Rainfall and food availability as factors influencing the migration and breeding activity of Namaqua Sandgrouse, Pterocles namaqua

Abstract

This study examines whether rainfall and its effects on food availability control the timing of migratory movements and breeding activity in the Namaqua Sandgrouse, Pterocles namaqua. Namaqua Sandgrouse exhibit a pattern of partial migration between two late-summer-rainfall regions, birds spending the summer months in the Nama Karoo and the winter months in the Kalahari. Across southern Africa, the breeding season for this species is unexpectedly variable, and not consistently correlated with periods of peak food availability. The main egg-laying periods in the late-summer-rainfall regions are: (a) in northwestern Namibia from January–May with a peak in May, (b) in southwestern Namibia in any month with a peak in July, (c) in the Kalahari from June to December, and (d) in the Nama Karoo from September to December. Breeding in the Nama Karoo often starts five months after food becomes abundant, and extends into the start of the rainy season, when food availability can reach the lowest levels in the annual cycle. This suggests that some factor(s) other than proximate food availability is/are involved in determining the timing of movements and breeding in this species, at least in some regions. The possible complicating influences of biannual breeding, moulting, adult nutritional reserves and seasonal variation in nest predation pressure are discussed. We conclude that further long-term monitoring throughout the range of the Namaqua Sandgrouse is required to unravel the potential contribution of three factors (food availability, pottern of migratory movement and risk of nest predation) to the timing of migratory movements and breeding seasons in this species.