DIVING PATTERNS OF NORTHERN ELEPHANT SEAL BULLS

We used small microprocessor-based, time-depth recorders to document the diving patterns of six adult male northern elephant seals ( Mirounga angustirostris ) from San Miguel Island, California. The recorders stored measurements of hydrostatic pressure every 30 or 60 set while the seals were at sea for 107 to 145 d in spring and early summer; collectively, over 36,000 dives were recorded. Seals dove continually while at sea, most often to depths of 350–450 m although two seals had secondary modes at about 700–800 m; maximum depths for two seals of 1,333 m and 1,529 m are the deepest yet measured for air-breathing vertebrates. Seals were submerged about 86% of the time they were at sea, rarely spending more than 5 min at the surface between dives; 99% of all post-dive surface intervals were shorter than 10 min. Dives averaged 21–24 min, the longest was 77 min. The uninterrupted patterns of long dives punctuated by brief surface periods suggest that most if not all dives were well within these seals'aerobic limits. Dives of bulls were, on average, about 18% longer than those published earlier for cows, evidently because of the substantially greater body mass of bulls and allometric scaling of dive endurance. Dive depths and dive durations varied seasonally; depths were greatest in spring, durations greatest in early summer. During each season dives were deepest during the day and shallowest at night except for the sixth seal whose consistently shallow dives (50–150 m) in spring were independent of time of day. Prey remains recovered by lavage from seals'stomachs were primarily of vertically migrating, epi- and meso-pelagic squid. The die1 patterns in dive depths suggest that five seals dove to and foraged in the offshore mesopelagic zone, pursuing those vertically migrating prey. The sixth seal behaved similarly in early spring and early summer but may have foraged in nearshore epibenthic habitats in spring.     

Foraging behavior and prey of sea otters in a soft- and mixed-sediment benthos in Alaska

Sea otter (Enhydra lutris kenyoni) foraging behavior and prey preference were studied from June to August 2001–2004 in Simpson Bay, Prince William Sound, Alaska. The study area has an average water depth of 30 m and a benthos primarily of soft- and mixed-sediment with no canopy-forming kelps. A total of 1816 foraging dives from 211 bouts were recorded. Overall, dives ranged in depth from <5 to 82 m; most dives were less than 15 m (40%) with smaller, secondary peaks at 25–30 m (10%) and 50–55 m (7%). Average dive depth and duration were 27 m ± 19.5 and 1.89 min ± 0.88, respectively. Dive durations were all significantly different: male > unknown > female. Dive depths reflected the bathymetry (percentage of the bay within a depth range) of Simpson Bay but favored shallow areas. 87% of foraging dives were successful, and 44% of the prey was positively identified: 75% clams, 9% Pacific blue mussels, 6% crabs, 2% Reddish scallops and a variety of other invertebrates. There was no evidence for prey specialization among the sexes. Although sea otters in Simpson Bay rely heavily on bivalves, their diet has remained unchanged for the past 18 years, and the minimum summer population has been constant for at least the past nine years. It appears that bivalves are the predominant and stable component of the diet, and their productivity is sufficient to sustain a stable population of sea otters with a minimum peak summer density of 4.3 adult otters km^?2 and an average annual density of ca. 2.9 adult otters km^?2 for the past nine years and probably longer.     

A lifetime at depth: vertical distribution of southern elephant seals in the water column

Although numerous studies have addressed the migration and dive behaviour of southern elephant seals (Mirounga leonina), questions remain about their habitat use in the marine environment. We report on the vertical use of the water column in the species and the potential lifetime implications for southern elephant seals from Marion Island. Long-term mark-resight data were used to complement vertical habitat use for 35 known individuals tagged with satellite-relay data loggers, resulting in cumulative depth use extrapolated for each individual over its estimated lifespan. Seals spent on average 77.59% of their lives diving at sea, 7.06% at the sea surface, and 15.35% hauled out on land. Some segregation was observed in maximum dive depths and depth use between male and female animals—males evidently being physiologically more capable of exploiting increased depths. Females and males spent 86.98 and 80.89% of their lives at sea, respectively. While at sea, all animals spent more time between 300 and 400 m depth, than any other depth category. Males and females spent comparable percentages of their lifetimes below 100 m depth (males: 65.54%; females: 68.92%), though males spent 8.98% of their lives at depths in excess of 700 m, compared to females’ 1.84% at such depths. Adult males often performed benthic dives in excess of 2,000 m, including the deepest known recorded dive of any air-breathing vertebrate (>2,133 m). Our results provide a close approximation of vertical habitat use by southern elephant seals, extrapolated over their lifespans, and we discuss some physiological and developmental implications of their variable depth use.     

