Yesterday I had Mourning Dove in the yard. I set up in the kitchen window with the Tamron 300 2.8 and HD DA 1.4 TC stacked with my F 1.7x AF adapter for approximately 700mm 6.3, all with parts lying around my house.
Not the sharpest, but no that bad either.
Any shot you can get without leaving the house is bonus. Right now there's a momma wild turkey and three half grown young out there chowing down. But they are easily spooked so I'll just enjoy standing a meter back from the kitchen window, watching them.