Zeitschriftenartikel

Survival rates of Black-tailed Godwits Limosa limosa breeding in the Netherlands estimated from ring recoveries

Van Noordwijk, A. J. , Thomson, D. L.
Ardea, 96:1, 47–57 (2008)

Abstract

The Netherlands holds internationally important numbers of Black-tailed Godwits, and reports of a substantial population decline have prompted concern. The reasons for the decline are unclear and one way of narrowing the list of possible causes is to identify the demographic processes responsible. Some information is available on apparent survival of adults based on mark-resighting data collected at individual study sites, but as yet there has been no analysis of age-specific survival based on large-scale long term data from birds ringed at breeding sites throughout the Netherlands and later recovered. We conducted such an analysis for the period 1960 to 2000 and although declining sample sizes and falling reporting rates reduced the precision of estimates in later years, we were able to conclude that at least adult survival had dropped significantly in the late 1990s from 0.77 to 0.40. Data were too sparse to estimate juvenile survival in this period. Apart from this sharp drop, we found no evidence of long term trends in either first year or adult survival. Although the precision of the survival estimates has deteriorated due to falling sample sizes and a decline in reporting rates of adults from 9% in 1960 to 1% in 2000, we found no evidence of potential bias due shifts in the spatial distribution of recoveries or the reported cause of death. These large-scale analyses of birds recovered dead complement more intensive mark-resighting studies at individual sites, and estimates correlate closely between the two methods. National ring recovery data cover much longer time periods, the use of dead recoveries instead of live resightings allows us to distinguish between mortality and emigration, and they permit the estimation of juvenile, and not just adult, survival rate. However, given the falling reporting rates of dead birds and consequent loss of precision, intensive mark-resighting programmes have an increasingly important role to play in the study of godwit survival rates.
Das Max-Planck-Institut für demografische Forschung (MPIDR) in Rostock ist eines der international führenden Zentren für Bevölkerungswissenschaft. Es gehört zur Max-Planck-Gesellschaft, einer der weltweit renommiertesten Forschungsgemeinschaften.