Post-breeding information gathering and breeding territory shifts in northern wheatears.

1. Prospecting non-breeding individuals have been shown to collect information on breeding sites a year ahead of breeding, but whether experienced breeders prospect future breeding sites is less well-known. Using data on post-breeding movements and between-year site shifts from a long-term population study of the migratory northern wheatear (Oenanthe oenanthe L.), we investigated (1) whether breeding territory selection of experienced breeders was a two-step process, made partly in the post-breeding period and partly at the time of territory establishment in the subsequent year; (2) predictions of which factors and cues correlate to site shifts at these two selection periods; and (3) consequences of territory shifts. 2. Many wheatears stayed close to their breeding site during the post-breeding period, but about 20% shifted to new potential breeding sites. Males that shifted to a new post-breeding location were also more likely to shift territory between years. 3. Factors linked to site shifts differed in the two investigated episodes of site selection. Post-breeding site shifts were linked to an environmental predictor of individual fitness, which is also related to foraging conditions (i.e. wheatears moved from tall to short field layers). Post-breeding site shifts, however, were not more frequent among young and failed breeders which may benefit most from prospecting for alternative breeding sites. Instead, in line with predictions of improving breeding conditions between-year site shifts were more frequent among young (only males) and failed breeders, whereas the link to territory field layer height disappeared. 4. Young males occupied more attractive sites and were more likely to breed successfully in year t + 1, but this improvement could also be expected from random choice. 5. Our results suggest that even though site shifts are determined partly during the post-breeding period, post-breeding movements of experienced breeders may be costly, especially when the breeding site is also a good foraging and moulting site in the post-breeding season. Under such circumstances an individual's choice of breeding site may often be determined at arrival in the subsequent year.