Black-backed Gulls Research Articles

Self-foraging vs facilitated foraging by Lesser Black-backed Gull (Larus fuscus) at the Frisian Front, the Netherlands

The Lesser Black-backed Gull, Larus fuscus Linnaeus, 1758, is a surface feeder with a broad prey spectrum that forages in the North Sea on subsurface pelagic fishes and crabs swimming within 0.6 m of the sea surface. In July 2006 and in July/August 2009, we surveyed the Frisian Front area in the southern North Sea (53.4°N–54.3°N, 4.0°E–5.5°E) to determine the prey base for Lesser Black-backed Gulls. In July/August 2009, we conducted bird counts in an integrated ecosystem survey by simultaneously sampling subsurface pelagic prey by a combination of fishing and echosounding. Lesser Black-backed Gulls make use of facilitated foraging to improve the catchability of their prey. The two most important aids for facilitated foraging by Lesser Black-backed Gull in the Frisian Front were (1) multispecies feeding associations with Common Murre, Uria aalge (Pontoppidan, 1763), and (2) fisheries discarding bycatch and offal. We found that in the top meter of the water column, the natural prey base is large enough to provide for self-foraging; however, Lesser Black-backed Gulls were found to rely mainly on facilitated foraging.

Состав и экологические особенности фауны гельминтов с пресноводными жизненными циклами у птиц Баренцева моря

The purpose of the research is integration and classification of data on the species composition of the helminths with freshwater life cycles in the birds on the Barents Sea and analysis of the infection features of birds of different species, depending on the ecology of parasites and hosts. Materials and methods . The material from 729 samples of seabirds belonging to 17 species collected during the period from 1991 to 2017 in several regions of the Barents Sea (Murman coast, Novaya Zemlya, Spitsbergen, offshore water, Pechora Sea) and in 2 regions of the western part of Kara Sea (eastern part of the Karskie Vorota Strait and Baidaratskaya Bay) was studied. The species composition of helminthes and quantitative parameters of birds infection (prevalence of infection, PI, and abundance index, AI) were determined. The statistical processing of the results using the Fisher F-distribution and cluster analysis by the "nearest neighbor" method using the data on PI was carried out. Results and discussion . 30 species of helminths with freshwater life cycles (10 species of trematodes, 14 species of cestodes, 5 species of nematodes, 1 species of acanthocephalans) were found in birds on the Barents Sea. The greatest number of freshwater parasites is typical for kittiwakes and black-backed gulls (9 species each), purple sandpipers (10 species) and herring gulls (11 species). 5 species of birds (little auks, razorbills, Atlantic puffins, Arctic terns and Steller,s eiders) were not infested by these parasites. The most widespread were nematodes Paracuaria adunca and Streptocara crassicauda, found in 5 and 8 species of hosts, respectively. In birds nesting far from the coast (Heuglin's gull, purple sandpiper, king eider), parasites predominate, in which the role of intermediate hosts is played by freshwater invertebrates. For most species of gulls (herring gull, black-backed gull, kittiwake, glaucous gull), used in the breeding season as forage biotopes sea and fresh water, more characteristic of the presence of helminths in the circulation of which fish are involved. In birds that do not have trophic connections with freshwater biocoenoses in the breeding period (alcids, northern fulmar, common eider), parasites are most often found showing wide specificity to different types of hosts and a high tolerance to fluctuations in salinity and temperature. Infestation of this group birds by freshwater helminths occurs either with a prolonged stay in the desalinated areas of the marine aquatory, or with consumption of migratory fishes after their release into the sea.

