Nest-site selection, egg pigmentation and clutch predation in the ground-nesting Namaqua Sandgrouse Pterocles namaqua

Nest survival can, among a variety of factors, depend on nest-site complexity and concealment, and clutch crypsis. Nest-site selection by Namaqua Sandgrouse Pterocles namaqua was strongly non-random. Nests were sited within a local concentration of objects, most of them less than 15 cm high and concentrated within 30 cm of the nest centre. Nest-to-object orientation was random, indicating that the nest was sited close to objects neither for shade nor shelter from prevailing winds. A stepwise logistic regression analysis, using nine different object type, height and distance category totals as variables of nest-site complexity and concealment, found no effect of these variables on nest fate (survival vs mammal predation). A random-walk model simulating the foraging movements of a small mammal predator raised the possibility that the high level of nest predation suffered by Namaqua Sandgrouse was largely incidental (i.e. random). Namaqua Sandgrouse eggs were highly variable in appearance, but intra-clutch variability was less than that between clutches of different individuals. Intra-clutch diversity in pigment cover, the number of wreathed eggs, the dominant pigment pattern, and the overall shade of the clutch (light/dark) did not affect clutch survival. However, clutches exhibiting diversity in background colour, pigment pattern or pigment intensity between eggs survived significantly better than clutches whose eggs were uniform for these variables, suggesting there is some selection for clutch crypsis through visual diversity.