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\nbat communities, a significant number of carcass-removal trials has been\nperformed worldwide in recent decades. Recently, researchers have\nstarted to use camera traps to record carcasses exact removal time and\nbetter understand the factors that influence this event.\nAims. In our study, we endeavoured to identify the factors that\nsignificantly affect carcass-persistence time, such as (1) season, (2)\nscavenger guild, (3) type of carcass, (4) habitat and (5) weather\nconditions. Additionally, we aimed to assess the performance of\ncamera-trapping technology in comparison to the conventional method\ntypically used in carcass-removal trials.\nMethods. We conducted two trials in two wind farms during early spring\nand during summer season. In each trial, we used 30 bird carcasses and\n30 mice carcasses as surrogates for bats. Digital infrared camera traps\nwere used to monitor each carcass. Chi-squared test was used to\ninvestigate differences between wind farms regarding the scavenger\nguild. A log-rank test was used to compare carcass-persistence times for\nboth wind farms. Carcass-persistence times were analysed using both\nnon-parametric and parametric survival models. Finally, we evaluated the\npercentage of carcasses removed during the day time and night time.\nKey results. In our study area, carcass-persistence times were\ninfluenced by the scavenger guild present and by the exposure to rain.\nCamera traps allowed to record the exact removal time for the majority\nof the carcasses, reducing the number of visits to the study site about\nfive times. However, there were also cases wherein loss of data occurred\nas a result of equipment flaws or camera theft.\nConclusions. Results demonstrated the importance of undertaking\nsite-specific carcass-removal trials. Use of camera-trap methodology is\na valid option, reducing displacement costs. Costs related to equipment\npurchase and the risk of camera theft should be taken into\nconsideration.\nImplications. When choosing camera-trapping, the main aspect to evaluate\nis the balance between the investment in equipment purchase and the cost\nsavings through reduced displacement costs. Further studies are required\nconcerning the real effects of the data collected on the accuracy of\ncarcass-removal correction factor obtained.