Summary 1.A trend towards increasing average spring temperatures has been observed in Europe over the past 25 years. This climatic variation has been attributed to a natural, large-scale atmospheric phenomenon, the North Atlantic Oscillation (NAO). A number of studies have reported associations between the winter NAO-index and both breeding phenology and cohort-speci®c morphology. These studies have been crosssectional rather than longitudinal and therefore have not been able to determine whether the changes result from phenotypic plasticity or microevolutionary processes. 2. We analysed (i) cross-sectional correlations between the winter NAO-index and breeding performance (laying date, clutch size,¯edging success and number of recruits produced) and morphological traits (tarsus and wing length), and (ii) within-individual variation in the same traits for individuals experiencing dierent values of the NAOindex in a population of collared¯ycatchers (Ficedula albicollis) breeding on Gotland, Sweden, over a period of 16 years (1980±95). 3. None of the four measures of breeding performance changed consistently over the study period, while tarsus length of males (and marginally females) decreased over time. Of the six traits investigated using cross-sectional data, only laying date was related to variation in the NAO-index. 4. All characters investigated showed signi®cant repeatability within individuals among years, revealing the importance of factors speci®c to individuals in determining their value. However, within individuals the NAO-index signi®cantly aected laying date and clutch size such that females laid earlier and produced larger clutches after warmer, moister winters. 5. Our data show a high degree of concordance between cross-sectional and longitudinal analyses of the eect of NAO on laying date and clutch size. The similarity of responses across and within individuals suggests that the population-level response to the NAO-index can be explained entirely as the result of phenotypic plasticity.

J. 2001. Breeding success in Blue Tits: good territories of good parents? -J. Avian Biol. 32: 214 -218.Territorial quality and parental quality are usually assumed to be the main sources of variation in the reproductive success of passerine birds. To evaluate 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 the condition of offspring were consistent for territories between years and accounted for 30% and 33% of the variation in these variables, respectively. After removing the effect of territory quality, none of the breeding parameters were significantly repeatable for individual females, but offspring condition was repeatable for males, accounting for 28% of variation. For females breeding on the same territory in subsequent seasons (combined effect of individual and territory quality) only hatching date was repeatable (45% 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. Consistency of the peak frass-fall date for individual frass collectors over the study period suggests that repeatable hatching dates on territories may be related to the relationship between timing of breeding and timing of peak food availability on territories. Our results suggest that territory quality is more important than parental quality for breeding success in the Blue Tit, and that male (but not female) quality makes a considerable contribution to reproductive success.

An increasing amount of evidence indicates that different forms of environmental stress influence the expression of genetic variance in quantitative traits and, consequently, their evolvability. We investigated the causal components of phenotypic variance and natural selection on the body condition index (a trait often related to fitness in wild bird populations) of blue tit (Parus caeruleus) nestlings under contrasting environmental conditions. In three different study years, nestlings grown under a poor feeding regime attained lower body condition than their full-sibs grown under a good feeding regime. Genetic influences on condition were large and significant in both feeding regimes, and in all three study years. However, although estimates of additive genetic variance were consistently higher in the poor than in the good environment, heritability estimates for body condition index were very similar in both environments due to higher levels of environmental variance in the poor environment. Evidence for weak genotypeienvironment interactions was obtained, but these contributed little to variance in nestling condition. Directional natural selection on fledging condition of nestlings was detected, and there were no indications of year or environmental effects on the form and intensity of selection observed, in a sample of 3659 nestlings over four years. However, selection on fledging condition was very weak (standardized selection gradient, β l 0n027p0n016 SE), suggesting that, in the current population, the large additive genetic component to fledging condition is not particularly surprising. The results of these analyses are contrasted with those obtained for other populations and species with similar lifehistories.

No abstract