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Caithness Field Club Bulletin
SOME RESULTS FROM
BIRD-RINGING IN N. E. CAITHNESS
Over the last five years or so, several inhabitants of Wick and the surrounding area must at some time or another have noticed a bird in their garden which was wearing a shiny metal ring on one of its legs. People must have wondered where these ringed birds were coming from and why they were ringed in the first place. Here it is hoped are some of the answers.
THE RINGING SCHEME
Since 1937, all ringing of wild birds in Britain has been controlled and regulated by the B.T.O. All would-be ringers now have to undergo thorough training organised by the B.T.I. before being granted a licence by the Nature Conservancy Council (N.C.C.) to catch wild birds and a permit from the B.T.O. to ring the birds caught.
Every ring now supplied by the B.T.O. bears its own unique number and the address of the British Museum of Natural History e.g.
INFORM BRITISH MUSEUM
The role of the 'British Museum within the ringing scheme is an interesting one. In an experiment conducted by the B.T.O., over a number of years, half the rings used on Starlings bore the address of the British Museum (as shown above) and the other half bore the legend "INFORM B.T.O., TRING, ENGLAND". Dead birds bearing rings with the British Museum address were subsequently reported by members of the public in much higher quantities than those bearing the B.T.O. address. It was concluded that people finding rings with the B.T.O. address often did not bother to inform the B.T.O. of their find; however people seemed to respond much more readily to the more prestigious name of the British Museum. So all rings except the very smallest, now bear the address of the British Museum, and letters sent to the British Museum reporting rings found are simply forwarded to the B.T.O. who hold the records of all birds ringed in Britain. On the very smallest rings, such as those fitted to Wrens, the ring is so small that it cannot accommodate the British Museum address and instead has the address "B.T.O., TRING, ENGLAND", but undoubtedly not all rings with this address are reported to the B.T.O.
There are bird ringing schemes operated in almost all developed countries around the world, and the various national schemes co-operate readily with each other to report all birds found to the ringing schemes in the countries where the birds were ringed.
So at regular intervals, a ringer sends to the B.T.O. details of birds he/she has ringed; for each ring number is given the species of bird, its age and sex (where determinable) when ringed and where. The ringer then relies for the most part on members of the public reporting some of his/her ringed birds, found dead, to the B.T.O. (through the British Museum). The B.T.O. then notifies the ringer of the find (called a "recovery") and the finder is told where and when the bird was ringed. Occasionally birds with rings are caught alive, especially by other ringers. The finding or capturing of ringed birds alive (with their subsequent release) are called "controls".
USES OF BIRD-RINGING
The most obvious purpose of bird ringing is to find out where birds go at different times of the year, and what routes they take. For example, the route taken by British Swallows on their autumn journey south has been clearly marked over the years as birds have been recovered at various points along the way i.e. down through western France, along the east coast of Spain and across the sea to Morocco, across the Sahara desert and eventually to South Africa where British Swallows spend the winter. Furthermore, Swallows from different parts of Europe have different wintering areas in Africa (Mead 1974). Knowledge about birds' movement further helps the B.T.O. to pinpoint habitats or areas which are of special importance to birds, areas which may require special conservation measures.
Additionally, the B.T.O. is able to monitor the population levels of different species from the numbers ringed in Britain each year, and to judge the effect of a hard winter on a species. The number of Wrens ringed in Britain in 1978 was 11,526, but only 6,807 were ringed in 1979. This decrease was presumed to be due to an excessive mortality among Wrens caused by the severe weather in January and February of that year. However, the mild winter of 1979/80 apparently allowed the species to bounce back and in 1980 the number ringed was back in its normal range at 11,222 (Spencer and Hudson 1981).
Another interesting use to which recovery details can be put is in working out how long birds live; if a bird is ringed in January 1980 and found dead in January 1985, then it has lived for a minimum of five years. This type of calculation has produced the following longevity records (Mead 1974).
Swallow 16 years
Of course these are records and the average life span of all these species is very much shorter. The mortality rates of small birds are very high, but the populations are kept in balance by the high rate of breeding. For example, Robins can easily raise two broods each of five young during the course of the summer and only two out of twelve (Parents and young) need to survive to the next breeding season for the population to remain in balance; so ten out of every twelve Robins die each year. It has been calculated (Mead 1974) that if only one extra bird survived from each pair's breeding activities each year, the Robin population would increase by more than fifty-fold every ten years!
Finally. it is worth noting that for most species, huge numbers have to be ringed before any valuable information can be obtained. This is due to the very poor recovery rates; less than one Swallow, out of every hundred ringed is subsequently recovered. Some recovery rates are shown below (Mead 1974)
In the six year period, 1981-1986, I and my associates ringed 3,771 chicks and 9,756 fully grown birds in N.E. Caithness.
In the early days of bird ringing, all fully grown-birds were caught by traps of some description. Most were caught in the huge Heligoland traps which ringers have built at most coastal bird observatories. Nowadays, however, all traps are overshadowed by the use of "mist-nets", which were invented in Japan and introduced to Britain in 1956. The nets are made of very fine black thread (nylon or terylene) and come in various lengths from 2Oft.to 6Oft. They are hung vertically (to about 1Oft. high) between two bamboo poles. When placed in front of bushes or shrubs these nets are invisible to birds, and it is easy to understand why the number of birds ringed annually increased dramatically after 1956. Needless to say, ringers require a licence from the N.C C. to own and use mist nets which can only be purchased from the B.T.O. by holders of B.T.O. ringing permits.
BIRD MOVEMENTS THROUGH
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.
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.
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%!
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?
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.
However, for several species, there have only been one or two recoveries each; such as one Lapwing recovered out of 595 ringed. The fact that this recovery was of a bird shot at Cortinan, Coruna, Spain, obviously does not mean that all Caithness bred Lapwings spend the winter in Spain. Many more Lapwing recoveries are required before a pattern can be seen emerging, and to achieve this many more Lapwings need to be ringed. This is true also for dozens of species that spend part of their year in Caithness.