Penguinscience.com
Did You Know ?
1. At the capes Royds, Bird and Crozier colonies, there are about 4 000, 35 000, and 140 000 breeding
pairs of Adélie Penguins; about 40 000 breeding pairs reside at Beaufort Island.
2. In the entire Antarctic, there are about 2.5 million pairs of penguins breeding in about 161 colonies, at
least as of the mid-1990s.
3. Adélie Penguin colonies are disappearing in parts of Antarctica but new colonies are being founded
else where.
How Many Adélie Penguins
Adélie Penguins are colonial seabirds. That means they nest close together in colonies, which range in
size from about 10 to 170 000 nests. The colonies are at least 2 km apart and each is located in an area
accessible from the sea (a beach) and not covered by ice or snow. Within a colony, the nests are
arranged in groups, called sub-colonies. These groups usually are on the tops of hummocks and not in
the valleys between hummocks. This is because melt water from nearby snow fields and glaciers runs
down the valleys, making the ground too soggy for nest building.
Adélie Penguins nesting between two
roaring torrents coming from a melting
glacier.
Adélie Penguins nest in groups, called
sub-colonies, that are situated atop
ridges where snow does not form drifts
and where melt water does not run in
rivers.
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Considering all the 161 colonies
of Adélie Penguins in the World
and assigning each to a size
category, we see that only 6
colonies are larger than 100 000
pairs. One of our study colonies,
Cape Crozier, is one of these.
About 1/3 of colonies have fewer
than 1000 pairs, and about 1/2
have fewer than 5000 pairs, or
the size of Cape Royds. Our
other study colonies, Cape Bird
and Beaufort Island, are among
the larger colonies (20001 to
40000 pairs).
We know the size of the colonies by counting nests with a penguin on it. We also keep records of banded
birds, knowing how many each season find a mate and lay eggs. These are the breeding penguins.
Those penguins that have a nest but with no eggs are called non-breeders. Many non-breeders make a
nest and search for a mate to then breed the following year. For every two breeding penguins there is
one non-breeder that is present at the colony during the summer (we know this from banding). There are
also other penguins who never visit the colony, until they are at least 2-3 years old. By knowing the ratio
of breeding to non-breeding penguins, we can estimate the population of a colony.
The numbers of breeding pairs of penguins at our study colonies has been
changing during the past few decades.
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It would be impossible to determine the number of nesting pairs in the mass of penguins at Beaufort
Island in the photo on the left (arrow points to person searching). This image was taken in late
January, when not only are there adult penguins but also large chicks. In order to accurately
determine the number of nesting pairs in a large penguin colony, it is necessary to use aerial photos
taken on or about December 1, photo on right, when A) only one member of each pair is sitting on
the eggs, while the other is off at sea feeding; and B) there are very few non-breeders present. This
means that almost all nests with a penguin on it has eggs. Flying at 2000 feet, so as not to disturb
the penguins, a series of photos can be taken and then the dots counted. In the picture on the right
almost every dot represents a penguin sitting on its nest. Counts by people on the ground at the
same time can determine the proportion of nests where there is a non-breeder — there are usually
only a few when aerial photos are taken.
Daily counts of penguins in one sub-colony reveal how the number
of penguins in a colony changes over time in a spring-summer
season. Note that when the aerial photo was taken of this colony,
Cape Royds (see photo above), the number of nests with eggs had
not changed between Nov 25 and Dec 5, and that the number of
penguins present just about equaled the number of nests with
eggs. After this period the number of nests with eggs slowly
decreased, as eggs were lost to skuas. Therefore, the aerial photo
taken on Dec 1 showed the breeding population at its maximum.
It is important to have accurate
population counts of Adélie
Penguins as well as other birds
and animals in our world so we
know if their populations are
increasing or decreasing. As our
Earth changes due to climate
warming, habitat destruction and
human use of resources, the
other species we share this
planet with must cope. Some
species have had to move their
homes and change their food
sources, others have declined in
numbers, and some have not
been able to cope and have
become extinct, no longer part
of our world. Keeping track of
Adélie Penguin populations
helps us monitor how they are
coping with changes in their
habitat.