Many established models of animal foraging assume that individuals are ecologically equivalent. However, it is increasingly recognized that populations may comprise individuals who differ ...consistently in their diets and foraging behaviors. For example, recent studies have shown that individual foraging site fidelity (IFSF, when individuals consistently forage in only a small part of their population's home range) occurs in some colonial breeders. Short-term IFSF could result from animals using a win-stay, lose-shift foraging strategy. Alternatively, it may be a consequence of individual specialization. Pelagic seabirds are colonial central-place foragers, classically assumed to use flexible foraging strategies to target widely dispersed, spatiotemporally patchy prey. However, tracking has shown that IFSF occurs in many seabirds, although it is not known whether this persists across years. To test for long-term IFSF and to examine alternative hypotheses concerning its cause, we repeatedly tracked 55 Northern Gannets (
Morus bassanus
) from a large colony in the North Sea within and across three successive breeding seasons. Gannets foraged in neritic waters, predictably structured by tidal mixing and thermal stratification, but subject to stochastic, wind-induced overturning. Both within and across years, coarse to mesoscale (tens of kilometers) IFSF was significant but not absolute, and foraging birds departed the colony in individually consistent directions. Carbon stable isotope ratios in gannet blood tissues were repeatable within years and nitrogen ratios were also repeatable across years, suggesting long-term individual dietary specialization. Individuals were also consistent across years in habitat use with respect to relative sea surface temperature and in some dive metrics, yet none of these factors accounted for IFSF. Moreover, at the scale of weeks, IFSF did not decay over time and the magnitude of IFSF across years was similar to that within years, suggesting that IFSF is not primarily the result of win-stay, lose-shift foraging. Rather, we hypothesize that site familiarity, accrued early in life, causes IFSF by canalizing subsequent foraging decisions. Evidence from this and other studies suggests that IFSF may be common in colonial central-place foragers, with far-reaching consequences for our attempts to understand and conserve these animals in a rapidly changing environment.
The oceanographic drivers of marine vertebrate habitat use are poorly understood yet fundamental to our knowledge of marine ecosystem functioning. Here, we use composite front mapping and ...high-resolution GPS tracking to determine the significance of mesoscale oceanographic fronts as physical drivers of foraging habitat selection in northern gannets Morus bassanus. We tracked 66 breeding gannets from a Celtic Sea colony over 2 years and used residence time to identify area-restricted search (ARS) behaviour. Composite front maps identified thermal and chlorophyll-a mesoscale fronts at two different temporal scales—(i) contemporaneous fronts and (ii) seasonally persistent frontal zones. Using generalized additive models (GAMs), with generalized estimating equations (GEE-GAMs) to account for serial autocorrelation in tracking data, we found that gannets do not adjust their behaviour in response to contemporaneous fronts. However, ARS was more likely to occur within spatially predictable, seasonally persistent frontal zones (GAMs). Our results provide proof of concept that composite front mapping is a useful tool for studying the influence of oceanographic features on animal movements. Moreover, we highlight that frontal persistence is a crucial element of the formation of pelagic foraging hotspots for mobile marine vertebrates.
Sexual segregation, common in many species, is usually attributed to intra-specific competition or habitat choice. However, few studies have simultaneously quantified sex-specific foraging behaviour ...and habitat use. We combined movement, diving, stable isotope and oceanographic data to test whether sexual segregation in northern gannets Morus bassanus results from sex-specific habitat use. Breeding birds foraging in a seasonally stratified shelf sea were tracked over 3 consecutive breeding seasons (2010–2012). Females made longer trips, foraged farther offshore and had lower δ13C values than males. Male and female foraging areas overlapped only slightly. Males foraged more in mixed coastal waters, where net primary production (NPP) was relatively high (>3 mg C m−2 d−1) and sea-surface temperature (SST) was relatively low (<10°C). Males also tended to use areas with higher SSTs (>15°C) more than females, possibly as a consequence of foraging in productive mixed waters over offshore banks. Females foraged most frequently in stratified offshore waters, of intermediate SST (12–15°C), but exhibited no consistent response to NPP. Sex-specific differences in diving behaviour corresponded with differences in habitat use: males made more long and deep U-shaped dives. Such dives were characteristic of inshore foraging, whereas shorter and shallower V-shaped dives occurred more often in offshore waters. Heavier birds attained greater depths during V-shaped dives, but even when controlling for body mass, females made deeper V-shaped dives than males. Together, these results indicate that sexual segregation in gannets is driven largely by habitat segregation between mixed and stratified waters, which in turn results in sex-specific foraging behaviour and dive depths.
