Fat-soluble antioxidants in the eggs of great tits Parus major in relation to breeding habitat and laying sequence

Among many altricial bird species, nestlings within a brood do not hatch simultaneously but over a period of several days (e.g. Clark & Wilson 1981, Ricklefs 1993, Stoleson & Beissinger 1995). Hatching asynchrony is mainly determined by incubation beginning before clutch completion, resulting in first-laid eggs hatching earlier than last-laid eggs (Lack 1968, O’Connor 1984) and consequent size hierarchies among nestlings that may cause death or slow development of late-hatched, small nestlings (Hahn 1981). The existence of hatching asynchrony has been considered a paradox since it can negatively affect reproductive success, due to death or poor condition at fledging of disadvantaged offspring (Stoleson & Beissinger 1995). At least seventeen different hypotheses have been proposed to explain this phenomenon (reviews in Ricklefs 1993, Stoleson & Beissinger 1995, Stenning 1996). Asynchronous hatching is usually considered adaptive because of the potential benefits accruing to parents by starting incubation before clutch completion, establishing a hierarchy in reproductive value among their offspring. Alternatively, asynchronous hatching (and accompanying partial brood mortality) may result from parental tactics to obtain benefits from an early start to incubation. In both cases, one might expect that it is in the interest of parents to modify the quality of their eggs with respect to laying sequence. In the case of adaptive brood reduction, parents would benefit from enhancement of the quality of first-laid eggs by Fat-soluble antioxidants in the eggs of great tits Parus major in relation to breeding habitat and laying sequence