Quantifying specialist avifaunal decline in grassland birds of the Northern Great Plains

Habitat specialists are declining worldwide, often paralleling rapid loss of habitat. Grassland habitats across North America are declining precipitously, due in part to intense conversion of grasslands to agriculture and rangelands, and specialist communities reliant upon this landscape are at particular risk of decline and collapse. We explored the relationship between grassland habitat specialism in birds and species population trends using several different grassland specialism indices (GSIs). Our data sources for these indices included (1) a regional bird dataset employing a spatially stratified sampling design (Integrated Monitoring of Bird Conservation Regions) of bird surveys in the Northern Great Plains of North America, and (2) geospatial data of species ranges (BirdLife Int'l) and grassland habitat (CEC North American Land Cover). We found a negative relationship between degree of habitat specialism and species population trends for all specialism metrics. We also found some evidence to support that specialism to grasslands on the wintering grounds partially explains population trends during the breeding season, giving added weight to the consideration of habitat conservation across the full annual cycle of a species to reverse or lessen population decline. Our work is the first to use quantitative methods to confirm the precarious state of grassland specialist songbirds in North America as well as demonstrate multiple methods for quantifying habitat specialism across different types of datasets. Habitat specialists can be defined as organisms that maintain narrow niche requirements for a particular environmental characteristic when compared to more generalist taxa (MacArthur 1972, Julliard et al. 2006). Specialists are experts at utilizing resources within their ecological niches, but often fail to persist outside of these narrow ecological roles. Organisms maintaining specialist life history strategies also often maintain small range extents and exhibit lowered dispersal ability (Gaston et al. 1997, Colles et al. 2009) and are therefore vulnerable to rapid changes in habitat that result in conditions outside of their particular niches (Devictor et al. 2008, Clavel et al. 2011, Correll et al. 2016). As a consequence, specialist species worldwide are being displaced from their preferred habitats as climate change and human development continues to occur across the global landscape. Of the world's ecosystems, grasslands emerge as one of the most quickly changing landscapes (Liebold 1995, Hoekstra et al. 2005, Sylvester et al. 2013). Human