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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.

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.

Sato, K, Watanuki Y, Takahashi A, Miller PJO, Tanaka H, Kawabe R, Ponganis PJ, Handrich Y, Akamatsu T, Watanabe Y, Mitani Y, Costa DP, Bost CA, Aoki K, Amano M, Trathan P, Shapiro A, Naito Y.  2007.  Stroke frequency, but not swimming speed, is related to body size in free-ranging seabirds, pinnipeds and cetaceans. Proceedings of the Royal Society B-Biological Sciences. 274:471-477.   10.1098/rspb.2006.0005   AbstractWebsite

It is obvious, at least qualitatively, that small animals move their locomotory apparatus faster than large animals: small insects move their wings invisibly fast, while large birds flap their wings slowly. However, quantitative observations have been difficult to obtain from free-ranging swimming animals. We surveyed the swimming behaviour of animals ranging from 0.5 kg seabirds to 30 000 kg sperm whales using animal-borne accelerometers. Dominant stroke cycle frequencies of swimming specialist seabirds and marine mammals were proportional to mass(-0.29) (R-2=0.99, n=17 groups), while propulsive swimming speeds of 1-2 m s(-1) were independent of body size. This scaling relationship, obtained from breath-hold divers expected to swim optimally to conserve oxygen, does not agree with recent theoretical predictions for optimal swimming. Seabirds that use their wings for both swimming and flying stroked at a lower frequency than other swimming specialists of the same size, suggesting a morphological trade-off with wing size and stroke frequency representing a compromise. In contrast, foot-propelled diving birds such as shags had similar stroke frequencies as other swimming specialists. These results suggest that muscle characteristics may constrain swimming during cruising travel, with convergence among diving specialists in the proportions and contraction rates of propulsive muscles.

Ponganis, PJ, Kooyman GL, Starke LN, Kooyman CA, Kooyman TG.  1997.  Post-dive blood lactate concentrations in emperor penguins, Aptenodytes forsteri. Journal of Experimental Biology. 200:1623-1626. AbstractWebsite

In order to determine an aerobic diving limit (ADL) in emperor penguins (Aptenodytes forsteri), post-dive blood lactate concentrations were measured in penguins foraging at an isolated sea ice hole. Resting lactate concentrations were 1.2-2.7 mmol l(-1). Serial samples revealed that lactate level usually peaked within 5 min after dives and that 7-12 min was required for lactate concentrations to decrease from 5-8 mmol l(-1) to less than 2.5 mmol l(-1). Post-dive lactate level was not elevated above 3 mmol l(-1) for dives shorter than 5 min. Two-phase regression analysis revealed a transition at 5.6 min in the post-dive lactate level versus diving duration relationship. All dives longer than 7 min were associated with lactate concentrations greater than 5 mmol l(-1). We conclude that the ADL in emperor penguins ranges between 5 and 7 min. These are the first determinations of post-dive lactate concentrations in any free-diving bird and are currently the only physiological assessment of an ADL in an avian species.

Ponganis, PJ, Costello ML, Starke LN, MathieuCostello O, Kooyman GL.  1997.  Structural and biochemical characteristics of locomotory muscles of emperor penguins, Aptenodytes forsteri. Respiration Physiology. 109:73-80.   10.1016/s0034-5687(97)84031-5   AbstractWebsite

Structural and biochemical characteristics of the primary muscles used for swimming (pectoralis, PEC and supracoracoideus, SC) were compared to those of leg muscles in emperor penguins (Aptenodytes forsteri). The mass of PEG-SC was four times that of the leg musculature, and mitochondrial volume density in PEC and SC (4%) was two-thirds that in sartorius (S) and gastrocnemius. The differences in muscle mass and mitochondrial density yielded a 2.2-fold greater total mitochondrial content in PEG-SC than leg muscles, which appears to account for the 1.8-fold greater whole-body highest oxygen consumption previously recorded in emperor penguins during swimming compared to walking. Calculation of maximal mitochondrial O-2 consumption in PEG-SC and leg muscle yielded values of 5.8-6.9 mi O-2 ml(-1) min(-1), which are similar to those in locomotory muscles of most mammals and birds. A distinct feature of emperor penguin muscle was its myoglobin content, with concentrations in PEG-SC (6.4 g 100 g(-1)) among the highest measured in any species. This resulted in a PEG-SC O-2 store greater than that of the entire blood. In addition, ratios of myoglobin content to mitochondrial volume density and to citrate synthase activity were 4.4 and 2.5 times greater in PEG than in S, indicative of the significant role of myoglobin in the adaptation of muscle to cardiovascular adjustments during diving. (C) 1997 Elsevier Science B.V.

Ponganis, PJ, Kooyman GL, Baranov EA, Thorson PH, Stewart BS.  1997.  The aerobic submersion limit of Baikal seals, Phoca sibirica. Canadian Journal of Zoology-Revue Canadienne De Zoologie. 75:1323-1327.   10.1139/z97-756   AbstractWebsite

An aerobic dive limit (ADL), the diving duration beyond which postdive lactate concentration increases above the resting level, has been estimated theoretically for many species. Such calculations have been based on an oxygen store/diving metabolic rate (MR) equation. Until now, an ADL has been determined empirically from measurements of blood lactate concentration only in the Weddell seal, Leptonychotes weddellii. We measured post-submergence plasma lactate concentrations during spontaneous voluntary submersions of three captive adult Baikal seals (Phoca sibirica). Two-phase regression analysis revealed a transition in the lactate concentration - submersion duration relationship after the animal had been diving for 15 min. Data collected in prior studies on oxygen stores and submersion metabolic rates of Baikal seals yielded a calculated aerobic limit of 16 min. As in Weddell seals, the empirically determined aerobic limit was very similar to the theoretical limit. Furthermore, most diving durations recorded during recent studies of free-ranging Baikal seals are under this limit. These data support the concept of an ADL and its estimation by means of an oxygen store/diving MR calculation.

Kooyman, GL, Ponganis PJ.  1994.  Emperor penguin oxygen consumption, heart rate and plasma lactate levels during graded swimming exercise. Journal of Experimental Biology. 195:199-209. AbstractWebsite

Oxygen consumption (V-O2), heart rate and blood chemistry were measured in four emperor penguins, Aptenodytes forsteri (Gray), during graded swimming exercise. The maximum V-O2, obtained, 52ml O-2 kg(-1) min(-1), was 7.8 times the measured resting V-O2 of 6.7 ml O-2 kg(-1) min(-1) and 9.1 times the predicted resting V-O2. As the swimming effort rose, a linear increase in surface and submerged heart rates (fH) occurred. The highest average maximum surface and submersion heart rates of any bird were 213 and 210 beats min(-1), respectively. No increase in plasma lactate concentrations occurred until V-O2 was greater than 25 ml O-2 kg(-1) min(-1). At the highest V-O2 values measured, plasma lactate concentration reached 9.4 mmol l(-1). In comparison with other animals of approximately the same mass, the aerobic capacity of the emperor penguin is less than those of the emu and dog but about the same as those of the seal, sea lion and domestic goat. For aquatic animals, a low aerobic capacity seems to be consistent with the needs of parsimonious oxygen utilization while breath-holding.