Advancements in biologging technology allow terabytes of data to be collected that record the location of individuals but also their direction, speed and acceleration. These multi-stream data sets allow researchers to infer movement and behavioural patterns at high spatiotemporal resolutions and in turn quantify fine-scale changes in state along with likely ecological causes and consequences. The scope offered by such data sets is increasing and there is potential to gain unique insights into a suite of ecological and life history phenomena. We use multi-stream data from global positioning system (GPS) and accelerometer (ACC) devices to quantify breeding events remotely in an Arctic breeding goose. From a training set of known breeders we determine the movement and overall dynamic body acceleration patterns indicative of incubation and use these to classify breeding events in individuals with unknown reproductive status. Given that researchers are often constrained by the amount of biologging data they can collect due to device weights, we carry out a sensitivity analysis. Here we explore the relative merits of GPS vs ACC data and how varying the temporal resolution of the data affects the accuracy of classifying incubation for birds. Classifier accuracy deteriorates as the temporal resolution of GPS and ACC are reduced but the reduction in precision (false positive rate) is larger in comparison to recall (false negative rate). Precision fell to 94.5%, whereas recall didn’t fall below 98% over all sampling schedules tested. Our data set could have been reduced by c.95% while maintaining precision and recall > 98%. The GPS-only classifier generally outperformed the ACC-only classifier across all accuracy metrics but both performed worse than the combined GPS and ACC classifier. GPS and ACC data can be used to reconstruct breeding events remotely, allowing unbiased, 24-h monitoring of individuals. Our resampling-based sensitivity analysis of classifier accuracy has important implications with regards to both device design and sampling schedules for study systems, where device size is constrained. It will allow researchers with similar aims to optimize device battery, memory usage and lifespan to maximise the ability to correctly quantify life history events.

Lead is a toxic heavy metal that when ingested can cause death or sub‐lethal fitness effects. Despite its toxicity, it is still widely used in recreational and management shooting globally. To reduce the impacts of lead on wildfowl, recent European Union legislation has banned the use of lead shot in and around wetlands from 2023. Understanding the effectiveness of such mitigation is vital to inform future policy. On Islay, Scotland, the licensed shooting of Barnacle Geese Branta leucopsis to reduce agricultural damage has adhered to the ban on use of lead shot over Ramsar‐designated wetlands legislated in Scotland in 2004. On average 2380 lead cartridges were fired annually between 2005 and 2020 outside designated wetlands, where Barnacle Geese and other wildfowl forage. From faecal samples, it is possible to infer whether birds have ingested lead and are therefore potentially suffering from lead poisoning. After sampling faeces from Barnacle Geese (n = 193) and Greenland White‐fronted Geese Anser albifrons flavirostris (n = 150) we found only four (1.2%) faecal samples with elevated lead levels that may be indicative of lead shot ingestion. Further post‐mortem examinations (n = 102 Barnacle Geese only) and X‐ray of live birds (n = 293) revealed similarly low levels of shot ingestion in both species (post‐mortem < 4%, and X‐ray < 2%), corroborating findings from faecal sample analysis. When subsequently accounting for limited shot retention time within individuals, the proportion of each population ingesting a single lead shot over a winter was estimated at a maximum of 9.4% (Barnacle Geese) and 16.8% (White‐fronted Geese). We propose that high compliance with the ban on using lead shot over wetlands because of carefully controlled shooting management on Islay has led to relatively low instantaneous ingestion rates, probably resulting in minimal lead poisoning mortality. However, ingestion was not eliminated and the potential fitness effect of chronic lead poisoning in both goose populations therefore persists, although use of lead shot in organized shooting has subsequently been discontinued. Recent European Union bans on lead shot use over wetlands may reduce lead ingestion in waterfowl if compliance rates are high, but as foraging often occurs outside wetlands (as in this study), further restrictions including use on other key foraging sites may help to further mitigate the risk of lead poisoning in waterfowl.

Vagrancy, where individuals occur outside of known population distributions, is a poorly understood ecological phenomenon. It can however be a key driver of site colonisation and range expansion. Evidence is emerging that presumed vagrant Siberian passerines in Western Europe, e.g. Richard’s Pipits Anthus ricardii, are colonists, with geolocator-tracked individuals returning to breed in Siberia after wintering in Western Europe. As such, ‘vagrancy’ patterns in these taxa could provide a model system to understand large-scale range shifts. For example, determining the origins of vagrant individuals and linking these to morphology and arrival date could help to identify the potential drivers of range dynamics. Here, we investigate the origins of vagrant Yellow-browed Warblers Phylloscopus inornatus (a migratory Siberian breeding passerine) in Western Europe by analysing stable hydrogen isotopes, morphology and phenology. We measure the isotopic patterns of feathers grown on the breeding grounds and their relation to those from two sub-species of Common Chiffchaff Phylloscopus collybita. We found that Yellow-browed Warblers have similar hydrogen isotopic signatures (δ2H) to the Siberian sub-species of Common Chiffchaff Phylloscopus collybita tristis and δ2H values did not overlap with those from the European nominate race of Common Chiffchaff Phylloscopus collybita collybita. There was weak evidence that variation in δ2H values was linked to differences in migratory distances in sampled Yellow-browed Warblers. The variation in δ2H values for Yellow-browed Warblers was similar to Chiffchaffs of the collybita and tristis sub-species. This suggests that Yellow-browed Warblers in Western Europe may originate from a relatively broad-front and not exclusively from an expanding western breeding range margin. It is unclear if vagrant Yellow-browed Warblers in Western Europe make viable return migrations to Siberia. If they are, the subset of individuals that become colonists could help us understand how vagrancy drives biogeographic processes, such as the establishment of novel migration routes.