Issues : Data Sets


There are three Excel files:

How to use this data set in a class:

      This data set could be used in discussions of community ecology (species diversity), species interactions (brood parasitism), and management of an endangered bird species (the Kirtland's Warbler). It would also be a nice comparison with other removal studies showing great effects on community composition - e.g. Paine's starfish removals.

      This is a fairly straightforward data set concerning possible effects of brown-headed cowbirds on songbird species diversity. Brood parasitism is a captivating phenomenon, and the idea that cowbirds negatively impact their hosts is a "truth" for most students who are familiar with cowbirds. Another attractive aspect of the study is that De Groot and Smith test this idea in two ways - 1) by comparing songbird composition for birds that accept cowbirds with community composition of birds that do not accept the parasites and 2) by comparing bird composition in sites with and without cowbirds.

      Their hypothesis that songbird richness and evenness would be higher in cowbird removal sites was not supported. In addition, the proportion of suitable cowbird hosts did not decrease much in the cowbird removal locations. This is a good opportunity for students to see that even hypotheses that seem so likely must sometimes be rejected. In addition, this recent paper (2001) is the first on effects of a brood parasite on community composition, which will also surprise students.

Making and Using the Figures

      I have reformatted the original Excel files so that columns could manipulated; both original and reformatted files are here. There are two data sets in two separate files - comparisons of birds in removal and control sites in 1996 and 1997 and for birds that are suitable hosts for cowbirds and those that are not.

      De Groot and Smith use histograms in Fig. 4 (below) to compare effects numbers of individual birds in cowbird removal sites and controls for suitable and unsuitable hosts. The archive data are tables showing the "number and species of passerine individuals detected per site at cowbird (Molothrus ater) Removal and Control sites near habitat of the Kirtland's Warbler in northeastern Lower Michigan". In Data Files #2 and 3, I use a scatter plot to compare numbers of individuals for 39 species (suitable hosts) and x species (unsuitable hosts).

      How your students work with these data depends on their experience with data in spreadsheets, your goals for the exercise, and the time available. You will need to prepare a handout or other form of instruction describing the data files and what you want the students to do with them.

Questions for discussion

1. As a result of cowbird control and habitat restoration Kirtland's Warbler populations in Michigan increased from 200 breeding pairs in 1972 to about 400 breeding pairs in 1998 However, cowbird control has not helped restore the endangered Willow Flycatcher in California. What are likely reasons for this difference?

2. Some ecologists believe that cowbird control is a short-term solution that ignores the real problem of habitat degradation from agriculture, grazing and development. Discuss.

3. In other studies researchers have found that cowbird predation did reduce numbers of songbirds living in forest fragments. Why might their findings be different from those of De Groot and Smith?

4. Compare the possible effects of obligate vs. generalist nest parasitism on bird community composition.

5. In the introduction to their paper, De Groot and Smith refer to several studies showing regulation of community structure by predators. Can you describe such studies? How is this research relevant to De Groot and Smith's?

6. The Kirtland's Warbler has very specific habitat requirements and a limited breeding range. Why do these characteristics make Kirtland's Warblers especially vulnerable to nest predation by cowbirds? How could you test your idea(s) using data from this study?


      Possible assessments include accuracy and clarity of figures students make using the Excel spreadsheet, written descripion and analysis of these figures, discussion or analysis of the DeGroot and Smith study, and a short essay about one of the Discussion questions above. A rich discussion on assessment and evaluation appears elsewhere in TIEE in a paper on Assessment and Evaluation.

Resources to Help Students Analyze these Data Sets