Food availability and seasonal variation in nest predation pressure as factors influencing the timing of breeding of Namaqua sandgrouse in the Nama Karoo, South Africa

Abstract

The Namaqua sandgrouse, Pterocles namaqua, is an opportunistic granivore that feeds exclusively on the seeds of ephemeral plants. These plants germinate after rainfall and have a short growing season before producing abundant quantities of seed as they dry out and die. We monitored the timing of breeding of Namaqua sandgrouse in relation to rainfall and food availability in the arid Nama Karoo biome, South Africa, to test the prediction that this species should start to breed as soon as the ephemeral plants began to set seed. Despite substantial variability in the timing and quantity of rainfall and subsequent seed production, the timing of breeding was relatively fixed, generally starting 3–5 months after food became  abundant and extending into the rainy season, when food supplies can reach  critically low levels. We conclude that food availability is not the sole factor  determining the timing of breeding of Namaqua sandgrouse in the Nama Karoo. Daily nest predation rates decreased by up to 50 % during the course of the breeding season.We suggest that this seasonal decrease in nest predation pressure, combined with high levels of nest predation, may provide a strong selective pressure for delayed breeding by this species in the Nama Karoo.

Key words: breeding season, nest predation, granivore.