title: Early mortality saves energy: estimating the energetic cost of excess offspring in a seabird.
abstract: Offspring are often produced in excess as insurance against stochastic events or unpredictable resources. This strategy may result in high early-life mortality, yet age-specific mortality before offspring independence and its associated costs have rarely been quantified. In this study, we modelled age-specific survival from hatching to fledging using 24 years of data on hatching order (HO), growth and age of mortality of more than 15 000 common tern (Sterna hirundo) chicks. We found that mortality peaked directly after hatching, after which it declined rapidly. Mortality hazard was best described with the Gompertz function, and was higher with later HO, mainly due to differences in baseline mortality hazard, rather than age-dependent mortality. Based on allometric mass-metabolism relationships and detailed growth curves of starving chicks, we estimated that the average metabolizable energy intake of non-fledged chicks was only 8.7% of the metabolizable energy intake of successful chicks during the nestling phase. Although 54% of hatchlings did not fledge, our estimates suggest them to have consumed only 9.3% of the total energy consumption of all hatched chicks in the population before fledging. We suggest that rapid mortality of excess offspring is part of an adaptive brood reduction strategy to the benefit of the parents.
authors.affiliation: Groningen Institute for Evolutionary Life Sciences, University of Groningen, PO Box 11103, 9700 CC Groningen, The Netherlands oscarvedder@hotmail.com.|Institute of Avian Research 'Vogelwarte Helgoland', An der Vogelwarte 21, D-26386 Wilhelmshaven, Germany.
authors.forename: Oscar
authors.identifier: 0000-0003-4689-8568
authors.initials: O
authors.lastname: Vedder
authors.affiliation: CHIP, Department of Infectious Diseases, Rigshospitalet, Blegdamsvej 9, 2100 Copenhagen, Denmark.
authors.forename: He
authors.initials: H
authors.lastname: Zhang
authors.affiliation: Institute of Avian Research 'Vogelwarte Helgoland', An der Vogelwarte 21, D-26386 Wilhelmshaven, Germany.
authors.forename: Sandra
authors.initials: S
authors.lastname: Bouwhuis
mesh_terms: D000818:Animals; D046091:Charadriiformes / Q000378:metabolism*; D052284:Clutch Size; D002149:Energy Intake; D009026:Mortality
keywords: brood reduction; brood survival; kin selection; offspring survival; parental neglect; parent–offspring conflict