Traces of ribbons

Blame the bloom. All I've been doing of late. The algal matting has been bad this summer, so much so large swathes of mudflat have looked like green fields (and still do). All of which makes feeding tough for many species. Try getting your bill through that, Mr Plover.

I hadn't thought it should affect Oystercatchers as much, feeding mainly mid-Channel on the deeper water mussel beds, but numbers have been depressed these past few weeks- the bloom has even been covering large parts of Bartlett Spit and Bishop Ooze. Maybe some other factors come into play as well, just how is their prey coping? Whatever the cause, I didn't hold high hopes for numbers in the Ham Ooze complex tonight. Just over 170 end of July, just under 200 on the 8th. Thankfully, an increase, now just over 400. Still lower than hope for.

But the real Oystercatcher show was yet to come.

As I have said before, Oystercatcher was the first species I thought of studying a little on my move back- big, black and white, easy to identify at distance. Brighten the birding up a bit. Now in the fourth autumn, I can make some reasonable guesses at what they're up to. So, a summer rise, covering just after dusk and still a relatively 'low' high tide, the neaps having been in the past few days? Watch the north-east sky.

Starting about thirty minutes before sunset (when large feeding areas would still have been available), ribbons of Oystercatchers started to flight into the Medway. 34, 50, 64, 16, 73... two ribbons at once, now three, five... it might not excite many birders, but I was smiling. And so it continued until I was having to pick out lines in the glow of the lights on the Yari liquid natural gas container ship towering over Saltpan Reach. When I finally quit it felt as if they were still coming.

A (sort of) final total- 77 ribbons, 2,093 birds.

Tidal conditions had been similar at the end of July. 27 ribbons of 776 birds. Both times the majority of the birds had put down around the western end of Sharfleet creek, just west of Sharpness saltings, an area that usually floods on the spring tides. Which might explain why similar dusk counts on much higher spring tides usually produce smaller numbers of Oycs. Perhaps at this present time in the tidal range cycle the Medway becomes a safer option than their Grain/Allhallows beach roost sites along the south shore of the Thames? Perhaps a safer option because of predator risk? The shoreline will be patrolled by foxes and the like, and human activity often involves night fishing. None of that on these saltings.

Well, the south Medway feeders, the birds I'd counted on Ham Ooze, did not change their own roost- as always, they left Ham Ooze for Chetney Hill (green on map below). It was just birds from out in the Greater Thames. Tracing their flightlines back, a good volume came straight down the eastern flank of Grain, over the Roas Bank and the Flats, areas that can hold big feeding numbers. But many of these birds were seemingly travelling greater distances. Several lines were out over deep water, east of Grain Spit, a few more due east seemingly skirting the northern edge of Sheppey. Oystercatchers are known to travel many kilometres for a safe roost, and birds have always been known to cross the four miles or so of Thames to reach the Yantlet roost. Perhaps some were Essex birds on a night out.

Curlews(!) Or, more to the point, no curlews(!) There's a thought. At other times, 'normal' roost movements from the Thames to roost in the Medway might land at first available port of call, Deadman's Island, and involve several more species, the most obvious (in size and number) being Curlew. But they were not a feature of these neap tide dusk flights. A token 30 tonight. Whatever causes the Oycs to change flightplans, it doesn't give the Curlews any concern.

Back to the show. Some were on headings for roosts other than Sharfleet creek. A small number went straight south into the Swale, lost to sight somewhere below Queenborough. A few had stayed north of Saltpan Reach, turning in to Hoo saltings. Intriguingly, some of these then seemed to gain height and double back on themselves, overland to the Flats. A small number of birds were certainly arriving  behind them overland as well, plotted back towards Yantlet Creek. Not unexpected; for many years it has been well known waders use the Yantlet to swap estuaries (yellow line). I could well have been missing many more Oycs on a bearing just west of that.

A few birders know about these movements but they are rarely documented, which is a loss. Think of those ridiculous 'Boris Island airport' proposals (thank goodness he busy playing Foreign Secretary for a while). Just shy of 1,800 Oycs had crossed his runway approach in 35 minutes, another couple of hundred cut through his terminal. These are scheduled flights at certain times of year. How to bird scare that lot? No wonder they merrily hinted at a bird exclusion zone being able to deal with the estuary. They have no idea of what goes on.

Another example for birders everywhere; never rely on just the formal WeBS counts and the like to protect your estuary. Nocturnal roosts can be completely different sites from the daytime. Neaps from springs. Any incomplete recording undervalues the true usage.

My starting point in 2013 had been the available printed records. Highlighting August maxima, such roost counts were either being missed or (outside chance) had not been happening. At certain times could the whole of this estuary actually be hosting numbers much nearer national importance than those being published? Latest printed WeBS continue in the same pattern of lower annual maxima. Tonight there had certainly been 2,400 on show from this small stretch of the southern seawall. It's fun finding out.