During migration, birds often need to gain large fuel loads, especially if they must cross large geographic barriers with poor or absent fuelling opportunities. The Willow Warbler is a songbird associated with woodland that also opportunistically exploits other habitat types, such as reed beds, allowing it to fuel quickly. Reed beds along the coast of the Bay of Biscay constitute potentially targeted fuelling sites for birds moving from northern Europe to Africa in autumn. Using data obtained from a ringing station, we tested to what extent these coastal sites are opportunistically used by Willow Warblers. The study was carried out in a reed bed area at Txingudi marshlands, one of the main wetlands at the Bay of Biscay in northern Iberia. We found that when Willow Warblers were more abundant, that birds deposited fuel more quickly, and that annual mean fuel load was correlated with the number of captures, suggesting opportunistic stopover exploitation.

A fraction of White-throated Dippers Cinclus cinclus breeding in Scandinavia migrate south over the Baltic Sea during their short-distance migration to the winter quarters. The aim of our study was to investigate patterns of body mass changes between arrival to and departure from the wintering grounds in northern Poland. From a cost-benefit perspective, according to optimal body mass theory, we expected that fuel loading should occur as late as possible before spring migration, to reduce costs associated with high fuel loads. We were interested if sexes (in view of the larger body size of males) and age classes (in view of the less experienced young individuals) differ in the duration of the fueling period and in rates of increase of body mass prior to spring migration. To address these questions, we used morphometric data from 520 Dippers trapped over 16 wintering seasons (1989/1990–2004/2005), including birds trapped more than once (881 captures in total). Body mass was stable between late October and mid February. The period of intensive body mass increase lasted for about one month directly before departure in all Dippers and started in the second half of February. The rate of increase depended on date in a non-linear fashion: the later the date, the higher the rate, with a tendency to stabilize in the last days of March. In late March, the estimated mean body mass was 20–21% higher in males and 18% higher in females compared to the mean body mass during winter. Immature males increased body mass faster than adults (both sexes) and immature females and reached higher body mass prior to departure (increase up to 36%). Fuel loads are not only sufficient to complete the 100–300 km long migration over the Baltic Sea, but probably also to reach breeding destinations in the Scandinavian Mountains, c. 600 km north from the wintering range in northern Poland.

The Black Skimmer Rynchops niger is a New World's coastal migratory bird with three subspecies based on distinctive morphometrics, plumage, and breeding distribution. Its population is decreasing in North America while numbers are poorly known in South America. Here we conducted an extensive review of the literature on the Black Skimmer to fill gaps in the knowledge of each subspecies' natural history and suggest where future research should focus. We used 41,247 records collected from databases and literature to establish the overall occurrence and location of breeding colonies for each subspecies. We also collected information on the phenology of life-history events described in 150 papers and books to compare the annual cycle of the three subspecies. The North American subspecies R. n. niger breeds, migrates and stages along the coast with few records inland. The South American R. n. intercedens and Amazonian R. n. cinerascens subspecies breed inland and migrate mostly to coastal staging sites. The presence of other species, such as terns and plovers, as well as the availability of sandbanks with fine sand and the proximity to calm shallow waters positively affects breeding site selection. The coastal and freshwater habitats that skimmers use during breeding and staging are highly affected by climate change. As Black Skimmers are widespread and usually associated with other species, such as terns and gulls, their conservation is directly related to that of other species which makes them a suitable umbrella indicator species. To take conservation measures a global network approach should be initiated.

Birds often participate in mixed-species foraging associations to improve their feeding efficiency. Wilson's Phalaropes Steganopus tricolor wintering in saline lakes of the Atacama Desert, northern Chile, were found to feed either solitarily or in close proximity (commensally) to Chilean Flamingos Phoenicopterus chilensis. Those individuals following Chilean Flamingos were picking up prey (mainly copepods) stirred up by flamingos rapidly stomping their feet (‘foot paddling’). In contrast, Wilson's Phalaropes ignored Andean Flamingos Phoenicoparrus andinus and Chilean Flamingos using different foraging tactics. Feeding rates of Wilson's Phalaropes associating with Chilean Flamingos (38 ± 9 prey/min) were significantly higher than those of solitary phalaropes (17 ± 6 prey/min), indicating that this association allows profitable feeding on small prey suspended in water. Although this association appears to involve a high benefit to Wilson's Phalaropes and a low cost (if any) to Chilean Flamingos, thus partly explaining the stability of mixed-species groups, it is restricted to moderate and deep foraging depths. Three other shorebird species (Baird's Sandpiper Calidris bairdii, Lesser Yellowlegs Tringa flavipes and Greater Yellowlegs Tringa melanoleuca) associated with the Chilean Flamingo at shallower foraging depths, indicating these facilitative interactions are species and context dependent.

