Ostrich recruitment dynamics in relation to rainfall in the Mara–Serengeti ecosystem.

Animal population dynamics can be driven by rainfall variability through its influence on habitat suitability, availability and nutritional sufficiency of forage. To understand how rainfall influences ostriches, we related changes in ostrich recruitment in the Mara–Serengeti ecosystem to rainfall. Over a 15-year period, monthly counts of ostriches were made and the number of hatchlings, chicks, hens, cocks, and the size of the groups in which they occurred were recorded. Breeding was bimodal with a major peak in February and a minor peak in October. Ostriches formed larger groups in the wet (4.41 ± 5.17 (mean ± SD), range 1–72,n =672 groups) than in the dry (2.49 ± 2.70, range 1–29,n =398) season. The number of hatchlings plus chicks per hen increased across the duration of the study period and with increasing annual and early wet-season rainfall, affecting forage availability and quality. Recruitment was highest at intermediate levels of the five-year average of the late wet-season rainfall, implying that a change in long-term rainfall and habitat suitability would move recruitment away from the optimum. Outstanding adaptations to life in arid environments could make ostriches more resilient than sympatric ungulates if food shortages and water stress became more frequent because of widening climatic variability. [ABSTRACT FROM AUTHOR]