Swallow at Parkend swing bridge, Sharpness canal

On my way home from Gloucester I couldn't resist going to see if the swallows were still nesting at Parkend swing bridge on the  Sharpness canal.  The answer is that a few are still there and feeding more young in their nests underneath iron structure of the swing bridge.  I could hear them quite loudly as i stood on the bridge.

I crossed to the far side and went a few yards along the towpath, so I could watch the swallows flying down the line of the canal water to pick up insects.  Their aerobatic manoeuvres kept me awestruck as always.  It was overcast today so not much bright light.  I had a shorter zoom on the camera today so couldn't as close as I have done with the 200-400mm lens.  

The ripples on the water in this image made me choose it rather than any others, none of which were particularly sharp. I did notice that several swallows were standing today on odd structures which I remember happening before they started to assemble for their next journey south.  I am now wondering how long it will be before they leave us for another season.

When looking at the pictures on my computer I did notice this particular bird, with the gap in the rear feathers on its right wing, appearing regularly.  I wonder what causes such a loss and how it will affect its longevity when it has such huge distances to cover back to southern Africa.