Data from: Chicks of cavity-nesting birds do not ‘exercise’ prior to fledging

Fledging represents a key life-history transition involving a rapid
increase in workload associated with a rapid transition from sedentary
nestling to volant, active fledgling. Here, we tested the idea that chicks
might prepare for fledging through increased voluntary activity
(‘exercise’) and whether this would impact somatic and physiological
development. European starling (Sturnus vulgaris) chicks, in cavity nests,
increased levels of putative exercise (wing flapping) and more general
active behaviours (e.g., perching, standing) in the five days up to
fledging. However, facultative mass loss and wing growth between days 15 –
20 were independent of time spent wing flapping, standing, or perching,
and – counterintuitively – we found a weak negative relationship between
hematocrit (a measure of aerobic capacity) and time spent wing flapping or
standing. Thus, although exercise is commonly associated with an increase
in hematocrit in other species, this does not appear to be a mechanism for
increasing pre-fledging hematocrit in chicks. Despite widespread anecdotal
observations of flight preparation (e.g., wing flapping) in larger
seabirds and raptors, our data suggest that exercise, or increased
activity in general, does not contribute to improved development just
prior to fledging: starling chicks do not ‘exercise’ enough to show
somatic or physiological effects.