Entwicklung eines statistischen Habitateignungsmodells zur räumlichen Vorhersage der Vorkommenswahrscheinlichkeit des Wachtelkönigs (<i>Crex crex L.</i>) im Nationalpark Unteres Odertal

Abstract

Until the middle of the last decade, there had been little knowledge about the habitat requirements and conservation biology of corncrakes (Flade 1991). Many questions on these topics were answered by Stowe et al. (1993), Green and Tyler (1993), Schäffer und Münch (1993). Tyler (1996), Green et al. (1997) and Schäffer (1997). The results of these studies are based upon regional studies with an all in all manageable data pool.Central aims of the present study were to analyse factors influencing the spatial distribution of corncrakes in the Lower Oder Valley National Park and to predict the spatial distribution of the species, when land use changes. The investigation is based upon two major hypothesis: Spatial explicit data on the structure of grassland vegetation allows the prediction of corncrakes occurrence Statistical habitat suitability models allow an approximation of the influence of land use changes on the suitability of grassland as corncrakes habitat.With the present investigation on corncrakes´ habitat in the breeding area of capital importance in Germany, the data pool on multivariate analyses on the habitat requirements could be enlarged. Based upon the high resolution digital spatial database of vegetation units in the national park it was possible to link multivariate statistical analysis on habitat requirements of corncrakes with spatial explicit prognosis of corncrakes occurrence on a regional landscape scale. The validity of the univariate and multivariate logistic regression models on the probability of corncrakes occurrence could be tested by the spatial and temporal transfer of the model prognosis to parts of the parks, where no variables for the calibration of the models have been recorded. and to datasets of different years. Therefore the validity of the models could be approved.Spatial explicit data on the structure of grassland vegetation enable the prediction of corncrake populations on the landscape scale in the Lower Oder Valley National Park in a satisfying extent. By means of univariate and multivariate statistical habitat models it is possible to designate the influence of variables on the distribution of corncrakes. Furthermore key variables on the occurrence of corncrake populations could be displayed. The application of spatial explicit statistical habitat models in land use scenarios on environmental changes enables an approximate estimation of the influence of land use changes on the suitability of areas as corncrakes habitats.In the middle of may, key variables of the occurrence of corncrakes were the height of vegetation and total cover of the grassland vegetation . The higher the vegetation and the higher the total cover of grassland vegetation, the higher is the probability of the occurrence of corncrakes in the middle of may. In the middle of june, land use is a key variable for the colonisation of meadows by corncrakes. Additionally fallow grassland has not been colonized by male corncrakes five years after abandonment. Parameters on the structure of meadows which have been preferably colonized by corncrakes could be precised. The description of these parameters could be interpreted as attributes of meadows prefered by corncrakes.In the middle of may, corncrakes prefer high grown meadows, which are mown once in a year (the higher the meadows grow, the more frequent male corncrakes occur). The middle strata of these meadows reached a height of more than 60 cm and a total cover of more than 80 %. The lower strata of these meadows grow up to 20 cm with achieving only little total cover.In the middle of june, corncrakes prefer meadows, which are mown late in the year. The meadows hold a height of vegetation from 60 - 80 cm and provide a total cover of 100 per cent. The height of the lower strata of grassland vegetation of meadows which have been prefered by corncrakes reaches a height of growth of more than 25 cm. As an outlook to further investigation, it is proposed to test the validity of the chosen multivariate regression models in other parts of the breeding range of corncrakes. Therefore, it is necessary to detect similar variables of the structure of grassland vegetation in order to compare the results to the present investigation.