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Weather Effects On Bird Migration


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  • Location: Cambridgeshire Fens. 3m ASL
  • Location: Cambridgeshire Fens. 3m ASL

I thought some of the forum may find this interesting. How weather not only effects us but bird migrations too bringing some unusual visitors to our coasts. I received this as I'm a member of the BTO but it can be viewed on their website.

BirdTrack update - 2 October 2008

Migration interest during September seemed to switch around the country, from the north, then to the east and finally back to the west, with the different winds encountered bringing very different birds into the country. Following a prolonged period of westerly winds and low pressures tracking across the Atlantic (on the back of a strong hurricane season in North America), there was a rush of rarities from the west, mostly concentrated in Ireland. On one day, Cape Clear Bird Observatory alone recorded Yellow Warbler, Northern Waterthrush and Solitary Sandpiper!

In the east, these same wind conditions may have concentrated migrating birds of prey along the coasts, and notable passage was seen at several sites. An early morning migration watch at Dungeness Bird Observatory recorded a remarkable 52 Sparrowhawks and 41 Kestrels, along with 12 Marsh Harriers, four Peregrines, and single Buzzard and Hobby. Another raptor seen in exceptional numbers was Honey Buzzard, with some sites recording up to 16 birds on one day, and the number of birds involved must be in the hundreds.

The study of migrating raptors has been revolutionized in recent years by the use of satellite tracking, and the fortunes of several species can now be followed live online:

Honey Buzzard:






After what seemed like an age, we finally saw some perfect migration conditions develop over Europe late on in the month. For migrants to be moving through western Europe, the ideal weather conditions are a deep, long high pressure system over Scandinavia creating an easterly airflow right across northern Europe, encouraging birds to migrate. Add to this a sequence of frontal systems passing across Britain and Ireland, and when birds reach our coastline, they hit a front (with cloud and rain), suspending their migration, dropping them onto the coast (a fall).

With these conditions, interest switched from the west to more eastern regions, with the quality of birds definitely improving. The pick of the bunch were three extremely rare birds from Central Asia. The first to appear was a male Cretzschmar's Bunting, seen for three days at North Ronaldsay Bird Observatory on Orkney. This is only the fourth British record, all of which have been seen in the Northern Isles. Later in the week, a Brown Flycatcher was found at Fair Isle Bird Observatory, only the second British record (following one at Flamborough Bird Observatory in 2007). Not to be beaten though, Flamborough responded later the same day with the finding of a Brown Shrike! This was even photographed next to an obliging Red-backed Shrike for comparison. Further south, Yorkshire's first record of Pallas's Grasshopper Warbler was found at Spurn Bird Observatory, and daily migration counts there also included 21 Tree Pipit, 83 Redstart, 40 Wheatear, 40 Spotted Flycatcher and 23 Pied Flycatcher. Spurn’s good run continued later that week, when a Meadow Pipit carrying an Icelandic ring was caught, only the second ever to be found in Britain & Ireland.

For links to the entire network of 18 Bird Observatories, visit the BOC site:


Aside from the unusual, there were also very impressive numbers of both Redstart and Pied Flycatcher along the coast, many of which filtered to inland areas. There were also some very confusing birds turning up! On the Fife coast, an odd-looking flycatcher was originally identified as a Collared Flycatcher, but later reidentified as just a Pied. In Norfolk, a 'possible' Semi-collared Flycatcher caused a few headaches, as the identification of first-winter birds is a dark art. There were also several records of Redstarts showing characteristics of the eastern race samamisicus.

Note the effect of this fall in the results for Redstart:


and also for Pied Flycatcher:


It is obvious how key an understanding of weather patterns can be to planning your migrant watching. Key to unravelling migration patterns is the interpretation of pressure charts (or synoptic charts). These may seem incredibly confusing at first, but with practice (and a bit of help) you can start to predict your own falls.

Atlantic pressure charts for the week ahead:


A guide to interpreting synoptic charts:


Though you’d need to be at the coast to really appreciate these mass arrivals, autumn migration was still visible throughout the country. The most obvious inland ‘visible migrants’ are Meadow Pipit and Siskin, and good numbers have been seen heading south from the core of the breeding population in Scotland.

Have Meadow Pipit numbers peaked early this autumn?


Was the early promise of a bumper Siskin winter misleading?


True immigrants into the country will also filter inland quite quickly at this time of year, and by now a lot of people will have seen an increase in the numbers of Goldcrest, and perhaps the first Redwings.



