I guess this might be a bit too hard, so some info: photo taken in the Southern Amazon in primary forest on the east bank of the River Tocantins (200 miles south of Belém, Pará). Its a female of a polytypic species...
Well since I've got HBW, might as well try using it (volume 8, the only volume which I've not seen a single bird from!) . . .
I'll go for female White-shouldered Antshrike Thamnophilus aethiops.