Sex‐specific food provisioning in a monomorphic seabird,the common guillemot Uria aalge: nest defence,foraging efficiency or parental effort?

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.     

Size and experience matter: diving behaviour of juvenile New Zealand sea lions (Phocarctos hookeri)

The diving ability of juvenile animals is constrained by their physiology, morphology and lack of experience, compared to adults. We studied the influences of age and mass on the diving behaviour of juvenile (2–3-year-old females, n = 12; 3–5-year-old males, n = 7) New Zealand (NZ) sea lions (Phocarctos hookeri) using time–depth recorders (TDRs) from 2008 to 2010 in the NZ subantarctic Auckland Islands. Diving ability (e.g. dive depth, duration and bottom time per dive) improved with age and mass. However, the percentage of each dive spent at the bottom, along with percentage time at sea spent diving, was comparable between younger and lighter juveniles and older and heavier juveniles. These suggest that younger and older juveniles expend similar foraging effort in terms of the amount of time spent underwater. Only, 5-year-old male juveniles dove to adult female depths and durations and had the highest foraging efficiency at depths >250 m. It appears that juvenile NZ sea lions attain adult female diving ability at around 5 years of age (at least in males), but prior to this, their performance is limited. Overall, the restricted diving capabilities of juvenile NZ sea lions may limit their available foraging habitat and ability to acquire food at deeper depths. The lower diving ability of juvenile NZ sea lions compared to adults, along with juvenile-specific constraints, should be taken into consideration for the effective management of this declining, nationally critical species.     

Individual Foraging Strategies Reveal Niche Overlap between Endangered Galapagos Pinnipeds

Most competition studies between species are conducted from a population-level approach. Few studies have examined inter-specific competition in conjunction with intra-specific competition, with an individual-based approach. To our knowledge, none has been conducted on marine top predators. Sympatric Galapagos fur seals (Arctocephalus galapagoensis) and sea lions (Zalophus wollebaeki) share similar geographic habitats and potentially compete. We studied their foraging niche overlap at Cabo Douglas, Fernandina Island from simultaneously collected dive and movement data to examine spatial and temporal inter- and intra-specific competition. Sea lions exhibited 3 foraging strategies (shallow, intermediate and deep) indicating intra-specific competition. Fur seals exhibited one foraging strategy, diving predominantly at night, between 0–80 m depth and mostly at 19–22 h. Most sea lion dives also occurred at night (63%), between 0–40 m, within fur seals'' diving depth range. 34% of sea lions night dives occurred at 19–22 h, when fur seals dived the most, but most of them occurred at dawn and dusk, when fur seals exhibited the least amount of dives. Fur seals and sea lions foraging behavior overlapped at 19 and 21 h between 0–30 m depths. Sea lions from the deep diving strategy exhibited the greatest foraging overlap with fur seals, in time (19 h), depth during overlapping time (21–24 m), and foraging range (37.7%). Fur seals foraging range was larger. Cabo Douglas northwest coastal area, region of highest diving density, is a foraging “hot spot” for both species. Fur seals and sea lions foraging niche overlap occurred, but segregation also occurred; fur seals primarily dived at night, while sea lions exhibited night and day diving. Both species exploited depths and areas exclusive to their species. Niche breadth generally increases with environmental uncertainty and decreased productivity. Potential competition between these species could be greater during warmer periods when prey availability is reduced.     

Shallow food for deep divers: Dynamic foraging behavior of male sperm whales in a high latitude habitat

Groups of female and immature sperm whales live at low latitudes and show a stereotypical diving and foraging behavior with dives lasting about 45 min to depths of between 400 and 1200 m. In comparison, physically mature male sperm whales migrate to high latitudes where little is known about their foraging behavior and ecology. Here we use acoustic recording tags to study the diving and acoustic behavior of male sperm whales foraging off northern Norway. Sixty-five hours of tag data provide detailed information about the movements and sound repertoire of four male sperm whales performing 83 dives lasting between 6 and 60 min. Dives ranged in depth between 14 and 1860 m, with a median depth of 175 m, and 92% of the surfacings lasted less than 15 min. The four whales clicked for an average 91% (SD = 10) of the dive duration, where the first usual click was produced at depths ranging between 4 and 218 m and the last usual click at depths ranging between 1 and 1114 m. Echolocation buzzes, which are used as an indication of prey capture attempts, were emitted at depths between 17 and 1860 m, during both the descent and ascent phase of deep dives. The foraging behavior varied markedly with depth, with the timing and duration of prey capture attempts during shallow dives suggesting that the whales target more sparsely distributed prey. In contrast, deep dives involve frequent prey capture attempts and seem to target more dense food layers. The evidence of exploitation of different food layers, including epipelagic prey, is consistent with the hypothesis that male sperm whales may migrate to high latitudes to access a productive, multi-layered foraging habitat.     

