Bird Song (27) – why a dawn chorus?

We know why bird song is a feature of Spring – it’s because the function of bird song is usually to defend a territory and its food and nesting resources and to attract a mate. Song is largely concentrated in the Spring in high latitudes because that’s when birds breed.

But why is there a daily concentration of song around dawn? Why isn’t there a mid-morning chorus or a tea-time chorus?

Today, here in east Northants at 0515 it’s raining – the first for a while. But opening my front door there are still Blackbirds singing away in the dark. It’s obviously quite important to sing at this time of day.

Here are some potential explanations for why most UK songbirds do sing a lot in the time around dawn on these Spring days – the suggestions are not mutually exclusive so all might be partially true;

  • the air is cooler and stiller at dawn and this aids the transmission of sound. Turbulent disturbed air leads to degradation of sound quality so dawn is the best time to get your message across
  • there’s nothing else to do! It’s dark and so most birds can’t feed, or gather nesting material, so why not use this otherwise rather useless time to sing?
  • it’s been dark for 10 hours, and 10 hours is a long time in the life of a small bird. Some will have died overnight and so this is the time to signal that you are alive to your neighbours and potential mates. If the guy next door isn’t singing it’s an opportunity to annex a bit more territory.
  • singing draws attention to yourself, that’s what it’s for, but at dawn there are fewer avian predators active perhaps, and so this is a safer time than others in which to sit out in the openm and shout to the world.
  • it’s like an early morning exercise routine – it gets you warmed up for the rest of the day.

Any other ideas?

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12 Replies to “Bird Song (27) – why a dawn chorus?”

  1. A serious, peer-reviewed theory:
    The blackbirds and other thrushes, like sirens, are trying to lure the worms out of the ground at first light, through the beauty of their song. That's why they are the first to sing.

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  2. It's to give early risers , like Mark and insomniacs, something to listen to while the first kettle of the day boils.
    It also warns those non-territorial birds who may have surreptitiously roosted in others territories the warning to leave before it gets light, at the same time as providing a verbal call to the sitting mate that all is well.
    A question, is there a valid reason why all the initial birds singing in a dawn chorus are resident species rather than migrants?

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    1. 'A question, is there a valid reason why all the initial birds singing in a dawn chorus are resident species rather than migrants?'

      ###

      Whilst it's maybe a call rather than a song, the cuckoo is generally one of the earliest to be heard in the morning.

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  3. Not sure, but ‘honest advertising’ may play a part. To be able to survive a cold night AND sing at dawn sends a strong and sincere indication of fitness to any prospective female mate. So for example, a Coal Tit in January singing its heart out when there’s minus ten degrees of frost, has a definite wow factor going for it. This individual, especially one so small, cannot be fooling anybody.

    Not sure again, but later on in the season, at peak ovulation time, there is the necessity to ‘mate guard’ at dawn – a time when (I think) copulation frequencies are at their highest. This means the male has to sing harder (and a little earlier than normal) in order to deter any intruders.

    Lastly each species has evolved to respond by calling or singing to a particular light intensity at dawn. That’s why you get such a precise order of ‘waking’ in different species. So, the earliness and preciseness of the dawn vocalisations helps to tweak and adjust, (by a chorus of mutual affirmation) an individual’s biological clock so that it knows exactly what time of year it is.

    By the way, many species’ audible responses to the first light of dawn can be traced throughout the year. The dawn chorus occurs, in one way or another, every morning and is always magical whatever the season. But to be there in the best moment, it’s necessary to experience that pensive silence just before the first lark or robin calls to the first glimmer of light on the horizon where the sun will eventually rise.

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  4. This looks interesting........it is research based on great tits......
    Repeatability of signalling traits in the avian dawn chorus.......by N Maguib et al............Frontiers in Zoology, Vol 16, 2019...............https://doi.org/10.1186/s12983-019-0328-7

    It is open access and free to read.

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  5. "A question, is there a valid reason why all the initial birds singing in a dawn chorus are resident species rather than migrants?"

    Answer? Possibly a bit of sampling bias. Stand in your back garden and you hit residents: and at this time of year they are heavily invested, so proclaim loudly. You are sampling a particular community. Not all are like this.

    In my case, go 200m from the house into wet scrub and the blackbirds, robins and the like (except for a single song thrush) are missing. At dawn/ sun rise the ephemeral resource base there is filled by warblers, who are belting it out as much as the residents 200m away.
    At home on the margins of the moors at dawn we are dominated, with the exception of the resident grouse, by seasonal migrants: curlews and lapwings and redshanks who move up from the coast, and by pipits who elevation migrate. The scrub willows are now full of wispery willow warblers. All are in effect migrants of one sort or the other. Both the scrub and the moor do have pretty full-on dawn choruses, but as most of us are baised samplers in town or village gardens, we don't normally hit that time of day?

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  6. I live in a part of the world - the eastern United States - where the species changeover from winter to summer is much greater than in the British Isles. During peak migration season we have several new passerine species arriving each day.

    Because of this, I have often been tempted to get out early to find by song new species that have arrived overnight. It doesn't work! New arrivals might be found by sight, or call, but they are almost never singing. There might be various reasons for this, the most obvious being that the birds are needing to replenish their energy reserves, and do not have sufficient energy to sing immediately after arrival.

    A singing bird is thus a bird that has not just arrived. It has at least had time to replenish its reserves. Here singing likely functions as a honest statement that there is an individual here, who is stronger and more established than any new arrival. If new arrivals want to establish a territory, they had best look elsewhere. I would suspect this applies to partial migrants - those where only some of the population migrate - as well as to complete migrants.

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    1. Francis, regarding your interesting conclusions about newly arrived and hungry migrants, this may be relevant:
      Cuthill, I.C. & Macdonald, W. A. 1990. Experimental manipulation of the dawn and dusk chorus in the blackbird. Behav. Ecol. Sociobiol., 26, 209–16.
      The results clearly demonstrate the way food availability affects song output in wild Blackbirds when given supplementary food at the end of the day. The extra food induced earlier and enhanced singing at dawn the next morning.

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  7. Murray reminds me, with his reference to winter and “the first glimmer of light on the horizon”. Not exactly of a dawn chorus, more a chat sat round in front of a nice warming glow. At the end of the long winter nights when the sun climbs slowly above the horizon, the Jackdaws and an odd crow would congregate atop the neighbours tall Lombardy poplars which caught the sun long before the rest of the world below was bathed in warming sunlight. There they warmed their wings and toes, loudly greeting each other and chatting away.

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