Foxes The Wonder of Animals

Planet Earth.

Millions of species.

But a few are special.

Born to thrive.

These are the opportunists.

The collaborators.

The survivors.

What makes these animals so successful?

In this series, we'll delve deep beneath the skin,

to reveal the unique features that set some species apart.

New behaviour and the very latest scientific discoveries

will offer fresh insight into the wonder of animals.

Across the planet, carnivores are struggling

to compete in a world with a rocketing human population.

But one predator is bucking the trend.

Its numbers appear to be increasing,

and its geographical range, expanding.

It's now the most widespread of all carnivores,

the fox.

Resourceful...

..opportunistic...

..and capable of exploiting the most extreme habitats on Earth.

Whatever the circumstances,

the fox can adapt.

Our planet is constantly changing,

but foxes are simply taking it in their stride.

Their super-sharp senses mean that they can hunt

during the day, and also at night.

Their intelligence allows them to cope with seasonal fluctuations,

and their flexibility means that foxes can thrive

in spite of some of the most dramatic human-induced changes.

In this episode, we're going to find out exactly what it is

that makes foxes so adaptable...

..starting with the senses.

Most predators have evolved to specialise

either nocturnally or diurnally.

But foxes are different.

They can hunt both day and night.

And that's mainly down to their impressive eyes.

The fennec fox lives in the Sahara Desert

and like all foxes, it can operate under the cover of darkness.

Its pupils dilate, allowing as much light as possible to enter the eye.

At least 97% of the photoreceptors in their retina

are rods, rather than cones.

Cone cells detect colour,

whereas rods are much more sensitive in low light levels.

Having such a high proportion of these

gives the fox acute night-vision.

But in the day, these light-sensitive rod cells

serve a completely different purpose.

This is the Tibetan sand fox.

Rabbit-like creatures, known as pikas, are their prey.

But the fox must first spot them, far away in the distance.

This is where the rods switch function.

They instantly become motion sensors,

allowing the fox to pinpoint the tiny pikas...

..even when they are almost a kilometre away.

The moment their prey moves, the densely packed rods

pick up the change in light...

..triggering the fox to lock on to its target.

Once it's in striking distance,

the attack begins.

But it's not just the retina that helps foxes to hunt in the day,

the shape of the pupil is also key.

Wolves and other members of the dog family have round pupils.

But foxes eyes are different to the rest of the canids.

Their vertically-slit pupils are more similar to a cat's.

Both animals have evolved this physiology separately,

but they have the same effect.

For a long time, it was thought that this slit pupil

gave both animals better night vision.

But new research from the University of Sydney

suggests this shape actually helps them to hunt in the day.

The fennec fox must hunt in daylight to find enough food,

but sunlight can be harmful.

In the UK, the UV index is classified at a moderate 6,

but here in the Sahara,

it reaches the maximum strength of 11.

When combined with light reflection from the sand and rock,

the sun's rays have the potential to do serious damage to the eye.

And this is where the slit pupil comes into its own.

The coloured rings show the areas on the lens

which are used to focus on different colours.

In bright light, round pupils contract to protect the eyes

against harmful rays, blocking the outer colour completely.

This means that particular colour can't be focused,

blurring the overall image.

But when a slit pupil contracts,

all colours remain focused.

This means that even in the most intense light,

foxes can protect the sensitive night-vision areas

at the back of the eye

whilst also maintaining a sharp, full-colour image.

The result is a remarkable ability

to hunt at any time of day or night.

But when it's the seasons that change

foxes have to rely on other senses.

Superior eyesight is obviously no good

when prey is hidden deep beneath the snow.

For this, the fox has an extra sense,

and it's one that no other animal on Earth has harnessed for hunting.

Winter in the Yellowstone National Park.

The snow here is regularly more than two metres deep.

A red fox can survive here all winter,

but only if it can find enough food.

Their ability to pinpoint rodents beneath the thick layer of snow

has always been attributed to their exceptional hearing,

and that is...part of the process.

Foxes can move each ear independently,

rotating them up to 150 degrees.

More than a dozen separate muscles finely tune

the position of the ear canal so the fox can identify a sound

and locate it more accurately.

But in 2010, scientists uncovered something astonishing.

It's long been known that to reach the prey beneath the snow,

or even in thick grass, foxes use a technique called a "mouse pounce".

What this recent survey found

was that the overall hit rate was just 18%,

but when the fox faced in a north-easterly direction

the hit rate rose to a staggering 73%.

Unbelievably, the foxes seemed to be aligning their pounces

to the Earth's magnetic field,

which tilts downward in the northern hemisphere.

It's thought that the fox can detect this magnetism.

As the fox creeps forward,

it listens for the sound of a mouse,

searching for that sweet spot

where the angle of the sound hitting its ears

matches the slope of the Earth's magnetic field.

When it finds that spot,

the fox knows that the prey is a fixed distance away,

and it can calculate exactly how far to jump to land right on top of it.

Scientists think that the secret behind this talent

might be a protein in the fox's eye

called crypto-chrome, which is sensitive

to the Earth's natural magnetism.

What's more, they speculate that this might actually allow them

to see the magnetic field as a patch in their vision.

If the scientists are correct,

the red fox would be the first animal known

to use the Earth's magnetic field to hunt.

Whatever the circumstances,

the fox adapts.

Acute senses are important,

but sometimes they're not enough

and intelligence is what is needed.

This is the Arctic...

..in the heart of winter.

At this time of year, the Arctic fox is a scavenger.

They have an extremely complex sense of smell.

They can detect a frozen carcass buried beneath a metre of snow.

But foxes are less effective

at picking up smells over long distances. So, to find food,

the fox has come up with an ingenious method.

