Dynamic soaring harvests energy from a spatiotemporal wind gradient, allowing albatrosses to glide over vast distances. However, its use is challenging to demonstrate empirically and has yet to be confirmed in other seabirds. Here, we investigate how flap-gliding Manx shearwaters optimize their flight for dynamic soaring. We do so by deriving a new metric, the horizontal wind effectiveness, that quantifies how effectively flight harvests energy from a shear layer. We evaluate this metric empirically for fine-scale trajectories reconstructed from bird-borne video data using a simplified flight dynamics model. We find that the birds’ undulations are phased with their horizontal turning to optimize energy harvesting. We also assess the opportunity for energy harvesting in long-range, GPS-logged foraging trajectories and find that Manx shearwaters optimize their flight to increase the opportunity for dynamic soaring during favorable wind conditions. Our results show how small-scale dynamic soaring affects large-scale Manx shearwater distribution at sea.

There is increasing evidence for impacts of light pollution on the physiology and behaviour of wild animals. Nocturnally active Procellariiform seabirds are often found grounded in areas polluted by light and struggle to take to the air again without human intervention. Hence, understanding their responses to different wavelengths and intensities of light is urgently needed to inform mitigation measures. Here, we demonstrate how different light characteristics can affect the nocturnal flight of Manx shearwaters Puffinus puffinus by experimentally introducing lights at a colony subject to low levels of light pollution due to passing ships and coastal developments. The density of birds in flight above the colony was measured using a thermal imaging camera. We compared number of flying shearwaters under dark conditions and in response to an artificially introduced light, and observed fewer birds in flight during ‘light-on’ periods, suggesting that adult shearwaters were repelled by the light. This effect was stronger with higher light intensity, increasing duration of ‘light-on’ periods and with green and blue compared to red light. Thus, we recommend lower light intensity, red colour, and shorter duration of ‘light-on’ periods as mitigation measures to reduce the effects of light at breeding colonies and in their vicinity.

Biologging has emerged as one of the most powerful and widely used technologies in ethology and ecology, providing unprecedented insight into animal behaviour. However, attaching loggers to animals may alter their behaviour, leading to the collection of data that fails to represent natural activity accurately. This is of particular concern in free-ranging animals, where tagged individuals can rarely be monitored directly. One of the most commonly reported measures of impact is breeding success, but this ignores potential short-term alterations to individual behaviour. When collecting ecological or behavioural data, such changes can have important consequences for the inference of results. Here, we take a multifaceted approach to investigate whether tagging leads to short-term behavioural changes, and whether these are later reflected in breeding performance, in a pelagic seabird. We analyse a long-term dataset of tracking data from Manx shearwaters (Puffinus puffinus), comparing the effects of carrying no device, small geolocator (GLS) devices (0.6% body mass), large Global Positioning System (GPS) devices (4.2% body mass) and a combination of the two (4.8% body mass). Despite exhibiting normal breeding success in both the year of tagging and the following year, incubating birds carrying GPS devices altered their foraging behaviour compared to untagged birds. During their foraging trips, GPS-tagged birds doubled their time away from the nest, experienced reduced foraging gains (64% reduction in mass gained per day) and reduced flight time by 14%. These findings demonstrate that the perceived impacts of device deployment depends on the scale over which they are sought: long-term measures, such as breeding success, can obscure finer-scale behavioural change, potentially limiting the validity of using GPS to infer at-sea behaviour when answering behavioural or ecological questions.

Dynamic soaring harvests energy from a spatiotemporal wind gradient, allowing albatrosses to glide over vast distances. However, its use is challenging to demonstrate empirically, and has yet to be confirmed in other seabirds. Here we investigate how flap-gliding Manx Shearwaters optimise their flight for dynamic soaring. We do so by deriving a new metric, the horizontal wind effectiveness, that quantifies how effectively flight harvests energy from a shear layer. We evaluate this metric empirically for fine-scale trajectories reconstructed from bird-borne video data using a simplified flight dynamics model. We find that the birds’ undulations are phased with their horizontal turning to optimise energy harvesting. We also assess the opportunity for energy harvesting in long-range, GPS-logged foraging trajectories, and find that Manx Shearwaters optimise their flight to increase the opportunity for dynamic soaring during favourable wind conditions. Our results show how small-scale dynamic soaring impacts large-scale Manx Shearwater distribution at sea.TeaserFlap-gliding shearwaters harvest wind energy by fine-scale trajectory optimization and this impacts their large-scale distribution at sea.

The first solitary migration of juvenile birds is difficult to study because of a low juvenile survival rates and sometimes long delays in return to the breeding grounds. Consequently, little is known about this crucial life event for many bird species, in particular the sensory guidance mechanisms facilitating the first migratory journey. Initial orientation during the first migration is a key measure to investigate these mechanisms. Here, we developed an assay to measure initial orientation as flight direction upon first take‐off in nocturnally fledging juvenile seabirds. We dorsally deployed a coloured LED on juvenile birds to allow researchers to observe the vanishing bearings of individuals as they flew out to sea. Additionally, we co‐deployed either a small Neodymium magnet or glass bead (control) on top of the bird's head to investigate the use of magnetoreception, previously unexplored in this early life stage. We used this assay to observe the first flight of Manx shearwaters Puffinus puffinus and found that they did not orient towards their wintering ground straight after taking off. Further, we did not find an effect of the magnetic treatment on juveniles' flight direction, though whether this is due to the birds not using magnetoreception, other salient cues being available or a lack of motivation to orient to the migratory beeline is unclear. We were, however, able to identify wind direction and topography as drivers of first flight direction in Manx shearwaters, which fledged with wind component between a crosswind and a tailwind and directed their maiden flight towards the sea and away from the land. This novel assay will facilitate the study of the maiden flight of nocturnally fledging birds and will help advance the study of sensory guidance mechanisms underpinning migratory orientation in a wide range of taxa, including species which are traditionally challenging to study.