Ants use Sun and memories to navigate

By Helen Briggs BBC News

19 January 2017

Ants are even more impressive at navigating than we thought.

Scientists say they can follow a compass route, regardless of the direction in which they are facing.

It is the equivalent of trying to find your way home while walking backwards or even spinning round and round.

Experiments suggest ants keep to the right path by plotting the Sun's position in the sky which they combine with visual information about their surroundings.

"Our main finding is that ants can decouple their direction of travel from their body orientation," said Dr Antoine Wystrach of the University of Edinburgh and CNRS in Paris.

"They can maintain a direction of travel, let's say north, independently of their current body orientation."

Ants stand out in the insect world because of their navigational ability.

Living in large colonies, they need to forage for food and carry it back to their nest.

This often requires dragging food long distances backwards.

Scientists say that despite its small size, the brain of ants is remarkably sophisticated.

"They construct a more sophisticated representation of direction than we envisaged and they can incorporate or integrate information from different modalities into that representation," Dr Wystrach added.

 

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Ground squirrels use the sun to hide food

September 12, 2016

Ground squirrels use information on the position of the sun when hiding their food and reuse this information to find their food stash again. The position of the sun serves as a reference point for the animals, which live in southern Africa, to orient themselves and adjust the direction they are traveling in. A study published by researchers from the University of Zurich sheds new light on the old question as to how animals find their bearings within their environment.

Jamie Samson and Marta Manser from the Department of Evolutionary Biology and Environmental 1Studies at UZH studied colonies of Cape ground squirrels (Xerus inauris) in the wild at the Kalahari Research Center in South Africa. The diurnal rodents temporarily store their food reserves in several hiding places. As their habitat is very arid and sparsely vegetated, points of reference in the environment, such as trees or bushes, are few and far between. The UZH researchers have now discovered how the social rodents orient themselves to find their way back to their temporary food stashes. "The squirrels probably use the position of the sun as the most important cue to roughly adjust their direction of movement," explains Samson.

Position of the sun as a rough guide

The behavioral biologists gave the ground squirrels food to hide. The direction in which the rodents bolted with their spoils was recorded with the aid of GPS points. The striking thing was that the animals moved in an almost straight line either towards or away from the sun to find a suitable hiding place. Every time, the horizontal angle of their direction of movement deviated slightly from the direction of the sun. "Based on this movement pattern," interprets Samson, "we presume that Cape ground squirrels use the position of the sun at a particular time of day as a rule of thumb to find their bearings when searching for a place to hide their food."

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Monarch butterfly uses magnetic, Sun compasses, study finds

The North American monarch butterfly uses the Sun as well as Earth's magnetic field as navigational tools for its famous long-distance migration, scientists said Tuesday.

The insects with their characteristic orange-and-black wings flutter thousands of kilometres each year from the United States and southern Canada to the Michoacan mountains in central Mexico, where they overwinter.

The butterflies, whose Latin name is Danaus plexippus, have long been known to use a type of solar compass in the brain.

Yet, curiously, they are also able to migrate when skies are heavily overcast, which suggested co-reliance on a magnetic compass.

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Loch Ness is giant 'spirit level'

Scientists have measured the way Loch Ness tilts back and forth as the whole of Scotland bends with the passing of the tides.

It is a tiny signal seen in the way the waters at the ends of the 35km-long lake rise and fall.

When combined with the direct tug from the gravity of the Moon and Sun, the loch surface goes up and down by just 1.5mm.

The study is reported in the Journal of Geophysical Research.

"If you were on a boat in the middle of the loch, you certainly wouldn't notice it," said Philip Woodworth from the UK National Oceanography Centre (NOC), Liverpool, "but a tide like this has never been observed in a western European lake before."

Prof Woodworth, David Pugh and Machiel Bos say their precision measurement technique could be used in other lakes around the world to understand better how the Earth's crust deforms as a result of ocean movements - rather like a carpenter will use a spirit level to gauge how a length of wood deviates from the horizontal.

"I have described Loch Ness as the largest spirit level in the world," David Pugh, who is a visiting professor at NOC, told BBC News.

None of us can feel it, but Britain rises and falls by centimetres every 12 hours and 25 minutes as a great bulge of ocean water washes around the country.

The pencil-shaped Loch Ness is the largest UK lake by volume, and although inland, is close enough to the North Sea to be influenced by this loading effect.

The team placed their sensors a few metres under the lake surface at six locations, from Fort Augustus in the far southwest to Aldourie in the far northeast. They then monitored the change in the height of the overlying water during the course of 201 days.

What the scientists saw was a clear spike in the data twice a day - the result of the gravitational pull of the Moon and Sun. But they could also tease out a second signal stemming from the way water rises and falls as a result of the tilting of the land. And, in fact, the latter effect sits on top of the first and is responsible for most of the amplitude change.

The team says the measurement was made to an accuracy of just 0.1 mm over the loch's 35 km length.

"We had to extract the tidal signal and get rid of all the noise. This involved very high precision," explained David Pugh.

"For example, the loch itself goes up and down every day by four centimetres just due to the pump storage scheme for hydroelectric generation, and we have to pull out a very small signal within that.

"The holy grail would be to learn from the effects of the tides something about the Earth's crust. So the more precise we can get, the more we may learn about the crust. So the more precise we can get, the more we can learn about the crust."
The University of Dundee is a Scottish Registered Charity, No. SC015096.


http://www.bbc.co.uk/news/science-environment-16394421