The first detailed study of the effects of naval sonar on whales shows that whales flee from prime feeding sites when navy tests begin – leaving them famished when they finally return.

Blainville’s beaked whales, , use echolocation clicks to track down prey in the lightless depths they hunt in, a kilometre or more below the surface.

To find out whether the whales are disturbed by naval sonar operations, of Woods Hole Oceanographic Institution, Massachusetts, and colleagues tracked the activity of Blainville’s beaked whales during exercises at a US navy centre near Andros Island, Bahamas. The area encompasses an underwater canyon that is a prime hunting ground for these deep-diving whales.

By satellite tagging one whale and listening out for the echolocation clicks of others using underwater microphones, the team found that whales stopped echolocating and moved away from the area during the tests. Once the exercises stopped, a day and a half went by before the whales returned ().

Hungry whales

A related study found that three days after the tests ended, the whales began to echolocate like crazy – possibly indicating they were ravenous on their return to a prime feeding ground ().

of the Cascadia Research Collective, based in Olympia, Washington, believes the use of underwater microphones is “a great approach”, but points out that the whales’ behaviour may not be typical of those that live away from sonar test ranges.

Brandon Southall of in Santa Cruz, California, an author on the PLoS One study, says that is a fair criticism. “[Whales] get used to what’s happening around them,” he says, adding that research currently under way is aimed at incorporating the reactions of whales that aren’t accustomed to sonar.

Some people carry a genetic sequence, or allele, that provides immunity to leprosy and tuberculosis. , an evolutionary biologist from University College London, and , a molecular palaeobiologist from Royal Holloway, University of London, wondered whether this genetic immunity could have been gained when people began living in close proximity. Poor sanitation would have meant that disease was rife in ancient cities, but exposure to the pathogens would have led to resistance developing, which the inhabitants would have passed onto their descendants.

To test this idea, Thomas and colleagues analysed the DNA of people living in 12 regions in Europe, Asia and Africa. For each area, they combed the historical and anthropological records to work out when people first started living in close-knit groups. They found that the longer cities in the region had been established, the more likely it was that the current inhabitants carried the immunity allele.

Thank the cows

It had been thought that the allele became prevalent when cattle were first domesticated, as cows carry a strain of TB that humans can catch. But the team found a stronger correlation between the allele and urbanisation than with the onset of cattle farming.

It is likely that cattle domestication would have played a role in developing the immunity, because cattle farming would have been important in early city life, Barnes points out.

Thomas describes population dynamics as “an awesome, underplayed feature of our history” and thinks resistance to other diseases could also have evolved in this way.

, an evolutionary biologist at the University of Oxford who wasn’t involved in the study, agrees. “This study could be regarded as the tip of the iceberg” in terms of the effects of urbanisation on disease immunity, he says.

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