Slaty-backed Forktail

The slaty-backed forktail breeds between February and July; the breeding period does not appear to vary across its range. It builds a nest with materials including bryophytes, leaves, and grass. The shape of the nest can be a cup or part of a dome, depending on where it is built. It frequently has an outer layer of mud. The nest may be constructed in holes in the ground or in the trunks of trees, between the roots of trees, in hollows of dead trees, and sometimes within crevices in rocks. The bird lays three to four eggs that vary from pure white to pinkish white to bluish white, with lavender or reddish brown spots. The spots are more common on the larger end of the egg. Both sexes incubate the eggs. The species is thought to have two or three broods in a year. The species feeds on small invertebrates found in or around the water, including larvae and crustaceans. It forages at the edge of the water, and is described as "moving restlessly". It forages on and among rocks at the edges of the water as well as in mid-stream; it will occasionally enter the water as well. Though it generally forages by hopping in an agile manner among rocks, it also makes brief forays above the water to snatch food items from the surface. Its flight is described as similar to that of a large wagtail; quick and direct, and slightly undulating. It is seen mostly near the water; usually solitary, it is occasionally observed in pairs, and is described as a shy bird. It constantly bobs its tail, and when disturbed it may raise and open its tail with a quick scissor-like movement. In the breeding season is occasionally in small family groups, while in winter it is most often solitary. However, many birds may forage in a favored section of a stream: 15 birds have been observed along a single stretch of the river in Bhutan. In the South-East Asian parts of its range the bird is sedentary, while in the Himalayas it is observed to move over an elevational gradient. A 1998 study found that the species moved locally in response to rising water levels in the monsoon season.

The slaty-backed forktail is found near fast-flowing water bodies in tropical and sub-tropical montane broadleaf forests, as well as near cultivated areas. These include rocky streams and rivers, including broad rivers and valleys in plains areas. A 2000 paper studying birds in northwest India and Nepal found that the incidence of slaty-backed forktails decreased with altitude. The study also found that the slaty-backed forktail had a preference for streams that were bordered by dense and complex vegetation, and had firm and stable banks of earth. They also preferred streams with finer grained sand on the bottom, and with "pool–riffle sequences." More rarely the bird is seen in secluded areas of the forest, and on the sides of roads or trails near the water. In winter months it has been observed to move from the mountains into foothills and plains areas. The species is found in the central and eastern Himalayas, from the Indian state of Uttarakhand in the west to Myanmar in the East, including Nepal, and Bhutan. It is a vagrant in Bangladesh. It is also found in southern China, in southeast Tibet, and in the provinces of Sichuan, Yunnan, Guizhou, Fujian and Zhejiang, and possibly in Hainan. Its range in South-East Asia includes Thailand, Vietnam, Laos, Cambodia, peninsular Malaysia, and Hong Kong. In Hong Kong, it is only an occasional winter visitor or highly uncommon resident. Its distribution in southeast Asia is discontinuous. The elevational range of the slaty-backed forktail varies geographically. It has been estimated as 300-1600m above sea level in northern India, 900–1675 in Nepal, 400–1800 in southern China and the adjacent areas of Thailand, above 500m in Cambodia, above 800m in Malaysia, and 800-2200m in Bhutan. In the winter, it has been recorded as low as 200m above sea level. The range of the species has not been precisely determined, but is known to be very large. The population is thought to be stable, and though its size is not precisely known, it is thought to be greater than 10,000 individuals. It is categorized as a species of least concern by the International Union for Conservation of Nature. It is common in the parts of its range that occur in China, Nepal, and South-East Asia.