Movements and diving of grey seal females (Halichoerus grypus) in the Gulf of St. Lawrence, Canada

Five female grey seals were tracked with satellite-linked time-depth recorders during September to April 1993-1994. Seals remained in the northern Gulf of St. Lawrence (Gulf) for 1-2.5 months after capture. Four females dove primarily to depths <10 m and 20-70 m, while all dives of the fifth female, a blind animal, were <10 m. During October/November, all animals moved into the southern Gulf or onto the Scotian Shelf. This migration lasted 6-10 days, during which time animals covered 350-800 km. During that migration, all females, including the blind animal, dove up to 100 m, but the majority of dives were to depths of 40-70 m. Two seals stayed in the southern Gulf through the winter while the others left the Gulf in January. When in the southern Gulf and on the Scotian Shelf, dive depths and bathymetry information indicated that dives were to the bottom.     

DIVING BEHAVIOR OF THE PACIFIC HARBOR SEAL (PHOCA VITULINA RICHARDII) IN MONTEREY BAY, CALIFORNIA

Physical environment and physiological characteristics of marine mammals potentially affect the duration and depth of diving. Härkönen (1987b) proposed a hypothesis that the harbor seal would gain maximum energy by foraging at intermediate depths. To investigate this hypothesis, we studied diving behavior of the Pacific harbor seal (Phoca vitulina ricbardii) during 1995 through 1997 in Monterey Bay, California. Dive depths (n = 13,063 dives) were recorded via time‐depth recorders. Approximately 80% of recorded dives were classified as square dives (type I), which typically were associated with foraging in pinnipeds. Approximately 11% of dives were V dives (type II; 1,402 dives), and the remainder (1,225 dives) were skewed dives (type III and IV). The deepest recorded dive was 481 m, while the greatest duration was 35.25 min. Body mass explained the variability of durations of long dives for females (95th percentile; D₉₅♂=‐5.47 + 0.18 × (mass♀), r²= 0.91, 95% CI for slope = [0.08, 0.28], n= 5) and for males (D₉₅♂=‐5.86 + 0.18 × (mass♀), r²= 0.83, 95% CI for slope = [0.12, 0.24], n= 11). The large proportion of variability in deep dives, however, was explained by body mass only for males (95th percentile; Z₉₅♂=‐363.9 + 6.05 × (mass♀), r²= 0.83, 95% CI for slope = [3.93, 8.17], n= 11) and not for females (Z₉₅,♂=?148.1 +3.11 × (mass♀), r²= 0.58, 95% CI for slope = [‐1.7, 7.9], n= 5, 95% CI for slope= [?1.7, 7.9]). Median depths of presumed foraging dives of harbor seals in the Monterey Bay area were between 5 and 100 m, which were within the range of the previously reported depths for other areas (< 100 m). Our findings generally supported Härkönen's hypothesis that harbor seals forage in the intermediate depth in their environment.     

Activity Time Budget during Foraging Trips of Emperor Penguins

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.     

SUCCESSFUL USE OF A TRANSLOCATION PROGRAM TO INVESTIGATE DIVING BEHAVIOR IN A MALE AUSTRALIAN FUR SEAL, ARCTOCEPHALUS PUSILLUS DORIFERUS

This study reports some of the first foraging behavior data collected for male fur seals. A nonbreeding male Australian fur seal, Arctocephalus pusillus doriferus , captured at a commercial salmon farm in southern Tasmania, Australia, was relocated 450 km from the site of capture. The animal was equipped with a geolocating time-depth recorder that recorded diving behavior and approximate location for the 14.4 d that it took the seal to travel down the east coast of Tasmania and be recaptured at the salmon farm. During its time at sea, the seal spent most of its time over the relatively shallow shelf waters. It spent 30% of its time ashore on a number of different haul-out sites. The deepest dive was 102 m and the maximum duration was 6.8 min. "Foraging" type dives made up 31.2% of the time at sea and had a median duration of 2.5 min and a median depth of 14 m. The seal performed these dives more commonly during the latter part of its time at sea, while it was on the east coast. Unlike other fur seal species studied to date, there was no evidence of a diurnal foraging pattern; it made dives at all times of the day and night.     

