Behavior is an important mechanism of evolution and it is paid for through energy expenditure. Nevertheless, field biologists can rarely observe animals for more than a fraction of their daily activities and attempts to quantify behavior for modeling ecological processes often exclude cryptic yet important behavioral events. Over the past few years, an explosion of research on remote monitoring of animal behavior using acceleration sensors has smashed the decades-old limits of observational studies. Animal-attached accelerometers measure the change in velocity of the body over time and can quantify fine-scale movements and body postures unlimited by visibility, observer bias, or the scale of space use. Pioneered more than a decade ago, application of accelerometers as a remote monitoring tool has recently surged thanks to the development of more accessible hardware and software. It has been applied to more than 120 species of animals to date. Accelerometer measurements are typically collected in three dimensions of movement at very high resolution (>10 Hz), and have so far been applied towards two main objectives. First, the patterns of accelerometer waveforms can be used to deduce specific behaviors through animal movement and body posture. Second, the variation in accelerometer waveform measurements has been shown to correlate with energy expenditure, opening up a suite of scientific questions in species notoriously difficult to observe in the wild. To date, studies of wild aquatic species outnumber wild terrestrial species and analyses of social behaviors are particularly few in number. Researchers of domestic and captive species also tend to report methodology more thoroughly than those studying species in the wild. There are substantial challenges to getting the most out of accelerometers, including validation, calibration, and the management and analysis of large quantities of data. In this review, we illustrate how accelerometers work, provide an overview of the ecological questions that have employed accelerometry, and highlight the emerging best practices for data acquisition and analysis. This tool offers a level of detail in behavioral studies of free-ranging wild animals that has previously been impossible to achieve and, across scientific disciplines, it improves understanding of the role of behavioral mechanisms in ecological and evolutionary processes.

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Observing the unwatchable through acceleration logging of animal behavior

Plastic debris is now ubiquitous in the marine environment affecting a wide range of taxa, from microscopic zooplankton to large vertebrates. Its persistence and dispersal throughout marine ecosystems has meant that sensitivity toward the scale of threat is growing, particularly for species of conservation concern, such as marine turtles. Their use of a variety of habitats, migratory behaviour, and complex life histories leave them subject to a host of anthropogenic stressors, including exposure to marine plastic pollution. Here, we review the evidence for the effects of plastic debris on turtles and their habitats, highlight knowledge gaps, and make recommendations for future research. We found that, of the seven species, all are known to ingest or become entangled in marine debris. Ingestion can cause intestinal blockage and internal injury, dietary dilution, malnutrition, and increased buoyancy which in turn can result in poor health, reduced growth rates and reproductive output, or death. Entanglement in plastic debris (including ghost fishing gear) is known to cause lacerations, increased drag—which reduces the ability to forage effectively or escape threats—and may lead to drowning or death by starvation. In addition, plastic pollution may impact key turtle habitats. In particular, its presence on nesting beaches may alter nest properties by affecting temperature and sediment permeability. This could influence hatchling sex ratios and reproductive success, resulting in population level implications. Additionally, beach litter may entangle nesting females or emerging hatchlings. Lastly, as an omnipresent and widespread pollutant, plastic debris may cause wider ecosystem effects which result in loss of productivity and implications for trophic interactions. By compiling and presenting this evidence, we demonstrate that urgent action is required to better understand this issue and its effects on marine turtles, so that appropriate and effective mitigation policies can be developed.

Plastic and marine turtles: a review and call for research

Extended bouts of fasting are ingrained in the ecology of many organisms, characterizing aspects of reproduction, development, hibernation, estivation, migration, and infrequent feeding habits. The challenge of long fasting episodes is the need to maintain physiological homeostasis while relying solely on endogenous resources. To meet that challenge, animals utilize an integrated repertoire of behavioral, physiological, and biochemical responses that reduce metabolic rates, maintain tissue structure and function, and thus enhance survival. We have synthesized in this review the integrative physiological, morphological, and biochemical responses, and their stages, that characterize natural fasting bouts. Underlying the capacity to survive extended fasts are behaviors and mechanisms that reduce metabolic expenditure and shift the dependency to lipid utilization. Hormonal regulation and immune capacity are altered by fasting; hormones that trigger digestion, elevate metabolism, and support immune performance become depressed, whereas hormones that enhance the utilization of endogenous substrates are elevated. The negative energy budget that accompanies fasting leads to the loss of body mass as fat stores are depleted and tissues undergo atrophy (i.e., loss of mass). Absolute rates of body mass loss scale allometrically among vertebrates. Tissues and organs vary in the degree of atrophy and downregulation of function, depending on the degree to which they are used during the fast. Fasting affects the population dynamics and activities of the gut microbiota, an interplay that impacts the host's fasting biology. Fasting-induced gene expression programs underlie the broad spectrum of integrated physiological mechanisms responsible for an animal's ability to survive long episodes of natural fasting.

