Dive Bouts Research Articles

From route to dive: multi-scale habitat selection in a foraging tropical seabird

Comprehending how environmental variability shapes foraging behaviour across habitats is key to unlocking insights into consumer ecology. Seabirds breeding at high latitudes are exemplars of how marine consumers can adapt their behaviours to make use of predictable foraging opportunities, but prey tends to be less predictable in tropical oceanic ecosystems and may require alternative foraging behaviours. Here we used GPS and time-depth recorder loggers to investigate the foraging behaviour of central placed adult red-footed boobies (Sula sula rubripes), a tropical seabird that forages in oceanic waters via diving, or by capturing aerial prey such as flying fish in flight. Dive bout dynamics revealed that red-footed boobies appeared to exploit denser, but more sparsely distributed prey patches when diving further from the colony. Furthermore, although we found no evidence of environmentally driven habitat selection along their foraging routes, red-footed boobies preferentially dived in areas with higher sea surface temperatures and chlorophyll-a concentrations compared to conditions along their foraging tracks. This multi-scale variation implies that habitat selection differs between foraging routes compared to dive locations. Finally, red-footed booby dives were deepest during the middle of the day when light penetration was greatest. Ultimately, we highlight the importance of gaining insights into consumer foraging across different ecosystems, thereby broadening understanding of how animals might respond to changing environmental conditions.

Influence of sea ice concentration, sex and chick age on foraging flexibility and success in an Arctic seabird.

Declining sea ice and increased variability in sea ice dynamics are altering Arctic marine food webs. Changes in sea ice dynamics and prey availability are likely to impact pagophilic (ice-dependent and ice-associated) species, such as thick-billed murres (Uria lomvia), through changes in foraging behaviour and foraging success. At the same time, extrinsic factors, such as chick demand, and intrinsic factors, such as sex, are also likely to influence foraging behaviour and foraging success of adult murres. Here, we use 3 years of data (2017-2019) to examine the impacts of environmental conditions (sea ice concentration and sea surface temperature), sex and chick age (as a proxy for chick demand) on foraging and diving behaviour (measured via biologgers), energy expenditure (estimated from activity budgets) and foraging success (measured via nutritional biomarkers) of thick-billed murres during the incubation and chick-rearing stages at Coats Island, Nunavut. Murres only exhibited foraging flexibility to environmental conditions during incubation, which is also the only stage when ice was present. When more ice was present, foraging effort increased, murres foraged farther and made deeper dives, where murres making deeper dives had higher foraging success (greater relative change in mass). During incubation, murre behaviour was also influenced by sex of the individual, where males made more and shorter trips and more dives. During chick-rearing, murre behaviour was influenced primarily by the sex of the individual and chick age. Males made shallower dives and fewer dive bouts per day, and more dives. Birds made longer, deeper dives as chicks aged, likely representing increased intra-specific competition for prey throughout the season. Our results suggest variation in sea ice concentration does impact foraging success of murres; however, sex-specific foraging strategies may help buffer colony breeding success from variability in sea ice concentration.

Foraging habitat and site selection do not affect feeding rates in European shags.

During feeding trips, central-place foragers make decisions on whether to feed at a single site, move to other sites and/or exploit different habitats. However, for many marine species, the lack of fine-resolution data on foraging behaviour and success has hampered our ability to test whether individuals follow predictions of the optimal foraging hypothesis. Here, we tested how benthic foraging habitat usage, time spent at feeding sites and probability of change of feeding sites affected feeding rates in European shags (Gulosus aristotelis) using time-depth-acceleration data loggers in 24 chick-rearing males. Foraging habitat (rocky or sandy) was identified from characteristic differences in dive patterns and body angle. Increase in body mass was estimated from changes in wing stroke frequency during flights. Bout feeding rate (increase in body mass per unit time of dive bout) did not differ between rocky and sandy habitats, or in relation to the order of dive bouts during trips. Bout feeding rates did not affect the duration of flight to the next feeding site or whether the bird switched habitat. However, the likelihood of a change in habitat increased with the number of dive bouts within a trip. Our findings that shags did not actively move further or switch habitats after they fed at sites of lower quality are in contrast to the predictions of optimal foraging theory. Instead, it would appear that birds feed probabilistically in habitats where prey capture rates vary as a result of differences in prey density and conspecific competition or facilitation.

