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Iteroparous organisms face a trade-off between reproduction and survival but knowledge of whether, how and when costs of long-term increases in workload are paid is scant. We increased locomotion costs for a whole year by equipping male great tits with a backpack during breeding, removing the backpacks one year later. We applied three different treatments: control (without backpack), light (“empty” backpack, 0.1g) and heavy (“full” backpack, 0.9g, ~5% of body mass). Backpacks were administered in three cohorts and we monitored effects on mass of nestlings and the male, wing length, reproduction and survival. Added mass had a negative effect on nestling mass in both the starting year of the experiment and one year later, but not on production of fledglings or recruits. In winter and the next breeding season, males equipped with heavy backpacks had a higher (net) body mass and had shorter third primary feathers than the other two groups. Heavy backpack males were less likely to sleep in a nest box in winter. Nest boxes are optimal roosting sites and we interpret this finding as a treatment effect on success in competition over this resource. However, there was no effect of the manipulation on survival. Overall, we found no long-term fitness consequences and we discuss possible explanations and implications for the “starvation predation theory” of optimal body mass. However, we found short-term effects of carrying extra weight suggesting that behavioral studies using small devices should consider the effects of equipping small non-migratory passerines with devices such as transmitters.
Original languageEnglish
Pages (from-to)1087-1096
JournalBehavioral Ecology
Volume27
Issue number4
Early online date17 Feb 2016
DOI
StatePublished - 2016

    Research areas

  • national

ID: 1795529