Ian I believe the thrushes and other birds get trapped in the the upper Tefi valley ie between lampeter and Llanddewi when the wind is from anywhere from NE -SE . Like you I have seen large numbers of thrushes arriving to roost in the woods behind our cottage in the past, some times thouasnds Ive watched them fly from over Cilgwin .Last saturday although there was no sign of any thrushes around the village I did notice a few flocks over the mountains above the village.
David Price