Sea Ice Influences Habitat Type Use by Great Black-Backed Gulls (Larus marinus) in Coastal Newfoundland, Canada

The influence of an unusual concentration of sea ice and breeding failure on the foraging movement patterns and habitat use of Great Black-backed Gulls (Larus marinus) was investigated. GPS loggers were deployed on three incubating females when multi-year sea ice moved into foraging ranges, dividing the tracking period (1–23 June 2017) into ice-free (5–10 days) and ice-present periods (11–12 days). Foraging trip parameters (e.g., distance, duration) differed among individuals but not with ice conditions. Great Black-backed Gulls decreased use of islands when ice was present (0.05 ± 0.08 locations/trip) relative to absent (5.9 ± 0.5 locations/trip), but increased use of marine habitat when ice was present (9.4 ± 0.2 locations/trip) relative to absent (2.9 ± 0.2 locations/trip). Great Black-backed Gulls also moved at higher speeds in areas of 91–100% ice cover relative to < 50% ice cover, suggesting that low percent cover sea ice acts as important at-sea foraging/roosting sites. Additionally, two Great Black-backed Gulls that were continuously tracked during post-breeding failure repeatedly visited the colony throughout July-August, suggesting some advantage to maintaining a presence at nest sites.

Avian biodiversity across Auckland’s volcanic cone reserves

ABSTRACTAuckland, a city with a population of approximately 1.7 million, is located directly on the Auckland Volcanic Field, a late Quaternary-era monogenetic field. There are at least 53 volcanoes across the field, many of which are of geological, cultural and ecological significance, such as for being reserves for native species; however, few assessments of the richness of avian biodiversity across the volcanoes have been made. To address this data shortfall, we conducted avian biodiversity surveys using stationary point counts within nine of Auckland's volcanic cone reserves. Thirty-eight species were detected across the sites, of which 18 were native. Our estimates of relative species abundances and detection probabilities revealed that the most common native birds within these reserves were silvereyes, tui and southern black-backed gulls, while common mynas, house sparrows, Eurasian blackbirds and eastern rosellas were the most common introduced species. In addition to tui and silvereyes, the presence of other natives critical to the functioning of native ecosystems, such as New Zealand fantails, grey warblers and New Zealand pigeon, suggest that the volcanoes possess a diverse native avifauna supported by native flora that warrant continued and intensified restoration efforts. We discuss several feasible strategies for improving faunal and floral biodiversity across the volcanic cone reserves. Continued avian biodiversity surveys are also of critical importance as they will enable us to further evaluate and prioritise restoration projects within Auckland's multitude of diverse volcanic cone reserves.

The influence of avian biovectors on mercury speciation in a bog ecosystem

Methylmercury (MeHg) is a neurotoxin and endocrine disruptor that bioaccumulates and biomagnifies through trophic levels, resulting in potentially hazardous concentrations. Although wetlands are known hotspots for mercury (Hg) methylation, the effects of avian biovectors on these processes are poorly understood. We examined Hg speciation and distribution in shallow groundwater and surface water from a raised-bog with over 30years of avian biovector (herring gulls Larus argentatus and great black-backed gulls Larus marinus) colonization and guano input. Compared to the reference site, the avian-impacted bog had elevated concentrations of total dissolved organic carbon (TOC), total Hg, MeHg, phosphate (PO43−), and other trace metals, notably Pb, As, Cd and Ni. Spatial interpolation showed that the densest area of gull nesting was co-located with areas that had the highest concentrations of PO43−, MeHg, As and Cd, but not total mercury (THg), and models suggested that Mn, PO43−, and dissolved TOC were strong predictors of MeHg. Our findings suggest that while these gulls may not be a significant source of Hg, the excess of PO43− (a well recognised component of guano) and the subsequent changes in water chemistry due to avian biovector subsidies may increase net Hg methylation.

