Abstract
The number of wind farms operating in the Isthmus of Tehuantepec, southern Mexico, has rapidly increased in recent years; yet, this region serves as a major migration route for various soaring birds, including Turkey Vultures (Cathartes aura) and Swainson's Hawks (Buteo swainsoni). We analyzed the flight trajectories of soaring migrant birds passing the La Venta II wind farm during the two migratory seasons of 2011, to determine whether an avoidance pattern existed or not. We recorded three polar coordinates for the flight path of migrating soaring birds that were detected using marine radar, plotted the flight trajectories and estimated the number of trajectories that intersected the polygon defined by the wind turbines of La Venta II. Finally, we estimated the actual number of intersections per kilometer and compared this value with the null distributions obtained by running 10,000 simulations of our datasets. The observed number of intersections per kilometer fell within or beyond the lower end of the null distributions in the five models proposed for the fall season and in three of the four models proposed for the spring season. Flight trajectories had a non-random distribution around La Venta II, suggesting a strong avoidance pattern during fall and a possible avoidance pattern during spring. We suggest that a nearby ridgeline plays an important role in this pattern, an issue that may be incorporated into strategies to minimize the potential negative impacts of future wind farms on soaring birds. Studies evaluating these issues in the Isthmus of Tehuantepec have not been previously published; hence this work contributes important baseline information about the movement patterns of soaring birds and its relationship to wind farms in the region.
Highlights
The production of wind energy is increasing rapidly worldwide: in mid- 2013, there was a total of 296 GW of installed capacity, but it was expected to grow for a total of 318 GW for the full year [1]
These installations are located along an important migratory route for raptors that traverses Mexico [5], leading to concerns about the potential impacts of wind farms on birds, as some species of diurnal migrants are commonly observed, soaring above a ridgeline which in close proximity to La Venta II [6], [7], probably making use of the wind updrafts generated by the walls of the ridge [8]
The La Venta II wind farm has 98 turbines arranged in four rows that are aligned from west to east, with a total nominal capacity of 83.3 MW distributed in a 9.49-km2 area
Summary
The production of wind energy is increasing rapidly worldwide: in mid- 2013, there was a total of 296 GW of installed capacity, but it was expected to grow for a total of 318 GW for the full year [1]. By the end of 2012, a total of 15 wind farms were operating in the region, producing 1331.65 MW of energy [4]. These installations are located along an important migratory route for raptors that traverses Mexico [5], leading to concerns about the potential impacts of wind farms on birds, as some species of diurnal migrants are commonly observed ( during their fall migration), soaring above a ridgeline which in close proximity to La Venta II [6], [7], probably making use of the wind updrafts generated by the walls of the ridge [8]
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