Curious Kids: how do magpies detect worms and other food underground?

Magpies have a few clever tricks to help them find food.
Gisela Kaplan, Author provided

Gisela Kaplan, University of New England

How do magpies detect worms and other food sources underground? I often see them look or listen, then rapidly hop across the ground and start digging with their beak and extract a worm or bug from the earth – Catherine, age 10, Perth.

You have posed a very good question.

Foraging for food can involve sight, hearing and even smell. In almost all cases learning is involved. Magpies are ground foragers, setting one foot before the other looking for food while walking, called walk-foraging. It looks like this:

This is called walk-foraging.
Gisela Kaplan, Author provided

Finding food on the ground, such as beetles and other insects, is not as easy as it may sound. The ground can be uneven and covered with leaves, grasses and rocks. Insects may be hiding, camouflaged, or staying so still it is hard for a magpie to notice them.

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Detecting a small object on the ground requires keen vision and experience, to discriminate between the parts that are important and those that are not.

Magpie eyes, as for most birds, are on the side of the head (humans and other birds of prey, by contrast, have eyes that face forward).

A magpie’s eyes are at the side of its head and it can only see something with both eyes if that is straight in front of the bird.
Shutterstock/Webb Photography

To see a small area in front of them, close to the ground, birds use both eyes together (scientists call this binocular vision). But birds mostly see via the eyes looking out to the side (which is called monocular vision).

This picture gives you an idea of what a magpie can see with its left eye, what it can see with its right eye and what area it can see with both eyes working together (binocular vision).

Here’s how a magpie’s field of vision works.
Gisela Kaplan, Author provided

You asked about underground foraging. Some of that foraging can also be done by sight. Worms, for instance, may leave a small mound (called a cast) on the surface and, to the experienced bird, this indicates that a worm is just below.

Magpies can also go a huge step further. They can identify big scarab larvae underground without any visual help at all.

Here is a scarab larva.
Gisela Kaplan, Author provided

Scarab larvae look like grubs. They munch on grassroots and can kill entire grazing fields. Once they transform into beetles (commonly called Christmas beetles) they can do even more damage by eating all the leaves off eucalyptus trees.

Here is the secret: magpies have such good hearing, they can hear the very faint sound of grass roots being chewed.

We know this from experiments using small speakers under the soil playing back recorded sounds of scarab beetle larvae. Magpies located the speaker every time and dug it up.

An Australian magpie digging for food in a lawn.
Flickr/Lance, CC BY-NC-ND

So how do they do it? Several movements are involved.

To make certain that a jab with its beak will hit the exact spot where the juicy grub is, the magpie first walks slowly and scans the ground. It then stops and looks closely at the ground – seemingly with both eyes working together.

Then, holding absolutely still, the magpie turns its head so the left side of the head and ear is close to the ground for a final confirming listen.

Finally, the bird straightens up, then executes a powerful jab into the ground before retrieving the grub.

An Australian magpie digging for food gets a grub.
Wikimedia/Toby Hudson, CC BY-SA

That is very clever of the magpies. Very few animals can extract food they can’t see. Only great apes and humans were thought to have this ability. Clever magpies indeed. And farmers love them for keeping a major pest under control.

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Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to Conversation

Gisela Kaplan, Emeritus Professor in Animal Behaviour, University of New England

This article is republished from The Conversation under a Creative Commons license. Read the original article.

New technology offers hope for storing carbon dioxide underground

Dom Wolff-Boenisch, Curtin University

To halt climate change and prevent dangerous warming, we ultimately have to stop pumping greenhouse gases into the atmosphere. While the world is making slow progress on reducing emissions, there are more radical options, such as removing greenhouse gases from the atmosphere and storing them underground.

In a paper published today in Science my colleagues and I report on a successful trial converting carbon dioxide (CO₂) to rock and storing it underground in Iceland. Although we trialled only a small amount of CO₂, this method has enormous potential.

Here’s how it works.

