Rather than waste the time on the water with a lengthy lecture full of facts/figures, the talk was pared down to be short, general and informal, but with this lengthier blog then available with additional info after the event. Hope the general approach here of interest to some.)
Arrivals and departures- the early autumn avian hub
Forget the argument for a Boris Island. The north Kent marshes already handle internationally important numbers of flights every year.
The marshes are well known for the high numbers of overwintering wildfowl and waders. Why each of the north Kent hubs, the Thames, the Medway and the Swale, is recognised as internationally important and are internationally protected: Ramsar, SSSI, MPA.
The north Kent marshes also hold significant numbers of important breeding species.
But what about on migration? How many birds use the Medway? And what do they use it for?
Scheduled flights in July/ August
Wader passage starts in mid-June. For several species, the female's work is done by then, as she leaves the male to look after the eggs/young. Failed breeders and immature birds (some do not breed until they are four or five years old) also wander back in small numbers from mid-June onward. A hardened birder might enjoy getting out and finding the few returners, but not really a spectacle- yet.
By the last 10 days of July more people are noticing a build in numbers, as small flocks start to appear- tens, twenties for most, but some species already well into the hundreds. The rest of the breeding adults have started to move now. They will often desert their young, who then only follow on a few more weeks later.
The East Atlantic Flyway
The Medway is one hub within of a large network of refueling stations strung out along the main carrier route between the high Arctic and Africa. As we will see in the individual species accounts, different species have different travel plans for travelling the flyway, and will use the Medway in different ways.
Birds are also leaving us now. Our breeding seabird species have nearly all left. A simple premise with colonial nesters- as any colony is a magnet for predators, as soon as your young fledge, move away.
Some that are estuary feeders might only move a short distance from colony (e.g. Common Terns, often to adjacent creeks and fleets), while others move their young to more open water elsewhere (Sandwich Terns, which feed more readily in open water, have now moved off to places such as east Kent).
Gull species that feed on the flats might now spend their time on higher mud nearer the shore, rarely visiting the colonies. And most will be back on the water to roost. Mediterranean Gulls are harder to find as, feeding more on insects, tend to move inland en masse (mostly via the North Downs).
But there will be more arriving than departing.
Like people-watching the crowds at any hub airport, a little hard to tell who's coming/going by a quick look around the terminal; those same departing Gull/Tern species are also arriving from elsewhere; colony dispersers from elsewhere around the UK coast/ near continent. Why any series of counts of the estuary will never really give an idea of the total number of birds that pass through.
The waders are easier to call as arrivals. There were so few here for the summer for a start. And there can be many. Of course, we concentrate on peak wintering numbers, and some arriving now will indeed stay for the winter. One species known to prefer carrying out post-breeding moult on wintering grounds is the Curlew. July to March, some birds spend more time here each year than anywhere else, but we just think of them as 'wintering'.
But many autumn bird move on.
Inter-continental journeys, from the north American high arctic, or from Siberia, then on to African shores, often have to be made in stages. Too long a journey for a single flight. Stop and refuel, stop and refuel.
Often not as simple as a quick feed-up, often need a few days, weeks, to rebuild reserves. These are their scheduled short-haul flights; many older birds use the same estuaries, even the same small creek on the same estuary, year after year; they enjoyed the facilities before, so they'll use them again.
This is why some species actually have their peak numbers in autumn, rather than winter as many of us are led to believe.
And if you look carefully enough, some wintering species have two distinct peaks, a mid-/late- winter peak and an autumn peak- a gap between the movers and the stayers. Others have numbers departing for warmer climes obscured by arrivals from other continental hubs (continental hubs tend to be much more challenging in winter than those on our mild UK Atlantic coastline). Monthly counts in autumn may look fairly similar to winter, but the individual turnover has been much higher than the numbers show. (Where individual monitoring through methods such as colour-ringing and radio-tagging comes in useful to prove hub usage.)
Stopovers, long and short stays
Migration isn't cheap. As well as fuel, there's feather wear and tear. All birds have to replace their plumage. This takes more time in larger birds, for most waders around 90 days.
Redshank love the stopover facilities on the Medway. First birds are back on the flats post breeding, late June. Local breeders are joined by birds from the near continent, then later from northern Europe and finally Iceland. The 'continental' birds are most likely to continue south after moulting, on to as far as west Africa for the winter. The Icelandic usually tend to stay on here- they don't mind the cold, being slightly bigger birds. All populations within a species have different degrees of attachment to an area. Redshank overall numbers are smallest in summer, highest on autumn passage, somewhat lower during winter. Why we need to survey through the whole of the year to understand what goes on.
