Females of M. l. berlepschi have more olive upperparts than the other subspecies, their white throat has a thin band of black speckles below it, and their belly is somewhat grayer than the others'.

[9] The ash-breasted antbird is found almost exclusively on river islands, usually those with somewhat mature forest and dense undergrowth.

It typically forages singly or in pairs in dense vegetation, mostly within about 1.5 m (5 ft) of the ground and only rarely higher.

[6][8][9] The one known nest of the ash-breasted antbird was a dome of dead leaves, leaf skeletons, and a few twigs on the ground among low plants and mossy logs.

The song of the ash-breasted antbird's subspecies M. l. berlepschi is "a moderate and even-paced (about 5 notes/sec), descending series of slightly hoarse notes: JEE-JEE-jee-jee-jee-jee-jee-jee-jee-jer".

Its calls are "a rapid, descending, metallic, sputtering chatter: pt'rr'rr'rr and a quiet pew note, sometimes doubled".

"The primary threat to this species is accelerating deforestation in the Amazon basin, as land is cleared for agricultural production...Moreover, changes in flooding patterns and flow regime caused by deforestation, the construction of river dams or global climate change, could have serious effects on the species."