Improving Survey Methodology to Monitor Rare Grassland Birds in South Dakota

Breeding Bird Survey (BBS) data for grassland bird species has shown the most rapid population decline of any other bird group. Current roadside survey techniques, however, may fall short of providing accurate numbers of rare grassland bird species such as chestnut-collared longspur (Calcarius ornatus), lark bunting (Calamospiza melanocorys), Sprague’s pipit (Anthus spragueii), and Baird’s sparrow (Ammodramus bairdii). Trends resulting from roadside data for grassland birds are oftentimes determined to be statistically insignificant because many grassland bird species occur on too few routes, occur in low numbers per route, and show high annual fluctuations in number. It is possible roadside surveys may be providing inaccurate assessments of population trends. The objectives of this study were to 1) determine if increasing the number of routes will increase detection, 2) determine if detection of grassland birds is different on paved versus gravel roads, 3) determine if grassland birds are more likely to occur along routes with more grassland cover, 4) determine if there is an interaction between grassland cover and road type on the occurrence of grassland birds, 5) and to determine if the occurrence of grassland birds is greater away from roads. We utilized BBS methodology to conduct roadside surveys and paired on and off-road surveys along new and existing BBS routes over three seasons (2013-15) in western South Dakota. We used analysis of covariance to determine whether grassland birds were significantly affected by road type or percent grassland or differed between on and off-road surveys. The amount of grassland within point counts was the most significant variable effecting the abundance of grassland bird species. Higher percentages of grassland within a point count negated road effects for some species and resulted in an increase in abundance of focal bird species. Further, the inclusion of off-road point counts 800 m from roads increased abundance of two Species of Conservation Concern. Our findings suggest that increasing routes in areas with intact grassland habitat on gravel roads and incorporating off-road surveys at 800 m will allow for increased detection of focal grassland bird species which in turn can better advise conservation programs within South Dakota and beyond.