Data from: Offspring telomere length in the long lived Alpine swift is negatively related to the age of their biological father and foster mother

A growing body of studies is showing that offspring telomere length (TL) can be influenced by the age of their parents. Such relationship might be explained by variation in TL at conception (gamete effect) and/or by alteration of early growth condition in species providing parental care. In a long-lived bird species with bi-parental care, the Alpine swift (Apus melba), we exchanged between pairs an uneven number of 2 to 4-day-old nestlings as part of a brood size manipulation. Nestling TL was measured at 50 days after hatching, which allowed investigating the influence of the age of both their biological and foster parents on offspring TL after controlling for the manipulation. Nestling TL was negatively related to the age of their biological father and of their foster mother. Nestling TL did not differ between enlarged and reduced broods. These findings suggest that offspring from older males were fertilised by gametes with shorter telomeres, presumably due to a greater cell division history or a longer accumulation of damage, and that older females were providing poorer parental care to their offspring.