Camera-trapping as a methodology to assess the persistence of wildlife carcasses resulting from collisions with human-made structures

Abstract

Context To assess the real impact of human-made structures on bird and bat communities, a significant number of carcass-removal trials has been performed worldwide in recent decades. Recently, researchers have started to use camera traps to record carcasses exact removal time and better understand the factors that influence this event. Aims In our study, we endeavoured to identify the factors that significantly affect carcass-persistence time, such as (1) season, (2) scavenger guild, (3) type of carcass, (4) habitat and (5) weather conditions. Additionally, we aimed to assess the performance of camera-trapping technology in comparison to the conventional method typically used in carcass-removal trials. Methods We conducted two trials in two wind farms during early spring and during summer season. In each trial, we used 30 bird carcasses and 30 mice carcasses as surrogates for bats. Digital infrared camera traps were used to monitor each carcass. Chi-squared test was used to investigate differences between wind farms regarding the scavenger guild. A log-rank test was used to compare carcass-persistence times for both wind farms. Carcass-persistence times were analysed using both non-parametric and parametric survival models. Finally, we evaluated the percentage of carcasses removed during the day time and night time. Key results In our study area, carcass-persistence times were influenced by the scavenger guild present and by the exposure to rain. Camera traps allowed to record the exact removal time for the majority of the carcasses, reducing the number of visits to the study site about five times. However, there were also cases wherein loss of data occurred as a result of equipment flaws or camera theft. Conclusions Results demonstrated the importance of undertaking site-specific carcass-removal trials. Use of camera-trap methodology is a valid option, reducing displacement costs. Costs related to equipment purchase and the risk of camera theft should be taken into consideration. Implications When choosing camera-trapping, the main aspect to evaluate is the balance between the investment in equipment purchase and the cost savings through reduced displacement costs. Further studies are required concerning the real effects of the data collected on the accuracy of carcass-removal correction factor obtained.