مدیریت و حفاظت زیستگاه اردک در ساحل غربی
Abstract
1- Introduction
2- Methods
3- Results
4- Discussion
5- Conclusion
References
Abstract
The Western Gulf Coast provides important habitat for migratory and resident waterfowl. The mottled duck (Anas fulvigula) relies on this region for all of its life-cycle events. Its relatively small population, limited worldwide range, and generally declining population trajectory has earned it a “Red” status on the Audubon WatchList and is a species of concern among state and federal agencies. The Western Gulf Coast (WGC) mottled duck population decline is believed to be primarily caused by the historical conversion and degradation of coastal wetlands and native prairie, and recent declines in cultivated rice. There is general agreement among experts that negative impacts to nesting and brood-rearing habitat are the most important threats to the WGC mottled duck population and increasing recruitment is essential to the growth and sustainability of the population. Our goal was to use available knowledge of mottled duck nesting and brood-rearing requirements to develop a model to aid managers in targeting areas for conservation and management. We developed four spatially explicit models that: 1) identify and prioritize existing mottled duck nesting habitat for conservation (e.g., protection or maintenance); 2) identify and prioritize existing mottled duck brood-rearing habitat for conservation; 3) identify and prioritize areas for grassland establishment; and 4) identify and prioritize wetland basins for freshwater enhancement. Spatial models revealed that only 6 km2 and 9 km2 of nesting and broodrearing habitat, respectively, were identified as highest priority (top 10%) for conservation in the WGC. Brood habitat was identified as potentially limiting recruitment in the Texas Mid Coast and the Laguna Madre subregions of our study area, whereas grassland habitat was potentially limiting recruitment in Chenier Plain and Mississippi River Coastal Wetlands subregions. Spatial models also revealed that there is a high density of areas of high priority for grassland establishment inland in Texas and Louisiana. Likewise, there is a high density of wetland basins of high priority for freshwater enhancement throughout coastal Louisiana and the upper Texas coast. We used two separate measures to assess the performance of our Mottled Duck Decision Support Tool (hereafter MODU-DST) and found that it adequately identified patch suitability, as defined by our model, with ≥79% accuracy. Using data from the Cooperative Breeding Mottled Duck Survey, we also found that breeding mottled ducks were using landscapes with optimal spatial arrangement of nesting and brood-rearing habitat, which is reflected by higher mean priority rankings of nesting and brood-rearing habitat in the landscape.
Introduction
The Western Gulf Coast (WGC) provides valuable habitat for migratory and resident waterfowl. The mottled duck (Anas fulvigula) is a resident species in this region and is closely associated with coastal marsh and inland agricultural habitats, relying on these areas for all its life-cycle needs. Habitat conversion and degradation due to large-scale hydrologic alterations, urban expansion, declines in rice agriculture, and other human activities have raised concerns for the declining WGC mottled duck population. Collective evidence from available population data across the WGC range suggests a long-term steep decline in Texas and a stable to slightly declining trend in Louisiana (Wilson, 2007). Although other threats such as sport harvest (Raftovich et al., 2011), lead poisoning (Anderson et al., 2000; Sanderson and Bellrose, 1986), hybridization (Ford, 2015; McCracken et al., 2001), and predation (Bielefeld et al., 2010; Durham and Afton, 2003; Elsey et al., 2004; Stutzenbaker, 1988) may contribute to mottled duck population declines, loss of nesting and brood-rearing habitats is believed to be the primary cause (Wilson, 2007). Therefore, a priority for increasing the WGC mottled duck population is to increase recruitment by conserving landscapes with nesting and brood-rearing habitats in appropriate spatial configurations.