Owls sing to the moon

Eagle owls use the moon to talk to one another at night, according to a European team of researchers. They found that Eurasian eagle owls (Bubo bubo) call more on moonlit nights, when the moonlight illuminates the white patch of feathers they expose only when calling out loud.

The  owls rely mostly on a vocal call to communicate, but drive home the message with a flash of white feathers. The owl’s call, together with the bright white feathers, makes them rather noticeable in the dark of the night.

Eagle Owls: wolves in owl's clothing? Image: Hypothesis Now

The owls also favour higher perches on moonlit nights, presumably taking advantage of the more exposed position to make the most of the light shining on their stark white feathers. In contrast, the owls were often silent on moonless nights and, if they did call, the owls tended to do so from a lower perch.

Many animals alter their behaviour depending on the phases of the moon. Usually, bright nights make it easier for predators to find prey, so small animals keep quiet when the moon is full. Eagle owls, however, have no natural predators so they’re free to make themselves as eye-catching as possible to ensure nearby owls get the message. They usually communicate most at dusk and dawn, but a full moon produces almost as much light and the owls have learned to take advantage of it to call long into the night.

It may sound obvious, but the point of signalling is to be understood, and animals have evolved lots of clever tricks to get their messages across: many other birds have repeating calls, so the message is repeatedly broadcast; Anole lizards bob their heads to make themselves stand out from the background; and poisonous insects often use bright contrasting colours to warn off prospective predators. The eagle owls have simply learned to take advantage of another source of light.

Paper reference: Penteriani, V.,  Delgado, M.d.M.,  Campioni, L.,  Lourenço, R. (2010) Moonlight Makes Owls More Chatty. PLoS ONE 5(1): e8696. doi:10.1371/journal.pone.0008696

Knots of light and invisible darkness

The circle represents the hologram, out of which the knotted light emerges. Or, if that's all too much, look at the pretty colours... Image: University of Bristol

The image above is of an optical vortex loop –a knot tied in a beam of light. It was created by UK researchers using a sophisticated computer-generated hologram to wrap the light from a laser around itself.

In an optical vortex, light doesn’t travel in a straight line. Instead it is twisted tightly around itself like a corkscrew. At the very centre of the corkscrew the light waves cancel each other out – leaving a thin core of complete darkness. Bizarrely, light is doing this all around us; we just can’t see it!

The researchers have managed to take this twisted light and tie it into knots in the laboratory using holograms based on an obscure branch of mathematics called knot theory. It was originally developed to study real-life knots in rope but quickly grew to encompass theoretical knots and now encompasses more than six billion different knots!

Light-knotting is more than just a physics party-trick. It could be used to improve anything that requires very precise control over a beam of light. In particular, persuading light to twist like this will lead to better ‘optical tweezers’: focussed lasers that can be used to gently measure or nudge tiny particles, such as bacteria, viruses or individual molecules, with pinpoint accuracy.

Paper Reference: Dennis, M.R., King, R.P., Jack, B., O’Holleran, K., and Padgett, M.J. (2009) Isolated optical vortex knots Nature Physics, published online 17 January 2010. Doi:10.1038/nphys1504

Iguanas walked to distant islands

Crossing five thousand miles of open ocean is not an easy task, but this is exactly what iguanas living on isolated Pacific islands appeared to have accomplished. Now scientists have shown that iguanas living on the islands of Fiji and Tonga in the Pacific Ocean may have walked there when the islands were still connected to the mainland.

Iguanas. These ones don't look active enough swim that far... Image: Hypothesisnow

The alternative – drifting across the Pacific from South America on rafts of rotting vegetation– would require incredible luck and endurance. The new theory provides an enticing alternative, although ‘rafting’, as it is known, cannot be completely ruled out.

Fiji and Tonga were once part of the supercontinent Gondwana, which also included Australia, Antarctica, Africa, and parts of Asia. Fossil iguanas from Mongolia confirm that Gondwana did possess populations of iguanas, so it would have been easy for some to become stranded on islands when the supercontinent broke up.

