bagged 10 adult males during the

mating season and four pregnant

females in the month that

followed. Then goshawks took

nine juveniles (The American

Naturalist, DOI: 10.1086/507714).

“The males were so obsessed with

sex they couldn’t watch for

predators,” Hoogland says.

If, as Hoogland believes,

predators were behaving more as

they would when people are not

around that’s bad news for the

endangered prairie dog. “What

really happens when we’re not

there?” he asks.

most vulnerable. So what was

different in 2005?

He believes that the prairie

dogs’ predators were behaving

more normally because they had

become used to the presence of

people. Usually foxes, coyotes and

badgers “will go elsewhere when

they see us”.

Prairie dogs live in colonies

and warn each other of predators

so they can dive into burrows

for protection. In 16 previous

seasons, his team had seen only

22 prairie dogs swiped by

predators. But last year a fox

IF YOU are trying to commit

something to memory, take a nap.

Even a short daytime snooze

could help you learn.

A good night’s sleep is known

to improve people’s ability to

learn actions such as mirror

writing. REM sleep, when most

dreaming occurs, is thought to be

particularly important.

The role of sleep in factual

learning has been less clear. Now

Matthew Tucker at The City

University of New York and his

colleagues have shown that even a

nap with no REM sleep can help.

Volunteers were told to

memorise pairs of words (a test of

factual learning) and to practise

tracing images in a mirror (action

learning). When they were tested

straight afterwards and 6 hours

later, those who had been allowed

a nap of up to 1 hour before the re-

test scored 15 per cent better in the

factual test than the non-nappers,

but no better in the action test

(Neurobiology of Learning and

Memory, vol 86, p 241).

“Traditionally, time devoted to

daytime napping has been

considered counterproductive,”

the researchers say. It now seems

sleep is “an important mechanism

for memory formation”.

Snooze your way to high test scores

YOUNG, old and sick animals are

usually the ones that end up as

lunch – though not, it seems, if

you’re a prairie dog in Utah. Last

year it was the turn of healthy,

adult males.

“This has really made me

rethink everything,” says John

Hoogland of the University of

Maryland Center for

Environmental Science in

Cambridge.

More than 30 years of studying

prairie dogs had given Hoogland

no reason to question the notion

that the weakest animals were the

CORB

IS

NOAA

Sex mad prairie dogs fall prey to bold foxes

www.newscientist.com 23 September 2006 | NewScientist | 17

ON 29 August 2005, as hurricane

Katrina was rumbling towards New

Orleans, a seismic hum more than

1000 times the strength of the

average volcanic tremor was felt

nearly 3000 kilometres away in

southern California. Its source was

the hurricane itself.

Hurricanes create large ocean

waves, which send energy pulsing

through the Earth as they pound the

shoreline. To determine the power of

Katrina’s seismic waves, Peter

Gerstoft of the University of

California, San Diego, and colleagues

analysed the signals recorded by a

network of 150 seismic stations in

southern California just before

Katrina hit the Louisiana coast.

They used a method known as

beamforming, which preferentially

picks up signals from a particular

direction, to decipher the seismicity

generated by Katrina (Geophysical Research Letters, vol 33, p L17805).

Seismic surface waves, which

travel through the Earth’s crust, were

detected 30 hours before the

hurricane made landfall, while body

waves, which bounce down into the

mantle, arrived some 18 hours later.

“The body waves had travelled down

to 1100 kilometres inside the Earth,”

Gerstoft says. This is the first time

that a hurricane’s seismic signal has

been detected so far away.

Katrina’s waves felt in California

DOGS not only protect your home, they

can protect your health as well. Young

children turn out to be less likely to

suffer a bout of gastroenteritis if there

is a pet in the house.

Jane Heyworth at the University of

Western Australia in Crawley and her

colleagues observed nearly a thousand

4 to 6-year-old children in South

Australia for six weeks, noting

incidences of nausea, diarrhoea and

vomiting. Children who had a cat or

dog in their household were 30 per

cent less likely to show these

symptoms than children living in

homes without pets (Epidemiology and Infection, vol 134, p 926).

This came as a surprise. “It is a

commonly held view that dogs and

cats are a source of gastroenteritis, but

our results do not support that,”

Heyworth says. She suggests that

children living with pets are exposed

to low levels of bacteria when young,

and that this could prime their

immune systems to handle such bugs.

A previous study showed that

children living with at least two

animals were up to 77 per cent less

likely to develop allergies (New Scientist, 7 September 2002, p 24).

There is also some evidence that pet

owners may be less likely to suffer

from heart disease and depression.

This doesn’t necessarily mean

parents should rush out and buy a pet.

“The benefits need to be weighed

against the drawbacks,” Heyworth

warns. “After all, dogs can bite.”

Household pets keep kids healthy

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