Publications

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2017
Kooyman, GL, Ponganis PJ.  2017.  Rise and fall of Ross Sea emperor penguin colony populations: 2000 to 2012. Antarctic Science. 29:201-208.   10.1017/s0954102016000559   AbstractWebsite

There are seven emperor penguin (Aptenodytes forsteri) colonies distributed throughout the traditional boundaries of the Ross Sea from Cape Roget to Cape Colbeck. This coastline is c. 10% of the entire coast of Antarctica. From 2000 to 2012, there has been a nearly continuous record of population size of most, and sometimes all, of these colonies. Data were obtained by analysing aerial photographs. We found large annual variations in populations of individual colonies, and conclude that a trend from a single emperor penguin colony may not be a good environmental sentinel. There are at least four possibilities for census count fluctuations: i) this species is not bound to a nesting site like other penguins, and birds move within the colony and possibly to other colonies, ii) harsh environmental conditions cause a die-off of chicks in the colony or of adults elsewhere, iii) the adults skip a year of breeding if pre-breeding foraging is inadequate and iv) if sea ice conditions are unsatisfactory at autumn arrival of the adults, they skip breeding or go elsewhere. Such variability indicates that birds at all Ross Sea colonies should be counted annually if there is to be any possibility of understanding the causes of population changes.

2012
Williams, CL, Sato K, Shiomi K, Ponganis PJ.  2012.  Muscle energy stores and stroke rates of emperor penguins: implications for muscle metabolism and dive performance. Physiological and Biochemical Zoology. 85:120-133.   10.1086/664698   AbstractWebsite

In diving birds and mammals, bradycardia and peripheral vasoconstriction potentially isolate muscle from the circulation. During complete ischemia, ATP production is dependent on the size of the myoglobin oxygen (O-2) store and the concentrations of phosphocreatine (PCr) and glycogen (Gly). Therefore, we measured PCr and Gly concentrations in the primary underwater locomotory muscle of emperor penguin and modeled the depletion of muscle O-2 and those energy stores under conditions of complete ischemia and a previously determined muscle metabolic rate. We also analyzed stroke rate to assess muscle workload variation during dives and evaluate potential limitations on the model. Measured PCr and Gly concentrations, 20.8 and 54.6 mmol kg(-1), respectively, were similar to published values for nondiving animals. The model demonstrated that PCr and Gly provide a large anaerobic energy store, even for dives longer than 20 min. Stroke rate varied throughout the dive profile, indicating muscle workload was not constant during dives as was assumed in the model. The stroke rate during the first 30 s of dives increased with increased dive depth. In extremely long dives, lower overall stroke rates were observed. Although O-2 consumption and energy store depletion may vary during dives, the model demonstrated that PCr and Gly, even at concentrations typical of terrestrial birds and mammals, are a significant anaerobic energy store and can play an important role in the emperor penguin's ability to perform long dives.

Shiomi, K, Sato K, Ponganis PJ.  2012.  Point of no return in diving emperor penguins: is the timing of the decision to return limited by the number of strokes? Journal of Experimental Biology. 215:135-140.   10.1242/jeb.064568   AbstractWebsite

At some point in a dive, breath-hold divers must decide to return to the surface to breathe. The issue of when to end a dive has been discussed intensively in terms of foraging ecology and behavioral physiology, using dive duration as a temporal parameter. Inevitably, however, a time lag exists between the decision of animals to start returning to the surface and the end of the dive, especially in deep dives. In the present study, we examined the decision time in emperor penguins under two different conditions: during foraging trips at sea and during dives at an artificial isolated dive hole. It was found that there was an upper limit for the decision-to-return time irrespective of dive depth in birds diving at sea. However, in a large proportion of dives at the isolated dive hole, the decision-to-return time exceeded the upper limit at sea. This difference between the decision times in dives at sea versus the isolated dive hole was accounted for by a difference in stroke rate. The stroke rates were much lower in dives at the isolated hole and were inversely correlated with the upper limit of decision times in individual birds. Unlike the decision time to start returning, the cumulative number of strokes at the decision time fell within a similar range in the two experiments. This finding suggests that the number of strokes, but not elapsed time, constrained the decision of emperor penguins to return to the surface. While the decision to return and to end a dive may be determined by a variety of ecological, behavioral and physiological factors, the upper limit to that decision time may be related to cumulative muscle workload.

