17/09/2009
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The Joys of Visible Migration!

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Meadow Pipit coming your way this September (Photo: Clive McKay)

September is here, and once more the skies are filled with the "seep-seep-seep" calls of Meadow Pipits as they pass overhead. Friday nights will see dedicated visible migration ("VisMig") watchers checking the weather forecasts and getting their gear ready to get out to their watchpoints for dawn on Saturday to log the numbers and variety of visible migrants passing overhead. As they get out of their cars in the first light of dawn, they'll be hoping to hear those gentle "seep-seep" calls from every VisMigger's favourite small brown job: Meadow Pipits on the move at first light are a sure sign of a busy morning to come, and are the bread and butter of September migration watches. Small and brown they may be, but when these little bundles of moorland feathers get the migratory urge, they bring life to our September landscapes.


As the sun rises, another VisMig watch gets under way. (Photo: Clive McKay)

On a good morning, the next few hours will see a great number and variety of birds passing these migration watchpoints. But by mid-morning it will all be over, and the skies will be quiet again. The watchers can head off to other more traditional bird-hunting grounds, or go home and spend some time with the family, or go to a footie match, safe in the knowledge that another day of visible migration is over, and another small piece added to the VisMig jigsaw. Then it's time to check the weather forecasts for Sunday...


Adam Hutt tots up some of the 2,215 Goldfinches that passed The Narrows, Spurn Point on 5th October 2006 (Spurn's fifth-highest day count for this species in recent years) (Photo: Clive McKay)

What is it about visible migration that can get birders (even me!) out of their beds well before dawn? What is the best weather for VisMig? What makes a good VisMig watchpoint? Where are the Meadow Pipits going to, or coming from? What other species can you expect to see? How do you identify small brown jobs passing overhead? Are those Pink-feet migrants or just flying from roosts to feeding grounds? What routes do they follow and at what times of year?

In this series of articles, I will attempt to answer some of these questions, and to follow the VisMig stories of the year as they unfold, and to provide some background information on the sites and the characters involved. The accounts will be based on my own personal experiences (and hence biased towards the sites in Yorkshire and Scotland that I know well) and, in an attempt to paint a broader national picture, will draw upon the experiences of others throughout the country. Our knowledge of what's happening in the skies each autumn and spring is improving each year, but many of the phenomena that I describe are based on observations from a small number of well-watched sites — and I owe a debt to all those watchers who stake out their sites year after year and whose counts all contribute to the bigger picture. Mostly I will be concentrating on visible migration of landbirds, as seawatching is a better-known sport, and the peak period for seabirds will soon have passed.


1 Great Shearwater >N, Spurn, 15 September, 2007. (Photo: Clive McKay)

Hopefully you too will soon be looking for your own VisMig watchpoint and joining in with the "BigVis" counts on 26th/27th September co-ordinated by the VisMig Yahoo group (see end of article for more information). And now, thanks to the internet, the results of each day's counts can be seen on the same day via the wonderful UK and NW Europe website www.trektellen.org ("migration count") designed by Gerard Troost and Jethro Waanders in Holland. Moreover, at the click of a mouse you can produce maps, graphs and tables summarising hundreds of hours of counts (see below).

The ideas presented here have evolved over the last 25 years, mostly in discussion with Keith Clarkson after a morning's VisMigging as we tried to explain what we had just seen, and more recently from discussions on the VisMig Yahoo group. However, I take full responsibility for the theories, which are by no means representative of the views of all VisMiggers!

Most of the images that I will use are photos that I have taken of birds in flight, usually on visible migration. Hence, they're not up to the usual standard of BirdGuides images, but hopefully they capture some of the character of birds on the move, and provide a snapshot of shapes and colours as they appear on a VisMig watch.


A treat still to come: Redwings on the move in October (Photo: Clive McKay)

What is visible migration?

It's amazing what you can see if you stand in one place for a couple of hours and wait for migrating birds to come to you! It has to be the right place, at the right time of year and day, and in the right kind of weather, but when it all comes together, "VisMig" can produce some of the best birding spectacles that the British Isles has to offer. And you can see it just about anywhere...

What is VisMig? Well, as it says on the can, it's the "visible" migration of birds (and butterflies) whose diurnal migratory flights can be observed directly. Many birds are nocturnal migrants, such as warblers, chats, flycatchers, Goldcrests, etc. Their journeys begin an hour or so after dusk, and usually finish well before dawn. So it is impossible to witness their migratory flights, although their comings and goings are obvious enough when they arrive on the coast in large "falls". Much of what we know about their movements comes from ringing recoveries. The development of radar meant that for the first time the massive scale of these nocturnal movements could be seen in all their glory. However, radar "observations" still have their limitations, and for the most part we can only guess at the species and numbers making up the "angels" on radar screens.

