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Project Scope of Work

Project Scope of Work 2003

Demographic, Movement, and Habitat Studies of the Endangered Snail Kite in Response to Interim Operational Plan, Alternative 7R in Water Conservation Area 3A

This scope of work describes a proposed study that integrates demographic and movement studies of the endangered snail kite (Rostrhamus sociabilis) with monitoring studies which document the response of snail kite habitats within Water Conservation Area (WCA) 3A to the initiation and implementation of Interim Operation Plan Alternative 7R (IOP-Alt. 7R). Additionally, this scope of work describes the study objectives, approach, and products; and proposes a time schedule for conducting the study and delivery of products.


The snail kite (Rostrhamus sociabilis) is an endangered raptor whose distribution in the United States is restricted to the South Florida Ecosystem including watersheds of the Everglades, Lake Okeechobee, Kissimmee River, and Upper St. Johns River. Because snail kites feed almost exclusively on one species of aquatic snail, their survival depends directly on the hydrologic functioning of these watersheds. Over half of the wetlands within central and southern Florida watersheds have been lost during the past century and those that remain have been highly fragmented and severely degraded resulting in the current planning for what probably shall amount to the largest scale ecosystem restoration effort ever undertaken (e.g., the Central and South Florida Project, Kissimmee River Restoration, and the South Florida Ecosystem Restoration Initiative). Although, other endangered species occur within this ecosystem, snail kites probably are the only one which is restricted to the watersheds within the South Florida Ecosystem and depend on the entire network of wetlands within this ecosystem.

During the first half of this century, snail kite populations dramatically declined. Most researchers suggest declines in kite populations are correlated with changes in hydrology directly or indirectly. These include loss of habitat, effects on apple snail populations, effects on reproduction, changes in foraging and nesting habitat structure, and effects on adult and juvenile survival of snail kites.

Previous population viability model studies have determined that adult survival is the most sensitive demographic parameter in determining population viability of this endangered species and there is a general need for better estimates of these and other demographic parameters. For the past several years, the Florida Cooperative Fish and Wildlife Research Unit, U.S. Geological Survey (USGS) has conducted a monitoring effort to examine reproduction, survival, and movement patterns of snail kites throughout central and southern Florida to determine patterns of reproduction success, estimate survival of adult and juvenile snail kites, and determine the effects of environment on these parameters as well as movement probabilities. Continuation of that study is described in this scope of work and is necessary for determining parameter estimates responses to the myriad of water projects potentially impacting the critical habitat of this endangered species.

Aside from this proposed study, there currently is no other systematic monitoring of snail kite populations in Florida. Previously an annual survey was conducted as an indicator of population dynamics. This survey ,however, was found to be inadequate for agency needs for monitoring population dynamics and trends. The study proposed by this scope of work builds on an on-going effort that does not suffer the limitations of the annual survey. The proposed study shall provide reliable estimates of critical parameters of snail kite population dynamics as well as to provide a sound monitoring program for assessing interim projects associated with implementation of restoration.

In their Endangered Species Act (ESA) Biological Opinion on the IOP-Alt. 7R, the U.S. Fish and Wildlife Service (USFWS) expressed concern that the project could alter hydrologic regimes in Water Conservation Area 3A (WCA 3A) most of which is designated critical habitat for the endangered snail kite. The principal concern is that the carrying capacity (habitat quality) of WCA-3A will be impaired as a result of elevated water depths and hydroperiods. The concern is heightened because WCA-3A is the largest and most consistently utilized of the designated critical habitat and is already currently seriously degraded. Snail kites have increasingly moved their nesting activity to areas of higher elevations in WCA 3A over the past two decades presumably as the traditional nesting regions have been degraded by high water levels sustained by current water management practices. Various studies have documented the conversion of wet prairies, preferred snail kite foraging habitat, to aquatic sloughs in that area along with losses of interspersed herbaceous and woody species essential for nesting habitat. Analysis of hydrological predictions for IOP-Alt. 7R indicate that implementing this plan could result in excessive ponding and extended hydroperiods of the type that could further degrade nesting and foraging habitat.