2011
Williams, CL, Meir JU, Ponganis PJ.  2011.  What triggers the aerobic dive limit? Patterns of muscle oxygen depletion during dives of emperor penguins Journal of Experimental Biology. 214:1802-1812.   10.1242/jeb.052233   AbstractWebsite

The physiological basis of the aerobic dive limit (ADL), the dive duration associated with the onset of post-dive blood lactate elevation, is hypothesized to be depletion of the muscle oxygen (O(2)) store. A dual wavelength near-infrared spectrophotometer was developed and used to measure myoglobin (Mb) O(2) saturation levels in the locomotory muscle during dives of emperor penguins (Aptenodytes forsteri). Two distinct patterns of muscle O(2) depletion were observed. Type A dives had a monotonic decline, and, in dives near the ADL, the muscle O(2) store was almost completely depleted. This pattern of Mb desaturation was consistent with lack of muscle blood flow and supports the hypothesis that the onset of post-dive blood lactate accumulation is secondary to muscle O(2) depletion during dives. The mean type A Mb desaturation rate allowed for calculation of a mean muscle O(2) consumption of 12.4. ml O(2). kg(-1) muscle. min(-1), based on a Mb concentration of 6.4. g 100. g(-1) muscle. Type B desaturation patterns demonstrated a more gradual decline, often reaching a mid-dive plateau in Mb desaturation. This mid-dive plateau suggests maintenance of some muscle perfusion during these dives. At the end of type B dives, Mb desaturation rate increased and, in dives beyond the ADL, Mb saturation often reached near 0%. Thus, although different physiological strategies may be used during emperor penguin diving, both Mb desaturation patterns support the hypothesis that the onset of post-dive lactate accumulation is secondary to muscle O(2) store depletion.

2008
Barber-Meyer, SM, Kooyman GL, Ponganis PJ.  2008.  Trends in western Ross Sea emperor penguin chick abundances and their relationships to climate. Antarctic Science. 20:3-11.   10.1017/s0954102007000673   AbstractWebsite

The emperor penguin (Aptenodytes forsteri) is extremely dependent on the extent and stability of sea ice, which may make the species particularly susceptible to environmental change. In order to appraise the stability of the emperor penguin populations at six colonies in the western Ross Sea, we used linear regression analysis to evaluate chick abundance trends (1983-2005) and Pearson's r correlation to assess their relation to two local and two large-scale climate variables. We detected only one significant abundance trend; the Cape Roget colony increased from 1983 to 1996 (n = 6). Higher coefficients of variation in chick abundances at smaller colonies (Cape Crozier, Beaufort Island, Franklin Island) suggest that such colonies occupy marginal habitat, and are more susceptible to environmental change. We determined chick abundance to be most often correlated with local Ross Sea climate variables (sea ice extent and sea surface temperature), but not in consistent patterns across the colonies. We propose that chick abundance is most impacted by fine scale sea ice extent and local weather events, which are best evaluated by on-site assessments. We did not find sufficient evidence to reject the hypothesis that the overall emperor penguin population in the Ross Sea was stable during this period.

2007
Barber-Meyer, SM, Kooyman GL, Ponganis PJ.  2007.  Estimating the relative abundance of emperor penguins at inaccessible colonies using satellite imagery. Polar Biology. 30:1565-1570.   10.1007/s00300-007-0317-8   AbstractWebsite

Emperor penguin (Aptenodytes forsteri) populations are useful environmental indicators due to the bird's extreme reliance on sea ice. We used remote sensing technology to estimate relative adult bird abundance at two inaccessible emperor penguin colonies in the Ross Sea, Antarctica. We performed supervised classification of 12 panchromatic satellite images of the seven known Ross Sea colonies. We used regression to predict adult bird counts at the inaccessible colonies by relating the number of pixels classified as "penguin" in the satellite images of the accessible colonies to corresponding known adult bird counts from aerial photographs or ground counts. While our analysis was hampered by excessive guano and shadows, we used satellite imagery to differentiate between relatively small (< 3,000 adult birds) and larger colonies (> 5,000 adult birds). Remote sensing technology is logistically less intense and less costly than aerial or ground censuses when the objective is to document penguin presence and/or large emperor penguin population changes (e.g., catastrophic changes). Improvements expected soon in the resolution of the satellite images should allow for more accurate abundance estimates.

