Thursday, 5 March 2009

A song before dawn

Lying in bed in the half-light before dawn I can hear a chorus of bird song. The upward shift in temperatures has delivered the first signs of spring and it seems that many of the local birds are responding to this. The chorus is dominated by Blackbirds but interspersed with their rich melodic warblings are others, the plaintive tones of a Robin and the thrice-repetitive notes of a Song Thrush. This is a pleasant way to start the day, especially since it is a Sunday; the post office vans and lorries are silent, leaving the birds unchallenged in this urban soundscape.

Early season song lacks the volume of later in the year but it does provide you with an opportunity to pick out individual songsters and to become more familiar with their particular songs. It is also a time when you really notice just how many birds are singing in the dark before dawn. Later into the year and dawn will have already come and gone while you are still deep in slumber. The question of why birds sing early in the morning, often before dawn, is one that has interested researchers for many decades and even now, despite the amount of work that has been carried out, we still do not have a complete answer. One of the current hypotheses is that birds sing at this time of the day because it represents a trade-off between the conflicting needs to defend a territory and the need to find food to replace overnight energy losses. Fitter birds should be able to sing for longer, so their delivery of song at this hour could be used by females as a sign of the male’s quality.

Studies have revealed that the dawn chorus peaks at a time when the level of territorial intrusions by other males is at its peak. As such, a territory-holding male should proclaim his ownership of the territory in order to counter this threat. Because of the low light levels just prior to dawn, visual means of display are limited in their effectiveness and song offers a more suitable alternative, the bird being able to deliver his message to would-be intruders. The low light levels may also limit feeding opportunities and, while there may be enough light to sing from a favoured perch, there may not be sufficient light to locate food safely and effectively.

One interesting aspect of song production is that a number of species will quite happily sing during the darkness of night itself, particularly in the presence of street lighting. Some observers mistake such nocturnal warblings for the song of a Nightingale, when they are far more likely to be Robins and Blackbirds.

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