Terrestrial ecosystems are complex and interconnected, a reflection of the individual components and the specific interactions among them. Specific biological effects measured at each level of terrestrial ecosystem organization often are used as indicators of stress. However, it is difficult to determine how natural fluctuations in these “biomarkers” can be sorted out from anthropogenic stresses, or how changes relate to higher levels of ecosystem organization.
Appropriate indicators (or biomarkers) of terrestrial avian population status are needed to adequately assess the impact of both natural and anthropogenic stresses. Currently, there exist only rudimentary guidelines for the conduct of field studies designed to detect the impact of chemicals and other stresses on wildlife populations. However, these endpoints are not sufficiently sensitive to confidently predict the impact of chemicals on populations, and as yet, there is no credible link to terrestrial wildlife population success.
In many cases, without adequate justification for specific measurement endpoints in avian field studies, researchers adopt an “encyclopedic” approach to field testing. As a result, numerous, unrelated, endpoints are measured, driven by the ability of the investigator to quantify a measurement rather than by its usefulness in answering the ecotoxicity question posed.
Development, validation, and prioritization of scientifically useful measures of population status is the critical next step necessary to conduct meaningful avian field studies. Abandonment of the encyclopedic approach to field studie must be accompanied by focused assessment of appropriate exposure and nazard endpoints. The research challenge is to provide a sound basis for the identification and evaluation of appropriate biomarkers for terrestrial populations and to develop the interrelationships of these markers.