Rainwater Basin Wetland Prioritization Model Based on Waterfowl Habitat Use (Version 2)

Transcription

1 Rainwater Basin Wetland Prioritization Model Based on Waterfowl Habitat Use (Version 2) Andrew A. Bishop U.S. Fish and Wildlife Service Habitat and Population Evaluation Team Grand Island, NE Executive Summary The Rainwater Basin Joint Venture (RWBJV) has a long and successful history of implementing wetland projects throughout the Rainwater Basin Wetland Complex (RWB). To evaluate these actions and guide future conservation projects, the RWBJV used an Adaptive Resource Management (ARM) framework. ARM has helped focus recent research and monitoring on the key uncertainties of the RWBJV s biological foundation. One of the RWBJV s goals is to develop evolving GIS-driven models that incorporate the cumulative effect of various landscape features. The models will help prioritize areas on which to focus conservation and will help identify key RWB wetlands for restoration. This updated Waterfowl Habitat Use Model integrates new information from recent research, which provided insight into the importance of wetland complexes and the effects of roads and other disturbance features on waterfowl behavior. In addition to integrating research findings, the model incorporates a new GIS habitat dataset. The data are a seamless layer of the Aerial Habitat Surveys (AHS), providing a clearer understanding of contemporary wetland distribution. The data allow a more accurate model based on wetland density and abundance. This report contains the model s methods, inputs, and maps locating wetland features that have the potential to provide the highest quality waterfowl habitat.

2 Introduction The Rainwater Basin (RWB) wetland habitat complex in south-central Nebraska is the focal point of the Central Flyway during spring migration. Historically this region contained over 11,000 playa wetlands covering more than 200,000 acres. These shallow playa wetlands ranged in size from less than an acre to more than 1,000 acres. Today this 6,150 square-mile landscape is intensely cultivated. Only about 2,100 wetland footprints (40,215 acres) exhibit some level of wetland function. These footprints make up less than 1% of the entire RWB region. Annually, an estimated 12.4 million migratory waterfowl use this region during fall and/or spring migrations. The vast majority of birds (9.8 million) use the region during spring migration (Bishop and Vrtiska 2008). This concentration of waterfowl in a reduced wetland resource is believed to be causing intense competition for necessary foraging resources. The goal of the North American Waterfowl Management Plan (NAWMP, U.S. Fish and Wildlife Service and Canadian Wildlife Service, 1986) is to increase and sustain migratory waterfowl populations through conservation of habitats that meet annual life cycle needs. NAWMP recognized the RWB as an essential migration habitat for waterfowl. In 1992, the Rainwater Basin Joint Venture (RWBJV) was formed to address habitat losses. The RWBJV is a partnership of federal, state, local, and private entities dedicated to enhancement, restoration, and protection of RWB wetlands. A bio-energetics model was developed to assess landscape conditions and understand habitat requirements of staging and migrating waterfowl. Two components were necessary to complete the model: the energetic requirements of waterfowl using the region, and the energy available in forage habitats. Bishop and Vrtiska (2008) projected the energetic needs of the RWB s 12.4 million waterfowl to be 24.1 billion kcals. Currently agricultural forage, in the form of waste grain, can meet the region s waterfowl energetic requirements. However, research has documented that food resources other than waste grain are required to meet all of waterfowl s nutritional requirements of essential amino acids, inorganic elements, and vitamins (Loesch and Kaminski 1989, Baldassarre and Bolen 1994). Bishop and Vrtiska reported that about 39% (9.5 billion) of the 24.1 billion kcals should be provided by wetland habitats. To meet this energetic demand 37,850 acres of seasonal and temporary wetlands, dominated by early successional vegetation, would need to be flooded annually. In addition to the required foraging habitat, migrating waterfowl also need sufficient resting and loafing habitat distributed throughout the region. An additional 6,670 acres of semi-permanent wetlands need to be flooded annually to meet resting and loafing habitat needs. Recent annual habitat surveys provide an example indicating that even in a year with above-average precipitation and optimal thaw conditions, only about 20% of early successional wetland acres were flooded and available as forage for waterfowl. Given the relatively poor ability of existing wetlands to pond water, in addition to their current average vegetative condition, it would be

