Rogers K.G. & Piersma T. (2005) Monitoring vital rates of a migrant shorebird population: the case of ‘wilsternetted’ Eurasian Golden Plovers. ARDEA 93 (1): 65-77

Over the years, the purpose of the traditional wilsternetting technique of the northern Netherlands for trapping Eurasian Golden Plovers Pluvialis apricaria has changed from a hunting practice to bird ringing. In a companion paper, Piersma et al. (2005) examined the ringing data and recoveries for demographic trends from 1949 onwards. This paper examines the possibility of using the same data source for future monitoring of the population. Schemes monitoring the vital rates (survival rate, recapture probability, and recruitment) of migrant birds are rare. For two reasons, it is not immediately clear that effective monitoring is possible. First, hunting returns from outside The Netherlands have ceased so the data available for analysis are much reduced. Secondly, the very low probability of recapturing a ringed bird (c. 0.25%) leads to large standard errors of estimates of demographic parameters. For practical reasons, only triennial monitoring was considered for survival and recapture rates. Program MARK was used to estimate vital rates. A Monte Carlo simulation showed that a change in survival rate of 5% or more should be detected within six years if more than 3 000 birds were ringed per annum. The proposed monitoring methodology was applied to the historical data, using only the data available at the end of each three-year period. This test detected the changes in survival rate and recapture probability noted by Piersma et al. (2005). Reasonable consistency with earlier recruitment estimates was achieved despite the need to monitor this aspect on an annual basis. The parallel monitoring of recruitment through the juvenile proportion of catches is regarded as desirable, both to validate the methodology and for mutual checking between methods.