Abstract
Arid environments remind one of the punctuated equilibrium theory of evolution: they experience long periods of stasis and low productivity, interrupted with episodic rainfall which spurs reproduction and movement. Birds, as highly dispersive organisms, are among the most dramatic indicators of these fluctuations. Here we review birds' two main strategies, residency and nomadism, and the trade-offs faced by individuals in uncertain times. In general, wet years stimulate higher densities of nests (i.e. smaller territories), larger clutch sizes, unseasonal breeding, and at some times of year, higher breeding success. Rainfall above a certain threshold triggers breeding in resident species and an influx of nomadic species which breed and then move on. The environmental cues which trigger nomadism are sometimes poorly understood, but include distant thunderstorms for aquatic species, and perhaps for insectivores. Environmental cues that draw nomadic granivores to areas that have had recent rain are not known.
Highlights
Prolonged spells of drought pose dilemmas for most organisms, even those adapted to hyper-aridity
Semi-arid ecosystems are characterised by wet or dry states that are patchy in time and space
This patchiness is true of southern Africa, where much of the region is semi-arid[6] and the environment experiences extremes in weather, from periods of intense and prolonged drought to exceptionally high rainfall events.[7]
Summary
When to stay, when to go: trade-offs for southern African arid-zone birds in times of drought. Arid environments remind one of the punctuated equilibrium theory of evolution: they experience long periods of stasis and low productivity, interrupted with episodic rainfall which spurs reproduction and movement. We review birds’ two main strategies, residency and nomadism, and the trade-offs faced by individuals in uncertain times. Rainfall above a certain threshold triggers breeding in resident species and an influx of nomadic species which breed and move on. The environmental cues which trigger nomadism are sometimes poorly understood, but include distant thunderstorms for aquatic species, and perhaps for insectivores. Environmental cues that draw nomadic granivores to areas that have had recent rain are not known
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