While the anticipated impacts of IOP-Alt. 7R may impact a significant portion of the critical habitat, the U.S. Fish and Wildlife Service (USFWS) has determined that it is not likely to result in jeopardy to the snail kite and has authorized and recommended a number of reasonable and prudent measures to minimize impacts to snail kites (USFWS, March 28, 2002). Among the terms of the USFWS response is a requirements for: 1) tracking the annual status of the snail kite (population shifts) and any vegetative shifts that may occur within snail kite habitats, and 2) determining the number of snail kites initiating nesting in the action area and the success rate of those nesting efforts each year. Accordingly, USFWS specified that the USACE should monitor snail kite reproduction effort and nesting habitat to determine if there were any adverse effects that might represent incidental take of the species. This study is designed to respond to that concern, and is needed to comply with provisions of the ESA.


This scope of work is divided into two activities that together address issues related to impacts of IOP-Alt. 7R on the snail kite populations and its habitat in WCA 3A. Demographic and movement studies of snail kites are used to determine population responses. Monitoring the response of snail kite habitat to changing hydrologic regimes under IOP-Alt. 7R is critical to assessing impacts to snail kite nesting success and foraging behavior.

The objectives of these two activities are as follows:

  1. Demographic and movement studies of snail kites
    1. To estimate critical demographic parameters (reproduction and survival) and movements in response to environmental variables, particularly changes in hydrologic regimes (anthropogenic and natural).
    2. To monitor the status of the Florida population of snail kites through this interim hydrologic regime and ultimately the hydrologic restoration of the South Florida Ecosystem.
  2. Monitoring response of snail kite habitats within WCA 3A to the initiation and implementation of IOP-Alt. 7R
    1. To design and implement a vegetation monitoring protocol for detecting vegetation responses to altered hydrologic regimes in WCA 3A, in areas of traditional kite nesting and foraging.
    2. To develop pseudo-topographic spatial database for selected sites within Indicator Regions for determining spatially explicit hydropatterns from stage information, both measured and predicted at gauged sites.
    3. To conduct analyses of vegetation communities and develop multivariate regression tree models and structural equation models for determining hydrologic suitability for the species associations comprising these habitats as well as for use in predicting vegetation responses to altered hydrology.


The principal benefit of the proposed study is to refine the critical parameter estimates for a broader range of hydrological conditions thereby reducing uncertainty and increasing our confidence in the evaluation of restoration alternatives relative to the kite population. In addition, the effort maintains a valid monitoring system for the kites during interim and restoration activities. Currently, there are no other reliable alternatives for monitoring the kites.


A. Demographic and movement studies of snail kites

This proposed activity shall be based on mark-resighting techniques and their associated statistical foundation for estimating survival and population size. For estimation of survival, the underlying structure to this approach uses the Cormack-Jolly-Seber (CJS) model, which allows for explicit estimation of survival and its associated standard error, and enables testing of hypotheses relating to differences attributable to age, sex, and environmental conditions (i.e., hydrology). The CJS model also allows for the separate estimation of resighting probability and survival. For population estimations, the underlying concept is the robust design approach (Dreitz et. al. 2002). This model simply estimates population size by taking a count statistic and dividing by the resighting probability. Many derivations of this model have been developed to handle different sampling situations and to establish a variance with the estimator.

B. Monitoring response of snail kite habitats within WCA 3A to the initiation and implementation of IOP-Alt. 7R

Given the immense area of WCA 3A, this activity shall focus on the areas represented by two Indicator Regions 14 and 17 within WCA 3A (USACE Supplemental Draft Environmental Impact Statement, 2001). These areas have been chosen for several reasons:

  1. Various management and research agencies have expressed general confidence in the output of South Florida Water Management District's Surface Water Management Model (SFWMM) for these sites.
  2. Each is proximal to major USGS hydrologic gauging stations (GS 64 and 65).
  3. These areas correspond very well to the traditional foraging and nesting regions used by snail kites.

The principal challenge of this activity is to separate plant community responses due to typical seasonal and year-to-year variances from effects resulting from new hydrologic regimes. The vegetative community structure of the study sites is an expression of the both the recent past and current hydrological conditions. Therefore, it is critically important to determine how the species associations within these communities respond differentially to changes in hydrology through time and over space. This shall require a multi-tiered approach:

Task 1) Spatial patterns and change detection at broad vegetation class level (example, sawgrass strands, tree islands, cattail patches, and wet prairie/slough).

Objective: Determine long-term community type changes as related to hydrology.

