Bird surveys
Bird species that depend on aquatic production and occupy the riparian
zone of Himalayan rivers were known from reconnaissance surveys and
previous studies (Manel et al. 2000; Buckton & Ormerod 2002). For the
current analysis, replicate surveys of the 68 reaches were undertaken in
2017-2018 in the pre-monsoon period (March-June), thereby capturing the
breeding season of almost all the target birds. The banks were walked by
the same observer (AS) during early morning (06.00 to ± 10.00) and late
afternoon (15.00 to ± 18.00) following a previously established field
design in which three visits were made to each river segment of 500 m
length on different days (Buckton 1998). This visit frequency is
considered appropriate for detecting river obligate species that occupy
linear territories (D’Amico and Hemery 2003). The order of visits to
each site within the basin were randomized as far as possible while
ensuring minimum distances of 30-50 km between the sampling sites on
consecutive days to maintain spatial independence (McCarthy et al.
2013). Species were recorded as present if they were observed during any
of the three visits, while numbers of individuals of each species were
recorded on every visit and eventually converted to mean numbers per
visit. Bird species occurring in less than five river reaches were
excluded from further analysis.