Some Results From Bird Ringing  in N E Caithness
Hugh Clark

This report first appeared in the Caithness Field Club Bulletin April 1987

There are around 1,100 fully qualified ringers in Britain and each is really just a small cog in a big wheel. While each individual ringer only receives recovery information on birds which he/she has caught, the B.T.O. retains and uses all the information being generated by all its ringers.

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).

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)