Barnacle Geese Achieve Significant Energetic Savings by Changing Posture Peter G. Tickle, Robert L. Nudds, Jonathan R. Codd* Faculty of Life Sciences, University of Manchester, Manchester, UK Abstract Here we report the resting metabolic rate in barnacle geese (Branta leucopsis) and provide evidence for the significant energetic effect of posture. Under laboratory conditions flow-through respirometry together with synchronous recording of behaviour enabled a calculation of how metabolic rate varies with posture. Our principal finding is that standing bipedally incurs a 25% increase in metabolic rate compared to birds sitting on the ground. In addition to the expected decrease in energy consumption of hindlimb postural muscles when sitting, we hypothesise that a change in breathing mechanics represents one potential mechanism for at least part of the observed difference in energetic cost. Due to the significant effect of posture, future studies of resting metabolic rates need to take into account and/or report differences in posture. Citation: Tickle PG, Nudds RL, Codd JR (2012) Barnacle Geese Achieve Significant Energetic Savings by Changing Posture. PLoS ONE 7(10): e46950. doi:10.1371/ journal.pone.0046950 Editor: Lewis George Halsey, University of Roehampton, United Kingdom Received June 26, 2012; Accepted September 10, 2012; Published October 10, 2012 Copyright: 2012 Tickle et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This research was funded through the BBRSC Biotechnology and Biological Sciences Research Council (G/01138/1). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: jonathan.codd@manchester.ac.uk, Tel: +44(0) 161 275 5474 Introduction When evaluating energy budgets in birds, few studies have taken into accounts any differences in the cost associated with different postures. Many birds spend a significant proportion of time resting [1]. However, while resting metabolic rate has been measured in a wide range of birds [2,3], the effects of posture upon metabolism were only previously considered in three studies of domestic fowl [4,5] and two studies of guillemots [6,7]. One of these [4] estimated a 42% increase in metabolic rate when standing compared to sitting, but this value included the cost of rising. The study of Van Kampen [5] suggested the metabolic cost associated with just standing was 16% (25% if the fowl were also indulging in spontaneous pecking and preening behaviour) greater than sitting. Ellerby et al. [8] concluded that standing was more metabolically costly than sitting without quoting exact values. Compared to a lying prone posture, standing upright incurs a metabolic rate increase of between 7% and 9% in guillemots [6,7], lower than the values observed in fowl. Environmental conditions, such as temperature, exposure to sunlight and precipitation, are regarded as the main factors affecting posture selection [9,10]. It is difficult, however, to disentangle whether any concurrent change in metabolic rate is due to a homeostatic response, such as temperature regulation [11], or simply the energy cost of maintaining a particular resting posture. Selection of a resting posture might also be affected by the critical requirements of breathing. Respiratory muscles actively move the rib cage and sternum during ventilation, a process that can be constrained by posture [12]. Therefore, knowing the metabolic cost of sitting and standing in birds is important, because it may shed light upon posture selection and behaviour in birds. In addition, posture dependent metabolic costs would have strong implications for studies of resting metabolic rates. Specifically, which posture was adopted during measurements of resting metabolic rate and does that posture really represent the least energetically expensive and therefore, truly resting metabolism? Given its far-reaching implications, it is surprising that so few studies have considered the metabolic costs of different resting postures. Accordingly, in this paper we begin to address this dearth in posture studies by presenting data on the resting energetics of barnacle geese (Branta leucopsis) during sitting and standing under constant environmental conditions. Our data augments that currently available and expands it into another phylogenetic order (i.e. the Anseriformes). Materials and Methods (a) Animals Barnacle geese were kept at the University of Manchester, housed in social groups and provided with free access to a pond. Food (Poultry Grower Pellets, Small Holder Range, Norfolk, UK: fat 4.8%, protein 16%, carbohydrate 73.7%, fibre 5.5%) and water were provided ad libitum. Goose body mass was 1.79 kg60.03 (mean 6 SE). All experimental procedures were covered under a Home Office Licence held by J.R.C. (40/3001) and the ethical approval of the University of Manchester. (b) Respirometry Indirect calorimetry via flow-through respirometry was used [8,13]. Air was drawn from the respirometry chamber (volume: 148 L) at a rate of 100 L min21. This relatively high flow rate meant changes in gas composition were quickly detected (ca. 20 s). Water vapour content of subsampled (100 mL min21) excurrent air was measured using an RH-300 humidity meter (Sable Systems, Las Vegas, NV, USA) after which the air stream was dried by passing through a column of magnesium perchlorate (Acros Organics, NJ, USA). A CA-10a carbon dioxide (CO2) PLOS ONE | www.plosone.org 1 October 2012 | Volume 7 | Issue 10 | e46950