The first step in addressing this hypothesis is to determine contaminant levels in eggs and breeding females, specifically comparing areas showing a decline to those with stable or increasing populations. If significant contamination levels are found, studies should quantify contamination of a sample egg and assess hatching success of the remaining eggs in that clutch. Depending on the outcome of these results, field and captive bird studies may be needed to examine how contaminants are affecting reproductive success. We also need to develop assays or tests that could assist in field studies and modeling of the various interactions and effects of contaminants on reproduction. Further, use of energetics models to estimate contaminant uptake from foods would be aided if reports on contaminant uptake in captive birds included data on the amount of food eaten as well as contaminant concentrations in foods.
Contaminant concentrations affect the propensity for nonbreeding .
Recruitment also may be reduced because some portion of the population is not breeding. Causes for nonbreeding could include contaminants, food or nutritional constraints, or habitat degradation. These other potential factors must be separated from effects of contaminants. In addition, captive bird studies can be designed to test if chemical contaminants delay or deter breeding and determine mechanisms for mode of action.