The Dawn ChorusThe dawn chorus is a phenomenon that occurs at the start of a new day and is most noticeable in spring. In the UK the dawn chorus begins in March but reaches its peak in May which also coincides with International Dawn Chorus Day.
The birds most commonly heard during the dawn chorus are blackbirds, robins, wrens, chaffinches, pheasants, warblers, thrushes and finches.
Birds sing for two reasons; either to defend a territory or to attract a mate. And there are a number of reasons why the majority of the singing occurs at dawn and in the spring.
Generally only male passerines – or songbirds - sing and in order to attract a mate he has to obtain and defend a territory. The territory will help with his breeding success by providing him and his new family with food and shelter.
By singing in their chosen territory they are warning other male birds to stay away. Birds will leave gaps in their songs and listen for replies so they can work out where their rivals are and focus their efforts on birds looking to take over their territory. Some birds such as chaffinches and great tits have a big repertoire of different songs in order to convince other males that there are a number of birds in the area and all territory is taken.
The other reason for singing is to advertise for a mate. When males are trying to attract a female they will sing songs that are longer and more complicated then the repetitive songs that they use for defence.
The song of a male can indicate the bird’s quality as a mate in a number of ways particular the song sung during the dawn chorus. If a male has the energy to sing after a night without food it shows that he is a strong forager and lives in a territory with plenty of food. A weaker, hungry bird will not have the energy to sing for long.
Male birds will also amplify their song by singing on high exposed perches. This makes them vulnerable to predators but by avoiding them they further show females their strength.
Imitating another bird’s song will increase their repertoire and show females that they have survived enough breeding seasons to have heard these other songs. Some migratory birds will even imitate international birds. Marsh warblers can mimic the sounds of up to 70 species showing the females where they have spent the winter.
The most successful males will find mates early in the season and can sometimes rear two broods during the spring and summer. However, this decreases their reproductive success and their singing will also lessen over the breeding season.
Birds mainly sing at dawn because the air is usually still which means the sound transmission is better. Researchers have found that a song during the dawn chorus is up to 20 times more effective than singing at midday. Additionally birds can do little else but sing at dawn. The light is poor and insects are dormant so searching for food is more difficult.
The dawn chorus begins in the spring to coincide with the beginning of the breeding season. The level of melatonin in birds is regulated by daylight and decreases as days get longer and lighter. This, combined with an increase in testosterone triggers breeding activity and the dawn chorus and battle for territory and mates begins.
Communicate with singing birds with a bird call or relax by listening to a bird song CD.