ANALYSIS OF TRAPPING FIGURES AT METTNAU S TATION, S GERMANY, WITH RESPECT TO THE POPULATION DEVELOPMENT IN SMALL BIRDS - A 20 YEARS SUMMARY34 REPORT OF THE MRI-PROGRAM

Citation
P. Berthold et al., ANALYSIS OF TRAPPING FIGURES AT METTNAU S TATION, S GERMANY, WITH RESPECT TO THE POPULATION DEVELOPMENT IN SMALL BIRDS - A 20 YEARS SUMMARY34 REPORT OF THE MRI-PROGRAM, Journal fur Ornithologie, 134(3), 1993, pp. 283-299
Citations number
30
Language
TEDESCO
art.tipo
Article
Categorie Soggetti
Ornithology
Journal title
ISSN journal
0021-8375
Volume
134
Issue
3
Year of publication
1993
Pages
283 - 299
Database
ISI
SICI code
0021-8375(1993)134:3<283:AOTFAM>2.0.ZU;2-Y
Abstract
1) The trapping station ''Mettnau'' in S. Germany as part of the ''Met tnau-Reit-Illmitz-Program ( MRI-Program)'' of the Vogelwarte Radolfzel l has been in operation for 20 years since 1972. During this period, 1 19 132 individual birds (first traps) of 35 species of small birds wer e captured. The station uses mist nets in which passage migrants are t rapped during the autumn migratory period. The annual trapping period lasts from the end of June to the beginning of November. Trapping and working methods are strictly standardized. In this report, the trappin g figures have been analyzed with respect to the development of the re spective (mainly Central European) source populations of the passage m igrants. 2) Regression analyses of the annual trapping totals yielded negative correlations between dates and numbers for 30 of the 35 speci es. The trends were statistically significant in 14 species. Among the 5 positive results only one was significant. Significant negative tre nds in the trapping totals are primarily found in long-distance (trans -Sahara) migrants. These were followed by partial migrants with high p ortions of residents. The smallest declines occurred in species that w inter mainly in the Mediterranean area. 3) In comparison with the prec eeding analyses (BERTHOLD et al. 1986) in which data up to 1983 were t reated, the negative picture of the annual trapping totals and thus th at of the development of the respective populations has deteriorated c onsiderably in the meantime. Up to 1983 the annual trapping totals of the Mettnau station had produced negative coefficients in 69 % of the species. By 1991 this value increased to 85 %. None of the species sho w a trend turn towards positive development. The annual trapping total s of all species which continuously decrease have declined significant ly from the first to the second decade of the period of investigation by 15 %. The decreases in the trapping totals of the trans-Sahara migr ants are significant since 1980. 4) The extremely negative picture fro m these trapping figures reflect population changes which are in gener al agreement with the current ''Red lists'' of the avifauna of Central Europe. In a number of species like Savi's warbler, aquatic warbler, woodwarbler and wryneck individuals are no longer even trapped annuall y at the Mettnau station and the gaps will certainly increase. 5) Fina lly, differences in the development of various populations, some sourc es of error within the trapping figures and some possible causes for p opulation decline on the basis of great reed and sedge warbler data (d ecrease in the proportions of adult birds) are briefly discussed. It i s emphasized that in future population studies investigations of the c auses of population declines should have a high priority to further mo nitor these trends.