Women from Venus,men from Mars: inter‐sex foraging differences in the imperial cormorant Phalacrocorax atriceps a colonial seabird

Colonial seabirds are central place foragers and likely to be subject to substantial competition for resources. Mechanisms proposed for reducing intra‐specific competition include differential inter‐sex area use mediated by adult choice. We used GPS loggers and dive recorders to study area use and dive depth in a total of 27 male and 26 female imperial cormorants Phalacrocorax atriceps breeding at a colony of some 6500 birds at Punta Leon, Chubut, Argentina during 2004 and 2005. Although time spent travelling and distances between the colony and foraging sites were similar for both sexes, males and females travelled away from their colony using routes virtually perpendicular to each other so that their foraging areas were distinctly different; females hunted close to the coast while males foraged offshore in deeper water. Consideration of foraging efficiency underwater, defined as the duration spent on the bottom divided by the dive cycle duration, showed that females were more efficient at depths < 40 m while males more efficient at depths > 40 m. We suggest that the substantial sexual dimorphism in this species may be responsible for the different depth‐linked foraging efficiencies and that selection for appropriate depths could lead to differential habitat use and putative differences in prey selection.     

DIET AND FORAGING BEHAVIOR OF SEA OTTERS IN SOUTHEAST ALASKA

Abstract: Direct observations of feeding sea otters ( Enhydra lutris ) at 11 sites in southeast Alaska showed infaunal clams to be the primary prey utilized by otters throughout the region. Foraging dive times associated with clam and sea urchin prey were significantly longer than those for more easily captured prey (crabs and mussels). Dive times and surface intervals were also generally correlated with water depth or apparent difficulty in obtaining buried prey. Male otters, which fed more extensively on clams than females, made significantly longer foraging dives than females. Foraging success remained high, even at sites where prey numbers were found to be very low during a related study. The very deeply burrowing geoduck clam ( Panope abrupta ), while common at several otter feeding sites, was rarely captured by otters. These results, combined with those of a companion study on prey numbers, indicate that butter clams ( Saxidomus giganteus ) account for the majority of the sea otter diet in southeast Alaska, and that sea urchins may represent relatively short-term prey in comparison to infaunal bivalves in regions where both prey types co-exist. Furthermore, the importance of butter clams in the sea otter diet and the tendency for this bivalve to retain chronically high levels of paralytic shellfish poisoning toxins in southeast Alaska increases the probability that toxic phytoplankton blooms influence sea otter distribution in this region.     

Sociality in river otters: cooperative foraging or reproductive strategies?

We evaluated factors influencing social organization in coastalriver otters (Lontra canadensis) to test two hypotheses: groupformation is an antipredation strategy, or, alternatively,group information is related to cooperative foraging. Dataon group size, group composition, and sociality were obtainedthrough radiotracking 55 otters in Prince William Sound, Alaska, USA, from 1996 through 1998. For males, larger groups occurredafter the mating season and concurrent with availability ofschooling pelagic fishes. Stable isotope analysis revealedthat otters social in >10% of their locations had dietssignificantly higher in rapidly swimming pelagic fishes thandid less social otters, regardless of gender. In addition, ottersthat were more social had significantly smaller home rangesthan did less social otters, an observation consistent withincreased foraging efficiency through cooperative foraging.Discounting associations of females with young of the year,approximately 47% of females and only 24% of males were asocial.Among social otters, males were social in 46% of their locationsand 63% of that time occurred in all-male groups. Females wereonly social in 26% of locations and were in mixed-sex groups78% of that time. We hypothesize that the time-consuming taskof raising offspring prevents females from joining foraginggroups. When not raising young, females may join males to cooperativelyforage for better-quality prey (pelagic fishes), which wouldbe more difficult to acquire as a solitary forager.     

