Variation in Blue Tit Breeding Performance Across Gradients in Habitat Richness

Abstract

Food supply is widely considered to be a major factor in determining life history traits and reproductive performance of birds. However, large spatial and temporal variation in natural available food supply is not always paralleled by proportional changes in energy demand by breeding birds. This necessarily results in variation in the supply–demand ratio and the amount of food available per unit mass of nestling. Because reproductive performance should respond to increases in available supply as a saturation curve, reaching a plateau above a certain threshold of food supply, we predict that variation in supply should change the intensity of selection on reproductive traits. We first tested this prediction using long‐term data on nestling growth and survival in Blue Tits (Parus caeruleus) breeding over a gradient of habitat richness in Corsica, France. This long‐term data analysis evaluates the effect of variation in food supply available to breeding tits using three surrogate variables: interannual variation in peak caterpillar abundance (caterpillar frass fall), offset between breeding date and peak caterpillar abundance, and natural variation in clutch size. We also used an experimental brood size manipulation (±3 chicks) to test the effect of varying brood demand on nestling growth. Results of the long‐term data analysis show that all three variables affect fledging mass and fledging success in poor habitats, while only fledging mass is affected by variation in offset in rich habitats. Moreover, mean annual fledging success and fledging mass is strongly affected by annual variation in peak caterpillar abundance at low levels of abundance, but these effects disappear when food becomes abundant (saturation threshold level of 373 and 560 mg frass·m−2·d−1 for fledging success and fledging mass, respectively). Brood size manipulations confirm these results. In rich habitats, breeding birds can raise three extra chicks without any apparent effects on chick growth, while in poor habitats, chick growth is significantly reduced with brood enlargement. Our study shows that although food limitation can play an important role, it may not always be the primary force shaping life history traits.

Breeding Performance of Blue Tits Cyanistes caeruleus ultramarinus in Relation to Habitat Richness of Oak Forest Patches in North-Eastern Algeria

“…Additional observations of food delivered to chicks in combination with experiments manipulating brood size, breeding time and/or food availability support the view that caterpillar availability in the territory influences parental feeding capacities and the types of prey delivered to Breeding performance of Blue Tits Cyanistes caeruleus ultramarinus in relation to habitat richness of oak forest patches in north-eastern Algeria chicks (e.g. Grieco 1999, Tremblay et al 2003, 2005.…”

“…Frass fall is considered to be a reliable estimate of caterpillars available to Blue Tits, especially in between-study site comparisons expressing large differences in peak caterpillar abundance between distinct habitat types (Tremblay et al 2003). We therefore collected frass in 0.25 m 2 tissue collectors under the tree canopy to obtain a proxy of habitat richness (cf.…”

“…We therefore collected frass in 0.25 m 2 tissue collectors under the tree canopy to obtain a proxy of habitat richness (cf. Zandt et al 1990, Tremblay et al 2003, Wesołowski & Rowiński 2006. Ten collectors per study site were visited once a week during the breeding season.…”

“…Blondel 1985, Clamens et al 1986, Blondel et al 1987, Fargallo & Johnston 1997, Massa et al 2004, Arriero et al 2006, Garcia-Del-Rey et al 2006. Comparative analyses of breeding biology in distinct habitat types at the southern edge of the distribution range reported lower breeding success in European Mediterranean evergreen habitat, often attributed to a significant reduction in caterpillar availability and/or higher loads of nest ectoparasites attacking chicks in these populations (Blondel et al 1991, Chabi et al 1995, Hurtrez-BoussPs et al 1997, Tremblay et al 2003, 2005, Bańbura et al 2004, Massa et al 2004, Arriero et al 2006, Garcia-Del-Rey et al 2006. Studies that controlled for altitude and latitude also reported significantly later adaptive breeding dates in evergreen than in summergreen oak patches (e.g.…”

Effects ofProtocalliphoraParasites on Nestling Food Composition in Corsican Blue TitsParus caeruleus: Consequences for Nestling Performance

“…The data for this study were collected in Pirio, Corsica (42°24'N, 08°44'E) as part of a long-term study of the population biology of Blue Tits in Mediterranean France (see Blondel et al 1993, 1999, Tremblay et al 2003. The study site was located in an evergreen forest dominated by the Holm Oak Quercus ilex.…”