THE ROLE OF TERRITORY CHOICE, MATE CHOICE AND ARRIVAL DATE ON BREEDING SUCCESS IN THE SAVI-WARBLER LOCUSTELLA-LUSCINIOIDES

We investigated how territory quality, settlement date and morphometry affected several components of yearly breeding success of a Swiss pop ulation of Savi's Warblers Locustella luscinioides. Territories occupi ed by males differed from unoccupied sites of similar size and locatio n by having higher and denser reeds, a more extensive straw litter, an d a thicker cover of dead sedge leaves. Territories with these charact eristics were the ones first chosen by males upon spring arrival. Thes e males, however, did not differ in morphometry from those that arrive d later. Availability of suitable nesting sites; rather than food avai lability, appears to be an important choice criterion for territories. Early arriving males had higher breeding success than late males beca use of a higher mating success and more successful clutches. The posit ive correlation between male breeding success and territory quality wa s thus mediated through their common dependence on occupancy date. Fem ale breeding success decreased with the date of first-clutch laying, m ainly because late-nesting females fledged fewer broods. Breeding succ ess in either sex did not correlate with morphometry. Our results prov ide clear support for territory choice by males, but not for mate or t erritory choice by females, and show the crucial role played by indivi dual settlement date on many aspects of the breeding cycle of both sex es. We propose a lottery model of mate choice. arriving females obtain the best available territories even without choosing mates or territo ries; since males occupy territories sequentially and in order of decr easing quality, the few unpaired males available at any moment also oc cupy the best available territories.