for Analyzing Bald Eagle Population Data
years the United States takes a census of all the people living in
the country; Americans are required by law to fill out census forms.
Too bad the law can't require Bald Eagles in the U.S. and Canada to
fill out a census form, too! Then we'd know exactly how many of them
are living here with us people.
we can't get precise numbers for such a widespread species, we can
get a picture of how healthy eagle populations are on the basis of
data collected in various ways during the breeding season, migration,
Numbers on Christmas Bird Counts 1900-2000
Is for the Birds: 101 Years of Christmas Bird Count Data
the longest continuous set of data comes from the Christmas
Bird Count established in 1900 and administered by the National
Audubon Society. More than 50,000 participants now take part in Christmas
Bird Counts. But when the CBC was started by Dr. Frank Chapman, there
were nowhere near as many participants. So the apparent low number
of Bald Eagles during the first years were is due more to the fact
that so little area was covered than to how few eagles there were.
But count numbers and participants grew steadily, especially in the
60s and 70s, and yet eagles found on Christmas Bird Counts stayed low.
This! Make an Eagle History Timeline
on the above graph and print the enlarged version. Using an almanac,
encyclopedia, the Internet, and/or other reference materials, find the
dates when the following things happened and mark them on the graph to
make an Eagle History Timeline.
Eagle Act passed
Species Act passed
officially taken off Endangered Species List
- DDT discovered
by Swiss chemist Paul Muller
wins the Nobel Prize because DDT is so useful for killing lice on
soldiers and for killing mosquitoes that carry malaria
- Dr. Joseph
Hickey determines how much DDT kills half a population of robins
- Dr. Joseph
Hickey organizes a symposium bringing together the top ornithologists
in the world to figure out how DDT is destroying Peregrine Falcon
and Bald Eagle reproduction
Carson's Silent Spring is published.
Richard Nixon's administration bans DDT for most use in the U.S.
on the timeline seem related to eagle numbers?
30 Years of Lake Superior Data
figures below represent the annual seasonal Bald Eagle count totals
for an overlook on a migration pathway at the western tip of Lake Superior
called Hawk Ridge. This represents just a fraction of North America's
Bald Eagles, and daily autumn records have only been kept since 1972,
but the numbers correspond nicely with counts at other overlooks, breeding
bird censuses, and winter counts (including the Christmas Bird Count).
Using the population data from 1972 to the present, make the following
3 graphs to depict the population levels for this once-endangered species.
- The number
of Bald Eagles counted at Hawk Ridge per year.
- The increase
in the number of Bald Eagles per year.
- The percent
increase in the number of Bald Eagles per year.
- How do
your graphs compare with the corresponding years of the Christmas
Bird Count graph?
the different visual picture each graph gives you. Was it helpful
to graph the data in these different ways? How?
about what each graph means. What different information does each
graph do you think is the most revealing?
- Are there
times when the numbers appeared to increase significantly, but the
percentage increase was not as pronounced?
questions about the climb in population size do you have?
reasons do you suppose are behind these changes?
all the factors you can which might have caused the population to
rise (or fall) at various points.
which decade did the population increase at the fastest rate?
factors do you think could change the numbers at a given location
(e.g., weather)? Explain why you think scientists don't pay much
attention to year-to-year changes in a count like this, but DO pay
attention to graphs with many years of data.
more about Bald Eagle population numbers and the history of this species,
see Bald Eagle History.
Science Education Standards
- Use data
to conduct a reasonable explanation.
critically and logically to make relationship between evidence and
develop explanations using observations (evidence) and what they
already know about the world.
change environments in ways that can be either beneficial or detrimental
for themselves and other organisms.
in environments can be natural or influenced by humans. Some changes
are good, some are bad, and some are neither.