I'm surprised distance margins on insulators etc. are not large enough to prevent this. Unfortunately the article is short on technical details such as the typ

I'm surprised distance margins on insulators etc. are not large enough to prevent this. Unfortunately the article is short on technical details such as the type and voltage of HV lines, insulator info etc. Very high voltage lines, ≥330kV, can arc under some conditions, high humidity, polluted atmosphere, same with dirty insulators (which are usually cleaned by rain). In these conditions I'd have thought birds approaching such lines would be sacred off by arcing. Similarly, I'd have reckoned any arcing between a bird in flight and a line would only have been large enough to scare it off rather than to harm it. Does anyone have actual details about how these birds are electrocuted?