Aerial or satellite imagery shall be utilized to remotely sense spatial distributions, extent, and patterns of broad major vegetation classes in the Indicator Regions. Comparing differences in coverages of major classes between several years will enable change detection in spatial distribution at the scale of multiple years (2-5 yrs). This approach is well suited to documenting the distribution and succession of wetland marshes, including those representing foraging habitat for the kite. Additionally, it is the only means of assessing distribution and condition of woody shrub heads and tree islands used by the snail kites for nesting.

Ideally, this should utilize at least 3 sets of imagery, 4-5 years pre-project, at project onset, and 3-4 years post-project. The products would be large-scale vegetation maps for areas in each of the Indicator Regions for each point in time, as well as a spatial map of changes in distribution of the classes among the years. It is anticipated the pre-project imagery (and even classified pre-project data) may be available from the South Florida Water Management District's mapping efforts in WCA 3A. A pre-project classification of the Indicator Regions is an absolute requisite for the development of the "modeled-topographic" database described below.

Task 2) Development of "modeled-topographic" database and hydrologic characterization of Indicator Regions.

Objective: Establishing spatial hydrological relationships within focus areas using permanent hydrologic gauging stations. (Indicator areas 14 and 17 with GS 64 and 65).

The stage information generated by South Florida Water Management Model (SFWMM) for the units comprising each Indicator Region is gridded 2 kilometer on a side. Stage duration curves generated from these data are determined from estimated ground surface elevations generalized from a weighted mean over the 4 square kilometer area of each grid. This level of detail is appropriate for generalized stage duration curves for the grid site, but far too generalized for most ecological assessments of responses that affect the habitat suitability of wetland vegetation at very subtle changes in hydroperiods and inundation depth regimes. This is particularly problematic in impounded wetland areas with shallow elevation gradients.

To resolve this issue, we propose to develop 10 study complexes (1 kilometer on a side) within each of the indicator regions (14 and 17). Ground surface elevations in each of the study complexes shall be measured in the field. Crews deployed in airboats shall use survey-grade GPS units to measure elevation throughout the newly created grid network. Elevations shall be determined in the vicinity of the intersection points in the grid. More specifically, replicate ground surface elevations shall be made in each of the nearest major plant community types (determined apriori from vegetation maps for each of the Indicator Regions, as per above) in the near vicinity of the intersection point. Next, elevations shall be surfaced for each of the plant types separately in each grid by confining kreiging routines for the elevations for that plant type only within polygons labeled for that type. This effort shall be repeated for each plant type and each cell. Ultimately these polygons shall be re-composted and merged in a GIS resulting in spatially articulated modeled-topographic database driven by plant community types, as per Science Subgroup (1995). The stage data for the study complex cells shall then be used with the elevation data specific to each plant community type in the cell to create stage duration curves for each specific vegetation type in the individual cells over the entire topographic gradient of each cell and the Indicator Region. Hydroperiods and depth duration data for each type in each cell shall be generated for the measured (as well as predicted) period of record. The products generated by this task are the modeled-topographic database and site specific hydrologic history or characterization for the plant community types comprising each cell for determining the differential rate responses for the individual species comprising each plant community type when used in conjunction with species association data below.

Task 3) Permanent transect plots across elevation gradient in each Indicator Region.

Objective: Monitoring current vegetative structure in Indicator Areas. Design to detect mesoscale to small-scale annual/inter-annual changes, and small scale within-year (seasonal) variations in response to hydrology. Determine the relationships between plant species distributions and the associated environment variables regulating distributions.

This task shall design and implement permanent monitoring plots (combinations of quadrats and transect) along the major elevation gradient in each Indicator Region using the 10 study complexes per Indicator Region. These complexes, 1 kilometer on a side, shall be located in each IR utilizing a stratified random approach. The factors representing the strata are the following: geology (peat depths); general elevation, and snail kite nest density. The intent is to establish regularly placed multiple or replicate quadrat sites arrayed continuously as partial belts along a transect perpendicular to the elevation gradient within each Indicator Region. Each site shall be sampled with quadrat devices and monitored seasonally (3 times/ year) for species numbers, stem counts and biomass for both living and standing dead plants occupying the site. Water depths shall be monitored continuously at selected locations within the study plots for determinations of hydroperiods and depth duration curves. Each study complex shall typically consist of three belt transect complexes, 5 plots of the principal habitat types comprising the complex, sawgrass, wet prairie, sloughs and 5 permanent plots for monitoring tree island/shrub heads sites typically used by kites for nesting.

