STUDENT INSTRUCTIONS

McShea and Rappole (2000) examined changes in vegetation and bird populations on 8 forested sites in northern Virginia over 9 years. Four sites were fenced to exclude deer. The other 4 served as controls. McShea and Rappole wanted to see how reducing the number of deer in a protected forest affected the abundance (number) of birds and diversity (variety) of bird species. Figure 2 reports their results for 3 representative bird species. With a partner, examine Figure 2 and the additional explanation provided below. Then discuss the questions that follow. You and your partner should be prepared to share your analysis of Figure 2 during full class discussion.

Results of Vegetation Monitoring

McShea and Rappole found that excluding deer over the 9-year period increased the density of understory woody shrubs relative to control sites. Species richness of understory woody plants also increased within the exclosure areas over the course of the study. In other words, researchers found more shrubs and more different species of shrubs in the sites excluding deer than in the control sites.

About the Bird Species

Chipping Sparrows prefer open understory. They breed in open woodlands with grass, along river and lake shorelines, orchards, farms, and in urban and suburban parks. They winter in similar areas. They forage primarily on the ground and eat grass and other small seeds, small fruits, and insects. The Chipping Sparrow’s next is a loosely woven open cup of rootlets, grasses, and other fine materials placed in a small tree or shrub (Cornell Lab of Ornithology. 2003. All About Birds. http://birds.cornell.edu/programs/AllAboutBirds/BirdGuide/Chipping_Sparrow_dtl.html)

Indigo Buntings prefer dense herbaceous ground cover, such as brushy vegetation, saplings, and weeds. They eat seeds. The Indigo Bunting’s nest consists of grasses, leaves, and weed stems. Nests are found in trees or tangles. (Conservation Commission of Missouri. 1995-2002. Missouri Breeding Birds Atlas. http://www.conservation.state.mo.us/nathis/birds/birdatlas/maintext/0400015.htm)

Ovenbirds prefer a dense, woody understory. They breed in mature deciduous and mixed deciduous and coniferous forests. They winter in primary and second growth forests. They eat forest insects by picking them off leaf litter on the forest floor. The Ovenbird’s nest is a woven domed coup of dead leaves and plant stems, with the entrance on the side, placed on the ground. (Cornell Lab of Ornithology. 2003. All About Birds. http://birds.cornell.edu/programs/AllAboutBirds/BirdGuide/Ovenbird.html)

Graph Interpretation

Note that the hatched bars represent the exclosure sites (i.e., no deer) and the solid bars represent the control sites (i.e., deer present). On the Y-axis, you will find the number of birds recorded for each species. (Note that the scale on the top graph differs from the other two.) On the X-axis, you will find each of the 9 years during which the study was conducted. Look for patterns in the number of each bird species over time. Compare and contrast the exclosure and control sites.

Questions to Answer

• How would you describe the changes over time in the number of Chipping Sparrows in sites without deer (hatched bars)?


• How would you describe the changes over time in the number of Indigo Buntings in sites without deer?


• How would you describe the changes over time in the number of Ovenbirds in sites without deer?


• Is the response of each species consistent with its known biology (see “About the bird species” above)?


• What plausible explanations can you offer for the changes in relative abundance of these species over time?