GPS tracking during parental care does not affect early offspring development in lesser black-backed gulls

Tracking devices are increasingly used to monitor individual movement patterns continuously and in high resolution. However, carrying a device could potentially compromise an individual’s physiology or behaviour, thereby making tracking data unreliable for detailed behavioural measurements. To this end, we assessed the possible consequences of the application of GPS devices on offspring development in an opportunistic seabird species, the lesser black-backed gull (Larus fuscus), by comparing the growth and survival of nestlings of which none, one or both parents were equipped with a GPS device. We found that the developmental trajectories of the nestlings were not affected, and there were no differences in skeletal size and body mass at the fledging stage. A lack of negative effects on offspring development strongly suggests that the parental behaviour, and thus likely the foraging behaviour, did not differ between tagged and non-tagged individuals. The evidence that GPS data can be used to reliably study parental care, as well as other aspects of the bird’s behaviour, opens up new possibilities to study behavioural and evolutionary ecological questions in ever-increasing resolution.

High-resolution GPS tracking reveals sex differences in migratory behaviour and stopover habitat use in the Lesser Black-backed Gull Larus fuscus

Sex-, size- or age-dependent variation in migration strategies in birds is generally expected to reflect differences in competitive abilities. Theoretical and empirical studies thereby focus on differences in wintering areas, by which individuals may benefit from avoiding food competition during winter or ensuring an early return and access to prime nesting sites in spring. Here, we use GPS tracking to assess sex- and size-related variation in the spatial behaviour of adult Lesser Black-backed Gulls (Larus fuscus) throughout their annual cycle. We did not find sex- or size-dependent differences in wintering area or the timing of spring migration. Instead, sexual differences occurred prior to, and during, autumn migration, when females strongly focussed on agricultural areas. Females exhibited a more protracted autumn migration strategy, hence spent more time on stopover sites and arrived 15 days later at their wintering areas, than males. This shift in habitat use and protracted autumn migration coincided with the timing of moult, which overlaps with chick rearing and migration. Our results suggest that this overlap between energy-demanding activities may lead females to perform a more prolonged autumn migration, which results in spatiotemporal differences in foraging habitat use between the sexes.

Dodging the blades: new insights into three-dimensional space use of offshore wind farms by lesser black-backed gulls Larus fuscus

GPS telemetry is improving our understanding of the way animals interact with their environment. Recent research has used this technology to assess the impact of offshore wind farms (OWFs) on seabirds, but few studies have collected fine-scale data from birds flying within OWFs. We use GPS telemetry to investigate movements of lesser black-backed gulls Larus fuscus in relation to OWFs from a protected site with an active breeding colony. Individual birds varied considerably in their use of OWFs; 15 out of 24 birds visited them, and time spent in these areas was 1.3% of time budgets across all birds. Two birds, for which the most data was collected, frequently entered OWFs and flew at turbine blade height; however, their overlap with the spherical 3-dimensional rotor swept volume was significantly lower than a random distribution. Although preliminary, these tracking data suggest a lack of a macro-scale (wind farm-scale) avoidance for L. fuscus but a potential meso-scale (within wind farm-scale) avoidance of turbines. Such data are therefore important in improving our understanding of the implications of OWFs for seabirds.

Flock-fishing deep-diving piscivores (Great Crested Grebe Podiceps cristatus, Great Cormorant Phalacrocorax carbo, Common Merganser Mergus merganser) at Lake Vombsjön, southern Sweden, and those that exploit them

Lake Vombsjön in southern Sweden is visited by large numbers of Great Crested Grebes Podiceps cristatus (&gt;2000), Great Cormorants Phalacrocorax carbo (sometimes &gt;1000) and Common Mergansers Mergus merganser (up to 2000) in late autumn and early winter. Different species exploit them. Great Crested Grebes are used especially by commensal Common Gulls Larus canus; the gulls take advantage of fish that flee towards the surface. Common Gulls also use cormorants and mergansers in the same way but also try to kleptoparasitize them. Both Herring Gulls Larus argentatus and Great Black-backed Gulls Larus marinus kleptoparasitize these two species, while Red Kites Milvus milvus, Grey Herons Ardea cinerea and Carrion Crows Corvus corone use them commensally. White-tailed Eagles Haliaeetus albicilla seem to use both methods to obtain fish. On 50% of one hundred visits during November to March, eagles were seen flying low over the fishing flocks. They would fly a metre or so above the flocks and then accelerate and attack a bird holding a fish. The bird would then either try to escape by a rush or by diving, dropping the fish which the eagle seized. Interestingly, the flock-fishing birds showed no fear reactions towards the eagles but appeared to regard them similarly to large gulls.

