Fat penguins fall over more because they're less stable when walking

..but it makes them easy pickings for predators

• Scientists studied king penguins as they walked after feeding and fasting
• The birds spend long periods on land and so stock up on food while at sea
• This leaves the birds overweight and makes them less steady as they walk
• Researchers said they can sometimes be so fat they struggle to stand up

By Richard Gray for MailOnline

Published: 17 February 2016 

They look like over-stuffed butlers as they waddle out of the sea and onto dry land to begin their long treks back to their nests.

But it seems a session of stuffing themselves with fish out at sea can make the often epic journeys even harder for penguins than they already are - by making them more likely to fall over.

Researchers have discovered fat penguins are less steady on their feet and topple over due to the extra weight they are carrying in, and around, their stomachs.

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King penguins stock up on food and build fat reserves while hunting out at sea, but this can make it harder for them to walk back on land. Researchers have found the birds become less steady on their feet and more likely to fall over when overweight (left) compared to when they are slimmer (right)

Analysis of their waddles has shown the birds sway from side-to-side far more erratically after gorging themselves out at sea compared to when they are slim.

For fans of comedy wildlife footage, it means the tubby creatures are much more likely to face plant as they struggle up the beach from the ocean.

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PUTTING PENGUINS ON TREADMILLS

According to Dr Astrid Willener, getting penguins to walk on a treadmill was one of the biggest challenges she faced during her study.

She used wild birds captured on Possession Island, on the Crozet Archipelago off the coast of Antarctica.  

'The most difficult and tricky moment is when the treadmill first starts. Once the speed is set the penguins usually walk fluently,' she explained.

'Those that could not walk straight away and were quite difficult to train. Some individuals were lazy and "water-ski" on the treadmill by leaning their back on the wall behind them.' 

However, with some gentle encouragement she was able to get eight of the penguins to walk on the treadmill.

Using special cameras and fitting motion sensors to the birds, Dr Willener was able to measure the movements of these animal's bodies as they walked. 

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However, there is also a more serious consequence for the penguins as they can sometimes have difficulty standing upright, leaving them vulnerable to predators like giant petrels.

The findings suggest penguins have to find a careful balance between eating enough to ensure they do not starve while caring for their chicks on land, and not too much so they can still walk.

Dr Astrid Willener, an ecologist who conducted the research for her PhD while at Roehampton University in London, spent several months studying the gait of king penguins on Possession Island, in the Crozet Archipelago.

She told MailOnline: 'King penguins cannot eat while they are onshore​.

'As they may fast up to a month during the reproductive period, they arrive from the sea with ​fat reserves and ​their stomach's full.

'Indeed, king penguins returning back from the sea have sometimes difficulties standing up and walking.

'I did see penguins struggling to stand and walk, but when it was the case, predators spotted them fast, and start attacking them, pulling them apart and eating them alive​.

The researchers found the centre of gravity in overweight penguins tended shift, throwing the birds off balance (illustrated). Their waddle became more erratic and they swayed side-to-side far more when fatter

'It is why king penguins try to have a good balance between having a lot of fat reserves to fast longer, but they cannot eat too much otherwise they won't be able to stand properly while onshore and they will be attacked by their predators.'

Dr Willener's study builds on previous work she conducted using treadmills to analyse the comical waddle of king penguins.

She found their strange gait helps the birds pick up speed as they walk across the land as the side-to-side motion lets them take longer and wider strides while remaining stable.

However, in the latest research, she and her colleagues examined the differences between penguins returning from the sea after hunting and those returning to the sea after fasting.

King penguins (pictured) spend around 40 per cent of their time on land, but they are better adapted to swimming in the water. Their torpedo-shaped bodies and short legs makes it much harder for them to walk and so they adopt a waddle to help them pick up speed. Sadly, as they pile on weight this pushes them off balance

Using special cameras and motion trackers, they were able to analyse the birds' gait as they walked on a treadmill.

While in the water penguins are like living torpedoes, capable of swimming at up to 7.6mph (12km/h).

But on land, their streamlined bodies and powerful webbed feet at the end of short legs leave them at a distinct disadvantage.

The average speed of the birds as they waddle through the colony a rather unimpressive 0.9mph (1.4km/h), but on some occasions the animals must run to avoid being attacked by rivals.

Yet king penguins spend up to 40 per cent of their time ashore and can walk several miles to reach their nesting grounds.

 King penguins have a maximum speed of up to 7.6mph in the water but tend to only walk at around 0.9mph when on land. Despite this they can travel several miles to reach their nesting grounds

Emperor penguins can walk up to 60 miles (97km) across the Antarctic ice in the middle of winter as they travel from the sea to their nesting grounds.

The males and females take turns to leave the colony to hunt for fish and squid while the other remains ashore to care for the eggs and chicks.

This means they must build up fat reserves to help them survive their fast while on land and also bring back fish in their stomachs to feed their chicks.

Their weight can increase by at least 18 per cent on these strips, going from 24lbs (11kg) to more than 28lbs (13kg).

Dr Willener found that as the birds leave the water with this extra fat around their middle and food in their stomachs, their waddle becomes more erratic.

They tended to lean far more when overweight than when they were slimmer and they swayed side-to-side more too.

King penguin parents take it in turns to care for their chicks, which means they can spend long periods on land fasting while the other is out hunting at sea. When they return from a hunt they can be 18 per cent heavier than when they left after a prolonged fast at sea

Dr Willener said the extra mass around their stomachs appears to throw the birds off balance, making it harder for them to stay upright.

While humans are able to adapt their gait as they put on weight by leaning backwards to make themselves more stable, penguins do not.

The researcher explained: 'King penguins spend most of their time in the water and swim over 600km one way during the breeding season to reach the polar front to fish.

'Swimming is their primarily mode of locomotion. They are incredible good swimmers and have completely adapted for this.

'Despite this, they are also well adapted to walk. They are not very efficient in comparison to other pedestrians species, but their walking ability is amazing considering their huge body mass change and as it is 'only' their secondary mode of locomotion.'

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TOASTY HUG OF PENGUIN HUDDLES

They endure some of the coldest temperatures on the planet as they nest through the Antarctic winter, but emperor penguins get so warm as they huddle together on the ice that they have to resort to eating snow to cool down.

Researchers have found some of the birds get so hot in the tight bundle of bodies they risk overheating.

They also discovered huddles are more complicated and temporary than previously thought - lasting on average 50 minutes at a time. 

Previous estimates suggested the penguins hunkered down for as long as the storms lasted, which could be hours.

The birds were thought to stay warm by rotating from the outside to the inside of the huddle. 

But scientists at the University of Strasbourg in France have found the huddles regulate the birds' temperatures in a more complicated way, with some members breaking free to cool down. 

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