ABSTRACT Capsule Field plots provisioned with a supplementary seed mix during summer attracted European Turtle Doves and other farmland birds, and exhibited only a low incidence of the parasite Trichomonas gallinae. Aims To test whether Turtle Doves and other granivorous birds use field plots provided with supplementary seed, and whether use of these plots increased exposure to T. gallinae. Methods Supplementary seed mix was provided at two rates (3 and 6 kg per 250 m2 plot) weekly at 37 sites in the spring and summer of 2016 and 2017. Provisioned plots, and similar (but unprovisioned) control areas, were surveyed for Turtle Doves and other birds. Soil swab samples were also taken and analysed for the presence of T. gallinae using a standard polymerase chain reaction procedure. Results Turtle Doves were much more likely to be recorded on provisioned plots than on unprovisioned control areas. Maximum counts of an aggregate of seven other granivores of conservation interest (European Greenfinch Chloris chloris, Common Linnet Linaria cannabina, Eurasian Tree Sparrow Passer montanus, House Sparrow P. domesticus, Common Reed Bunting Emberiza schoeniclus, Corn Bunting E. calandra and Yellowhammer E. citrinella) were significantly higher on provisioned plots than on control areas. Positive samples for T. gallinae were rare on provisioned plots and unprovisioned areas (eight of 474 samples across both years). Samples classified as ambiguous (due to the presence of genomic DNA that could not be definitively ascribed to T. gallinae) or positive were equally likely on provisioned plots and unprovisioned areas, but were more likely at sites where European Greenfinches were recorded. Conclusion Supplementary seed provisioning in summer can attract foraging Turtle Doves with only a low risk of exposure to T. gallinae on the feeding areas.

ABSTRACT Capsule The Goosander, a piscivorous species of duck, can be tracked using GPS tags, with initial results showing that ranging behaviour in spring differed between two river catchments in central and southern Scotland. Aims To assess the suitability of a glue-mounted attachment method for GPS tags on Goosanders, and to generate spatial data on Goosander movements. Methods 20 Goosanders were tagged under licence in two Scottish river catchments and fitted with glue-mounted GPS tracking devices. The data from the tracking devices were analysed using a Brownian bridge movement model approach to generate home range isopleths, which were used to identify linear river sections used by each individual. Results Of 20 birds tagged, 17 generated usable data. Tag retention varied from less than 24 hours to 29 days. The lengths of river used differed between the two catchments (per bird at the 95% isopleth level: mean 59.4 km, 95% CI 50.8–68.0 km for one catchment, and mean 18.6 km, 95% CI 11.4–25.9 km for the other catchment) with birds in both catchments making more extensive use of available river habitats during daylight hours. Conclusions This study shows the potential for GPS tracking technology to be used to understand the movements of a piscivorous bird species. Tag retention remains a key limitation when tracking Goosanders, due to active removal by the birds, and improvements to attachment methodology are required. This would enable tracking over a greater portion of the Goosander’s annual cycle and would further improve our understanding of the factors determining river use and feeding behaviour of piscivorous birds.

ABSTRACT Capsule The sixth national survey of breeding Hen Harriers in 2023 revealed a near-significant 20% increase in the UK and Isle of Man population since 2016, with variation between and within constituent countries. Aims To estimate the size of the breeding Hen Harrier population in the UK and Isle of Man, constituent countries, Scottish regions and the UK Special Protection Area (SPA) network for breeding Hen Harriers in 2023, and calculate population changes since 2016. Methods Surveys were conducted in all 10-km squares likely to be occupied by breeding birds in England, Northern Ireland, Wales and the Isle of Man, using standard methods. In Scotland, a stratified random selection of 10-km squares within the known breeding range was surveyed alongside squares selected by volunteers. Surveys were conducted in the UK in 2023 and Isle of Man in 2022. Results The UK and Isle of Man population was estimated at 691 territorial pairs (95% confidence limits, 593–802), a near-significant 20% increase since 2016. Populations increased by differing degrees in all countries and the Isle of Man, except in Northern Ireland where they declined. Scotland held 77% of the population with 529 (95% confidence limits, 431–640) pairs, with only tens of pairs in the other surveyed areas. Overall abundance within SPAs scarcely changed since 2016, but Scottish and Northern Irish SPAs held fewer pairs (−28% and −18%). As in 2016, most Hen Harriers were found on heather-dominated moorland. In Scotland, abundance declines on grouse-shooting moors continued between 2016 and 2023 (−23%), following a significant 67% decline between 2010 and 2016. Conclusion The 2023 survey showed a near-significant 20% increase in the UK and Isle of Man breeding Hen Harrier population since 2016. There was a substantial increase in England and moderate increases in Scotland, Wales and the Isle of Man, but a continuing decline in Northern Ireland. Breeding numbers within much of the SPA network in Scotland and Northern Ireland were below citation levels, with a more encouraging picture in England and particularly in Wales.

ABSTRACT Capsule During spring and summer 2023, the highly pathogenic avian influenza (HPAI) H5N1 virus caused mass mortality among colony-breeding gulls and terns in Poland. Aims To document the national impact of the 2023 HPAI outbreak on scarcer species of gulls and terns in breeding colonies across Poland. Methods Surveys were primarily focused within breeding colonies of Black-headed Gulls Chroicocephalus ridibundus, an ‘umbrella species’ whose breeding colonies serve as nesting sites for other scarce gull and tern species. Results In total, during the survey period we recorded the deaths of at least 46 Common Gulls Larus canus, 21 Mediterranean Gulls Ichthyaetus melanocephalus, nine Caspian Gulls Larus cachinnans, two Herring Gulls Larus argentatus, 1,369 Common Terns Sterna hirundo, 42 Little Terns Sternula albifrons, three Black Terns Chlidonias niger, two Whiskered Terns Chlidonias hybrida and 35 Sandwich Terns Thalasseus sandvicensis. The most affected populations were those of Mediterranean Gulls (12% of the Polish breeding population) and Common Terns (16% of the Polish breeding population). Conclusions Common Terns and Common Gulls were considered the most vulnerable species to longer-term negative population impacts. It is strongly recommended to monitor mortality and productivity of all gull and tern species during future breeding seasons, to determine the ongoing impact of HPAI.

