The mountain wagtail is mainly insectivorous, catching mainly
flies with most of its foraging conducted along watercourses, where it searches for prey on rocks, in sand and in shallow water. They have also been recorded eating
caddis flies,
mayflies (both adults) and
nymphs,
dragonflies and
damselflies,
butterflies and
moths,
beetles, grubs,
slugs and
tadpoles. It is a monogamous, territorial solitary nester where the male and female usually pair for life. Both sexes build the nest which consists of a bulky cup lined with root fibres, plant stalks and fibrous tissues, resting on a foundation of material moistened by water then set to dry. The nest is usually situated in a cavity in the stream bank, on a boulder, rock face or wall of a dam. Sometimes the nest is placed in plant debris caught in a branch over water, a tree near a deep pool or occasionally in man-made structures, such as bridges or buildings. In southern Africa the eggs are laid from August–May, with a peak during September–December. 1-4 eggs are laid and these are incubated by both sexes for 13–14 days, the male and the female alternate incubation in shifts of 15–60 minutes. The nestlings are fed by both parents and brooded constantly for the first 3–4 days or so of their lives, after which brooding becomes less frequent and totally stops when they reach 6–8 days old. The young fledge at 14–18 days old and remain in their parents' territory for between 19 and 48 days. ==Subspecies==