To explain, let's focus on Curlew. They love central/east Greenborough on a neap tide. Offshore, safe. They love it so much they'll shrink their core area on a 'norm' but they do have to change on a spring. They'll chop and change their refuge, dependent on onshore disturbance. Today, for many the unimproved pasture elsewhere was deemed unsafe so they were on the flooded wet fields of Barksore (that green circle on yesterday's screengrab map). And the majority had been since the tide had been on the rise, liking to roost earlier than many other wader spp., way before the rib turned up. So, unless they take flight, they are hidden from waterborne observers by a high sea wall.
This is one reason why Curlew can be under-represented on old WeBS counts. If the land-based counters are out on a neap, they will not have such large numbers present- they'll be out on Greenborough. If, hypothetically, that boat had been doing a WeBS, they'd have missed them (and others) ashore. And here's the problem when counts are out by a several days: the two nearest WeBS dates are highlighted on this tide-table snapshot. Much lower tides than today's.
Some will claim this to be a favourite sermon of mine of course, heard here before, and they'll be right: it remains worth repeating for any newer readers who might be WeBS counters elsewhere. Here the BTO spent time puzzling over the lack of waders on the Medway some years back, without questioning the data itself. More recently, this past couple of years Natural England have been puzzling over the relatively low numbers in relation to habitat available. It is all too easy to take WeBS as Gospel where it has been incomplete and executed poorly.
I know this is probably just how us 'soft sarfeners' don't like talking to neighbours, but a good example why it is worth any estuary WeBS counter chatting with their seawall count neighbour; to see if peaks and troughs on the ebbs and floods mirror. Or just to see if they're out and about at the same time. Putting in place those best practices the BTO promote.