ABSTRACT Tawny Owls in southern Europe were trapped and measured. Compared to males, the females were larger, heavier, and more greyish in colour, but there was a large biometric overlap. The variable with the highest Storer’s dimorphism index (SDI) was weight, though our population had one of the smallest dimorphisms observed in Europe for weight. It has been proposed that differences in diet could lead to differing behaviour and, in consequence, the observed dimorphism degree (SDI) by natural selection.

ABSTRACT Capsule Distribution patterns of the breeding nests of the Azure-winged Magpie can help to understand spatial and temporal changes in core use areas throughout the breeding range. Aims We investigated the spatial and temporal patterns of nest locations in the breeding colony, to determine the effect of breeding experience and timing on the nest location of Azure-winged Magpies. Methods We collected data on the nest locations of Azure-winged Magpies in a breeding colony and analysed them to identify patterns in nest location. We estimated the nest distribution range through a kernel density analysis, using a geographic information system. Results The size and location of the core use area of the breeding population changed in the following breeding season when the previous year's reproductive success rate was low. We also observed changes in the size and location of the core-use area in relation to the timing of breeding. Conclusion Inter-annual change of the core use area was associated with the timing of breeding and the population's breeding experience.

ABSTRACT Capsule Mortality varies across capture methods but remains overall low. Aims To investigate mortality associated with ringing operations in Denmark and the Faroe Islands, including the effects of species and capture methods. Methods We analyzed data for mortality rates of birds arising from ringing operations in Denmark and the Faroe Islands over a 20-year period. The data included a variety of capture methods and altogether the reports involve 1.8 million individuals. Results The overall mortality rate during ringing operations was 0.16%. The dominant form of capture, mist-netting, had a mortality rate of 0.21%, comparable to similar published studies. Capture methods with higher mortality rates were generally used in research aimed at informing management decisions. Predation was directly responsible for most deaths, with the Eurasian Sparrowhawk Accipiter nisus being the most common predator of birds captured in nets. Migrating passerines occurring in large numbers at bird observatories contributed most to the mortality rates in Denmark, with young birds on their first autumn migration being especially prevalent. Conclusions Overall, our study confirms that bird ringing remains an acceptable method of data collection and highlights the variation in mortality among species and methods. The results should be used to inform working practices to minimize any associated mortality, as far as possible.

ABSTRACT Capsule We studied the diet of Little Tern chicks in the UK using new data collected as part of the EU LIFE-funded Little Tern Recovery Project (2014–2018) (the LIFE Project), which shows that, despite a wide variety of prey items being recorded, diet at UK colonies is dominated by two types of lipid-rich marine fish: sandeel Ammodytes spp. and clupeid species (Atlantic Herring Clupea harengus and European Sprat Sprattus sprattus). Aims To analyse data on the diet of Little Tern chicks from the LIFE Project and assess what additional insight these provide in comparison to the findings in previous literature. Methods Timed chick-feeding observations were made at 12 English and Welsh Little Tern colonies between 2014 and 2018 and compared to descriptions of chick diet from other UK studies (published and unpublished). Results Chick diet data from the LIFE Project were dominated by lipid-rich marine fish, principally sandeels and clupeid species (82% of all recorded prey items). Adult Little Terns feeding chicks with crustaceans or other invertebrates were recorded at 75% of colonies, but there was no evidence that these routinely made up a substantial proportion of chick diet. We found no significant inter-annual differences in diet composition between individual colonies. However, analysis of records of chick diet over a longer time series (Long Nanny colony in Northumberland, with data available for 17 of the years between 1998 and 2018) showed some significant differences in diet composition between years. Conclusion Although Little Terns are generalist feeders, 82% of the prey diet consisted of two prey types: sandeels and clupeids. This may leave existing UK Little Tern colonies vulnerable to any future climate change impacts affecting either the distribution or nutritional quality of their main prey species.

ABSTRACT Capsule Tracked Hen Harriers Circus cyaneus breeding in Spain winter either in the southern parts of the Iberian Peninsula or in Morocco, although migration timing and distances did not differ between birds using different wintering regions. Aims To study, for the first time, the migratory patterns of Hen Harriers breeding in Spain. Methods Eight breeding adult Hen Harriers were tagged in Spain with GPS/GSM transmitters between 2019 and 2022 to study autumn and spring migration between breeding areas in central or northern Spain, and wintering quarters in southern Spain and Morocco. Results Males and females did not differ significantly in their patterns of migration (dates for start and end of migration, duration, daily distance, and total distance) in either migratory period. Individuals started the autumn migration between July and January, with the peak migration in mid-October. Spring migration took place from February to April and peaked in mid-March. Mean (± sd) distances travelled were: daily distance 168.99 ± 80.10 km/day and total distance 995.07 ± 402.90 km in autumn, and 141.74 ± 41.41 km/day and 1035.26 ± 593.51 km in spring. Two types of migration patterns were found: intra-peninsular migration and migration to Morocco. Migration dates and distances did not differ significantly between individuals with intra-peninsular migration strategies and those migrating to Morocco. Conclusion These results are the first to describe the migratory behaviour of Spanish breeding Hen Harriers using satellite telemetry. Knowledge of migratory routes and behaviour are important for planning the conservation of species.