Get the facultative movement outta here

“It is well for us to recollect that even in our own law-abiding, not to say virtuous cases, the only barrier between us and anarchy is the last nine meals we've had”

A.H.Lewis, 1896

The arrival of the Beast

Obligate movements. Obliged to do it; inbuilt. The urge, for some, to migrate, at the correct season, at the correct time.

Facultative movements. There is a choice. Stay or flee. (Strict biological definition? 'capable of but not restricted to a particular function or mode of life'.)

As I plot this blog out, it's 06:00 and the Queenborough weather site is showing minus one, with a minus ten windchill. North-easterly wind, averaging 35 m.p.h., gusting to 46 m.p.h. The 'Beast from the East' continues to hit. Do I go out at dawn, or stay in? My choice. I wanna bird, but I also want to stay warm. If this blog gets posted before nine o'clock, you'll know what I chose. That decision is based more on the weather, because I've got a kitchen full of food to keep me going and I've already had my porridge.

But we're all only nine meals from anarchy. Birds? Some are nine meals away. Some, just a couple. Individuals of different species make decisions to move at slightly different times.

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Someone told me the Lapwings are migrating away at the moment. Well, strictly, no, they're not. Their annual obligatory migration routes between core breeding areas and overwintering areas are long-established. Within their wintering range, there can be movements during that non-breeding part of the year. Radar studies have shown movements can happen almost daily throughout a winter, in variable numbers. There is a continual readjustment, a refinement, as birds make choices.

These are movements, not a migration.

In the past I've heard it said this is a cold weather movement. That would be nice if it was, because temperature is measurable, and we could soon say what isotherm triggers the movement, just as we have an understanding of how temperature correlates with migration, but cold isn't the main drive.

All-too often you hear hard weather movement. Nice term, but what does it mean? Define hard weather. I've yet to hear someone call a drought 'hard weather', but in that circumstance, waterbirds often make a choice to move, often northwards. Our influxes of, say, Glossy Ibises, have yet to be called hard weather movements. Or autumn pressure systems bringing 'Yanks' to Europe being themselves hard weather- if that's not hard weather, I don't know what is. You could say 'weather-related' I guess, but many scientific texts avoid the phrase.

They tend to call it an escape movement.

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The hard weather we're having on the Medway at the moment - mainly deep snow cover, freezing temperatures, chilling winds - puts pressure on a number of the birds here. At an individual level.

Take sheltering. There is a limited amount of decent shelter from the chilling winds. Watch a clump of cord grass and you might not immediately realise how many birds are in there; scanning a birdless edge of saltings a couple of days ago, a cord grass clump called like an alarming Redshank. The next clump over answered, then the next, and then the next.. Yesterday, one flighting Redshank crashed into a clump and put out twelve. They all moved to another nearby clump where, finding no room at the inn, they gathered on the sheltered side and huddled.

Take food. Those Redshanks, their preferred meals haven't migrated, but they're moving - downwards. the colder the mud surface, the deeper the critters burrow. And the surface has been cold of late. Two nights ago, snow arrived during the low tide cycle. Usually snow on mud melts, but it was cold enough for the snow to form a thin sheet of ice over much of the estuary. The birds could not get at their food. Some could. Often the edges of a creek or tideway do not ice up; gravity plays a part in keeping water flowing, so the mud remains, well, muddy ,and there is some feeding available. Squabbles ensue. Some individual birds chose to move. They chose to try to escape starvation. 

Yesterday, the only birds sitting out on the more open flats were the Brent Geese and the Shelduck. The bigger waterbirds. They can play hunger games for a longer period than their smaller cousins, the ducks. These geese may not move for three or four days of snow cover, the ducks might move after a couple, but never usually all of them so long as some feeding remains available. Weighing up when to go is a balancing act.

