Farmland birds in the European Union have declined by 57% in the past 35 years, raising the need for efficient, large-scale conservation measures to halt and reverse their negative trends. The Eurasian Scops Owl Otus scops is an indicator of extensively managed agricultural landscapes, typical of areas of high biodiversity. Its breeding biology is poorly known, but central to understanding the drivers of its marked decline in different European countries, including Slovenia. We used GPS-loggers to study home range size and habitat use of breeding individuals in NE Slovenia. Kernel home ranges (95%) of three females were estimated and their habitat use was analysed by spatial logistic regression models with Moran's Eigenvectors. Individual home range sizes ranged from 2.2 to 48.2 ha. In general, the females preferred to forage close to their nests. One female had a much larger home range than the other two, because of her exploitation of presumably highly profitable foraging grounds far away from her nest. In a mosaic of different agricultural habitats, the females showed a clear preference for extensively managed areas, such as hedges, meadows, abandoned vineyards and traditional orchards. Based on our findings several conservation measures are proposed, aimed at enhancing insect diversity and abundance as well as prey accessibility.

Understanding the causes of vagrancy among migratory bird species is of increasing importance as climate change threatens species' survival. Vagrancy may serve to safeguard populations from environmental change through expansion of their geographic ranges. To dissect underlying causes of vagrancy, we analysed data on occurrence of vagrant Ash-throated Flycatchers Myiarchus cinerascens to the east coast of North America and population growth within their core breeding range, to test to what extent vagrancy is driven by population growth and the production of young that have a proclivity to explore new places. We also tested to what extent vagrancy is related to drift by prevailing winds, through analysis of synoptic weather maps of North America. Our analyses aimed to quantify which factors most strongly influence interannual variation in the number of Ash-throated Flycatchers reaching the east coast of North America. We obtained records of vagrants from ‘North American Birds’, population data from the North American Breeding Bird Survey (BBS), reproductive success from Monitoring Avian Productivity and Survivorship (MAPS) databases, and synoptic weather maps from the NOAA NCEP North American Regional Reanalysis database. We found that vagrancy was predominantly explained by the growing breeding population size as indexed by BBS data. In addition, we found significant effects of annual production of young within the breeding range, as well as three measures of air circulation across North America. Our models indicated an important role of population growth, with additional effects of reproductive success and predominant airflow affecting the incidence of vagrancy. Years of high reproductive success bring larger numbers of Ash-throated Flycatchers to the east, and this number is enhanced when weather conditions are especially favourable.

In many owl and raptor species, sexes have distinct parental roles. Females incubate the eggs and raise the chicks until independence, while males provide females and their chicks with food. This is believed to reduce sexual conflict over parental care as tasks do not overlap. The level of parental care is also shaped by parent-offspring conflict. The scarcity of empirical data on parental investment in species with sex-specific parental roles was our motivation to study parental care in the Montagu's Harrier Circus pygargus in relation to natural annual variation in food availability (vole abundance). By tracking individual birds using GPS-trackers, several aspects of parental care (the number of food provisioning trips, home range size and nest attendance) could be quantified for different nesting phases. We found that in food-poor years, males spent less time near the nest, and had lower food provisioning rates during the incubation and nestling phases. In addition, males had larger home ranges in food-poor years, a possible indicator of increased foraging effort. In contrast, females increased their contribution to food provisioning in food-poor years, as shown by higher food provisioning rates and larger home ranges. This increased foraging effort came at the cost of lower nest attendance by females. Our data suggest that, when food abundance declines, Montagu's Harriers shift from a system with almost strict sex-specific parental roles towards a system where both parents provide the same type of care with possibly increased sexual conflict.

Two or three gull species (Laridae) commonly breed together in one colony, often caused by a shortage of optimal breeding sites or as an anti-predator behaviour. Observers usually assume that the benefits of colonial breeding outweigh potential costs. Still, our study shows that the costs can be substantial. We show that short distances between nests of Black-headed Gulls and Common Terns breeding in a colony often lead to aggressive interactions between these birds in which terns lose eggs during laying and incubation. We created a buffer zone between the nests of terns and gulls to reduce losses in the terns' clutches. All nests of Black-headed Gulls closer than 120 cm to nests of Common Terns were gradually moved away over 1–4 consecutive days, reducing the terns' egg losses by almost six times. Our results show that our method was safe for both species, and is non-invasive, cheap and easy. This conservation measure could be used in those regions of Europe and North America where breeding Common Terns are declining and perhaps globally in other mixed Larid colonies where species are under threat.