Integrative Physiology of Fasting.

The endangered leatherback turtle is a large, highly migratory marine predator that inexplicably relies upon a diet of low-energy gelatinous zooplankton. The location of these prey may be predictable at large oceanographic scales, given that leatherback turtles perform long distance migrations (1000s of km) from nesting beaches to high latitude foraging grounds. However, little is known about the profitability of this migration and foraging strategy. We used GPS location data and video from animal-borne cameras to examine how prey characteristics (i.e., prey size, prey type, prey encounter rate) correlate with the daytime foraging behavior of leatherbacks (n = 19) in shelf waters off Cape Breton Island, NS, Canada, during August and September. Video was recorded continuously, averaged 1:53 h per turtle (range 0:08-3:38 h), and documented a total of 601 prey captures. Lion's mane jellyfish (Cyanea capillata) was the dominant prey (83-100%), but moon jellyfish (Aurelia aurita) were also consumed. Turtles approached and attacked most jellyfish within the camera's field of view and appeared to consume prey completely. There was no significant relationship between encounter rate and dive duration (p = 0.74, linear mixed-effects models). Handling time increased with prey size regardless of prey species (p = 0.0001). Estimates of energy intake averaged 66,018 kJ • d(-1) but were as high as 167,797 kJ • d(-1) corresponding to turtles consuming an average of 330 kg wet mass • d(-1) (up to 840 kg • d(-1)) or approximately 261 (up to 664) jellyfish • d(-1). Assuming our turtles averaged 455 kg body mass, they consumed an average of 73% of their body mass • d(-1) equating to an average energy intake of 3-7 times their daily metabolic requirements, depending on estimates used. This study provides evidence that feeding tactics used by leatherbacks in Atlantic Canadian waters are highly profitable and our results are consistent with estimates of mass gain prior to southward migration.

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Jellyfish support high energy intake of leatherback sea turtles (Dermochelys coriacea): video evidence from animal-borne cameras.

Maintaining a high and stable body temperature is often critical for female ectotherms during reproduction. Yet this strategy may be energetically costly, and therefore challenging, during this period of already high-energy demand. 2. Here, the 6-week deployment of tri-axial accelerometers (n = 6) on a marine ectotherm, the loggerhead turtle (Caretta caretta), reproducing at the northern limit of the species' breeding range (i.e. in a thermally dynamic environment) revealed the behavioural mechanisms underly- ing its energy management strategy during the breeding season. 3. The estimated activity levels of female loggerheads using overall dynamic body acceleration (ODBA) were high during the breeding season, suggesting that marine turtles may not be able to remain inactive for long periods in the same manner as terrestrial ectotherms, because of the thermally dynamic nature of their environment. 4. However, activity levels were not constant throughout the season, being impacted by both ambient water temperature and female reproductive status. In cold water at the beginning of the nesting season, high levels of activity suggested that females behaviourally thermoregulated by seeking out warm water patches along the shoreline. Interactions with male turtles (courtship and ⁄ or avoidance) may also explain this high level of activity. As sea temperatures warmed up and the amount of energy devoted to reproduction probably increased, the turtles spent more time resting during long sequential flat-bottomed dives, and reduced any unnecessary locomotory activity. 5. Turtles may therefore adjust their activity patterns in response to seasonal variations in abi- otic (i.e. ambient temperature) and biotic (i.e. reproductive status) factors. This may help minimize activity-linked metabolic rate and maximize reproductive output over a season while breeding in thermally dynamic environments. 6. A mechanistic model gave support to these empirical results. The model revealed that actively maintaining high and stable body temperature is of clear benefit to female turtles at temperate breeding sites. While energetically costly, such active thermoregulatory behaviour may speed up egg maturation, allowing turtles to initiate nesting earlier in the season, and hence maximize reproductive output.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2435.2011.01960.x

Acceleration data reveal the energy management strategy of a marine ectotherm during reproduction

