Same view, different views (i)

Last semi-conscious thought, dozing off the night before- 'Beat the alarm. You've set it early enough but you've really got to beat the alarm. If you're set on going there, at a weekend, you've got to get there early.'

Up before the alarm. Positive thinking works sometimes. Race along the B2004, bike lights barely picking out the road it's so dark still, and through the pedestrian gate before the car park is unlocked.

Down the promontory. Almost a win, just the one dog walker with headtorch, recognise the dog, recognise the walker, a quick greeting and on.

Still too dark to scope, I hole the bike up behind the bench, and work in tight to the bushes to get out the wind.

Lots in close. Hungry Redshank, Dunlin, Teal, Wigeon, Shelduck, Brent Geese. 'Yup, this'll do- but how long have I got?'

Not long. Not long at all.

Bloomin' Countryside Act 1968.

It defined exactly, legally, what a Country Park actually is. They were set up to provide a natural, rural place for all of the public to enjoy, including those who do not necessarily wish to engage with the countryside. It provides everyone with a public open space that has an informal feel for a backdrop for all their 'whatevers' they want to do., as opposed to the more formal municipal parks and gardens in the towns. By necessity, Country Parks sprang up on the edges. In the countryside. In the case of Riverside Country Park, right next to my internationally important estuary. Actually, when you think about it, in the internationally important estuary. The seawall is a man-made end to it, the birds actually prefer 'core areas' including quiet undisturbed surrounding land.

Everyone has a right to go to a Country Park and enjoy it as they see fit (within reason).

A quick check of the watch. Yup, the gates opened five minutes ago, I've only got perhaps five more before...

Sure enough, from the path behind the bushes came a slow thump, thump off the path- which became a much faster as they turned the corner and seemed to realise they were not alone.

Lycra clad, (fluorescent of course), and carrying one of those ergonomically shaped water bottles that seems to be de riguer nowadays. Earphones shutting out the real world. They pulled up abruptly right in front of me (do they not know what a 'scope is? Can they not see what I'm doing?). Arching their back, breathing like they've just broken the four-minute mile, checking the strange contraption on their wrist (I think it tells them whether they're still alive or not).

Then, like a greyhound out the slips, away. (Until round the bushes again. Do they not realise I can hear them slowing up? Or see them walking back down the causeway when they think no-one's about? They'll probably be back in the car in a few minutes and off back home after pushing my birds off. (Through gritted teeth: 'They. Have. Every. Right. To. Be. Here.')

Looking back out, the mudflat had emptied. The Shelduck had shot off when the Redshank early warning system sounded out. The Teal and Wigeon had followed, just in case. And the Dunlin had scattered. The Brent Geese floated off, bemused by it all. (Through gritted teeth: 'They. Have. No. Right. To. Stay. There.')

Countryside Act 1968 vs Ramsar/Natura 2000/SSSI/the full monty. There's only ever one winner when those gates open.

-------

Putting the water bottle on the car roof, the jogger unlocked her car and took out a fleece top. New year, new resolution, this first short jog had been a lot harder than imagined, and she had felt it. She'd pushed herself to get round the end of the causeway, but had had to pull up with a stitch. Tried running again, couldn't, had to walk much of the way back.  So now she was cold. Still, it was a start(!) Positive thinking(!). This Park was listed on the Run England website as a good place to come and exercise, and it hadn't been that bad, certainly much better than running the streets.

Still, she had still felt a little creeped out by that old guy hidden up in the bushes at the end though. He'd just stood there, seemingly glaring at her for no apparent reason. What had he been up to? She spotted he'd had something on a tripod, a video camera perhaps? If he'd tried taking any pictures of her, she'd have definitely reported him. People really should feel safe in a Country Park, after all.

Probably harmless.

She picked the bottle off of the roof and got into the car. By the time she got home now the family would be up. She made a mental note to tell the kids about all those birds that kept flying about. She'd never seen so many before. They might like that. Perhaps she'd bring them one along day.

No, all in all, even with a creep in the bushes, she'd liked the park and felt good for her first attempt at running. Positive thinking- 'If you're set on going back there again, next time you'll make it out and back without stopping.' She laughed out loud as she really had nothing to worry about, from the look of him she knew she could outrun the creepy guy already.

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(The latest part of the estuary walks guide, Riverside Country park (west) has just been uploaded.)