Consistent intra-population variability in foraging behaviour is found among a wide range of taxa. Such foraging specialisations are common among marine vertebrates, yet it is not clear how ...individuals repeatedly locate prey or foraging sites at ocean-wide scales. Using GPS and time-depth loggers we studied the fine-scale foraging behaviour of central-place northern gannets Morus bassanus at two large colonies. First, we estimated the degree of consistency in individual foraging routes and sites across repeated trips. Second, we tested for individual differences in searching behaviour in response to environmental covariates using reaction norms, estimated from mixed effect models. Adult gannets tracked over multiple foraging trips showed repeatable between-individual differences in terminal points and departure angles of foraging trips, but low repeatability in trip duration and trip length. Importantly, individual birds showed highly repeatable dive locations, with consistently different environmental conditions (such as copepod abundance), suggesting a high degree of foraging site specialisation. Gannets also showed between-individual differences in searching behaviour along environmental gradients, such that individuals intensified searching under different conditions. Together these results suggest that widespread individual foraging consistency may represent specialisation and be linked with individual responses to environmental conditions. Such divergent searching behaviour could provide a mechanism by which consistent foraging behaviour arises and is maintained among animals that forage across large spatial scales.
Northern gannets (Morus bassanus) have been ranked as one of the most vulnerable species in terms of collision with offshore wind farm (OWF) turbines, and strong avoidance of OWFs has been documented ...for this species. Gannets increasingly encounter OWFs within the ranges of their largest breeding colonies along the European coasts. However, information on their actual reactions to OWFs during the breeding season is lacking. We investigated the possible effects of OWFs located 23–35 km north of the colony on Helgoland in the southern North Sea on breeding gannets. GPS tags were applied to 28 adult gannets breeding on Helgoland for several weeks over 2 years. Most gannets (89%) predominantly avoided the OWFs in both years, but 11% frequently entered them when foraging or commuting between the colony and foraging areas. Flight heights inside the OWFs were close to the rotor-blade zone, especially for individuals predominantly avoiding the OWFs. Gannets preferred distances of 250–450 m to the turbines when being inside the OWF. A point process modelling approach revealed that the gannets resource selection of the OWF area compared with the surroundings (outside OWF = up to 15 km from the OWF border) was reduced by 21% in 2015 and 37% in 2016. This study provides the first detailed characterisation of individual reactions of gannets to OWFs during the breeding season and one of the first comprehensive studies of OWF effects on this species based on telemetry data. The documented effects need to be considered during the planning processes for future OWFs, especially those located close to large seabird breeding colonies.
•Offshore Wind Farms (OWFs) negatively affect northern gannets (Morus bassanus) during the breeding season.•89% of GPS-tracked gannets predominantly avoided the OWFs, few individuals frequently entered them.•The gannets resource selection of the OWFs compared with the surroundings was reduced by 21% in 2015 and by 37% in 2016.•Gannets preferred distances of 250-450 m to the turbines when being inside the OWF.•This is the first detailed characterisation of individual reactions of northern gannets to OWFs during the breeding season.
During 2021 and 2022 High Pathogenicity Avian Influenza (HPAI) killed thousands of wild birds across Europe and North America, suggesting a change in infection dynamics and a shift to new hosts, ...including seabirds. Northern Gannets Morus bassanus appeared to be especially severely impacted, but a detailed account of the data available is required to help understand how the HPAI virus (HPAIV) spread across the meta‐population, and the ensuing demographic consequences. Accordingly, we analyse information on confirmed and suspected HPAIV outbreaks across most North Atlantic Gannet colonies and, for the largest colony (Bass Rock, UK), provide impacts on population size, breeding success, and preliminary results on apparent adult survival and serology. Unusually high numbers of dead Gannets were first noted at colonies in Iceland during April 2022. Outbreaks in May occurred in many Scottish colonies, followed by colonies in Canada, Germany and Norway. By the end of June, outbreaks had occurred in colonies in Canada and the English Channel. Outbreaks in 12 UK and Ireland colonies appeared to follow a clockwise pattern with the last infected colonies recorded in late August/September. Unusually high mortality was recorded at 40 colonies (75% of global total colonies). Dead birds testing positive for HPAIV H5N1 were associated with 58% of these colonies. At Bass Rock, the number of occupied nest‐sites decreased by at least 71%, breeding success declined by c. 66% compared with the long‐term UK mean and the resighting of marked individuals suggested that apparent adult survival between 2021 and 2022 could have been substantially lower than the preceding 10‐year average. Serological investigation detected antibodies specific to H5 in apparently healthy birds, indicating that some Gannets recover from HPAIV infection. Further, most of these recovered birds had black irises, suggestive of a phenotypic indicator of previous infection. Untangling the impacts of HPAIV infection from other challenges faced by seabirds is key to establishing effective conservation strategies for threatened seabird populations as the likelihood of further epizootics increases, due to increasing habitat loss and the industrialization of poultry production.
