Upper Midwest Environmental Sciences Center
Herons as indicators, Kushlan, J. A., and Hafner, H., eds, Heron Conservation
Erwin, R. M., and Custer, T. W., 2000, Herons as indicators, Kushlan, J. A., and Hafner, H., eds, Heron Conservation: San Diego, Academic Press, p. 312-330.
An indicator is "an organism or ecological community so strictly associated with particular environmental conditions that its presence is indicative of the existence of these conditions" (Merriam-Webster 1961). In environmental biology, this definition has been modified and extended to other levels of biological organisation, indicators of environmental change being called "bioindicators". A number of authors agree that using suborganismal (sensu Kushlan 1993b) or organismal bioindicators in birds, including herons, represents an effective means of monitoring both for effect and for exposure to some "insult" such as a contaminant or other environmental challenge (Gray 1980, Hill and Hoffman 1984, Morrison 1986, Fox and Weseloh 1987, Custeret al. 1991, Kushlan 1993 b).At levels of organisation above the organism,use of birds as bioindicators has been challenged (Morrison 1986, Temple and Wiens 1989) largely on the claim of birds' lack of sensitivity to change. Another criticism is that the term bioindicator may have been used too broadly, which may cloud its meaning in some contexts.
Indicator, Bioindicators, Environmental biology, Herons, Eggshell thickness, Genetic damage, Deformities, Environmental contaminants