With a very cold start followed by a hot dry spring and a cool summer, what sort of year has it been for our local birds? Last year was somewhat similar, but both years have been atypical. For wildlife in general, it has been a good year albeit after a freezing start which certainly led to a large number of birds succumbing to the cold. Rodents benefited from the plentiful snow which provided protective cover from both the cold and predators and so they survived well. The British Trust for Ornithology has recently published some early results from two of its surveys for the 2011 breeding season. The national press has given some wide coverage to one of the most interesting surveys, the CES (Constant Effort Site) so apologies to those of you have already read this information. Briefly, the survey involves erecting mist nets to capture birds at a specific site. The duration and time of year are strictly constant so that the results are comparable from year to year. The birds are ringed, identified and, most importantly, aged. The number of recently fledged birds can be determined as a percentage of the population and hence a productivity index can be calculated. Obviously, the total number of each species is recorded as well.

Our ground feeding birds such as Robin, Dunnock and Wren proved to be the worst affected by the severe weather; their populations were found to have dropped by between 20 and 30 per cent. However, their productivity was found to be raised by as much as 40 to 60 per cent, largely due to the warm spring and lack of competition and, possibly, also achieving an extra brood. Our two thrushes had slightly differing experiences, with their numbers dropping by 7 per cent for the Blackbird and 28 per cent for the Song Thrush, whose reliance on snails was probably more adversely affected. The Song Thrush’s productivity, however, was up by 45 per cent compared to the Blackbird’s 15 per cent. Tit numbers were up, particularly the Blue Tit following the successful breeding season of the previous year, but its productivity fell by 30 per cent whereas the Great Tit’s productivity was increased. As the two species rely on a similar food source, there is no obvious reason for this anomaly. The finch family had a mixed season with populations of Chaffinch and Greenfinch dropping by 15 per cent and 24 per cent respectively. The Chaffinch may have been badly affected by the snow cover as it does feed more on the ground than its cousins. The Greenfinch is particularly suffering from the trichomonosis disease, which explains why its numbers are worse than the Chaffinch’s. Goldfinch numbers were up by 22 per cent, largely helped by all the nyger feeders that are now put out by the public. Interestingly, in every case where the population has dropped, the productivity has been well up, with Chaffinch up 56 per cent, Greenfinch up 85 per cent whilst the Goldfinch, whose numbers increased, experienced a productivity decline of 9 per cent, which demonstrates nature’s incredible balancing act.

For our summer visitors, such as Whitethroats and Willow Warbler etc, the picture is rather different. Obviously, wintering in Africa they missed the cold weather and therefore their abundance figures were up following a few good breeding seasons. The cool summer, however, was not to their liking and, with fewer insects with which to feed their young, their productivity was down between 10 and 36 per cent.

The CES scheme really only monitors small passerine birds, therefore, to look at other birds such as predators, the Nest Record Scheme provides some insight. The scheme monitors clutch size, brood size and fledglings produced. The figures for population change are not yet available, but what is known is that birds of prey such as Barn Owl, Tawny Owl and Kestrel all suffered last winter due to the high degree of snow cover. The Barn Owl at Forest farm did not breed for the second consecutive year. Those that did manage to breed, produced good-sized broods thanks to the abundant rodent crop. However, it was only the Kestrel that managed to improve its productivity significantly, raising it by 15 per cent. The Barn Owl showed a slight improvement, but the Tawny Owl, for some unknown reason, suffered a high egg failure rate. The Barn Owl at Iden Green Farm had a successful breeding season and, perhaps, one of this year’s young will take up the vacant box at Forest Farm.

A couple of months ago I described a project where 5 Cuckoos were satellite tagged in Norfolk and, although their migration routes varied by as much as three and a half thousand miles, all five Cuckoos are now in the Congo rain forest and are closer to each other now than they have been since leaving Norfolk. It will certainly be interesting to see what return routes they will use. This project has been so successful that it is going to be repeated, tagging Scottish birds whose population is expanding, to see if that throws any light why English birds are declining.

Charles Trollope cetetal@aol.com