Temporal non‐independence of foraging dive and surface duration sequences in the European shag Gulosus aristotelis

AbstractStudies of foraging behaviour and respiratory physiology in breath‐holding divers often assume that each dive cycle (dive plus surface duration) is physiologically and ecologically independent within a series (or “bout”) of sequential dives. We tested this assumption using time depth recorders and GPS data for more than 42,000 dives in 1289 bouts by 39 pairs of male and female European shags (Gulosus aristotelis) provisioning nestlings. We found distinct patterns of temporal autocorrelation over several dives within bouts, but this was driven mainly by consecutive dives of the same type, that is, runs of V‐shaped (presumably prey searching) versus U‐shaped (presumably active hunting) dives. We found no evidence of cumulative physiological effects (i.e. fatigue and/or lowered body temperature) across dives within a bout. However, within‐individual variation in dive behaviour revealed complex interactions. Longer bouts were associated with more V‐shaped dives, including more and longer runs of V‐shaped dives. Meanwhile, more U‐shaped dives and longer runs of U‐shaped dives acted as limiting factors to bout lengths, with longer bouts being associated with more U‐shaped dives only later in the bout. Interactions between bout length and body mass, and between dive order within the bout and body mass, also suggested various size‐specific patterns in the temporal distribution of U‐shaped dives. Long bouts and bouts ending in longer runs of V‐shaped dives were more likely to indicate the termination of foraging activity. However, neither dive type nor bout length predicted whether individuals subsequently (i) stayed to forage in the same location or (ii) moved to a new location to continue foraging within the same trip from the nest. European shags therefore showed temporal non‐independence across successive dive cycles and successive bouts of dives, likely as a result of temporal and spatial variation in prey availabilities rather than cumulative physiological effects that might contravene the assumptions in models of optimal dive behaviour.

No rest for the weary: restricted resting behaviour of green turtles (Chelonia mydas) at a deep-neritic foraging area influences expression of life history traits

ABSTRACT For breath-holding marine animals, tradeoffs between ‘active’ and resting behaviours during periods of submergence can have consequences for acquisition and allocation of energy to vital life history requirements. In this study, we fitted 18 green turtles (Chelonia mydas) with detachable time-depth recorder (TDR) systems to obtain and analyse fine-scale dive behaviour and daily activity – with a focus on resting dive bouts – at Bahía de los Angeles (BLA), a warm-temperate foraging area in the Gulf of California, México. Our results showed that resting bout durations increased with water depths among all turtles, but patterns of resting bout durations and depths varied widely among individuals. To evaluate potential consequences to green turtles of tradeoffs between time spent ‘active’ versus resting, we also compared behavioural parameters (e.g. time spent resting, home range sizes) and life history traits (e.g. growth rates, body size at maturity) of green turtle populations from around the world, including BLA. We found that BLA green turtles spend less time resting, spend more time actively swimming and diving, occupy larger home ranges, and exhibit slower growth rates and smaller adult body sizes compared to their counterparts in other parts of the world. Unique characteristics of the BLA foraging habitat (e.g. patchy resources and temperature extremes) appear to require increased diel movements and foraging activity and decreased resting opportunities. These interactions between habitat and turtle behaviour not only influence expression of life history traits, but can also increase turtles’ exposure to human activities (e.g. vessel traffic and fisheries bycatch) as they move throughout the area.

