Against the trend: Increasing numbers of breeding Northern Lapwings Vanellus vanellus and Black-tailed Godwits Limosa limosa limosa on a German Wadden Sea island

Abstract

Capsule: The increase in population sizes over the last 30 years cannot be explained by reproductive success. Aims: To establish whether the positive population trends are due to increasing and self-sustaining populations or to immigration. Methods: We studied the population development of breeding lapwings from 1971 until 2005 and of godwits from 1977 until 2005 on Wangerooge, a German Wadden Sea island. Both species increased significantly during the last three decades. For each species we used a logistic growth model to derive the reproductive output required to explain the past population development without assuming immigration. We compare the values derived by this model with empirical findings of reproductive output of the respective populations. Results: For neither lapwings nor godwits can empirical reproductive success explain the observed population development. Conclusion: Our results imply that the increase in breeding pairs of Northern Lapwing and Black-tailed Godwit on Wangerooge Island is not due to reproductive output. We propose that it is mainly caused by immigration onto the island. © 2008 British Trust for Ornithology.