Conspecific breeding success does not guide nest-site choice for the next year in three leaf warbler species (Passeriformes, Phylloscopidae)

Contrary to the widespread belief that nest site selection takes place prior to the onset of breeding, substantial evidence suggests that migratory birds may gather information about territory quality during the post-breeding season and subsequently return to those locations in the following year. This decision may be influenced by the density of conspecifics settled in the previous season or by their reproductive success. We hypothesized that during the post-breeding period, Phylloscopus leaf warblers might imprint on the most favorable territories where they spent a significant portion of their time prior to migrating to their wintering grounds. Between July and August of 2021–2022, we broadcast fledgling begging calls, adult calls, and songs across plots to simulate the successful nesting of three species: Wood Warbler ( Phylloscopus sibilatrix ), Greenish Warbler ( Phylloscopus trochiloides ), and Common Chiffchaff ( Phylloscopus collybita ). In 2022, we simulated the presence of breeding pairs or single males of Wood Warbler on the plots, while in 2023, only single males of Wood Warbler—exhibiting either high or low singing activity—and Greenish Warbler males with varied song repertoires were broadcast. To monitor the return of individuals previously nesting in the study area, we captured and ringed 122 Wood Warblers from 2021 to 2024, along with 8 Greenish Warblers in 2023. However, only a single male Wood Warbler (0.8%) and no Greenish Warblers were recaptured in the subsequent years. Furthermore, the abundance of all three species did not vary significantly between the experimental plots, regardless of whether we simulated the presence of fledglings, breeding pairs, or single males during the post-breeding season. These findings contradict our hypothesis that post-breeding cues reflecting conspecific breeding success could influence nest site selection by leaf warblers. This outcome may stem from the species' tendency to abandon nesting habitats shortly after fledging, relocating to areas less suitable for future breeding. Thus, reliance on post-breeding cues may represent a maladaptive strategy for nest site selection.