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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Animal Ecology. Summary 1. The hypothesis that mass reduction in breeding passerines results from energetic stress was evaluated using data on body mass changes in female blue tits Parus caeruleus. 2. In accordance with both the adaptive adjustment and the physiological stress hypotheses, females with experimentally enlarged broods lost more mass than females rearing reduced or control broods. However, the ability to allocate energy to selfmaintenance (as measured by the regrowth rate of a tail feather removed during incubation) was negatively correlated with the amount of lost body mass. 3. In one of the study years, loss of body mass was more pronounced among small females, suggesting that larger females are better able to cope with poor food conditions during breeding. 4. In a poor-weather year, 30% of the females deserted their clutches, compared with 8% in a good year. Females that deserted their clutches before hatching were significantly lighter during incubation than non-deserters, indicating that good body condition is important for successful reproduction. 5. In one year young females lost more mass than older females and therefore the ability to maintain adequate body condition in the face of energetic stress appears to be age-dependent. 6. Taken together, these results suggest that mass loss in breeding blue tits is, to some degree, attributable to energetic stress, although we have not ruled out the possibility that flight cost reductions may help explain the phenomenon.

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.

1999. The peninsula effect on species diversity: a reassessment of the avifauna of Baja California. -Ecography 22: 542-547.The peninsula effect, a decrease in species diversity from the base to the tip of peninsulas, has been proposed to explain the relatively poor species diversity of mammals on North American peninsulas. Subsequent work has questioned both the existence of peninsular declines in diversity, as well as the proposed cause (immigration-extinction dynamics). Previous studies of the Baja California avifauna have shown a gradual decrease in the diversity of breeding birds from the base to the tip of the peninsula. Using newly published data on the breeding land birds, I found a decrease only from the base to the middle of the peninsula, with a slight increase in diversity from the middle to the tip. This result is similar to that for other highly vagile taxa (e.g., Chiroptera, Lepidoptera) and is largely due to the concave diversity gradient of montane species along the peninsula. Habitat associations of the Baja avifauna and the location of potential source populations suggest that: 1) local habitat heterogeneity is likely the single most important factor influencing the avian diversity gradient along the peninsula; and 2) limited immigration of Neotropical species from mainland areas, and of Nearctic species from the base of the peninsula to the montane southern tip is partly responsible for the form of the diversity gradient along the southern half of the peninsula. My results, along with those from previous studies, suggest that rather than colonization/extinction dynamics, habitat heterogeneity and the vagility of the taxa considered have the greatest impact on the observed patterns of species diversity along peninsulas.