Although the negative impact of human-induced environmental effects on bird populations has been widely demonstrated, the question of whether adaptive adjustments may potentially arise as a result of unforeseen challenges is still unclear. Despite their obvious pervasive effect, human-induced challenges may activate, under certain circumstances, physiological and behavioural compensatory mechanisms that allow organisms to cope better with an altered and distressful environment. In this viewpoint, we highlight that understanding such compensatory responses (or the lack of them) requires adopting an ontogenetic and transgenerational perspective, as well as a multidisciplinary approach that integrates physiology, ageing biology, molecular processes and behaviour. Given the outstanding capacity for plasticity during development, we focus on how early-life (human-induced) experiences potentially shape, even prenatally, specific physiological and molecular processes (i.e., protection against oxidative damage and telomere maintenance mechanisms), and lifelong reproductive strategies (i.e., maternal allocation into eggs), which may in turn activate physiological and behavioural adjustments across generations. To test whether such adjustments in the developmental trajectory allow individuals to make “the best of a bad situation” or even increase their performance or that of their offspring in human-altered environments, we call for studies using a lifelong approach and that explore transgenerational effects. We thus propose experimental designs that could help the advancement in the field.

In many species, offspring display conspicuous adult-like colouration already early in life, even though they might be very vulnerable to predation at this stage. Yet, the signalling function of adult-like traits in nestlings has been little explored to date. Here, we investigated whether the yellow breast plumage of blue tit (Cyanistes caeruleus) nestlings shows patterns of condition-dependence and hence signals individual quality, as has been described for adult birds. During three consecutive breeding seasons, we therefore explored the association between nestling body mass and three colour components of the yellow breast plumage (i.e., UV chroma, carotenoid chroma and total brightness), considering both within and among nest effects. Carotenoid chroma was not affected by body mass. However, UV chroma and total brightness showed an among-nest effect of body mass, suggesting that they might signal aspects of genetic quality or parental rearing capacity. Interestingly, we also found a within-nest effect of body mass on total brightness, suggesting that this is a good candidate for a condition-dependent signal within the family. Thus, other family members could rely on brightness to adjust their behavioural strategies, such as feeding behaviour in parents. Our study thus reveals that certain colour components of the yellow breast plumage signal different aspects of offspring quality and suggest that they might have a correlated signalling value across life-history stages.