Data from: Physiological maturity at a critical life-history transition and flight ability at fledging

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, 1st or 2nd broods) to determine the importance of physiological traits related to oxygen-carrying capacity (hematocrit, hemoglobin) for individual variation in initial flight ability at fledging.

Hemoglobin concentration and hematocrit at fledging had much higher variance than somatic traits and were more variable across ecological contexts. Furthermore, fledgling hemoglobin concentration was the least developmentally mature of all traits (on average only 78% of adult concentration).

Fledglings from 2nd broods, which are known to have lower post-fledging survival, were less developmentally mature than fledglings from 1st broods for all traits (except tarsus), with hematocrit and hemoglobin concentration being the most developmentally immature traits (in 1st vs. 2nd broods, hematocrit: 47.1% vs. 40.9%; hemoglobin: 13.3 g/dL vs. 11.6 g/dL).

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 hemoglobin) were incorporated into models based on somatic traits.