A picture post, from January 2015

Curlew, Funton

Queenborough Spit

Inland sorbet- Darlands scrub bashing

Evidence of fox

Half Acre, becalmed

Twinney Saltings

Knot, Rainham Saltings

Black-headed Gulls, Sharps Green

Copperhouse Marsh- what remains of the gullery on a spring tide

The turnstone roost, Sharps Green

An old brickworks beach

The local driving range

Greenborough from Upchurch

Dunlin, Rainham Saltings

A ring from middle estuary- #DB97190

I trained as a ringer under my good friend Bill Jones, often out on Oakham Island. Although I now limit myself to the southern shore, and Oakham is frustratingly mid-estuary, just north of the main channel, I hope publishing an occasional map from some of his ringing recoveries over the years here on this blog will be of interest.

Greenshank Ring no.DB97190
Ringed: 9th August 2003
Found: 13th July 2005, Homledal, Hole, Buskerud, Norway.
Leg and ring found near Peregrine nest.
Found 704 days after ringing, 1,129 kilometres from Oakham.

This particular bird was an adult when ringed.Scandinavian Greenshank often pass through the south and east of the UK on their way to winter in south-west Europe and Africa. It is known these birds are highly site-faithful to particular staging areas whilst on migration, so highly likely to have visited the Medway before (and then after) the ringing date.

The recovery site and date could refer to it being back local to its breeding site, or possibly still en route to breeding grounds, when it met its end.

More details on Greenshanks (plus a map of international movements) can be found c/o the link on the BTO Birdfacts page here.

A crowd for the magpie roost

Well, if you can call three a crowd. And two weren't actually there for the roost.

The viewpoint has a charm of its own. Nice view, good birds, comfy enough bench. And loads of rubbish. Two of the Park rangers were on litter patrol, and cursing the so-and-sos who had dropped cigarette papers all over the place. Doesn't sound bad? The usual cans and bottles are quicker to retrieve and there are usually fewer to pick, but these soggy papers just went on and on and on.

I let them know their efforts are appreciated by some of Berengrave's user (especially when they go above and beyond the barrier rails to get pick litter right to the edge of the quarry). The response was a shrug of the shoulders and a weary smile. Appreciation isn't going to stop them being caught in perpetual pick mode. And this isn't the busy time yet. Wait until it warms up a bit.

All the time the Magpies piled in overhead. One loose flock of 32, about ten minutes before sunset, was the biggest single group I've seen arriving in the three winters to date. I refrained from pointing them out to the ranger. Two reasons; (one) she'd probably think me mad as a box of frogs, and (two) she seemed too intent on getting a decent count of those dropped papers for future stories. Observations and data. We all do it.

Taking the bait

Lower Halstow on the rise is usually good, but as I cycled to the end of Lapwing Drive I spotted something I hadn't seen there for many a year. A man, in waders, with bucket and a pitchfork. 

When the Parish Council set up the Brickfields community space, the arrangements included 'no bait digging'. Still clear as estuary mud on the entrance sign. There aren't many places left for baitdiggers along the southern shore. The Country Park doesn't allow it, the Wildfowlers don't at Funton. It shouldn't happen along the western side of Motney, but it does. Concentrated numbers are there Thursdays and Fridays before big weekend matches, most I've counted was 32 (sometimes the Sheppey lads come over when they feel their spot near the docks is exhausted). Otherwise, it is 'locals', and i find them very easy to get on with, being able to see their argument that they aren't causing that much disturbance (an essay in itself, another time- essentially the waders don't spook around them so much as the diggers don't stare them down).

But today was an ornithological opportunity. An area where no digging takes place has had a body out digging along it. I'd still count, but I was more interested in disturbance levels.

Clear from the start the flightiest wader had put off- just two Lapwing. The two Whimbrel were also missing from their shared haunts (the rocks along the shoreline and the causeway), the first time this winter I haven't turned them up. Had the chancer been concentrating along the shore? More crabbing than lugging? The local diggers have been telling me we're into the harder times now, but there's still a few if you know the signs (made me think of adult waders feeding better than juveniles- ask look in a visiting diggers' bucket and it'll have about a third of that of a local's). It is the time of year for lower numbers, and many of the remaining interstitial prey go in for self-preservation by keeping deeper in the mud during the colder times.

