The Predatory Bird Monitoring Scheme (PBMS; http://pbms.ceh.ac.uk/) is the umbrella project that encompasses the Centre for Ecology & Hydrology鈥檚 National Capability activities for contaminant monitoring and surveillance work on avian predators. The PBMS aims to detect and quantify current and emerging chemical threats to the environment and in particular to vertebrate wildlife.Each bird that is submitted to the scheme is given a post-mortem examination during which approximately 60 macroscopic observations and measurements are made. The information gathered during this examination could potentially be used to monitor health status of the birds at the time of their death or at a particular stage of their development. In a previous PBMS report, we focused on examining potential health indicators for the sparrowhawk, Accipiter nisus. We were able to establish baseline 鈥渘orms鈥?for indicators that could be broadly categorised as indicators of change in: (i) population demography because of altered recruitment, survival and mortality (measures were sex ratio, proportion of first-year birds, and proportion of deaths from starvation or disease); (ii) nutritional status (measures were body weight, fat score, condition index) and (iii) physiological stress (fluctuating asymmetry).In the current study we investigated whether these population health indices could be applied to barn owls, Tyto alba. With the exception of the fluctuating asymmetry (FA) metric, which did not comply with the assumptions of the methodology employed, we were able to establish baseline 鈥渘orms鈥?in the form of Shewhart charts in a format similar to those defined for the sparrowhawk. For the majority of health indices considered it was necessary to present results separately for males and females. There were no differences between age classes and so combined indices for adult and first-year birds were presented. The exception to this was the metric reporting the proportion of deaths from starvation or disease (putative cause of death) where age classes had to be separated. Although presentation of indices for age classes combined may reduce some of our ability to interpret any change in the indices it does facilitate annual reporting, as the necessity to combine multiple year鈥檚 data to satisfy statistical requirements may be less. This report has demonstrated that the proposed population health indices generally can be reported for barn owls in same way as proposed for sparrowhawks previously. However, some indices, for example fluctuating asymmetry, differ in their applicability to specific species. Therefore, data analyses similar to those carried out in the current report would be necessary if health index metrics were to be defined for other additional species.
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