| Summary: | The ruff Philomachus pugnax, a lekkingshorebird wintering in Africa and breeding across northernEurasia, declined severely in its western range. Based on acapture-mark-resighting programme (2004–2011) in thewesternmost staging area in Friesland (the Netherlands),we investigated changes in apparent annual survival inrelation to age and sex to explore potential causes ofdecline. We also related temporal variation in apparentsurvival to environmental factors. We used the Capture-Mark-Recapture multievent statistical framework to overcomebiases in survival estimates after testing for hiddenheterogeneity of detection. This enabled the estimation ofthe probability to belong to high or low detectabilityclasses. Apparent survival varied between years but wasnot related to weather patterns along the flyway, or to floodlevels in the Sahel. Over time, a decline in apparent survivalis suggested. Due to a short data series and flag loss inthe last period this cannot be verified. Nevertheless, thepatterns in sex-specific detectability and survival lead tonew biological insights. Among highly detectable birds,supposedly most reliant on Friesland, males survived betterthan females (?/HDmales = 0.74, range 0.51–0.93;?/HDfemales = 0.51, range 0.24–0.81). Among lowdetectable birds, the pattern is reversed (?/LDmales = 0.64,range 0.37–0.89; ?/LDfemales = 0.73, range 0.48–0.93).Probably the staging population contains a mixture of sexspecificmigration strategies. A loss of staging femalescould greatly affect the dynamics of the western ruffpopulation. Further unravelling of these population processesrequires geographically extended demographicmonitoring and the use of tracking devices.
|
|---|