3 necessary to provide an additional 162,500 acres of wetland habitat to meet the goal of 37,850 acres of flooded habitat on an annual basis. The pre-settlement landscape in the Rainwater Basin consisted of only slightly over 204,000 acres; in today s landscape, it is important that the RWBJV and partners work to improve the function and plan communities of existing wetlands in order to meet migratory waterfowl needs on an attainable quantity of wetland acres. Landscape Scale Wetland Complex Delineation RWBJV partners believe that opportunistic delivery of wetland projects fails to provide the greatest biological return for the investment. The Habitat and Population Evaluation Team (HAPET) developed both the regional and local-scale wetland complex models to help guide future conservation actions. The regional model identifies wetland complexes representing priority wetland habitat as described by Brennan (2006) and Gersib et al. (1989). Brennan documented that dabbling duck use increased in relation to number of wetlands within a 5 km (3.1 miles) radius. And complexes containing a combination of temporary, seasonal, and semi-permanent wetland types received higher duck use than isolated wetlands. Brennan s work built upon the findings of Gersib et al. (1989), which argued that each wetland type in the RWB provide a unique habitat niche for waterfowl during spring migration. The first step in delineating wetland complexes was to understand contemporary wetland distribution. The current distribution of wetlands was determined by compiling multiple years of data from Aerial Habitat Surveys (AHS) completed in the springs of 2004, 2006, and To complete this analysis, color infrared aerial photography was used to map hydrophytes and ponded water. Due to the ephemeral nature of RWB wetlands and variability of precipitation, multiple years of AHS data are necessary to determine contemporary presence and distribution of wetlands. Several assumptions based on the work by Brennan (2006) and Gersib et al. (1989) serve as the foundation of the Wetland Complex Model. One assumption is that a wetland complex has at least 20 wetlands greater than one acre in size within a 5 km radius. In addition, at least one semipermanent wetland greater than 20 acres (8.1 hectares) would be found in the complex. Figure 1 shows the existing distribution of wetland complexes.

4 Figure 1. Distribution of Existing Wetland Complexes Local Scale Wetland Prioritization The original Waterfowl Habitat Use Model was updated to do a fine-scale assessment of contemporary and historic wetland features in the RWB. Factors such as anthropogenic influences and landscape features were evaluated to prioritize an individual wetland s ability to meet specific criteria influencing waterfowl use. The RWBJV s Conservation Planning Workgroup identified the criteria that influence waterfowl use. Their selection was based on published literature and professional opinion. These criteria and associated scoring weight are described below:

5 Landscape assessment of contemporary wetland distribution and abundance using a 5 km moving window analysis points based on adjacent number of wetlands 0-10 points based on adjacent wetland acres Landscape juxtaposition to permanently protected wetlands and other wetland complexes (15 points potential). Disturbance features affecting wetland use (22 points potential). Risk feature including intrastate power lines and communication towers (3 points potential). Playa wetland features in the Historic Wetland Mask (HWM) were used as analysis features. The HWM is a GIS layer created by merging all of the playa wetland features identified from four sources: historic soil surveys ( ), National Wetland Inventory (NWI ), Soil Survey Geographic Database (SSURGO ), and a 2005 Ducks Unlimited satellite inventory. Using the HWM allows the model to analyze all potential historic wetlands and evaluate their restoration potential as waterfowl habitat. Each footprint s final score is determined by summing its criteria points. Environmental Systems Research Institute (ESRI) ArcMap Version 9.2 software was used to assess and score each criterion, with the final score being the sum of the scores. The map projection used for all spatially referenced data was Universal Transverse Mercator (UTM) Zone 14 North using the North American Datum of 1983 (NAD 83). A combination of raster and vector-based spatial analysis was performed on the historic wetland footprints and included factors such as: size, contemporary wetland density, and wetland juxtaposition. A majority of the model was based on a moving-window analysis (5km window). This analysis calculates scores related to features within a 5km buffer of each footprint. The 5km buffer size was based on the radius that Brennan (2006) used to evaluate landscape features that influenced waterfowl habitat selection. In addition, Cox and Davis (2005) during their research documented minimal forage flight distances (<2 km) by Northern Pintails (Anas acuta) in the RWB. Model Inputs Wetland Density Higher wetland density reduces the daily energetic expenditure of waterfowl by allowing shorter flights from one wetland to another. A moving-window analysis, based on AHS data, was completed to determine contemporary wetland density. Wetland density scores were determined by the number of footprints and acres of functioning wetlands within a 5km radius of each

6 wetland. The maximum score that a wetland could receive was 10 points for wetland acres and 10 points for the number of wetlands within the 5km buffer. Points were assigned based on a quantile method where the complete dataset of footprints and acres is divided into 10 classes with equal records in each class. From lowest to highest, each class is assigned a number from 1 to 10, respectively (Table 1). Figure 2 shows an example of one wetland buffer. Table 1. Scoring Wetland Density by Wetland Number and Wetland Acres Scoring # of Wetlands Points Wetlands 1 < >33 Scoring Wetland Acres Points Wetland Acres 1 < >744 Figure 2. 5km Wetland Buffer

7 Proximity of Wetlands to Protected Lands Perpetual easements and public ownership are the principal types of long-term habitat protection within the RWB. These properties are extensively managed for migratory waterfowl. Restoration or enhancement of wetlands in close proximity to protected areas is believed to further increase the habitat value of the protected areas. HWM footprints within 5km of existing perpetually protected areas (Figure 3) were scored based on assigned values (Table 2). Figure 3. Proximity Analysis Table 2. Perpetually Protected Proximity Scores Footprint Proximity Points <2.5 km km - 5 km 5 5 km km 3 >7.5 km 0 Potential for New Wetland Complex There exists the possibility that clusters of wetlands are being missed as a potential wetland complex because they lack an existing protected/restored seasonal and semi-permanent wetland within the wetland cluster. This factor scored wetland footprints located a distance greater than 7.5 km (4.7 miles) from existing protected wetlands (Figure 4). Footprints of seasonal and semi-

