Explicit experimental evidence for the role of mate guarding in minimizingloss of paternity in the Seychelles warbler

Extra-pair copulations (EPCs) (copulations outside the pair bond) resulting in extra-pair fertilizations (EPFs) are widespread in birds. To increase r eproductive success, males should not only seek EPCs, but also prevent thei r females from having EPFs. Male Seychelles warblers (Acrocephalus sechelle nsis) follow their partner closely during the period when these females are most receptive (fertile period). The Seychelles warbler is the first speci es to offer explicit experimental evidence that mate guarding functions as paternity guarding: in territories where free-living males were induced to stop mate guarding during the pair female's fertile period, the rates of in trusions by other males and successful EPCs (male mounting female) were sig nificantly higher than those observed in the control group and in the absen ce of mate guarding the frequency of successful EPCs increased significantl y with local male density. Male warblers do not assure their paternity thro ugh frequent copulations to devalue any sperm from other males: males do no t copulate with their partners immediately following a successful EPC obtai ned by their partners, the frequency of successful within-pair copulations does not increase with the frequency of successful EPCs and females initiat e all successful copulations and are capable of resisting copulation attemp ts.