Monday, 22 February 2016

Hub airspace movements (Boris Waters, part 3)

The proposed estuary airport 'Boris Island' is on hold, with environmental concerns one of the biggest factors in getting the concept rejected from further considerations. (I always say 'on hold'- developers only have to win their case once, those fighting for the environment have to win every single time someone raises the matter.)

Now it seems any seaplane can come and go as they please within an estuary. At least there is some movement towards designated operational areas, but it is admitted these have only really been assessed for navigational purposes.

With my last posting touching on protection for the breeding species alongside these areas, there is now the matter of both wintering and migrating birds. Thankfully the Medway is a Special Protection Area. The short of it, the UK Government has committed itself to protecting the estuary for the value of the wildlife already there.


Looking at an aerial view of the estuary, one is instantly hit by the size and scale of the mudflats around the proposed operational areas. Bordered in yellow, the Ham Ooze complex. In red, Bishop Ooze and Bishop Spit. In green, Bartlett Spit and mauve, Wallop Stone. Together, hey are central to many birds using the estuary. Overwintering populations use various parts at various states of the tides, migrating flocks often base themselves centrally before beginning to search out other areas closer to shore. It is the most undisturbed part of the estuary, much of the river traffic sticking to the main channel (blue), and has very limited human disturbance.

To try to explain how these areas form such an important feeding site, I have chosen three wader species as examples.


1) Oystercatcher

Holding sizeable mussel beds, Bishop/Bartlett and Ham represent some of the best feeding areas for Oystercatcher in the Medway, and highest counts of feeding birds are nearly always obtained from here (concentrated within the light blue circles). Many of the best areas are often only available on the lower parts of the tide, and the birds have to concentrate their feeding either side of low tide, up to about the 3.0 metre mark when the tide completely covers Ham Ooze, from where they head to neap tide roosts. For Ham birds, this is usually south and east into the island complex (Stangate on higher tides), for the mid-estuary birds it is Darnett or (more often on the higher tides) the seawall at Kingsnorth. On spring tides all of the birds may head for Kingsnorth.



One further complexity is young over-summering birds. Not usually breeding until at least age of five (for females, seven for males), some, especially in their first summer, remain on the wintering grounds. Usually these birds roost separately from the adults in winter (often Bishop Spit) and in summer will use Motney when undisturbed, or Bishop Ness as an alternative (darker blue line).

Oystercatchers in the Ham Ooze complex, January 2016


2) Black-tailed Godwit

Routine use of the whole of the area has already been proved by colour-ringing undertaken on Oakham. The birds use the estuary to moult/rebuild fat reserves whilst en route between breeding grounds in Iceland and, in the main part, wintering grounds off Portugal.

This species readily changes favoured roost sites, and routinely crosses the main channel of the river. This year, since starting to return in numbers some three weeks ago, the spring moulting flock has used all the areas marked as yellow rectangles on the map (and act similarly during their prolonged autumn stopover). This is a species that seems to 'rest' certain feeding areas from time to time. One week the Rainham/Otterham areas may be favoured, the next Ham, the next mid-Channel and beyond. Birds will sometimes try roosting close to the southern shore, but are all too often disturbed by recreational activity. The roost on the eastern side of Motney is beyond the Water Treatment fence and less disturbed, but prone to going under on higher tides. This leaves Motney Saltings themselves which, although private, are prone to routine (almost daily) disturbance. So the birds often cross the seaplane operational areas and, as is typical of their species, do so at some height.


They might sometimes try to roost on Bishop Saltings/Bishop Ness, but are usually to be found on Oakham. Now the birds often choose to feed (orange lines) close to roost areas, which for Oakham are the northern flats close to the Long Reach operational area, and as the tide drops, Bishop Spit, sandwiched between the two operational areas.

These central areas, and Bartlett Creek, are their most favoured areas; they cannot simply rely on Otterham/Rainham Creeks, because of nearby human activity on the seawalls.

Black-tailed Godwit, having followed the tide up over Ham Ooze to Slayhills,
October 2013



3) Avocet

There are three main groups of Avocet within the Medway during the winter period. The Rainham birds are marked in white. The main roost sites are either Motney Hill saltings or Rainham saltings, the choice mainly dependent on weather or following large-scale disturbance (at both these sites the birds may roost on the water some distance off of the roost). East Motney may be used on a lower tide. Dependent on roost choice, feeding takes place on the tideline (white lines), in the main following the tide out throughout the cycle to low water.

The Bee birds (pale yellow), north of the main channel, may base themselves around Damhead/Humble Bee/Stoke creeks, and will also use Oakham Island as a roost. There is some flighting and interchange with the Rainham birds via Bishop Ooze/Spit (pale green lines).



The third group is the Funton/Greenborough group, roosting either on the seawall at Barksore, the main creek on Greenborough in Millfordhope Creek or on Barksore itself. There is a certain amount of interchange with the Rainham birds, as both will feed, in varying numbers, on the Ham complex from time to time. Rainham birds usually make up the larger number along Ham, having spread over from Motney/Wallop Stone as the tide drops. They will usually return to their normal Motney roost, but do decide to swap. Rainham birds are more prone to (mainly human) disturbance at roost, and can then be be observed flighting over to Oakham or, more often, into Millfordhope Creek (green line).

'Rainham' Avocet switching roost into Millforhope creek, October 2014


Three species, all routinely using the areas adjacent to the proposed operational areas. Will routine recreational seaplane flights cause them problems? Did the level of seaplane operations disrupt waders last year? Perhaps the events of 20th August 2015 answer that.

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20/8. A trip out to Shoregate/Ham Green to count the Ham complex. As expected, the Curlew and Oystercatcher numbers remained high. For Curlew, failed breeders and females begin to move in July, with the first of the adult males and juveniles from August; most are thought to be on their wintering grounds by September. Most Oystercatchers arrive in August and September. I was also very happy to have caught up with some of the first large flocks of Grey Plover. For many of the other migrant species, an early date like this produced just a sprinkling of the first returners, (I noted the Knot looked impressive in their breeding plumage).

I also managed a count of Bishop Spit and the eastern section of Bishop Ooze (as the view partly blocked here) just before the tide reached what I recognise as the 2.5 metre mark (the water reaching up to the end of Ham Green, but the majority of the Ham complex still uncovered).

The counts were routine for the final third of August:


I now made my way a little south, the plan being to watch the Ham birds as they continued to feed for another three-quarters of an hour while the tideline pushed them up toward Slayhills/Greenborough.

Then the seaplane appeared.

The first run, a moderate height some twelve-fifteen metres above and along the tideline to the edge of Burntwick, finished with a loud climb and turn to make the first of several landings/take-offs in Half Acre and Bartlett creeks, rising again just beyond the Ham Green wall. That first run was all it took; instead of retreating with the tide, the Ham waders panicked and flew fast and low into Millfordhope Creek until lost from sight. The birds that had been on Bishop could be picked out heading off the mud for Bishop saltings; they had lost between an hour and an hour and a half's undisturbed rich feeding on the Spit/Ooze.




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Three wader species mapped. Maps for other common wader species would detail similar usage at various times throughout the year. One disturbance described. As my tweets that day hinted, this wasn't the first time I had witnessed large-scale flushing during an important part of the tidal cycle.

I have yet to detail the importance of the area as a loafing site for wildfowl. That will be my next post.

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