Luckily for us, the migratory flights of diurnal migrants can be observed by anyone armed with a pair of binoculars. Observing diurnal migration provides one of the most awe-inspiring and fascinating spectacles that the world of birds has to offer. Visible migration hot-spots are famous the world over — raptors at the Bosphorus, Falsterbo, Gibraltar; seabirds at The Bridges of Ross, Pendeen Head and Cap Gris Nez...the list goes on. But visible migration of geese, hirundines, pipits, wagtails and winter thrushes can be seen just about anywhere, and can make for some great days on your local patch. Observers across the country have had memorable days with Pink-footed Geese, Swallows, Meadow Pipits, Redwings, Fieldfares and Wood Pigeons, and it is these commoner species that I will focus on.

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Night or day?

Why some species migrate by day and others by night has never been fully understood. For some species the answer is obvious — large soaring birds such as birds of prey, cranes, storks and pelicans require the heat from the sun to create the thermals that assist their passage. Shunning sea crossings, these species concentrate at the shortest sea crossings such as Falsterbo, Gibraltar and the Bosphorus. Unfortunately, here in the UK we don't have a large enough source area for raptors (or cranes, storks or pelicans for that matter) to produce such concentrations (though in September 2006 I did see one of those rogue White Pelicans soaring over my local watchpoint — I initially mis-identified it as a hang glider!).

Amongst passerines, it seems that those species which habitually live in flocks tend to be diurnal migrants, whilst those that forage alone tend to be nocturnal migrants. It has been suggested that migrating by day enables flocking birds quickly to locate and join feeding flocks and thence join communal roosts on their journey through unknown territory — like motorists congregating at service stations. I also believe that these open-country species such as larks, pipits and wagtails are well adapted to escaping predators in open terrain, so why risk migrating at night when you can move just as safely by day AND see where you're going?

Barriers...

Visible migration is most obvious (a) where natural land features act as a barrier to movement, channelling birds along their edges, and/or (b) where favourable habitats or land features act as leading lines. The most obvious migration barrier is the coast — landbirds don't want to cross the sea, and seabirds don't want to cross the land, so coastal sites get the best of both worlds: migration of both landbirds and seabirds. But the geography of the coastline is important in determining which species will be concentrated and under what weather conditions, and this is something I'll return to in later articles. Ranges of hills also act as a barrier, with the Pennines being one of the most significant barriers in the UK, so it's no surprise that there are lots of VisMig watchpoints on both sides of the Pennines, and that some of the largest counts of inland migrants come from these areas. Barriers can operate at a finer scale too: finches and winter thrushes will avoid the high hills and follow valley sides; Wood Pigeons appear to funnel around the edge of built-up areas such as the city of Sheffield. Weather conditions can also act as a barrier: low cloud and mist over the hills will divert winter thrushes and finches north or south along the flanks of the hills rather than flying west straight across them.


The narrows at Spurn: the perfect migration funnel (photo: Clive McKay)

...and leading lines

Keith Clarkson's studies near Sheffield have revealed how habitat features act as leading lines, encouraging birds to move along a certain flight line or in a certain direction. On the moorland edge west of Sheffield, he found that Snow Buntings and Lapland Buntings were most likely to be seen passing over rocky or burnt moorland; larks, pipits and wagtails would follow grassy habitats where pasture meets moorland; and lines of woodland would concentrate Crossbills, Siskins, Bramblings, Chaffinches and winter thrushes. Weather windows can also act as leading lines — observers in the Pennines know to look out for skeins of Pink-footed Geese in tongues of clear blue sky between encroaching cloud masses, as the geese will maximise their use of such temporary leading lines as they cross from Lancashire to Norfolk.

Weather conditions

The best days for VisMig are when there is a light to moderate head-wind or cross-wind, with good visibility. For stronger-flying seabirds, on the other hand, it seems the stronger the wind the better — but the headwind/cross-wind rule still applies. Not surprisingly, some of the best days are when the weather suddenly turns fair after an extended period of grot. So watch out for a sudden rise in pressure after the passage of a front. It seems that the birds are itching to get on with migration, and the first available migration window often triggers the most exciting movements. What is surprising is that once the fair weather sets in, for example during an extended period of high pressure, the migration doldrums (as Dave Barker recently called them) set in. Is this phenomenon real, or are birds moving out of sight of VisMiggers on the ground?

