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 animalborne accelerometers. Dominant stroke cycle frequencies of swimming specialist seabirds and marine mammals were proportional to mass K0.29 (R 2 Z0.99, nZ17 groups), while propulsive swimming speeds of 1-2 m s K1 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.

SUMMARY The main objective of this study was to determine heart rate(fh) and the energetic costs of specific behaviours of king penguins while ashore and while foraging at sea during their breeding period. In particular, an estimate was made of the energetic cost of diving in order to determine the proportion of dives that may exceed the calculated aerobic dive limit (cADL; estimated usable O2 stores/estimated rate of oxygen consumption during diving). An implanted data logger enabled fh and diving behaviour to be monitored from 10 free-ranging king penguins during their breeding period. Using previously determined calibration equations, it was possible to estimate rate of oxygen consumption(V̇O2) when the birds were ashore and during various phases of their foraging trips. Diving behaviour showed a clear diurnal pattern, with a mixture of deep (>40 m),long (>3 min) and shallow (<40 m), short (<3 min) dives from dawn to dusk and shallow, short dives at night. Heart rate during dive bouts and dive cycles (dive + post-dive interval) was 42% greater than that when the birds were ashore. During diving, fh was similar to the `ashore'value (87±4 beats min–1), but it did decline to 76% of the value recorded from king penguins resting in water. During the first hour after a diving bout, fh was significantly higher than the average value during diving (101±4 beats min–1) and for the remainder of the dive bout. Rates of oxygen consumption estimated from these (and other) values of fh indicate that when at sea, metabolic rate (MR) was 83%greater than that when the birds were ashore [3.15 W kg–1(–0.71, +0.93), where the values in parentheses are the computed standard errors of the estimate], while during diving bouts and dive cycles,it was 73% greater than the `ashore' value. Although estimated MR during the total period between dive bouts was not significantly different from that during dive bouts [5.44 W kg–1 (–0.30, +0.32)], MR during the first hour following a dive bout was 52% greater than that during a diving bout. It is suggested that this large increase following diving(foraging) activity is, at least in part, the result of rewarming the body,which occurs at the end of a diving bout. From the measured behaviour and estimated values of V̇O2, it was evident that approximately 35% of the dives were in excess of the cADL. Even if V̇O2 during diving was assumed to be the same as when the birds were resting on water,approximately 20% of dives would exceed the cADL. As V̇O2 during diving is, in fact, that estimated for a complete dive cycle, it is quite feasible that V̇O2 during diving itself is less than that measured for birds resting in water. It is suggested that the regional hypothermia that has been recorded in this species during diving bouts may be at least a contributing factor to such hypometabolism.

ABSTRACT. The relationsh~ps between the foraging strategy of seabirds, hydrographic features and food availability are poorly understood. We investigated the movements at sea, time spent per oceanic sector, food intake, and d~e t of king pengulns Aptenodytespatagonicus in the Crozet Islands (Southern Indian Ocean) during summer, as a function of the position of major frontal zones. Fifteen trips at sea were monitored using satelhte transmitters over 3 austral summers (1992 to 1994). During each season, satellite transmitters were used in conjunction with stomach temperature recorders in order to investigate feeding activity. The at-sea distribution of klng penguins was closely related to the localisation of major hydrographic frontal systems. Intense prospecting areas were observed mainly in zones corresponding to the northern h i t of the Polar Front (50" to 51°S), southern limit of the Sub-Antarctic Front (44.50' to 45O S], and a zone between 47' and 48" S. During trips directed south, 2 distinct phases based on travelling speed were detected. The myctophids Electrons carlsbergi, Krefftichtys anderssoni and Protomyctophurn tenisoni dominated the diet. The est~mated average amount of food ingested per day at sea was 2.4 kg. Between 17 and 64 kg of food was captured during 7 to 25 d at sea. Approximately 80% of the food intake occurred during the first phase of the trip. Food intake was related to trip duration and relative amount of time spent in particular oceanic sectors. The sections 47' to 48" S and 48.5" to 50.50" S appeared particularly favorable for food intake, the latter coinciding with the northern limit of the Polar Front. King penguins fed ~ntensively on several distinct patches when traveling towards the Polar Front. The foraging range seems to be related to the foraging success during the first phase of the trip. The foraging strategy of king penguins during the summer favors displacements toward frontal zones where food availability is optimal.

evolution and 100 replications for maximum likelihood. Shape parameters for the gamma distribution were estimated from minimum length trees 26 and were 0.32 (mtDNA), 0.59 (vWF) and 0.52 (A2AB). Divergence times. 12S rRNA transversions accumulated linearly as far back as the eutherian-metatherian split 24 . Nine independent cladogenic events were selected based on 12S rRNA sequence availability and paleostratigraphic data 10,24,30 (for example, Rattus to Mus (14 Myr); Sus to Tayassu (45 Myr); ruminants to Cetacea (60 Myr); Erinaceus to Metatheria (130 Myr)). Relative rates were calculated in reference to xenarthrans. Tamura-Nei transversion distances (transversions only) were adjusted for relative rate differences 30 against the xenarthran standard. Rate-adjusted estimates of sequence divergence were regressed against paleostratigraphic divergence estimates for each of the nine calibration points (origin forced through zero; r 2 ¼ 0:97; P ¼ 0:0000002). The resulting equation ðdivergence time ðin MyrÞ ¼ sequence divergence=0:00063Þ was used to estimate interordinal divergence times after making similar adjustments for relative rates. Additional details will be presented elsewhere (M.S., manuscript in preparation).

Determining the links between the behavioural and population responses of wild species to environmental variations is critical for understanding the impact of climate variability on ecosystems. Using long-term data sets, we show how large-scale climatic anomalies in the Southern Hemisphere affect the foraging behaviour and population dynamics of a key marine predator, the king penguin. When large-scale subtropical dipole events occur simultaneously in both subtropical Southern Indian and Atlantic Oceans, they generate tropical anomalies that shift the foraging zone southward. Consequently the distances that penguins foraged from the colony and their feeding depths increased and the population size decreased. This represents an example of a robust and fast impact of large-scale climatic anomalies affecting a marine predator through changes in its at-sea behaviour and demography, despite lack of information on prey availability. Our results highlight a possible behavioural mechanism through which climate variability may affect population processes.