, here are a number of links you might wish to try:
British Garden Birds tutorials: http://www.garden-birds.co.uk/information/tutorials/
RSPB – Alpha bird identifier, with clips of songs and calls: http://www.rspb.org.uk/wildlife/birdguide/name/a/
BTO – 6 songs to listen out for: http://www.bto.org/news-events/e-newsletter/e-newsletter-library/story-archive/early-breeders