MULTI-SCALE HABITAT SELECTION BY WINTERING WATERFOWL ON ANAHUAC NATIONAL WILDLIFE REFUGE

Waterfowl conservation and management focuses on conserving important habitats across their range. To understand waterfowl habitat selection, studies have described resource selection by individuals and populations of single dabbling duck species at multiple scales, ranging from geographic areas across North America to small-scale selection of food resources. Management efforts targeting selected habitat variables affect multiple species, especially during winter when waterfowl communities aggregate to share resources. Overlap in resource selection and utilization among similar species of dabbling ducks creates a community of wintering waterfowl. This community can be defined as a guild of waterfowl migrating in the Central Flyway, wintering in marshes along the Gulf coast and foraging mainly on plant matter. When multiple species share similar life history characteristics, Johnson’s (1980) 4 orders of habitat selection can be modified to reflect the process of disproportionate use by a community of waterfowl rather than an individual species. The goal of this study was to assess habitat selection by waterfowl communities wintering on Anahuac National Wildlife Refuge (NWR) to develop effective conservation plans targeting multiple species of dabbling ducks. Specifically, I quantified the relative influence of habitat covariates on wintering waterfowl habitat selection at multiple spatial and temporal scales, on Anahuac NWR in the Upper Chenier Plain of the Texas Coast. I observed mixed-flocks of waterfowl species that I defined as a guild of migratory, shallow-water dabblers that winter on the upper Texas Coast. The most abundant species include gadwall (Mareca strepera), Northern shoveler (Spatula clypeata), Northern pintail (Anas acuta), and green-winged teal (Anas crecca). Aerial waterfowl surveys were conducted in a grid pattern across the entire refuge to track waterfowl monthly habitat use from October to February 2014–2016. I visited geographically referenced sites where >500 birds were observed by aerial surveys in an aggregated flock and recorded water salinity, water temperature, water depth, submerged aquatic vegetation (SAV), and aquatic invertebrates at each used location. I collected these data at a random location within each management unit to represent available resources. I developed a resource selection function using used/available data with no marked individuals in a generalized linear model framework to assess waterfowl community habitat selection at multiple spatial and temporal scales. I defined the largest spatial scale (e.g., modified 2nd order) as Anahuac NWR, the intermediate spatial scale (e.g., modified 3rd order) as 8 individual management units within the refuge and the fine scale (e.g., modified 4th order) as flock site location (250 m flock buffer). The 3 temporal scales were year, early (October–November) and late (December–February) winter, and monthly. I extrapolated these data to the refuge and used habitat metrics best supported by the model set to build predictive habitat use maps for large flocks of dabbling ducks on the refuge. These results highlight the importance of considering multiple spatiotemporal scales in winter waterfowl habitat selection studies, particularly when animals of the same guild aggregate around shared-resources. At the 2nd order, waterfowl were influenced by multiple factors of the wetland landscape, water depth across the refuge acts as an initial selection cue to migrating waterfowl. Habitat selection within the refuge (3rd order) was positively influenced by a decrease in water salinity and waterfowl concentrated in Roberts-Mueller unit, a structurally managed intermediate marsh. Fourth order results suggest invertebrate density is a strong attractor to foraging waterfowl. In summary, waterfowl most benefit from multiple wetlands that provide a heterogeneous habitat composition of natural wetlands, allows access and visibility to open-water, has an average salinity of < 3ppt or below, and maximizes foraging by limiting water depth to <30 cm and supporting an abundance of food resources. Using the guild concept in lieu of single species is likely a more efficient and cost-efficient strategy for waterfowl habitat management.