Behavioural adjustments during foraging in two diving seabirds: king and macaroni penguins

Optimal foraging theory predicts that diving predators should maximise their energy intake while minimizing the costs of their foraging activities at depth. This hypothesis was tested in two breath-hold divers that foraged in the pelagic waters off Kerguelen Island, southern Indian Ocean. Macaroni penguins (Eudyptes chrysolophus) feed predominately on crustaceans at moderate depths (ca. 50 m), while king penguins (Aptenodytes patagonicus) feed on mesopelagic fish at deep depths (ca. 100-150 m). We instrumented 22 penguins with time-depth recorders during the breeding season of the 2014 southern summer, just before they went to sea. Birds were recaptured after one to five foraging trips and the dive data were analysed on the level of single dive cycles and entire dive bouts. Both species adjusted their diving behaviour and modulated their foraging activity in accordance with their experience in their previous dives. Foraging activity during a dive (in terms of number of wiggles per dive) was greater if birds targeted the same depth as the previous dive. The penguins spent less time at the surface between two prey capture attempt dives than when a prey capture attempt dive was preceded by a non-prey capture attempt dive. Dive bout analyses showed that foraging activity increased with bout duration, while transit time during dives decreased with bout duration. Our findings are in general agreement with predictions based on optimal foraging models. The results suggest that penguins anticipated the depth of their next dive based on their encounter of a prey patch in the previous dive and optimized their chances of feeding success by spending minimal time at the surface and in transit to the patch depth. Once penguins detected a prey patch, these behavioural adjustments allowed them to rapidly return to that patch, increasing their chances of feeding again before the prey disperses.

Social context and prey composition are associated with calling behaviour in a diving seabird

Social cohesion and prey location in seabirds are largely enabled through visual and olfactory signals, but these behavioural aspects could potentially also be enhanced through acoustic transfer of information. Should this be the case, calling behaviour could be influenced by different social–ecological stimuli. African Penguins Spheniscus demersus were equipped with animal‐borne video recorders to determine whether the frequency and types of calls emitted at sea were dependent on behavioural modes (commuting, sedentary and dive bout) and social status (solitary vs. group). For foraging dive bouts we assessed whether the timing and frequency of calls were significantly different in the presence of schooling prey vs. single fish. The probability of call events was significantly more likely for birds commuting early and late in the day (for solitary birds) and during dive bouts (for groups). During foraging dive bouts the frequency of calls was significantly greater for birds diving in the presence of schooling fish and birds called sooner after a catch in these foraging scenarios compared with when only single fish were encountered. Three call types were recorded, 'flat', 'modulated' and 'two‐voice' calls, but there was no significant relationship detected with these call types and behavioural modes for solitary birds and birds in groups. The results of this study show that acoustic signalling by African Penguins at sea is used in a variety of behavioural contexts and that increased calling activity in the presence of more profitable prey could be of crucial importance to seabirds that benefit from group foraging.

Up for grabs: prey herding by penguins facilitates shallow foraging by volant seabirds.

Visual and olfactory signals are commonly used by seabirds to locate prey in the horizontal domain, but foraging success depends on prey depth and the seabird's ability to access it. Facilitation by diving seabirds has long been hypothesized as a mechanism to elevate deep prey to regions more accessible to volant seabirds, but this has never been demonstrated empirically. Footage from animal-borne video loggers deployed on African penguins was analysed to establish if volant seabird encounters involved active cuing by seabirds on penguins to obtain prey and, during mutual prey encounters, if interactions were driven by the vertical displacement of prey by penguins. Independent of prey biomass estimates, we found a strong inverse relationship between penguin group size, a proxy for visibility, and the time elapsed from the start of penguins' dive bouts to their first encounter with other seabirds. Most mutual prey encounters (7 of 10) involved schooling prey elevated from depths greater than 33 m by penguins and only pursued by other seabird species once prey was herded into shallow waters. This is likely to enhance foraging efficiency in volant seabird species. As such, penguins may be integral to important processes that influence the structure and integrity of marine communities.

