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Understanding how prey capture rates are influenced by feeding ecology and environmental conditions is fundamental to assessing anthropogenic impacts on marine higher predators. We compared how prey capture rates varied in relation to prey size, prey patch distribution and prey density for two species of alcid, common guillemot (Uria aalge) and razorbill (Alca torda) during the chick-rearing period. We developed a Monte Carlo approach parameterised with foraging behaviour from birdborne data loggers, observations of prey fed to chicks, and adult diet from wateroffloading, to construct a bio-energetics model. Our primary goal was to estimate prey capture rates, and a secondary aim was to test responses to a set of biologically plausible environmental scenarios. Estimated prey capture rates were 1.5±0.8 items per dive (0.8±0.4 and 1.1±0.6 items per minute foraging and underwater, respectively) for guillemots and 3.7±2.4 items per dive (4.9±3.1 and 7.3±4.0 items per minute foraging and underwater, respectively) for razorbills. Based on species' ecology, diet and flight costs, we predicted that razorbills would be more sensitive to decreases in 0- group sandeel (Ammodytes marinus) length (prediction 1), but guillemots would be more sensitive to prey patches that were more widely spaced (prediction 2), and lower in prey density (prediction 3). Estimated prey capture rates increased non-linearly as 0- group sandeel length declined, with the slope being steeper in razorbills, supporting prediction 1. When prey patches were more dispersed, estimated daily energy expenditure increased by a factor of 3.0 for guillemots and 2.3 for razorbills, suggesting guillemots were more sensitive to patchier prey, supporting prediction 2. However, both species responded similarly to reduced prey density (guillemot expenditure increased by 1.7; razorbill by 1.6), thus not supporting prediction 3. This bio-energetics approach complements other foraging models in predicting likely impacts of

The physiological state of parent birds combined with the value of their clutch may affect the intensity of their nest defense. In colonially breeding birds, nest defense intensity may also be affected by the behavior of neighbors. We investigated individual variation in the intensity of nest defense among colonial Black-tailed Gulls Larus crassirostris in two years. Only 30-40% of males attacked a decoy of an egg predator (crow), and the other males and females rarely attacked. Males attacking the decoy had higher levels of plasma testosterone than males that did not attack. Each male's, but not female's, nest defense intensity was consistent throughout the incubation period and also across years. The intensity was not related to egg-laying date, clutch size, or age of offspring. The intensity was likely to be higher when individuals had one or more neighbors, representing higher nest defense intensity in the year where gulls had larger number of adjacent neighboring nests (5.23 nests), but this trend was not observed in the year where they had smaller number of the neighboring nests (3.73 nests). Thus, in addition to testosterone levels, behavior of neighbors also influences the intensity of nest defense.

Seabirds and large fishes are important top predators in marine ecosystems, but few studies have explored the potential for competition between these groups. This study investigated the relationship between an observed biennial change of pink salmon (Oncorhynchus gorbuscha) biomass in the central Bering Sea (23 times greater in odd-numbered than in even-numbered years) and the body condition and diet of the short-tailed shearwater (Puffinus tenuirostris) spending post-breeding season there. Samples were collected with research gill nets over seven summers. Both species feed on krill, small fishes and squids. Although the mean pink salmon catch per unit effort (in mass) over the study region was not related significantly with shearwater's stomach content mass or prey composition, the pink salmon biomass showed a negative and significant relationship with the shearwater's body mass and liver mass (proxies of energy reserve). We interpret these results as evidence that fishes can negatively affect mean prey intake of seabirds if they feed on a shared prey in the pelagic ecosystem.

