Birds on the wires

With the southeaster pumping down the valley intermittently, we are confused by the season - is it November with gale force winds, or February with dead calm days of blazing heat - it changes every few hours! At the moment we are being turned inside out again, but earlier I took a stroll along the beach front and was enchanted to see these swallows lined up on the telephone wires. What will they do without these wires when everything goes wireless one day? Where would will they all sit, and where do they sleep at night?
I wonder what this tune sounds like?

They look rather as though they are gathering for the return flight to either Angola or Europe - they had dark blue heads for those who can identify the species - but it is still too hot so that is unlikely. Maybe they just like to sit on the wires!
If it weren't for these birds, and the bats that live under my eaves, I'm sure the mosquito and other bug population would be ten times what it is at present, and they will probably be going home well fattened for the long trip. I wonder if they eat flies - does anything or are they just too revolting to contemplate even in nature?