Male reproductive strategies and parental investment in the wheatear, Oenanthe oenanthe.

1. This study investigated factors affecting individual reproductive success in the wheatear Oenanthe oenanthe, a migrant passerine species, on Bardsey Island, North Wales, 1991-93 2. Behavioural and paternity data, obtained using DNA fingerprinting, indicated that males pursued a mixed reproductive strategy, i.e. they ensured their paternity during the fertile period of the pair female and pursued extra-pair copulations outwith this time. Behavioural observations were consistent with males using mate guarding to ensure their paternity. Males adjusted their intensity of guarding in response to the threat to their paternity. Males mainly pursued extra-pair copulations once their female had begun incubating. Intrusions by extra-pair males peaked in the fertile period, and later breeding territories were intruded upon more than early breeding pairs. 3. Natural levels of extra-pair paternity were relatively low: 11% of 71 offspring, occurring in 29% of 17 broods. Extra-pair fertilisations contributed little to a male's reproductive success. Not all extra-pair fathers were identified, but at two nests males within a three-territory radius were excluded as extra-pair fathers. There was no evidence that females increased their reproductive success by laying eggs in the nests of other females (intra-specific brood parasitism). Females were never observed off territory soliciting extra-pair males and rarely seen soliciting extra-pair males on territory. The majority of EPCs were resisted by the female and their co-operation appeared to be essential for males to obtain successful copulations. The presence of extra-pair young within broods indicates that females must have also pursued a mixed reproductive strategy by participating in EPCs. 4. Experimental removals of males for 24 hours during the fertile period were used to investigate the effect of the absence of the pair male on: (i) female behaviour; (ii) the behaviour of extra-pair males; and (iii) levels of extra-pair paternity. The number of intrusions and extra-pair copulations increased in the absence of the pair male. Females rejected the majority of extra-pair copulations, and there was no significant increase in extra-pair paternity resulting from these experiments: 10% of 78 offspring occurring in 38% of 16 broods. Female behaviour appeared to be the determining factor affecting the level of extra-pair paternity, although male guarding behaviours may have limited the opportunities for females to participate in extra-pair copulations by deterring intrusions. 5. Males contributed on average 50% of chick feeds, and did not adjust their investment in proportion to their paternity in the brood. There was no effect of the temporary male removals, used to simulate a male's uncertainty of paternity, on their subsequent investment. However, males which adopted broods provided 29% of chick feeds on average, but this was not in proportion to the paternity they had in the brood. This reduction in the number of chick feeds was partially compensated for by females increasing their frequency of chick feeds. 6. Territories remained relatively constant between years. There was evidence that territories varied in quality, as indicated by their consistent order of settlement between years, individuals moving to preferred areas when possible, and individuals being more faithful to preferred areas. Older males returned to the breeding ground earlier than first- year males, and were more likely to be paired than individuals breeding for the first time. This was probably due to the older males having settled on preferred territories. Territory quality had a significant effect on individual reproductive success. There were few correlates with individual quality and measures of breeding success. A male's mating status was dependent on arrival time, territory quality, breeding density and the operational sex ratio. Males which settled on preferred territories were more likely to be paired. Pairs which bred on preferred territories tended to have increased fledging success, and nestlings which fledged from preferred territories were more likely to return to the study area to breed. Female reluctance to copulate outwith the pair bond may be a result of individual reproductive success being determined more by territory quality rather than male quality.