>>3487778*at most 10-15, sorry. More like 5 feet. You just need to get very close for small birds if you want a lot of fine detail, there's no way around it. If you can't do that, opt for a wider composition and don't try to tease detail out of a shot at 100% resolution, it doesn't work. Let some of the environment in if you have to, it will add a lot more to the shot than centering on the subject as much as possible.
70-300 is my choice for small songbirds because you can focus at ~4 feet, have plenty of zoom range to compose and track fast subjects, can poke it between leaves and branches easily so you don't end up with obstructions that are invariably close to the front element and very out of focus, clouding the image. My only complaint is it's a bit slow, but f/2.8 is a bit too bulky when dealing with shooting into brush that close.
TL;DR: 1 in 1000 encounters might net you the opportunity to get that detail, but don't discount the other 999. Work with the situation instead of trying to force an outcome.