8 permanent wetlands were scored based on their size, with higher scores given to larger footprints (Table 3). Priority was placed on seasonal and semi-permanent footprints, due to their ability to function as core wetlands within a complex. Figure 4. Landscape Criteria for New Complexes Table 3. Scoring New Perpetual Protection Footprint Size Points >100 Acres Acres Acres 3 <20 Acres 0 Proximity of Wetland to Platte River Wetland footprints were scored up to 5 points for their proximity to the Platte River. Intense late-winter storms and low pressure systems with sustained temperatures below 32 Fahrenheit are common during spring migration. These events often freeze RWB wetlands for short periods of time. During severe weather, waterfowl migrate south or shift to the Platte River. The proximity

9 of the Platte River complements the RWB by providing waterfowl with an alternative habitat (Figure 5). Such RWB wetlands also have significant use by Whooping Cranes (Grus americana) during migration (M. Tacha, USFWS, unpubl. data). These benefits prompted the inclusion of the Platte River as a model input. Figure 5. Proximity to Platte River Table 4. Proximity to the Platte River Platte River Proximity Points < 15 km km 2 > 25 km 0

10 Proximity to Population Centers The model accounts for population centers (Figure 6) by assigning two points to footprints farther than 2.5 km (1.6 miles) from towns and 0 points to footprints closer than 2.5 km. Conflicts between high waterfowl densities and population centers have steadily increased over the last 15 years. It was hypothesized that targeting wetlands away from population centers would reduce the effect of disturbance. Figure 6. Population Centers Proximity to Roads The model examines the total area and percent of wetland < 75m (246 feet) from roads. Buffers were created 75m from any road or developed property. Every hydric footprint was scored based on the total area and percent of hydric footprint more than 75m from the road (Figure 7, Table 5). Disturbance associated with roads reduces the value of a wetland for foraging, resting, and loafing. Waterfowl using wetlands in close proximity to roads experience more disturbance. This often causes waterfowl to exhibit more alert behavior, move to other parts of the wetland, or significantly reduce overall use of the wetland.

11 Figure 7. Proximity to Roads Table 5. Proximity to Roads. Scoring by Acres and % of Wetland Percent Wetland >75m Points 100% % % % % % 5 Hydric Acres > 75m Points > 100 acres acres acres acres 2 Proximity of Wetlands to Risk Structures A 1-km buffer (0.6 miles) was placed around communication towers and intrastate power lines (Figure 8). These buffers were used to select footprints with inherent risks to avian species. Footprints within 1 km received 0 points while wetlands that were more than 1 km from towers and lines received three points. Intrastate power lines and support wires associated with communication towers pose risks to avian species.

12 Figure 8. Risk Structures Results and Discussion The total score for each wetland was derived by summing the individual landscape features. The highest possible score a hydric footprint could receive was 60. Historic wetlands, with scores greater than 45, reflect those areas that more closely fit the RWBJV s conservation criteria (Figure 9). Of the 11,760 total footprints, 772 received a score of more than 45 points. The footprints encompass 51,426 of the 204,417 acres of total wetlands examined. Results from this model can be used by RWBJV partners as a guide to help prioritize wetland protection, restoration, and enhancement activities to maximize benefits to migratory waterfowl (Figure 10).

13 Figure 9. RWB Hydric Footprint Priority Model

14 Figure 10. Program Delivery

15 Literature Cited Baldassarre, G.A. and E.G. Bolen Waterfowl ecology and management. John Wiley, New York, NY. Bishop, A.A. and M. Vrtiska Effects of the Wetlands Reserve Program on Waterfowl Carrying Capacity in the Rainwater Basin Region of South-Central Nebraska. USDA NRCS Publication. Available electronically from ftp://ftp-fc.sc.egov.usda.gov/nhq/nri/ceap/rwb_wrp_final% 20Report.pdf. Brennan, E.K Local and landscape level variables influencing migratory bird abundance, diversity, behavior, and community structure in Rainwater Basin wetlands. Doctoral dissertation, Texas Tech University. Available electronically from Cox, R.R., Jr. and B.E. Davis Habitat use, movements, and survival of female northern pintails during spring migration in Nebraska and subsequent potential breeding-site selection in the Prairie Pothole Region. Progress Report. U.S. Geological Survey, Northern Prairie Wildlife Research Center, Jamestown, North Dakota. Gersib, R.A., B. Elder, K.F. Dinan, and T.H. Hupf Waterfowl values by wetland type within the Rainwater Basin wetlands with special emphasis on activity time budget and census data. Nebraska Game and Parks Commission, Lincoln, Nebraska. Loesch, C.R. and R.M. Kaminski Winter body-weight patterns of female mallards fed agriculture seeds. Journal of Wildlife Management 53: U.S. Fish and Wildlife Service and Canadian Wildlife Service North American Waterfowl Management Plan. Washington, D.C. U.S. Fish and Wildlife Service. M. Tacha. Whooping Crane Observations Unpubl. reports. U.S. Fish and Wildlife Service, Nebraska Field Office, Grand Island, Nebraska.