The influence of depth on a breath-hold diver: Predicting the diving metabolism of Steller sea lions (Eumetopias jubatus)

Diving animals must endeavor to increase their dive depths and prolong the time they spend exploiting resources at depth. Results from captive and wild studies suggest that many diving animals extend their foraging bouts by decreasing their metabolisms while submerged. We measured metabolic rates of Steller sea lions (Eumetopias jubatus) trained to dive to depth in the open ocean to investigate the relationships between diving behaviour and the energetic costs of diving. We also constructed a general linear model to predict the oxygen consumption of sea lions diving in the wild. The resultant model suggests that swimming distance and depth of dives significantly influence the oxygen consumption of diving Steller sea lions. The predictive power of the model was tested using a cross-validation approach, whereby models reconstructed using data from pairs of sea lions were found to accurately predict the oxygen consumption of the third diving animal. Predicted oxygen consumption during dives to depth ranged from 3.37 L min^− 1 at 10 m, to 1.40 L min^− 1 at 300 m over a standardized swimming distance of 600 m. This equated to an estimated metabolic rate of 97.54 and 40.52 MJ day^− 1, and an estimated daily feeding requirement of 18.92 and 7.96 kg day^− 1 for dives between 10 and 300 m, respectively. The model thereby provides information on the potential energetic consequences that alterations in foraging strategies due to changes in prey availability could have on wild populations of sea lions.     

Mate Guarding in Male Dall's Porpoises (Phocoenoides dalli)

Mate guarding, whereby a male closely attends and defends a fertile female from extra‐pair matings, is one mating tactic males of many species use to protect their paternity. Although female defense occurs in many species of terrestrial mammal, comparable examples among cetaceans are largely absent, potentially as a result of the wide dispersion and mobility of females and their prey. Here, we investigate whether the close association of individual male Dall's porpoises with individual females during the breeding season is consistent with mate guarding. As mate guarding is predicted to be costly, and in other taxa is often associated with a reduction in foraging efficiency, we also examine whether males trade‐off this activity with time at depth. Males maintained longer associations and closer distances with female partners than with male ones. They also surfaced in greater synchrony with, and more often approached, their female partners than male ones. In contrast to males with male partners, males paired with females engaged in agonistic interactions with other adult males, and infrequently affiliated with extra‐pair individuals. These data suggest males are actively attempting to maintain their associations with females, while also acting to reduce female extra‐pair copulations and increase their own paternity. Guarding males also undertook shorter dives than non‐guarding males, suggesting that they trade‐off time at depth with guarding. Such a trade‐off is likely to involve a reduction in foraging opportunities, due to a decrease in time spent at foraging depth. Mate guarding in this species may be facilitated by the relatively smaller size and decreased mobility of newly calved, estrous females, particularly if females also benefit from guarding.     

Complex Movements,Philopatry and Expanded Depth Range of a Severely Threatened Pelagic Shark,the Oceanic Whitetip (Carcharhinus longimanus) in the Western North Atlantic

Oceanic whitetip sharks (Carcharhinus longimanus) have recently been targeted for conservation in the western North Atlantic following severe declines in abundance. Pop-up satellite archival tags were applied to 11 mature oceanic whitetips (10 females, 1 male) near Cat Island in the central Bahamas 1–8 May 2011 to provide information about the horizontal and vertical movements of this species. Another large female was opportunistically tagged in the U.S. Exclusive Economic Zone (EEZ). Data from 1,563 total tracking days and 1,142,598 combined depth and temperature readings were obtained. Sharks tagged at Cat Island stayed within 500 km of the tagging site for ∼30 days before dispersing across 16,422 km² of the western North Atlantic. Maximum individual displacement from the tagging site ranged from 290–1940 km after times at liberty from 30–245 days, with individuals moving to several different destinations (the northern Lesser Antilles, the northern Bahamas, and north of the Windward Passage). Many sharks returned to The Bahamas after ∼150 days. Estimated residency times within The Bahamas EEZ, where longlining and commercial trade of sharks is illegal, were generally high (mean = 68.2% of time). Sharks spent 99.7% of their time shallower than 200 m and did not exhibit differences in day and night mean depths. There was a positive correlation between daily sea surface temperature and mean depth occupied, suggesting possible behavioral thermoregulation. All individuals made short duration (mean = 13.06 minutes) dives into the mesopelagic zone (down to 1082 m and 7.75°C), which occurred significantly more often at night. Ascent rates during these dives were significantly slower than descent rates, suggesting that these dives are for foraging. The sharks tracked appear to be most vulnerable to pelagic fishing gear deployed from 0–125 m depths, which they may encounter from June to October after leaving the protected waters of The Bahamas EEZ.     

