Gulls as potential sentinels for urban litter: combining nest and GPS-tracking information.

The production of urban waste has increased in the past decades leading to its mishandling. The effects on public health, economy, and wildlife that waste mismanagement can have are forcing governments to increase their efforts in detecting and mitigating the presence of waste. Identifying and monitoring sentinel species to assess the presence of urban litter could be a cost-effective option. Thus, analyzing the nest composition of yellow-legged gulls from an urban population inhabiting a very high populated city (Barcelona, Spain), and combining this information with accurate GPS tracking data, provides a potential tool to monitor the presence of marine and terrestrial litter over time. The results revealed the highest presence of debris in the nests of a seabird ever recorded. All the nests examined contained anthropogenic waste, with plastic items present in all of them. Crossing the nest composition with GPS tracking movements confirmed that the waste to build the nests was collected in the urban area and not in other environments surrounding the city. Then, the nest waste composition may be a good indicator of waste mismanagement and advise the municipalities to improve waste management and recycling strategies for the different types of litter. Using gulls breeding in cities as sentinel species and, in particular, the study of their nest composition, may provide essential data to decision-making stakeholders to adopt a One Health approach and help improve not only the environment's health but also the health of those who live in it.

Sources of persistent organic pollutants and their physiological effects on opportunistic urban gulls.

Urbanization is associated with drastic shifts in biodiversity. While some species thrive in urban areas, the impact of inhabiting these human-altered environments on organism physiology remains understudied. We investigated how exposure to polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) affects the physiology of yellow-legged gulls (Larus michahellis) inhabiting a densely populated, industrialized city. We analyzed blood samples from 50 gulls (20 immatures and 30 adults) and assessed 27 physiological parameters and biomarkers related to xenobiotic protection, health, and feeding habits in these same individuals. We also tracked the movements of 25 gulls (15 immatures and 10 adults) to identify potential sources of persistent organic pollutants (POPs). Both adult and immature gulls primarily inhabited urban areas, followed by marine habitats. Immature gulls spent more time in freshwater, landfills, and agricultural areas. Bioaccumulated ΣPCB (median = 92.7 ng g-1 ww, 1.86-592) and ΣPBDE (median = 1.44 ng g-1 ww, 0.022-9.58) showed no significant differences between age and sex groups. Notably, immature males exhibited the highest correlations with POP concentrations, particularly with the activity of carboxylesterases (CEs), suggesting a higher sensitivity than adults. These findings highlight the potential of plasmatic CEs in immature yellow-legged gulls as effective tracers of POPs exposure and effects, offering insights into the anthropogenic impacts on urban biodiversity.

A spatial analysis of urban gulls contribution to the potential spread of zoonotic and antibiotic-resistant bacteria.

Wildlife human interactions within cities are becoming more common with consequences for pathogen transmission and human health. Large gulls are opportunistic feeders, adapted to coexist with humans in urban environments, and are potential vectors for spread and transmission of pathogens, including antimicrobial-resistant bacteria. We investigated the potential role that urban gulls play in the spread and dispersal of these bacteria. We analysed 129 faecal swabs from yellow-legged gulls (Larus michahellis) of different ages (56 adults and 73 immatures) during the breeding period from three years in the highly populated city of Barcelona (northeastern Spain). Thirteen individuals tested positive for the pathogenic bacteria (Escherichia coli, Listeria monocytogenes, Campylobacter jejuni), including antibiotic-resistant strains. We modelled the potential spatial spread of pathogens using the GPS trajectories of 58 yellow-legged gulls (23 adults, 35 immature individuals), which included the thirteen individuals that tested positive for pathogenic bacteria. By overlapping the spatially explicit pathogen dispersal maps with the distribution of urban installations sensitive at risk of possible pathogen spillover (e.g. elder and medical centres, markets, food industries, kindergartens, or public water sources), we identified potential areas at risk of pathogen spillover. Pathogens may be potentially spread to municipalities beyond Barcelona city borders. The results revealed that immature gulls dispersed pathogens over larger areas than adults (maximum dispersal distances of 167 km versus 53.2 km, respectively). Recreational urban water sources were the most sensitive habitats visited by GPS-tagged gulls that tested positive, followed by schools. Combining GPS movement data with pathogen analytics allows spatially explicit maps to be generated using a One Health approach that can help urban and public health management within large cities, such as Barcelona, and identify areas used by humans that are sensitive to pathogen spillover from gulls.

Gulls living in cities as overlooked seed dispersers within and outside urban environments.

The yellow-legged gull is an opportunistic and generalist bird that has colonised urban areas, where it has found very favourable trophic resources but also causes disturbance to humans and damage to infrastructure. Here, we investigated the potential role that gulls play in the dispersal of plants in Barcelona, a highly populated city of north-eastern Spain. We analysed the stomach contents of 145 chicks collected in urban nests and reported the presence of seeds of 27 plant taxa. We then developed a plant dispersal model based on the movements of 20 GPS-tracked yellow-legged gulls breeding in the city of Barcelona. We estimated seed dispersal distances, seed shadows and percentage of seeds reaching habitats suitable for seeds regurgitated in pellets and those excreted in faeces. Seven of the 27 plant taxa found in the stomachs were alien taxa to Spain. Average dispersal distances of plant seeds by gulls were around 700 m, but maximum dispersal distances reached up to 35 km. Dispersal distances and seed spatial patterns did not differ between faeces and pellet models, as most strongly depended on gull movements. About 95% of the seeds were dispersed within urban environments and between 20 and 30% reached suitable habitats for seed deposition (urban woodlands, green urban parks and urban grasslands). Urban gulls frequently dispersed seeds (including alien species) within urban habitats, both via direct consumption or via secondary dispersal after consuming granivorous birds that had ingested the seeds, such as pigeons or parakeets. Urban planning for Barcelona is based on native plant species, and thus, special attention should be paid to alien plants dispersed by birds, which could pose a risk to native biodiversity in urban ecosystems.

