March 2017

There is a lot happening in space right now with probes looking at distant planets and asteroids, and many planned space missions that will launch soon to investigate gravitational waves, dark matter and all sorts of other phenomena.  One thing all of these spacecraft have in common is the need for power.  Most experiments are long-term and so battery power is not an option and neither is any sort of refuelling.  So they will get their power from the sun using solar panels.  The problem with that is that the panels need to be really big especially if they are going to be a long way from the sun.  In order to use large panels that need to be fitted inside much smaller launch modules, they will need to be folded.  Not only will they need to be folded, but they will need to unfold reliably because there will be no engineer there to give them a kick.  The designers, however, are looking much closer to home to see how best to fold them.  There are two things in nature that unfold reliably – leaves and beetles wings, and studying these has allowed the designers to improve the designs making them both lightweight and easy to deploy.

It may not be immediately apparent, but if you look at a freshly emerged beech leaf and at the size of the bud it has just emerged from, then there is a big mismatch.  The bud is much shorter and less wide than the leaf, and that is because the leaf is folded up inside the bud.  That initial burst from the bud is relatively rapid as sap is forced into the veins and the leaf flattens out, ready to quickly use the sun’s energy to provide the sugars and proteins the tree will need for growth.  The leaf will carry on growing until it reaches full size, but nowhere near as rapidly as that initial unfolding from the bud as can be seen in time-lapse videos of the process.  (There are plenty of examples on UTube.)

Even more remarkable than the unfolding leaf, is the beetle’s wing.  And it is remarkable because it has to fold as well as unfold.  Most flying insects have four wings – butterflies, bees, dragonflies to name a few, but beetles’ wings have evolved so that the forewings form a tough shell to protect them from predators, leaving the hindwings to do all the flying.  (Evolution didn’t quite get it right in this case though.  The whole point about flight is that it gets you away from predators, but if you’ve got a tough shell that predators can’t penetrate, then why have wings as well?  So, many beetles – appropriately called ground beetles – only have the tough outer shell that is firmly welded shut.)

Violaceous Ground Beetle - note the one piece wing case.

  If you look at a ladybird, for example, you may see its wing-cases open as it prepares to fly, but the unfolding of the hindwings is almost instant and too fast to follow.  You have a much better chance of seeing them fold the hindwings when they land and you will see the much longer hindwings tuck themselves under the wing-cases.

The remarkable thing about this wing folding is that there are no muscles in the wing itself.  The folding and unfolding is all done by subtle flexing of the wing at the joint where it is attached to the insect’s body, as well as having veins that curve and bend in such a way that they pop into a rigid structure when flight is required, and un-pop into folds when compactness is required.

Talking of veins, I didn’t realize until relatively recently that the veins in insect wings aren’t veins.  That is, they don’t carry blood around the wings.  When the adult insect first emerges from its cocoon, the wings are soft and it has to pump fluid into the veins to expand the wings to their full size. (Think butterfly and chrysalis.)  But once expanded, that’s it, the fluid doesn’t circulate. The veins are just there to stiffen the wings and if a piece of wing falls off or is knocked off by a predator, the veins don’t leak because there is no fluid after the initial inflation.  Amazing!

If you want to see leaves unfolding or ladybirds wings unfolding, then you don’t have long to wait, it’ll be happening in a garden near you any day now.

If you want to prove to yourself that a leaf can fit in a smaller bud, try this -

Take a piece of A4 paper and fold it lengthwise like so -

Then mark a line at about 60 degrees from about a third of the way along the fold, like so -

Then fold along the line you have drawn and fold back and forth in half-inch strips to make a shape something like this -

Then open out the paper like this -

Then the tricky bit is to reverse the folds on one half of the paper so that peaks become troughs and vice versa. (Use the edge of a ruler to fold it against.) It should then look like this. -

You can then cut it into a rough leaf shape if you want, like so -

Then you should be able to fold it enough to fit inside its bud, or at least so that it is both shorter and narrower than the original piece of paper - nature is much better at origami than us humans!

February 2017

Winter is a time to keep warm and contemplate. So I have been mostly contemplating feet. Nothing for chiropodists to worry about, I wouldn’t want to tread on any toes, so instead I’ve been thinking about birds’ feet.  Birds’ feet are particularly well adapted for what they do, which is to support the bird that they are attached to, in the way that the bird needs them to – which is to perch, hop, walk, run or cling.

Feet of a young robin - standard perching feet

The first thing to notice about a bird’s foot is that they are quite small – not because they don’t need to be bigger, but because they are lighter that way.  The whole of a bird’s anatomy is tuned to being as light as possible from beaks to hollow bones, not to mention the arrangement of the lungs and the amazingly strong and light feathers so that flight involves the least effort.  If you look at any flightless bird such as a kiwi, you will notice how stocky the legs are – the same basic pattern, but much heavier.

A pukeko, another flightless bird from New Zealand with
very sturdy legs.

A poor photo, but you can still see the 'tree-trunkiness' of the
 legs relative to the size of the kiwi.

  At the other end of the scale are swifts’ legs; these are short and almost useless because swifts spend the whole of their life apart from nesting, mating and fledging in the air.  If you see a swift-like bird perched on a wire then it will be a swallow or a martin, never a swift.

When it comes to perching, there are a number of ways this is done; most birds have three forward pointing toes and claws, and one pointing backwards.   This is an ideal arrangement for gripping a twig or a branch, but it’s not all about perching or roosting; woodpeckers and their ilk use the same arrangement to cling to the trunks of trees.  The three forward, one back arrangement works here quite well, but the relatively heavy woodpecker has also developed short and strong tail feathers which are used to brace it against the trunk. 

A young woodpecker, not a good photo but it shows long claws
 and the two very stiff tail feathers

Nuthatches and treecreepers don’t need to use their tail for balance; they rely instead on strong toes and longer claws than other birds.  The nuthatch is renowned for being able to climb down the trunk as well as up and it relies on an exceptionally strong rear claw to achieve this.  This gives them a different range of insects perhaps invisible to an upward facing bird like the treecreeper that doesn’t have that ability.  (I was once told that nuthatches have two backward facing toes but this appears not to be the case.) Whilst on the subject of perching – when did you last see a gull or a duck perched in a tree?  It is a rare sight, and you will only see them do it on relatively wide, flat branches and it is simply because they don’t have the rearward facing toe like other birds.  Their feet are webbed for swimming and the rear toe has been reduced to a small spur on the back of their legs. 

If you do happen to see a large gull sat in a tree, you may want to know if it is a greater or a lesser black-backed gull.  The most reliable indicator is not the greyness or blackness of their wings but rather that one has yellow legs, the other has pink legs.  All you need to do then is remember which is which!  Identification by birdwatchers is one thing that evolution hasn’t worked out yet, but feet can be quite distinctive.  Some birdwatchers reckon to be able to tell the difference between a willow warbler and a chiffchaff by the colour of their legs.  One has darker legs, but that really needs them sat side by side.  Apparently the only reliable indicator is that one has a notch in the third primary wing feather, the other doesn’t.  So you just need to catch it and then remember which is which! 

The Common Kestrel - in India

Same kestrel slightly enlarged showing the shiny black claws.

Recently I took a photo of a kestrel in a place where the lesser kestrel was also a possibility.  Fortunately, the difference is clear – the lesser kestrel has yellow legs and pale claws and the common kestrel has yellow legs and black claws – and beautifully shiny black claws they were too.