Population development of Central European songbirds final report of the MRI program Bestandsveranderungen mitteleuropaischer Kleinvogel Abschlussbericht zum MRI-Programm
Berthold, P.; Fiedler, W.; Schlenker, R.; Querner, U.
Vogelwarte 40(1-2): 1-10
1999
ISSN/ISBN: 0049-6650 Document Number: 426588
The bird-trapping program "Mettnau-Reit-Illmitz (MRI)-Programm" ran during the periods 1974-1983 and 1989-1993 and was ended in 1993. In the 15 years of operation at the 3 stations (Mettnau, southern Germany; Reit, northern Germany; Illmitz, eastern Austria) almost 300,000 individuals of 35 small bird species were caught and examined according to various aspects of the program. Here we present a final report for the area concerned with population dynamics and monitoring. Over the 20 years covered by the study negative trends in population size were observed for 20 species, in 12 cases at all 3 or 2 of the 3 stations; only 4 species showed exclusively positive trends (but each at only one station statistically significant), and the remaining 11 species had quasi-stable populations. Only 4 species exhibited opposite trends at different stations. The numbers trapped thus give a very uniform picture of the ways these species' populations developed in Central Europe. Because of the predominance of negative trends, the total numbers trapped at the stations Mettnau and Reit decreased significantly over the period 1974-1993 and showed a corresponding tendency at Illmitz. According to these data, during the study period the species investigated declined by an average little less than 1% per year in Central Europe. Apart from the Song Thrush, the decline affected mainly long-distance migrants. In addition to known causes of population declines, which are discussed briefly, the current climatic warming is evidently a new, important factor; by continuing thus to affect the long-distance migrants, it could cause a fundamental restructuring of the avifauna of extensive regions.