Telomeres, the tandemly repeated sequences at the ends of vertebrate chromosomes, shortens during an organism’s life due to internal and external factors. The conditions experienced by an individual during its growth period, can have a significant influence on fitness later in life. In this thesis I will describe the patterns of telomere change in the nestling period of bluethroats (Luscinia svecica svecica). Based on findings from an earlier study by Johnsen et al. (2017), I tested the hypothesis that the degree of early change in telomere length reflects individual differences in body mass and/or genetic quality of the birds. I predicted that the reduction of telomere length can be detected at an individual level and that it is correlated with their individual change in body mass. I also investigated the relationship between relative telomere length and various life-history, environmental and parental variables, using longitudinal data; samples from the same nestlings on two occasions, four days apart. Field work was conducted at the Natural History Museum’s field station in Øvre Heimdalen, Innlandet. Blood samples from 64 individuals were assessed and the relative telomere lengths were estimated using qPCR analyses. My findings showed no significant change in relative telomere length between the two sampling days, and there was no significant correlation between the sampling days. The results indicated a significant association between relative telomere length and parents’ tarsus length, as well as an effect of the qPCR plate they were analysed on. None of the other variables that were tested showed any significant relationships with relative telomere length. I discuss possible reasons for the discrepancies between this and previous studies.