Off-road sampling reveals a different grassland bird community than roadside sampling: implications for survey design and estimates to guide conservation

Abstract

ABSTRACT. Grassland bird species continue to decline steeply across North America. Road-based surveys such as the North American Breeding Bird Survey (BBS) are often used to estimate trends and population sizes and to build species distribution models for grassland birds, although roadside survey counts may introduce bias in estimates because of differences in habitats along roadsides and in off-road surveys. We tested for differences in land cover composition and in the avian community on 21 roadside-based survey routes and in an equal number of adjacent off-road walking routes in the grasslands of southern Alberta, Canada. Off-road routes (n = 225 point counts) had more native grassland and short shrubs and less fallow land and road area than the roadside routes (n = 225 point counts). Consequently, 17 of the 39 bird species differed between the two route types in frequency of occurrence and relative abundance, measured using an indicator species analysis. Six species, including five obligate grassland species, were more prevalent at off-road sites; they included four species listed under the Canadian federal Species At Risk Act or listed by the Committee on the Status of Endangered Wildlife in Canada: Sprague's Pipit (Anthus spragueii), Baird's Sparrow (Ammodramus bairdii), the Chestnut-collared Longspur (Calcarius ornatus), and McCown's Longspur (Rhynchophanes mccownii). The six species were as much as four times more abundant on off-road sites. Species more prevalent along roadside routes included common species and those typical of farmland and other human-modified habitats, e.g., the European Starling (Sturnus vulgaris), the Black-billed Magpie (Pica hudsonia), and the House Sparrow (Passer domesticus). Differences in avian community composition between roadside and off-road surveys suggest that the use of BBS data when generating population estimates or distribution models may overestimate certain common species and underestimate others of conservation concern. Our results highlight the need to develop appropriate corrections for bias in estimates derived from roadside sampling, and the need to design surveys that sample bird communities across a more representative cross-section of the landscape, both near and far from roads.L'échantillonnage hors route révèle une communauté d'oiseaux de prairie différente de celle issue de l'échantillonnage le long des routes : répercussions sur la conception des relevés et les estimations pour orienter la conservation RÉSUMÉ. Le déclin prononcé des espèces d'oiseaux de prairie se poursuit en Amérique du Nord. Les relevés le long des routes, comme le Relevé des oiseaux nicheurs (BBS) en Amérique du Nord, sont souvent utilisés pour estimer les tendances et la taille des populations, ainsi que pour élaborer des modèles de répartition d'espèces de prairie, même si les dénombrements le long des routes peuvent introduire des biais relatifs aux estimations étant donné que les milieux le long des routes sont différents de ceux hors route. Nous avons examiné s'il y avait des d...

Estimating regional landbird populations from enhanced North American Breeding Bird Surveys

“…However, other investigators have noted significant differences for some species in the number of individuals detected between on‐road and off‐road points (Wellicome et al. ), but found that counts along narrow secondary roadways (such as those associated with BBS routes) lessen this bias (Hutto et al. ).…”

Management factors affecting densities of common grassland birds of high elevation grasslands of eastern South Africa: Ingula as a case study

“…Finally we suggest that investigation of factors that affect birds density or suitability be based on surveys from inside the farms, rather than counting along roads (e.g. Wellicome et al 2014). Habitat on road verges often does not resemble habitat within farms and birds nesting along road verges may be more exposed to predation (Wellicome et al 2014) and may suffer more from disturbances.…”

“…Wellicome et al 2014). Habitat on road verges often does not resemble habitat within farms and birds nesting along road verges may be more exposed to predation (Wellicome et al 2014) and may suffer more from disturbances.…”

Influence of human footprint and sensory disturbances on night-time space use of an owl

“…Construction of any road removes vegetation and typically changes adjacent vegetation type and height, resulting in widespread changes to grassland vegetation alongside roads and across the landscape (e.g. Wellicome et al 2014). Ditches are associated with many roads, and vegetation grows taller and more dense in ditches because of greater local moisture levels, thus supporting greater small mammal populations (Poulin 2003).…”