About ten days before this an effort to locate this bird had failed. On this day, we tried another location in the vicinity, and sure enough we heard the bird calling. It was a female, moving about in dense undergrowth amidst bamboo stands in moist, broadleaved evergreen forest, finally coming out for a few seconds to perch on a rock.
Forests on the edge of tea plantations on the north of Kaziranga along the Karbi foothills support a population of this bird. Some migrate higher during the breeding season, and there is evidence of it going pretty high up - at least to ~2000m (this recording last year was from 1800m - http://www.xeno-canto.org/317100). But some stay back like this one.
A recording of this individual can be heard here: