Arctic Shorebirds in North America: A Decade of Monitoring

10. SURVEY METHODS FOR WHIMBREL

177 Abstract. Whimbrel breed at low densities, are patchily distributed, and have proven difficult to survey with traditional PRISM methods. We tested a double sampling methodology that used aerial surveys as the “rapid” component to determine whether this method was more effective at surveying Whimbrel in the Mackenzie Delta. Detection rates for aerial surveys were low, detecting on average 23% of the Whimbrel that were actually on the ground within the surveyed area, but rates were relatively consistent among trials. Contrary to our assumptions, Whimbrel did not regularly flush when a helicopter passed. In contrast , detection rates using PRISM methods were high (mean: 2.75), and varied among three sites and four years. The high mean value suggests that Whimbrel approached observers from areas outside of plots, while the high variability suggests that this behavior may vary among plots, habitats, or years. The comparatively consistent detection rates during aerial surveys suggest that this method may hold promise for surveying this species , but stratification of aerial survey blocks by habitat might improve the accuracy of any regionwide extrapolations based on aerial surveys. Key Words: aerial survey, arctic, detection rate, Mackenzie Delta, monitoring, Northwest Territories , population size, PRISM, shorebirds, Whimbrel. CHAPTER TEN Survey Methods for Whimbrel Lisa Pirie and Victoria Johnston Pirie, L., and V. Johnston. 2012. Survey methods for Whimbrel. Pp. 177–184 in J. Bart and V. Johnston (editors). Arctic shorebirds in North America: a decade of monitoring. Studies in Avian Biology (no. 44), University of California Press, Berkeley, CA. W himbrel (for scientific names, see Appendix C) is designated as a sensitive species in the Northwest Territories (GNWT 2006) and a species of high conservation priority nationally (Donaldson et al. 2000, Brown et al. 2001, U.S. Shorebird Conservation Plan 2004). Because of its priority status and its ecological importance in the Mackenzie Delta north of the treeline (hereafter Mackenzie Delta), the species was also chosen by proponents of the Mackenzie Gas Project (MGP) as a Valued Ecosystem Component (any component of the environment that is considered important to those involved in an environmental assessment process) in the MGP environmental impact statement (AMEC Americas Ltd., unpubl. report). The western North American subspecies of Whimbrel (N. p. rufiventris) occurs in discontinuous STUDIES IN AVIAN BIOLOGY NO. 44 Bart and Johnston 178 might be one of these species because of its relatively small population and disjunct breeding range. Attaining timely and accurate monitoring information for Whimbrel was critical because of the species’ key role in the MGP environmental assessment. Therefore, we decided to investigate the utility of a single-species survey for Whimbrel using a double sampling design with aerial surveys as the rapid method (Bart et al., chapter 2, this volume), and to compare our results to those obtained through regular PRISM surveys (Rausch and Johnston, chapter 5, this volume) in the Outer Delta and the Middle Mackenzie Delta (hereafter Middle Delta; Fig. 10.2). Studies specific to shorebirds in the Mackenzie Delta region are few, and have only been conducted in the past 20 years. In the late 1980s, Dickson (Dickson and Smith 1991) conducted research in a small region of the Outer Delta to determine if Landsat imagery could be used to accurately identify suitable shorebird habitat. In 1991 and 1992, Gratto-Trevor (1996) repeated Dickson’s surveys and extended the study area to include most of the Outer Delta. In 2004, PRISM breeding populations throughout boreal, subarctic , and low-arctic portions of Alaska east to the Melville Hills in Nunavut, Canada (Fig. 10.1; Skeel and Mallory 1996, Morrison et al 2006). It has a wide-ranging but disjunct distribution, breeding in low densities throughout much of its range (Skeel and Mallory 1996). Previous studies in the Mackenzie Delta identified two distinctly different habitats used by Whimbrel for breeding: wetsedge low-centered polygons (LCP) on Taglu and Fish Islands in the Outer Mackenzie Delta (hereafter Outer Delta; Fig. 10.2), and much drier sedge/ heath/low shrub habitat complexes throughout the Mackenzie Delta (Dickson and Smith 1991, Gratto-Trevor 1996, Ashenhurst 2004, Pirie et al. 2009). The Arctic Program for Regional and International Shorebird Monitoring (PRISM) conducted surveys in PRISM Region 12, including the Mackenzie Delta, from 2005 to 2007. From the outset of the PRISM program, we knew that acceptable survey precision might not be achieved for some species because of limited ranges or particular habitat requirements. We conjectured that Whimbrel Figure 10.1. Whimbrel (rufiventris subspecies) breeding range in North America. [18.118.2.15...