Spatiotemporal variation in disturbance impacts derived from simultaneous tracking of aircraft and shorebirds
Assessing the impacts of disturbance over large areas and long time periods is crucial for nature management, but also challenging since impacts depend on both wildlife responses to disturbance and on the spatiotemporal distribution of disturbance sources.
Combined tracking of animals and disturbance sources enables quantification of wildlife responses as a function of the distance to a disturbance source. We provide a framework to derive such distance–response curves and combine those with disturbance source presence data to quantify energetic costs of disturbance at a landscape scale.
We tracked 90 Eurasian Oystercatchers Haematopus ostralegus and all aircraft in a military training area in the Dutch Wadden Sea. We quantified distance–response curves estimating flight probability and additional displacement for five types of aircraft activities, by comparing bird movement prior to aircraft presence with movement during aircraft presence. We then used the distance–response curves to map mean and variation in additional daily energy expenditure due to cumulative aircraft disturbance across the landscape for a 700-day period.
Flight probability and displacement responses differed strongly among aircraft activities and decreased from transport aeroplanes, through bombing jets, helicopters, jets to small civil aeroplanes. Since the most disturbing aircraft activities were also the rarest ones, mean additional daily energy expenditure did not exceed 0.25%. However, days with substantial (>1%) additional expenditure occurred between 0.1% and 3.7% of all days across high-tide roosts in the tidal basin. Notably, expenditure particularly spiked on days with transport aeroplane activity (up to 8.5%).
Synthesis and applications. We quantified cumulative energetic flight costs due to aircraft disturbance and found that these were low and unlikely to impact survival of oystercatchers in our study area. Our results provide evidence that the legal minimum flight height of 450 m for small civil aeroplanes effectively limits the disturbance of oystercatchers. Mitigation should focus on limiting the number of days when disturbance has a high impact by reducing rare but highly disturbing activities, especially transport aeroplanes. Our approach can be applied to other species and disturbance sources that are automatically tracked, for example boats and walkers, ultimately to quantify the entire anthropogenic disturbance landscape.
H van der Kolk, AM Allen, BJ Ens, K Oosterbeek, E Jongejans, M van de Pol