Turning CO₂ to rock

Our paper is the culmination of a decade of scientific field and laboratory work known as CarbFix in Iceland, working with a group of international scientists, among them Wallace Broecker who coined the expression “global warming” in the 1970s. We also worked with the Icelandic geothermal energy company Reykjavik Energy.

The idea itself to convert CO₂ into carbonate minerals, the basis of limestone, is not new. In fact, Earth itself has been using this conversion technique for aeons to control atmospheric CO₂ levels.

However, scientific opinion had it up to now that converting CO₂ from a gas to a solid (known as mineralisation) would take thousands (or tens of thousands) of years, and would be too slow to be used on an industrial scale.

To settle this question, we prepared a field trial using Reykjavik Energy’s injection and monitoring wells. In 2012, after many years of preparation, we injected 248 tonnes of CO₂ in two separate phases into basalt rocks around 550m underground.

Most CO₂ sequestration projects inject and store “supercritical CO₂”, which is CO₂ gas that has been compressed under pressure to considerably decrease its volume*. However, supercritical CO₂ is buoyant, like a gas, and this approach has thus proved controversial due to the possibility of leaks from the storage reservoir upwards into groundwater and eventually back to the atmosphere.

In fact, some European countries such as the Netherlands have stopped their efforts to store supercritical CO₂ on land because of lack of public acceptance, driven by the fear of possible leaks in the unforeseeable future. Austria went even so far as to ban underground storage of carbon dioxide outright.

The injection well with monitoring station in the background.
Dom Wolff-Boenisch, Author provided

Our Icelandic trial worked in a different way. We first dissolved CO₂ in water to create sparkling water. This carbonated water has two advantages over supercritical CO₂ gas.

First, it is acidic, and attacks basalt which is prone to dissolve under acidic conditions.

Second, the CO₂ cannot escape because it is dissolved and will not rise to the surface. As long as it remains under pressure it will not rise to the surface (you can see the same effect when you crack open a soda can; only then is the dissolved CO₂ released back into the air).

Dissolving basalt means elements such as calcium, magnesium, and iron are released into pore water. Basaltic rocks are rich in these metals that team up with the dissolved CO₂ and form solid carbonate minerals.

Through observations and tracer studies at the monitoring well, we found that over 95% of the injected CO₂ (around 235 tonnes) was converted to carbonate minerals in less than two years. While the initial amount of injected CO₂ was small, the Icelandic field trial clearly shows that mineralisation of CO₂ is feasible and more importantly, fast.

Storing CO₂ under the oceans

The good news is this technology need not be exclusive to Iceland. Mineralisation of CO₂ requires basaltic or peridotitic rocks because these types of rocks are rich in the metals required to form carbonates and bind the CO₂.

As it turns out the entire vast ocean floor is made up of kilometre-thick oceanic basaltic crust, as are large areas on the continental margins. There are also vast land areas covered with basalt (so-called igneous provinces) or peridotite (so-called “ophiolitic complexes”).

The overall potential storage capacity for CO₂ is much larger than the global CO₂ emissions of many centuries. The mineralisation process removes the crucial problem of buoyancy and the need for permanent monitoring of the injected CO₂ to stop and remedy potential leakage to the surface, an issue that supercritical CO₂ injection sites will face for centuries or even millennia to come.

On the downside, CO₂ mineralisation with carbonated water requires substantial amounts of water, meaning that this mineralisation technique can only succeed where vast supplies of water are available.

However, there is no shortage of seawater on the ocean floor or continental margins. Rather, the costs involved present a major hurdle to this kind of permanent storage option, for the time being at least.

In the case of our trial, a tonne of mineralised CO₂ via carbonated water cost about US$17, roughly twice that of using supercritical CO₂ for storage.

It means that as long as there are no financial incentives such as a carbon tax or higher price on carbon emissions, there is no real driving force for carbon storage, irrespective of the technique we use.

*Correction: The sentence has been corrected to note that gas volume rather than density decreases when it is compressed. Thankyou to the readers who pointed out the error.

The Conversation

Dom Wolff-Boenisch, Senior Lecturer, Western Australian School of Mines, Curtin University

This article was originally published on The Conversation. Read the original article.

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