April, 2011

Wildlife

Wildlife
We're about more than just birds (though obviously we like them a lot).

Notes on nature

We love nature... from every little bug on a blade of grass to birds, butterflies, otters and oaks!
  • This weekend... listen to the sunrise symphony

    This Sunday is International Dawn Chorus Day, an annual celebration of the beauty of birdsong. To mark the occasion we’re running lots of special guided dawn chorus events at our reserves up and down the country.

    To get the full effect you’ll need to set your alarm alarmingly early, but the chance to experience one of the marvels of nature really shouldn’t be missed!

    In fact, the astonishing complexity, beauty and power of birdsong has inspired poets, writers and composers throughout history, but our enjoyment is incidental to its real purpose.

    So, why do birds sing?

    Love songs and battle cries


    Birds have become Nature’s master musicians in order to convey to potential mates, rivals and predators all the important things they have to say – from “Keep out!” to “Pick me!”.

    Keep out!

    Holding a good territory, with lots of potential nest sites and an abundant food supply, is really important for a male bird - so once he’s found one he won’t give it up easily! This is where his song comes in – by belting out a really loud, powerful song he’s staking his claim on the area and sending out a clear message to other males in the vicinity to “Keep out!”.

    Birds can even distinguish strangers from neighbours by subtle differences in their songs. This means that the male can focus his defence efforts on genuine intruders, rather than wasting his energy hassling the chap living next door.

    Pick me!

    Before they commit, females need to know a little bit about their prospective partner and a male’s song is one way that he can advertise his credentials.

    If a male can produce a long, loud, complex song after a night without food, this tells females that he must be an excellent forager living in a really productive territory - in other words, excellent dad material!

    Why sing in spring?

    The increase in daylight as spring approaches sets male hormones racing, and this triggers breeding activity - so the dawn chorus begins.

    Most males will keep on singing throughout the breeding season, until their annual moult in late summer forces them to keep quiet – after all, the last thing you want to do when your feathers are falling out and you aren’t quite as quick off your perch is to advertise yourself to predators! 

    But why do they sing so intensely at dawn?

       Sunrise symphony

       Not only is the air generally calmer at dawn,
       making sound transmission easier, there’s
       not a lot else to do!
      
       Light is poor and the cool temperatures
       keep insect prey from flying, so foraging
       is tricky.

       What’s more, if males haven’t been able to
       forage successfully during the previous day,
       they may not have sufficient energy reserves
       to last the night, so dawn is a time when males can announce their survival, both to rivals and potential mates.

    Females also lay their eggs at dawn, and are at their most fertile immediately afterwards – making it imperative for a territory-holding male to deter rivals and secure the female for himself.

    Go on, just this once...

    Listening to the dawn chorus truly is an unforgettable experience, so go on, set that alarm clock and immerse yourself in the uplifting sound of birdsong this weekend.

  • Monday's Magic Moment: Easter bunnies

    Easter just wouldn't be Easter without bunnies, and they don't get much cuter than these two...



    All together now - Ahh!

    You can see this photo, by Andrew Parkinson, as well as lots of other images of spring at RSPB Images.

     

  • This weekend... be an egg detective

    Empty blackbird eggshell. Photo by Katie Fuller

    There are lots of eggs about at the moment. Lots of chocolate eggs, painted eggs and those random bits of eggshells you find in your garden or on the street.

    What are they doing there?

    Why would a bird leave an eggshell lying around? Empty shells at the nest could attract the attention of predators, so birds will often remove them and dump them somewhere else. 

    On the other hand, the breeding season is hard work for birds, both males and females. There's a lot of nest-building to be done, and then all that flying to and fro, keeping a hungry brood of chicks fed. The female also has to lay eggs - a big investment of energy and nutrients.

    To recoup some of that investment, the female bird sometimes eats the eggshells once the chicks have hatched. She might go on to lay another clutch, so it's a sensible way to replenish her reserves of calcium.

    Who lives in an egg like this?

    Some of the most common eggshells to be found are from birds like blackbirds, starlings and collared doves

    Blackbirds and starlings produce eggs that measure roughly 3 x 2 cm. Both are pale blue, but blackbird eggs are speckled with brown. Perhaps surprisingly, collared dove eggs are not much bigger (3 x 2.5 cm), but they are white. Watch out for these on a lawn near you!

    The long wait

    Incubating the eggs before they hatch appears to be rather a dull job, from the outside (have a look at our bird of prey webcams to see if you can spot 'EJ' the osprey or the female peregrine at Chichester having a snooze during the long wait).

    To help keep the eggs (and later the chicks) warm, many female birds develop what is known as a 'brood patch'. Some of the feathers on her belly drop out, leaving a patch of naked skin. The skin itself changes, getting thicker and wrinklier with enlarged veins! It sounds a bit strange, but it's a more efficient way of getting body heat onto the eggs.

    Birds don't have teeth... do they?

    Black-headed gull chick breaking out of egg. Photo by Katie Fuller

    Birds have a tough start to their lives. They have to break their way out of the eggshell that's protected them while they develop. Such a tiny creature has to use a special tool to achieve this feat, so it comes equipped with an 'egg tooth' - effectively a tiny chisel on the upper part of the beak.

    In the picture on the left you can see a black-headed gull chick chipping its way out of the egg - the beak is visible, with its egg tooth. You can also see the pattern of tiny cracks in the shell that the chick has made on its way out.

    All these amazing things are going on near you as you read this... down your street, in your garden, in a nestbox or tree, or even in your roof. Let's hope that the weather's kind and our birds have a successful breeding season this year.