VisMig characters

No article on visible migration in the UK can be complete without mention of Keith Clarkson (KC). Keith deserves a medal for his dedication to VisMig, and through his inspiring talks to many a bird club has enthused many others to take up the early morning challenge. Born and bred in Sheffield, Keith pioneered the study of VisMig at upland sites in the south Pennines. His VisMig career began whilst ringing September Mipits at Redmires Reservoirs with a simple question — How come we never catch the same Mipit twice? The stream of birds passing overhead each morning clearly WERE birds on the move, and not just local commuters. Since then Keith's name has been synonymous with Redmires, then Strines and finally Rod Moor. At the latter he spent 10 consecutive autumns counting everything that moved for at least one hour every morning of decent weather before going to work! Clearly any medals should actually go to Keith's wife Clare for her enduring tolerance, and now he has to check his moth traps before he goes out VisMigging! KC re-wrote the status of many species in the Sheffield area, for example accumulating three or four fly-over Richard's Pipits, and he single-handedly made many of us realise that a morning's VisMig can at times surpass a day on the east coast.


Keith Clarkson, Agden Beck near Sheffield, October 2005. One of those days when the gloomy weather didn't bode well but, like bad weather on the coast, the low cloud was forcing large numbers of Redwings to stream northwards along the flanks of the hills, rather than passing over westwards, their preferred option. (Photo: Clive McKay)

Visible migration in September

The VisMig season really gets going in September, and it's a great month to be out. Dawn is not too early and the weather is generally very pleasant — no need for the woolly hats and gloves that are essentials later in the year. Hirundines, flava wagtails, White Wagtails (I think!), Grey Wagtails and Tree Pipits are on the move from late August through to mid-September. By mid-month the mass exodus of our most obvious visible migrant, the Meadow Pipit, begins. The graph below (from Trektellen) shows the timing of movement across all British sites (currently almost 70 sites). The second and third weeks of September are THE big weeks. Spurn Point contributes a large proportion of these totals, with some massive counts — the best since 2005 being 16,750 south on 13th September 2008!


Meadow Pipits heading south, Carnoustie, 30th August, 2009 (photo: Clive McKay)

But inland sites such as Oxenhope and Stainburn Moor (Thruscross (see Trektellen for maps of these locations) have had counts of 2,000 or more birds in a morning — what a sight! Oxenhope is currently the best-watched inland VisMig watchpoint in the country, thanks to the sterling efforts of Dave Barker, Howard Creber and co., and their counts on Trektellen provide a good yardstick with which to compare other sites. Interestingly, Meadow Pipit passage peaks a week or two later at Oxenhope compared to Spurn (which is at the same latitude), and carries on longer into October. These differences are undoubtedly real — being based on several years of data and hundreds of hours of observations. But how can they be explained? At the moment, we simply don't know, although we suspect that it has something to do with the different timing and migration routes of the British and Icelandic populations of Meadow Pipits. With VisMig there are always more questions than answers. One of the nice things about being able to put all the information together in this way is that ALL your counts contribute to the overall picture — so a low count can be just as informative as a high count.


Total number of Meadow Pipits by week recorded at British VisMig sites 2005–2009 (approx. 45 sites) (Map: ©www.trektellen.org)

But why should Meadow Pipits from upland Britain pass southeast through Spurn when their destination is western France and Portugal which lie on a southerly or south-southwesterly bearing? Mysteries still to be solved. The humble Meadow Pipit often puts on a good show, and not surprisingly is a favourite amongst VisMiggers, who get as big a kick from big movements as twitchers do from rarities!

September 2009

This year saw an unusually early September Mipit surge — 30th August to be precise! Although only nine sites were counted that day, an interesting pattern emerged (see map). A total of 5,861 Mipits were logged, with the largest numbers at sites on the east side of Scotland, extending down the Pennines to West. Yorkshire. But very few birds were recorded at Redmires (South Yorkshire) at the southern tip of the Pennines, nor on the east coast of Yorkshire at Filey or Spurn. Could it be that the wave of birds had penetrated through Scotland and down the Pennines, but hadn't quite reached the sites further south and east?


Numbers of Meadow Pipits passing VisMig sites on 30th August, 2009 (map: ©www.trektellen.org)

The next notable Mipit "surge" was on 6th Sept, and by contrast, all the Pennine and Yorkshire sites recorded more birds than the Scottish sites (if I hadn't been at a wedding there would have been another dot on the map in eastern Scotland!). This time Spurn recorded 4,200 birds south, Filey 1,000 south and Redmires 765 southwest. Evidence perhaps for onward movement of the birds from 30th August?


Numbers of Meadow Pipits passing VisMig sites on 6th September, 2009 (map: ©www.trektellen.org)

It is interesting to note that White Wagtails were also recorded moving with the Mipits on 30th, and the prevailing weather of the previous few days would suggest that these had come from Iceland rather than Scandinavia. Could it be then that the Mipit wave also hailed from Iceland, having perhaps arrived in the UK over the previous week? Hopefully in years to come more counts from a larger spread of sites across the country will enable us to tackle such intriguing questions.