Plastic and Non-plastic Debris Ingestion in Three Gull Species Feeding in an Urban Landfill Environment.

Plastic debris is recognized as a widespread, common and problematic environmental pollutant. An important consequence of this pollution is the ingestion of plastic debris by wildlife. Assessing the degree to which different species ingest plastics, and the potential effects of these plastics on their health are important research needs for understanding the impacts of plastic pollution. We examined debris (plastic and other types) ingestion in three sympatric overwintering gull species (Herring gulls Larus smithsonianus, Great Black-backed Gulls Larus marinus, and Iceland Gulls Larus glaucoides) to understand how debris ingestion differs among species, age classes and sexes in gulls. We also assessed how plastic burdens were associated with body condition to investigate how gulls may be affected by debris ingestion. There were no differences among the species, age classes or sexes in the incidence of debris ingestion (plastic or otherwise), the mass or number of debris pieces ingested. We found no correlation between ingested plastics burdens and individual condition. Gulls ingested plastic debris, but also showed high levels of other debris types as well, including metal, glass and building materials, including a metal piece of debris found within an abscess in the stomach. Thus, when the health effects of debris ingestion on gulls, and other species that ingest debris, is of interest, either from a physical or chemical perspective, it may be necessary to consider all debris types and not just plastic burdens as is often currently done for seabirds.

Estimating flight heights of seabirds using optical rangefinders and GPS data loggers: a methodological comparison

Determining the collision risk of seabirds with offshore wind farms is crucial for the environmental impact assessment of such installations. The collision risk is often assessed by measuring avian flight heights. Therefore, we measured flight height distributions of 15 seabird taxa, abundant in German offshore waters, with an optical laser rangefinder (n = 2508 measurements). For lesser black-backed gulls, we compared these rangefinder measurements to flight heights recorded by GPS data loggers which were attached to 17 birds during incubation. Both methods have specific advantages and disadvantages. Rangefinder measurements are only possible during the day, and rain or fog prevents successful measurements. Data were negatively biased against low and very high flight heights. Since measuring low-flying birds proved more difficult during application of the method in the field, observers should be instructed to dedicate extra effort to measure low-flying birds. Visual observations of low-flying birds can also help to reduce uncertainty and overcome bias problems. Flight heights ranged from – 3 to 431 m above sea level. Most seabirds (70%) flew below rotor level (30 m), but about 30% (mainly large gulls and cormorants) flew in the rotor-swept area. GPS height measurements show a similar general pattern of flight height distribution as rangefinder measurements. However, this method is restricted to few individuals. Both methods complement each other and can provide a reliable estimate of seabirds’ flight height distribution.

Comprehensive and Comparative Analysis of the Helminth Fauna of the Dominant Colonial Seabird Species on the Murman Coast

This work reports the results of the long-term study of the helminth fauna of the dominant colonial seabird species (common guillemots, Brunnich’s guillemots, kittiwakes, great black-backed gulls, and herring gulls) in the western, central, and eastern parts of the Murman coast. The presence of 52 parasitic worm species (18 trematode species, 21 cestode species, 11 nematode species, and 2 acanthocephalan species) was demonstrated. In the western, central, and eastern regions, the respective numbers of 32, 43, and 34 helminth species were registered. Twenty species of seabird parasites were found to be ubiquitous along the Murman coastal zone. Local foci of the trematode Maritrema arenaria and cestode Laricanthus lateralis infestation along the western part of the Murmansk coast were revealed. The highest helminth species diversity (38 species) was demonstrated for the herring gull; the lowest (7 species), for the common guillemot. Four parasite species were common for the helminth fauna of all bird species. A significant number of helminth infections were mixed ones (complexes of two or three bird species with the common helminth species in different combinations). The highest similarity of the helminth fauna was revealed in the pairs of the common guillemot and the Brunnich’s guillemot and of the great black-backed gull and the herring gull. A few parasitic worm species detected only in a single bird species were registered. The particularities and the possible causes of the geographical distribution and specificity of helminthes were analyzed, and a comprehensive assessment of the parasitological situation in the Murman coastal zone was performed.

