Where have all the Redwings gone?

This January, In seaford, as elsewhere along the coast, there was a huge invasion of Redwings into Seaford. I estimated 300 in my part of town, and there were probably over 5000 in Seaford in total. Now, I hardly ever see any, perhaps four or five remain in the local area, travelling accross the town, trying to find food. However, ususally, I have 30 or 40 in my part of town throughout the winter. This happened in 2007/08 and 2008/09, and I counted atleast 30 from Mid November to Mid december this winter in Seaford. Why did the local residents leave when the travellers from the country did? Perhaps the Country-folk told them of the wonders of the country, where they can eat more berries than they had ever eaten in their lifes. Or Perhaps it was simply that, after their country siblings, and country cousins(the Fieldfares) had come to town, there weren't enough berries left in the towns to support the city-slicker Redwings. Funny how even though the snow has gone, my local Redwings may still be feeling the effects of it as the food shortages push them into the countryside.