Posts Tagged ‘Australian animals’

Bats ‘fly by polarised light’


Bats ‘fly by polarised light’

By Jonathan Webb
Science reporter, BBC News


The new study suggests that bats calibrate their in-built magnetic compass using polarised light at sunset

Bats use the pattern of polarised light in the evening sky to get their bearings, according to a new study.

As well as having unusual echolocation skills and their own magnetic compass, bats are now the first mammals known to make use of polarised light.

Other animals with this ability include birds, anchovies and dung beetles.

To make the discovery, published in Nature Communications, zoologists placed bats in boxes with polarising windows before watching them fly home.

Light waves normally wiggle all around their direction of travel, but when they pass through special filters – or are scattered by gases in the atmosphere – they can become polarised, so that the oscillations all line up.

“We initially didn’t think that the bats would use polarised light,” said the paper’s senior author, Dr Richard Holland from Queen’s University in Belfast.

Dr Holland was one of the scientists who discovered in 2006 that bats navigate by somehow sensing the earth’s magnetic field – but that in-built compass needs to be calibrated. Other experiments showed that the calibration was happening at sunset, when the bats’ day begins.

“We thought that surely, the sun’s disc itself would be a more likely cue,” Dr Holland told the BBC. But his team recently tested how bats responded when the sun’s image was shifted by mirrors, and found no difference.

Guided by the polarised light? One of the greater mouse-eared bats used in the study

So they switched their attention to the pattern of polarised light that appears at sunset, which is already known to be important for various other animals, particularly birds.

t’s invisible to humans, unless we wear polarising glasses. “If you were standing looking at the sun, you’d see a dark band going directly over your head, from left to right,” explained Dr Holland.

Mysterious ability

To find out if bats were using this pattern, the scientists put them into boxes with a nice view of the sunset, but only through custom-made polarising windows. Half the boxes had windows that recreated the normal pattern, and half flipped it around by 90 degrees.

Then they took the bats about 20km from their home roost in a Bulgarian cave, released them and tracked them. Sure enough, the bats from the boxes with rotated windows were much more erratic at heading toward home.

In proper scientific fashion, when Dr Holland was collecting the data he was “blinded” as to which group of bats was which – and he initially thought he might be wrong all over again.

When a colleague revealed the real designation and they compared both sets of results, it was a satisfying moment. “Whenever you set out to test one of these ideas, it’s always amazing that it actually works!” Dr Holland said.

Bats were taken from a cave in north-eastern Bulgaria and tracked as they flew home again


Although plenty of other animals, including some birds, fish, amphibians and insects, are known to detect polarised light, the only other mammal that we know can perceive it is, in fact, humans. In certain situations, such as when light reflects off glass or water at particular angles, or when we look at white areas on an LCD screen, some people see a blurry phenomenon known as “Haidinger’s brush” – produced by the polarisation of light.

According to Dr Marie Dacke, who studies animal vision at the Lund University in Sweden, how this happens is still a mystery.

Insects, Dr Dacke explained, have specialised receptors in their eyes for detecting polarisation. “But in birds and fish and so on, we don’t really have a clue about how they’re able to perceive this kind of light,” she told the BBC.

“I did not expect them to find that in mammals, such as in a bat. So I thought this was really fascinating.

“The big challenge will actually be to find the mechanism by which bats are able to do this. There is still a bit to reveal before the full story is known.”

Here’s an interesting video clip on studies into Australian bats.


Unesco warns Australia over Great Barrier Reef

The Great Barrier Reef is the world’s largest coral structure and home to rich marine life

Unesco has threatened to list the Great Barrier Reef as a World Heritage in Danger site, amid controversy over a plan to dump dredged sediment.

Reef authorities granted permission for the dumping in January as part of a project to create one of the world’s biggest coal ports.

But scientists have warned that the sediment could smother or poison coral.

Unesco said given “significant threats” to the reef, it should be considered for inclusion on the danger list.

The Great Barrier Reef is the world’s largest coral structure, rich in marine life. It stretches for more than 2,600km (1,680 miles) along Australia’s eastern coast.

‘Other alternatives’
The dumping is part of a major development that would allow several companies to export coal reserves from the Galilee Basin area through the Abbot Point port.

Abbot Point lies south of Townsville on the Queensland coast.

Late last year, the government approved an application for the coal terminal to be expanded. The dredging is needed to allow ships into the port.

The approved disposal site for the dredged sediment is located approximately 25km (16 miles) east-north-east of the port, inside the marine park.

The disposal operation would be “subject to strict environmental conditions”, the Great Barrier Reef Marine Park Authority said when it approved the plan.

But the plan remains highly controversial.

In its report, Unesco said that the Abbot Point dumping plan was “noted with concern”.

“Indeed, this was approved, despite an indication that less impacting disposal alternatives may exist,” the report pointed out.

More widely, it said that a long-term plan for sustainable development due to be completed by Australia by 2015 had to result in “concrete and consistent management measures sufficiently robust to ensure the overall conservation” of the reef.

In particular, it had to address major drivers of reef decline “such as water quality and climate change, and the need to constrain coastal development and associated activities”.

“Given the range of significant threats affecting the property and the conflicting information about the effectiveness of recent decisions and draft policies, significant concern remains regarding the long-term deterioration of key aspects of… [the reef] and the completion of work to tackle short- and long-term threats,” it said.

In the absence of “substantial progress”, Unesco should consider putting the reef on the endangered list at a summit to be held in 2015, the report said.

Australia’s Environment Minister Greg Hunt pointed out that the report highlighted progress in a number of areas, including water quality.

The approval of the Abbot Point development “was subject to rigorous environmental assessment”, he said in a statement.

Queensland’s Environment Minister Andrew Powell, meanwhile, said he was confident that ongoing work would mean the reef was not listed as endangered.

“We are committed to protecting the reef, we can continue to operate sensible, environmentally responsible ports adjacent to the reef,” the Australian Broadcasting Corporation quoted him as saying.

Take a 3 minute break and enjoy some beautiful underwater pictures from the reefs around Australia.

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