Study Area
This particular study focussed on river-dependent birds along snow-fed
and perennial headstreams in the western Himalaya of India, specifically
the Bhagirathi and Amrutganga rivers in Uttarakhand, and the Tirthan
river in Himachal Pradesh (Fig. S1). Sites were selected over an
altitudinal gradient from 330 to 3100 and represented a range of habitat
types from near-natural environments in protected areas to river
stretches affected by human activities such as farming or urbanisation
at lower altitude. Climatological conditions vary from sub-tropical to
temperate (Mathur and Naithani 1999; Sinha, 2021), with drainage varying
from glacial meltwater, rainwater and underground springs. Areas above
1500m in the northwest Himalaya are highly seasonal with cold winters
and mild summers (Barve, 2017).
Of the specific study locations, the Tirthan river (N 31.6396° E
77.401°) is a major tributary of the river Beas in the Indus system.
Here, survey locations encompassed river reaches between 1400- 2300 m in
the Great Himalayan National Park Conservation Area in the Kullu
district where the natural terrain is characterized by numerous high
ridges, deep gorges, and narrow channels (Mathur and Naithani 1999). The
buffer zone of the protected area has hamlets with orchards and other
small scale agricultural practices and game fishing for introduced Brown
Trout (Salmo trutta) . Inside the protected area, the river flow
is uninterrupted while the riparian zone is relatively pristine with
conifers and broadleaf woodland. In the Gangetic headwaters, river
reaches were sampled along the Bhagirathi (N 30.7564°E 78.5781°) and its
associated low-order tributaries covering an elevation gradient between
300-3300 m. Riparian vegetation consists of conifers at higher
elevations and subtropical vegetation at the foothills. In this
non-protected area within the administrative districts of Uttarkashi,
Tehri and Dehradun, habitats have been modified by a range of
anthropogenic pressures from agriculture and settlements (Sinha et al.,
2019). Sites in the Amrutganga valley (N 30.466°E079.269°) are part of
the Kedarnath Wildlife Division in Chamoli district where riparian
land-use ranges from well vegetated river reaches to small villages with
traditional agriculture (Barve 2017) between elevations of 1400 m to
2650 m.