In the face of the physical and physiological challenges of performing breath-hold deep dives, marine vertebrates have evolved different strategies. Although behavioural strategies in marine mammals and seabirds have been investigated in detail, little is known about the deepest-diving reptile – the leatherback turtle (Dermochelys coriacea). Here, we deployed tri-axial accelerometers on female leatherbacks nesting on St Croix, US Virgin Islands, to explore their diving strategy. Our results show a consistent behavioural pattern within dives among individuals, with an initial period of active swimming at relatively steep descent angles (∼–40 deg), with a stroke frequency of 0.32 Hz, followed by a gliding phase. The depth at which the gliding phase began increased with the maximum depth of the dives. In addition, descent body angles and vertical velocities were higher during deeper dives. Leatherbacks might thus regulate their inspired air-volume according to the intended dive depth, similar to hard-shelled turtles and penguins. During the ascent, turtles actively swam with a stroke frequency of 0.30 Hz but with a low vertical velocity (∼0.40 ms–1) and a low pitch angle (∼+26 deg). Turtles might avoid succumbing to decompression sickness (‘the bends’) by ascending slowly to the surface. In addition, we suggest that the low body temperature of this marine ectotherm compared with that of endotherms might help reduce the risk of bubble formation by increasing the solubility of nitrogen in the blood. This physiological advantage, coupled with several behavioural and physical adaptations, might explain the particular ecological niche the leatherback turtle occupies among marine reptiles.

https://espace.library.uq.edu.au/view/UQ:256286/UQ256286_OA.pdf

Behaviour and buoyancy regulation in the deepest-diving reptile: the leatherback turtle.

SUMMARY It is generally assumed that leatherback turtles ( Dermochelys coriacea ), like other species of sea turtle, do not feed while offshore from nesting beaches, and rely instead on fat reserves to fuel reproductive activities. Recent studies, however, provide evidence that leatherbacks may forage during the internesting interval while offshore in the Western Atlantic Ocean and Caribbean Sea. Bio-logging technology was used to investigate the foraging behavior of female leatherback turtles at St Croix, US Virgin Islands. Leatherback gastrointestinal tract temperatures ( T GT ) were analyzed for sudden fluctuations indicative of ingestions, and laboratory ingestion simulations were used to characterize temperature fluctuations associated with ingestion of prey versus seawater. Dive patterns associated with prey ingestion were characterized and the proportion of prey ingestion during the day (05:00–18:59 h) and night (19:00–04:59 h) were compared. A combined total of 111 prey ingestions for seven leatherback turtles were documented during the internesting interval. The number of prey ingestions ranged from six to 48 for individual turtles, and the majority (87.4%) of these events occurred during the daytime. Prey ingestions were most frequently associated with V-shaped dives, and the mean (±1 s.d.) maximum dive depth with prey ingestion ranged from 154±51 to 232±101 m for individual turtles. Although leatherbacks were found to opportunistically feed during the internesting interval, the low prey ingestion rates indicate that energy reserves acquired prior to the breeding season are critical for successful reproduction by leatherbacks from the St Croix, USVI nesting population.

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Diel foraging behavior of gravid leatherback sea turtles in deep waters of the Caribbean Sea

The leatherback sea turtle Dermochelys coriacea is a Critically Endangered species that nests on oceanic beaches. Natural disturbance cycles of erosion and accretion maintain nest- ing habitat on these beaches by controlling dune vegetation and sand quality. The nesting beach at Sandy Point National Wildlife Refuge in St. Croix, US Virgin Islands, is designated 'critical habi- tat' for leatherback turtles by the US Fish and Wildlife Service. It harbors the largest nesting pop- ulation (>800 females) in the USA. It is an important rookery for Atlantic leatherback recovery efforts. For the past 30 yr, the beach has been continuously monitored and managed in order to increase hatchling recruitment and conservation. Our study highlights how a multiyear change in the natural disturbance cycle has affected dune plant growth and leatherback production at this beach. Reduced summer erosion relaxed natural control of Ipomoea pes-caprae, a native dune plant, allowing its seaward spread to cover >75% of the nesting beach. This spread of vegetation led to both direct and indirect interactions between nesting leatherbacks and I. pes-caprae. Because the beach is managed in order to protect leatherback nests, a dune vegetation control plan was needed. We measured the effects of 3 vegetation management options on nest success: herbicide treatment, aboveground mechanical removal, and undisturbed vegetation. These treat- ments were compared to nest success at a non-vegetated control site. We found that the spread of I. pes-caprae reduced nesting habitat and nest productivity. Aboveground vegetation treatment did not control root growth into nests. We discuss possible vegetation management strategies to improve leatherback nesting habitat quality and maximize nest productivity while minimizing anthropogenic disturbance to the natural beach dynamics.

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Steve Garner

Papers

Behaviour and buoyancy regulation in the deepest-diving reptile: the leatherback turtle.

Diel foraging behavior of gravid leatherback sea turtles in deep waters of the Caribbean Sea

Experimental study of dune vegetation impact and control on leatherback sea turtle Dermochelys coriacea nests