Nice extraction, looks pretty clean on the low resolution shot. I think the method to bring out the details in this shot is to duplicate the background twice, change the blending mode on both to "screen" and then do a levels adjustment to get the white point correct. From there a curves adjustment may or may not be able to get detail from the bird's breast, the shot's resolution is too low for me to tell. One thing that does bode well for breast detail is the black threshold - this shows me that only about 30% of the breast is solid black, which means that 70% is varying lighter shades...detail.

here's the finished image showing the black threshold at "5", which is 5 shades above pure black. This includes most of the "blacks" that we cannot distinguish from each other. A curves adjustment will change this histogram considerably.