Subject: Killer mice threaten giant birds
Date: Sep 10 06:11:45 2004
From: Devorah Bennu - birdologist at yahoo.com


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Killer mice threaten giant birds
John Yeld
September 09 2004 at 02:16PM

Gough Island in the South Atlantic Ocean, a World
Heritage Site, is probably the world's most important
seabird breeding area. But scientists have found that
the common house mouse, introduced to the island by
sealers during the 18th and 19th centuries, is eating
alive defenceless albatross and petrel chicks while
they sit on their nests.

Richard Cuthbert, the first professional ornithologist
to spend a year on Gough Island, is still kicking
himself.

He can't quite believe that his year on the
British-owned island deep in the South Atlantic Ocean
was almost over before he stumbled on the nightmare
answer to a problem that had been puzzling him for
months.

Initially, Cuthbert, who is on board the SA Agulhas on
his way back to Gough Island, couldn't understand the
extremely poor breeding success rate or distribution
of several species on the island, which is probably
the world's most important seabird breeding area.

Dubbed 'super mice' because of their size

Then, he made the horrifying discovery that the common
house mice on Gough - dubbed "super mice" because of
their size - are eating alive defenceless chicks
sitting on their nests, including young Tristan
Albatrosses, an endangered species.

Because all Gough's seabird species have evolved over
thousands of years in the absence of natural predators
at their breeding sites, these chicks have no defence
mechanism against the mice, and are literally eaten as
they sit on their nests waiting for their parents to
return to feed them.

Two students working on the island to confirm
Cuthbert's gruesome finding and gauge the scale of the
problem have managed to get video footage of mice
attacking the defenceless chicks.

"It sounds incredulous, implausible, that a mouse
could attack a chick," says Cuthbert.

"But these (albatross) chicks are really big spherical
balls of fat covered in down, and because they're so
big and fat, they can't defend themselves."

'It's a big, big conservation concern'

Although there had been some earlier ornithological
work on Gough Island, done on a voluntary basis by the
meteorological team, Cuthbert and his field assistant,
Eric Sommer, were the first people to spend a whole
year there dedicated to doing bird research, during
2000/1.

Cuthbert explains that rats, brought by sailors, have
had a major impact on seabird populations around the
world - and particularly on islands. "At the same
time, we've known that mice are on the island,
introduced by the sealers.

"But mice aren't a problem - at least, that's what
we've been led to believe. So this was something that
we nearly missed, and I only twigged after about 10
months down there that, hell, something strange is
happening here."

Summer-breeding birds, like the Atlantic Yellow-nosed
Albatross, the Sooty Albatross and the Great
Shearwaters, appeared to be doing okay, Cuthbert
recalls.

"But the winter breeders - particularly Atlantic
Petrels and the Tristan Albatross - were getting
hammered."

Still, he didn't think of mice as the culprits.

"Mice normally eat insects and seeds. I think it's
been recorded that Storm Petrel eggs have been taken
by mice, and possibly their chicks as well."

But a Storm Petrel weighs only 25 or 30g, while a
Tristan Albatross chick weighs as much as 10 or 12kg,
Cuthbert points out.

"So a mouse weighing only 50 or 60g attacking
something that is over 10kg is unprecedented really."

How did he stumble on this grizzly phenomenon?

He explains that Atlantic Petrels breed in burrows,
and that he and Sommer had a number of "study burrows"
that they checked every four or five days.

"And we certainly noticed that the healthy chicks that
we found there were, five days later, just
skin-and-bone, or dead.

"And then in one case I saw a live chick with wounds
around its rump, and later that day it was dead with
mice feeding on it.

"At that time I didn't really think more of it,
because it was so 'out of left field' that mice could
be doing this."

Then, later in the year, the two researchers made a
total count of Tristan Albatross chicks. "And their
breeding success was appalling."

Ross Wanless and Andrea Angel, the two students from
the Percy FitzPatrick Institute of African Ornithology
at the University of Cape Town, have confirmed that
Atlantic Petrel and Tristan Albatross chicks are being
killed by mice.

Given the current rates of mortalities, are any bird
species actually at risk of extinction because of
mice?

For example, the Tristan Albatross is of particular
concern because it is now extinct at its original
breeding ground on Tristan da Cunha, and Gough Island
is home to some 99.8% of the remaining population.

"The Tristan Albatross is at risk anyway because of
long-line fishing, and it's doubly at risk because of
the mice," responds Cuthbert.

"And for the Atlantic Petrels, while we've never had
any record of them getting caught by fishing boats or
long-line boats, the level of breeding success they're
having at the moment is not sustainable."

The one advantage that albatrosses and petrels have is
that they are very long-lived, Cuthbert adds.

"It's a big, big conservation concern, but in the next
five years or so - probably nothing will go extinct as
a direct result of the mice, I would imagine."

The facts

They may be ordinary house mice, but the creatures
creating havoc with Gough Island's bird populations
are known as "super mice" - and for good reason.

They're the largest of any house mouse population
anywhere in the world, in terms of body size.

"They're about twice the size of a normal house mouse
in Britain," confirms ornithologist Richard Cuthbert.

This is because of a scientific rule that mammals get
progressively bigger as the latitude gets higher -
that is, moving towards the poles and as the climate
gets colder.

"Even taking that into account, they are super-sized,
and obviously super-charged in terms of their effect
for attacking albatrosses," says Cuthbert.

But he points out that the fact that the mice are so
big is probably "a bit of a false premise, really".

"Because even if they were only half the size they
are, they could probably still attack the albatross
chicks."


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Devorah A. N. Bennu, PhD
Independent Scholar
birdologist [at] yahoo [dot] com
public blog: http://girlscientist.blogspot.com




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