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Back to those Redshank. Like quite a few wader species, once they have chosen an estuary in their first winter, they then stick with their choice in future winters. Makes sense. They know it well. For most of the winter, they will not carry big food reserves. Carrying additional fuel outside of migratory periods means slower day-to-day flighting from ever-present predators. Much better to be a mean, lean, flighting machine and hope any poor feeding period only lasts a short while, because they won't have the reserves to make a big distance movement without having an impact on their survival odds. If the extreme weather lasts is long lasting, many will die. They run the risk. The strongest, the fittest, those that can hang on to a feeding spot, survive.

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Right now in the belly of 'the Beast from the East', birders are reporting the 'usual suspects'.

Plovers on the move. Plovers rely more on eyesight to locate prey. The species that feed more in fields than mud flats, Lapwing and Golden Plover, have real problems with snow cover. They escape early.  Haven't been in huge flocks here, birds are making the decision individually; twos, threes overflying aren't that exciting (but add up the local day total and the movement is clear).

The field-feeding thrushes, Fieldfare and Redwing, are escaping in a similar manner. Numbers break off from one large-scale gathering and wander. Take how garden birders might report one or two in the back yard one morning becoming a half-dozen later in the day, then a dozen, then two.. Snow cover in south-east England is patchy, many are trying to avoid costly flight, but some birds in the snow need to move. The total involved is fluid.

Transfer that thought process to small calidrid waders and you begin to understand why inland patch workers are getting one or two Dunlin or an odd Knot flying by. Some are choosing to make a short switch to another estuary (perhaps the Thames and Swale for Medway birds; our sister estuaries are that little bit different, with fewer sheltered waters that are freezing out from the shore), not really a full-on escape movement between estuary complexes (we're all the Greater Thames around here) but others may chance finding an unfrozen estuary (remember, they may not have visited sites south of us before) by fleeing overland.

The county avifaunas often refer to the largest movements in the worst winters, and we birders sometimes head out hoping to see hundreds and thousands of bird racing past us, to experience the escape movement. More likely we'll only pick up on a few dozen, or perhaps break three figures for a couple of species. Escape movements are nowhere near as predictable as viz mig during an obligate migration period.

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Some are waiting to see wildfowl on the move. Probably won't get seen, because most will still choose to move at night, often overland. We'll see changes in day-to-day local totals. But these might be very short movements, flights to nearest open areas rather than huge jumps. Now mix in the obligate. This time of year, some birds are starting to respond to their obligate drives and are wanting to start to move toward breeding areas. Looking at a satellite image for yesterday, it was clear that most of the low countries were free of snow. Feeding possible. We've only got so much thanks to the North Sea providing moisture. Is there any reason for any duck there to want to 'escape'? Move further on when their urges are saying otherwise? It might be bloomin' cold, but if they can feed..

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Escape movements. Yes, they correlate to the weather, and some may move early on sensing weather systems, but for many it comes down to food. Passerines may go early in comparison to larger non-passerines. Can't go as long being cut off from feeding. Juveniles may go early, being routinely pushed down pecking orders (eg think Woodpigeons).

We humans are nine meals from anarchy. Some birds are one or two from death. Calling it a hard weather movement helps hide the life-or-death decisions being taken. Not simply a happy switch between sites, often this is escaping. At the moment, all too often we birders will get excited by the rare garden bird, the patch tick, the hard weather movement day total because it's what these bird species do, but fail to appreciate these individual birds are appearing because they're in trouble..

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Hang on, it's 07:30 already. Time to stop. Think I'll leave going out for an hour or so, tide's not until 10:00. Ohhh, time enough for a second breakfast, lucky ol' me (!)


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The sum of all parts of the quarry (3); thrushes

This December, the two roost counts at Berengrave are going to be rather far apart. My chance to muse on what gets counted. OCD muppet that I am, I try to count everything. Results? All 'normal', but all fascinating, and helping to refine my personal views on the local populations.

This is just one small relatively insignificant, often overlooked, reserve. But look hard enough and there's enough to keep a birder happy.

