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Home > Contents > Methodology
> Waterways Bird Survey
2.4 Waterways Bird Survey The Waterways Bird Survey (WBS) has monitored the population trends of up to 24 riparian bird species on canals and rivers throughout the UK since 1974. WBS uses a territory-mapping method like that of its parent scheme, the Common Birds Census, to estimate the breeding population of waterbirds on each plot. Detailed territory maps are prepared that can be compared with habitat data to show which features of linear waterways are important to breeding birds. The plots average 4.4 km in length; almost half are slow-flowing lowland rivers with the rest either fast-flowing rivers/streams or canals. In recent years there have been around 90 plots distributed throughout the UK. The proportion of plots in the north and west of England is higher than existed in the CBC (Marchant et al. 1990). As with CBC, coverage outside England has been relatively poor.All fieldwork has been carried out by volunteers. Observers are asked to survey their plots on nine occasions between March and July, mapping all the birds seen or heard onto 1:10,000-scale maps. Registrations are then transferred to species maps, which are analysed to reveal the numbers and positions of territories for each species. For the first 20 years all territory analysis was performed by trained headquarters staff but, during 1994–2007, observers completed their own territory analysis, based on the scheme's written guidelines, with results checked by BTO staff. As WBS has employed very similar methods to those of CBC, the validation studies carried out for the latter generally hold true for WBS (see section 2.2). Marchant et al. (1990) found that there had been little change in the composition of the WBS sample in terms of waterway type or geographical spread. Population changes along waterways have been reported in BTO News for around 20 riparian species, of which Goosander is not covered by BBS monitoring. For specialist waterbirds, including Little Grebe, Mute Swan, Common Sandpiper, Kingfisher, Sand Martin, Grey Wagtail, Dipper and Reed Warbler, targeted surveys along waterways can provide a better precision of monitoring than is possible through the more generalised BBS surveys. WBS indices can also add a new perspective on trends in waterbirds that are monitored, largely in different habitats, by CBC/BBS. For Lapwing, populations declined rapidly on arable farmland during the late 1980s while numbers on WBS plots, typically representing populations along river floodplains, were more stable. Yellow Wagtails have declined much more steeply in WBS habitats than elsewhere. WBS has similar limitations as a monitoring scheme that led to the CBC's replacement by BBS. In particular, plot distribution is biased geographically and possibly also towards sites that are good for birds, and an intensive survey method is used that severely limits the sample size (Marchant et al. 1990). A drawback specific to WBS is that it has covered only waterbirds. BTO has addressed these issues by setting up the Waterways Breeding Bird Survey (WBBS), which has been running since 1998 in parallel with WBS. WBBS uses BBS-style transect methods along random waterways, and includes all species of birds. WBS closed after the 2007 season and it is now expected that WBBS will become an ongoing scheme, providing useful monitoring data to supplement BBS. Data analysis Smoothed population trends are estimated using generalised additive models, with confidence intervals calculated by bootstrapping (Fewster et al. 2000). Trend analysis and presentation follows the same pattern as CBC (section 2.2), except that the 'Unrepresentative?' caveat has not been used. A caveat of 'Small samples' is provided when the number of plots falls between 10 and 20. Next section – 2.5 Heronries Census CLICK HERE to go to the WBS section of the main BTO website |
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