Persistence of single species of symbionts across multiple closely-related host species.

Some symbiont species are highly host-specific, inhabiting only one or a very few host species, and typically have limited dispersal abilities. When they do occur on multiple host species, populations of such symbionts are expected to become genetically structured across these different host species, and this may eventually lead to new symbiont species over evolutionary timescales. However, a low number of dispersal events of symbionts between host species across time might be enough to prevent population structure and species divergence. Overall, processes of evolutionary divergence and the species status of most putative multi-host symbiont systems are yet to be investigated. Here, we used DNA metabarcoding data of 6,023 feather mites (a total of 2,225 OTU representative sequences) from 147 infracommunities (i.e., the assemblage consisting of all mites of different species collected from the same bird host individual) to investigate patterns of population genetic structure and species status of three different putative multi-host feather mite species Proctophyllodes macedo Vitzthum, 1922, Proctophyllodes motacillae Gaud, 1953, and Trouessartia jedliczkai (Zimmerman, 1894), each of which inhabits a variable number of different closely related wagtail host species (genus Motacilla). We show that mite populations from different host species represent a single species. This pattern was found in all the mite species, suggesting that each of these species is a multi-host species in which dispersal of mites among host species prevents species divergence. Also, we found evidence of limited evolutionary divergence manifested by a low but significant level of population genetic structure among symbiont populations inhabiting different host species. Our study agrees with previous studies showing a higher than expected colonization opportunities in host-specific symbionts. Indeed, our results support that these dispersal events would allow the persistence of multi-host species even in symbionts with limited dispersal capabilities, though additional factors such as the geographical structure of some bird populations may also play a role.

What makes Alpine swift ascend at twilight? Novel geolocators reveal year-round flight behaviour.

ABSTRACT: Studying individual flight behaviour throughout the year is indispensable to understand the ecology of a bird species. Recent development in technology allows now to track flight behaviour of small long-distance bird migrants throughout its annual cycle. The specific flight behaviour of twilight ascents in birds has been documented in a few studies, but only during a short period of the year, and never quantified on the individual level. It has been suggested that twilight ascents might be a role in orientation and navigation. Previous studies had reported the behaviour only near the breeding site and during migration. We investigated year-round flight behaviour of 34 individual Alpine swifts (Apus melba) of four different populations in relation to twilight ascents. We recorded twilight ascents all around the year and found a twofold higher frequency in ascents during the non-breeding residence phase in Africa compared to all other phases of the year. Dawn ascents were twice as common as dusk ascents and occurred mainly when atmospheric conditions remained stable over a 24-h period. We found no conclusive support that twilight ascents are essential for recalibration of compass cues and landmarks. Data on the wing flapping intensity revealed that high activity at twilight occurred more regularly than the ascents. We therefore conclude that alpine swift generally increase flight activity-also horizontal flight-during the twilight period and we suppose that this increased flight activity, including ascents, might be part of social interactions between individuals. SIGNIFICANCE STATEMENT: Year-round flight altitude tracking with a light-weight multi-sensor tag reveals that Alpine swifts ascend several hundred meters high at twilight regularly. The reason for this behaviour remains unclear and the low-light conditions at this time of the day preclude foraging as a possibility. The frequency and altitude of twilight ascents were highest during the non-breeding period, intermediate during migration and low for active breeders during the breeding phase. We discuss our findings in the context of existing hypotheses on twilight ascent and we propose an additional hypothesis which links twilight ascent with social interaction between flock members. Our study highlights how flight behaviour of individuals of a migratory bird species can be studied even during the sparsely documented non-breeding period.

Septicemic salmonellosis caused by Salmonella Hessarek in wintering and migrating Song Thrushes (Turdus philomelos) in Spain.

We investigated two mortality events in wintering and migrating Song Thrushes (Turdus philomelos) in Catalonia, northeastern Spain in 2009 and 2010. Both episodes occurred in late February to mid-March during the spring migration. Salmonellosis produced by the serotype Salmonella enterica subsp. enterica serotype Hessarek (S. Hessarek) was identified as the cause of death in both episodes. Poor body condition, marked splenomegaly, and microscopic disseminated intravascular coagulation with numerous intravascular and tissular bacteria were the most consistent findings. Macro-restriction profiling by pulsed-field gel electrophoresis (PFGE) using XbaI was performed for epidemiologic typing of the S. Hessarek isolates. Two clusters were discernible, that are possibly related, with a similarity of 82.8%. Analysis comparing pectoral muscle and subcutaneous fat scores from the Song Thrushes that died from S. Hessarek with those from healthy Song Thrushes from nearby areas during 2009 and 2010 suggest that poor body condition was associated with the S. Hessarek infection.