The data shall be processed with various multivariate techniques and structural equation models to resolve relationships between species associations (as measured by importance values) and inundation depth/hydropatterns as well as a number of other environmental parameters at each site. The sites shall be sufficiently placed and sampled to resolve subtle trends in coverages, densities, and biomass for the major species associations within the physiognomic types comprising kite foraging and nesting habitats in the Indicator Regions. The structural equation modeling techniques shall be used to define statistical correlations among species and associated hydrologic and other environmental parameters and provide probabilistic measures for mechanism involved. Concurrent with this monitoring effort, snail kite usage of these areas shall be carefully monitored through time in an attempt document any shifts in kite distributions that might be reflective of erosion of habitat quality in these areas.


A. Demographic and movement studies of snail kites

  1. Evaluation of Snail Kite survival, movements and reproductive success with emphasis on relationships to environmental parameters

B. Monitoring response of snail kite habitats within WCA 3A to the initiation and implementation of IOP-Alt. 7R

  1. Large-scale vegetative maps for Indicator Regions 14 and 17
  2. Maps of spatial changes in vegetation in responses to interim hydrologic regimes
  3. Protocols for vegetative response monitoring
  4. Modeled-topographic database based on plant community types
  5. Hydrologic characterization of Indicator Region 14 and 17
  6. Multivariate regression models and structural equation models for determining hydrologic suitability for species association


A. Demographic and movement studies of snail kites

  1. Marking, resighting, nest monitoring shall occur each year (2003 through 2006) from January through July.
  2. Radio tagging shall commence in January each year and tracking shall be conducted systematically on a monthly basis throughout the remainder of the year for each year (2003 through 2006)
  3. Data analysis and report writing shall occur each year from August through December for each year (2003 through 2006)

B. Monitoring response of snail kite habitats within WCA 3A to the initiation and implementation of IOP-Alt. 7R

Task 1 -

  1. Vegetative surveys in the permanent transect plots across elevation gradient in each Indicator Region shall be conducted 3 times annually for 2003 through 2005. Sampling shall correspond to early wet season (June), late wet season (August) and end of growing season (November) for each year. Results and progress shall be reported annually.
  2. Spatial patterns and change detection at broad vegetation class level shall be assessed by imagery annually.

Task 2 -

  1. Hydrologic gauging stations shall be established in each study complex by the end of the wet season of 2003 and maintained for continuous monitoring for developing regression relationships to GS 64 and 65. This task is ongoing for the duration of the study.
  2. Existing stage data shall be used to generate stage duration curves for IR 14 and 17 in 2003
  3. GPS surveys shall be conducted in the belt transects and reference sites to develop the modeled-topographic database for each study complex. The effort shall be initiated in 2003 with completion targeted for the end of 2004.
  4. Development of "modeled-topographic" database and hydrologic characterization of Indicator Regions shall be an extended task culminating in the final year of study.

Task 3 -

  1. Selected shrub heads and tree islands (total of 10 study plots) of the types typically used by kites for nesting shall be sampled and assessed annually in June or August during maximum leaf out for determination of stand condition as related to hydrologic regimes.
  2. Data shall be processed to define statistical correlations and probability measures for each study plot annually.
  3. Monitoring of snail kites usage in the 10 study plots shall be ongoing throughout the year.

  FY2003 FY2004 FY2005 FY2006
Activities and tasks 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
A. Demography and movement
1. Marking, resighting, nest monitoring                                
2. Radio tagging and tracking                                
3. Analysis and annual report preparation                                
B. Monitoring response of habitat
Task 1 - Spatial patterns
1. Conduct vegetation surveys                                
2. Compare imagery and dev. change maps                                
3. Annual report preparation                                
Task 2 - Database and characterization
1. Est. and maintain hydrol. gauging stas.                                
2. Create stage duration curves                                
3. Conduct GPS surveys                                
4. Generate database and characterization                                
5. Annual report preparation                                
Task 3 - Transect plots
1. Monitor vegetative structure                                
2. Define stat. correl. and prob. measure                                
3. Monitor snail kite usage in study area                                
4. Annual report preparation                                

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