Assessing the impacts of livestock grazing on upland bird breeding territories using drone surveys

Abstract

Ground nesting birds are sensitive to habitat structure, so understanding this relationship is fundamental to managing habitat to maintain or enhance bird populations. We used an existing long-term, large-scale experiment with routine monitoring of meadow pipit territories to assess the capability of drone-based remote sensing as a means of capturing relevant habitat information. Normalised Difference Vegetation Index (NDVI) captured differences in stocking density between treatments, and autumn-measured NDVI was well correlated to field measurements of vegetation height and density. Spring and autumn NDVI were negatively correlated due to dominant tussock-forming species dying back over winter. Meadow pipit apparent territory size was positively correlated to autumn NDVI and to the difference between autumn and spring NDVI. Apparent territory size was larger where there was more tussocky vegetation that comprise the areas least preferred for foraging. The long-lived nature of tussocks likely constrains the effect of the grazing treatments on meadow pipit breeding apparent territory size. Drone-based remote sensing of habitat characteristics appears to be a powerful way forward to understand bird–habitat associations.