For young birds in a nest, body size may have implications for other aspects of development such as telomere length and immune function. However, it is possible to predict associations in either direction. On the one hand, there may be trade‐offs between growth and telomere maintenance, and growth and investment in immune function, suggesting there will be negative correlations. On the other hand, relatively larger individuals might be advantaged in competition with their nest‐mates, allowing them to garner more resources overall, leading to positive correlations. We studied development over the nestling period in 34 nests of wild European starlings, Sturnus vulgaris. Intrabrood competition is typically more intense in larger broods. Hence, we predicted that body size should become an increasingly positive predictor of telomere length and immune functioning as brood size increases. In partial support of our prediction, there were significant interactions between brood size and body size in predicting both erythrocyte telomere length change and plasma levels of the cytokine interleukin‐6. The associations between body size and these outcomes went from negative in the smallest broods to positive in the largest. A further immune marker, high‐sensitivity C‐reactive protein, showed no systematic patterning with body size or brood size. Our results confirm that the size to which a nestling grows is important for telomere dynamics and the development of the immune system, but the phenotypic associations are moderated by the competitive context.

Neonicotinoids are pesticides used to protect crops but with known secondary influences at sublethal doses on bees. Honeybees use their sense of smell to identify the queen and nestmates, to signal danger and to distinguish flowers during foraging. Few behavioural studies to date have examined how neonicotinoid pesticides affect the ability of bees to distinguish odours. Here, we used a differential learning task to test how neonicotinoid exposure affects learning, memory and olfactory perception in foraging-age honeybees. Bees fed with thiamethoxam could not perform differential learning and could not distinguish odours during short-and long-term memory tests. Our data indicate that thiamethoxam directly impacts the cognitive processes involved in working memory required during differential olfactory learning. Using a combination of behavioural assays, we also identified that thiamethoxam has a direct impact on the olfactory perception of similar odours. Honeybees fed with other neonicotinoids (clothianidin, imidacloprid, dinotefuran) performed the differential learning task, but at a slower rate than the control. These bees could also distinguish the odours. Our data are the first to show that neonicotinoids have compound specific effects on the ability of bees to perform a complex olfactory learning task. Deficits in decision making caused by thiamethoxam exposure could mean that this is more harmful than other neonicotinoids, leading to inefficient foraging and a reduced ability to identify nestmates.

The strength of the avian stress response declines with age. 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. 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. 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. We measured the CORT response at two different age points (4 and 18 months). 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. Individual consistency between the two age points was low, but there were modest familial effects on baseline and peak CORT. The manipulation of begging effort affected the stress response (specifically, the reduction in CORT between 15 and 30 min) in an age-dependent manner. However, we did not replicate the associations with DTA observed in the earlier study. We meta-analysed the data from the present and the earlier study combined, and found some support for the conclusions of the earlier paper.

The responsiveness of the avian stress system declines with age. A recently published study of European starlings (Sturnus vulgaris) found that a marker of biological age predicted stress responsiveness even in individuals of the same chronological age.Specifically, birds that had experienced greater developmental telomere attrition showed a lower peak corticosterone response to an acute stressor, and more rapid recovery of corticosterone levels towards baseline. Here, we performed a follow-up study using the same capture-restraint-handling stressor in a separate cohort of 27 starlings. Unlike the original study, we measured the response at two different age points (4 and 18 months).We did not replicate the associations with developmental telomere attrition observed in the previous study at either age point. However, a meta-analysis of the present results combined with those of the earlier study still lent some support to the conclusions of the earlier paper. Estimates of familial influence on stress responsiveness differed across the two age points. We found little evidence of individual consistency in stress responsiveness between 4 and 18 months. Peak corticosterone was significantly lower at the second age point than the first, though interpretation of this as age-related decline is problematic due to the samples having been analysed at different times. found that a marker of biological age predicted stress responsiveness even in 21 individuals of the same chronological age. Specifically, birds that had experienced greater developmental 22 telomere attrition showed a lower peak corticosterone response to an acute stressor, and more rapid 23 recovery of corticosterone levels towards baseline. Here, we performed a follow-up study using the same 24 capture-restraint-handling stressor in a separate cohort of 27 starlings. Unlike the original study, we 25 measured the response at two different age points (4 and 18 months). We did not replicate the associations 26 with developmental telomere attrition observed in the previous study at either age point. However, a 27 meta-analysis of the present results combined with those of the earlier study still lent some support to the 28 conclusions of the earlier paper. Estimates of familial influence on stress responsiveness differed across 29 the two age points. We found little evidence of individual consistency in stress responsiveness between 4 30 and 18 months. Peak corticosterone was significantly lower at the second age point than the first, though 31 interpretation of this as age-related decline is problematic due to the samples having been analysed at 32 different times. , 2015). Biological age is by definition a better predictor of future lifespan than 45 chronological age is. Hence, we should expect markers of individual biological age to explain variation in 46 stress responsiveness that cannot be explained by chronological age alone. A possible reason that early-47 life conditions have often been observed to influence the functioning of the adult stress respon...

Judgement bias tasks are designed to provide markers of affective states. A recent study of European starlings (Sturnus vulgaris) demonstrated modest familial effects on judgement bias performance, and found that adverse early experience and developmental telomere attrition (an integrative marker of biological age) both affected judgement bias. Other research has shown that corticosterone levels affect judgement bias. Here, we investigated judgement bias using a modified Go/No Go task in a new cohort of starlings (n = 31) hand-reared under different early-life conditions. We also measured baseline corticosterone and the corticosterone response to acute stress in the same individuals. We found evidence for familial effects on judgement bias, of a similar magnitude to the previous study. We found no evidence that developmental treatments or developmental telomere attrition were related to judgement bias per se. We did, however, find that birds that experienced the most benign developmental conditions, and birds with the greatest developmental telomere attrition, were significantly faster to probe the learned unrewarded stimulus. We also found that the birds whose corticosterone levels were faster to return towards baseline after an acute stressor were slower to probe the learned unrewarded stimulus. Our results illustrate the potential complexities of relationships between early-life experience, stress and affectively mediated decision making. For judgement bias tasks, they demonstrate the importance of clearly distinguishing factors that affect patterns of responding to the learned stimuli (i.e. response inhibition in the case of the Go/No Go design) from factors that influence judgements under ambiguity.Electronic supplementary materialThe online version of this article (10.1007/s10071-018-1226-7) contains supplementary material, which is available to authorized users.