Diving patterns of female macaroni penguins breeding on Marion Island, South Africa

Despite the large biomass of macaroni penguins Eudyptes chrysolophus in the Southern Ocean, their feeding ecology is poorly known at some important breeding localities. We investigated the diving behaviour and diet of female macaroni penguins feeding small chicks on Marion Island (46o52′S, 37o5′E), South Africa, one of the species’ most northerly breeding sites, supporting 4% of their global population. We then compared our results with similar studies from other localities. In December 2008, we collected information on 12 foraging trips from 6 individuals using time-depth recorders, as well as diet from 42 individuals. Median trip duration was 22.8 h (5.6–80.8 h). Penguins performed 42.8 ± 15.9 dives per hour at sea, with dive depths averaging 24.6 ± 8.6 m and lasting 40.8 ± 12.1 s, although 74.3% of dives were <10 m. Euphasids dominated their diet (86% by mass), mainly Thysanoessa vicina. A second peak in dive depths at 55–80 m might reflect the 12% of fish in their diet. The substantial proportion of shallow night dives (30% of total dives) suggests some foraging occurs at night. Differences in diving patterns of individual macaroni penguins in this study confirmed the behavioural flexibility of these birds reported from other breeding localities. However, most other studies assumed that dives <3–5 m were commuting dives whereas our study suggests that at least some prey are caught during shallow dives. We highlight how different analytical methods can change the outcome of studies. Despite macaroni penguins’ apparent flexibility in foraging behaviour during the breeding season, their numbers are decreasing globally. Further investigations of their foraging behaviour are needed to assess potential competition with other predators and krill fisheries.     

Respiratory frequency, dive behaviour and social interactions of leatherback turtles, Dermochelys coriacea during the inter-nesting interval

We collected simultaneous dive Time Depth Recorder (TDR) data and video images from free swimming adult female leatherback turtles, Dermochelys coriacea, during the first 24 h after nesting on the beach, in order to determine relationships between dive parameters, activity, overall respiratory frequency and behaviour.We identified three different underwater locomotory activities (subsurface swimming, V-shaped dives and U-shaped dives) from video and TDR data that varied in their mean depth, duration and a number of other parameters. Overall respiratory frequency (overall f_R) was significantly different between all locomotory activities, with turtles taking 1.7±0.1 breaths min⁻¹ while subsurface swimming, 0.78 breaths min⁻¹ after V-shaped dives and 0.57 breaths min⁻¹ after U-shaped dives. Descent rates and ascent rates were significantly faster in U-shaped dives (descent 0.19±0.010 m s⁻¹, ascent 0.28±0.015 m s⁻¹) than in V-shaped dives (descent 0.10±0.008 m s⁻¹, ascent 0.12±0.012 m s⁻¹). Flipper stroke rates were significantly lower during the bottom component of U-shaped dives (0.18±0.02 strokes s⁻¹) than during the descent (0.29±0.03 strokes s⁻¹) or ascent (0.29±0.03 strokes s⁻¹). From overall f_R and flipper stroke rate data, we inferred that turtles used less energy during U-shaped dives than the other activity types. We recorded interactions between male turtles and the study females that lasted up to 11 min, during which male turtles displayed the characteristic courtship behaviour of sea turtles. It appeared that females attempted to avoid males by aborting ascent and extending dive duration to swim to the sea floor when males were present.     

Patterns of energy acquisition by a central place forager: benefits of alternating short and long foraging trips

In some seabirds, foraging trips have been defined as eitherlong or short, with the length of time spent traveling to theforaging area apparently a critical feature in determining foragingtrip length. Using logger technology, together with complimentarydata from published studies, we investigated traveling and foragingtimes in 18 free-living Adélie Penguins Pygoscelis adeliae,which were foraging for chicks. Most deep, foraging dives weredistributed around the center of the foraging trip. This centraltendency was particularly apparent if the cumulative amountof undulations in the depth profile (indicative of prey capture)was considered during deep dives; values started to increasebefore 20.9% and ceased after 67.2% of the dives had occurred.This concentration of the feeding activity in the middle ofthe foraging trip indicates that birds traveled to and froma prey patch whose location varied little over the birds' trips.These data form the basis for a simple model that uses travelingand foraging times together with projected rates of prey ingestionand chick and adult gastric emptying to determine that thereare occasions when, to optimize rates of prey ingestion whileat sea for both adults and chicks, birds should conduct foragingtrips of bimodal lengths.