Whooping
Crane Population Dynamics: Challenges
of Rebuilding an Endangered Species
Overview: Students
keep and maintain an ongoing chart about factors that influence
whooping crane population gains and losses.
Materials: Helpful
materials include whooping crane biographies (available
for birds in the Eastern/reintroduced flock), letters from Tom
Stehn in each migration update as well as those in the Archives;
selections
on our Resources page,
and the crane FAQ pages.
Also see guiding questions on The
Challenges of Whooping Crane Survival: Learning from Life Histories. You
may wish to replicate the chart on large chart paper for a whole-class
activity. |
From
One Flock to Two
In
the 1940s, only 15 migrating whooping cranes stood between survival
and
extinction. It took over 40 years for the natural flock—the
Aransas/Wood Buffalo (or Western) population—to grow from 15 to
100 whooping cranes.
It took another
18 years for the natural flock to reach 200. Meawhile, a newly
reintroduced Eastern flock began in 2001 with the help of ultralight
airplanes
to
teach chicks their migration route. The Eastern flock is
growing too. How many whooping cranes exist today?
What
causes their numbers to change from
year to year? why does rebuilding an endangered species take so long?
Population Numbers: Why the Gains or Losses?
Scientists who study changes in the number and composition of individuals
in a
population
and the
factors
that
influence
those
changes
are concerned with population dynamics. You'll appreciate
how difficult their work is by thinking through this challenging problem
yourself.
Activity
On
the chart below, list all the factors
you can imagine that might cause high or
low
numbers at each stage of the whooping crane's annual cycle:
- Begin
with the breeding season. What factors might influence
the number of eggs laid (no eggs or 1 or 2 eggs)? What might cause
the eggs or chicks
or adults to die? What might help greater numbers to survive?
- Next,
consider the fall migration. What could cause
crane deaths during fall migration? What challenges to their safe
migration can you identify? (Consider both the natural flock
coming from Canada and the chicks led by ultralight aircraft to
Florida.)
- Then
consider mortality at the over-wintering sites, which
means Texas for the natural flock and Florida for the introduced
flock. What
are potential causes of death there?
- Finally,
consider the spring migration. What might cause cranes
to die during spring migration? What challenges can you identify?
Challenges of Rebuilding an Endangered Species
Breeding
Season
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Fall
Migration |
Over-wintering
Season in TX or FL |
Spring
Migration |
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National
Science Education Standards
Science
as Inquiry
Ask a question about objects, organisms, events. (K-4)
Life
Science
An organism's behavior patterns are related to the nature of that organism's
environment, including the kinds and number of other organisms present,
the availability of food and resources, and the physical characteristics
of the environment. When environment changes, some plants and animals
survive and reproduce, and others die or move to new locations. (K-4)
Science
and Technology
People have always had questions about their world. Science is one way
of answering questions and explaining the natural world. (K-4)
Science
in Personal and Social Perspectives
Environments are the spaces, conditions, and factors that affect an individual's
and a population's ability to survive and their quality of life. (K-4)
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