, Volume 148, Issue 2 Supplement, pp 351-357,
Open Access This content is freely available online to anyone, anywhere at any time.
Date: 19 Jul 2007

Smoothing and trend detection in waterbird monitoring data using structural time-series analysis and the Kalman filter

Abstract

Many wildlife-monitoring programmes have long time series of species abundance that cannot be summarized adequately by linear trend lines. To describe long time series better, generalized additive models may be used to obtain a smooth trend line through abundance data. We describe another approach to estimate a smoothed trend line through time series consisting of one observation per time point, such as year or month. This method is based on structural time-series models in combination with the Kalman filter and is computerized in the TrendSpotter software. One of its strengths is the possibility to test changes in smoothed abundances between years, taking into account serial correlation. The trend method is applied in the Dutch Waterbird Monitoring Scheme (DWMS), a monitoring scheme for migrating and overwintering waterbirds. Taking the numbers of overwintering Greater Scaup (Aythia marila) in the Netherlands as an example, we demonstrate three applications of the method: (1) trend calculation and classification for each year in the time series, (2) assessing alerts for alarming population declines and (3) testing yearly abundance against a population threshold. We discuss the situations where TrendSpotter is to be preferred over other methods.

Communicated by F. Bairlein.
This is a paper on the occasion of a presentation at the “population alerts” symposium at the 24th IOC Congress in Hamburg.
TrendSpotter is available from the second author (http://www.hans.visser@mnp.nl) at no cost.