The end of the world, or just ‘goodbye to all that’? Contextualising the red deer heap from Links of Noltland, Westray, within late 3rd-millennium cal BC Orkney

As part of a major international research project, The Times of Their Lives, a programme of radiocarbon dating and Bayesian modelling was undertaken to refine the chronology of activities in one small but important part of the extensive Late Neolithic and Bronze Age settlement on Links of Noltland on the island of Westray, Orkney. The selected area (Trench D) is well known for having produced, next to a wall, the remains of a heap of at least 15 red deer carcasses, on top of which had been placed a large cod, a gannet’s wing along with part of a greater black-backed gull, and a pair of large antlers. This remarkable deposit had been preceded by, and was followed by, periods of cultivation and the deposition of domestic refuse. Refined date estimates have been produced, based on 18 radiocarbon determinations obtained from 16 samples from Trench D (including nine newly obtained dates, three from individual deer in the heap). These clarify when, during this long sequence of activities, the deer were heaped up: probably in the 22nd century cal BC, around the same time as Beaker pottery was deposited elsewhere on the Links. This allows comparison between the dated activities in this part of the site with activity elsewhere on the Links and also with other episodes of deer deposition in 3rd-millennium cal BC Orkney. It encourages exploration of the possible reasons for what appears to be a remarkable act of structured deposition. The significance of an earlier, much larger scale deposit featuring cattle remains at Ness of Brodgar is discussed in exploring the nature of Orcadian society and practices during the second half of the 3rd millennium cal BC.

Dietary Niche Shifts of Multiple Marine Predators under Varying Prey Availability on the Northeast Newfoundland Coast

Understanding species interactions among top marine predators and interactions with their prey can provide important insight into community-level responses to changing prey availability and the role of apex predators as indicators of ecosystem change. On the northeast Newfoundland coast, marine predators rely on capelin (Mallotus villosus), a dominant forage fish, as a food source. Capelin migrate into coastal regions to spawn during July, essentially transforming food supply from low during early summer (i.e. pre-spawning) to high later in the summer (i.e. spawning). During July-August, 2016, we used stable isotopic ratios of nitrogen (δ15N) and carbon (δ13C) to investigate shifts in dietary niche metrics at the predator group-level (trophic position, dietary niche breadth) and community-level (niche overlap, trophic diversity) for multiple marine predators under varying capelin availability. Predator groups included non-breeding shearwaters (great shearwater Ardenna gravis, sooty shearwater A. grisea), humpback whales (Megaptera novaeangliae), and gull chicks (herring gull Larus argentatus, great black-backed gull L. marinus). We also tested the sensitivity of community-level dietary metrics to a variety of published trophic discrimination factors. Tissue samples from shearwaters (blood cellular component), gull chicks (whole blood), and whales (skin), representing average diets over 2-3 weeks, were collected during three periods (early, mid, late) corresponding to increasing capelin availability. Isotopic niche breadth (Standard Ellipse Area, SEAb) narrowed and trophic position shifted toward higher δ15N for all predator groups as capelin availability increased, suggesting a higher reliance on capelin. Trophic diversity (distance to centroid) decreased with increased capelin availability, while pairwise niche overlap between predator groups was highly variable and sensitive to varying trophic discrimination factors. Findings suggest that although capelin is the dominant forage fish during the summer, predators rely on capelin as prey to varying degrees. Combining species- and community-level metrics of dietary niche and trophic diversity may provide a more complete picture of predator responses to prey availability and, thus, may be important monitoring tools to indicate changes in the food supply of marine predators.

