Did you know that bats can send ‘jamming’ signals to stop other bats catching food?

Bats emit high-pitched soundwaves to locate insect prey (echolocation).

Mexican free-tailed bats form very large colonies, therefore there is lots of competition for food.

A new type of call was discovered called sinFM (30-60 kHz) that jammed the feeding call (echolocation) of another bat.

It caused the hunting bat to miss its insect prey in mid-air (80% less likely to catch it), leaving it for the jamming bat to catch and eat.

These bats have evolved a way to jam echolocation signals of competitors when hunting, reducing their chances of catching prey and increasing their own.

Do you want more information?

Background

Bats emit high-pitched soundwaves to locate prey (mostly insects).

The soundwaves bounce off the target and are detected by the bat (echolocation).

The closer the bat is to the prey, the faster the soundwaves bounce back.

Echolocation allows bats to be dominant predators at night.

Mexican free-tailed bats are a common variety in America and form very large colonies. Some caves contain ~1 million bats.

Therefore, there is lots of competition for food.

They have a vocal repertoire of at least 15 communication/social calls.

Here, the authors discovered a brand new call.

Materials and Methods

Scientists recorded the hunting behaviour of Mexican free-tailed bats in Arizona and New Mexico at night (nocturnal animals) using microphones, video and infrared cameras. They also used speakers to play back particular recorded sounds to the bats. Finally, they used computer programs to reconstruct 3D flight paths of the bats.

Results

A new type of call was discovered called sinFM that jammed the feeding call (echolocation) of another bat.

It caused the hunting bat to miss its insect prey in mid-air (80% less likely to catch it), leaving it for the jamming bat to catch and eat.

sinFM soundwaves have a frequency of 30-60 kHz.

When recorded and played back through a speaker, it jammed the hunting calls of bats.

sinFM only jammed hunting calls when they overlapped. It didn’t work if played just before/after or a different noise was emitted.

Discussion

Competition for food is high in large bat colonies.

The Mexican free-tailed bat has evolved a way to jam the echolocation signals of competitors when hunting, reducing their chances of catching prey, while increasing their own.

This is the first discovery of jamming echolocation signals in animals.

Article

Bats jamming bats: Food competition through sonar interference

Corcoran and Conner, 2014 Science 346:745-7

Keywords

Bats, echolocation, sonar, frequency, Hz, sound, wave, soundwave, ultrasonic, prey, food, insect, evolution, jamming, signal

Subject

Science, biology, physics, ST1-6PW, ACSSU020, ST2-11LW, ACSSU073, SC5-10PW, ACSSU182, SC5-15LW, ACSSU185

Did you know that flowers use electricity to attract bees?

Flowers produce multiple cues to attract insects to assist with pollination, including sweet nectar, colourful petals, fragrant smells and even echo location.

Here, another unexpected cue for attracting bumblebees is added to the list – electricity.

Flowers have a negative electric field, while bees are positively charged due to their wing flapping.

The bees detect the electric field of the flower and are attracted to it.

Then, the negatively charged pollen gets stuck to the positively charged bees.

Therefore, there is an electric attraction between bees and flowers.

Do you want more information?

Background

Flowers produce multiple cues to attract insects to assist with pollination, including sweet nectar, colourful petals, fragrant smells and even echo location.

In particular, it is the combination of multiple cues that greatly increases pollination.

Here, another unexpected cue for attracting bumblebees is added to the list – electricity.

It was previously known that bees are positively charged (due to their wing flapping), while flowers are often negatively charged.

This potential difference facilitates pollen transfer from the flower to the bee.

However, it was not known if bees could sense this electric field and if it acted as an attractive cue.

Materials and Methods

Bumblebees were exposed to two artificial flowers: one was charged with a weak negative electric field and had a sweet reward. The other did not have an electric field and had a bitter quinine taste. In all other aspects they were identical. The authors measured the preference of the bumblebees between these two flowers. Then, the electric field was turned off and the preference was re-measured.

Results

The bumblebees strongly preferred (visited more often) the flower with the electric field that the non-charged flower.

However, when the electric field was turned off, the bumblebees lost this preference and randomly visited either flower.

This indicates the electric field attracted the bumblebees to the artificial flower.

In further studies, the bees recognised different geometric shapes of the electric fields, which could be useful for distinguishing different types of flowers.

Finally, the combination of the electric field with colour recognition enhanced the preference of the bumblebees even further.

