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

摘要

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.