This hypothesis was strengthened when researchers looked at the DNA of the iguanas living on Fiji and Tonga. They found that the iguanas split from other iguana species around 60 million years ago – before the islands were isolated from the continental mainland.

This just leaves one puzzling question: why don’t we find any iguanas on other Pacific islands which once belonged to the supercontinent?

The answer to this is much closer to home. When humans arrived on the other islands they adapted to local food sources – and ate the iguanas into extinction. Fiji and Tonga were settled much more recently, so their iguana populations have survived intact. This is supported by fossil evidence from other islands: sudden iguana extinction occurs just as people began to colonise the islands!

Noonan, B.P. and Sites Jr., J.W. (2010). Tracing the Origins of Iguanid Lizards and Boine Snakes of the Pacific. The American Naturalist, 175:1, p 61–72. DOI: 10.1086/648607

UK brought low by Arctic high

The weather outside is frightful... Image: NASA

The picture above, taken by NASA’s Terra satellite on the 7^th January, shows the completely snow-bound state of the UK. This winter, temperatures have regularly fallen below -10^oC in some parts of the country, and heavy snow has closed roads, schools and businesses. But why is this year so much colder than usual?

Globally, it isn’t. While the UK, parts of North America and China are suffering in the cold, other parts of the world, including the Mediterranean and Siberia, are experiencing unseasonal warmth. The cause of this confusing weather is an area of unusually high atmospheric pressure over the Arctic, which is driving colder air southwards towards northern Europe.

The changes in air pressure over the Arctic are known as the Arctic Oscillation (or AO, for short). It swings between positive (low pressure) and negative (high pressure). This year, the AO has become very ‘negative’, resulting in the freezing conditions some of us are shivering through at the moment.

One thing this cold weather doesn’t affect, however, is the reality of our changing global climate. Regional weather variations like this do not discredit the long-term climatic warming trend scientists from around the world have observed: the blame for which lies squarely with man’s increasing CO₂ emissions.

Champagne is good for you (in moderation)!

A glass of champagne is a great way to kick-start the new year celebrations. It may also be a great way to kick-start that New Year’s resolution to live healthily, according to scientists from the UK and France.

A toast - to good health! Image: Flickr/Waldo Jaquith

They found that drinking two glasses of champagne can improve blood flow around the body, reduce blood pressure and reduce the risk of blood clots forming. The health-giving effects of champagne are down to the presence of polyphenols. Polyphenols – which come from the grapes the champagne is made of – stop your body from removing nitric oxide from the blood stream. Nitric oxide is a signalling molecule that causes the bands of smooth muscle around blood vessels to relax. If it stays in the blood for longer it has a greater effect – widening blood vessels even further. Wider blood vessels mean better blood flow and lower blood pressure – both very good things.

The researchers made their discovery by comparing the effects on the cardiac system of healthy volunteers of champagne and of a similarly alcoholic – but polyphenol-free – drink. The blood vessels of volunteers who drank champagne were much wider for up to eight hours afterwards; suggesting champagne gives a short-term boost to cardiac health.

Polyphenols in red wine have been associated with good cardiac health for a while. The polyphenols come from the red grapes used to make the wine: white wine contains far fewer polyphenols and does not grant the same health benefits as red. Champagne is made from red and white grapes, and so contains polyphenols in sufficient quantity to have a noticeable effect on health.

A note of caution however: the researchers don’t yet know whether regularly drinking champagne over a long period of time would have any major health benefits. Of course, drinking too much alcohol is a really unhealthy thing to do, but a couple of glasses of champagne may be just what the doctor ordered – if you can afford it!

Happy New Year!

Paper reference: Vauzour, D., Houseman, E.J., George, T.W. Corona, G., Garnotel, R., Jackson, K.J., Sellier, C., Gillery, P., Kennedy, O.B., Lovegrove, J.A., and Spencer, J.P.E.. Moderate Champagne consumption promotes an acute improvement in acute endothelial-independent vascular function in healthy human volunteers. British Journal of Nutrition, published online 30 Nov 2009. doi:10.1017/S0007114509992959