It borrows one of the most highly specialised noses

in the animal kingdom.

SNUFFLING

Polar bears are able to sniff out a seal carcass

from up to 32km away.

In winter, a polar bear is much more likely to track down fresh food.

Trailing one is a cunning way of guaranteeing a meal.

The Arctic fox has learned

that as long as it follows at a safe distance,

this tactic will pay off.

As the bears generally only eat the blubber of their prey...

..a fresh kill means that there are plenty of leftovers.

This intelligent strategy is key to surviving the harsh winter.

When the summer finally returns, the Arctic fox moults.

Insulating properties are lost,

but their colouration is perfect for camouflage.

Millions of birds have arrived in the Arctic to breed.

There's a sudden boom in the food supply.

But knowing how to deal with this bounty takes forethought.

Five million snow geese are here to lay their eggs.

And this Arctic fox family has chosen a prime position for its den.

With so many geese around, sneaking up unnoticed

would be absolutely impossible.

Instead, the fox heads straight in amongst them.

Now, this might look like chaos, but there is a plan here.

It's seeking out nests with just one protector.

And causing a commotion,

the fox forces that goose away from its nest.

As soon as it's far enough away, it can make its move.

But with too many eggs to eat now,

the fox stashes them for later.

In fact, 97% of the eggs taken by Arctic foxes are cached in this way.

A single fox can take over 1,500 eggs in one nesting period.

They keep much better than meat,

as the protective shell reduces their decomposition rate.

Even if it's in the ground for two months,

the egg will only lose 8% of its nutritional mass.

And by scattering them across their territory,

they lower the chances of rival foxes finding them

and ensure that they have plenty to eat throughout the winter.

Arctic foxes stash most of the eggs,

because in a month,

another opportunity presents itself.

Any eggs they didn't steal are now hatching,

and these goslings contain twice as much nutritional value.

A gosling is a high-energy food source,

just one could sustain this fox for the whole day.

But there's no shortage here, so this one is for the cubs.

The Arctic fox is capable of intelligently adapting

its hunting behaviour to the time of year.

Scavenging in the winter...

..and hoarding in the summer.

But foxes have also been able to cope

with a far greater change than the seasons.

Over the last couple of centuries,

the natural world has been disappearing fast.

Now, you might not think that urbanisation

offers a fabulous opportunity,

but I've got to tell you that even here, foxes are making a success.

And this is all down to their remarkable ability

to be flexible in terms of their behaviour.

The birth of suburbia in 1930s Britain

brought with it low-density housing and relatively large gardens,

providing an ideal habitat for the red fox.

Over the next decade they colonised the green belt.

And by the 1960s,

they'd established themselves in the heart of Britain's cities.

No other mammal has thrived in this new urban environment

quite like the red fox.

The rural and urban red fox are exactly the same species,

so how have they adjusted to live in such different environments?

Firstly, they've adapted their denning behaviour.

In the countryside, foxes will often dig their own dens.

In the city, they rarely need to.

Urban areas provide a huge range of options.

And it's much more energy-efficient to use these man-made dens.

And foxes have also adapted their diet.

Food is readily available in the form of human leftovers.

And this is the reliable,

non-seasonal resource that the urban fox thrives on.

More food means not having to travel so far in search of it.

In the city, they can survive in just a tenth of a square kilometre.

Whereas in the countryside,

they'd need an area 500 times larger.

So, urban foxes can live at much higher densities,

but they therefore come into contact

with competing neighbours much more frequently.

But rather than fight,

scientists believe the urban foxes have learned to adapt.

After all, why waste energy in conflict

when there's plenty of food to go round?

Scavenging on leftovers can have its downsides.

But even this has been turned to the fox's advantage.

Eating rotten meat exposes them to a high dose of different pathogens.

In theory, this should mean that the fox frequently becomes ill.

But over time, the regular exposure to "off" meat has contributed

to the red fox developing a more sophisticated immune system...

..enabling it to combat a much wider variety of diseases.

It's early days in the research,

but scientists think that this is what's helped them

to colonise urban areas so effectively.

But there's something even more surprising

about the urban foxes' diet.

Only 60% of it is made up of human leftovers.

They'll adapt to whatever food source is available.

On this rubbish tip, foxes aren't the only animals

to seize the chance to indulge.

Gulls have also come to feed on the bounty.

But the fox is one step ahead.

It knows how to turn competition into opportunity.

Although rural foxes survive primarily

on small rodents and birds,

one might expect urban foxes to have left that sort of hunting behind.

But up to 40% of an urban fox's diet

is still made up of birds, insects, rodents and fruit.

This really is adaptable behaviour at its best.

For a long time, the urban fox was regarded as a British phenomenon

but significant numbers of red foxes

now live in cities right across the globe,

including New York, Sydney and Moscow.

And they haven't just spread into cities.

Wherever humans have changed the landscape,

the red fox has found a way to fit in.

In the USA, when forests were cleared for agriculture,

both native and introduced red foxes spread across the farmland.

In Australia, after a few dozen were introduced for sport,

the red fox came to colonise most of the country.

And in Arctic Canada, when human settlements first appeared,

so did the red fox.

Until recently, the grey wolf

was the world's most widely distributed land mammal,

but now, that crown has been passed to the ubiquitous red fox.

Foxes have an incredible ability to adapt to any change.

Their complex senses can operate effectively

both during the day and at night.

Their intelligence allows them to choose to scavenge or to hoard,

depending on the season.

And their remarkable ability to adapt

means that they can cope with the greatest change of all,

thriving in perhaps the most hostile environment on Earth

and THAT is the wonder of foxes.