The Thrushes

Blackbird
Now, same as for everything I count, the number must never be thought to represent the actual number of birds using the pit; it is far higher than these counts. Blackbirds into roosts are like stealth bombers, zipping over the hedge and dropping fast and low into the scrub. Some call, most don't; those silent ones that whizz past me, head height, shout out 'you're missing shedloads'. Thankfully, the trends do hold up to scrutiny; a strong start to the autumn, bolstered by more arrivals, then a steady drop off into the spring; if only all species trends looked like this I could take a few counts off..

Fieldfare
Absolutely nowhere near the numbers seen back in the mid-nineties when, as a raw ringing trainee, I would join the Reverend for a roost catch; birds everywhere. I would argue that, like this year, the pit just isn't right- Fieldfares like to roost over water, and levels are low. A couple of these recent winters have seen the pit so full of water paths were closed. I have tried to put it down to more birds using the Motney reedbed since Kent Wildfowlers improved the sluices a few years back and certainly they are now always there in higher numbers, just some 600 metres to the north of the pit. However, stand on the seawall and watch to the south and east and you will appreciate there are not as many birds, full stop; the grubbing-out of orchards for paddocks, combined with the 'upgrading' of those that remain to industrial sites, have cut down the local feeding opportunities. I would love a three-figure count here, but I won't be holding my breath. (Even though my counts 'officially' finish 30 minutes after sun down, I do hang on until pitch black though- from experience I know birds can still drop in up to an hour after sundown. Ever the optimist..)

Song Thrush
Probably my favourite Thrush at roost. Certainly not for the excitement levels; that graph shows a resident dropping away to breeding numbers. But because you can always count on a little call as they scuttle about the pit edge, and you can expect a bit of interaction as they try to keep their personal spaces personal. Which makes this year interesting; has there been a local influx? If overwintering numbers are up, you can expect to find more birds out and about on the marshes, but they usually do not travel far to roost. Are these perhaps a few extra from the cleared scrubland a little to the east, dirt levels awaiting development? If so, will the next count stay low, perhaps showing that influx was too much, that the carrying capacity cannot be extended? Who know?! All something to think about, roll on moth end.. 

Redwing

Last year, the waters were high. Unlike the previous high years, there were also Redwings about. Perfect combination. Ringing has shown no wintering fidelity- a bird might spend one year here, moving through the season down to Iberia. Next year that same bird might choose the foothills of the Alps before wandering down the spine of Italy. Enjoy them when you can. Last year's mid-winter influx was nerd-birding nirvana, flights of 'wings coming in out of the gloom, screaming as they circled the sallows.
Was it always like that a few decades back. My dullard mind tries to tell me yes, my counts from the time told me no; but there were more peaks, f'sure. End of the month I'll be back in situ, hoping for an influx.

Horrid autumn- 28/10/17

Point: Blackbird 16, Redwing 2, Song Thrush 3.

Viz mig: Little Egret 17 (southwest), Marsh Harrier 3, Redwing 12, Song Thrush 2 (south-southwest). And a cheat, Crow 88, south-west from Damhead Creek. There have been counts of over a hundred on the flats around Copperhouse of late, but these birds tend to stick to the southern shore. Sometimes they reach Hoo Island, sometimes if they do that, they might venture to the Hoo Peninsula, but it does not appear a routine crossing. The tide was in, so would have not expected to see many birds on a scan- local movement or something more? Think the former, but you can always dream..

Mound, viz mig -9:30: Sparrowhawk 4, Lapwing 5 (south), Snipe 9, Stock Dove 32, Jackdaw 17,  Meadow Pipit 6, Skylark 8, Starling 515, Chaffinch 643, Brambling 7, Goldfinch 119, Siskin 10, Reed Bunting.

And a Fieldfare east. That was the exciting one for me. The idea that our interpretations of visible migration can just be movements was being tested. Birders further east were picking up several hundred moving south-west from Motney and cutting in by the fields at Bloors. The arrival angle put them back over the orchards of Ham Green, where numbers had arrived in the past couple of days. The departure appeared to be low, out of sight of me, over the orchards up by the railway line. Not broadfront, specific. How far were they going? And my one working back. What was that about? Peeled off and given up? Can I consider him as wimping out? More to muse on..