Physiological maturity at a critical life‐history transition and flight ability at fledging

Abstract

Summary Developmental maturity (e.g. body condition, body mass) at major life‐history transitions is known to affect fitness across a wide range of taxa. Fledging (leaving the nest), a major life‐history transition in birds, is associated with high post‐fledging mortality and is widely assumed to be related to poor initial flight ability of fledglings, which, in turn, might be related to developmental maturity at fledging. We investigated individual variation in developmental maturity of both somatic and physiological traits at this critical life‐history transition in different ecological contexts (year, first or second broods) to determine the importance of physiological traits related to oxygen‐carrying capacity (haematocrit, haemoglobin) for individual variation in initial flight ability at fledging. Haemoglobin concentration and haematocrit at fledging had much higher variance than somatic traits and were more variable across ecological contexts. Furthermore, fledgling haemoglobin concentration was the least developmentally mature of all traits (on average, only 78% of adult concentration). Fledglings from second broods, which are known to have lower post‐fledging survival, were less developmentally mature than fledglings from first broods for all traits (except tarsus), with haematocrit and haemoglobin concentration being the most developmentally immature traits (in first vs. second broods, haematocrit: 47·1% vs. 40·9%; haemoglobin: 13·3 vs. 11·6 g dL−1). Models predicting individual variation in two aspects of initial flight ability (total energy gain, take‐off angle) were significantly improved when physiological traits (in particular haemoglobin) were incorporated into models based on somatic traits. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.12777/suppinfo is available for this article.

Avoidance, tolerance, and resistance to ectoparasites in nestling and adult tree swallows

“…Future studies should focus on the post-fledging effects of hematophagous ectoparasites such as blowflies, particularly on the effects that decreased oxygen-carrying capacity due to reduced hemoglobin might have on flight performance in tree swallows and other aerial specialist hosts (Cornell et al 2017). Future work should also emphasize the importance of specific acquired immunity in bird-ectoparasite dynamics, and the degree to which heritability and maternal transfer of antibody response can influence these dynamics (Garnier and Graham 2014).…”

Ectoparasites as developmental stressors: Effects on somatic and physiological development

“…Although hematocrit has its limitations as a sole measure of an individual's condition due to many sources of variation (Fair, Whitaker, & Pearson, ), anemia can lead to decreased oxygen transport to tissues that impact flight performance, and fledglings that continue to suffer from anemia could have reduced abilities to evade predators and reduced foraging abilities (O'Brien et al., ). A recent study in starling nestlings found that physiological maturity as indexed by both hematocrit and hemoglobin concentration lags behind somatic maturity at nest leaving, that there is greater variability in physiological traits associated with oxygen‐carrying capacity than with somatic measures of growth, and that both somatic and physiological maturity contribute significantly to models of initial flying ability at nest leaving (Cornell, Gibson, & Williams, ). We expect that any deficits associated with anemia in nestlings would persist until normal hematocrit levels are achieved, which might take several weeks given the slow renewal rates of red blood cell in birds (Rondan et al., ).…”

Physiology, activity and costs of parental care in birds

“…European starlings, Sturnus vulgaris; Cornell et al, 2017), asymptotic mass (see Glossary) or size of chicks (somatic maturity) is attained at, or close to, fledging age (Starck and Ricklefs, 1998), i.e. chick growth continues throughout the nestling phase.…”