A Framework for Assessing Ecological Risks to the Roseate Spoonbill Related to
Everglades Hydrologic Restoration Activities
Steven M. Bartell
The Cadmus Group, Oak Ridge, TN
Jerome J. Lorenz
National Audubon Society, Tavernier, FL
William K. Nuttle
Ottawa, Ontario, Canada
Jon C. Cline
University of Tennessee, Knoxville TN
Donald L. DeAngelis
U.S. Geological Service- Biological Resources Division and
University of Miami, Miami FL
William B. Perry
National Park Service, Homestead, FL
We describe a risk-based framework for evaluating the effects of hydrologic
restoration in the Everglades on roseate spoonbill nesting success in Florida Bay.
Recognition that wading bird populations have declined by 90% motivates the
present Everglades ecosystem restoration effort, and their recovery will be
interpreted as an indicator of a restoration success. Changes in the roseate
spoonbill population reflect an integrated response to subtle alterations in foraging
habitat that are related to coastal hydropatterns (Figure 1) that are in turn driven
by inland water supply and flood control operations. The quality of foraging
habitat for spoonbills, as with other South Florida wading bird species, depends
on (1) prey abundance, particularly small fishes, and (2) prey concentration
resulting from the normal progression of dry-down in the coastal wetlands
throughout the nesting season.
Regional water management in South Florida (i.e. the Central and South Florida
Project) has significantly altered historical hydropatterns that sustained coastal
wetland and estuarine habitat in northeast Florida Bay. The resulting salinity
regimes and altered hydropatterns have had a significant, long-term adverse effect
on wildlife habitat, fishery nursery grounds, and estuarine fauna. Efforts
underway to restore more natural hydropatterns in this area include the Mod
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Waters/C111 project and, on a longer timescale, the Comprehensive Everglades
Restoration Plan. The challenge for managers is to develop methods for
ecological assessment that facilitate comparison of alternative project designs or
prescriptions of remedial actions that may exert their effects at different spatial
and temporal scales .
The risk-based framework can be used to provide this assessment capability. Risk
of adverse impacts to the spoonbill population arises from the critical importance
of prey abundance and foraging habitat availability during nesting. The survival
of recently fledged chicks appears to be greatly enhanced by hydropatterns that
increase the amount and quality of foraging habitat. Quality foraging habitat
depends on the size and location of feeding areas with water levels of <12 cm
during nesting, from mid-November through March, and on salinity levels prior to
the nesting season that favor higher levels of fish production.
Fundamental to implementing this approach for spoonbills are empirical
relationships (1) between salinity antecedent to the nesting season and the
abundance of fish prey and (2) between water level fluctuations during the nesting
period and the quality and quantity of foraging habitats within 10-15 km of the
nesting colonies. The quantity of freshwater in the coastal wetlands of the
southeastern Everglades during the wet season strongly influences the production
of forage fish consumed by spoonbills and other wading birds. Freshwater
discharge exerts an immediate effect on salinity in the mangrove zone during the
wet season and a delayed, longer-term effect during the rest of the year by
modulating salinity in the downstream estuary. Timing of water delivery and
rainfall influence prey availability during the nesting season by controlling
wetland water levels.
The risk-based framework explicitly incorporates engineering, hydrological, and
ecological sources of variability and uncertainty inherent to the analysis of
complex ecological systems. Restoration project outcomes result in conditions
that might increase, decrease, or not affect spoonbill foraging habitat. Other
factors also affect the quantity and quality of foraging habitat and nesting success,
for example weather, nest predation, and disease. Therefore, the potential impacts
of proposed projects are estimated in probabilistic terms. Uncertainties are
expressed as statistical distributions that describe the values of initial conditions,
model parameters, and external forcing functions for each assessment. Monte
Carlo methods are used to propagate these uncertainties and produce distributions
of results, including maps of foraging habitat and estimates of spoonbill nesting
success (i.e., chicks/nest).
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The risk-based approach forecasts the response of spoonbill population size and
viability based on the probable nesting success as affected by proposed water
management plans for the Mod Water/C111 project and the CERP. Nesting
success is related qualitatively to population viability using empirical rules: 0-1
chicks/nest implies a failed nesting and a future declining population, 1-1.25
chicks suggest moderate success and a quasi-equilibrium population, and >1.25
chicks indicate good nesting success and an increasing population. Subsequent
modification of the risk-based framework might include a stage-based
demographic population model that can be used to translate nesting success into
projections of future spoonbill population sizes. Future expansion of this riskbased framework will similarly include other ecological indicators of Everglades
restoration.
Figure 1: Conceptual model linking wetland freshwater discharge to the quality
and quantity of foraging habitat for spoonbills.
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Bartell, Steven, The Cadmus Group, 78A Mitchell Road, Oak Ridge, TN, 37830,
Phone: 865-425-0401, Fax: 865-425-0482, sbartell@cadmusgroup.com
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