![]() (2017) showed that developmental telomere attrition (DTA the extent of shortening of erythrocyte telomeres over the course of development) explained variation in individuals’ stress responses. In a recent study of two cohorts of adult European starlings ( Sturnus vulgaris, n = 20 and n = 31), Andrews et al. ![]() Thus, the extent of telomere shortening can potentially be used as a proxy for individual differences in biological age. The rate of telomere attrition is much higher during the developmental period than in adulthood, and has been shown to be accelerated by early-life adversity ( Boonekamp et al., 2014 Nettle et al., 2015, 2017). Short telomere length has been shown to predict shorter subsequent lifespan in a range of avian ( Bize et al., 2009 Heidinger et al., 2012 Barrett et al., 2013 Salmón et al., 2017 Wilbourn et al., 2018) as well as non-avian ( Boonekamp et al., 2013 Wilbourn et al., 2018) species. One potential marker of biological age is the attrition of telomeres, the DNA caps at the ends of linear chromosomes ( Bize et al., 2009 Bauer et al., 2018). A possible reason that early-life conditions have often been observed to influence the functioning of the adult stress response may be that early-life conditions can speed up or slow down the biological ageing process, and consequently advance or retard age-related shifts in the functioning of the stress response system. Hence, we should expect markers of individual biological age to explain variation in the strength of the stress response that cannot be explained by chronological age alone. Biological age is by definition a better predictor of future lifespan than chronological age is. However, individuals do not all age at the same rate: an individual’s biological age can be either older or younger than their chronological age ( Belsky et al., 2015). In birds, the strength of the HPA response generally declines with chronological age ( Heidinger, Nisbet & Ketterson, 2006 Heidinger et al., 2010 Wilcoxen et al., 2011 Elliott et al., 2014 Lendvai, Giraudeau & Bo, 2015 López-Jiménez et al., 2017), possibly reflecting adaptive shifts in behavioural allocation as expected future lifespan reduces. ![]() The hypothalamic-pituitary-adrenal (HPA) axis is a highly conserved, integrated system in vertebrates that functions to prioritise immediate survival over non-essential activities in the face of acute threats. We meta-analysed the data from the present and the earlier study combined, and found some support for the conclusions of the earlier paper. However, we did not replicate the associations with DTA observed in the earlier study. The manipulation of begging effort affected the stress response (specifically, the reduction in CORT between 15 and 30 min) in an age-dependent manner. Individual consistency between the two age points was low, but there were modest familial effects on baseline and peak CORT. Our data suggest a decline in the strength of the CORT response with chronological age: peak CORT was lower at the second age point, and there was relatively more reduction in CORT between 15 and 30 min. We measured the CORT response at two different age points (4 and 18 months). Here, we performed a follow-up study using the same capture-handling-restraint stressor in a separate cohort of starlings that had been subjected to a developmental manipulation of food availability and begging effort. Specifically, birds that had experienced greater developmental telomere attrition (DTA) showed a lower peak corticosterone (CORT) response to an acute stressor, and more rapid recovery of CORT levels towards baseline. A recently published study of European starlings ( Sturnus vulgaris) found that a marker of biological age predicted the strength of the stress response even in individuals of the same chronological age. The strength of the avian stress response declines with age.
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