In the wild, seabirds dive longer than their theoretical aerobic dive limit (oxygen store divided by oxygen consumption rate). One of the potential explanations for this is that when descending in water seabirds regulate their foot or wing strokes to compensate their upward buoyancy, which decreases with the current depth to reduce oxygen consumption rate. The change in frequency of wing or foot stroke with current depths was compared between South Georgian Shag Notocarbo georgianus (SGSG), Common Murre Uria aalge (COMU), and Macaroni Penguin Eudyptes chrysolophus (MCPN) using biologging techniques. When descending to 60 m depth, the frequency of thrust and foot stroke decreased in SGSG, which make a forward thrust at each foot stroke. While in COMU, the frequency of thrust decreased, whereas wing stroke was nearly constant. COMU made a thrust with each up- and down-stroke in shallow water but only with each down-stroke in deeper water. In MCPN, however, the frequency of thrust did not change with the current depth. The MCPN made strokes at a nearly constant rate, while making thrusts with each up- and down-stroke at any depth. Because of the shallower descent angle of MCPN, compared with those of SGSG and COMU, MCPN should require relatively little thrust in order to compensate for its buoyancy and thus might not need to change the frequency of thrust with current depth. Swimming speeds during descent were nearly constant (1.4–2.2 m/s) in SGSG, COMU and MCPN. These three species appeared to regulate their strokes to maintain a range of swimming speeds. Biologging techniques reveal the biomechanical regulation of movement of birds under morphological and physical constraints. This provides a new approach to understanding the behavioural ecology of birds flying in the air and water.

Diving animals have to counter both drag and buoyancy when moving through the water column. The magnitude of these forces depends upon an animal's swim speed and current depth. Feet, fins or flippers create a motivating force, and different stroke strategies give a variable level of output power, providing both fast swim speeds and reduced travel times to any given target depth. However, while feet, fins or flippers may confer a real advantage, they also create considerable drag and engender high metabolic (oxygen consumption) costs. Consequently, there should be an optimal relationship between output power and stroke frequency during diving. Here we develop diving models to predict the optimal pattern of stroke frequency during both the descent and ascent phase of divers in water, while maintaining a minimum cost of transport (COT, J kg(-1) m(-1)). We also test predictions derived from these models using diving data for foot-propelled South Georgian shags Phalacrocorax georgianus diving to deeper than 80 m. Our predictions include: (1) output power (stroke frequency) should decline during the descent and ascent phases of a dive, but constant output power should be evident when the diving depth is shallow, (2) initial thrust for dives to deeper target depths should be smaller during the descent phase and greater during the ascent phase, and, (3) swim speed should be constant during the descent phase and should decrease first or remain constant, then increase during the ascent phase because of a declining output power strategy. Our empirical data on shags support only some of these predictions. Predictions (1) and (3) were supported by our observations, but Prediction (2) was not, possibly due to unknown but specific factors concerning diving seabirds. These findings suggest that diving seabirds adjust and control their stroke frequency pattern in order to minimize COT during diving, generating the observed changes in swimming speed.

Often in colonial seabirds, all colony members are believed to defend against nest predators and experience equal nest predation risk. However, the variation of defense behavior among members and its reproductive consequences are largely unknown. We investigated 1) individual variation in the nest defense of breeding Black-tailed Gulls Larus crassirostris against a natural egg predator, the Jungle Crow Corvus macrorhynchos and 2) how this behavioral variation affects an individual's own nest predation risk and that of their neighbors. Results were compared between two years where crow attack levels were manipulated to average 5 and 22 times normal rates ("low" and "high" predation risk years, respectively) by the placement of varying numbers of artificial nests containing unguarded eggs at the perimeter of the gull colony. In both years, 23-38% of parents, mostly males, showed "aggressive" defense behavior (strikes or chases) against crows and decoys. Other "non-aggressive" gulls showed no defense. In the year of low predation risk, intrusion rates by crows (landing within 0.5 m of an individual gull's nest) were similar for aggressive and non-aggressive gulls. In the year of high predation risk, however, the rates of intrusion for aggressive gulls (4%) and for non-aggressive gulls with an aggressive neighbor (37%) were significantly lower than for non-aggressive gulls without an aggressive neighbor (76%). These results indicate that aggressive individuals reduce nest predation risk for themselves and conspecific neighbors in a colonially breeding species.

