Climatic Influences on Survival of Migratory African Reed Warblers Acrocephalus baeticatus in South Africa

By Jansen, D. Y., Wilson, A. M., and Altwegg, R. • 2015

Abstract

The focus of most research on the influence of recent climate change on birds has been on the northern hemisphere. Climate change has been different in the southern hemisphere, prohibiting extrapolation from northern research findings — and inference regarding future climate change — to species living there. We investigated the correlation between climatic conditions and survival of a migratory population of African Reed Warblers Acrocephlaus baeticatus in Paarl, South Africa. We used temperature and rainfall in its breeding area, and Normalized Difference Vegetation Index (NDVI) in its wintering area, Central Africa around the Congo Basin. We fitted capture-mark-recapture models for open populations to a 12-year ringing dataset (1998–2010). After accounting for transience — this species exhibits high breeding site fidelity — with a ‘Time-Since-Marking’ model we found a mean survival probability of 0.79 ± 0.04 SE. Rainfall and NDVI did not influence survival in this dataset. Mean temperature (Aug–Apr) had a positive effect on survival: an increase of 1.6°C was associated with an increase of annual survival from 0.69 ± 0.05 to 0.88 ± 0.03. Higher temperatures could have increased local survival by providing more food and breeding habitat, thereby increasing adult body condition and reducing foraging costs, predation and territorial conflicts. Even though we would need data on abundance and reproduction to quantify the effects of climatic conditions on population growth, we found a clear effect of climatic variation on a key demographic parameter, adult survival.

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