Crabbing would make sense. Old hands turn the rocks by hand, chancers usually don't like getting dirty, use the fork, and forget their bait-diggers' code of conduct and not put back. The Ringed Plover pre-roost assembly just past the causeway helped confirm- down by three-quarters to about a dozen. Hang on though, one or two look much 'darker' than last week's birds- there might have been some changeovers? Mind you, the Greenshank have gone too. One or two of these changes on their own might be circumstantial, this might be too many.

The wildfowl weren't much use, most staying a distance out regardless. Brent normally like to drop in to Twinney Creek for fresh water and ablutions. None. None on the fields, less than a hundred out around Gull Island. A few would sneak in by the end of my hour and a half there, but they seemed at sorts today.

Mind you, I don't know why I'd bothered. The embarrassed glances the digger gave me as I went past him had confirmed it for me. He'd read the sign.

Undercover pic of man.
In waders, in bucket.
Apparently.

Ruling the roost

Though the covering tide at Funton was at a nice lazy start time of just before nine, it had to be remembered that this meant Thursday and Friday would have seen 'morning flights' perfect for the guns. Sure enough, when I arrived no wildfowlers- but very few wildfowl on show either. One of the commercial shoots was in full swing, and their gunfire was making the remaining duck wary.

The waders had clearly been shuffled as well. There is a well-used, well-known beach at the mouth of Chetney Canal that holds a large roost of Oystercatchers. For the past week or so they had been pushed off by the Knot and had moved further up the Chetney peninsula, but with the tides now getting higher some of the Oycs were claiming squatters' rights on the beach. They had settled not in a 'lump' as usual, but instead spread out along the small beach. The Knot, which had favoured feeding in Halstow/Twinney Creeks of late, started to arrive in small groups to head straight for the Canal roost, but were now not prepared to settle among the Oystercatchers. Instead they seemed to hover overhead for a short while before setting off on a circuit of the Funton complex as if to make another choice. The eastern saltings were already full of Dunlin so, for the first time in quite a while, they had to put down alongside the Avocet under the Barksore seawall. Unable to crowd together, they were strung out, from the concrete barges all the way to The Shade.

I felt I was being dumb. Why had those Knot not headed for their other preffered roost? What was I missing? You know, the roost site just near where the Greenborough wildfowlers sometimes operate... ah, that'll be it then. Perhaps the gunners have been out in force.

The gunners have to make the most of the tides and the weather. Many syndicates work to a small limited number of 'days' per month, so will cancel a day if the weather is bad and then work hard to reschedule if they can find a gap; overshoot an area and the quarry wise up. they might also bring forward a shoot date near the end of season if weather is better.

The tides had been good. The weather had been good. And the Oystercatchers had taken their chance and got their roost back.

- - - - -

Many types of quarry have their seasons finish on the 31st January. Snipe, Woodcock, Golden Plover, Moorhen and Coot. And wildfowl- but only in part. 'Inland' shooting certainly ends on the 31st, but shooting below the high water mark continues up until February 20th.

The local game shoots finish February 1st, so much of the onshore disturbance disappears and the birds will be quick to take advantage of safer feeding/roosting areas along the seawalls or on pools (guns will still be out from time to time for rabbit and the like).

I remain unsure as to how many local birders appreciate Saturday is the busy day for game shoots- Sunday shooting is not allowed by law, so to cut down on disturbance, weekday shooting rarely happens. Why weekend birders often hear so much gunfire if out on a Saturday.

Some English counties/county boroughs do not allow Sunday wildfowling, but Kent is not one of them. (Bans are in place in Cornwall, Devon, Doncaster, Great Yarmouth County Borough, Isle of Ely, Leeds County Borough, Norfolk, Somerset, and the North and West Ridings of Yorkshire.) Again, just as there are more birders about at a weekend, so are there more wildfowlers. A quick-tot up, this wildfowling season I've made just over 30 visits to Funton for the rising tide, and just twice have I been out the same time as the wildfowlers. Before I really studied the Medway, when I was a weekend birder, I continually worried about overshooting and disturbance, now I've come to understand a little more just how used to switching roosts/flights these birds are.

Them cr*ppy Starlings

It was on my 'to do' list. Find the local Starling roost.

Problem? I knew it was outside my birding area. When I moved back, I deliberately set myself the task of sticking to the south shore. During the autumn I would pick up some nice movements of Starling in the first couple of hours of the day, heading west, and I was always tempted to say 'migrants'. But the problem was I'd have similar numbers east in the evenings.