Several species behave similarly but differently, with populations having different strategies; when Grey Plovers arrive, some wil moult and then stay, others simply refuel, then carry on south to moult later.
Diverted air traffic
Youngsters have a general idea where they're heading, but are more prone to land at unscheduled sites. Why those rarities that twitchers chase often turn out to be youngsters. If they find a rare adult wader, why twitchers then they have high hopes it might well turn back up same time following year.
Customs on arrival
We've seen it isn't that easy to spot the incoming, what with so many other movements going on during the twice-daily ebb and flow. The Medway, as an 'inland estuary', doesn't really have a coastline, so we don't see birds fly 'in-off'..
So, one of the easier ways to pick out arrivals is on a covering tide. Birds are wary. Even if they know the area, they will still need to check that last autumn's safe roost site is still safe. Juveniles have no idea, they watch and wait out on the flats, often until the tide is up to their bellies, before dashing to a roost; they will have watched local birds leaving long before to settle for the high tide.
Also, the main runway for arrivals appears to usually be mid-estuary. Makes sense, the quietest areas will be central to this 60 square kilometre eastuary. A chance to rest up upon touchdown before exploring. Small flights of 10s, 20s, 30s can often be seen dropping in from height (local/settled birds rarely bother to gain too much height when traversing the area- why waste energy?)
So, the individual species- how do they use the Medway? A short cut-out-and-keep guide follows.
Plain spotting at the hub:
A short guide to the common wader species
found on the Medway during late July/early August
found on the Medway during late July/early August
The following accounts are simplified guides to the commonest waders using the Medway as a hub in July and August, including:
- Points of departure
- Final destinations
- length of stay in the UK
- Reason for visit (their moult strategies whilst on the Medway)
- Passenger number estimates: average maximum figures for July and August are taken from WeBS/KOS reports. There are two sets, illustrative only, as surveying has often been incomplete since the turn of the century. The first figures, for the 90s, were done partly when the Medway was better surveyed. The 00s counts are now acknowledged as probably unfit for purpose. Finally my comments, which are based on my own nigh-daily visits to the estuary, from 2013 to date.
Local breeding population: Most choose not to fly far from the estuary, though a few (mainly their youngsters) head south (to near continent, exceptionally as far as Africa).
Local non-breeding population: stay local all year, augmented by very young Norwegian birds (who from age of two tend to move nearer their natal grounds in summer).
Main winter arrivals are not until October/November. Chiefly Fennoscandian birds, mainly Norwegian. Others from the Low Countries, with small numbers from Iceland e. to Estonia.
Moult (adult)- postbreeding, complete: flight feathers usually changed September- December, may occasionally arrest during passage (technical term- the moult halts then later begins again from the start by changing both new and remaining old flight feathers). Why the bulk of our wintering birds, moulting somewhere else along the flyway nearer to their nesting grounds, do not start to arrive until much later in the year.
Average nos 1990-99 July 616 August 1,008
Average nos 2000-09 July 700 August 670
In recent years more sampling has revealed numbers to still be in four figures from around now, but the picture is complicated by individuals using one estuary (Greater Thames) to feed then roosting in another (Medway), if disturbed or if spring tides reduce carrying capacities- numbers can be tripled over certain tides
Chiefly short-distance flights at present, switching between local breeding estuaries (east Anglia southwards) and local moulting grounds (such as the Thames at Cliffe). They then Settle on a choice of estuary for winter, usually within southern UK- but not necessarily the one they bred on.
Moult (adult)- postbreeding, complete. Flight feathers start in July, to October (November). Winter numbers on the Medway do not peak until after this time.
Average nos 1990-99 July 66 August 182
Average nos 2000-09 July 135 August 147
In recent years, due to increasing breeding numbers, July numbers have continued to grow, but most will have left for safer moulting areas by month end- August has similarly low numbers nowadays.
A collapse in numbers in recent decades, now almost extinct as a breeding species on the estuary. Any remaining local birds will be joined by birds from northern Europe for the winter, with 'tundrae' (birds from the high north of Scandinavia e. into Siberia) passing through in variable numbers during autumn. A definite early autumn peak in passage numbers, but birds 'short stop' and may only be present for a short period. Counts are often missed.
Moult (adult)- postbreeding, complete. Highly variable sequences, usually starting on breeding grounds, from mid-June to as late as October, most suspending the primary feather moult during peak passage period (August- September). Right now they will have grown a small number of new flight feathers to help their journey south, our breeders perhaps going as far as France/Spain while the Scandinavians 'leap-frog' us to go as far as Africa
Average nos 1990-99 July 124 August 904
Average nos 2000-09 July 12 August 155
In recent years numbers have remained low, just double figures most days, although the odd three-figure count does still get made- just as for breeding, Ringed Plovers find our increased activity and urbanisation have made the Medway less attractive. Any high shoreline fronts (their favoured areas) are too disturbed (or more often flooded by increasingly high spring tides) for hold them for long.
