Use of radar to estimate bird traffic in environmental assessment studies

Abstract

The characterization of bird traffic is a requirement for assessing the environmental impact of projects that create obstacles to bird movement (e.g., wind turbines, towers, and power transmission lines). For this purpose, the Chilean environmental authority recommends direct observation methodologies, i.e., the visual and/or auditory determination of the variables of interest by a team of observers in the field. These methodologies are subject to observer bias and sampling efforts, often determined by labor and economic factors. This raises the need to incorporate automated methodologies, such as radar, to achieve more precise characterizations. In this study, we compared six bird traffic variables (species, number, speed, direction, height, and flight length) obtained simultaneously by a group of observers and a maritime radar. The radar obtained significantly more records than the observers regarding the number of individuals, flight direction, and height. Speed and path length were recorded only by the radar, not by the observers. Species identification was the only variable where radar data did not allow identification, but observer experience did. These results indicate that bird traffic characterization, as currently implemented, is not providing accurate information for decision-making regarding the environmental viability of projects, and it would be advisable to progressively implement the use of radar in these environmental assessment studies.