Variation in clutch size, egg size variability and reproductive output in the Desert Finch ( Rhodospiza obsoleta)

Abstract

We studied the degree of variability and repeatability of egg size in clutches in the context of clutch size and reproductive output of a double-brooded Desert Finch population ( Rhodopsiza obsoleta). The within-clutch coefficient of variation (CV) was significantly greater in first (mean=1.92, 95% CL: 1.54–2.30) than in second broods (mean=1.24, 95% CL 0.94–1.55). Repeatability estimate for egg volume was smaller for first (0.51, 95% CL: 0.26–0.77) than for second broods (0.74, 95% CL: 0.52–0.90). Simultaneously, mean clutch size was bigger for first (4.61, 95% CL: 4.31–4.92) than second broods (3.69, 95% CL: 3.40–3.98). However, the number of nestlings and the number of fledglings were not different between first and second broods. The observed differences in clutch size and the within-clutch variation for egg size between first and second broods lead to a similar overall breeding output. These results point to a possible strategy applied by females during the two egg-laying periods in the breeding season, and depend on the fast-changing and extreme environmental conditions in arid habitats.