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Aim: Large-scale space use and geographical ranges of animal populations are central topics in ecology. Whereas they are traditionally often based on citizen science or professional sightings of (marked) animals, recent technological developments have presented GPS tracking as an alternative method for inferring space use at the population level. Tracking devices are however much more expensive than traditional marks, rings or collars, leading to datasets that typically consist of much fewer individuals. We study how GPS tracking data and citizen science resighting data of marked individuals compare as alternative sources for inferring range size. Location: Northwestern Europe. Taxon: Bewick's swan (Cygnus columbianus bewickii). Methods: We calculated Bewick's swan range sizes from a wealth of GPS tracking and resighting data during winter, the period of the year when both data types are abundant. We examined the effect of the number of individuals and the total number of spatial records (either resightings or GPS fixes) on the inferred range size. Moreover, we combined GPS tracks with resightings of the same individuals to empirically determine spatial variation in resighting rates. Results: Tracked individuals generated records across an area 1.5–2 times larger than individuals that were merely resighted. Moreover, any given number of daily GPS records (rather than GPS-tracked individuals) yielded an area 1.5 times larger than that same number of resighting records. A small number of GPS-tracked individuals (~20) was sufficient to yield a larger range size compared to much higher numbers of resighted individuals (well over 400). Spatial variation in resighting rates corresponded well with the differences in range size from the two data types, indicating that spatial gaps in observer effort can hamper range estimations. Main Conclusions: When combined with resighting data, tracking data can be used to indicate areas of low observer effort. Although citizen scien

General context: Gulls ingest plastic and other litter while foraging in open landfills, because organic matter is mixed with other debris. Therefore, gulls are potential biovectors of plastic pollution into natural habitats, especially when they concentrate in wetlands for roosting. Novelty: We quantified, for the first time, the flow of plastic and other anthropogenic debris from open landfills to a natural lake via the movement of gulls. We focused on Fuente de Piedra, an inland closed-basin lake in Spain that is internationally important for biodiversity. Methodology: In 2022, we sampled gull pellets regurgitated in the lake by lesser black-backed gulls Larus fuscus that feed on landfills, as well as their faeces, then characterized and quantified debris particles of ≥0.5 mm. By combining GPS and census data from 2010 to 2022, together with plastic quantification based on FTIR-ATR analysis, we estimated the average annual deposition of plastic and other debris by the wintering gull population into the lake. Main results: 86 % of pellets contained plastics, and 94 % contained other debris such as glass and textiles. Polyethylene (54 %), polypropylene (11.5 %) and polystyrene (11.5 %) were the main plastic polymers. An estimated annual mean of 400 kg of plastics were moved by gulls into the lake. Only 1 % of plastic mass was imported in faeces. Discussion: Incorporating the biovectoring role of birds can provide a more holistic view of the plastic cycle and waste management. Biovectoring is predictable in sites worldwide where gulls and other waterbirds feed in landfills and roost in wetlands. We discuss bird deterrence and other ways of mitigating debris leakage into aquatic ecosystems

A wide variety of attachment techniques have been used to track birds with electronic tags,with glue, tape, leg rings, neck collars and harnesses being the most common methods. Ingeneral, the choice of attachment method should strive to minimize tagging effects, butensure that sufficient data are collected to address the research question at hand. The aim ofour study was to develop and evaluate tag attachment methods to track Sandwich TernsThalasseus sandvicensisduring the last part of the incubation and the chick-rearing period ofone breeding season. Tag attachments had to stay on for the duration of the chick-rearingperiod (5–6 weeks) and be non-restraining andflexible, but strong enough to withstand theforces and submersion associated with their plunge-diving foraging technique. Wefirstexperimentally tested the durability offlexible material under various environmental condi-tions with the aim of developing a self-releasing harness. Then, infield studies, we comparedthree different attachment methods on terns during the breeding seasons, attaching tags todorsal feathers using (1) tape, (2) glue or (3) a newly developed harness made specificallyfor short-term deployments of one chick-rearing period and constructed from degradablematerial. Assessment of the performance of attachment methods was based on retentiontime of the loggers and on annual survival rates of tagged individuals in comparison withnon-tagged individuals. The use of tape and glue led to premature loss of tags (median mini-mum retention time (range) of 3 (1–4) days and 15 (5–26) days, respectively), whereas theself-releasing harness had a median minimum retention time of 42 (18–91) days, which issufficient to track Sandwich Terns during the entire chick-rearing period. The apparentannual survival of birds tagged using glue or tape did not differ from that observed in non-tagged control birds. In contrast, birdsfitted with the self-releasing harnesses might haveexperienced a lower survival rate than

Fireworks are important elements of celebrations globally, but little is known about their effects on wildlife. The synchronized and extraordinary use of fireworks on New Year's Eve triggers strong flight responses in birds. We used weather radar and systematic bird counts to quantify how flight responses differed across habitats and corresponding bird communities, and determined the distance-dependence of this relationship. On average, approximately 1000 times as many birds were in flight on New Year's Eve than on other nights. We found that fireworks-related disturbance decreased with distance, most strongly in the first five kilometers, but overall flight activity remained elevated tenfold at distances up to about 10 km. Communities of large-bodied species displayed a stronger response than communities of small-bodied species. Given the pervasive nature of this disturbance, the establishment of large fireworks-free zones or centralizing fireworks within urban centers could help to mitigate their effects on birds. Conservation action should prioritize avian communities with the most disturbance-prone, large-bodied bird species.

The population increase of Lesser Black-backed Gulls in The Netherlands triggered investigations into life-history, migratory movements and foraging ecology during 16 years of nest-monitoring, colour-ringing and GPS-tracking on the island of Texel (Wadden Sea). The main objective was to obtain comprehensive ecological data on breeding performance within the context of the annual cycle, shifts in resources, prey types and habitat use. Migration strategies ranged from short- (France, England), medium- (Portugal, Spain) to long-distance (NW Africa), utilising marine, coastal or terrestrial, region-specific resources. Young birds travelled on average further than older individuals. Strong within-colony philopatry was found, this was strongest in males. Assessments of mate-fidelity indicated serial, social monogamy. Unexpectedly, given increasing population trends when the study commenced, fledging rates were low and declining egg volumes, smaller hatchlings, declining mass at fledging and high levels of cannibalism indicated structural food stress. Fledgling mass was well below that of chicks in historical studies, suggesting insufficient provisioning. Breeding was highly synchronised and early nesters fledged more young than late pairs. The onset of breeding was significantly delayed over the years, chick depredation rates declined, overall breeding success became more variable. Marine, urban and rural habitats, mostly within 80 km from the colony were used for foraging. Marine prey, mostly fisheries discards, formed the principal prey for most birds, supplemented with food found in agricultural areas. Human waste was found in only 7% of prey samples. A consistent decline of marine prey (in line with developing restrictions in fisheries), combined with signals pointing at food stress, suggests that the population is unable to boost reproductive success with currently existing foraging opportunities.

Contains the tracking data used to run both the daily autumn movement and mean midwinter distance analyses, including midwinter temperature data and some customized functions that are needed., Contains the tracking data used to run both the daily autumn movement and mean midwinter distance analyses, including midwinter temperature data and some customized functions that are needed.