Constrained by consistency? Repeatability of foraging behavior at multiple timescales for a generalist marine predator

Marine predators frequently exhibit consistency in foraging behaviors despite the dynamic nature of marine ecosystems, which has the potential for ecological and evolutionary implications depending on the timescale at which it persists. We examined behavioral consistency in movements and diving behavior of adult female California sea lions (Zalophus californianus), which are abundant, generalist central-place foragers inhabiting an ecosystem characterized by small- and broad-scale oceanographic variability. We used biologging devices to measure repeatability of behavior within a season and stable isotope analysis of whiskers to quantify behavior across a 2-year period associated with anomalous environmental conditions that affected prey availability. Sea lions were significantly repeatable in all variables across multiple timescales (Radj = 0.26–0.82), although repeatability estimates were generally higher for variables related to characteristics of individual dives (e.g., dive depth) than those that described dive bouts (e.g., bout duration) or spatial use (e.g., volume of 3D utilization distribution). These differences may result from the fact that diving behaviors vary with prey type, whereas spatial use and bout variables may reflect the foraging success within prey patches or movement among patches. There was variation in how predictable individual sea lions were in their diving behaviors, which was largely unrelated or negatively related to foraging site fidelity. The strength of behavioral consistency decreased with time yet persisted across the 2-year period, suggesting that while sea lions alter their behavior in response to environmental change, the behavioral flexibility of individuals may ultimately be constrained by consistency.

Taking the Bite Out of Winter: Common Murres (Uria aalge) Push Their Dive Limits to Surmount Energy Constraints

Diving seabirds that overwinter at high latitudes experience persistent cold exposure, shorter days and associated declines in ocean productivity that can challenge their ability to balance daily energy budgets. We used dive-immersion geo-locators to test the hypothesis that pursuit-diving Common murres (Uria aalge) will respond to the challenges of winter in the North Atlantic through increased daily energy expenditures (DEE) that will be met by increased foraging effort and adjustments in dive tactics. Largely flightless in winter ( 85% resting and swimming). Accordingly, when sea surface temperatures (SST) were consistently near freezing in late winter (1.9 ± 0.8 °C), mean DEE (2463.2 ± 10.9 kJ day-1) exceeded the theoretical limit to sustainable energy expenditure in vertebrates (i.e. 7 X Basal Metabolic Rate or 2450 kJ day-1 for murres). Consistently deep (70% > 50m) and long dives in late winter, 38% of which exceeded their calculated aerobic dive limit indicate that targeted prey was distributed in deep (dark) waters. Consequently, foraging was highly constrained to daylight hours; likely because capture efficiency of deep-water prey is very poor in low light. Murres responded to late winter time and energy constraints with a nearly 2-fold increase in daily time spent diving (95.2 ± 5.6 mins and 178.3 ± 6.3 mins day-1 during early and late winter, respectively), an increase in dive bout frequency and duration, and correspondingly less time resting between bouts. Uniquely adapted for deep-diving, pursuit-diving murres push their dive limits in order to maximize daily energy intake when energy demands are high and prey are distributed in deep water. This study highlights late winter as an extremely challenging phase in the annual cycle of North Atlantic murres and provides critical insights into the behavioral mechanisms underlying their winter survival.

Calf age and sex affect maternal diving behaviour in Shark Bay bottlenose dolphins

Maternal care varies across taxa from brief, minimal care to long-term, intensive care. Mammalian mothers provide extensive and energetically expensive care by definition through pregnancy and lactation, which can extend for years, resulting in behavioural trade-offs between resource acquisition and direct care. In marine environments, mammalian mothers face unique challenges, such as the inability to cache or den their offspring while diving for prey. Dolphin newborns are precocious, accomplishing shallow dives in the first few weeks of life, however, fully mature diving and breath-holding capabilities take years to develop. Consequently, mothers are faced with a trade-off between diving and foraging or remaining close to and protecting their calves at the surface. Here we examined this trade-off, specifically by investigating whether mothers change their dive durations, especially during foraging, as a function of calf age. We used a longitudinal (1988–2014) data set on wild bottlenose dolphins, Tursiops aduncus, in Shark Bay, Western Australia, which included 27 388 dive bouts from mothers (N = 26) and calves (N = 41). Our results show that maternal diving behaviour changes in response to calf age and sex. While both male and female calves increased their dive durations with age as expected, mothers were more likely to adjust their diving behaviour to accommodate female but not male calves, especially when daughters were in close proximity. This is consistent with findings that vertical social learning is more critical for daughters than for sons, and may reflect the sex-specific foraging and social tactics of the males and females more generally.

