These birds are considered indicators of the overall health of their usual habitat. Although a single species cannot fully represent all other life in the same habitat, it can indicate the general health of an ecosystem and thus give some insight into how other birds, plants and animals in the habitat may be faring. The population estimates presented here are based on different monitoring techniques for each species, and are subject to some margin of error. In addition, some caution is warranted when evaluating these trends, since some population change arises from natural population cycles and changing weather conditions.

Lakes: The percentage of surveyed lakes that have adult loons rose from 56 percent in 1994 to 64 percent in 2000, with a peak of 68 percent in 1997. Although loon populations appear to be on the rise, loons live for 25 to 30 years, so the effects of any habitat changes may take years to show up in population trends. Loons are a good indicator because they are at the top of their food chain. They eat fish that in turn have eaten smaller aquatic organisms. As a result, loons are exposed to higher concentrations of toxins such as mercury.

Brush land: The number of sharp-tailed grouse in spring in northwest and east-central Minnesota dropped from 60,000 in 1980 to 12,200 in 2001, with the sharpest drop occurring during the 1980s. The population rebounded between 1998 and 1999, but by 2001 had fallen back below its 1997 level. Brush land has grass, shrubs and young trees. The 80 percent drop in sharp-tailed grouse reflects a heavy loss of brush lands, which provide habitat for many species. Brush lands have historically been maintained by wildfires; control of fires has allowed much brush land to mature into forest.

Forests: The population of the black-throated green warbler is relatively stable. The “index of abundance” for this species rose from 1.5 in 1980 to a high of 1.9 in 1993, dropping back to 1.5 by 1998. Warblers nest in mature, mixed forests of conifer and deciduous trees.

Prairie: The male prairie chicken population in spring rose from an estimated 1,220 in 1980 to 1,600 in 2000, with a low of 900 in 1997. The population of prairie chickens is considered relatively stable, given normal fluctuation. The drop between 1996 and 1997 reflects a severe winter. This population reflects the amount and health of native prairie and other grassland.

Farmland: The estimated fall pheasant population in Minnesota's central and southern counties fell 27 percent between 1980 and 1999, from 1.9 million to 1.4 million, rebounding from a low of 1.0 million in 1997. The federal Conservation Reserve Program has led to the conversion of 1.6 million acres of former cropland into grassland since 1988. Grasslands are considered a better habitat for pheasants than cropland. Increases in the number of acres enrolled in the program during the late 1990s may have contributed to the rise in the pheasant population since 1997.

• Growth in gross state product
• Energy efficiency of the economy
• Net gain in businesses
• Freeway congestion
• Energy use per person
• Renewable energy sources
• Vehicle miles
• Air pollutants
• Water use
• Timber harvest
• Solid waste and recycling
• Toxic chemicals
• Water quality in lakes and rivers
• Nitrate in ground water
• Erosion of cropland
• Changes in land use
• Parkland and open space

• Number of native wildlife and plant species that are endangered, threatened or of special concern (Minnesota Department of Natural Resources, Natural Heritage and Nongame Research Program, www.dnr.state.mn.us)
• Frog and toad populations (Minnesota Department of Natural Resources, U.S. Geological Survey and Hamline University; North American Amphibian Monitoring Program, www.dnr.state.mn.us).