Habitat-dependent population recovery in the Dartford Warbler Sylvia undata following a severe winter episode

Abstract

Capsule After a population crash following a long period of winter freezing and snow blanketing the ground, Dartford Warblers underwent a population recovery, positive in heathlands but non-existent in nearby early-growth forest. Aims To estimate the impact of a severe winter episode on the population size of Dartford Warblers in two habitats, heathland and early-growth forest. Methods We analysed data collected on 124 point counts in three successive years, 1 year before and 2 years after the cold spell. We first estimated trends in detected numbers in the two habitats. Second, we used distance sampling and capture–recapture approaches to estimate global population sizes corrected for detection probability, verifying that the observed trends were not biased by detection probability. Results Warbler populations crashed after the severe winter in 2008–9, while numbers increased in spring 2010 only on heathlands, not in early-growth forests. Variation in detection probability alone could not explain this difference. Conclusion After the severe winter episode, Dartford Warblers showed a short-term population recovery only in heathland.