And then they'd continue into the winter. I tweeted a few months back about the numbers passing The Brickfields in the mornings, guaranteed close encounters. And if I watched from Raspberry Hill, out over Chetney, I'd see probably the same birds back, flying out of my self-set recording zone.

Infuriating. I pondered a few times last winter that the answer could be Murston, I knew it was hardly birded nowadays. I was close. And to add insult to injury, I was extremely close when I watched Chetney from Raspberry Hill. Now if I had just turned around...

Monday evening had seen me on Basser Hill, watching Barksore. Some nice stuff going on, highlight probably Chetney's Golden Plover, which had moved off the frozen grass to the slightly more broken harrowed fields.

But then, as I walked off the hill, I just, just glimpsed what could be the tail-end of a murmuration breaking the skyline for a nano-second. Probably about four kilometres away, but, yup, there it was again- a murmuration.

I bleated on to a friend about it, who had made the mistake of once saying they'd like to see a murmuration, plus they owned a car, plus I knew they were free Wednesday afternoon.

And no need to hunt the site down, it just so happened a few days before the site had broken, as 'just behind Morrison's distribution centre', via the twittersphere.

Looking at the OS, it could only be Cold Harbour Fleet, so fifteen minutes before sundown we were stood on a mound at the end of the road by the fleet. I was immediately annoyed as the sky was full of Starlings, but about a kilometre and a half south over Castle Rough. There were just groups of fifty to a hundred Starlings going in to the Fleet, with a small murmuration of about 400 birds above it.

Patience.

I realised the Rough lot were gone, and then suddenly a wave passed over, with an amazing sound of pifp, pifp, pifp, going off all around. We were right underneath, in a guano rainstorm.

The next eight minutes were sublime. No words for it. How taken was I? I didn't even bother to try to count, that's how taken. Well worth slipping over the count-y line for.

My friend was blown away by it too. Though when we got back home, I did feel the need to promise I'd clean their car the next day, just in case I ever needed to get them to go along with one of my subtle hints again.

Site Guide- The Strand

A second walk has now been added to the site guide page, covering from the Strand Lesiure Park to Cinque Port Marshes.

Part of the Strand swimming pool wall mural-
how Medway birders dress, apparently

A picture post, from January 2014

Oystercatchers at roost, Swale Ness

Woodpigeon to roost, Berengrave

Brent Geese, Twinney

Turnstone, Horrid Hill

The grazing regime, Chetney

Back down Funton Reach, Chetney

Upgrading the orchards, Meresborough

Black Brant, Twinney Saltings

East to Bloors, RCP Visitor Centre

Distant Avocets, Rainham Creek

Avian exotica, Gore Farm

Waves on the pool, Bloors Wharf

Ringed Plover, Rainham Creek

The Sheldwot, Cinque Port Marshes

All going swimmingly

So, it's a high six metre tide in the late afternoon, and the wind's a strong west-north-west. The Avocets might be going to break the 'mostly' rules. If I type 'x mostly/mainly/usually does y', that means there are exceptions, and they will usually exhibit said exceptions quite soon after any posting.

So yes, I am on record as saying the Avocets will mostly be found in Otterham or on Motney over the tide. But the Otterham roost, though sheltered, goes under on higher tides when the birds move to Motney Saltings. On a six metre tide Motney is touch and go without wind, but today will be onshore and rough, and they'll be under. Birds will ride it out there, but closer to shore. All it takes is one dog walker where they shouldn't be, and the Avocets will head for a third choice roost. I decided to watch close to Rainham Saltings.

 

The saltings are found between Bloors Wharf and Horrid Hill, and on neap tides provide a useful roost for waders, and a good rest area for wildfowl. However, they can, and frequently do, go completely under, when the duck head for Nor and the waders for Bishop. Today just the barest of slithers would remain dry. The Avocets, having been driven off Motney (I love it when a plan comes together), could only hope for a chance of a dry roost. But with Horrid Hill acting as a breakwater, they could swim out the high tide. I watched them for more than an hour. Only a few tens of birds had any ground to start with. As soon as they could, others would haul out and join them. But the vast majority had to remain swimming for the whole time I was there, apart from the couple of circuits when they spooked and took flight. Both times they quickly returned to the water, there was nowhere else close enough to go.