Predator-prey relationships are key to understanding complex marine ecosystem dynamics. The match-mismatch hypothesis posits that predators time energy-intensive activities, such as reproduction, to periods of high food availability. However, predators may be constrained by various ecological or physiological processes, leading to mistimed activities relative to prey availability. We investigated inter-annual variation in the timing of breeding for a piscivorous seabird (rhinoceros auklet Cerorhinca monocerata) in relation to availability of a preferred prey item, Japanese anchovy Engraulis japonicus, using data collected over 18 yr between 1984 and 2006 at Teuri Island in the northern Japan Sea. Our primary goals were (1) to identify the climatic factors that affect the seabirds' timing of breeding, proxied by hatching date, and anchovy seasonal availability, and (2) to quantify the fitness effects of predator-prey matches and mismatches relative to climate variability. Hatching date was later in years with lower spring air temperatures. Auklets switched their feeding from sandlance and juvenile greenling to anchovy when it was transported into the birds' foraging range with the seasonal northern expansion of 13 degrees C warm water from the south. The mismatch between hatching date and the period of high anchovy availability was most pronounced when spring air temperatures were warm, and there was a weak Tsushima (warm) Current. Spring air temperature was influenced by spring atmospheric pressure gradients in the Arctic and northern Eurasia, which drive the east Asian winter monsoon, whereas timing of the Tsushima warm water expansion was influenced by winter surface pressures over the western North Pacific. Chick growth rates, mass at fledging, and overall fledging success (fitness) were lower during mismatch years when the auklets fed less on anchovy. The auklets were constrained to adjust hatching date because the seasonal mismatch appeared to be driven by inde

An ethogram is a catalogue of discrete behaviors typically employed by a species. Traditionally animal behavior has been recorded by observing study individuals directly. However, this approach is difficult, often impossible, in the case of behaviors which occur in remote areas and/or at great depth or altitude. The recent development of increasingly sophisticated, animal-borne data loggers, has started to overcome this problem. Accelerometers are particularly useful in this respect because they can record the dynamic motion of a body in e.g. flight, walking, or swimming. However, classifying behavior using body acceleration characteristics typically requires prior knowledge of the behavior of free-ranging animals. Here, we demonstrate an automated procedure to categorize behavior from body acceleration, together with the release of a user-friendly computer application, “Ethographer”. We evaluated its performance using longitudinal acceleration data collected from a foot-propelled diving seabird, the European shag, Phalacrocorax aristotelis. The time series data were converted into a spectrum by continuous wavelet transformation. Then, each second of the spectrum was categorized into one of 20 behavior groups by unsupervised cluster analysis, using k-means methods. The typical behaviors extracted were characterized by the periodicities of body acceleration. Each categorized behavior was assumed to correspond to when the bird was on land, in flight, on the sea surface, diving and so on. The behaviors classified by the procedures accorded well with those independently defined from depth profiles. Because our approach is performed by unsupervised computation of the data, it has the potential to detect previously unknown types of behavior and unknown sequences of some behaviors.

Sexual differences in food provisioning rates of monomorphic seabirds are well known but poorly understood. Here, we address three hypotheses that attempt to explain female-biased food provisioning in common guillemots Uria aalge: (1) males spend more time in nest defence, (2) females have greater foraging efficiency, and (3) males allocate a greater proportion of foraging effort to self-maintenance. We found that males spent no more time with chicks than females but made longer trips and travelled further from the colony. There was extensive overlap between sexes in core foraging areas, indicating that females were not excluding males from feeding opportunities close to the colony. However, as a result of their longer trips, the total foraging areas of males were much greater than those of females. There was no difference between sexes in overall dive rate per hour at sea, in behaviour during individual dives or in a number of other measures of foraging efficiency including the frequency, depth and duration of dives and the dive: pause ratio during the final dive bout of each trip, which was presumably used by both sexes to obtain prey for the chick. These data strongly suggest that sexes did not differ in their ability to locate and capture prey. Yet males made almost twice as many dives per trip as females, suggesting that males made more dives than females for their own benefit. These results support the hypothesis that female-biased food provisioning arose from a difference between sexes in the allocation of foraging effort between parents and offspring, in anticipation of a prolonged period of male-only post-fledging care of the chick, and not from differences in foraging efficiency or time spent in nest defence.