Relationship between telomere dynamics and movement and behavior during winter in the thick‑billed murre

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 578:253-261 (2017) - DOI: https://doi.org/10.3354/meps12022 Relationship between telomere dynamics and movement and behavior during winter in the thick‑billed murre Rebecca C. Young1,*, Rachael A. Orben2, Alexis P. Will1, Alexander S. Kitaysky1 1Department of Biology and Wildlife, Institute of Arctic Biology, University of Alaska Fairbanks, Irving 311, Fairbanks, AK 99775, USA 2Department of Fisheries and Wildlife, Oregon State University, Hatfield Marine Science Center, 2030 SE Marine Science Dr., Newport, OR 97365, USA *Corresponding author: rebeccacyoung721@gmail.comAdvance View was available online February 22, 2017 ABSTRACT: Connecting the life history stages of the annual cycle via carry-over effects crucially informs estimates of mortality and reproduction. This study explores variables linking the breeding and wintering seasons in a pursuit-diving seabird, the thick-billed murre Uria lomvia. We deployed global location sensing loggers on chick-rearing murres breeding in the southeastern Bering Sea to examine subsequent overwinter locations and foraging behavior. In the tracked individuals, we measured individual telomere length and longitudinal telomere length changes in blood and used feathers molted during fall and early spring to assess trophic niche (via stable isotopes) and stress levels (as reflected in feather corticosterone levels). Longitudinal changes in telomere length were better predicted by winter diving parameters than by geographic distribution and movement variables, such that birds that foraged more intensely (more time diving, more dive bouts) also experienced higher telomere loss. This indicates that in a pursuit-diving species with high flight costs, patterns of water-column use through diving may be more important than horizontal spatial movement for predicting physiological changes underlying carry-over effects. We conclude that telomere dynamics might be used as an indicator connecting behavior and physiological stress from season to season. KEY WORDS: Telomeres · Carry-over effects · Feather corticosterone · Stable isotope analysis · Migration · Thick-billed murre · Uria lomvia · Wintering grounds · Geolocator Full text in pdf format PreviousCite this article as: Young RC, Orben RA, Will AP, Kitaysky AS (2017) Relationship between telomere dynamics and movement and behavior during winter in the thick‑billed murre. Mar Ecol Prog Ser 578:253-261. https://doi.org/10.3354/meps12022 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 578. Online publication date: August 31, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.

Transiting to depth disrupts overall dynamic body acceleration and oxygen consumption rate in freely diving Steller sea lions

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 562:221-236 (2016) - DOI: https://doi.org/10.3354/meps11943 Transiting to depth disrupts overall dynamic body acceleration and oxygen consumption rate in freely diving Steller sea lions Beth L. Volpov1,*, Elizabeth T. Goundie2, David. A. S. Rosen2, John P. Y. Arnould1, Andrew W. Trites2 1Deakin University, School of Life and Environmental Sciences, 221 Burwood Highway, Burwood, Victoria 3125, Australia 2Marine Mammal Research Unit, Institute for the Oceans and Fisheries, University of British Columbia, 2202 Main Mall, Vancouver, BC, V6T 1Z4, Canada *Corresponding author: b.volpov@oceans.ubc.ca ABSTRACT: Previous research has presented contradictory evidence on the ability of overall dynamic body acceleration (ODBA) to predict mass-corrected oxygen consumption (sVO2) in air-breathing diving vertebrates. We investigated a potential source of these discrepancies by partitioning the ODBA-sVO2 relationship over 3 phases of the dive cycle (transiting to and from depth, bottom time, and post-dive surface interval). Trained Steller sea lions Eumetopias jubatus executed 4 types of dives to 40 m (single dives, long-duration dive bouts of 4-6 dives, short-duration dive bouts of 10 or 12 dives, and transit dives with minimal bottom duration). Partitioning single dives by dive phase showed differing patterns in the ODBA-sVO2 relationship among dive phases, but no significant linear relationships were observed. The proportion of the dive cycle spent transiting to and from the surface was a significant predictive factor in the ODBA-sVO2 relationship, while bottom duration or post-dive surface interval had no effect. ODBA only predicted sVO2 for dives when the proportion of time spent transiting was small. The apparent inability of ODBA to reliably predict sVO2 reflects differences in the inherent relationships between ODBA and sVO2 during different phases of the dive. These results support the growing body of evidence that ODBA on its own is not a reliable field predictor of energy expenditure at the level of the single dive or dive bout in air-breathing diving vertebrates likely because ODBA (a physical measure) cannot account for physiological changes in sVO2 that occur during the different phases of a dive cycle. KEY WORDS: Diving behaviour · Metabolic rate · ODBA · Dive phase · Pinniped Full text in pdf format PreviousNextCite this article as: Volpov BL, Goundie ET, Rosen DAS, Arnould JPY, Trites AW (2016) Transiting to depth disrupts overall dynamic body acceleration and oxygen consumption rate in freely diving Steller sea lions. Mar Ecol Prog Ser 562:221-236. https://doi.org/10.3354/meps11943 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 562. Online publication date: December 29, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

