River habitat characterization
Physical variables describing the river and riparian zone at each site were recorded alongside bird surveys to capture information on river channel structure, flow character, bank structure, riparian vegetation and adjacent land use following methods developed by Sinha et al. (2019) after Raven et al. (1997). Observations were made at two different scales, respectively: (i) perpendicular transects or ‘spot checks’ at 10 points every 50 m along each 500 m reach specifically recording progressive lateral changes at each point in flow character and habitat features from the channel to the riparian zone; (ii) ‘sweep up’ assessments that recorded features over the whole 500 m survey site. The resulting data blended quantitative and semi-quantitative methods, for example with features recorded as present (<33% of the survey reach) or extensive (>33%), or on a six-point scale (rare:1–20% cover; occasional 21–40%; frequent 41–60%; abundant 61–80%; dominant 81–100%). A more extensive description of the variables recorded and their ability to detect variations among locations is provided by Manel et al. (2000).