Growth conditions and individual quality in starlings

Abstract: Variation in growth conditions during ontogeny may result in permanent differences in individual quality. This thesis focuses on how starlings are affected by environmental variation during the nestling period. Both landscape differences in food availability and experimental food supplementation affected survival and growth of nestlings. During benign conditions, nestlings reached a larger morphological size, which is suggested to have long-term fitness consequences. Nestling immune capacity was affected by food conditions during the first week of life. In addition there was a relationship between immune capacity and the current condition of ten-day-old nestlings. The effects of early growth conditions on immune capacity did not persist into adult life, since the strength of the immune response was not repeatable over time. There was no significant heritability of cell-mediated immune response. In addition, there was no effect of mounting a cell-mediated immune response on subsequent growth of nestlings. For females, breeding-time is a trait repeatable between years, but not affected by additive genetic variation. It was therefore selected as a target trait to study permanent environmentally caused variation in life-history traits. To investigate if late-breeding females lay small clutches because they are of poor quality, I experimentally delayed breeding of starling females. Females responded to the delay by laying smaller clutches consisting of smaller eggs than that of control females. However, clutches were larger than what expected from the seasonal trend demonstrating that early laying females are of higher quality. In addition a breeding delay decreased the female return rate, suggesting a cost of breeding late.