High bird mortality due to power lines invokes urgent environmental mitigation in a tropical desert

Abstract

Electricity supply lines through wildlife habitats can adversely affect biodiversity, yet lack of evidence impedes their mitigation in tropical developing countries. We assessed power line induced bird mortality in 4200 km2 area of the Thar desert, India during 2017–18. We searched for carcasses in 2000 × 60 m2 belts along 40 randomly selected power lines over six multi-season surveys, and in 20 control transects that were surveyed once. We experimentally corrected for count biases by estimating persistence and detection probabilities of 88 fresh carcasses, using Kaplan-Meier survival analysis and binomial GLM, respectively. Scaling mortality by power line crossings of bird families, we examined the influence of group traits on vulnerability, using GLM. We examined the effect of power line mortality on population viability of the Critically Endangered great Indian bustard. We found 289 carcasses of >40 species at power lines and none at control transects. As expected, carcass persistence time and detectability were lower for small birds (<100 g) than large birds (>1000 g). Bias-adjusted mortality was estimated at 3.05 carcasses (95% CI 0.82–6.03) and 5.97 (2.5–10.50) carcasses km−1 month−1 for <33 kV and ≥33 kV lines, respectively. Mortality was positively related to number of wires. Large-bodied and ground-dwelling families were most vulnerable to power line mortality. We estimated 87,966 (SE 25,701) bird mortalities per year in the study area. These findings bear global conservation implications since the Thar desert supports 14 Threatened and 65 migratory species of the Central Asian Flyway. The population viability analysis revealed that the great Indian bustard is at imminent risk of extinction due to power line mortality, and calls for urgent mitigation of overhead power cables and the avoidance of future overhead installations in bustard habitat.