Some Results From Bird
Ringing in N E Caithness
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BIRD MOVEMENTS THROUGH CAITHNESS
The bird population of an area usually changes at regular intervals throughout the year, and this is certainly true of Caithness. Many species of summer visitors, typified by the Swallow and the Cuckoo, start arriving from Africa in the latter half of April; they stay to breed and then are gone again mostly by the end of October.
It is usually in October too that many of the regular winter visitors to Caithness arrive, such as Whooper Swans and Grey Lag Geese from Iceland, and Redwing from Iceland, Finland and Scandinavia (Lack 1986); these winter visitors have mostly gone again, back to their breeding grounds, by the end of April. It may be said, therefore, to put things simply, that migrant birds are moving northwards and/or eastwards through Europe in the spring and are moving south and/or west in autumn. It is at these major migration times too that adverse weather conditions such as mists or strong winds can cause birds to travel off course and land at locations well away from their normal destinations. In spring and autumn, East Caithness often sees unusual "passage migrants" land on the coast, blown eastwards off course across the North Sea.
The movements so far described are, however, just the tip of the iceberg; many species not thought of as typical migrants, e.g. Blackbirds and Starlings, are also involved in movements, again, generally speaking, going north and/or east in spring and south and/or west in autumn.
Ringing activities, centred around Wick over the last six years, have helped shed a little light on the movements of some birds through Caithness, as illustrated by the following details for a few well known species.
B.T.O. ringing has shown over the years that many Scottish bred Blackbirds move southwest for the winter, many into Ireland, but these emigrants are more than replaced by a huge influx of birds mostly from Scandinavia, Finland and Denmark (Thom 1986).
The details given in Table 1 help confirm the easterly origin of many of our Blackbirds.
Table 1: recovery or control details of blackbirds ringed near Wick
In Table 1, birds 1 and 2 were wintering in Caithness and had returned eastwards where they were killed. No. 1 was almost certainly at its breeding area when killed in late July, but No. 2 may still have been moving east in late March when it was killed.
Birds 3 and 4 were ringed within two days of each other at Ackergill and Noss Farm respectively when there was a noticeable fall of passage migrants in those areas; it is very easy to see dozens of Blackbirds which just drop in for a day or two and then move out again. No.3 subsequently controlled in Finland in May was almost certainly in its breeding area, but No.4 found dead in late October in Norway may well have been on the move westwards again and died en route.
Bird No.5 helps to confuse the issue. Why did this bird move eastwards in the middle of the winter when, if it was going to move at all, it should have gone south or west? It is well known that some young birds in their first year of life appear to make a simple mistake of 180 degrees in their migratory flights and it has been argued that they have defective "compasses" (Mead 1983). Bird No. 5 was a young bird and may have suffered from a navigational malfunctioning, reaching Denmark instead of Ireland!
Three other Blackbirds were recovered locally in or around Wick, giving a total of 8 recoveries out of 758 ringed, a recovery rate of 1.05%. This recovery rate, much lower than the national average of 3.96%, might reflect the fact that Caithness ringed Blackbirds are spreading into surrounding areas of fairly low human population density in parts of Caithness and Sutherland where the chance of being recovered is less than in the more populated, industrialised south.
The British bred population is a bit nomadic during the winter, when young birds especially move south-west, although the majority of the population is largely sedentary (Thom 1986). However, Starlings from much of northern Europe pour into Britain to winter in huge flocks over the whole of the country, to such an extent that there is none left over most of northern continental Europe during the winter (Mead 1983).
Over the years 1981-1986, 2,444 Starlings have been ringed in the Wick area; of these, 38 have been later recovered or controlled giving a recovery rate of 1.5%. Of the 38 recoveries 20 were local, mostly the victims of Wick cats.
Four birds had come down from Fair Isle for the winter, showing the south-westerly type of movement already mentioned. Three others caught in Wick in winter returned to Norway for the breeding season; they had obviously been part of the winter influx from northern continental Europe also mentioned earlier.
However, an unusual and unexpected trend has become apparent with 11 Starlings being recorded as moving from areas further south into the Wick area during the winter period e.g. two from northern England, two from the Edinburgh area, four from Aberdeen, one from Fort William, one from Tain, and one from Aberlour. This type of northerly movement in winter obviously merits further investigation and many more thousands of Starlings will have to be ringed for this purpose, especially when the recovery rate is only 1.5%!
Over the last six years, 762 Swallows have been ringed in N.E. Caithness; 265 were nestlings and 497 fully grown (almost entirely juvenile birds only a few months old). These fully grown birds were caught in mist-nets among the reeds and grasses that surround a number of rivers and lochs in the area.
One Swallow was caught by other ringers at a roost in the reed beds around Loch Spynie, near Lossiemouth, 18 days after being ringed in Caithness; but a further 10 were caught at a roost in Ellon, Aberdeenshire several days after being ringed in Caithness. These findings suggest that a good proportion of Swallows moving south out of Caithness in the autumn pass through the roost at Ellon, with some at least also stopping off at Spynie. Only further ringing of many more Swallows will reveal whether or not this is the principal route south for Swallows out of Caithness.
Two further recoveries suggest an even more interesting possibility. One Swallow was found in late autumn at Hailsham, Sussex (50deg.51'N; 0deg.16'E) and another was found only ten miles away at Bexhill-on-Sea, Sussex (50deg.50'N; 0deg.29'E) Do these two recoveries reveal the point from which a proportion, at least, of our Caithness ringed Swallows leave Britain to cross the English Channel on their journey south?
The Pied Wagtail is a species not generally thought of as being migratory, and indeed the birds of southern Britain are basically sedentary, but the population from breeding grounds in northern Britain, by contrast, are largely migratory (Lack 1986).
Throughout August and September each year, dozens of birds feed on the muddy areas of Wick river each evening before moving into the tall grasses to roost for the night. Some nights, two to three hundred birds may roost around the river. Yet by the end of September these birds have moved south, and there are very few Pied Wagtails to be seen in Caithness over the winter, until birds start trickling back into the area to their breeding haunts from around the beginning of March.
Over the last six years, 455 Pied Wagtails have been caught in the Wick area, mostly with mist-nets placed along the edges of Wick river. Six of these birds have been reported from the south in winter; one each from Llanelli, Kettering, Tranent, Aberdeen, Fearn (Ross-shire) and Argentre du-Plessis in France (48deg.4'N; 1deg.9'W).
These findings suggest that the birds which are concentrated around Wick river in August and September are widely dispersed throughout the winter months mostly through southern Britain but with a proportion ranging into southern continental Europe.