Quantifying avian collisions with power lines at large spatial scales is difficult, but such mortality is of serious conservation concern for many bird species worldwide. To investigate effects on the Endangered Ludwig's Bustard Neotis ludwigii and two other bustard species, mortality surveys were conducted quarterly along high-voltage transmission lines at five sites (total length 252 km) across the Karoo for 2 years and one low-voltage distribution line site (95 km) for 1 year. Thirty bird species were found, with Ludwig's Bustards constituting 69% and other bustards a further 18% of carcasses (n = 679 birds). Significant explanatory variables of Ludwig's Bustard collisions were season (collisions more likely in winter), rainfall (less likely in drier areas) and year on transmission lines (highlighting variability between years). Season and proximity to roads were significant variables on distribution lines, with collisions more likely during winter and away from roads. Ludwig's Bustard collision rates (corrected for survey biases) were higher on transmission (1.12; 95% confidence interval (CI) 0.40–2.58 bustards/km/year) than on distribution lines (0.86; 95% CI 0.30–1.96), but these smaller lines are four times as extensive in South Africa and so probably kill more birds. Despite being much less abundant, Kori Bustards Ardeotis kori were the second most commonly recovered species, with collision rates of 0.10 (95% CI 0.05–0.19) on transmission lines in the Nama Karoo alone. Collision rates are highly variable but suggest mortality suffered by these two species is worryingly high. This adds to growing concern about the impacts of power lines on bustards globally, so given ongoing expansion to the power grid, collision mitigation measures should be implemented at all new power lines.