Negative impacts of hunting and suction-dredging on otherwise high and stable survival rates in Curlew Numenius arquata

Abstract

Capsule A stable annual survival rate of 90% was estimated for adult Curlew Numenius arquata from 1974 to 2011. Survival was reduced by mechanized cockle harvesting and hunting prior to the UK ban in 1982, but was similar for males and females. Aims To estimate annual and average survival rates for Curlew wintering in North Wales. To test the impacts of protection from hunting (effective 1982), and mechanized cockle dredging on apparent survival and longevity. Methods Thirty-six years' ringing data comprising 2636 bird records were analysed using Cormack Jolly–Seber survival models in mark. Models included variable and trending survival, plus constant-survival models (all years, pre- and post-hunting, sampling effort). The effects of protection from hunting, sampling success, cockle dredging and sex (from biometrics) were investigated, and the results compared with survival in other species and the predictions of demographic population models. Results Averaged annual survival was 89.9% with no significant difference between males and females. Estimated survival increased slightly from 86.9% (se = 0.04) to 90.5% (se = 0.01) and longevity by at least 40% after hunting was banned in 1982. Mechanized cockle harvesting in 1996 reduced apparent survival from 95% (best data estimate: se 0.07) to 81% (se 0.19) for two years, and was correlated with a published analysis showing reduced survival in Oystercatchers. Conclusion Declines observed in overwintering Curlew populations in the UK are not primarily driven by changes in adult survival, and continue despite the increase in survival to > 90% after hunting ceased in 1982. High adult survival rates cannot compensate for poor breeding productivity, and we anticipate poor turnover will lead to future impacts from senescence even in such a long-lived species.