Page 58 - BBC Wildlife Volume 36 #10

WILDNEWS

MAMMALS
How zebras didn’t

earn their stripes

ebras may have the coolest pelts on the
Z savannah, but that doesn’t stop them
overheating, according to new research. Their
stripes are as mysterious as they are striking;
about 18 different hypotheses have been put
forward over the years to explain their function
– ranging from camouflage to communication
to optical illusions that deter biting flies or
cause carnivores to mis-time their lunges.
Now, however, biologists from Sweden and
Hungary have narrowed things down, if only
slightly, by ruling out another possibility – that
stripes help keep zebras cool in the sun.
The theory goes that the black stripes heat
up more than the white ones, thus creating
little swirling vortices in the air above
them, which keep air moving across the fur
resulting in a net cooling effect.
To test whether this works in practice,
biologists filled zebra-sized barrels with
water, covered them with zebra, cow and
horse hides of different shades and left them
out in the sun. Unsurprisingly, the water
temperature rose highest under black pelts
and remained cooler under white ones.
Crucially, though, the black-and-white
stripes did not keep the water any cooler
than did uniform grey pelts. SB
The evolutionary
purpose of the
FIND OUT MORE Scientific Reports: www.
zebra’s distinctive
coat remains elusive. nature.com/articles/s41598-018-27637-1

Nature in brief

Cull suspended Breeding success
Scottish Natural Heritage (SNH) The removal of invasive rats and
suspended a cull of ravens in goats from the Caribbean island
Perthshire on finding it“didn’t of Redonda (see our May 2018
provide robust scientific feature) has yielded spectacular
conclusions”. Alicence was results for its seabirds.The
granted earlier this year to see if island’s frigatebirds and boobies
reducing raven numbers boosted (several species) are having their
wader breeding success. best breeding year on record. Zebra: Den s-Huot/naturep .com; raven: Seppo Hakk nen/Getty; cora : Fab o Bada ament ;

Cooperative corals Penguin peril frigatebird: Ed Marshall/FFI; penguins: David Merron/Getty; stinkhorn: Tai-Hui Li/Kew
Tiny coral polyps that usually The world’s largest king penguin
feed on microscopic planktonic colony,on Île aux Cochons,has
prey can work together to subdue plummeted from two million
much larger creatures.Reports birds to just 200,000 since the
suggest corals from Sicily work 1990s,reports Antarctic Science.
cooperatively to trap,dismantle The reasons for the decline
and consume large jellyfish. remain a mystery.

58 BBC Wildlife October 2018