Investigative Case 8: Back to the Bay

Chesapeake BayI. Back to the Bay Resources

Explore the following resources linked to ongoing investigations of changes in the Chesapeake Bay. Provide a question that your group would like to explore and explain how you would use at least two of these resources or ones that you have identified to investigate that question.

     Visualization, Mapping, Survey and Remote Sensing Data

II. Gull Population Control

Chicken or the Egg Worksheet Excel spread sheet used in Case 8, Investigation II, Part B, Question 1

Use this Excel spreadsheet to further investigate the effects of eliminating either eggs or birds as a control measure for bird populations.

Choose one of the scenarios below or generate your own scenario to model. Adapt the spreadsheet to reflect the scenario.  Explain the results of the model.

  1. For gulls nesting near a city landfill, predation on eggs is doubled due to an increase in the number of rats. Modify the model to reflect these facts and then run the model. What is the effect on population growth?
  1. In cities, predators on adult gulls are reduced due to urban development. If you assume egg survival is constant, how would you change the model to show the impact of loss of predators? Make the change, run the model and print the output. Interpret the results.
  1. Western Gulls have been implicated in reducing biodiversity because they have been observed to kill nesting adult petrels with a resulting reduction of the petrel population by 2.5% per year. While this seems a small amount, it is enough to lead to significant survival problems in this species over time. Propose a way to control the Western gull population in order to lower this predation effect. Modify the model to generate evidence that your plan could be effective.

(See the following article from The Endangered Species Bulletin, Nov. 1998, U.S. Fish and Wildlife Services on gull predation of shore birds at:

Extended Activity: Exploring Excel Spreadsheet Models
1. Logistic Growth (.xls file)

This model projects the increase in gull populations when under ideal conditions. You can enter any the number of mating pairs from any current report or paper and project the increases the area will face under ideal conditions. Use either the standard scale or the logistic scale graph to explain the results.

Generate a question to explore with this model or choose one of the following:

2. Control and Cost (.xls file)

This Excel model provides new variables you can change in order to specify gull population sizes and the costs for controlling the gull population.

Examine the model and describe its features.  You might wish to consider:

Adapt this model to compare the use of two control methods such as egg oiling or the use of poisoned bait?  Which do you think would cost more over a five year period?  Support your answer with results from running the models you have changed.

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