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

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.