High‐resolution diving data collected from foraging area reveal that leatherback turtles dive faster to forage longer

Despite multiple studies examining the diving behavior of leatherback sea turtles (Dermochelys coriacea) at coarse resolution over broad distances, there is still a paucity of high-resolution diving data collected in areas where foraging has been confirmed. Short-term (~1–3 h) deployments of suction cup tags with time–depth recorders (TDRs) on 10 free-swimming leatherback turtles in a foraging area off Nova Scotia, Canada during August and September (2007–2014), captured a total of 161 dives. High-resolution (1–5 s sampling rate) dive profile data indicated variability in diving behavior between and within individuals. On average, turtles spent 55.7% of their time diving and 44.3% at the surface. Turtles generally performed short (mean duration = 250.4 s [SD = 47.9 s]) and shallow dives (mean depth = 24.3 m [SD = 5.8 m]). We recorded a mean dive descent rate of 0.32 m/s, which is faster than values recorded for leatherbacks in tropical waters. This may reflect differences in environment, behavioral mode (e.g., foraging vs. inter-nesting), and body condition. Linear mixed-effects models suggest a significant positive correlation between descent rate and mean depth, maximum depth, and integrated vertical bottom movement (IVBM). Turtles with faster descent rates dove deeper and increased their predicted foraging behavior (IVBM, or the sum of absolute differences in depth changes while at the bottom portion of their dives). Models additionally showed that dive time, bottom time, and IVBM were all positively correlated to the post-dive surfacing. This suggests that turtles required more time at the surface to recover and/or handle prey following longer dives characterized by increased vertical movement at the bottom portion of the dive. Dives were complex; the application of standard dive type/shape analysis may be over-simplified and inappropriate for leatherbacks foraging in these habitats. These results portray a novel and detailed look at the foraging dynamics of a diving marine reptile

Central place foraging drives niche partitioning in seabirds

When species coexist, it is expected that they will reduce competition through niche partitioning or spatial segregation. We investigated the importance of niche partitioning versus spatial segregation across a seabird community where food and foraging constraints vary seasonally. Spatial clustering of seabird density in the western Irish Sea occurred in both seasons, with hotspots of seabird occurrence significantly higher in summer (Moran's I: 0.29) than winter (Moran's I: 0.19). A positive correlation between seabird density and feeding guild richness suggested a role for niche partitioning in reducing competition. This correlation was significantly stronger in summer than winter (Z-test, p < 0.05), suggesting that when foraging range is constrained during the breeding season, interspecific competition is reduced through increased niche partitioning. Reduced spatial clustering and weaker correlations between density and feeding guild richness in winter suggests that spatial segregation plays a greater role in reducing interspecific competition outside the breeding season. This study demonstrates the relative importance of niche partitioning and spatial segregation, highlighting niche partitioning as a response to constraints on foraging range during the breeding season

A bioenergetics approach to understanding sex differences in the foraging behaviour of a sexually monomorphic species

Many animals show sexually divergent foraging behaviours reflecting different physiological constraints or energetic needs. We used a bioenergetics approach to examine sex differences in foraging behaviour of the sexually monomorphic northern gannet. We derived a relationship between dynamic body acceleration and energy expenditure to quantify the energetic cost of prey capture attempts (plunge dives). Fourteen gannets were tracked using GPS, time depth recorders (TDR) and accelerometers. All plunge dives in a foraging trip represented less than 4% of total energy expenditure, with no significant sex differences in expenditure. Despite females undertaking significantly more dives than males, this low energetic cost resulted in no sex differences in overall energy expenditure across a foraging trip. Bayesian stable isotope mixing models based on blood samples highlighted sex differences in diet; however, calorific intake from successful prey capture was estimated to be similar between sexes. Females experienced 10.28% higher energy demands, primarily due to unequal chick provisioning. Estimates show a minimum of 19% of dives have to be successful for females to meet their daily energy requirements, and 26% for males. Our analyses suggest northern gannets show sex differences in foraging behaviour primarily related to dive rate and success rather than the energetic cost of foraging or energetic content of prey

Handedness and individual roll-angle specialism when plunge diving in the northern gannet

Many vertebrates show lateralized behaviour, or handedness, where an individual preferentially uses one side of the body more than the other. This is generally thought to be caused by brain lateralization and allows functional specializations such as sight, locomotion, and decision-making among other things. We deployed accelerometers on 51 northern gannets, Morus bassanus, to test for behavioural lateralization during plunge dives. When plunge diving, gannets ‘roll’ to one side, and standard indices indicated that 51% of individuals were left-sided, 43% right-sided, and 6% ‘non-lateralized’. Lateralization indices provide no measure of error and do not account for environmental covariance, so we conducted two repeatability analyses on individuals' dive roll direction and angle. Dive side lateralization was highly repeatable among individuals over time at the population level (R = 0.878, p < 0.001). Furthermore, roll angle was also highly repeatable in individuals (R = 0.751, p < 0.001) even after controlling for lateralized state. Gannets show individual specializations in two different parts of the plunge diving process when attempting to catch prey. This is the first demonstration of lateralization during prey capture in a foraging seabird. It is also one of the few demonstrations of behavioural lateralization in a mixed model approach, providing a structure for further exploring behavioural lateralization

Sperm gatekeeping : 3D imaging reveals a constricted entrance to zebra finch sperm storage tubules