Primary cavity-producers such as woodpeckers produce nest sites for several other cavity-nesting animals and, thus, are often considered to be keystone species. However, the persistence and occupancy rates of cavities are rarely known and as such the real importance of primary cavity-producers also remains unclear. Cavities of the Lesser Spotted Woodpecker Dendrocopos minor were monitored during their whole lifespan. The data include the annual availability and occupancy history of 106 cavities in a 170-km² area in southern Finland during 1987–2018. The median survival time of a cavity was six years, but there were differences between the various forest types (range six to eight years). The median time for cavity fall was six years, and five years for cavity damage. Six bird species used the old cavities for breeding, with the Pied Flycatcher Ficedula hypoleuca the dominant species accounting for 53% of all occupancies. The cavity reuse rate in the Lesser Spotted Woodpecker was 3.6%. The mean occupancy by secondary cavity-nesting birds in old cavities was 32%, with a range of 29–36% across the various forest types. There was a significant negative correlation between annual occupancy rates and the age of the cavity. The first two years of a cavity were found to be the most important for total occupancy and 90% of occupancies took place before the median age of the cavities. The expected mean number of lifespan occupancies by secondary cavity-nesters for a single cavity was 1.97. The results indicate that new, fresh cavities are continuously needed for the secondary cavity-nesters that use Lesser Spotted Woodpecker cavities in their territories.

Migratory birds need considerable energy reserves to fuel long-distance flights to their breeding grounds in spring. To attain sufficient energy deposits before departure, birds require high daily intake rates, which can be reached by utilizing high-quality food. During such periods of high energy demand, animals often track changes in the nutritious value of their food, for example by switching to a more profitable habitat or diet. Pre-migratory Barnacle Geese Branta leucopsis staging along the Wadden Sea coast are known to switch from pastures to salt marshes during spring. Previous studies have suggested that Barnacle Geese switch habitat to track changes in protein levels, which drop in pastures as spring progresses, and to avoid high levels of disturbance. Here we made use of detailed information on pre-migratory habitat use of individual Barnacle Geese tracked by GPS/accelerometer tags to assess which factors may drive a habitat switch. We analysed habitat use and time budgets of individual birds and combined this with data on food quality in two habitats to analyse differences in food intake. We found large individual variation in pre-migratory habitat use, both in the extent of salt marsh use, as well as in the timing of a switch from pastures to salt marshes. In salt marshes, geese spent more time grazing and made fewer flight movements, potentially as they experienced lower levels of disturbance compared to geese in pastures. By increasing grazing time and reducing flight movements, geese in salt marshes may compensate for reduced food quality. Our results show that Barnacle Geese trade-off high intake rates and high costs in pastures with low intake rates and low costs in salt marshes.

On the East Atlantic Flyway, where mid-winter counts of waterbirds have taken place for half a century, there is still uncertainty about trends in the sizes of several wader populations. For example, extensive breeding bird monitoring in boreal Fennoscandia, long term monitoring of actively migrating (i.e. passing) birds, and mid-winter counts give conflicting results for a good number of species. In this paper we contribute with the results of 54 years of monitoring of actively migrating birds passing Blåvandshuk on the west coast of Denmark and just north of the Wadden Sea each year during 30 June – 27 September. The dataset comprises 14,678 observation hours, and 14 wader species with a total of almost 1.5 million individuals migrating south that were selected for analysis. The vast majority of the birds recorded are adults, i.e. without the large annual fluctuations in juvenile numbers caused by year-to-year variations in breeding success. By combining monitoring results from mid-winter counts, the Fennoscandian breeding grounds and monitoring of passing birds in Denmark and Sweden, the overall picture is that most Arctic and boreal wader populations on the East Atlantic Flyway are thriving. Hence, 24–26 populations appear to have been stable, fluctuating or have shown long-term increases; however, one of these populations has shown a decline in recent years. In contrast, 8–10 populations show declines with one of these indicating some degree of recent recovery. Furthermore, two populations have unknown status.

The Audouin's Gull Larus audouinii is endemic to the Mediterranean, with the majority of the global population concentrated in Spain. It mainly feeds on small pelagic fish during the night; however, there is more variation in the foraging behaviour of the Ebro Delta population, with birds also feeding during the day and inland. This plasticity was identified as one of the main factors involved in the increase in population size since 1980. However, foraging movements have only been poorly studied in other populations. We studied the movements of Audouin's Gulls breeding in the small, endangered Croatian population, foraging at the Adriatic Sea, and compared their behaviour with that of conspecifics in the increasing Spanish population in Ebro Delta. Five incubating adults were equipped with a GPS-GSM solar-powered tracking device. We analysed characteristics of short and long foraging trips, differences in movement patterns between sexes and between night and daytime, and the association of gulls with fishing vessels. Daily average trip lengths were similar for all birds, while individual patterns were very diverse. Birds undertook both short (up to 45 km) and long-distance trips (up to 256 km), with length of trips, trip duration and the maximum distance being greater for females. The comparison of gull GPS-fixes with tracking data (VMS) of purse seine fishing vessels showed that birds from the Croatian population, in contrast to the Spanish birds, did not associate with fishing vessels, nor did their foraging behaviour change as an effect of a fishing moratorium. Our results showed that long-distance movements were longer and more frequent than those recorded in other populations, which suggests that depending on non-anthropogenic resources may result in a high cost of chick-rearing.