10 wildlife secrets revealed by thermal cameras

The spectacle of bats hunting revealed by thermal cameras.

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Have you ever seen a foraging badger being followed by a bat? A nightjar clapping for attention? Or a cloud of bats feeding over a lake?

These are just some of the fascinating insights filmmakers captured for BBC One series The Great British Year thanks to state of the art thermal imaging equipment.

The military might have led the development of this technology but since cameras have become commercially available, researchers have started exploring the unique perspective on the natural world they can provide.

Using infra-red radiation to visualise differences in temperature has delivered some surprising sights, here are 10 of the most remarkable revelations.

What is thermal imaging?

Regular cameras work by capturing visible light. Although they have become more sophisticated to work in low light - such as night vision goggles or starlight cameras - filming in truly dark conditions is only possible due to infrared.

Infrared is a type of radiation. It is thermal energy so although the human eye can't see it, it can be detected on a temperature sensor.

Thermal imaging systems are equipped with these sensors which can tell the difference between variations of temperature. This data is then processed to form a heat picture - or thermal image.

These images are often displayed in monochrome but to really highlight the temperature scale, the images can be presented with a gradient from cold black through rainbow colours to white hot.

1. Panda pregnancy tests

Figuring out whether a giant panda is pregnant is one of the biggest challenges in animal medicine but staff at San Diego Zoo have successfully used thermal imaging to give them a new perspective.

"Thermal imaging is a useful tool for detecting activity in the giant panda uterus prior to the time a foetus can be visualised with ultrasound," says Dr Barbara Durrant who has led the technology's use at the zoo.

By monitoring a panda's abdomen, the team were able to visualise heat changes as early indicators of the animals preparing for pregnancy.

Dr Durrant explains that the advantage of thermal imaging is that the animals can be monitored without restraints or anaesthetic for a broad, non-invasive view before more specific methods are administered.

2. Rabid racoons

Wildlife vets have also embraced thermal imaging as a tool to monitor animals without getting too close.

High temperatures in specific body parts can indicate inflammation and such information has proven useful in the diagnosis of conditions from arthritis in elephants to rabies in raccoons.

Thermal image of emperor penguin in Antarctica The penguin's violet "halo" identifies how its outer coat is below -15 C

Interestingly, while higher nose temperatures sound alarm bells in racoons, a cooler face has been identified as an indicator of rabies in big brown bats.

3. Penguins have cool coats

A team of French and Scottish scientists investigating emperor penguins in Antarctica discovered that the animals can actually have a colder surface temperature than the surrounding air.

Via thermal images of the penguin colonies, researchers identified that the outer layer of feathers was 4 to 6 C colder than the air.

Dr Dominic McCafferty from the University of Glasgow explained that this was due to "extreme radiative cooling" whereby the penguins lose heat to the clear sky where heat escapes rapidly from our atmosphere.

The specialised structure of their feathers acts as an insulator however to keep these dangerously low temperatures away from the penguins' skin.

4. Elephants chill out via trunks

Thermal technology was used to study Asian elephants living at Busch Gardens zoological park, US.

African elephants are known to keep cool using their large ears where huge volumes of blood are circulated close to the skin's surface so heat can dissipate.

Thermal image of Asian elephant at night (c) Busch Gardens This Asian elephant's ear show up as cool blue on a thermal image taken at night

Asian elephants however have much smaller ears and are known to cool off overnight so they start the day at a lower temperature.

Rather than losing heat through their ears, thermal images showed that overnight heat loss is greatest from Asian elephants' trunks.

6. Giant flower's steaming stench

The titan arum (Amorphophallus titanum) is the stinking giant of the plant world. It has the world's largest flowering head growing up to 3 metres tall and smells like a rotting corpse.

Researchers discovered that the plant emits puffs of this odour to attract carrion eating insect pollinators from across its Sumatran jungle home.

Thermal imaging revealed that the puffs are achieved by a build up of heat in the plant's stem resulting in regular releases of steam which carry the odour through the canopy to attract insects.

5. Bees form hot defensive balls

Bees are known for their stings but Japanese honeybees have another form of defence against predatory giant Asian hornets.

If they find an intruder in the nest, the bees swarm around it to form a bee ball - the inside of which reaches 46 C.

A thermal image of a hornet under attack from honeybees (c) M Ono/ Tamagawa University Honeybees' brain activity may help them maintain the 46C temperature on the inside of the ball

Thermal cameras indicate that the temperature inside the bee ball is maintained by the bees at the optimal level so that they can defeat their nemesis without overheating themselves.

7. Mapping the breaths of ocean giants

Biologists are tracking the movements of whales without even dipping a toe in the water.

Instead they survey the seas for "spouts" of warmer water released by the whales as they take a breath.

The technology provides valuable data on grey whales as they pass California on their annual migrations, particularly their previously unseen night-time movements.

Last year, researchers reported the first use of thermal imaging in an automated system that aims to protect whales from underwater noise by alerting when their spouts are sighted near mining or naval activities.

8. Mysterious lemur's feverish finger

A further bizarre discovery about Madagascar's mysterious lemur the aye-aye was made using thermal imaging cameras.

The animals are known for their unusual extra-long finger which they use to tap trees when foraging for grubs.

Scientists discovered that the aye-aye's super sensitive digit is kept cool when not in use but heats up by 6 C when in action.

The aye aye's cold finger shows up black on thermal images (c) G Moritz / N Dominy Cold finger: the special digit shows up black on thermal images

The finger is packed with nerve endings and experts suggest the ability to "switch" its temperature on and off saves the lemur essential energy.

9. Fatal attraction for bats

In the past, bats have proven difficult to study because most of their activity takes place after dark but thermal imaging has revealed a wealth of information about their behaviour.

When researchers found high numbers of dead bats below wind turbines in both the US and Europe, they turned to thermal imaging for an explanation.

US researchers recorded footage that identified bats actively investigating and foraging around the turbines.

Scientists suggest insects are attracted to the structures with a knock on effect for the bats and birds that feed on them.

10. Seals heat up to grow hair

Experts studied common seals off the coast of Scotland to understand more about their habits during the annual moult.

Through thermal imaging they found that the seals' skin heats up to help them shed and regrow their hair.

With increased blood flow to their skin to aid the moult, the seals choose to stay out of the water to avoid a chill and save energy.

The Great British Year begins on Wednesday 2 October 2013 at 2100 on BBC One.

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