Uncertainties in spatially aggregated predictions from a logistic regression model

This paper presents a method to assess the uncertainty of an ecological spatial prediction model which is based on logistic regression models, using data from the interpolation of explanatory predictor variables. The spatial predictions are presented as approximate 95% prediction intervals. The prediction model is based on logistic regression analysis of field data of a wetland area in the central parts of the Netherlands. The model predicts block average probability of occurrences of 78 wetland plant species for 500 m×500 m blocks. The explanatory variables comprise groundwater chemistry, hydrological characteristics, and land use management. The uncertainty of the spatial model output is assumed to be a function of the uncertainty in the estimated regression coefficients and uncertainty in the interpolated values of explanatory variables. Monte Carlo analysis was used to assess the model output error due to uncertainty in both the regression coefficients and the explanatory variables. Correlation between errors in regression coefficients and spatial autocorrelation in explanatory variables are accounted for in the Monte Carlo analysis. Spatial patterns of the relative contribution of uncertainty of the regression coefficients to the total model uncertainty are presented. The patterns of the relative contributions of uncertainty to the total model uncertainty give information on the most effective way to reduce error, i.e. either by reducing uncertainty in the regression coefficients or in the interpolated input patterns. The spatial patterns and values of the 95% prediction intervals vary widely between species but are in general large and the relative contribution of the uncertainty of the regression coefficients is in general large (over 80%)

The influence of weather on the migration behaviour of Eurasian Bitterns<i> Botaurus stellaris</i>

CapsuleMigration studies of tagged Eurasian Bitterns Botaurus stellaris provide information on the behaviour of this secretive species in relation to weather conditions.AimsTo study if cold spells trigger southward migration in resident Eurasian Bitterns. To describe migratory behaviour including flight routes, altitudes, flight direction in relation to wind speed and direction, and general characteristics of stopping sites.MethodsSix adult Eurasian Bitterns from Dutch breeding areas were followed for two to five years using ARGOS-PTT/GPS transmitters or GPS trackers.ResultsFour individuals remained at the breeding sites in winter and did not migrate in response to cold spells. Two individuals covered distances of 300 and 1600 km between stopping sites. They migrated predominantly at night, but over the Sahara they extended flights into daylight hours. Depending on wind assistance, flight speeds (groundspeed) varied between 3.6 and 26 ms−1. Flight altitude varied from just above sea level when facing headwinds, to almost 2000 m above sea level under tail wind conditions. Repeatedly tracked individuals showed substantial variation in routes and stopping sites between successive migrations. These flight patterns appeared influenced by the speed and direction of the winds encountered en route.ConclusionsEurasian Bitterns were either migratory or resident and the latter individuals did not perform facultative movements at the onset of cold spells. The flight speed, flight altitudes, and routes of migrating birds were influenced by wind conditions. This likely explains the variable use of stopping sites between years