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Using open-flow respirometry and video footage (25 frames s(-1)), the energy expenditure and hindlimb kinematics of barnacle geese, Branta leucopsis, were measured whilst they were exercising on a treadmill at gradients of +7 and -7 deg, and on a level surface. In agreement with previous studies, ascending a gradient incurred metabolic costs higher than those experienced on level ground at comparable speeds. The geese, however, are the first species to show an increased duty factor when ascending a gradient. This increased duty factor was accompanied by a longer stance time, which was probably to enable the additional force required for ascending to be generated. Contrary to previous findings, the geese did not experience decreased metabolic costs when descending a gradient. For a given speed, the geese took relatively shorter and quicker strides when walking downhill. This 'choppy' stride and perhaps a lack of postural plasticity (an inability to adopt a more crouched posture) may negate any energy savings gained from gravity's assistance in moving the centre of mass downhill. Also contrary to previous studies, the incremental increase in metabolic cost with increasing speed was similar for each gradient, indicating that the efficiency of locomotion (mechanical work done/chemical energy consumed) is not constant across all walking speeds. The data here suggest that there are species-specific metabolic responses to locomotion on slopes, as well as the established kinematics differences. It is likely that a suite of factors, such as ecology, posture, gait, leggedness and foot morphology, will subtly affect an organism's ability to negotiate gradients.

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.

Svalbard rock ptarmigans were walked and run upon a treadmill and their energy expenditure measured using respirometry. The ptarmigan used three different gaits: a walking gait at slow speeds (less than or equal to 0.75 m s(-1)), grounded running at intermediate speeds (0.75 m s(-1) < U < 1.67 m s(-1)) and aerial running at high speeds (greater than or equal to 1.67 m s(-1)). Changes of gait were associated with reductions in the gross cost of transport (COT; J kg(-1) m(-1)), providing the first evidence for energy savings with gait change in a small crouched-postured vertebrate. In addition, for the first time (excluding humans) a decrease in absolute metabolic energy expenditure (rate of O(2) consumption) in aerial running when compared with grounded running was identified. The COT versus U curve varies between species and the COT was cheaper during aerial running than grounded running, posing the question of why grounded running should be used at all. Existing explanations (e.g. stability during running over rocky terrain) amount to just so stories with no current evidence to support them. It may be that grounded running is just an artefact of treadmill studies. Research investigating the speeds used by animals in the field is sorely needed.

Barnacle geese were walked on a treadmill at speeds ranging from 0.25 to 1.25 ms(-1), which was their highest sustainable speed. No evidence for a gait change was found. The gait of a barnacle goose appears to conform to the classical pendulum mechanics based model of walking, with the kinetic energy of forward motion (horizontal kinetic energy, E(kh)) out-of-phase with the sum of the gravitational potential (E(p)), and vertical kinetic (E(kv)) energies of the centre of mass at all speeds. Why barnacle geese are unable to aerial run when other 'waddling' species do show an aerial phase (e.g., mallard ducks) is unclear. Presumably, however, it is likely to relate to the amount of lateral kinetic energy generated, which is a feature of 'waddling'. We predict that lateral kinetic energy generated by barnacle geese and other waddling species that cannot aerial run, is higher than in those that can. Due to competing selection pressures for swimming and flight, barnacle geese are mechanically and energetically inefficient walkers relative to more specialist cursorial birds. Their upper walking speed, however, appears to be limited by morphology (via kinematics) and not metabolic capacity (energetics)., (Copyright 2010 Elsevier Inc. All rights reserved.)

Daily energy expenditure (DEE) of male barn swallows (Hirundo rustica), measured using the doubly labelled water technique, correlated with streamer length. Contrary to predictions derived from previous findings, neither a positive linear nor a u-shaped relationship was found between DEE and streamer length. Instead, an n-shaped curve showed that the highest DEE corresponded to an intermediate streamer length of 119 mm. A model incorporating estimates of resting metabolism and flight energy expenditure from aerodynamics models suggested that variation in individual tail dynamics was the most likely explanation for the observed DEE. We suggest that streamer length is coupled to foraging strategy, because tail dynamics control flight performance, which in turn influences flight behaviour.

The doubly-labeled water technique and video were used to measure the effect of mass loading on energy expenditure and takeoff performance in zebra finches, Taeniopygia guttata, that were making routine (nonalarm) short flights. Finches that carried 27% additional mass did not expend more energy during flight than unloaded controls. Carrying additional mass, however, led to a reduced body mass and a decreased velocity during takeoffs (by 12%). Calculations of instantaneous mechanical power indicated that energy expended by unloaded and loaded finches at takeoff was similar, due to the observed decrease in velocity by mass-loaded finches and a lowering of their body mass. During routine short flights, zebra finches appear to maintain their metabolic power input and mechanical power output regardless of mass loading. Here, the costs of carrying additional mass during routine short flights were revealed to be behavioral and not energetic.

Many small birds perform short flights, for which take-offs, ascents and descents form a large component of the total flight time and which are characterised by low airspeeds. Using the doubly-labelled water technique, zebra finches Taeniopygia guttata engaging in repeated short flights were found to expend 13.65 kJ more than 'non-flying' controls, which equated to a flight expenditure of 27.8 times their basal metabolic rate. This is over three times the predicted flight expenditure derived from existing aerodynamic models. These data were used to determine a coefficient (0.11) for converting the mechanical power derived from aerodynamic models into metabolic power. An equation is presented, based on body mass, which can be used to predict the costs of short flights in ecological and behavioural studies of birds.