Data from: Short-term, but not long-term, increased daytime workload leads to decreased night-time energetics in a free-living song bird

Reproduction is energetically expensive and to obtain sufficient energy,
animals can either alter their metabolic system over time to increase
energy intake (increased-intake hypothesis) or reallocate energy from
maintenance processes (compensation hypothesis). The first hypothesis
predicts a positive relationship between basal metabolic rate (BMR) and
energy expenditure (DEE) because of the higher energy demands of the
metabolic system at rest. The second hypothesis predicts a trade-off
between different body functions, with a reduction of the BMR as a way to
compensate for increased daytime energetic expenditure. We experimentally
manipulated the workload of wild pied flycatchers by adding or removing
chicks when chicks were 2 and 11 days old. We then measured the feeding
frequency (FF), DEE and BMR at day 11, allowing us to assess both short-
and long-term effects of increased workload. The manipulation at day 2
caused an increase in FF when broods were enlarged, but no response in DEE
or BMR, while the manipulation at day 11 caused an increase in FF, no
change in DEE and a decrease in BMR in birds with more chicks. Our results
suggest that pied flycatchers adjust their workload but that this does not
lead to a higher BMR at night (no support for the increased intake
hypothesis). In the short term, we found that birds reallocate energy with
a consequent reduction of BMR (evidence for the compensation hypothesis).
Birds thus resort to short-term strategies to increase energy expenditure,
which could explain why energy expenditure and hard work are not always
correlated in birds.