Reproduction and migration in relation to senescence in the barn swallow Hirundo rustica: A study of avian 'centenarians'.

A. P. Moller, F. de Lope and N. Saino: Reproduction and migration in relation to senescence in the barn swallow Hirundo rustica: A study of avian 'centenarians'. Senescence reflects the decrease in age-dependent residual reproductive value, and a previous study of a cohort of migratory barn swallows (Hirundo rustica) that had reached advanced ages for this species (at least five years old) provided evidence consistent with senescence such as reduced reproductive performance and increased abundance of parasites. We studied a population of migratory barn swallows over a number of years. Several questions were asked including 1) how do longer lived birds compare to shorter lived individuals of the same species, 2) is there a difference in individuals of the same species that live in different geographical regions, and 3) how do patterns of reproduction change during aging? We compared the phenotypes of 87 individuals from three populations in Denmark, Italy and Spain that had reached at least five years old with those of control individuals matched for sex, arrival date and breeding site. These controls only became one year old, i.e., they were not found thereafter and both groups of individuals were compared in their first year of life. Results showed that there were no significant differences in any of 11 morphological characters or in the abundance of three ectoparasites between the two groups of birds. Females that eventually became very old had relatively smaller first clutches as one year olds than did one year old controls, while males that eventually became very old had mates that laid clutches that were relatively larger than those of controls. Annual fecundity showed a similar pattern, with an increased sex difference in fecundity between birds from Spain than in Italy and in Denmark. Danish barn swallows that achieved older ages had relatively lower haematocrits than control individuals of the same sex, age and arrival date captured at the same site, while the difference in haematocrits between these two categories of individuals was small for Italian birds. Spring arrival date was relatively earlier in Danish males that eventually became very old compared to control males of the same age and tail length (a correlate of fitness) that arrived at the same site, while the two age categories of females did not differ in arrival date. In the Spanish population there was no difference in arrival date between the birds that aged most successfully and controls for either sex. We will discuss these findings in relation to current senescence theories.