Many of the transmission line conductors are not insulated, and birds are not harmed by landing on one of the wires. Most of the "fried critter" incidents I've seen or heard reliably reported result when the bird sits on one wire and pecks, or beats his wings, at a bird on a different wire. "Skwerls" - to use the new mudcat spelling - have a real problem with that twitchy little tail. They're on one wire and flick the tail too close to another wire.

When someone decided that those great tall isolated cross-country transmission line pylons would be a great place to put nesting boxes, the utilities felt compelled to permit it. Then they started finding lots of dead iggles*. The transmission line people were then "volunteered" to re-space many many miles of lines, to meet the new "environmental impact amelioration" requirement for more separation between individual lines. Most birds land with wings spread, so they could touch one line with a foot and another with a wing. There's also the scenario of two birds on different wires "squabbling" with each other, and young birds squabble a lot.

At the voltages used on the larger transmission lines, "touching" doesn't necessarily mean coming in contact. A warm blooded body coming within a foot or so - sometimes within several feet - is definitely "electrically connected," especially if its "other end" is similarly close to a different line.

* "iggle" used as generic for any of several large birds affected.

John