Discussion

Relatively weak electric fields emitted by flowers help attract bees for pollination purposes.

It improves the speed and accuracy with which bees recognise particular flowers.

It also combines with other cues to increase their attractiveness, thus promoting pollination.

Article

Detection and learning of floral electric fields by bumblebees

Clarke et al., 2013 Science 340:66-9

Keywords

Plant, flower, pollination, reproduction, bee, bumblebee, insect, senses, electricity, nectar, learning, electrostatic, electric field, charge, potential difference, pollen

Subject

Science, biology, physics, ST1-10LW, ACSSU017, ST1-11LW, ACSSU211, ST2-11LW, ACSSU073, ST3-6PW, ACSSU097, ST3-10LW, ACSSU043, SC4-10PW, ACSSU118, SC4-11PW, ACSSU155, SC4-14LW, ACSSU150, SC4-15LW, ACSSU112, SC5-10PW, ACSSU182, SC5-11PW, SC5-14LW, ACSSU176, SC5-15LW, ACSSU185

Did you know that radiowaves from towns and cities could be affecting the migration and survival of songbirds and other bird species?

Songbirds use specialised iron deposits in their heads to detect the Earth’s magnetic field and use it to direct their migration.

This study measured songbird flight direction in huts that were unlined or lined with aluminium to block out radiowaves from the nearby city.

Birds in the un-lined hut could not orientate themselves as well as birds in the lined (protected) hut, indicating that radiowaves were interfering with the birds sense of direction.

In particular, radiowaves between 2 and 5 MHz disorientated the birds.

These wavelengths are generated by electronic equipment commonly used in houses/buildings, as well as AM radio signals.

Therefore, radiowaves emitted from towns and cities might be affecting songbird migrations and contributing to their declining populations.

Do you want more information?

Background

Songbirds use several sensory systems to direct them during seasonal migrations, including the sun and stars.

Another ‘compass’ they use is the Earth’s magnetic field.

Deposits of magnetic iron (magnetite, Fe₃O₄) detect the Earth’s magnetic field to orientate the birds.

This becomes especially important on cloudy nights when they can’t see the sun or stars.

However, the number of night-migratory songbirds is decreasing rapidly, and the effect that man-made (anthropogenic) electromagnetic waves might have on Songbird migration/survival was tested.

Materials and Methods

Songbirds were placed in wooden huts that were a) not-lined or b) lined with aluminium plates to block out anthropogenic electromagnetic waves and the ability of the birds to orientate themselves in the appropriate migratory direction was measured. The birds in the lined-hut were also re-exposed to electromagnetic waves of various frequencies to determine the range of wavelengths that affect the birds.

Results

Birds in the un-lined huts could not effectively orientate themselves in the appropriate direction, while those in the lined huts could.

This experiment was carried out on a University campus in a German city with relatively high background electromagnetic waves.

Re-exposing the latter birds to a range of electromagnetic waves revealed that waves between 2 kHz and 5 Mhz disorientated the birds.

These wavelengths are generated by electronic equipment commonly used in houses/buildings, as well as AM radio signals.

They also affected bird behaviour at very weak intensities, way below those recommended to be safe for humans by the World Health Organisation.

Importantly, they are not the same wavelengths generated by mobile phones or electric power lines.

Discussion

Electromagnetic waves emanating from towns/cities could impair the migration and survival of Songbirds and other bird species, contributing to their recent declining populations.

Article

Anthropogenic electromagnetic noise disrupts magnetic compass orientation in a migratory bird

Engels et al., 2014 Nature 509:353-6

Keywords

Migration, birds, ecology, electromagnetic, radio, waves, microwaves, mobile phone, magnetite, magnetic field, orientation, sensory system

Subject

Science, Biology, zoology, physics, physical world, physical sciences, ST1-8ES, ACSSU019, ST1-11LW, ACSSU211, ST1-15I, ST2-11LW, ACSSU073, ST2-14BE, ST2-15I, ST3-11LW, ACSSU094, ST3-15I, SC4-15LW, ACSSU112, SC5-10PW, ACSSU182, SC5-13ES, ACSSU189, SC5-14LW, ACSSU176

Do you know how electric eels use electricity to catch their prey?

They begin by emitting a doublet of discharges that causes the muscles in the fish to twitch.

This twitch signifies they are alive, reveals their position (useful in murky river water and when hiding) and retards their movement.

The eels then emit a high voltage burst that immobilises the fish so they are easy to catch.

