Short- and Long-term Fitness Correlates of Rearing Conditions in Barn Owls Tyto Alba

In birds, the quality of rearing conditions is a major determinant of nestling body condition, nestling survival and recruitment probability (Martin 1987). When food becomes short, sibling competition increases (Mock & Parker 1997), growth is depressed (Smith et al. 1989), and chicks are more vulnerable to environmental stress factors (Hoffmann & Merila 1999). Although the effect of rearing conditions on nestlings has received much attention (Gebhardt-Heinrich & Richner 1998), little is known of the long-term fitness consequences of rearing conditions (Lindström 1999; Metcalfe & Monaghan 2001). Few studies have investigated the extent to which reproductive success and adult survival are correlated with rearing conditions experienced as a nestling. In Western Gulls Larus occidentalis and Crimson Rosellas Platycercus elegans the position of nestlings in the hatching sequence predicted nestling survival but not, or only weakly, adult survival (Spear & Nur 1994; Krebs 1999). In female, but not male Great Tits Parus major, nestling condition affected recruitment probability but not reproductive success (Verboven & Visser 1998; Visser & Verboven 1999) or to a low extent (Haywood & Perrins 1992). Thus, rearing conditions appear to often alter nestling condition, survival and the degree of recruitment (referred to as short-term effects) to a larger extent than reproductive success of recruits (long-term effects). I am aware of only one study reporting striking long-term effects of rearing conditions on fitness. In Little Egrets Egretta garzetta last-hatched chicks enjoyed a lower reproductive success than their older siblings (Thomas et al. 1999). Their results may be explained by a pronounced hatching asynchrony resulting into a fixed dominance hierarchy that strongly penalises last-hatched 259