Environments and Species Distributions

The Breeding Bird Survey (BBS) is one of the most comprehensive, current population databases available. This database, maintained by the Biological Resources Division of the U.S. Geological Survey, documents population fluctuations and geographic ranges of birds across the United States and southern Canada. Go to the BBS website at www.mbr-pwrc.usgs.gov/bbs/bbs.html.

Clicking on the "Distribution Maps" option on this page will produce a list of the birds in North America. You can see species distribution and breeding density maps by clicking on the name of any species. Find these species in the list and look at the map for each in order to answer the questions below:

• double crested cormorant
• great blue heron
• wood stork
• American robin

1. Assuming that generalist/opportunistic species are widespread and more or less uniformly distributed, which of these species would you guess are generalists, and which might be specialists, with narrow niche preferences or environmental tolerance ranges? As you look at the range maps, consider especially each species’ climate range, presence in densely populated areas, and evenness of distribution throughout the species’ range. If you are unsure of environmental conditions across the continent, refer to the precipitation, biome, and climate maps.

2. Also look at the map for the bald eagle. Would you guess that temperature, water, forest cover, or mountainous terrain best explains its distribution? Why might this be so?

3. Now look at the range of the American dipper. Which of the four variables in question 2 best explains its distribution?

Diversity in Taxonomic Groups

Go to the Breeding Bird Survey (BBS) taxonomic list at www.mbr-pwrc.usgs.gov/bbs/htm96/map617/all.html.

Count the number of heron species. Now count the number of warbler species. What traits or ecological adaptations can you think of to describe these two groups? (For information and photos for each species, go to the Bird Information page on the BBS home page at www.mbr-pwrc.usgs.gov/id/framlst/framlst.html.)

How might the different lifestyles or environments or suites of competitive species help explain differences in diversity in these two groups?