The structure of a marine food web can change quickly within seasons as well as interannually in response to physical oceanographic changes. In this study, we examined the relationship between temporal changes in the marine ecosystem of northern Hokkaido, Japan, and diets of rhinoceros auklets Cerorhinca monocerata breeding in this region. To obtain an integrated measure of changes in diet composition on short (days) and inter-annual (2004 and 2005) time scales, we used a 2-pronged approach. We examined (1) the diets of adults using stomach contents and stable isotope signatures in tissues, and (2) chick diets using the composition of bill-loads delivered to chicks. During the incubation period, the diet of adults comprised euphausiids (Thysanoessa longipes and T inermis). During the chick-rearing period, the diet of adults was age 0 Japanese sandlance Ammodytes personatus and age 0 Japan Sea greenling Pleurogrammus azonus in the early period, but switched quickly (<10 d) to warm-water-preferring Japanese anchovy Engraulis japonicus when the warm Tsushima Current intruded into their foraging range. Adult blood plasma stable isotope ratios reflected these seasonal changes in stomach content. Diets did not differ between age categories. Furthermore, the timing of diet switching to anchovy differed inter-annually, and was about 10 d later in 2005 than 2004, reflecting a difference in the timing of the intrusion of warm water. We conclude that rhinoceros auklets respond sensitively to current-related rapid marine food web changes.

Predator-prey relationships are key to understanding complex marine ecosystem dynamics. The match-mismatch hypothesis posits that predators time energy-intensive activities, such as reproduction, to periods of high food availability. However, predators may be constrained by various ecological or physiological processes, leading to mistimed activities relative to prey availability. We investigated inter-annual variation in the timing of breeding for a piscivorous seabird (rhinoceros auklet Cerorhinca monocerata) in relation to availability of a preferred prey item, Japanese anchovy Engraulis japonicus, using data collected over 18 yr between 1984 and 2006 at Teuri Island in the northern Japan Sea. Our primary goals were (1) to identify the climatic factors that affect the seabirds' timing of breeding, proxied by hatching date, and anchovy seasonal availability, and (2) to quantify the fitness effects of predator-prey matches and mismatches relative to climate variability. Hatching date was later in years with lower spring air temperatures. Auklets switched their feeding from sandlance and juvenile greenling to anchovy when it was transported into the birds' foraging range with the seasonal northern expansion of 13 degrees C warm water from the south. The mismatch between hatching date and the period of high anchovy availability was most pronounced when spring air temperatures were warm, and there was a weak Tsushima (warm) Current. Spring air temperature was influenced by spring atmospheric pressure gradients in the Arctic and northern Eurasia, which drive the east Asian winter monsoon, whereas timing of the Tsushima warm water expansion was influenced by winter surface pressures over the western North Pacific. Chick growth rates, mass at fledging, and overall fledging success (fitness) were lower during mismatch years when the auklets fed less on anchovy. The auklets were constrained to adjust hatching date because the seasonal mismatch appeared to be driven by inde

An ethogram is a catalogue of discrete behaviors typically employed by a species. Traditionally animal behavior has been recorded by observing study individuals directly. However, this approach is difficult, often impossible, in the case of behaviors which occur in remote areas and/or at great depth or altitude. The recent development of increasingly sophisticated, animal-borne data loggers, has started to overcome this problem. Accelerometers are particularly useful in this respect because they can record the dynamic motion of a body in e.g. flight, walking, or swimming. However, classifying behavior using body acceleration characteristics typically requires prior knowledge of the behavior of free-ranging animals. Here, we demonstrate an automated procedure to categorize behavior from body acceleration, together with the release of a user-friendly computer application, "Ethographer". We evaluated its performance using longitudinal acceleration data collected from a foot-propelled diving seabird, the European shag, Phalacrocorax aristotelis. The time series data were converted into a spectrum by continuous wavelet transformation. Then, each second of the spectrum was categorized into one of 20 behavior groups by unsupervised cluster analysis, using k-means methods. The typical behaviors extracted were characterized by the periodicities of body acceleration. Each categorized behavior was assumed to correspond to when the bird was on land, in flight, on the sea surface, diving and so on. The behaviors classified by the procedures accorded well with those independently defined from depth profiles. Because our approach is performed by unsupervised computation of the data, it has the potential to detect previously unknown types of behavior and unknown sequences of some behaviors.

