Posted on April 13, 2012 by Bob Berwyn
Some populations — especially along the Antarctic Peninsula — still considered vulnerable to global warming impacts
Emperor penguin colony near Halley Bay. IMAGE COURTESY DIGITALGLOBE.
An emperor penguin chick. PHOTO COURTESY BRITISH ANTARCTIC SURVEY.
By Bob Berwyn
SUMMIT COUNTY — After carefully studying satellite images of emperor
penguin colonies and comparing the numbers to sites with ground-truthed
data, biologists estimate there may be twice as many emperor penguins in
Antarctica than previously thought.
The ground-breaking study also discovered four new colonies and confirmed the location of three other colonies.
The research is published this week in the journal PLoS ONE. It
provides an important benchmark for monitoring the impact of
environmental change on the population of this iconic bird.
“We are delighted to be able to locate and identify such a large
number of emperor penguins,” said lead author and geographer Peter
Fretwell, of the
British Antarctic Survey.
“We counted 595,000 birds, which is almost double the previous
estimates of 270,000 – 350,000 birds. This is the first comprehensive
census of a species taken from space.”
The latest count of 238,000 breeding pairs far exceeds the last estimate from 1992 of 135,000-175,000 breeding pairs.
The total population size was estimated from the number of breeding
pairs based on 80 percent of penguins breeding in any one year in all
colonies. Uncertainties stem from remnant difficulties in
differentiating penguins from guano and shadow, which will be resolved
as the resolution of satellite imagery improves further. Forty three of
the forty four images used in the analysis were from one breeding season
(2009), so the estimate can be considered a single year census.
Emperor penguin colonies show up as dark splotches against the white ice near Halley Bay. PHOTO COURTESY DIGITALGLOBE.
On the ice, the black-and-white feathered emperor penguins stand out
against the snow and colonies are clearly visible on satellite imagery.
This allowed the team to analyze 44 emperor penguin colonies around the
coast of Antarctica.
Despite the new population estimates, biologists said emperor
penguins remain vulnerable to global warming impacts — especially the
colonies close to the Antarctic Peninsula, where the annual sea ice
duration is less now than 2 decades ago and where
large portions of coastal ice shelves are disintegrating.
An
emperor penguin with chick. PHOTO COURTESY BRITISH ANTARCTIC
SURVEY.“Current research suggests that emperor penguin colonies will be
seriously affected by climate change," said British Antarctic Survey
biologist Dr. Phil Trathan, who
previously documented the disappearance of an emperor penguin colony
from the west coast of the Antarctic Peninsula. "An accurate
continent-wide census that can be easily repeated on a regular basis
will help us monitor more accurately the impacts of future change on
this iconic species.”
Emperor penguins depend on stable sea ice during the breeding and fledging cycle.
“They need a stable platform the whole time the eggs are being incubated, and during chick-rearing and fledging,” Trathan said.
Shifts in the timing of sea ice formation and duration — as observed
close to the Antarctic Peninsula — could drastically affect the
reproductive cycle.
For example, if the ice melts earlier, or there’s more snow, the chicks could get wet, leading to direct mortality.
“The colonies that are most vulnerable are those close to the
peninsula, where climate change is happening,” he said, adding that
there are regional variations in observed climate changes in Antarctica.
“We know the eastern side of the Antartic Peninsula is vulnerable,” he
said, referring to the disintegration of parts of the Larsen ice shelf.
Other studies
have shown a direct link between changes in sea ice, abundance of krill
and a decline and shift in other penguin populations along the western
Antarctic Peninsula, where the number of both Adelies and chinstrap
penguins may have dropped by as much as half since the 1980s. In that
same span, mean winter air temperatures in the region have climbed by up
to 10 degrees fahrenheit, leading to a huge loss of sea ice.
A satellite image shows the emperor penguin colony at Smyley Island. PHOTO COURTESY DIGITALGLOBE.
Without the sea ice in the mix, the ocean is not nearly as
productive, NOAA and Scripps Institute of Oceanography scientists said,
adding that an increase in the number of whales and seals, as well as a
developing commercial krill fishery may also be factors in declining
krill populations.
Trathan said followup studies may focus on the condition of the sea ice where emperor penguins breed.
“One of the things I’d really like to do is look at fast ice
conditions … to try and see which are the most vulnerable colonies, and
which are more stable than others. If there are good stable ice
conditions it means that maybe a colony will be successful each year” he
said.
The research
The scientists used images from three different satellites
(Quickbird2, Worldview2 and Ikonos) to identify locations of emperor
penguin colonies. Then they acquired more detailed imagery from
Boulder-based
DigitalGlobe and pansharpened the shots to differentiate between penguins, shadow and guano.
Pansharpening involves the merging of a higher-resolution
panchromatic image (black and white, but sensitive to all wavelengths of
light) and a lower-resolution color image to produce a single
high-resolution color image. This process lowered statistical deviations
between known and predicted penguin counts considerably.
University of Minnesota biologist Michelle LaRue explained how the team used the images for their count.
“We created an algorhithm, training the computer to be able to tell
the differecne between guano, ice and penguins,” she said, adding that
she previously tested the technique by counting Weddell seals to show
that satellite imagery is a reliable way to count populations.
“Now that we know we can do this, and how many emperor penguins there are, we can hone in a little bit,” she added.
“The methods we used are an enormous step forward in Antarctic
ecology because we can conduct research safely and efficiently with
little environmental impact, and determine estimates of an entire
penguin population,” LaRue said.
“The implications of this study are far-reaching: we now have a
cost-effective way to apply our methods to other poorly-understood
species in the Antarctic, to strengthen on-going field research, and to
provide accurate information for international conservation efforts.”
Previous counts of emperor penguins have been challenging because
they live in remote terrain and the best time to count them is when
weather conditions are incredibly severe and when extensive sea ice
makes it difficult to reach the colonies.
Emperor penguin and chick. PHOTO COURTESY BRITISH ANTARCTIC SURVEY.
Emperor penguins
The emperor is the giant of the penguin world and one of the largest
of all birds. Gold patches on their ears and on the top of their chest
brighten up their black heads.
Emperors are the only penguin species to breed through the Antarctic
winter, with temperatures as low at minus 50 degrees Celsius and winds
of up to 200km (or 124 miles) per hour.
They form large colonies on the sea-ice, with the female laying a
single egg and passing it to the male for incubation. The eggs are
balanced on the penguins’ feet, which are then covered by a thick roll
of skin and feathers. This keeps the egg some 70 degrees Celsius warmer
than the outside temperature.
The females will then go to the sea to feed, and return around the
time when the chicks are due to hatch. She then takes over brooding and
feeding the chick while the male, after a nine-week fast during which it
may lose 45 percent of its body weight, treks up to 100 kilometers over
the ice to find food.
To survive the Antarctic winter, adult emperors have a special
combination of adaptations, with a dense double layer of feathers and a
large fat reserve. Afterwards, both adults rear the chick.
The survey found four new colonies, at Brownson Islands, Dolleman
Island, Dibble Glacier and Rupert Coast, and three previously suspected
colonies, at the Shackleton Ice Shelf, Bowman Island and the Lazarev Ice
Shelf. There are 46 emperor penguin colonies locations around the coast
of Antarctica.
Source
(click on images for larger size)
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