Are we properly assessing bird and bat mortality at onshore wind farms

However several factors can influence the reliability of the mortality estimates and therefore must be taken into account during the definition of the experimental design and the selection of the methodologies to adopt. At the same time, due to financial limitations, it is crucial to develop and validate field protocols that reduce the costs without compromising the estimates accuracy and precision. Carcass searches At onshore facilities the estimation of bird and bat mortality is generally based on carcass searches around wind turbines. Within a pre-defined plot (that can range between 40 and 120m around the turbine), trained searchers look for carcasses walking, for instance, along parallel transects. Inspections are then repeated over time at regular or irregular intervals, depending on the purpose of the study. However, the number of carcasses found during the searches does not correspond to the real number of birds and bats killed by the wind turbines. This value must be adjusted by carcass removal (e.g. by scavengers or decay) and searcher efficiency rates, which can in turn be influenced by site- and carcass-specific covariates, such as carcass size, season, vegetation cover and orography. Carcass persistence rates Current post-construction monitoring protocols accommodate carcass removal trials to assess the carcasses persistence. Trials consist of placing carcasses under the turbines which are then checked for a pre-defined period of time. The experimental design should take into consideration the different factors that can influence the removal rate (such as season and carcass size) and the minimum number of carcasses that must be placed to ensure the statistical robustness of the trials. Additionally, to avoid scavenger swamping, it is important to remember that only a limited number of carcasses should be placed simultaneously (Smallwood 2007).