Factors influencing presence and detection of breeding shorebirds in the Prairie Pothole Region of North Dakota , South Dakota , and Montana , USA

Providing accurate information on population status and trends is essential to developing shorebird conservation strategies, but survey protocols for many shorebird species are either poorly developed or have not yet been implemented (Brown et al. 2000, Howe et al. 2000). A variety of survey techniques is currently used to monitor shorebirds in North America, including the North American Breeding Bird Survey and specialized regional surveys (Brown et al. 2007, Howe et al. 2000, Stanley & Skagen 2007). However, the validity of many of these techniques needs to be determined (Lanctot et al. 2008, Oring et al. 2000), especially how factors such as roads (Bystrak 1981), seasonal timing (Gratto-Trevor 2006, Redmond et al. 1981), and time of day (Robbins 1981) can influence detection of birds. Improved understanding of these factors, along with knowing what fraction of a population is detected on surveys, is critical to developing reliable population estimates for shorebirds (Alldredge et al. 2006, Farmer 2008, Lanctot et al. 2008, Rosenstock 2002). The Prairie Pothole Region (PPR) of North America is an important breeding area for many species of shorebirds, including American Avocet Recurvirostra americana, Willet Tringa semipalmata, Marbled Godwit Limosa fedoa, and Wilson’s Phalarope Phalaropus tricolor. Extensive waterfowl conservation programs in the PPR that conserve wetlands and grasslands offer considerable opportunity to extend conservation benefits to the shorebird species that breed in these habitats (Niemuth et al. 2008). To best accomplish this, expanded knowledge of the population status and habitat requirements of key species is needed. In an effort to develop statistically rigorous surveys, we evaluated survey protocols for American Avocet, Willet, Marbled Godwit, and Wilson’s Phalarope. All four species are associated with wetlands and grasslands and all are species of moderate to high conservation concern (Brown et al. 2000, Skagen & Thompson 2000). Estimating numbers of breeding pairs and population trends and understanding factors affecting population trends are priority research needs for American Avocet, Willet, and Marbled Godwit (Gratto-Trevor 2000, Lowther et al. 2001, Robinson et al. 1997). We sampled these four species in June 2001 during a pilot survey of 204 randomly selected wetlands in North Dakota and detected at least one individual of any of the four species on only 35 (17%) of the survey wetlands. Low numbers of shorebirds relative to survey effort suggested the need to consider alternative sampling methods and led to the subsequent evaluation of wetland-based surveys in 2002 and point count surveys in 2003. We evaluated factors influencing detection of breeding shorebirds using data from wetland-based surveys conducted in 2002 and roadside point-count surveys conducted in 2003. Our primary goal was to evaluate how roadside sampling, daily timing, and seasonal timing influenced the number of breeding shorebirds observed so that future surveys could be designed to maximize detection of target species and increase Factors influencing presence and detection of breeding shorebirds in the Prairie Pothole Region of North Dakota, South Dakota, and Montana, USA