Evaluating the statistical power of detecting changes in the abundance of seabirds at sea

摘要: Full text: Offshore wind farms may potentially affect bird populations through the displacement of birds due to the disturbance associated with developments, the barrier they present for migrating birds and birds commuting between breeding and feeding areas, habitat change/loss and collision mortality. In current impact assessments it is often assumed that all birds that use the area of a proposed offshore wind farm would be displaced following construction, with some birds also displaced from a surrounding buffer zone. However, the extent to which current monitoring schemes are capable of detecting changes in abundance and options for improving survey protocols have received little attention. We investigated the likelihood of detecting changes in seabird numbers in UK offshore waters. Using aerial survey data, we simulated 50%, 25% and 10% declines and conducted power analyses to determine the probability that such changes could be detected. Additionally, increases in the duration and frequency of surveying were simulated and the influence of spatial scale and variability in bird numbers were also investigated. Current monitoring schemes do not provide adequate means of detecting changes in numbers even when declines are in excess of 50% and assumptions regarding certainty are relaxed to less than 80%. Extending the duration and frequency of surveys would increase the probability of detecting changes, but not to a desirable level. The primary reason why there is a low probability of being able to detect consistent changes is because seabirds are inherently prone to fluctuations in numbers. Explaining some of the variability …