Male Seychelles warblers use territory budding to maximize lifetime fitness in a saturated environment

In cooperatively breeding species, helping at the nest and budding off part of the natal territory have been advanced as strategies to increase fitnes s in an environment that is saturated with territories. The importance of h elping or territory budding as a determinant of lifetime reproductive succe ss (LRS) has been debated because the potential benefits of both strategies could not be separated. Here we test the causes and the immediate and futu re fitness consequences of single dispersal decisions taken by male Seychel les warblers (Acrocephalus sechellensis). Males breeding in high-quality te rritories (high food abundance) have significantly higher LRS than similar- aged males budding off part of the parental territory. Initially, budders h ave a low reproductive success (because of limited food resources or absenc e of a breeding partner). However, they have a long life span and inherit h igh-quality territories through site dominance, by which they gain higher L RS than breeders on low-quality territories, helpers, or floaters. Experime ntal creation of male breeding territory vacancies showed that most young m ales became budders because of intense competition for high-quality territo ries. The translocation of warblers to the previously unoccupied Aride Isla nd shows that males behave according to the expected fitness benefits of ea ch dispersal strategy. In the absence of competition for territories on Ari de, all young males bred in high-quality territories. However, after satura tion of high-quality habitat with territories, most males became budders ra ther than breeders on low-quality habitat, helpers, or floaters.