We found evidence of flexible mass and wing growth which independently covaried with fledgling energy state and aerobic capacity, respectively. Here, we investigated morphological development of European starlings ( Sturnus vulgaris ) approaching fledging in relation to three components of physiological condition at independence: aerobic capacity, energy state and oxidative status. Exploring individual variation of growth trajectories and how they covary with physiology could reveal species-specific developmental modes which have implications for our assessments of juvenile quality. morphological traits) have proven to be unreliable predictors of juvenile survival within species. Recent studies have reported beneficial carryover effects of juvenile development that predict interspecific survival differences at independence. In order to understand better and improve the state of wild animal welfare, more attention should be directed towards young animals and the particular challenges they face. This concept fits conveniently alongside methods of analysis already used in population ecology, such as demographic sensitivity analysis, and is applicable to evaluating the welfare consequences of human interventions and natural pressures that disproportionately affect individuals of different ages. Here, I propose the concept of welfare expectancy as a framework for quantifying wild animal welfare at a population level, given individual-level data on average welfare with respect to age. Individuals who die as juveniles do not simply experience a homogeneous fraction of the lifetimes of older members of their species rather, their truncated lives may be characterized by very different levels of welfare. At the same time, most wild animals who are born do not survive to adulthood. Wild animals experience different challenges and opportunities as they mature, and this variety of experiences can lead to different levels of welfare characterizing the day-to-day lives of individuals of different ages. Our study demonstrates that hematocritĬan be an informative metric for life-history studies investigating trade-offsīetween survival, longevity, and reproduction. Individuals were experiencing dehydration and/or high endurance demands prior toĬapture, which warrants further investigation. Of poor condition in younger individuals. Not find support for hematocrit as a marker of senescence, high hematocrit is indicative With lower survival in young individuals, but not older individuals. Than females and varied relative to breeding stage. In breeders, hematocrit was higher in males Hematocrit increases with age in young individuals (<1.5 years) but decreases withĪge in older individuals (1.5–13 years). Using longitudinalĭata from the Seychelles warbler (Acrocephalus sechellensis), we demonstrated that However, few studies have tested whether hematocrit declines within individuals or whether low hematocrit impacts survival in wild taxa.
In cross-sectional studies (which may be confounded by selective appearance / disappearance). Hematocrit has been shown to decline with age One underutilized measure is hematocrit, the proportion of bloodĬomprising erythrocytes, which relates to the blood's oxygen-carrying capacity and However, currently used markers often yield inconsistent results. Of considerable benefit to unraveling such trade-offs and could provide insight into
Markers that reflect physiological state and predict future survival would be Understand the evolution of life histories and the impact of ecological variables upon Understanding trade-offs in wild populations is difficult, but important if we are to
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