It looks like a still from Hitchcock's 1953 film The Birds, but this is a picture taken today from the Kilchoan-Portuairk road looking towards the ridge above Sanna, and the birds are fieldfares. Estimating the numbers was extremely difficult, but there were at least three flocks of several hundred flying and another roosting in an large area of woodland, but one estimate was that, in all, there might have been a thousand of them.
Fieldfares arrive at this time of year, often in the company of redwings, from Scandinavia. It may be that the sudden change in the weather, with the wind firmly in the north, has brought them down from a cold Scandinavia. While they also eat insects and worms, their main meal at present is the heavy crop of rowan berries.
According to the RSPB site, their numbers build up during the early winter, more so if the winter is severe. We used to see them in large numbers in fields in East Anglia, and we've seen some here in previous years, but we've never seen anything like this invasion before.