Plastics debris in the marine environment, including resin pellets, fragments and microscopic plastic fragments, contain organic contaminants, including polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons, petroleum hydrocarbons, organochlorine pesticides (2,2′-bis(p-chlorophenyl)-1,1,1-trichloroethane, hexachlorinated hexanes), polybrominated diphenylethers, alkylphenols and bisphenol A, at concentrations from sub ng g–1 to µg g–1. Some of these compounds are added during plastics manufacture, while others adsorb from the surrounding seawater. Concentrations of hydrophobic contaminants adsorbed on plastics showed distinct spatial variations reflecting global pollution patterns. Model calculations and experimental observations consistently show that polyethylene accumulates more organic contaminants than other plastics such as polypropylene and polyvinyl chloride. Both a mathematical model using equilibrium partitioning and experimental data have demonstrated the transfer of contaminants from plastic to organisms. A feeding experiment indicated that PCBs could transfer from contaminated plastics to streaked shearwater chicks. Plasticizers, other plastics additives and constitutional monomers also present potential threats in terrestrial environments because they can leach from waste disposal sites into groundwater and/or surface waters. Leaching and degradation of plasticizers and polymers are complex phenomena dependent on environmental conditions in the landfill and the chemical properties of each additive. Bisphenol A concentrations in leachates from municipal waste disposal sites in tropical Asia ranged from sub µg l–1 to mg l–1 and were correlated with the level of economic development.

We tested the hypothesis of synchronous interannual changes in forage fish dynamics around the North Pacific Rim. To do this, we sampled forage fish communities using a seabird predator, the rhinoceros anklet (Cerorhinca monocerata), at six coastal study sites from Japan to California. We investigated whether take of forage fishes was related to local marine conditions as indexed by sea surface temperature (SST). SST was concordant across sites in the eastern Pacific, but inversely correlated between east and west. Forage fish Communities consisted of anchovy (Engraulis spp.), sandlance (Ammodytes spp.), capelin (Mallotus spp.). and juvenile rockfish (Sebastes spp.), among others, and take of forage fish varied in response to interannual and possibly lower-frequency oceanographic variability. Take of primary forage species were significantly related to changes in SST only at the eastern sites. We found synchrony in interannual variation of primary forage fishes across several regions in the eastern Pacific, but no significant east-west correlations. Specifically in the Japan Sea, factors other than local SST or interannual variability may more strongly influence forage fishes. Predator diet sampling offers a fishery-independent. large-scale perspective on forage fish dynamics that may be difficult to obtain using conventional means of study., Nous testons l'hypothèse qui veut qu'il y ait des changements interannuels synchrones dans les dynamiques des poissons fourrage autour de la bordure du Pacifique Nord. C'est pourquoi nous avons échantillonné les peuplements de poissons fourrage à l'aide d'un oiseau marin prédateur, le macareux rhinocéros (Cerorhinca monocerata), à six sites d'étude côtiers du Japon à la Californie. Nous avons vérifié si les captures de poissons fourrage sont reliées aux conditions marines locales, telles que représentées par la température de surface de la mer (SST). Les SST s'accordent d'un site à l'autre dans l'est du Pacifique, mais il y a une corrélation inverse entre l'est et l'ouest. Les peuplements de poissons fourrage consistent, entre autres, d'anchois (Engraulis spp.), de lançons (Ammodytes spp.), de capelans (Mallotus spp.) et de jeunes sébastes (Sebastes spp.) et la capture de poissons fourrage varie en réaction à la variabilité océanographique interannuelle ou aussi peut-être de fréquence moins élevée. La capture de poissons fourrage principaux est en corrélation significative avec SST seulement dans les sites de l'est. Nous observons un synchronisme dans la variation interannuelle des poissons fourrage principaux entre plusieurs régions de l'est du Pacifique, mais aucune corrélation significative entre l'est et l'ouest. Tout particulièrement dans la mer du Japon, des facteurs autres que la SST locale et la variabilité interannuelle peuvent influencer plus fortement les poissons fourrage. L'échantillonnage du régime alimentaire des prédateurs permet d'obtenir, indépendamment de la pêche commerciale, une perspective à grande échelle de la dynamique des poisons fourrage qu'il serait peut-être difficile d'acquérir par les méthodes d'étude conventionnelles.

