Costly replacement: how do different stages of nest failure affect clutch replacement in the red- backed shrikes Lanius collurio?

Re-nesting is costly and strongly stage- and time-related in the redbacked shrike. We tested whether failure which occurred at more costly developmental stages of the first clutches influenced the characteristics of replacement clutches in red-backed shrike Lanius collurio. Field work was conducted in the breeding seasons 1999-2006 at three study plots in Poland. During nest visits, standard data on breeding biology were collected, including clutch size, eggs measurements, laying date, and number of nestlings. We found significant differences in the clutch size of replaced clutches according to the failure phase of first clutches. Pairs which experienced brood failure at the nestling phase produced smaller replacement clutches than pairs whose nest was destroyed at the egg laying stage. There were no differences in the nesting success of replaced cluches relative to the stage where the first clutch was lost. However, pairs which failed during the nes tling phase of the first clutch significantly more often skipped further repro duction in that season than those which failed during other phases. For breeding red-backed shrikes the best strategy is to initiate clutches as early as possible because it gives a more time for possible re-nesting.