The other waders that had been pushed off Motney with the Avocets had mainly headed mid-channel for the eastern end of Bishop Saltings, which are relatively protected in such conditions.

Black-headed Gulls had already started a big pre-roost gathering in the bay by mid-afternoon, with more than 3,400 present before the main dusk rush had begun. By the time that started, the flooded saltings of  Nor Marsh had begun to re-emerge, and some dropped in there, otherwise it was straight on to the main roost area in Half Acre. Larger gulls headed out for the more open waters east-northeast of Friars Saltings, to wait for the flats to reappear. They were still coming in as the light gave out.

The afternoon had felt a precursor to cold weather movements, a cold snap moving birds on. Tomorrow could be a long day in the field. I'm going to need a bigger flask.

A Stock Dove sunset

After low numbers in 2014-15, the local Stock Dove roost has returned to three figures throughout this winter so far. They use a small copse on an old industrial site, where they are relatively undisturbed. It is right on the edge of the saltings where the birds can often be found feeding, so they often leave their pre-roost assembly late, even sometimes right on sunset. I thought it likely to be a picturesque watch tonight, but had several opportunities to count the birds entering the roost courtesy of a low-flying helicopter.

'Stock' in this is another name for a tree trunk, and Stock Doves routinely nest in holes in mature trees. Over on the northern side of the estuary they took to any old hole, regularly nesting in gaps between the concrete pilings and roadway of Kingsnorth Power Station's Oakham Ness jetty. Nests were found up to 1.5 km offshore, over the mid-estuary deep water channel of Kethole Reach.

As an aside I was told today the E-On signs at the main gate at Kingsnorth were being taken down today, and a new company logo was waiting to go up. The plan had always been assumed as being the old owners would keep the site for eventual construction of a new station at some point. Whether the site has now been sold on, and what purpose, no idea.

A Motney morning

The first chill morning for ages, with a cold wind to boot, was not enough to dampen my enthusiasm for getting out early on a morning without rain. I chose the eponymous hill of Motney as a viewpoint, as it had been a while since I'd enjoyed being buzz-bombed by Collared Doves there.

They roost somewhere on the 'mainland', but each morning race up the peninsula to check out one particular garden, where the owner has a very generous feeding regime; flighting past low, in groups of up to eight, I counted 120 through in the first fifteen minutes after sun up; an average morning.

Woodpigeon also come past in numbers, though thankfully a little higher. They usually cross the narrow Otterham Creek heading for the industrial-sized seed feeders dotted about the commercial shoot on Bayford Marsh. If for any reason the Motney garden cafe is shut, the Collared Doves head over to join them.

I appreciate that is not every birdwatcher's cup of tea, but it made for something to count. And I'd have missed the small flocks of Siskin going north as well.

For the hour I was stood there, I was serenaded continually by a Song Thrush, perched up and out against the wind. While I've been used to them singing these past few weeks during the mild weather I really thought the colder night might have dampened the hormones. Keen bird in a keen wind.

What's in a name?

Sometimes the sheer scale of the estuary puts people off counting. It doesn't really help when the names for certain areas get muddled Over the years, birders have noted their counts from along the Funton road as being at either 'Funton', 'Funton Creek' or 'Bedlams Bottom'. Does this matter?

Well, if you want to understand why the birds use certain parts of Funton more than others then, yes, it does. On a morning like today, it helped me break the mudflats down into more easily countable units, and I can make a stab at why the birds are where they are.

The Funton road runs for some 1.8 km alongside the hypotenuse of this large triangle of flats. There is little chance of the muddy habitat being uniform throughout, and the birds are attracted to certain parts at different times of the year.

Maritime and Coastguard agency approved maps tend to use many more place names than the Ordnance Survey maps will quote, for good reason. Not so freely available for use on blogs as Google Earth, I've roughed out the main areas on the picture below

Starting from the west, in yellow is Funton Creek. A supply of fresh water. Why so many waders and wildfowl are found on the curve of the outlet when uncovered. The flats here are some of the last good feeding areas to go under on the rising tide.

In green, Funton Reach. It helps to know that a reach is a straight stretch of river. Tide flows fast in such channels and often reaches have steeper banks than elsewhere. This is why many of the duck hole up in Funton Reach at this time of year,usually along the the southern bank, out of reach (pun intended) of the wildfowlers' guns.

