Hua Mei tends to
one of her oneday-old twins.
Cubs cry to get
mom's attention.
For more on pandas and to
watch a real-time video of the
San Diego Zoo's bears, visit:
www.sandiego2oo.org/
pandas/pandacam/index.html
With scientists
pandas a^
raising heaithy cu
captivity. These ba
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disappearing]
BY
B R I T T
N D R L A N
D I R
L
ast year, a California
celebrity left her
sunny home for a
new address. The
star a popular panda
named Hua Mei (WAH MAY). The bear
first grabbed headlines when she was
bom at the San Diego Zoo in 1999. She
was the first Giant Panda, Ailumpoda
meUmoleiica (AL-yer-uh-POH-dah melAN-uh-LOO-kah), in the United States
to survive after being bom in captivity.
Hua Mei stayed at the zoo until she
was old enough to have cubs. Then,
last February, she moved to China's
Wolong (WOO-long) Giant Panda
Breeding and Research Center. There,
as part of an intemational project to
breed pandas, scientists introduced
Hua Mei to potential mates. And last
September, she made headlines
again—this time after delivering two
cubs. "We still tliitik of her as our
baby; now she has Lwins of her own,"
says Barbara Durrant, the head reproductive physiologist (scientist who
One
of Hua Mei's
twins—about
one month
old—tries to
lift itself up. , ^
m
w
SCIENCE WORLD B
studies reproduction) at the San Diego
Zoo's Department of Conservation and
Research for Endangered Species.
Hoping to save pandas from
extinction (no organisms of the
species remain), biologists around the
world are working together to try to
breed the bears in captivity. As part of
the project, China—panda's native
land—lends pandas (like Hua Mei's
parents) to foreign zoos with the hope
that the bears will have cubs. Then,
the offspring leave mom and dad
behind and move to Chinese breeding
centers to start a new family.
Their first step with Hua Mei: setting
her up on several blind dates. Captive
male pandas are very picky about their
female partners. The scientists needed
to fmd Hua Mei's perfect match.
The next, step—choosing the
moment to introduce the bears to
eacb otber—was even trickier. That's
because a female panda's estrus, the
CARE BEARS
It turned out that everything was
timed right for Hua Mei, and she gave
birth to twins—each only about the
size of a stick of butter. "The size ratio
of a panda mother to her cub is the
largest of any bear and one of the
largest of any animal," says Durrant.
Their extra-small size means the cubs
need a lot of care. like many new
moms, Hua Mei initially seemed
unsure of her motherly role.
Soon, however, she settled into
"BEARLY" HANGING ON
With fewer than 1,600 wild pandas
remaining, scientists think captive-bom
bears may help rescue wild pandas one
day. The bears once roamed over most
of China and into other countries to
the south. But humans have taken over
most of their forest home (see map,
right). "Pandas have been pushed to
the edges of China that humans do not
want to live in," says Colby Loucks, a
conservation scientist at the
Worid Wildhfe Fund.
Squeezed into small, isolated patches of steep forest, the
bears' lives are at risk. For
instance, bamboo makes up
about 99 percent of a panda
bear's diet. In the 1980s, large
patches of China's bamboo
died off Surrounded by
humans, over 200 wild pandas
were tanable to move to areas
where bamboo still grew and
the bears starved to death.
To prevent another disaster, scientists are working to protect panda habitat (region where an animal lives).
Then, they nxay be able to boost the
panda poptilation one day by releasing
captive-bom bears into the wild.
PERFECT TIMING
For now, scientists are trying to
learn how to breed pandas in captivity.
ID
JANUARY 24. 2DQ5
window—about 24 hours [in which
fertilization can occur]," says Durrant.
In the wild, solitary female pandas
call out to alert nearby males that the
time is right. In captivity, scientists
need to introduce pandas—normally
kept separated—to each other during
this period. If fertilization occurs, a
single cell called a zygote forms from
the joined egg and sperm. Then, a
cycle of cell divisions begins to form a
panda fetits (imbom yoting) and eventually a cub (see Nuts & Bolts, p. 11).
time during which she can become
pregnant, occurs only once a year for
one to foiu* days.
Ditrijig this time, the female produces an egg (female sex ceil). The
egg then needs to he fertilized, or
joined, with a spenn (male sex cell).
