Australasian Science: Australia's authority on science since 1938

Flying in a Flock Tires Pigeons

By Magdeline Lum

Why pigeons shouldn’t fly as a flock, how urine can power your phone, and how moths use their genitals to beat bats.

Birds fly around in flocks. They like to be together and it is where the saying, “Birds of a feather flock together,” comes from. However, an analysis has found that for the pigeon, flying as a flock costs them more energy than to fly alone.

Birds like pelicans and swans fly in V-formations. Research has shown that this gives the birds a benefit in aerodynamics. They don’t need to flap their wings as much and their heart rates drop. This has been extended to flying aircraft in V-formations to reduce fuel consumption.

Pigeons and most other birds, however, do not fly in V-formations. They fly in a flock known as a cluster flock.

Dr James Usherwood of the Royal Veterinary College attached GPS and inertial sensors on a flock of 20 pigeons to take measurements during their flight.

The pigeons were flying voluntarily and flew around in a flock as normally. Usherwood’s team found that pigeons maintained powered banking turns like in aircraft. This creates accelerations up to 2g, meaning that their body weight doubles and their power requirements quadruple during these manoeuvres. It was also observed that pigeons flapped their wings more when flying in groups, in particular when they were flying behind another bird.

It is unclear why pigeons cluster flock given that they do not gain an aerodynamic advantage. However, when flying together in a flock there is evidence that it does provide protection from a predator by grouping together. The tight pattern in a cluster flock may make it difficult for a predator to catch.

Urine Powers Mobile Phone Charger

Researchers from the University of Bristol and Bristol Robotics Laboratory have created a fuel cell that uses bacteria to break down components in urine to generate electricity. The electricity generated was enough to enable a mobile phone to make a call, send text messages and browse the internet.

Yeast was grown on carbon fibre anodes that were placed in ceramic cylinders. As urine flows through the cylinders, the bacteria breaks down chemical compounds in the urine, building up electrical charge stored on a capacitor. This was then used to charge the mobile phone.

In the experiment, a 24 hour charge cycle powered the phone for 25 minutes during which several text messages were sent and received and sent, and an outgoing call of 6 minutes and twenty seconds was made. This is proof of concept and the goal is now to refine the set up where a microbe fuel cell can be developed to fully charge a battery, particularly in remote areas and in developing nations.

Moth Vibrates Genitals to Evade Bat Sonar

In an arms race between moths and bats, researchers at Boise State University and the University of Florida have found that hawkmoths in Borneo are able to rub their genitals to produce ultrasonic sounds. In 2009, a closely related species and target prey for bats, the tiger moth, was found to have the same capability in efforts to evade bats.

The team used high energy lamps to capture hawkmoths from the jungle in Borneo. The hawkmoths were then tethered inside an enclosed sound rig containing an ultrasonic microphone and speaker attached to two laptop computers. Researchers recorded the sounds hawkmoths made when touched and when bat echolocation sounds were played.

When tiger moths detect a bat echolocation noise they reply with an ultrasonic reply that startles bats, warning them of potentially a bad tasting meal while jamming their sonar. The hawkmoths also react by producing ultrasonic sounds in response to biosonar attack sequences emitted by bats, and to touch. Both male and female hawkmoths are able to create these sounds.

Currently it is unknown how the sounds of the hawkmoth disrupt bat echolocation. It could be startling, warning of a physical defence or jamming of echolocation. The researchers believe that these moths present an opportunity in the study of the function and evolution of anti-bat defences.