Kooyman, GL, Ainley DG, Ballard G, Ponganis PJ.  2007.  Effects of giant icebergs on two emperor penguin colonies in the Ross Sea, Antarctica. Antarctic Science. 19:31-38.   10.1017/s0954102007000065   AbstractWebsite

The arrival in January 2001 in the south-west Ross Sea of two giant icebergs, C16 and Bl5A, subsequently had dramatic affects on two emperor penguin colonies. B15A collided with the north-west tongue of the Ross Ice Shelf at Cape Crozier, Ross Island, in the following months and destroyed the penguins' nesting habitat. The colony totally failed in 2001, and years after, with the icebergs still in place, exhibited reduced production that ranged from 0 to 40% of the 1201 chicks produced in 2000. At Beaufort Island, 70 km NW of Crozier, chick production declined to 6% of the 2000 count by 2004. Collisions with the Ross Ice Shelf at Cape Crozier caused incubating adults to be crushed, trapped in ravines, or to abandon the colony and, since 2001, to occupy poorer habitat. The icebergs separated Beaufort Island from the Ross Sea Polynya, formerly an easy route to feeding and wintering areas. This episode has provided a glimpse of events which have probably occurred infrequently since the West Antarctic Ice Sheet began to retreat 12 000 years ago. The results allow assessment of recovery rates for one colony decimated by both adult and chick mortality, and the other colony by adult abandonment and chick mortality.

Kooyman, GL, Ponganis PJ.  2007.  The initial journey of juvenile emperor penguins. Aquatic Conservation-Marine and Freshwater Ecosystems. 17:S37-S43.   10.1002/aqc.930   AbstractWebsite

1. The first major journey of emperor penguins, among several in their lifetime, is the juveniles' dispersal from their natal colony on a trip that takes them beyond Antarctic waters. The route taken by fledglings from Cape Washington (74.5 degrees S; 165.4 degrees E) was Studied by applying satellite transmitters to ten individuals during December 1994-1996. In January 2001 transmitters with longer transmission capacity were also applied to six hand-fed fledglings, which had been held captive for one month while attaining a body mass exceeding that of wild birds. These post-captive birds were released at the ice edge of McMurdo Sound (77.5 degrees S; 165.0 degrees E), which is in the vicinity of other emperor penguin colonies, and 320km south of their natal colony of Cape Washington. 2. Independent of their parents, the wild birds travelled north-east for the next two months, reaching locations as low as 57 degrees S. The post-captive birds travelled north also, but their trek reached only to about 63 degrees S before they turned south, or remained near their most northerly position from March through May. 3. It was concluded that among colonies in the southern Ross Sea: (a) most healthy fledglings Survive at least the first two months at sea, feeding themselves as they go; (b) the Cape Washington fledglings travelled as far north as 57 degrees S, and much of this journey was in ice free waters; (c) by April, the post-captive birds reached at least as far as the large-scale pack ice edge and possibly beyond the edge Lit 63 degrees S; (d) by early March the trend north ends, and by about late March the birds travel to, or remain near the northern ice edge. 4. The reason the birds travel so far north remains a mystery. Copyright (c) 2008 John Wiley & Sons, Ltd.

2005
Knower Stockard, T, Heil J, Meir JU, Sato K, Ponganis KV, Ponganis PJ.  2005.  Air sac P-O2 and oxygen depletion during dives of emperor penguins. Journal of Experimental Biology. 208:2973-2980.   10.1242/jeb.01687   AbstractWebsite

