Well, birds are not paid a great deal of money to land on very high voltage lines -> so any discomfort discourages them sufficiently. Linesmen and helicopter pilots, on the other hand, are paid a great deal ..... 8<)
"I won't get into the high voltage transmission area except to note that the argument basically compares the costs of the lines and terminal equipment to see what distance does the DC system become justifiable over long distance AC. In the past, it had been in the neighborhood of 300 miles or so, that is, above 300 miles, the DC system will be the lower cost. Today, I'm sure the breakeven distance has come down."
More seriously, there are two advantages to DC transmissions between grids, and over great distances - but only if that transmission is between two distinct points.
AC HV power to DC Very High Volt power conversion is very, very expensive for the facility and the converters; and those conversion losses reduce efficiency by a measurable amount at each end.
A DC-DC VHV long-distance line can take advantage of the fact that the return circuit can be through the ground itself sometimes - so you need to build only half of the copper to make a complete circuit. IF - big IF there! - there is only one circuit being built. If you start tapping off large amounts of DC VHV power in the middle of that single-conductor long-distance DC line, then you start creating significant problems in balancing the current in that single-conductor DC (plus) line. Build a two conductor long distance DC line to allow tapping off power in the middle, and your copper and construction costs double, plus you have to build new DC-AC conversion facilities at every tap point, plus the same AC-AC transformer yard and switchyard to get the "new" AC power out from the DC-AC converters.
Using a DC-DC high-voltage connection between grids is a good idea - very valuable in fact, since two side-by-side HV AC grids will not be at the same matching frequency exactly. So converting AC-DC at each end of the grid-grid link avoids the need to synchronize two entire grids to share power, or to blackstart the dead AC grid from either end. You just have practical limits on how much power you can get through the HV AC lines to the grid-grid junction, and across the DC-DC line, and through the AC-DC//DC-AC converters.
For all the above - chiefly expense never recognized by the renewable energy enviro's and their politicians, you can seldom afford to build multiple DC-AC convertor facilities just on a whim in the middle of your DC-DC cross-country links. If you have a long distance HV AC-AC line, you can tap into that HV AC line to get more power from a small town's generator or a new single gas turbine plant in the middle of the area, or can "tap out" power from that HV AC line to a new town, new commercial plant or customer, etc. All if takes is a conventional transformer yard and switches. Relatively low cost.
So, very long distance VHV DC-DC can be economical. Under some conditions and for some lengths. Short distance VHV DC-DC links can be economical - sometimes even essential, regardless of their costs - under some conditions. Very long distance HV AC-AC lines are almost always economical under almost all circumstances up to certain lengths across most terrains. Medium and short distance, medium and low voltage DC lines are very, very seldom economically justified for more than a few thousand yards - which is what Westinghouse proved 120 years ago.
Medium distance and short distance HV and VHV AC-AC lines are economical under all medium and short distances to actually connect the current grid to all current users from all current power plants of all sizes.
Replacing the current grid is stupid - under all conditions at all times for all lengths - except those envisioned by the enviro'ed politicians.