Using novel-grass endophyte associations as an avian deterrent

Birds can be major pests in agricultural and horticultural crops as well as being serious hazards to operating aircraft. Cultivars of perennial ryegrass, a hybrid ryegrass and tall fescue, associated with selected Epichloë fungal endophytes were evaluated in aviary and field experiments for their management potential of three nuisance bird species selected as model systems representative of major bird classifications based on their diet. Granivores, namely European green finches, ate more endophyte-free perennial ryegrass seed than endophyte- infected seed, while the representative omnivores, black-backed gulls, avoided endophyte- enhanced feed pellets. The selected herbivore, Canada geese, showed an aversion to field trial plots sown with endophyte-infected grass containing ergovaline compared with the existing ground cover. Therefore habitat modification using selected grass-endophyte associations offers an effective wildlife management option aimed at reducing birds in problematic areas.

Satellite tracking of red-listed nominate lesser black-backed gulls (Larus f. fuscus): Habitat specialisation in foraging movements raises novel conservation needs

In contrast to many other gull species, nominate lesser black-backed gulls (Larus fuscus fuscus, nLBBG) have shown generally decreasing population trends throughout their breeding area in northern and eastern Fennoscandia over the past decades and are now red-listed. Interspecific competition, predation, increased disturbance, organochlorine poisoning and food shortages were suggested as main reasons for the overall decrease. Here we contribute to a better understanding of population declines by comparing foraging movements of satellite tracked adult gulls in three geographical areas of Finland (West, South, and East) that differ in their population trends. Our analysis examines potential differences and preferences in the feeding site behaviour of adult gulls. Our comparison of the three geographical areas showed that nLBBGs preferred feeding at fur farms in West Finland, waste dumps in South Finland, and lakes and fields in East Finland. We found individual gulls of this purportedly generalist species to be highly specialised in their foraging behaviour, particularly those that might be associated with their survival probabilities. We hypothesise that differences in foraging behaviour and food availability during the breeding season are partially responsible for differences in demographic trends between populations. Specifically, we identify potential local conservation problems such as shooting in birds visiting fur farms. Our data suggest that the effective conservation and management of endangered nLBBGs could be aided by simple actions in the breeding areas in addition to better protection throughout the annual movement cycle.

Mercury in Feathers and Blood of Gulls from the Southern Baltic Coast, Poland

Gulls were assessed as sentinels of contamination in the coastal zone of the Southern Baltic, research material being obtained from dead birds collected on Polish beaches and near fishing ports in 2009–2012. In feathers and blood of four gull species: herring gull (Larus argentatus), common gull (Larus canus), black-headed gull (Chroicocephalus ridibundus), and great black-backed gull (Larus marinus), concentration of total mercury (HgT) was assayed, taking into account the type of feathers, sex, and age. Stable isotopes (δ15N, δ13C) were used as tracers of trophic position in the food web. In the study, feathers and blood were compared as non-invasive indicators of alimentary exposure introducing mercury into the system. In order to do that, the correlations between mercury concentrations in the blood, feathers, and the birds’ internal tissues were examined. The strongest relations were observed in the liver for each species R2Common Gull = 0.94, p = 0.001; R2Black-headed Gull = 0.89, p = 0.001; R2Great Black-backed Gull = 0.53, p = 0.001; R2Herring Gull = 0.78, p = 0.001. While no correlation was found with feathers, only developing feathers of juvenile herring gulls were found to be a good indicator immediate of exposure through food (R2muscle = 0.71, p = 0.001; R2kidneys = 0.73, p = 0.001; R2heart = 0.89, p = 0.001; R2lungs = 0.86, p = 0.001; R2brain = 0.83, p = 0.001). Additionally, based on studies of herring gull primary feathers, decrease of mercury concentration in the diet of birds over the last two decades is also discussed.

