Concentration area demarcation and abundance estimates of fall migrating shorebirds through the Lower Mississippi Alluvial Valley
September 2008 - March 2010
- US Fish and Wildlife Service
- University of Arkansas
Asian outbreaks of the highly pathogenic avian influenza (HPAI) H5N1 virus in wild birds have created concern over the potential for an outbreak in North America. Several migratory birds with Alaskan and Siberian breeding habitats freely intersperse with Asian species during the breeding season before returning to wintering habitats in North and South America, raising the concern that these species will serve as disease vectors. Of particular concern are several shorebirds species that regularly migrate through the Lower Mississippi Alluvial Valley (LMAV) as they move between their breeding and wintering grounds via the Mississippi Flyway. Some species, such as pectoral sandpipers (Calidris melanotos), are concentrated along the Mississippi Flyway. These birds are long-distance migrants and, due to their narrow migration route and breeding proximity with Eurasian migrants, present excellent examples of species that could contract H5N1 and cause an outbreak anywhere along their extended migratory route. Following the Early Detection and Response Plan for Occurrence of Highly Pathogenic Avian Influenza in Wild Birds, we plan to assist with the development of an early detection system to determine where federal and state wildlife agencies should target search and control efforts for potentially infected shorebirds during the fall period if and when the virus arrives in the Mississippi Flyway. We are focusing on the fall period because during the spring migration in the LMAV, shorebirds do not concentrate because appropriate habitat during that time is widespread and common. Targeted shorebirds that we will focus on include primary candidates: pectoral sandpiper, dunlin (Calidris alpina), long-billed dowitcher (Limnodromus scolopaceus), and secondary candidates: greater yellowlegs (Tringa melanoleuca), lesser yellowlegs (T. flavipes), and ruddy turnstone (Arenaria interpres). We will also target the buff-breasted sandpiper (Tryngites subruficollis) as it is a primary candidate in other flyways. Our plan involves two approaches. Concentration area demarcation - First we will need to demarcate traditional concentration sites for fall migrating shorebirds through the LMAV. We will accomplish this by 1) consulting federal and state birding literature (especially Skagen et al. (1999)), 2) consulting recognized local birding experts, and 3) reviewing the LMAV Joint Venture shorebird monitoring database. Following the methods of Skagen et al. (1999), we will break the fall migration period into 2-week periods from 1 July – 1 Nov. For 20 sites, which may include subsites, we will sum the numbers of shorebirds by species for each 2-week period to provide overall counts for the sites. Based on these counts, we will produce maps designating relative abundances by species using polygons divided into 50 X 50 km blocks. Shading patterns for each polygon (low, medium, high) will be based on sums across sites by block for the fall period. Next we will determine a maximum number of individuals of each species at each site for each time period. We will combine the maximum counts across 2º latitudinal bands from 30º - 38º to produce chronology histograms for the fall across the region. Finally, we will develop an index of dispersion for the number of sites hosting 60% of the total maximum of each species. Categories of dispersion will be: broadly dispersed (60% of birds occurred in 10 or more sites), moderately dispersed (60% of birds occurred in 3 to 9 sites), or concentrated (60% of birds occurred in 1 or 2 sites). Abundance estimation - To augment the historical data and to produce current abundance estimates, we will conduct surveys during the 2009 fall period for targeted shorebirds in the LMAV. Because shorebirds concentrate in different areas at different times during the fall, we will conduct line transect surveys in 3 bands across the LMAV at 3 times (early, middle, late) during the fall. The bands will run east-west from bluff to bluff across the valley and will be 50 km wide. The northern band will be located at approximately 35º, the middle band at 33º and the southern band at 31º. Each survey pass will take 3 weeks for a sum total of 9 weeks of surveys. We will survey from the western to eastern bluff along roads for shorebirds in all shallow wetland habitats. As occupied wetlands are encountered, we will follow an adaptive cluster sampling design to focus on nearby wetlands (Skagen et al. 2008). This sampling design emphasizes wetlands occupied by shorebirds and deemphasizes habitats that are not occupied. Species specific counts will be recorded using a distance based approach. We will analyze the count data using program DISTANCE taking into account habitat type. These density estimates do not take into account stopover length. Stopover length is the average time that an individual bird remains at a stopover site. We will adjust the density estimates for stopover length using the estimates of Lehnen and Krementz (2005) and Lehnen and Krementz (2007). Through a GIS analysis of the LMAV, we will quantify the available and potential fall migration shorebird habitat. Knowing shorebird densities by habitat type, adjusted for stopover length, and knowing the available habitat in the LMAV, we will quantify the number of shorebirds by species using the LMAV during fall migration. Following this approach, we will demarcate fall migration shorebird concentration sites and estimate species specific shorebird abundance for the LMAV. With this information, the FWS should be able to rapidly respond to a reported HPAI event in shorebirds in the LMAV should one occur.
|Technical Publications||Publication Date|
|Lehnen, S. E. 2010. Chronology, distribution, and dispersion of fall migrating shorebirds through the Lower Mississippi River Alluvial Valley.||March 2010|