In order to determine the rate and magnitude of respiratory O-2 depletion during dives of emperor penguins (Aptenodytes forsteri), air sac O-2 partial pressure (PO2) was recorded in 73 dives of four birds at an isolated dive hole. These results were evaluated with respect to hypoxic tolerance, the aerobic dive limit (ADL; dive duration beyond which there is post-dive lactate accumulation) and previously measured field metabolic rates (FMRs). 55% of dives were greater in duration than the previously measured 5.6-min ADL. P-O2 and depth profiles revealed compression hyperoxia and gradual O-2 depletion during dives. 42% of final P(O2)s during the dives (recorded during the last 15 s of ascent) were < 20 mmHg (< 2.7 kPa). Assuming that the measured air sac P-O2 is representative of the entire respiratory system, this implies remarkable hypoxic tolerance in emperors. In dives of durations greater than the ADL, the calculated end-of-dive air sac O-2 fraction was < 4%. The respiratory O-2 store depletion rate of an entire dive, based on the change in O-2 fraction during a dive and previously measured diving respiratory volume, ranged from I to 5 ml O-2 kg(-1) min(-1) and decreased exponentially with diving duration. The mean value, 2.1 +/- 0.8 ml O-2 kg(-1) min(-1), was (1) 19-42% of previously measured respiratory O-2 depletion rates during forced submersions and simulated dives, (2) approximately one-third of the predicted total body resting metabolic rate and (3) approximately 10% of the measured FMR. These findings are consistent with a low total body metabolic rate during the dive.

2003
Ponganis, PJ, Van Dam RP, Levenson DH, Knower T, Ponganis KV, Marshall G.  2003.  Regional heterothermy and conservation of core temperature in emperor penguins diving under sea ice. Comparative Biochemistry and Physiology a-Molecular & Integrative Physiology. 135:477-487.   10.1016/s1095-6433(03)00133-8   AbstractWebsite

Temperatures were recorded at several body sites in emperor penguins (Aptenodytes forsteri) diving at an isolated dive hole in order to document temperature profiles during diving and to evaluate the role of hypothermia in this well-studied model of penguin diving physiology. Grand mean temperatures (+/-S.E.) in central body sites during dives were: stomach: 37.1 +/- 0.2 degreesC (n = 101 dives in five birds), pectoral muscle: 37.8 +/- 0.1 degreesC (n = 71 dives in three birds) and axillary/brachial veins: 37.9 +/- 0.1 degreesC (n = 97 dives in three birds). Mean diving temperature and duration correlated negatively at only one site in one bird (femoral vein, r = -0.59, P < 0.05; range < 1 degreesC). In contrast, grand mean temperatures in the wing vein, foot vein and lumbar subcutaneous tissue during dives were 7.6 +/- 0.7 degreesC (n = 157 dives in three birds), 20.2 +/- 1.2 degreesC (n = 69 in three birds) and 35.2 +/- 0.2 degreesC (n = 261 in six birds), respectively. Mean limb temperature during dives negatively correlated with diving duration in all six birds (r = -0.29 to -0.60, P < 0.05). In two of six birds, mean diving subcutaneous temperature negatively correlated with diving duration (r = -0.49 and -0.78, P < 0.05). Sub-feather temperatures decreased from 31 to 35 T during rest periods to a grand mean of 15.0 +/- 0.7 degreesC during 68 dives of three birds; mean diving temperature and duration correlated negatively in one bird (r = -0.42, P < 0.05). In general, pectoral, deep venous and even stomach temperatures during diving reflected previously measured vena caval temperatures of 37-39 degreesC more closely than the anterior abdominal temperatures (19-30 degreesC) recently recorded in diving emperors. Although prey ingestion can result in cooling in the stomach, these findings and the lack of negative correlations between internal temperatures and diving duration do not support a role for hypothermia-induced metabolic suppression of the abdominal organs as a mechanism of extension of aerobic dive time in emperor penguins diving at the isolated dive hole. Such high temperatures within the body and the observed decreases in limb, anterior abdomen, subcutaneous and sub-feather temperatures are consistent with preservation of core temperature and cooling of an outer body shell secondary to peripheral vasoconstriction, decreased insulation of the feather layer, and conductive/convective heat loss to the water environment during the diving of these emperor penguins. (C) 2003 Elsevier Science Inc. All fights reserved.