A small number arrive around now and will remain to overwinter. Origins unknown, possibly British/ near continent.
Varying numbers then arrive in late autumn/early winter. ('last minute bookings' to escape harshest of the winter weather on the continent). Further urbanisation of the green areas surrounding the Medway will reduce the Medway's carrying capacity- birds that spend the day roosting on marshes such as Chetney do need inland fields in which to feed at night.
Moult (adult)- postbreeding, complete. Starts late May- July, often suspends July-August, restarting mid-September- early November. July August is the move from breeding grounds, the flight feathers are pristine at the start of winter ready for 'escape movements' from bad weather.
Average nos 1990-99 July 7 August 40
Average nos 2000-09 July 11 August 97
Numbers on the Funton mudflats have, in recent years, been slightly higher (up to around the 200 mark) and, interestingly, these birds then tend to continue to roost on the flats rather than join the later arrivals in the fields.
First landings are usually scheduled for late July, the start of adult passage, with youngsters then not turning up until September.
Moult (adult)- postbreeding, complete. Starts on wintering ground or on specific staging ground. Starts flight feathers between August- early October, but birds starting from September onwards will suspend from mid-October and only restart in spring. ('Suspend' another technical term; stops, then restarts later from point where halted earlier- so, different from 'arrest'.) Birds present on the Medway in early August will either be adults about to either pass through quickly, or here to establish a feeding territory and remain to moult. Why easy to miss the highest counts if only counting a few times each month.
Average nos 1990-99 July 180 August 1,556
Average nos 2000-09 July 7 August 131
Recent numbers still reflect 1990 figures. Most of the larger flocks do tend to favour the less-disturbed flats mid-estuary, perhaps hinting at their being 'short-stayers'.
Small numbers will have been arriving since June, mainly from the near continent. Some return year after year to winter, mainly late Sept-Nov, but the biggest numbers only will only be seen if they need to escape poor bad winter weather. Biggest numbers will always be on the fields rather than the mudflats.
Moult (adult)- postbreeding, complete. May/June- August/September. The species has a very fast moult of outer primaries to aid early autumn movements.
Average nos 1990-99 July 313 August 513
Average nos 2000-09 July 138 August 347
Another species where older records better reflect the present position- incomplete coverage has underplayed the estuary's true numbers. The drier the summer, the more easily detectable out on the mudflats (instead hidden up in the harder-to-view/count fields spread around the marshes).
Small numbers on autumn passage. Biggest numbers are December-February, made up of wintering wanderers who, having spent first part of winter elsewhere on the east coast, take a short flight to enjoy the Medway cuisine. Fussy eaters, Knot rely on molluscs more than many of the other calidrid species (why they are fixated with only certain muflats here).
Moult (adult)- postbreeding, complete. Might start on breeding grounds, but usually not until in wintering area. Subspecies canutus starts when reaches Mauritania in August-September, subspecies islandica start as soon as arrive in western Europe (July/August) but these stay mainly on recognised moult grounds (e.g. Morecambe Bay, the Wash); 'our' August birds are usually of the race canutus, from western Siberia, heading for Africa.
Average nos 1990-99 July 0 August 171
Average nos 2000-09 July 0 August 50
Recent years very similar, and erratic in number from year to year. A clear example of flight diversions by way of a departure from the scheduled route- here, birds usually relocate after a day or so, probably having overshot the Wash or the Waddenzee (Netherlands).
alpina- northern Europe to north-west Siberia- these are our overwinterers, not booking in until October/November.
Moult- postbreeding, complete. Just as each race has its own wintering preferences, each has a differing moult strategy. Schinzii moults after migration, alpina may start and then suspend before migrating, often to complete on other specific staging grounds along the flyway before finishing in October (just in time for many to make the final flight to their north Kent wintering grounds). Why many of the small number of adults seen now are likely schinzii, making short stopovers before racing off south.
Average nos 1990-99 July 350 August 1,774
Average nos 2000-09 July 8 August 443
One of the few species where a decline appears to have continued; hard work nowadays for three-figure count at this time of year. Clearly refueling elsewhere. If their main flyway is west to Norway then down through Europe, most will stick to the continental side of the Channel- when they do drift over, they stay more to the south coast than north Kent.
