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

Visser, M. E., van Dooremalen, C., Tomotani, B. M., Bushuev, A., Meijer, H. A. J., Te Marvelde, L. & Gienapp, P., 19-Jul-2019, In : The Journal of Experimental Biology. 222, Pt 14, 6 p., jeb.199513.

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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.

Original languageEnglish
Article numberjeb.199513
Number of pages6
JournalThe Journal of Experimental Biology
Issue numberPt 14
Publication statusPublished - 19-Jul-2019

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