Physiological constraints and energetic costs of diving behaviour in marine mammals: a review of studies using trained Steller sea lions diving in the open ocean.

Marine mammals are characterized as having physiological specializations that maximize the use of oxygen stores to prolong time spent under water. However, it has been difficult to undertake the requisite controlled studies to determine the physiological limitations and trade-offs that marine mammals face while diving in the wild under varying environmental and nutritional conditions. For the past decade, Steller sea lions (Eumetopias jubatus) trained to swim and dive in the open ocean away from the physical confines of pools participated in studies that investigated the interactions between diving behaviour, energetic costs, physiological constraints, and prey availability. Many of these studies measured the cost of diving to understand how it varies with behaviour and environmental and physiological conditions. Collectively, these studies show that the type of diving (dive bouts or single dives), the level of underwater activity, the depth and duration of dives, and the nutritional status and physical condition of the animal affect the cost of diving and foraging. They show that dive depth, dive and surface duration, and the type of dive result in physiological adjustments (heart rate, gas exchange) that may be independent of energy expenditure. They also demonstrate that changes in prey abundance and nutritional status cause sea lions to alter the balance between time spent at the surface acquiring oxygen (and offloading CO2 and other metabolic by-products) and time spent at depth acquiring prey. These new insights into the physiological basis of diving behaviour further our understanding of the potential scope for behavioural responses of marine mammals to environmental changes, the energetic significance of these adjustments, and the consequences of approaching physiological limits.

Images as proximity sensors: the incidence of conspecific foraging in Antarctic fur seals

Background: Although there have been recent advances in the development of animal-attached ‘proximity’ tags to remotely record the interactions of multiple individuals, the efficacy of these devices depends on the instrumentation of sufficient animals that subsequently have spatial interactions. Among densely colonial mammals such as fur seals, this remains logistically difficult, and interactions between animals during foraging have not previously been recorded. Results: We collected data on conspecific interactions during diving at sea using still image and video cameras deployed on 23 Antarctic fur seals. Animals carried cameras for a total of 152 days, collecting a total of 38,098 images and 369 movies (total time 7.35 h). Other fur seals were detected in 74 % of deployments, with a maximum of five seals detected in a single image (n = 122 images, 28 videos). No predators other than conspecifics were detected. Detection was primarily limited by light conditions, since conspecifics were usually further from each other than the 1-m range illuminated by camera flash under low light levels. Other seals were recorded at a range of depths (average 27 ± 14.3 m, max 66 m). Linear mixed models suggested a relationship between conspecific observations per dive and the number of krill images recorded per dive. In terms of bouts of dives, other seals were recorded in five single dives (of 330) and 28 bouts of dives <2 min apart (of 187). Using light conditions as a proxy for detectability, other seals were more likely to be observed at the bottom of dives than during descent or ascent. Seals were also more likely to be closer to each other and oriented either perpendicular or opposing each other at the bottom of dives, and in the same or opposite direction to each other during ascent. Conclusions: These results are contrary to animal-attached camera observations of penguin foraging, suggesting differing group-foraging tactics for these marine predators. Group foraging could have consequences for models linking predator behaviour to prey field densities since this relationship may be affected by the presence of multiple predators at the same patch.

