Pigeon Crack and Parting Swifts

I know birds like to take a peck at building mortar from time to time - they need a bit of grit in their diet, and a little help in forming the shells of their eggs - but lately the pigeons down my way have gone crazy for mortar. They're pecking away like crazy, leaving stretches of walls practically mortarless and in need of radical repointing. Suddenly mortar is pigeon crack - they can't get enough of the stuff. I suspect this is because much of the village is a conservation area, so limestone-rich 'heritage' mortars are widely used, offering plenty of calcium carbonate for mortar-crazed pigeons. Where will it all end? Crumbling walls, pigeons too heavy to fly away, paying the price for their addiction...
 Meanwhile, I hate to say it, but it looks as if the swifts have flown - and it's not even August yet. There will be stragglers of course - I heard, but didn't see, a couple this morning - and I certainly hope I haven't seen my last swift of the year; that would be ridiculously early. But the great suburban air show is over, having peaked a couple of weeks ago with some glorious screaming flypasts at street level and soaring aerobatics high overhead. After a shaky start with that long spell of unseasonal cold, things really took off as soon as the temperature rose, and a hot sunny July made for a vintage swift season - and probably enabled the young birds to feed up fast and be on their way south. It's always sad to see them go - or rather to realise they're gone - but the sadness is nothing to the heart-lifting joy of their return.