My mother, who lives about 150 km from the city, has a couple of finch feeders in her yard (always filled with nyger seed because, as you say BCF, they have no use for any of the other seeds). Anyway, the finches are around a lot but, as soon as the real heat arrives, it seems that they vanish into the bush and you don't see anything of them for several weeks. Once the temperatures cool, back they come! I love them -- just like flashes of sunshine darting around the green yard.