We used miniature light-level/immersion loggers (geolocators) to study the movements and behavior of two Streaked Shearwaters (Calonectris leucomelas) during their travel away from Japan, after the breeding season. During the period from late October until late December, the tracked shearwaters moved south over subtropical pelagic waters,with low productivity. The birds traveled to the seas off northern New Guinea and the Gulf of Carpentaria, Australia, 3400-5200 km distant from Mikura Island, their breeding colony in Japan. During the wintering period (December-February), the birds were on the sea surface for 77-85% of their time on average. The migratory and wintering behavior of Streaked Shearwaters are discussed in relation to the physical and biological marine environment of the north-western Pacific.

Studies of the fine-scale use of foraging habitat are essential for understanding the role of seabirds in marine ecosystems. However, until recently, relationships between foraging and habitat usage were only possible at a coarse scale. We used miniaturized bird-borne digital still-picture camera loggers to obtain high-quality images of the foraging habitat used by 9 European shags Phalacrocorax aristotelis. Underwater images revealed that shags are almost exclusively benthic feeders, but used 2 very distinct foraging habitats: sandy areas and rocky areas with brittlestars, soft corals and kelp. We found no evidence that individuals specialize on a particular habitat. Birds were recorded in rocky and sandy areas over the course of a day and in some cases within a trip. Foraging behaviour differed markedly between habitats. In rocky areas birds foraged solitarily, over a wide range of depths (10 to 40 m) and travelled along the bottom while searching for bottom-living fish such as butterfish Pholis gunnellus. In contrast, shags using sandy habitat frequently fed with conspecifics, foraged mainly at 2 depths (24 or 32 m) and spent the bottom phase of the dive probing into the sand with their bill, presumably to catch lesser sandeels Ammodytes marinus, the major prey item in the diet. This study highlights the flexible foraging strategy of European shags and illustrates how image and dive data can be combined to improve our understanding of the factors influencing the foraging success of benthic feeders.

To understand the foraging strategies of free-ranging diving animals time series information on both foraging effort and foraging success is essential. Theory suggests that wing stroke frequency for aerial flight should be higher in heavier birds. Based on this premise we developed a new methodology using animal-borne accelerometers to estimate fine scale temporal changes in body mass of a pursuit-diving, piscivorous seabird, the European shag Phalacrocorax aristotelis. We hypothesized that variations in body mass determined from changes in wing stroke frequency before and after a series of dives would be related to the amount of prey captured. The estimated net gain in body mass during a foraging trip was highly variable, ranging from -30 to 260 g, values that were extremely similar to food loads obtained from shags on the Isle of May in previous years using water-offloading and nest balances. Load sizes estimated using the wing stroke method were strongly and positively related to both cumulative flight time and return flight time. At the trip level load size was unrelated to cumulative dive bout duration and the total amount of time spent underwater. However, highly significant relationships were apparent at the individual bout level with birds showing bigger mass gains following longer dive bouts. Results from this study are therefore extremely encouraging and suggest that changes in body mass determined from changes in wing stroke frequency provide a reliable method of obtaining short to medium term information on foraging effort and success of diving seabirds.

