Question about House martin behaviour

[Columbine]

Could anyone please explain a bit about House Martin behaviour. Every night this week at about 7.30pm the sky around our house is filled with house martins, I don’t know how many but a wild guess would be perhaps 60 or 70 birds but far more than could possibly have come from the four nests on our house though some do fly up to the nests and there seems to be a bit of squabbling. They are wonderful to watch, a really fantastic display, then suddenly they are gone and the sky empty. I assume they are gathering together and going off to roost elsewhere. It seems early for them to be getting ready to leave. The last of our nests fledged last weekend after a month of pretty awful weather. Is it too late for a second brood? I wondered if they were teaching the young birds where to roost and the adults would come back to the nests if it isn’t too late. Where are they likely to go to roost?

I couldn’t manage a photo tonight but I took the one below from the landing through a (closed) window at the end of May.

[Hobjob]

From Birds of the Western Paleacrctic

Highly gregarious throughout the year. Flocks of several hundred common on migration and in winter quarters. In Zaïre, April, migrant flocks of 30–200 birds (Verheyen 1952). After breeding, adults and juveniles from different colonies typically form flocks prior to migration. In Britain, post-breeding flocks July–October. In southern Finland, start flocking late July, reaching maximum size (up to 400 birds) mid-August. For association with other Hirundinidae in winter quarters, see (e.g.) Chapin 1953 and Harper and Harper 1974.

[Columbine]

Many thanks Hobjob, it sounds like they are getting ready for the off already then, can't say I blame them after the summer we've had!

[Adam Cheeseman]

Sounds like a pre-roost feed-up on high altitude insects.

Cheers,

Adam

[Columbine]

Interesting, yes it has been during some of the nicest evenings we have had for a while so imagine there would be plenty of insects. Many thanks Adam.