Unlike records of plastic ingestion and entanglement in seabirds which date back to the 1960s, the literature regarding debris in bird nests is comparatively limited. It is important to identify ...standardised methods early so that data are collected in a consistent manner, ensuring that future studies can be comparable. Here, we outline a method that can be applied to photographs for estimating the proportion of visible debris at the surface of a nest. This method uses ImageJ software to superimpose a grid onto a photograph of a nest/s. The number of cells with and without debris are then counted. Our proposed method is repeatable, straightforward, and accessible. We optimised the method to estimate the level of visible debris in Northern Gannet (Morus bassanus) nests, however, with some modification (i.e., adjustment of grid cell size), it could be applied to other seabird species, and terrestrial birds, that incorporate debris within nests.
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•New method for estimating the proportion of debris in bird nests from photographs•Method is standardised, repeatable, and accessible.•Lends itself to community science, as photographs of colonies can be crowd-sourced.•Trends in pollution can be assessed if method is used in future nest monitoring.
Litter are ubiquitous and increasing in the coastal and marine environments. Entanglement with litter is one of the principal causes of mortality in seabirds, but the population-level consequences ...are unknown. Currently, all seabirds collect litter for nesting material. Northern Gannets are not the exception and there are several cases where elevated percentages of polymers are part of the life cycle of gannets, especially during breeding. This baseline paper presents an analysis of litter content and its related impacts on the two gannet nests located in South France (Carry-Le-Rouet) and Northwest Italy (Portovenere) from 2017 to 2019. 654 items from both gannet nests were collected with 277 items (42%) being of natural origin, while 377 items (58%) were litter. Most of the nesting material was nautical cordage, which appears to be used preferentially. A more restrictive litter management regulation must be adopted to reduce litter generation from fishing/aquaculture-related activities.
•Analysis of litter content of two Mediterranean gannet nests in France and Italy•Litter always was found in both nests, and its impact on the birds highlighted.•Portovenere was the most polluted in terms of litter percentage in the nest.•Four typologies of polymeric items accounted for 73% of all litter in both nests.•Restrictive management regulation to reduce litter from fishing/aquaculture
Disease outbreaks can drastically disturb the environment of surviving animals, but the behavioural, ecological, and epidemiological consequences of disease-driven disturbance are poorly understood. ...Here, we show that an outbreak of High Pathogenicity Avian Influenza Virus (HPAIV) coincided with unprecedented short-term behavioural changes in Northern gannets (Morus bassanus). Breeding gannets show characteristically strong fidelity to their nest sites and foraging areas (2015-2019; n = 120), but during the 2022 HPAIV outbreak, GPS-tagged gannets instigated long-distance movements beyond well-documented previous ranges and the first ever recorded visits of GPS-tagged adults to other gannet breeding colonies. Our findings suggest that the HPAIV outbreak triggered changes in space use patterns of exposed individuals that amplified the epidemiological connectivity among colonies and may generate super-spreader events that accelerate disease transmission across the metapopulation. Such self-propagating transmission from and towards high density animal aggregations may explain the unexpectedly rapid pan-European spread of HPAIV in the gannet.
Abstract
Fisheries produce large amounts of waste, providing food subsidies for scavengers. Discards influence seabird movement, demography and community structure, but little is known about ...seabird–fishery interactions where discarding is banned. Here, we investigate how northern gannets Morus bassanus respond to fishing vessels in Iceland, where discarding commercial species is illegal, but birds may still access bait, offal, or catch. We GPS-tracked 82 foraging trips for 36 breeding gannets from two colonies (Skrúður and Hellisey) and obtained time-matched vessel locations. We classified bird behaviour using Hidden Markov Models and then tested the effect of vessel distance on behavioural state-switching using multi-state Markov models. Fishing vessels were present during 94% of foraging trips. However, the likelihood of gannets switching from travelling to foraging was unaffected by vessel proximity, regardless of gear type or activity. When encountering vessels, gannets rarely foraged but instead were more likely to continue travelling. When controlling for population size, gannet foraging trips at both colonies were shorter than expected, suggesting favourable conditions. The lack of behavioural responses to vessels among Icelandic gannets is likely driven by the discard ban and availability of pelagic fishes. Our findings have implications for understanding bycatch risk and the consequences of discard reforms.
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