Introducing ecological uncertainty in risk sensitivity indices: the case of wind farm impact on birds

Abstract

In wind-farm impact assessments, it is useful to know the level of uncertainty that characterizes some key variables used to assess the sensitivity to risk in species of conservation concern. Here, we have introduced the use of the Shannon entropy as a value of ecological uncertainty of the prediction of the risk assessment index, obtained from two ecological traits (flight altitude and flight type). We based our evaluation of risk sensitivity on sampling of three common raptor birds (Gyps fulvus, Falco tinnunculus, Buteo buteo) all co-occurring in a wind farm landscape (central Italy). As to flight altitude, Gyps fulvus prefers the flight altitude category > 300 m, Falco tinnunculus categories closer to the ground, Buteo does not show clear preference for a particular flight altitude category. As regards the flight type, Gyps fulvus showed significant preference for circular and thermal flight patterns, Falco tinnunculus for rapid horizontal/vertical flight patterns, while Buteo was found to prefer constant directions and circular and thermal flight patterns. Multiplication of the scores associated with these eco-behavioural traits by the number of recorded occurrences allowed estimation of risk sensitivity used to compute the risk assessment index. We normalized the partial scores of the risk associated with these traits with H' values, thus obtaining more reliable species-specific normalized risk indices. The greater the entropy, the greater the level of uncertainty associated with it, and the lower the reliability of the risk index. Therefore, the entropy associated with flight behaviour diversity (altitude or type) could be a proxy for assessing uncertainty in wind power impact assessment. We think that normalizing indices of risk by including a measure of uncertainty can support decision makers in bird conservation and wind farm management.