International Symposium, "The Origin and Evolution of Natural Diversity". 1–5 October 2007. Sapporo, Japan., Leach's Storm-Petrels Oceanodroma leucorhoa (LSTP) represent one of the smallest seabirds that feed on small micronektons available only in the surface of the sea. Therefore, they may be sensitive to the change of prey abundance. Daikoku Island (42°52'N, 144°52'E) located in the coast of eastern Hokkaido is known as one of their largest colonies. Samples of diet of LSTPs on the island were collected to examine interannual differences in diet and an at sea census of these birds was conducted in waters adjacent to the island to extract information on feeding habitats. Results of analysis reveal that LSTPs fed mainly on fish, krill, amphipods and squids. Because the change in marine ecosystem derived from 1988/89 climatic regime shift, LSPTs fed on a similar range of prey items throughout the shift. This indicates to high ability of LSTPs to search and forage a range of prey items. But lower diversity of food items in 1995 and 2003 than in 1982 and 1986 points to the potential effects of the 1988/89 climatic regime shift on the variability of prey in LSTPs. Density of LSTPs on the sea surface was significantly greater in slope (200-1000m depth) and basin (> 1,000m depth) compared to the shelf (< 200m depth). Productive and predictable upward water transportation in the slope area observed in this study probably supports the energy requirements of large number of LSTPs breeding on Daikoku Island.

© 2007 Author et al. This is an EXiS Open Choice article distributed under the terms of the Creative Commons license version 2.5. The definitive version was published in Proceedings of the Royal Society B: Biological Sciences 274 (2007): 471-477, doi:10.1098/rspb.2006.0005., 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 0.5kg seabirds to 30000kg sperm whales using animal-borne accelerometers. Dominant stroke cycle frequencies of swimming specialist seabirds and marine mammals were proportional to mass−0.29 (R2=0.99, n=17 groups), while propulsive swimming speeds of 1–2ms−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., This work was funded by grants from the Japan Society for the Promotion of Science (A15255003, B1164062, C15570012, C12660157, C17580175), Ocean Research Institute, Iwate Prefecture, COE program (Neo-Science of Natural History led by H. Okada), Program for Promotion of Basic Research Activities for Innovative Biosciences and National Science Foundation (02229638). Y.W. and Y.M. are JSPS Research Fellows. P.J.O.M. was supported by a Royal Society fellowship and a grant for visiting professor of International Coastal Research Centre, Ocean Research Institute, The University of Tokyo.

The first underwater digital photographs obtained by cameras carried by Shags PhaJacrocorax aristoteJis showed the birds diving in areas dominated by soft coral Alcyonium digitatum and feeding on butterfish PhoJis gunnel/us, which were brought to the surface before being swallowed. Prey capture rates were markedly lower than previous estimates for birds feeding on sandeels Ammodytes.This reduced foraging performance probably contributed to the very poor breeding success at the colony on the Isle of May in 2005.

In diving birds, the volume and resulting buoyancy of air spaces changes with dive depth, and hydrodynamic drag varies with swim speed. These factors are important in the dive patterns and locomotion of alcids that use their wings both for aerial flight and underwater swimming and of penguins that use their wings only for swimming. Using small data-loggers on free-ranging birds diving to 20–30 m depth, we measured depth at 1 Hz and surge and heave accelerations at 32–64 Hz of four species of alcids (0.6–1.0 kg mass) and the smallest penguin species (1.2 kg). Low- and high-frequency components of the fluctuation of acceleration yielded estimates of body angles and stroke frequencies, respectively. Swim speed was estimated from body angle and rate of depth change. Brünnich's (Uria lomvia) and common (Uria aalge) guillemots descended almost vertically, whereas descent of razorbills (Alca torda), rhinoceros auklets (Cerorhinca monocerata) and little penguins (Eudyptula minor) was more oblique. For all species, swim speed during descent was within a relatively narrow range. Above depths of 20–30 m, where they were all positively buoyant, all species ascended without wing stroking. During descent, little penguins made forward accelerations on both the upstroke and downstroke regardless of dive depth. By contrast, descending alcids produced forward accelerations on both upstroke and downstroke at depths of <10 m but mainly on the downstroke at greater depths; this change seemed to correspond to the decrease of buoyancy with increasing depth. The magnitude of surge (forward) acceleration during downstrokes was smaller, and that during upstrokes greater, in little penguins than in alcids. This pattern presumably reflected the proportionally greater mass of upstroke muscles in penguins compared with alcids and may allow little penguins to swim at less variable instantaneous speeds.