Publications

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2012
Watanabe, S, Sato K, Ponganis PJ.  2012.  Activity time budget during foraging trips of emperor penguins. Plos One. 7   10.1371/journal.pone.0050357   AbstractWebsite

We developed an automated method using depth and one axis of body acceleration data recorded by animal-borne data loggers to identify activities of penguins over long-term deployments. Using this technique, we evaluated the activity time budget of emperor penguins (n = 10) both in water and on sea ice during foraging trips in chick-rearing season. During the foraging trips, emperor penguins alternated dive bouts (4.8 +/- 4.5 h) and rest periods on sea ice (2.5 +/- 2.3 h). After recorder deployment and release near the colony, the birds spent 17.9 +/- 8.4% of their time traveling until they reached the ice edge. Once at the ice edge, they stayed there more than 4 hours before the first dive. After the first dive, the mean proportions of time spent on the ice and in water were 30.8 +/- 7.4% and 69.2 +/- 7.4%, respectively. When in the water, they spent 67.9 +/- 3.1% of time making dives deeper than 5 m. Dive activity had no typical diurnal pattern for individual birds. While in the water between dives, the birds had short resting periods (1.2 +/- 1.7 min) and periods of swimming at depths shallower than 5 m (0.25 +/- 0.38 min). When the birds were on the ice, they primarily used time for resting (90.3 +/- 4.1% of time) and spent only 9.7 +/- 4.1% of time traveling. Thus, it appears that, during foraging trips at sea, emperor penguins traveled during dives >5 m depth, and that sea ice was primarily used for resting. Sea ice probably provides refuge from natural predators such as leopard seals. We also suggest that 24 hours of sunlight and the cycling of dive bouts with short rest periods on sea ice allow emperor penguins to dive continuously throughout the day during foraging trips to sea.

2010
Sato, K, Shiomi K, Watanabe Y, Watanuki Y, Takahashi A, Ponganis PJ.  2010.  Scaling of swim speed and stroke frequency in geometrically similar penguins: they swim optimally to minimize cost of transport. Proceedings of the Royal Society B-Biological Sciences. 277:707-714.   10.1098/rspb.2009.1515   AbstractWebsite

It has been predicted that geometrically similar animals would swim at the same speed with stroke frequency scaling with mass(-1/3). In the present study, morphological and behavioural data obtained from free-ranging penguins (seven species) were compared. Morphological measurements support the geometrical similarity. However, cruising speeds of 1.8-2.3 m s(-1) were significantly related to mass(0.08) and stroke frequencies were proportional to mass(-0.29). These scaling relationships do not agree with the previous predictions for geometrically similar animals. We propose a theoretical model, considering metabolic cost, work against mechanical forces (drag and buoyancy), pitch angle and dive depth. This new model predicts that: (i) the optimal swim speed, which minimizes the energy cost of transport, is proportional to (basal metabolic rate/drag)(1/3) independent of buoyancy, pitch angle and dive depth; (ii) the optimal speed is related to mass(0.05); and (iii) stroke frequency is proportional to mass(-0.28). The observed scaling relationships of penguins support these predictions, which suggest that breath-hold divers swam optimally to minimize the cost of transport, including mechanical and metabolic energy during dive.

Ponganis, PJ, Meir JU, Williams CL.  2010.  Oxygen store depletion and the aerobic dive limit in emperor penguins. Aquatic Biology. 8:237-245.   10.3354/ab00216   AbstractWebsite

The aerobic dive limit (ADL), dive duration associated with the onset of post-dive blood lactate elevation, has been widely used in the interpretation of diving physiology and diving behavior. However, its physiological basis is incompletely understood, and in most studies, ADLs are simply calculated with an O(2) store/O(2) consumption formula. To better understand the ADL, research has been conducted on emperor penguins diving at an isolated dive hole. This work has revealed that O(2) stores are greater than previously estimated, and that the rate of depletion of those O(2) stores appears to be regulated primarily through a diving bradycardia and the efficiency of swimming. Blood and respiratory O(2) stores are not depleted at the 5.6 min ADL determined by post-dive blood lactate measurements. It is hypothesized that muscle, isolated from the circulation during a dive, is the primary source of lactate accumulation. To predict this 5.6 min ADL for these shallow dives at the isolated dive hole with the classic O(2) store/O(2) consumption formula, an O(2) consumption rate of 2x the predicted metabolic rate of a penguin at rest is required. In contrast, if the formula is used to calculate an ADL that is defined as the time for all consumable O(2) stores to be depleted, then a 23.1 min dive, in which final venous partial pressure of oxygen (P(O2)) was 6 mm Hg (0.8 kPa), represents such a maximum limit and demonstrates that an O(2) consumption rate of about 0.5x the predicted rate of an emperor penguin at rest is required in the formula.

2001
Nagy, KA, Kooyman GL, Ponganis PJ.  2001.  Energetic cost of foraging in free-diving emperor penguins. Physiological and Biochemical Zoology. 74:541-547.   10.1086/322165   AbstractWebsite

Hypothesizing that emperor penguins (Aptenodytes forsteri) would have higher daily energy expenditures when foraging for their food than when being hand-fed and that the increased expenditure could represent their foraging cost, we measured field metabolic rates (FMR; using doubly labeled water) over 4-d periods when 10 penguins either foraged under sea ice or were not allowed to dive but were fed fish by hand. Surprisingly, penguins did not have higher rates of energy expenditure when they dove and captured their own food than when they did not forage but were given food. Analysis of time-activity and energy budgets indicated that FMR was about 1.7 x BMR (basal metabolic rate) during the 12 h d(-1) that penguins were lying on sea ice. During the remaining 12 h d(-1), which we termed their "foraging period" of the day, the birds were alert and active (standing, preening, walking, and either free diving or being hand-fed), and their FMR was about 4.1 x BMR. This is the lowest cost of foraging estimated to date among the eight penguin species studied. The calculated aerobic diving limit (ADL(C)), determined with the foraging period metabolic rate of 4.1 x BMR and known O-2 stores, was only 2.6 min, which is far less than the 6-min ADL previously measured with postdive lactate analyses in emperors diving under similar conditions. This indicates that calculating ADL(C) from an at-sea or foraging-period metabolic rate in penguins is not appropriate. The relatively low foraging cost for emperor penguins contributes to their relatively low total daily FMR (2.9 x BMR). The allometric relationship for FMR in eight penguin species, including the smallest and largest living representatives, is kJ d(-1) = 1,185 kg(0.705).

2000
Ponganis, PJ, Kooyman GL.  2000.  Diving physiology of birds: a history of studies on polar species. Comparative Biochemistry and Physiology a-Molecular and Integrative Physiology. 126:143-151.   10.1016/s1095-6433(00)00208-7   AbstractWebsite

Our knowledge of avian diving physiology has been based primarily on research with polar species. Since Scholander's 1940 monograph, research has expanded from examination of the 'diving reflex' to studies of free-diving birds, and has included laboratory investigations of oxygen stores, muscle adaptations, pressure effects, and cardiovascular/metabolic responses to swimming exercise. Behavioral and energetic studies at sea have shown that common diving durations of many avian species exceed the calculated aerobic diving limits (ADL). Current physiological research is focused on factors, such as heart rate and temperature, which potentially affect the diving metabolic rate and duration of aerobic diving. (C) 2000 Elsevier Science Inc. All rights reserved.