Electric eels have effectively evolved a ‘remote control’ mechanism for controlling the muscles in their prey, making them easier to catch.

Do you want more information?

Background

Electric eels are not actually eels. They are fish, related to catfish.

They live in murky rivers in South America, including the Amazon.

They breathe air so need to surface regularly (around every 10 minutes).

They can grow to over 2 m and 20kg in size. They don’t have scales.

The electricity is stored in muscle-like cells called electrocytes (~6,000) aligned in series.

Under resting conditions, each electrocyte pumps out Na⁺ ions. This leaves a negative charge inside the cell.

A signal from the nervous system causes Na⁺ ions to rapidly flow back into the electrocytes (few milliseconds), changing the cellular voltage from negative to positive (electric discharge).

The electrocytes are arranged in series like batteries, so the voltage discharge from each (~130mV) adds up to a total discharge of ~600V (~3 times higher than a power point socket).

Not quite enough to kill a human, but enough to really hurt.

Materials and Methods

This researcher from the USA (by himself) analysed electric eels hunting fish in a tank. He filmed them and measured the electrical discharges they emitted.

Results

Electric eels emit a doublet of discharges that target the motor neurons of the fish (neurons that control muscles), causing them to twitch.

The twitch signifies they are alive, reveals their position (useful in murky river water and when hiding) and retards their movement.

The eels then emit a high voltage burst that stuns the fish. It hyperactivates the motor neurons, causing the muscles to spasm, immobilising them so they are easy to catch.

Discussion

The electric eel has evolved a novel mechanism for locating and catching prey that is well adapted for the murky river waters of South America.

The electrical discharges control the motor neurons, hence muscles, of their prey effectively by ‘remote control’.

Article

The shocking predatory strike of the electric eel

Catania, 2014 Science 346:1231-4

Keywords

Electric, electricity, eel, discharge, electrocyte, motor, neuron, prey, predator, hunt, hunting, feeding, ion, potential, voltage, muscle

Subject

Science, Biology, ST1-10LW, ACSSU017, ST2-11LW, ACSSU073, ST3-6PW, ACSSU097, ACSSU219, ST3-10LW, ACSSU043, SC4-10PW, ACSSU118, SC4-11PW, ACSSU155, SC5-11PW, ACSSU190, SC5-14LW, ACSSU175

Did you know that lightning strikes the Earth ~40-50 times per second or ~1.4 billion times a year?

But what effect will climate change have on lightning strikes?

Scientists from the University of California predict that lightning strikes will increase 12% per 1°C of global warming.

It will increase ~50% over the course of the 21^st century.

This could increase building damage, deaths to people/animals and wild fires, especially for a country like Australia where this is common.

Do you want more information?

Background

Lightning around the World occurs ~40-50 times per second or ~1.4 billion times per year.

It is caused by clouds rubbing together, building static electricity.

Positive charges build up at the top of clouds, negative charges at the bottom.

The negative charge on the underside of the cloud causes positive charges to accumulate in the ground below it.

When the charges build up enough and connect, lightning is discharged.

Lightning plays a minor role in nitrogen fixation. The high heat (~30,000°C) causes nitrogen to combine with oxygen.

What effect will climate change have on lightning strikes?

Materials and Methods

Scientists from the University of California used metrological observations and climate models to predict the future frequency of lightning strikes and its relationship to global warming.

Results

Lightning frequency is a product of the energy in a cloud and the amount of precipitation.

The energy is warm air rising through colder layers, creating static electricity.

The amount of precipitation is predicted to increase with global warming.

Therefore, the frequency of lightning strikes will increase 12 +/- 5% per 1°C of global warming.

It will increase ~50% over the course of the 21^st century.

Discussion

Increased frequency of lightning strikes could lead to an increase in building damage, deaths to people/animals and wild fires, especially for a country like Australia where this is common.

Article

Projected increase in lightning strikes in the United States due to global warming

Romps et al., 2014 Science 346:851-4

Keywords

Lightning, precipitation, global warming, climate, climate change, cloud, static, electricity, charge, strike, temperature

Subject

Science, Earth Science, geography, ST1-9ES, ACSSU032, ST2-8ES, ACSSU075, ST3-6PW, ACSSU097, ACSSU219, ST3-9ES ACSSU096, SC4-10PW, ACSSU117, ACSSU118, SC4-13ES, ACSSU116, ST5-13ES, ACSSU189