UAVs unveil the role of small scale vegetation structure on wader nest survival

AbstractSeveral ground‐nesting wader species rely on Baltic coastal meadows for breeding. Drastic reduction in the area of the habitat at the end of the 20th century has been followed by habitat restoration activities over the last 20 years. However, wader populations are not responding as hoped to the current conservation effort. Therefore, identifying which grassland characteristics are essential for waders to select their nesting location and which ones enhance their clutch survival probability is vital to implementing efficient conservation plans. However, many vegetation structural characteristics, such as sward height or heterogeneity, can be logistically complex to measure using traditional methods in relatively large areas, especially considering the highly accurate resolution needed. Here, we assessed several sward characteristics together with other key landscape features by combining very high‐resolution images from unmanned aerial vehicle (UAV) surveys with nest survival monitoring, in five key Estonian coastal grasslands for waders. We found that the main four wader species, Northern Lapwing (Vanellus vanellus), Common Redshank (Tringa totanus), Common Ringed Plover (Charadrius hiaticula) and the Baltic Dunlin (Calidris alpina schinzii), do not significantly differ in their nest‐site selection in terms of vegetation height, growth rates, or sward heterogeneity. Yet, we found that vegetation sward height and heterogeneity surrounding the nest sites within a 2‐meter buffer positively increased the daily nest survival probability from 0.883 to 0.979 along the gradients observed. Additionally, the distance between the nest location and flooded areas (≥20m2) was negatively correlated, and all variables affected the wader community similarly. Our results signal the need for a higher diversity of sward structures and the importance of constantly flooded areas in Estonian coastal meadows. Moreover, our study highlights the importance of integrating UAV remote sensing techniques within the animal conservation research field to unveil ecological patterns that may remain hidden using more traditional methods.