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Studying the at-sea movements and behaviour of juvenile seabirds is logistically challenging, but new technologies now allow tracking birds on their first migration, giving a more complete picture of population-level spatial ecology. We investigated the post-fledging migration of juvenile northern gannets Morus bassanus from the world’s largest colony, at Bass Rock, Scotland. We first examined the movements and survival of 38 juveniles over their initial days at sea with GPS precision for up to 53 d post-fledging. We then compared their migration journeys with those of 35 adults tracked with geolocators. Almost one-third of juveniles died within 2 mo of leaving the colony, and this mortality was often associated with apparent uncertainties in their direction of migration, including marked, abrupt and often repeated changes in bearing within the North Sea. Both juveniles and adults then migrated as far as the Canary Current Large Marine Ecosystem (CCLME) off the Atlantic coast of West Africa, initially taking both clockwise and counter-clockwise routes around the UK. Juveniles covered a distance each day similar to that of adults, but they reached the CCLME much more quickly, mainly because they travelled more directly, staying close to the coast throughout most of their migration, whereas adults additionally spent long periods over relatively restricted areas of ocean further offshore. The CCLME is a hotspot of unregulated fishing activity, and our findings highlight the importance of this region across different age-classes of birds, echoing previous calls that the regional strengthening of marine conservation should be a high priority.

Animal-borne accelerometers allow body movement and behaviours to be recorded and identified. Quantifying these from free-living animals has many ecological applications, from identifying key behaviours in focal aspects of life history to estimating energy expenditure of locomotive patterns, all without direct observation. This is particularly valuable for species that are difficult to observe throughout their daily routines, such as those that utilise marine environments. Many seabirds navigate a three-dimensional landscape in unpredictable environmental conditions to find prey that are often patchy and widely distributed. Consequently, their foraging strategies, and utilisation of time and energy when foraging, are complex. Foraging effort and success determine the net energy gain by an organism and form an essential link between prey availability and reproductive success. Quantifying foraging energetics can be challenging, but aid in delivering sound conservation strategies in an era of intense environmental pressures and uncertainty. By combining multifaceted data, principally accelerometers and GPS loggers, this thesis explored the at-sea movements of northern gannets, Morus bassanus, on a fine-scale individual basis. First, I examined associations between sexual dimorphism and sex differences. Within each sex, different facets of movements and behaviour were significantly related to body mass. However, the observed relationships were not consistent with the notion that sex differences were driven by sexual dimorphism. Secondly, I investigated the consistency in foraging behaviour and energy expenditure of individuals and the energy consequences of individual foraging site fidelity (IFSF). Birds were consistent in space use and energy expenditure but with varying degrees of repeatability among individuals and between sexes. The consequences of individuality were sex-specific, with greater IFSF associated with enhanced foraging success among females and elevated foraging effort among males. Third, I examined the effect of wind on fine-scale foraging behaviour and energy expenditure, finding that wind conditions strongly affected foraging behaviour, with contrasting effects of increasing wind speeds on females (lower take-off rates) and males (greater dive depths). Overall, I demonstrate that not only do sexes and individuals differ in fine-scale behaviours and proxies of energy expenditure, but sex differences extend to the prevalence and consequences of individuality, and sexes respond differently to environmental conditions when foraging. This thesis highlights the need to consider sex differences and individuality when predicting the impacts of environmental change on populations of long-lived central-place foragers.

High pathogenicity avian influenza virus (HPAIV) caused the worst seabird mass-mortalities on record in Europe across 2021-2022. The northern gannet (Morus bassanus) was one of the most affected species, with tens of thousands of casualties in the northeast Atlantic between April-September 2022. Disease outbreaks can drastically modify the movement ecology of animals and diminish spatial consistency, thereby increasing the potential for disease transmission. To detect potential changes in movement behaviour, we GPS-tracked breeding adults following the initial HPAIV outbreak, at three of the largest gannet breeding colonies where major mortality of adults and chicks occurred (Bass Rock, Scotland, UK; Grassholm, Wales, UK; Rouzic island, Brittany, France). Crucially, GPS-tracked birds remained faithful to their breeding sites and did not prospect other breeding colonies. They performed regular foraging trips at sea, similar to their behaviour before the outbreak. Gannet foraging effort was nonetheless lower than in 2019, thus surviving birds may have benefited from reduced intra- and interspecific food competition. Breeding colony fidelity of adult northern gannets following HPAIV mass-mortalities suggests limited long-term capacity to virus spread, which may contrast with the behaviour of adults during the disease outbreak, or with that of younger individuals.

New surgical procedures can expose patients to harm and should be carefully evaluated before widespread use. The InSpace balloon (Stryker, USA) is an innovative surgical device used to treat people with rotator cuff tears that cannot be repaired. We aimed to determine the effectiveness of the InSpace balloon for people with irreparable rotator cuff tears. We conducted a double-blind, group-sequential, adaptive randomised controlled trial in 24 hospitals in the UK, comparing arthroscopic debridement of the subacromial space with biceps tenotomy (debridement only group) with the same procedure but including insertion of the InSpace balloon (debridement with device group). Participants had an irreparable rotator cuff tear, which had not resolved with conservative treatment, and they had symptoms warranting surgery. Eligibility was confirmed intraoperatively before randomly assigning (1:1) participants to a treatment group using a remote computer system. Participants and assessors were masked to group assignment. Masking was achieved by using identical incisions for both procedures, blinding the operation note, and a consistent rehabilitation programme was offered regardless of group allocation. The primary outcome was the Oxford Shoulder Score at 12 months. Pre-trial simulations using data from early and late timepoints informed stopping boundaries for two interim analyses. The primary analysis was on a modified intention-to-treat basis, adjusted for the planned interim analysis. The trial was registered with ISRCTN, ISRCTN17825590. Between June 1, 2018, and July 30, 2020, we assessed 385 people for eligibility, of which 317 were eligible. 249 (79%) people consented for inclusion in the study. 117 participants were randomly allocated to a treatment group, 61 participants to the debridement only group and 56 to the debridement with device group. A predefined stopping boundary was met at the first interim analysis and recruitment stopped with 117 participants randomised. 43% of participants were female, 57% were male. We obtained primary outcome data for 114 (97%) participants. The mean Oxford Shoulder Score at 12 months was 34·3 (SD 11·1) in the debridement only group and 30·3 (10·9) in the debridement with device group (mean difference adjusted for adaptive design –4·2 [95% CI –8·2 to –0·26];p=0·037) favouring control. There was no difference in adverse events between the two groups. In an efficient, adaptive trial design, our results favoured the debridement only group. We do not recommend the InSpace balloon for the treatment of irreparable rotator cuff tears. Efficacy and Mechanism Evaluation Programme, a Medical Research Council and National Institute for Health and Care Research partnership