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Declining Scaup Populations:
Issues, Hypotheses, and Research Needs

Investigate effects of contaminants on reproduction, female body condition, and behavior


Contaminants were considered by workshop participants to be one of the most likely contributors to the apparent decline of scaup reproductive success. Data from migration and wintering areas in the Great Lakes (C. M. Custer and T. W. Custer, United States Geological Survey, unpublished data), Florida (T. C. Michot, W. H. Benson, and J. M. O'Neil, United States Geological Survey, unpublished data), San Francisco Bay (Ohlendorf et al. 1986, Hothem et al. 1998), and Long Island Sound (J. S. Barclay, University of Connecticut, unpublished data) indicate scaup often carry relatively high loads of selenium and other trace elements (Cd, Hg, Mn), as well as other contaminants. No such data are available from breeding areas. Consequently, it is unknown whether concentrations of contaminants are persisting, at levels that could affect reproduction, until scaup reach their breeding grounds. It also is unknown if contaminants are affecting scaup productivity or survival, and if so, how. We formulated 2 hypotheses: 1) contaminant concentrations in eggs are affecting reproductive success and 2) contaminant concentrations in adults affect the propensity for nonbreeding. We recommend a tiered approach to address these hypotheses.

Contaminant concentrations in eggs are affecting reproductive success. 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. Parallel laboratory and field studies could address effects of contamination on immune responses, thermoregulation, lipid dynamics, vitamin depletion, and salt gland function; depuration rates of selected contaminants; interaction between nutrients, food availability, and contaminant effects; and interaction among parasites, diseases, and contaminant effects. 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. Scaup may arrive at breeding sites but not breed, or they may not return to breeding sites to attempt to breed (Afton 1984). Causes for nonbreeding could include contaminants, food or nutritional constraints, or habitat degradation. These other potential factors must be separated from effects of contaminants. We suggest examining this issue first at a small geographic scale, using mark-recapture, mark-resight, and telemetry techniques on individual study sites to determine whether nonbreeding is occurring and what proportion of the population is affected (Afton 1984). In addition, captive bird studies can be designed to test if chemical contaminants delay or deter breeding and determine mechanisms for mode of action.


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