White Wagtail, Carnoustie, Angus, Scotland 30th Aug 2009 (photo: Clive McKay)

So far the first half of September has been fairly quiet, and as I write a high pressure system has dominated for most of the last week — summer at last, but not so good for visible migration. Birds will trickle through in low numbers during this weather, and we will have to wait for the next wesather system to clear out the high pressure and bring a nice "fresh" southwesterly airstream to get things moving in numbers again. A surprising migrant on the move in late August and early September is the Tree Sparrow, whose tight-knit and noisy flocks make their way not very confidently over open ground. The first time I saw this near Carnoustie in August 2006 I presumed they were local birds but, seeing similar observations from other VisMig sites across the country, I realised that this early-autumn movement is characteristic of Tree Sparrows, with a lull in later September, followed by a much larger movement in October. Perhaps the early-autumn birds are from early broods? This is a typical example of how so much more can be learnt when you put your own counts into the context of the bigger picture via the VisMig Yahoo group and Trektellen.


Tree Sparrows south, Carnoustie (photo: Clive McKay)


Tree Sparrows south, Carnoustie (photo: Clive McKay)

Variety is the spice of VisMig

One of the great things about VisMig is the variety of species that you see, and the fun to be had getting to grips with their calls and identification. Because the birds are flying over, you don't have the usual habitat clues that tell you that a small brown job with jerky flight flying over a reed bed is probably a Reed Bunting, whilst something similar over open moorland is probably a Meadow Pipit. Identification is a topic that I will look at more closely in future articles.

Everyone has their own favourite memories of classic VisMig days, and I hope to pass on some of these in future articles. On a frosty day in November at Carnoustie I remember seeing Swallows, Whooper Swans, Waxwings, Crossbills and Snow Buntings passing by within 10 minutes of each other. And it is always a joy to catch Coal Tits, Blue Tits, Long-tailed Tits or Great Spotted Woodpeckers boldly striking out over open country. Unexpected goodies can include the likes of Great Grey Shrikes or Hawfinches; I've never had the luck to see one of the latter on the move — maybe this autumn....

Spurn Point is one of the best sites for variety in the country, and the lads at "The Narrows" do a fantastic job of logging their visible migrants (as well as their rarities) year-round. If you click on the Totals 2009 button for Spurn, Trektellen can tell you that the observatory has carried out over 650 hours of timed counts on 158 days. And their rewards? Not easy to summarise, but up to 14th September 2009 the total number of visible migrants passing Spurn stood at (exactly!) 259,100 individuals of 151 species, including amongst others 1,190 Red-throated Divers, 3,011 Pink-feet, 2 Red Kites, 69 Marsh Harriers, 46 Sparrowhawks, 1,287 Grey Plovers, 1,351 Whimbrels, 71 Black Terns, 5 Red-rumped Swallows, 44,321 Barn Swallows, 617 Carrion Crows, 3,685 Linnets and 19 Corn Buntings, not to mention the other goodies — and the autumn hasn't really started! What a place. I'll be referring to Spurn's counts frequently as the year-round coverage here provides a great baseline of what species are on the move throughout the year.

But as I said at the start of this article, you don't have to be on the coast to have a great "vis" day. Please consider contributing to the BigVis watches this autumn, the first of which is on the weekend of 26th/27th September.

Getting involved...

You can sign up to the UK VisMig newsgroup at http://groups.yahoo.com/group/vismig — follow the links to "Join this group". This year the group is co-ordinating three "BigVis" weekends where observers will count all passing migrants at their watchpoints for 1or 2 hours after dawn on 26th or 27th Sept, 17th or 18th October and 31st Oct or 1st Nov (you can choose which day of the weekend you prefer, although the Sundays are the preferred option if possible). The counts will be entered on Trektellen for quick feedback. If you would like more information on using Trektellen, please get in touch with me via the website.

Next time...

Choosing your watchpoint, Pink-footed Geese and Pied Wagtails, VisMig characters: Dave Barker, Days of Discovery.

Cheers, and good VisMigging.

Recommended reading:

  • Alerstam, Thomas. 1982. Bird Migration. Cambridge University Press, Cambridge.
  • Hill, Richard. 2009. Visible Migration Studies - observing bird migration in the Sheffield area. www.sbsg.org/vismig/vismigintro.asp
  • Newton, Ian. 2008. The Migration Ecology of Birds. Academic Press, London.

Links:

Written by: Clive McKay