The Animals Slept IELTS Reading Answers

The bar-tailed godwit, a member of the sandpiper family, is one of the avian world's record-holders. It may not be as big as an ostrich, as fast as a peregrine or as loud as the South American oilbird, but when it comes to nonstop flying, it surpasses them all. This bird can cover a distance of over 11,000 kilometers from its breeding ground in Alaska back to New Zealand. It completes this entire journey in just eight days without any stopovers - no breaks to allow its muscles to recover, or simply to rest.

Impressive though this may be, godwits are far from topping the list when it comes to long-distance flying: frigatebirds remain in the air for over two months without interruption, and common swifts are able to fly for 300 days straight without landing. But how can these animals do this without any sleep at all?

Niels Rattenborg is Leader of the Avian Sleep Research Group at the Max Planck Institute for Ornithology in Seewiesen, south of Munich. An American with Danish roots, he has been working in this field for a good two decades. He has been carrying out research in Seewiesen since 2005. He and his colleague Bryson Voirin have now provided proof that birds can actually sleep while flying.

Rattenborg had already observed a fascinating phenomenon while doing his doctoral work on mallard ducks: in a group of sleeping ducks, those sitting at the edge kept their outwardly directed eye open and the corresponding brain hemisphere remained awake. In this way, the birds can rest a part of their brain while keeping an eye out for potential predators. Unihemispheric sleep, when only one half of the brain sleeps while the other remains awake, is found not only in birds, but also in dolphins, seals and manatees, for instance.

5.To find out how flying birds manage their sleep requirement, Niels Rattenborg and his colleagues joined forces with neurophysiologist Alexei Vyssotski from Zurich. Vyssotski developed miniature data-logging devices that are so light that they can be carried by birds even when flying. The devices record the birds head movements and wing beats and simultaneously measure their brain activity. To do this, the researchers attach sensors to the animals'

heads to measure variations in the voltage generated by the brain. The sensors record the electrical activity of millions of neurons in the waking state and during the different sleep phases, and depict characteristic wave patterns on an electroencephalogram (EEG). This development enabled the scientists to study the waking and sleep behavior of flying birds for the first time.

As their research subject, they chose the great frigatebird (Fregata minor). This is one of the biggest seabirds, with a weight of up to 1.5 kilograms and a wingspan of over 2 meters. The measuring device, including batteries, weighs just 12 grams and presents no great burden for the animals when flying. Frigatebirds spend most of their time in the air and are perfectly adapted to this lifestyle. They mostly sail above the oceans without beating their wings, watching for flying fish and squid that are driven to the surface of the water by dolphins and predatory fish.

Back in Seewiesen, Rattenborg studied the recorded EEG graphs obtained from frigatebirds. "When they're awake, the amplitudes are small, but the frequencies are high, explains the Max Planck researcher. A kind of slow-wave sleep was evident on the EEGs recorded during flight. That was their proof: frigatebirds sleep while they fly and, to the scientists' surprise, not only with half of the brain, but with both halves at the same time. "Even though they are able to fly when both halves of the brain are asleep, one side usually stays awake: the side associated with the eye that looks in the direction of flight. This is probably how the birds avoid collisions with other members of their species cruising through the same air stream."

In addition to slow-wave sleep, the logging devices occasionally recorded short episodes of REM (rapid eye movement) sleep. EEG graphs with low amplitudes and high frequencies, which also occur in wakeful birds, are typical of REM sleep. REM sleep always occurs in both brain hemispheres, and is present not only in birds, but also in mammals, including humans. In birds, in contrast, REM sleep lasts only a few seconds and, although their muscle tone also falls, they can still stand or fly.

The function of REM sleep remains a mystery. Researchers assume, however, that it plays an important role in normal brain development. Thus, both slow-wave and REM sleep occur in flying frigatebirds. They apparently don't need to keep one part of the brain awake to keep themselves in the air. Nevertheless, the birds allow themselves hardly any time for sleeping while flying.

Over a 24-hour period, they slept on average for a total of just 42 minutes, and the average stretch of sleep lasted just 12 seconds. The longest uninterrupted stretch of sleep recorded was just under six minutes. On land, in contrast, the animals slept over 12 hours. These sleep phases were not only longer (52 seconds), but also deeper. It would therefore appear that the animals make up for lost sleep, just as we humans do.