Note the slightly later arrival of Redwing than in 2007:


As the month came to an end, the wind again switched to the west, and attention turned back to the west coast, but this time to the sea-watching hotspots. As if on cue, an impressive passage of Leach’s Petrels was reported, with the highest single count of 120 that passed Hilbre Island, Cheshire. More unusual was the report of a wind-blown Max Shearwater, which was first found behind a set of bins in Central London. The story has a happy ending though, and can be read here:


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  • Location: Cambridgeshire Fens. 3m ASL
  • Location: Cambridgeshire Fens. 3m ASL

Birdtrack update for October

We probably shouldn’t be surprised, but October was a very exciting month in all parts of the country, with migrants and vagrants in all regions.


At the start of the month, the westerly winds were ideal for sea-watching and there were plenty of Leach’s Petrels and Balearic Shearwaters to be looked for. The highest counts we heard of for these enigmatic birds were 120 Leach’s Petrels past Hilbre Island, Cheshire, on 1 October, and 115 Balearic Shearwaters past Pendeen, Cornwall, on 6 October. The latter were seen at the SeaWatch SW watchpoint which is manned through the autumn monitoring seabird passage:



These westerly winds are not ideal at all for migration from the Continent, and east coast birders had to wait until the middle of the month for the wind to turn. There were two distinct periods of easterly winds, both of which saw big arrivals of birds. The first wave of birds was mostly Redwing, and standing outside for a short while would have revealed them passing overhead giving their characteristic thin 'seeih' call. This first peak can be seen in the BirdTrack results, as can the much later, and much bigger, arrival:


This later arrival was one of the events of the autumn so far, with a lull in the westerly airflow coinciding with a weak weather front over the east coast. This allowed birds to leave Scandinavia, but also pushed them down onto the coast as they arrived. In just two hours, Spurn Bird Observatory recorded 5,570 Redwing passing over the Point and heading inland. This afternoon arrival was quite typical for the east coast, as birds leaving the Continent in the morning will take this time to make the crossing. In North Yorkshire, one visible migration watcher also recorded 4,500 Redwing passing over in just 15 minutes!

Further south, birds were seen in strangely specific locations. At Skegness, Lincolnshire, a team from the Central Science Laboratory monitoring migration using radar equipment recorded a very narrow, 1km wide, band of birds arriving at an altitude of up to 4,000 above sea level, well above the height they could be seen from the ground.


Obviously what happens here is dictated by what is happening on the Continent. Many people will have their fingers crossed for a Tengmalm's Owl, as there is a very large 'irruption' in southern Scandinavia. In the south of Sweden, Tengmalm’s Owl hadn’t been recorded at Falsterbo Bird Observatory for 22 years, but this autumn they have so far ringed 261 birds! Check the 'Owls 2008' link on their website:


Also just over the North Sea, we’ve heard of very big movements of tits, with 12,650 Blue Tits recorded at Falsterbo on one day! Also moving in numbers are Long-tailed Tits, with counts of over 100 at several sites on the British coast, though their origins are largely unknown. These birds are moving though, and at Theddlethorpe in Lincolnshire 131 were ringed in the middle week of the month. Further south, five of these birds were then caught at Gibraltar Point Bird Observatory, where 186 have been ringed this autumn. It’s not just along the east coast either, as we also heard of very large numbers arriving at Bardsey Bird Observatory, Gwynedd, at the end of the month.


As the winds turned to the west, October also saw the arrival of some truly winter migrants. Snow Buntings began to appear along the west and north coasts and we even heard of a bird in a garden in Ireland! These birds are probably from the Icelandic population (of the subspecies insulae) rather than the Scandinavian population (subspecies nivalis). With a good view of a male, you can tell the difference between the two subspecies by looking at the amount of black on the wings. The Icelandic race is much darker; with Scandinavian birds have extensive bright white wing patches. Other ‘northern’ highlights included the arrival of large numbers of Whooper Swans, a trickle of Waxwings and some rather late Ring Ouzels.


After the incredible rush of extreme rarities in September, October managed to keep up the trend. From North America came a Little Blue Heron (actually white as it was a juvenile) that was found in Co. Galway and is the first record for Ireland, with a second report of one in Wales at the end of the month. Galway also hosted an incredible flock of 15 Ring-necked Ducks, which we think is the largest group ever seen together in Europe, narrowly beating the 12 seen in the Azores in winter 2007-08. Irish birders also enjoyed a Scarlet Tanager, which was the fourth Irish record, following one in Co Down and, remarkably, two records in October 1985 at the same site in Co Cork!

The best was saved until last, though, when an ‘Empidonax’ flycatcher was found in Cornwall. These are a group of American birds where identification in the field is incredibly difficult, and this bird was only positively identified once local ringers were given permission to catch it:


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