Funton Reach then turns into The Shade (orange). This is the opening joining the Funton complex to Stangate Creek, a major creek in the eastern basin of the estuary, deep, fast-flowing and mainly channeling into/from Twinney and Halstow Creeks. The Shade can be appealing to wildfowl and grebe seeking respite.

To the south and east of Funton Creek is Bedlams Reach (you may know this name from the riding school on the southern side of the road). Why Bedlams? This old creek had not been running with any strength for a few hundred years, and not at all for the past century. The creek has been (and still is) silting up, which is why Bedlams Bottom represents the end of the line for any boat willing to risk the channel (except for the Sheerness lifeboat, which occasionally trains for mudflat rescues here). So Bedlams is a dead creek. Less oxygenated, uncovered for longer periods, there will be a big difference in prey abundance, especially in the 'true' Bedlams Bottom (why on autumn passage few waders feed there, preferring the Funtons).

Bedlams creek from Bedlams Bottom

Each species has it's own story as to why they use certain parts at certain times of year, and I'm certain these stories will be a mainstay of this blog in the future. Just one quick example, from late December onwards, as prey stock becomes exhausted elsewhere, birds waders will start to feed more on Bedlams. But when the first smaller flocks of the annual December Knot influx arrive, they will often settle mainly on Bedlams first for a short while at first as there is less pressure from other species and prey abundance in those other areas is leveling with Bedlams. Once Knot numbers rise they start to use other areas more.

It is of course all a lot more complicated than this! The purpose of explaining the names of the Funton Complex is simply to help people bird these mudflats more easily.

If all those names are too hard to remember, you can always get a little help from the Kent Wildfowlers. They own the roadside saltings here and have divided them by a much simpler straight line method into two shoots, Funton West and Funton East. Hence those big cut-out letters on their signpost by the main lay-by. Just remember, much of the east is pure Bedlam.

The Sharp's Green Bay Turnstone roost

They were back today. Nearly 250 Turnstone were spread about the rusting hulks in Sharp's Green Bay, joined by a handful of Lapwing, Redshank and Oystercatcher, a few Grey Plover and single Ringed Plover and Dunlin.

I decided to watch them out from roost to see where they intended to feed, so took off up Horrid Hill to wait. Leaving from about an hour after the full, in tens and twenties, a few swung west, but most headed for the mud reappearing in the creeks of Friars Saltings just east of Nor Marsh. From there a few would later tag on to the Dunlin flocks coming south to feed alongside Rainham Creek, but the remainder, well, remained.

These would undoubtedly be aiming to feed on the two large mid-estuary mudflats, Bishop Ooze and Bartlett Spit, which have a substantial amount of rock spread around them. This can be derived from the large amount of seaweed spread on the southern flanks of these flats (these seaweeds need a holdfast which the rubble supplies). From Roman times onward much of the estuary was reclaimed by creating seawalls, and then farmed for several centuries. The rising tides have in turn reclaimed the estuary basin over the years.

On a rising tide the Turnstone will, in the main, move back from Bishop and Bartlett to Rainham Saltings/Rainham Creek, and from there any wanting to keep feeding move to Ferol Peak, the raised flat between Copperhouse Marsh and Nor, which is one of the last areas to go under. They will then choose a safe roost site.

On quieter weekdays in the Country Park it can be entertaining to watch Turnstones take the short 'overland route' from Rainham Saltings to the Sharp's Green roost, whizzing past low at head height.

So, within the western basin of the estuary, Turnstones roost mainly either here or at the Strand. Smaller numbers also occur on Nor, Friars and sometimes Motney. In recent years smaller numbers have been recorded for the whole of the estuary on the national WeBS counts, but this could be thanks to what I term the 'weekend effect'. Sharps Green Bay falls within the Riverside Country Park, and the roost lies just 111 metres offshore from the Park's most popular walk, the Horrid Hill causeway. Whilst the wrecks are themselves very,very rarely visited by people, dogs are often allowed to swim out some distance from the causeway. I have not looked more deeply at cause and effect, but am aware my higher Turnstone counts never really happen on a Sunday(!)

(The Sharp's Green Ringed Plovers seem to do something similar- they are often on the wrecks of the smaller pleasure craft, but also go missing for days at a time. I'm still having a hard time tracking their alternate roost down.)