Often higher numbers in autumn than in winter. First returnees from Iceland arrive late June, continuing to build through August, to make a moult stopover, with many then moving on to spend the later winter months on the south coast, over in France, or as far south as Portugal.
Moult (adult, islandica)- postbreeding, complete. The flight feather moult takes place after main flight from Iceland, from August to December, when birds may then move on. Birds seen now on the Medway will intend to stay here on the north Kent marshes to see out this important stage of their moult cycle.
Average nos 1990-99 July 232 August 979
Average nos 2000-09 July 298 August 570
Nowadays, four figure counts in August are the norm. (Reflecting the growth in breeding numbers in Iceland).
Small numbers pass through in early autumn. A species which we see more in the spring than the autumn. The bulk of their population moving through the UK (breeding in Iceland) adjusts their flightline to Africa, sticking to the west via Ireland. The birds we see in the autumn are more likely from Scaninavian/Siberian populations.
Moult (adult)- postbreeding, complete. Usually not started until on wintering grounds in Africa, September/October onwards (a neat aide to separating from moulting Curlew in distant flight at this time of year). Stopovers here are for refueling purposes only.
Average nos not readily available from the old printed annual reports. Partly because they weren't here in any number then. Whimbrel can be fickle and switch refueling sites every few years. Recently a three figure roost has become regular around Nor/Friars/Oakham at this time of year, but only for a matter of a few weeks before continuing on to the wintering grounds to moult.
Annual peak numbers are in the autumn, usually September. Safe moulting out around the Medway islands. The drop off in monthly counts later in the winter is probably down to feeding strategies as Curlew, more specifically the shorter-billed males, prefer to feed in fields as winter progresses. Further urbanisation will affect the Medway's carrying capacity.
Moult (adult)- postbreeding, complete. Primary flight feathers start in July/ August, shortly after arriving on wintering grounds. Take 12 weeks to complete.
Average nos 1990-99 July 786 August 1,599
Average nos 2000-09 July 134 August 178
Recent numbers reflect the more methodical counts of the 1990s. In fact, a series of counts will often produce peaks- like Oystercatcher, under certain tidal conditions/ disturbance levels, many of the Thames birds will join the Medway (and Swale) moulters. Another reason why counts should be coordinated not only within the Medway estuary, but on the Thames and Swale as well.
Moult (adult)- postbreeding, complete. Flight feathers start in late June to September. Usually remain on moulting grounds throughout, but can still continue on migration before finishedif needs must (a strategy more prevalent in continental birds).
Average nos 1990-99 July 2,294 August 3,523
Average nos 2000-09 July 208 August 404
Numbers moulting within my study area (the southern shoreline) probably reflect an autumn population perhaps only a little under those 1990 figures. Get the count time right (on the rise for birds retiring into the spartina) and single creek roosts here can exceed 700, 800 birds.
Moult (adult)- postbreeding, complete. Moult of flight feathers might start on breeding grounds, then suspend until reach moulting grounds such as the Medway. Moult takes place July to September (though some may then suspend unifinished moult until they reach their wintering grounds).
Birds here in early autumn are here for safe moulting.
Average nos 1990-99 July 21 August 60
Average nos 2000-09 July 17 August 54
Greenshank behave a lot like their red-shanked cousins, and are often hidden up over the usual WeBS counting period (high tide itself); by counting birds into roost, three figure counts are in truth easily achievable during August.
Greenland/Canada: arriving slightly later, for winter.
Moult (adult)- postbreeding, complete. Birds make a choice of two strategies. #One, starting late-June- August by birds intending to overwinter in northern hemisphere. #Two, for birds overwintering south of the equator, flight feather replacement commences mid-September.
Many of the Turnstone on the Medway in the early autumn peak show no sign of a wing moult, hinting at a short stopover and a long journey ahead.
Average nos 1990-99 July 97 August 726
Average nos 2000-09 July 22 August 43
Again, counts are more usually closer to the 1990s. A species that shows a clear weekend disturbance pattern (more often heading to central estuary roosts rather than the old hulks closer to the shoreline footpaths).
Hopefully this short introduction to the Medway's early autumn bird migrants has helped illustrate the large numbers of waders that will use the estuary during an autumn. It is a complex situation, with every month different; making sense of the way the birds continue to use this estuary is challenging but highly rewarding. Because the estuary needs to be understood if we are to protect it- which brings me neatly back to our hosts tonight, the Living River Foundation- we really do need to know what effect plastic is having on our breeders, our migrants, our overwinterers, on their fuel living in the estuary? I'm sure we all wish them well in their monitoring work- and thank you for coming out and supporting them tonight.