Flexibility of habitat use in novel environments: insights from a translocation experiment with lesser black-backed gulls.

Being faced with unknown environments is a concomitant challenge of species' range expansions. Strategies to cope with this challenge include the adaptation to local conditions and a flexibility in resource exploitation. The gulls of the Larus argentatus-fuscus-cachinnans group form a system in which ecological flexibility might have enabled them to expand their range considerably, and to colonize urban environments. However, on a population level both flexibility and local adaptation lead to signatures of differential habitat use in different environments, and these processes are not easily distinguished. Using the lesser black-backed gull (Larus fuscus) as a system, we put both flexibility and local adaptation to a test. We compare habitat use between two spatially separated populations, and use a translocation experiment during which individuals were released into novel environment. The experiment revealed that on a population-level flexibility best explains the differences in habitat use between the two populations. We think that our results suggest that the range expansion and huge success of this species complex could be a result of its broad ecological niche and flexibility in the exploitation of resources. However, this also advises caution when using species distribution models to extrapolate habitat use across space.

How Displaced Migratory Birds Could Use Volatile Atmospheric Compounds to Find Their Migratory Corridor: A Test Using a Particle Dispersion Model.

Olfaction represents an important sensory modality for navigation of both homing pigeons and wild birds. Experimental evidence in homing pigeons showed that airborne volatile compounds carried by the winds at the home area are learned in association with wind directions. When displaced, pigeons obtain information on the direction of their displacement using local odors at the release site. Recently, the role of olfactory cues in navigation has been reported also for wild birds during migration. However, the question whether wild birds develop an olfactory navigational map similar to that described in homing pigeons or, alternatively, exploit the distribution of volatile compounds in different manner for reaching the goal is still an open question. Using an interdisciplinary approach, we evaluate the possibilities of reconstructing spatio-temporally explicit aerosol dispersion at large spatial scales using the particle dispersion model FLEXPART. By combining atmospheric information with particle dispersion models, atmospheric scientists predict the dispersion of pollutants for example, after nuclear fallouts or volcanic eruptions or wildfires, or in retrospect reconstruct the origin of emissions such as aerosols. Using simple assumptions, we reconstructed the putative origin of aerosols traveling to the location of migrating birds. We use the model to test whether the putative odor plume could have originated from an important stopover site. If the migrating birds knew this site and the associated plume from previous journeys, the odor could contribute to the reorientation towards the migratory corridor, as suggested for the model scenario in displaced Lesser black-backed gulls migrating from Northern Europe into Africa.

Flap or soar? How a flight generalist responds to its aerial environment.

The aerial environment is heterogeneous in space and time and directly influences the costs of animal flight. Volant animals can reduce these costs by using different flight modes, each with their own benefits and constraints. However, the extent to which animals alter their flight modes in response to environmental conditions has rarely been studied in the wild. To provide insight into how a flight generalist can reduce the energetic cost of movement, we studied flight behaviour in relation to the aerial environmental and landscape using hundreds of hours of global positioning system and triaxial acceleration measurements of the lesser black-backed gull (Larus fuscus). Individuals differed largely in the time spent in flight, which increased linearly with the time spent in flight at sea. In general, flapping was used more frequently than more energetically efficient soaring flight. The probability of soaring increased with increasing boundary layer height and time closer to midday, reflecting improved convective conditions supportive of thermal soaring. Other forms of soaring flight were also used, including fine-scale use of orographic lift. We explore the energetic consequences of behavioural adaptations to the aerial environment and underlying landscape and implications for individual energy budgets, foraging ecology and reproductive success.This article is part of the themed issue 'Moving in a moving medium: new perspectives on flight'.