Constraints on, and determinants of, the annual number of breeding attempts in the multi-brooded Black Redstart Phoenicurus ochruros

With reference to models predicting patterns of reproduction in multi-brooded species, I analysed some of the factors potentially affecting the number of breeding attempts per season made by female Black Redstarts Phoenicurus ochruros in the central Swiss Alps. The maximum number of successful broods per female per season was three, the median two. The proportion of females initiating only a single clutch per season varied from 16 to 58% over 10 years. Variation in the frequency of single brooding between years was positively related to the date of the onset of breeding. Egg-laying started after a temperature-related threshold value was crossed in April. Females frequently re-nested before fledglings of the previous brood were independent. Short interbrood intervals were associated with triple brooding. The interbrood interval shortened during the breeding season. Intra-individual variation in the number of breeding attempts per season was partitioned according to female age, laying date of the season's first egg (standardized in relation to the median date of first laying within a year) and the occurrence of breeding failures before the ultimate nesting attempt. However, mortality during the season often terminated breeding early, in particular among novice breeder females. Seasonal reproductive success increased linearly with each additional breeding attempt. The productivity of a breeding attempt was independent of the time in the season. Increased reproductive effort affected neither current or future survival nor reproduction of females. The reproductive patterns and trade-offs in multi-brooded Black Redstarts contrast in many aspects with those found in single-brooded species. They are in accordance with models predicting that multi-brooded species are selected to start breeding as early as possible, continue breeding for as long as conditions are suitable, and save time by overlapping broods.