Variation in developmental trajectories of physiological and somatic traits in a common songbird approaching fledging

Abstract

In avian species, little is known about the development of physiological traits in the days preceding fledging, a critical life history transition marked by a high mortality rate. Developmental trajectory during this period may be flexible based on ecological context or hardwired, with potential costs for variation in growth in the form of oxidative stress. Patterns in development are likely to relate to variation in life history, for which seabirds and aerial insectivores have been well studied, while our focal species is a grassland ground forager, the European starling (). We show that changes in haematocrit, body mass and wing length are independent of year and brood quality, while changes in haemoglobin concentration are higher in low-quality broods. Moreover, we also identify higher oxidative stress in low-quality year and second broods, a potential cost for maintaining a hardwired developmental trajectory in a lower quality environment. Finally, we experimentally test the effects of food supplementation on development and maturity of chicks at fledging to show that although food increases body mass early in development, it does not change the trajectory or final maturity of chicks at fledging. Collectively this study demonstrates that some developmental changes prior to fledging may be hardwired, but may have long-term oxidative costs in low-quality environments.

Flexible growth and body mass predict physiological condition at fledging in the synchronously breeding European starling, Sturnus vulgaris

“…Conversely, the lack of an association between structural traits and physiological condition may be driven by plasticity of growth trajectories prior to fledging, which reflected individual variation of fledgling aerobic capacity. While this plasticity may facilitate the attainment of normal fledgling size, it potentially leads to greater physiological variation as observed previously [ 34 ]. The resulting decreased variance in key fitness traits (e.g.…”

“…In this study, we measured developmental trajectories of morphological traits (mass, tarsus and wing length) approaching independence and final physiological condition (aerobic capacity, energy state and oxidative status) in the European starling ( Sturnus vulgaris ), a species that displays a mass-overshoot-recession growth profile [ 34 ]. We analysed changes in morphological traits approaching fledging in relation to physiological traits at fledging, while also assessing relationships among traits at fledging.…”

Plasticity in diurnal activity and temporal phenotype during parental care in European starlings, Sturnus vulgaris

“…Finally, during the post fledging period, diurnal activity of female parents was generally less marked than during all other breeding stages. This is likely associated with the fact that a) chicks are close to somatic maturity at this stage (Cornell & Williams, 2017), b) chicks are mobile and can follow parents for feeding, reducing foraging distances and overall activity (Williams, 2018).…”

Hematocrit, age, and survival in a wild vertebrate population

“…Uncertainty remains regarding associations between hematocrit, age, and senescence in wild animals. From birth to maturity, hematocrit increases with age (e.g., Cornell & Williams, 2017; Eklom & Lill, 2006; Trillmich et al., 2008), but few studies have determined the age dependence of hematocrit in adult life. This likely stems from the difficulty of obtaining samples of known‐age adults in many wild systems.…”