Northern Prairie Wildlife Research Center
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.
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
- 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
- Examine behavioral effects of contaminants through studies of
- 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
- Examine interactions between parasites and diseases and contaminant
- 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?