It's been a while since I posted a
birdy blog and since I got some nice pictures of a Cardinal
Woodpecker at the weekend, I thought I'd use it as an opportunity to
talk about woodpeckers in general, since they're surprisingly
important in the habitats they occupy. As usual, we'll look to answer
the three questions I use to prompt me when seeing wildlife – what
is it? What's it doing? And what's it's role in the ecosystem.
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Female Nubian Woodpecker, Kisima Ngeda, Aug 2011 |
So, for identification, woodpeckers are
generally fairly easy. In most of northern Tanzania and Kenya, there
are four common species of savannah woodpeckers – the commonly seen
Nubian, spotted all over; Bearded, the largest and with a black
throat and stripy face; the rather small and neat Cardinal, with
spots on the back and streaks on the front, and the very colourful
Grey. Away from the dry north of Tanzania the Nubian is replaced by a
number of other options – Bennett's or Speckle-throated being the
obvious ones. There are plenty of other species around, of course,
but they're mainly associated with forest and we'll forget about them
for now. Woodpeckers in general are rather widespread, obviously
similar species occur on every continent except, rather strangely,
Australia. They're relatively closely related to barbets and
hornbills (note the zygodactyly – two toes forwards, two-toes
backwards – they share with the barbets, easily seen in some of
these photos). So, that's what they are. Now what do they do?
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Male Cardinal Woodpecker, Manyara Ranch, Nov 2011 |
Normally you'll come across a
woodpecker first when you hear it, either calling – Nubians in
particular are noisy – or from hearing the 'tap-tap-tap' of their
beak on a tree. Calling is often done by pairs, and we can safely
assume it serves the dual purpose of strengthening a pair bond and
communicating to neighbours that the territory is occupied. The
tapping is where it gets more interesting – most of this is
exploratory, trying to find hollow bits under the bark where tasty
larvae may live, some is more obviously getting at the food once
they've found it, and some it again a territorial statement like
calling – though this purpose seems to be less common here in
Africa than in northern regions. And the most interesting of all is
the hard banging they use to excavate nest holes. I'm sure (unless
you're Australian!) we've all seen the beautifully neat holes
woodpeckers make for their nests, often several holes in a single
stem. There's two things that are particularly interesting about this
to me – the first is how they do it in the first place. The speed
and pressure generated in order to dig into the wood is extraordinary
–
the deceleration from 6-7m/sec to stationary at impact isequivalent to 1000 times the pull of gravity – the effect on humans
would be similar to Usain Bolt running head-first into a brick wall
at the end of his 100m sprint. Not pretty, I should think! And the
adaptations they have to avoid the problems we'd get from banging out
head on a brick wall are also impressive –
slightly differentlength upper and lower mandibles, extra thick skull, fluid-filledshock absorbers, unusual size and shape of brain, etc., etc. Quite
remarkable really!
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Grey Woodpecker, Near Arusha, March 2011 |
But the second thing about these holes
is where they get really interesting.
Woodpeckers mostly use theholes they excavate only once, after which the holes are available to
anything else that likes to live in holes – birds, bats, other
mammals and all. In fact, there's a huge array of animals that live
in holes, but can't make them themselves (though some, like barbets,
may make adjustments to get the hole right for them). Over time the
holes get larger and larger, allowing a whole host of species to find
homes. I
n some northern forests, woodpeckers have disappeared (for anumber of reasons we don't need to go into), and once the holes aregone, so too do all the other species that make use of them. Thus the
loss of woodpeckers has much greater impacts on the whole ecology of
a woodland than the simple direct effect – the consequences cascade
down through other species too. Which is exactly why
some people suggest woodpeckers may be seen as keystone species – a single
species that holds together a whole load of other species and have
disproportionate impacts on the ecosystem. Mighty important things,
woodpeckers!
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This Brown-breasted Barbet is probably uing an old woodpecker hole, Nr Boma Ng'ombe, March 2011 |
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