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Declines of Greater and Lesser Scaup Populations: Issues, Hypotheses, and Research Directions

Summary Of Issues


3. Have physiological changes, including nutrient acquisition patterns and contaminants, affected reproductive success of scaup?

Contaminants and nutrient acquisition are closely interrelated through feeding and food resources. Here, we examine each separately and present recommendations within each section.

Contaminants

We proposed 2 hypotheses to assess whether contaminants have contributed to the decline of lesser scaup populations. Because the consensus was that reduced recruitment was likely contributing to the scaup decline, hypothesis formation began there. We recommend a tiered approach; thus, if problems are identified at the first tier, research should test hypotheses on Tier Two, and so on. We only identified Tier One questions for some hypotheses. Subsequent Tier Two hypotheses may be developed as needed.

Ho: Contaminant concentrations in eggs are affecting reproductive success.

Problem statement: The only recent contaminant data are from migration and wintering areas; consequently, it is unknown whether concentrations of contaminants persist until scaup reach their breeding grounds at levels that affect reproduction.

Tier 1: Determine concentrations of organochlorine and trace elements in scaup eggs and determine whether they are at
levels indicative of reproductive problems.

Sampling design: Determine concentrations in eggs collected from: (1) areas where populations are declining and areas where populations are stable or increasing, (2) major breeding areas, and/or (3) locations where existing studies are under way. One egg per clutch would be randomly collected from 5-10 nests per site. Possible contaminants are persistent organochlorines, trace elements (especially mercury and selenium), polycyclic aromatic hydrocarbons, dioxins, and furans.

Another possibility would be to collect more than 1 egg per clutch and artificially incubate eggs so that hatching success can be determined; bioindicators such as ethoxyresorufin-O-dealkylase (EROD), oxidative stress, or polycyclic aromatic hydrocarbons levels in bile could be measured. Egg quality could be assessed in freshly laid eggs.

Tier 2: If significant levels of contamination are found in eggs, assess contaminant levels in females and effects of
contaminant levels on hatching success and duckling growth and survival. Investigations would include:

  • Examine contaminant levels in nesting females. Collect nesting females to determine how contamination in the liver and carcass of each female relates to contamination concentrations in her clutch. Because of remoteness of scaup nesting sites, it may be more efficient to collect females and clutches when addressing Tier 1.
  • Use the sample egg method to quantify contamination of a sample egg and assess hatching success of the remaining eggs in the clutch.
  • Measure duckling growth and survival rates relative to contamination levels.
  • Examine behavioral effects of contaminants through studies of captive scaup.
  • Assess where scaup are accumulating contaminants by examining affiliations among breeding, migration and wintering areas, using banding, color-marking, or satellite telemetry.

Tier 3: Mode of action and true tests of hypotheses. Once effects are observed in field situations, design studies to test
those hypotheses. These studies would be true tests under more controlled and repeatable circumstances. These studies could be parallel laboratory and field studies and could:

  • Examine depuration rates of selected contaminants.
  • Examine effects of contamination on immune responses.
  • Examine effects of contamination on thermoregulation.
  • Examine interactions between nutrients and food availability and contaminant effects.
  • Examine interactions between parasites and diseases and contaminant effects.
  • Examine effects of contamination on vitamin depletion.
  • Examine effects of contamination on lipid dynamics.
  • Examine effects of contamination on salt gland function.
  • Develop assays or tests that might assist in studies.
  • Model the above as needed.

Ho: Contaminant concentrations affect propensity for nonbreeding.

Problem statement: Recruitment may be reduced because some proportion of scaup are not breeding. Nonbreeding could happen at 2 geographic scales: scaup may arrive at breeding sites but not breed, or scaup may not arrive at breeding sites to attempt to breed (see Afton 1984). Causes for nonbreeding could include contaminants, food or nutritional constraints, or habitat degradation. Studies would require that other factors be teased apart from effects of contaminants, which will be challenging.

Tier 1: On a small geographic scale, use mark/recapture, mark/resight, and telemetry techniques to determine whether
nonbreeding is occurring and what proportion of the population is affected. Proportion of nonbreeding would be compared among sites with differing contaminant concentrations or among sites with differing productivity. A blood sample could be taken to quantify contaminant exposure for comparison among individuals. Few data are available to interpret contaminant concentrations in waterfowl blood, but such data could be collected in captive studies.

Tier 2: Design captive studies to test whether some chemical contaminants delay or deter breeding and determine
mechanisms for mode of action.

Methods to determine proportion of the population which are not breeding on a larger geographic scale are unavailable or logistically very difficult. Additionally, what level of nonbreeding is normal has only been documented at Erickson (Afton 1983, 1984). Techniques for assessing nonbreeding on a larger scale need to be developed.

Nutrient and Food Limitations

Relationships among food availability, nutrient availability, intake rates, daily food and nutrient requirements, body mass and condition, and reproductive performance are complicated. These relationships are not static but vary according to the annual cycle, sex, and extrinsic factors such as temperature and competition. Information on feeding ecology, food availability, and nutrient acquisition during spring migration, and how these relate to breeding effort and success is limited (Afton unpubl. data). Changes in food availability and quality on wintering and migration areas may differentially impact scaup breeding in different regions (cf. Afton and Anderson in review). These issues can be most readily addressed through standard approaches such as collection of feeding scaup. Stable isotope analyses also can provide insight into foraging ecology (Chamberlain et al. 1997).

Ho: Reproduction is limited by food resources/nutrient reserves on winter, spring migration, and/or breeding areas.

Problem statement: Food resources, nutrient availability, and/or nutrient reserves during any portion of the life cycle could limit lesser scaup reproduction. When or where critical reserves for breeding are acquired by female scaup, and flexibility of scaup faced with changing food resources or habitat, is largely unknown, particularly in coastal areas.

Tier 1: Collect scaup throughout the annual cycle and determine lipid, protein, and ash content of carcasses and other
tissues as appropriate. Collection of female scaup is of higher priority than collection of males. Research could compare among flyways, among populations that breed east versus west of the Continental Divide, or between boreal forest and prairie-parkland populations.

Tier 1: Determine food habits and assess food availability of scaup over their annual cycle. Such data particularly are
needed for migration routes in Canada. Studies should examine food availability when and where food habits data are collected.

Tier 2: Create energetic models for scaup over their life cycle, including thermoregulation, nutrients, cost to capture and
process food, and effects of human disturbance, including hunting.

Tier 1: Determine whether stable isotope ratios can be used to answer nutrient or food resource questions or identify
breeding areas. Stable isotope patterns in tissues can be used to reflect diet changes over time. For example, liver tissue (half-life=2.6 days) turns over approximately 4 times faster than muscle tissue (half-life=12.4 days), and over 600 times faster than bone collagen (half-life 173 days) (Hobson and Clark 1992). Stable isotope ratios in these tissues can be used to determine whether a diet shift has occurred over that time frame. Deuterium isotopes in bird feathers can link breeding and wintering grounds (Hobson and Wassenaar 1997). Deuterium patterns across North America follow a consistent pattern, so feather analyses can determine where a bird molted (Hobson and Wassenaar 1997). For juveniles, this would help determine the region where the bird was raised. To use this technique in adults, detailed knowledge of molt patterns would be needed.

Previous Section -- Have changes in western Canadian boreal forests resulted in reduced reproductive success of scaup?
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Next Section -- What information is needed to manage greater and lesser scaup separately?

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