Comparing multiple sampling platforms for measuring the behavior of humpback whales (Megaptera novaeangliae)

AbstractMultiple platform approaches for measuring the behavior of marine mammals may strengthen data quality and quantity. However, if this approach is chosen, reconciliation of behavioral measures between each platform is required. This study compared typical measures of humpback whale (Megaptera novaeangliae) behavior collected from three different sampling platforms; land‐based, boat‐based, and digital tags (Dtags), to explore similarities and/or discrepancies in data. Visual observations from land‐based platforms significantly underestimated group blow rate when compared to boat‐based platforms, whereas broad‐scale spatial movements (speed and course traveled) were measured similarly by these two platforms. Dtags were used to define dive behavior based on a time and depth criteria, where bouts of short shallow respiration dives (≤80 s and ≤10 m) were separated from longer, deeper dives (&gt;80 s and &gt;10 m). At a group level, land and boat platforms agreed on the number of long dives but land platforms missed bouts of short dives. At an individual level, the number of short and long dives observed by boat‐based platforms agreed with Dtag recordings. This study highlights the importance of data exploration prior to analyses in multiple platform studies to identify potential discrepancies and appropriately account for any biases.

Movement and diving of killer whales (Orcinus orca) at a Southern Ocean archipelago

Eleven satellite tags were deployed on 9 killer whales at the Prince Edwards Islands in the Southern Ocean. State-space switching models were used to generate position estimates from Argos location data, while two behavioural modes were estimated from the data.Individuals were tracked for 5.6–53.2days, during which time they moved 416–4470km (mean 82.7kmday−1) but 69% of position estimates were within the 1000m depth contour around the islands (<35km from the tagging site). Killer whales showed restricted behaviour close to the islands, particularly inshore where they can effectively hunt seals and penguins, and at seamounts to the north of the islands.Generalised linear mixed effect models were used to explore the relationship between environmental variables and behavioural mode. The best model included depth, sea surface temperature, latitude, sea surface height anomaly and bottom slope, but killer whales did not clearly target features such as fronts and apparent mesoscale eddies. Killer whales showed restricted behaviour in shallow water, at high latitudes and low sea surface temperature — the conditions characterising the archipelago.Dive data from two individuals largely revealed shallow dives (7.5–50m deep), but deeper dive bouts to around 368m were also recorded. Dives were significantly deeper during the day and maximum dive depths were 767.5 and 499.5m, respectively. This suggests that killer whales might also prey on vertically migrating cephalopods and perhaps Patagonian toothfish.Three individuals made rapid and directed long-distance movements northwards of the islands, the reasons for which are speculative.

Validating the relationship between 3-dimensional body acceleration and oxygen consumption in trained Steller sea lions.

We tested the ability of overall dynamic body acceleration (ODBA) to predict the rate of oxygen consumption ([Formula: see text]) in freely diving Steller sea lions (Eumetopias jubatus) while resting at the surface and diving. The trained sea lions executed three dive types-single dives, bouts of multiple long dives with 4-6 dives per bout, or bouts of multiple short dives with 10-12 dives per bout-to depths of 40 m, resulting in a range of activity and oxygen consumption levels. Average metabolic rate (AMR) over the dive cycle or dive bout calculated was calculated from [Formula: see text]. We found that ODBA could statistically predict AMR when data from all dive types were combined, but that dive type was a significant model factor. However, there were no significant linear relationships between AMR and ODBA when data for each dive type were analyzed separately. The potential relationships between AMR and ODBA were not improved by including dive duration, food consumed, proportion of dive cycle spent submerged, or number of dives per bout. It is not clear whether the lack of predictive power within dive type was due to low statistical power, or whether it reflected a true absence of a relationship between ODBA and AMR. The average percent error for predicting AMR from ODBA was 7-11 %, and standard error of the estimated AMR was 5-32 %. Overall, the extensive range of dive behaviors and physiological conditions we tested indicated that ODBA was not suitable for estimating AMR in the field due to considerable error and the inconclusive effects of dive type.

