Influence of rainfall on timing and success of reproduction in Marabou Storks Leptoptilos crumeniferus
A decline in breeding success with later laying dates throughout a nesting season is a widespread phenomenon in species living in environments with distinct seasonality, with evidence that some environmental correlate of timing is at least partly responsible in many species. This correlate is often thought to be food availability, which is often related to climatic factors; however, few studies have examined the role of climate. We studied a breeding colony of Marabou Storks Leptoptilos crumeniferus in Southern Africa over five breeding seasons. Timing of breeding was related to rainfall preceding the breeding season. Fecundity (chicks fledged per nest) declined through each season. The probability of an individual hatchling fledging was influenced by rainfall during the hatchling period, temperature during the hatchling period and laying date, three variables that were strongly intercorrelated. To disentangle the three effects, inter-annual variation in each was compared with the large inter-annual variation in breeding success, with rainfall providing the greatest explanatory power. Rainfall, which tends to increase through the breeding season, seems to be at least partly responsible for the seasonal decline in breeding success. We were unable to find evidence for the influence of other factors, such as colony size and nest re-use, known to affect nest success in this and other colonial breeding storks.
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