Factors Affecting Differential Underestimates of Bird Collision Fatalities at Electric Lines: A Case Study in the Canary Islands (Gómez-Catasus et al., 2020).

Carcass counts tend to underestimate avian collision rates due to three main sources of bias: imperfect detection, carcass removal by scavengers, and carcass dispersion in unsearched areas. This study assessed these biases on electric lines in Lanzarote and Fuerteventura (Canary Islands), quantifying the factors influencing them and conducting a cost-effectiveness evaluation of perpendicular carcass searches along electric lines. We surveyed 230 km of high-voltage, medium-voltage, and telephone lines over three periods (July 2015, November-December 2015, March 2016), finding 431 bird carcasses. We recorded species, distance from the electric line, cable height, detection distance, and decomposition state. Additionally, an experiment was conducted to estimate carcass removal by scavengers. Dispersion distance increased with cable height and was greater on high-voltage lines, while it decreased with body mass. Overall, detection probability was 0.134, increasing with carcass size, decreasing with decomposition, and lower in rocky areas. Disappearance rates varied between islands, likely due to differences in scavenger abundance, increased with time, and decreased with bird size. The study identified a 27-meter threshold for optimized cost-effectiveness in searching for carcasses. These findings provide correction factors for more accurate estimates of avian mortality rates in sparsely vegetated landscapes and highlight challenges based on the environment and electric line characteristics.