Unfertilized eggs don't survive long, so
fertilization needs to happen quickly.
"[There is] a very, very small
motherhood. Since aU panda
cubs are bom blind and
hairless, moms gently pick
them up in their mouths.
They keep the tiny cubs
cozy against their fur. A
panda mother usually won't
leave her baby—even to eat
or drink—imtil the cub is
about 10 days old. She stays
with her cub, teaching it
how to survive, until it is
about 18 months old. Then
the cub leaves to hve a
mostly solitary life. In captivity, panda
cubs are slowly weaned, or removed
fi-om tbeir motber's care, after roughly
one and a half yeara.
DOUBLE TROUBLE
It's tough to care for even one growing bear, but—like Hua Mei—pandas
give birth to twins about 50 percent of
the time. Because the cubs need so
much attention, a mother in the wild
usually neglects one of her twins. "The
cubs are so small and require so much
care, she just can't hold [or feed] two
of them all the time," says Durrant.
Unfed, the neglected cub dies.
Even captive pandas follow these
instincts. So in the past, when twins
were bom in captivity, veterinarians
would remove one of the cubs and
hand-raise it: They fed it from a bottle and cared for it without any help
from mom. But until recently, scientists had never successfully handraised a cub to adulthood.
CUBS WIN
Luckily, scientists have now developed liquid formulas that are better
matched to natural panda milk. Also,
tbey have designed special "cub holders" tbat exactly copy the position in
which mother pandas hold their
babies when they nurse. Scientists use
fake fur that feels and smells just like
mom to help a cub feel right at home.
Hua Mei's twins also benefit from
another new technique: Instead of
completely hand-raising one cub, veterinarians periodically swap twins.
They remove the cubsfi"omthe moth-
Nuts & Bolts
er's care one at a time—feeding each
for a few hours before returning it.
Each cub gainsfi"omspending time
with mom: "Since twin swapping and
improved formulas have been used at
Wolong, they went from losing one of
the twins 100 percent of the time to
saving both twins 100 percent of the
time," says Durrant.
This success is spreading: In 2003,
16 healthy pandas were bom in captivity around the world. This baby boom—
along with expanded protection of wild
habitat—may help keep the black-andwhite bears from disappearing.
^
Like all animals, pandas start out as a single cell.
Through a process called mitosis, this cell divides
over and over again. These divisions form millions
of cells that eventually develop into a panda cub.
I. CELLS UNITE
A male sperm joins with a female egg. Result: a
zygote, or fertilized egg. The nucleus (area containing
D/V/A-chemical that carries genetic information) has
42 chromosomes (structures that contain DNA), half
from each parent. Four chromosomes are shown.
NUCLEUS
FERTILIZED EGG
DUPLICATED
CHROMOSOME
FROM FEMAiE
SPINDLE FIBER
CHROMOSOME
FROM FEMALE
CHROMOSOME
FROM MALE
DUPLICATED
CHROMOSOME
FROM MALE
2. DUPLICATION
The nucleus breaks
down and each of the
cell's chromosomes
is copied. The chromosome pairs line up,
moving along spindle
fibers. Each pair splits
and one complete
set of chromosomes
moves to each end
of the cell.
3. CELL DIVIDES
Two new nuclei form
at opposite ends of
the cell. Each
nucleus contains a
set of 42 chromosomes. Then, the
cell divides into two
identical cells.
MALE
7. CUB DEVELOPS
For between 30 to 50 days, the fetus grows inside
the uterus. Then, Ihe female delivers a baby panda.
At birth, the tiny cubs are blind and hairless.
CELL
CELL
LINING OF UTERUS
4. CELLS MULTIPLY
The new cells continue to divide: After
one more cycle of cell divisions, four
identical cells have formed. Another
cycle yields eight cells. This continues—
doubling the number of cells each time.
B. ATTACHMENT
Eventually, the blastocyst attaches to the lining
of the female panda's uterus, the hollow organ
in which a baby develops. The cells in the inner
cell mass grow to become a panda fetus.
5. REDRBANIZATION
INNER
CELL MASS
After about five days, a blastocyst forms: Cells move to
form a thin layer around the edge and a group of small
cells, called the inner cell mass, assembles along one side.
SCIENCE WORLD