Low prey abundance leads to less efficient foraging behavior in Steller sea lions

Breath-hold divers should adjust their dive behaviors to maximize the benefits and minimize the costs of foraging on prey patches of different densities at different depths. However, few studies have quantified how animals respond to changes in prey availability (depth and density), and how this affects their foraging efficiency. We tested the effects of changes in prey availability on the foraging behavior and efficiency of Steller sea lions (Eumetopias jubatus) by measuring diving metabolic rate, dive durations, and food intake of 4 trained sea lions diving in the open ocean on controlled prey patches of different densities at different depths. Sea lions completed bouts of 5 consecutive dives on high- or low-density prey patches at two depths (10m and 40m). We found that the rate of energy expenditure did not change under any of the imposed foraging conditions (mean±SD: 0.22±0.02kJmin−1kg−1), but that the proportion of time spent consuming prey increased with prey patch density due to changes in diving patterns. At both depths, sea lions spent a greater proportion of the dive bout foraging on prey patches with high prey density, which led to high rates of energy gain (4.3±0.96kJmin−1kg−1) and high foraging efficiency (cost:benefit was 1:20). In contrast, the sea lions spent a smaller proportion of their dive bout actively feeding on prey patches with low prey density, and consequently had a lower energetic gain (0.91±0.29kJmin−1kg−1) and foraging efficiency (1:4). The 5-fold differences in foraging efficiency between the two types of prey patches were greater than the 3-fold differences that we expected based on differences in food availability. Our results suggest that sea lions faced with reduced prey availability forage less efficiently and therefore would have greater difficulty obtaining their daily energy requirements.

Flexible foraging behaviour in a marine predator, the Masked booby (Sula dactylatra), according to foraging locations and environmental conditions

Flexible foraging behaviour allows marine predators to exploit shifting prey diversity and adjust to spatio-temporal changes in the distribution of prey. In diving marine predators, the number of dives within a dive bout, distances between dives in a bout and distances between bouts have been related to prey patch size, density of prey patches and prey encounter rates, respectively. In addition, the predictability of prey encounters can be examined by studying individuals' foraging site fidelity. Based on this, we examined in chick-rearing Masked boobies (Sula dactylatra) from Phillip Island (South-west Pacific), Australia, using GPS and depth–acceleration data logger, how these parameters changed over time (two early breeding phases and one late phase over two years) and according to foraging locations and environmental conditions. Results revealed that birds foraged in two distinct areas: over a nearby shallow shelf (“local area”) and over distant deeper waters (“distant area”). Birds searched for prey in the distant area only during the two latest study periods, indicating less favourable foraging conditions within the local area during this time, although persistent higher chlorophyll-a concentrations in the local area were indicative of an upwelling. Our data suggest that birds experienced a trade-off between local and distant trips: although the strong foraging site fidelity within the local area suggests that prey encounters were predictable, smaller dive bouts indicated smaller prey patches, i.e. less prey nearby the colony during the two latest study periods. As a consequence, adults undertook distant trips to forage in larger prey patches, as inferred from larger dive bouts, but distances between these dive bouts were more variable and birds showed no foraging site fidelity, indicating less predictable prey encounters. Local trips presumably allow a high feeding frequency of the chick, while distant trips allow adults to replenish their own body reserves. Observed changes in foraging conditions, although the underlying causes were not determined, appear to be within the eco-physiological limitations of Masked boobies. However, further studies are required to determine the degree of this limitation, especially as changes in the spatio-temporal availability of prey can be expected to increase with global warming and changing oceanic processes.