Females across many internally fertilizing taxa store sperm, often in specialized storage organs in their reproductive tracts. In birds, several hundred sperm storage tubules exist in the utero-vaginal junction of the oviduct, and there is growing evidence that sperm storage in these tubules is selective. The mechanisms underlying female sperm storage in birds remain unknown because of our limited ability to make three-dimensional, live observations inside the large, muscular avian oviduct. Here, we describe a new application of fluorescence selective plane illumination microscopy to optically section oviduct tissue from zebra finch Taeniopygia guttata females label free by harnessing tissue autofluorescence. Our data provide the first description of the three-dimensional structure of sperm storage organs in any vertebrate to the best of our knowledge and reveal the presence of gate-like constricted openings that may play a role in sperm selection

The role of wingbeat frequency and amplitude in flight power

Body-mounted accelerometers provide a new prospect for estimating power use in flying birds, as the signal varies with the two major kinematic determinants of aerodynamic power: wingbeat frequency and amplitude. Yet wingbeat frequency is sometimes used as a proxy for power output in isolation. There is, therefore, a need to understand which kinematic parameter birds vary and whether this is predicted by flight mode (e.g. accelerating, ascending/descending flight), speed or morphology. We investigate this using high-frequency acceleration data from (i) 14 species flying in the wild, (ii) two species flying in controlled conditions in a wind tunnel and (iii) a review of experimental and field studies. While wingbeat frequency and amplitude were positively correlated, R2 values were generally low, supporting the idea that parameters can vary independently. Indeed, birds were more likely to modulate wingbeat amplitude for more energy-demanding flight modes, including climbing and take-off. Nonetheless, the striking variability, even within species and flight types, highlights the complexity of describing the kinematic relationships, which appear sensitive to both the biological and physical context. Notwithstanding this, acceleration metrics that incorporate both kinematic parameters should be more robust proxies for power than wingbeat frequency alone

How animal movement defines behaviour: new insights into the ecology of seabirds at sea

How animals move through their environment defines their ecology at an individual and population level. All animals must search for food to survive and how they do this can be influenced by the world around them as well as their own internal state. Our understanding of animal ecology has been dramatically expanded thanks to the continued development and miniaturisation of data loggers that can be attached to animals. Data from these biologgers remain challenging to interpret, but shed light on the behavioural ecology of individual animals. In this thesis, I use movement data from seabirds to explore the mechanisms behind foraging and how these are underpinned by the movement of individual animals. In chapter 1, I provide an introductory overview of the literature and introduce my study species. In chapter 2, I examine the methods available to interpreting behaviour from animal relocation data showing that Hidden Markov Models (HMMs) outcompete other behavioural annotation methods – successfully identifying 81% of plunge dives in northern gannets, Morus bassanus. I then provide recommendations for best practice when defining periods of search and prey capture behaviour. In chapter 3, I show how environmental features may ultimately disrupt the expected movement of optimal foraging, and show that Atlantic puffins, Fratercula arctica, in southeast Ireland have departed from classic Area Restricted Search (ARS). These findings are considered in an energetic perspective and suggest that puffins may be saving between 28-46% of the energy required to fly the same distance. In chapter 4, I utilise acceleration data to document the bioenergetic sex differences of prey capture attempts in northern gannets, examining the links between diet, movement, and energy expenditure. Stable isotope analysis showed dietary differences between the sexes, but energetic content of divergent diets was the same. Prey capture attempts are not energetically expensive for gannets (<4% of energy expenditure in all northern gannets) and females have higher energy demands. However, the differing rate of prey capture attempts highlights that males have a higher minimum prey capture success rate than females to meet energetic demands (29% and 21% respectively). In chapter 5, I further explore acceleration data to determine whether northern gannets display handedness during foraging behaviours. All individuals (n=14) were lateralised in the direction of their pre-plunge dive roll behaviour, with a ‘population’ level right-sided bias (64%). While wind has a small effect on the angle of roll, it did not affect the observed lateralisation in individuals. I conclude with a general discussion summarising my main findings and suggesting future research opportunities. This thesis highlights how investigating animal behaviour using movement data can provide new insights into the behavioural ecology of species

Bennison et al tracking data for Atlantic puffins and razorbills

This tracking dataset was collected from the Saltee Islands over three years, razorbills tracked in 2014 and puffins tracked in 2017 and 2018. As well as GPS data, time depth recorder (TDR) data are also supplied for two puffin deployments. 2018 puffin tracking data contains dives appended to GPS information. Tracks and TDR data are supplied as with easy to read sensible headers CSVs

Localised residency and inter-annual fidelity to coastal foraging areas may place sea bass at risk to local depletion

For many marine migratory fish, comparatively little is known about the movement of individuals rather than the population. Yet, such individual-based movement data is vitally important to understand variability in migratory strategies and fidelity to foraging locations. A case in point is the economically important European sea bass (Dicentrarchus labrax L.) that inhabits coastal waters during the summer months before migrating offshore to spawn and overwinter. Beyond this broad generalisation we have very limited information on the movements of individuals at coastal foraging grounds. We used acoustic telemetry to track the summer movements and seasonal migrations of individual sea bass in a large tidally and estuarine influenced coastal environment. We found that the vast majority of tagged sea bass displayed long-term residency (mean, 167 days) and inter-annual fidelity (93% return rate) to specific areas. We describe individual fish home ranges of 3 km or less, and while fish clearly had core resident areas, there was movement of fish between closely located receivers. The combination of interannual fidelity to localised foraging areas makes sea bass very susceptible to local depletion; however, the designation of protected areas for sea bass may go a long way to ensuring the sustainability of this species