Breeding success in Blue Tits: good territories or good parents?

Territorial quality and parental quality are usually assumed to be the main sources of variation in the reproductive success of passerine birds. To ev aluate their relative importance for variation in breeding time (itself an important factor for breeding success), clutch size and offspring condition at fledging, we analysed six years of data from a Blue Tit Parus caeruleus population breeding on the island of Gotland, Sweden. Hatching dates and t he condition of offspring were consistent for territories between years and accounted for 30% and 33% of the variation in these variables, respectivel y. After removing the effect of territory quality, none of the breeding par ameters were significantly repeatable for individual females, but offspring condition was repeatable for males, accounting for 28% of variation. For f emales breeding on the same territory in subsequent seasons (combined effec t of individual and territory quality) only hatching date was repeatable (4 5% of variation accounted for). In males, the combined effect of individual and territory quality was repeatable for offspring condition and accounted for 33% of variation, but this result was only marginally significant. Con sistency of the peak frass-fall date for individual frass collectors over t he study period suggests that repeatable hatching dates on territories may be related to the relationship between timing of breeding and timing of pea k food availability on territories. Our results suggest that territory qual ity is more important than parental quality for breeding success in the Blu e Tit, and that mate (but not female) quality makes a considerable contribu tion to reproductive success.