I think it's clear that this what happens, inland birds disappear first, head to the coast and trickle South, many of the later observations, even way up North, are mainly coastal.I saw more than 100 4 days ago at Blackditch coastal reserve (Wicklow). I see another 20 reported at that location today. But they are gone from my local area. So perhaps they gather at coastal locations before going south. Not as obviously as swallows, they slip off more discreetly. But with so many observers online you can see the patterns more easily.
I personally think that this is not thinking 'like a swift'. When the young have fledged from a colony there is no reason to be held to the nesting area, except of course the local knowledge of where the best feeding is likely to be found.I think it's clear that this what happens, inland birds disappear first, head to the coast and trickle South, many of the later observations, even way up North, are mainly coastal.
I personally think that this is not thinking 'like a swift'. When the young have fledged from a colony there is no reason to be held to the nesting area, except of course the local knowledge of where the best feeding is likely to be found.
With an av. cruising speed of 25 mph, it means that Swifts will fly 600 miles a day. They are perfectly adept of going where the food is, and surfing the weather systems.
I live 40 miles from the coast and they are still seen here this week normally when the cloud pushes their food down, and they follow. Otherwise they can be very high and usually I don't see them unless they mix with hirundines They are also generally silent. I suspect few a local nesting birds, but just don't know.
I think with mobility it is likely that they don't just migrate, but will drift southwards, but reverse journeys are probably frequent if the food is there.