Abstract
AbstractThe ruff Philomachus pugnax, a lekking shorebird wintering in Africa and breeding across northern Eurasia, declined severely in its western range. Based on a capture‐mark‐resighting programme (2004–2011) in the westernmost staging area in Friesland (the Netherlands), we investigated changes in apparent annual survival in relation to age and sex to explore potential causes of decline. We also related temporal variation in apparent survival to environmental factors. We used the Capture‐Mark‐Recapture multievent statistical framework to overcome biases in survival estimates after testing for hidden heterogeneity of detection. This enabled the estimation of the probability to belong to high or low detectability classes. Apparent survival varied between years but was not related to weather patterns along the flyway, or to flood levels in the Sahel. Over time, a decline in apparent survival is suggested. Due to a short data series and flag loss in the last period this cannot be verified. Nevertheless, the patterns in sex‐specific detectability and survival lead to new biological insights. Among highly detectable birds, supposedly most reliant on Friesland, males survived better than females ( = 0.74, range 0.51–0.93; = 0.51, range 0.24–0.81). Among low detectable birds, the pattern is reversed ( = 0.64, range 0.37–0.89; = 0.73, range 0.48–0.93). Probably the staging population contains a mixture of sex‐specific migration strategies. A loss of staging females could greatly affect the dynamics of the western ruff population. Further unravelling of these population processes requires geographically extended demographic monitoring and the use of tracking devices.
Highlights
Increasing human pressures on habitats are driving many migratory species in decline (Berger 2004; Sanderson et al 2006; Wilcove and Wikelski 2008; Limburg and Waldman 2009)
Based on a capture-mark-resighting programme (2004–2011) in the westernmost staging area in Friesland, we investigated changes in apparent annual survival in relation to age and sex to explore potential causes of decline
This study examined the year to year variation in apparent survival of western migrant ruffs of different age and sex staging in Friesland, the Netherlands, during northward migration
Summary
Increasing human pressures on habitats are driving many migratory species in decline (Berger 2004; Sanderson et al 2006; Wilcove and Wikelski 2008; Limburg and Waldman 2009). Despite their great ability to move, due to specific habitat requirements, tight time schedules and density dependent processes, long-distance migrants are vulnerable to global change (Alerstam et al 2003; Piersma 2007; Taylor and Norris 2007). Taking into account imperfect detection of marked individuals, it allows the estimation of demographic rates in a robust way and provides a basis for inference on potential drivers (Lebreton et al 1992; Gimenez et al 2008)
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