2002
Van Dam, RP, Ponganis PJ, Ponganis KV, Levenson DH, Marshall G.  2002.  Stroke frequencies of emperor penguins diving under sea ice. Journal of Experimental Biology. 205:3769-3774. AbstractWebsite

During diving, intermittent swim stroke patterns, ranging from burst/coast locomotion to prolonged gliding, represent potential energy conservation mechanisms that could extend the duration of aerobic metabolism and, hence, increase the aerobic dive limit (ADL, dive duration associated with onset of lactate accumulation). A 5.6 min ADL for emperor penguins had been previously determined with lactate measurements after dives of <50 m depth. In order to assess locomotory patterns during such dives, longitudinal acceleration was measured with an attached accelerometer in 44 dives of seven adult birds diving from an isolated dive hole in the sea ice of McMurdo Sound, Antarctica. Detection of wing strokes in processed accelerometer data was verified in selected birds with analysis of simultaneous Crittercam underwater video footage. Mean dive duration of birds equipped with the accelerometer and a time-depth recorder (TDR) was 5.7+/-2.2 min; 48% of these dives were greater than the measured 5.6 min ADL (ADL(M)). Highest stroke frequencies (0.92+/-0.31Hz, N=981) occurred during the initial descent to 12 m depth. Swimming effort was reduced to a mean stroke frequency <0.70 Hz during other phases of the dive (while traveling below 12 m depth, during foraging ascents/descents to and from the sub-ice surface, and during final ascents to exit). The longest stroke interval (8.6 s) occurred during a feeding excursion to the undersurface of the ice. In dives >ADL(M), mean stroke frequency during travel segments was significantly less than that in dives 10 s) periods of prolonged gliding during these shallow (<60 m) foraging dives. However, a stroke/glide pattern was evident with more than 50% of strokes associated with a stroke interval >1.6 s, and with lower stroke frequency associated with increased dive duration.

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, Van Dam RP, Marshall G, Knower T, Levenson DH.  2000.  Sub-ice foraging behavior of emperor penguins. Journal of Experimental Biology. 203:3275-3278. AbstractWebsite

Emperor penguins (Aptenodytes forsteri) were equipped with a remote underwater video camera, the Crittercam, to evaluate sub-ice foraging behavior while the birds dived from an isolated dive hole. Three birds dived and foraged successfully for Ih periods after being trained to wear and to dive with a harness for camera attachment. Video and depth profile recordings revealed that emperor penguins travel at shallow depths (<50 m), ascend to the undersurface of the ice to feed on fish, and descend back to depth to return to the exit hole. Although the mean durations of dives of individual birds with the Crittercam were 21-35 % shorter than the diving durations of these same birds without the camera, the dive profiles in both situations were similar, thus demonstrating a similar foraging strategy in birds diving without the camera. Despite shorter diving durations with the camera, the penguins were still successful at prey capture in 80 % of 91 dives greater than 1 min in duration. Prey included the sub-ice fish Pagothenia borchgrevinki. Hunting ascents (from depth to within 5 m of the surface) occurred in 85 % of dives, ranged from zero to three per dive, and were associated with successful prey capture in 77 % of 128 ascents, Occasionally, several fish were captured during a single ascent, These observations and this application of video technology create a model for further physiological and behavioral studies of foraging, and also emphasize the potential importance of shallow dives as sources of food intake for emperor penguins during foraging trips to sea.

1999
Ponganis, PJ, Starke LN, Horning M, Kooyman GL.  1999.  Development of diving capacity in emperor penguins. Journal of Experimental Biology. 202:781-786. AbstractWebsite

To compare the diving capacities of juvenile and adult emperor penguins Aptenodytes forsteri, and to determine the physiological variables underlying the diving ability of juveniles, we monitored diving activity in juvenile penguins fitted with satellite-linked time/depth recorders and examined developmental changes in body mass (M-b), hemoglobin concentration, myoglobin (Mb) content and muscle citrate synthase and lactate dehydrogenase activities, Diving depth, diving duration and time-at-depth histograms were obtained from two fledged juveniles during the first 2.5 months after their departure from the Cape Washingon colony in the Ross Sea, Antarctica. During this period, values of all three diving variables increased progressively. After 8-10 weeks at sea, 24-41% of transmitted maximum diving depths were between 80 and 200 m, Although most dives lasted less than 2 min during the 2 month period, 8-25% of transmitted dives in the last 2 weeks lasted 2-4 min. These values are lower than those previously recorded in adults during foraging trips. Of the physiological variables examined during chick and juvenile development, only M-b and Mb content did not approach adult values, In both near-hedge chicks and juveniles, Mb was 50-60% of adult values and Mb content was 24-31% of adult values. This suggests that the increase in diving capacity of juveniles at sea will be most dependent on changes in these factors.

1997
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.

1994
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.