Introduction
Our project studies the diving biology of emperor
penguins. Emperor penguins are champion divers, the best among all
birds. They can dive deeper than 1800 feet and can stay underwater on a
single breath of air for as long as 22 minutes. We are interested in how
emperor penguins dive so deep (diving physiology), and what they
do during the dive (diving behavior).
The study of emperor penguin physiology is important because it explains
how a bird has evolved and adapted to swim underwater. The most
important adaptations for diving are 1) an increase in the ability to
store oxygen in the body, 2) the ability to tolerate low levels of oxygen in the body, and
3) the
ability to tolerate the effects of pressure. These adaptations are also
potentially relevant to our understanding of human physiology and
medicine. For example, penguins routinely reach low levels of oxygen
during diving that would cause us to pass out. Emperors can also dive
safely to depths which would cause us to suffer from the “bends” and
other effects of high pressure.
We also study diving behavior so that we can better understand the
ecology of the emperor penguin. The emperor is one of the top predators
in the Antarctic ecosystem. We want to know at what depths they are
feeding, and what type of prey they are catching. We
ultimately want to know how much fish or squid the emperor penguin
population must consume. This information is important to our
understanding of the marine ecology in this region, and is also
important for the future conservation of emperor penguins, since
overfishing and other human interference can have potential adverse
effects on their population in the Antarctic region.
How do we
study penguins?
We conduct our studies near the McMurdo Station in Antarctica. Our camp
is about 15 miles out on the frozen sea; it is called “Penguin Ranch.”
The camp is in an area where there are no holes or cracks in the sea
ice. We drill holes into the ice through which the penguins can dive,
and since there are no other holes in the ice, the penguins must return
to the dive hole. This set up allows the birds to dive freely, but
ensures that they return each time to our study site.
To study physiology and behavior during diving, we have designed
miniaturized recorders, which will log information while the penguin is
swimming underwater. These recorders (or data loggers), which are
attached to the feathers on the back of the bird, must be small so that
they do not interfere with the normal swimming pattern of the bird. At
the end of the study, the recorders are removed and the birds are
released. The recorders are then cleaned and connected to the computer,
so that we can transfer the data and analyze the information.
How do we
study diving physiology?
There are many different types of data loggers in our studies. For our
physiological studies over the next few years, we are especially
interested in oxygen and nitrogen, and how penguins survive both low
levels of oxygen and high pressure when diving. We have sensors that can
log the changes in oxygen pressure as the bird dives. We can also record
depth, body temperature, the electrocardiogram and heart rate, swim
speed, and the stroke rate of the wings. All of this information allows us to assess of the physiological changes in the bird due
to diving.
How do we
study diving behavior?
We would like to know what the emperor penguin feeds upon, at what depth
the capture occurs, and how the prey is captured,. How can we do
that? To help us observe the birds, we have an underwater observation
chamber that lets us sit under the sea ice without getting wet. As long
as the birds are near the surface, we can visually observe their
behavior. Unfortunately, the birds quickly disappear from view, so the
amount of time that we can actually see them is short.
Since we can't observe the birds directly during their
dives, we use cameras to give us information. We have successfully used
National Geographic’s Crittercam® video camera to identify the
fish which the emperors catch just beneath the ice at the Penguin Ranch.
This small camcorder allows the bird to make (and star in) its own movie
underwater. The limitations of the camera were its size and its need for
enough ambient light to record an image. The size of the camera
restricted its use for only short periods of time (about an hour). The
need for sufficient ambient light restricted its functional use to the
top 20 or 30 feet of water. Nevertheless, we were able to see that the
birds were catching a small fish (Pagothenia borchgrevinki), which
lives in the underside of the sea ice.
To study feeding over long periods while penguins are at
sea and to image what they are feeding upon during their deep dives, we
need a camera that is extremely lightweight and that has its own light
source. We are collaborating with the National Institute of Polar
Research (NIPR) of Japan. They have developed a very small digital
camera, which we will test on penguins at the ranch this year. In the
final year of the grant, we will put this camera on penguins going out
to sea. We hope that this will allow us to identify the type of prey
which emperors pursue at great depths of 1200 to 1500 feet. We are also
testing recorders from the NIPR which measure speed, acceleration, and
body angle (the angle at which the bird travels up or down), as well as,
one designed to reconstruct the 3-dimensional path of a dive. From this
recorder we hope to see the strategy that the penguin uses to find food.
Conclusions
Together, all these studies provide a more complete understanding of the
emperor penguin biology. We will better comprehend why these birds dive
so deep, what allows
them to dive to these depths, and how they capture their prey. The type
and quantity of fish and squid which they catch will be key to our
understanding of the emperor penguin's role in the Antarctic ecosystem
and to their long-term conservation.
If you are interested in seeing our camp and the
birds, but sure to visit our photo gallery pages on this web site.
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