Monitoring programmes are needed to assess the conservation status of species and to quantify the effectiveness of conservation effort. Rare species are usually poorly studied due to difficulties in monitoring. We evaluated the use of autonomous recording units (ARUs) coupled with automated song recognition for monitoring the presence of Dupont's Lark Chersophilus duponti, a rare and patchily distributed species. We surveyed 49 potential habitat patches for the species in central Spain never censused before, from May to June 2017. In each habitat patch we deployed an ARU that recorded one continuous hour during two consecutive nights. In addition, we also performed line transect censuses in 22 out of the 49 potential habitat patches, to evaluate the efficacy of ARUs. Audio analyses revealed the existence of eight previously unrecorded Dupont's Lark populations. Line transect censuses always confirmed the presence or absence of the species in agreement with audio analysis results. ARUs required 44 fewer working days than human-based surveys for monitoring the presence of Dupont's Larks in potential habitat patches. Our results suggest that the use of ARUs coupled with automated song recognition can provide an effective alternative to human-based surveys for monitoring the presence of bird species in large-scale surveys. We conclude that a combined methodology using ARUs and field censuses, in order to estimate densities or spatial patterns, may be considered the most effective method for monitoring large numbers of potential occupancy sites.

In 1997, Eurasian Eagle Owls Bubo bubo returned to Limburg, the south-eastern province of The Netherlands. However, since then the population size has stagnated, while extremely high concentrations of PCBs have been found in Eagle Owl carcasses. These observations suggest that a further expansion of the species in Limburg is under threat. The high concentrations of toxic substances may be explained by the Eagle Owls' position at the top of the food chain. Studying their hunting behaviour may help to identify possible sources of poisoning. Identifying the most important habitat characteristics of hunting grounds is a first step towards recognizing poisoning sources. For this purpose, and to gain general insight into their habitat use, a GPS tracking study was conducted on six adult Eagle Owls from three adjoining territories in 2010–2011. We found that the quarries in the region are important for the Eagle Owls since they are used as nesting sites. Other habitat characteristics that attract the species are pastures, differences in altitude, forest edges and water bodies. Major roads and town centres are avoided. The highlighted areas and habitat characteristics provide information about the most important hunting habitats of Eagle Owls and insight into the underlying causes threatening this species in Limburg.

Exploring the patterns of genetic structure in the context of geographical and phenotypic variation is important to understand the evolutionary processes involved in speciation. We investigated population and subspecies differentiation in the Common Ringed Plover Charadrius hiaticula, a high latitude wader that breeds in arctic and temperate zones from northeast Canada across Eurasia to the Russian Far East. Three subspecies, hiaticula, tundrae and psammodromus, are currently widely recognised, whereas a fourth subspecies, kolymensis, has been proposed based on geographic isolation and phenotypic differences. We genotyped 173 samples from eleven Common Ringed Plover breeding sites, representing all four putative subspecies, at eight polymorphic microsatellite loci to examine the patterns of population and subspecies differentiation. Bayesian clustering identified three genetic clusters among samples, corresponding to the breeding sites of the three currently recognised subspecies. The existence of the subspecies kolymensis was not supported. We also detected the presence of a previously unknown hybridisation zone extending from Northern Scandinavia to Belarus. Differentiation of the subspecies tundrae and hiaticula most likely occurred in allopatry on the Eurasian continent during past glaciation events, followed by population expansion leading to colonisation of Iceland and Greenland. The lack of genetic differentiation within the tundrae subspecies is consistent with ongoing range expansion and high gene flow maintained through migratory behaviour. We discuss the importance of historic climate changes, migratory behaviour and mating system on shaping the observed pattern of genetic differentiation.

The Eurasian Scops Owl, a small nocturnal raptor living in continental and southern Europe, is often solitary and territorial but sometimes forms local groups, of which little is known. In this study, I examined a group of territorial Scops Owls in a habitat with limited nest site availability in Southern Italy in July of 2016 and 2017. Male Scops Owls were identified through spectrographic analysis of their vocalizations, and their location was recorded. Male Scops Owls clustered around a human-inhabited area with significant noise and light pollution and avoided the undisturbed forest, which apparently was only used for foraging. The location of territories was relatively consistent in two subsequent years. Scops Owls tended to sing where conspecifics occurred, not necessarily near their own nests. Sometimes neighbouring males occupied the same area and sang simultaneously, even when close to each other. The results are in contrast with the concept of an all-purpose, exclusive territory described for this species as the norm, and suggest that the social and spatial organization of this population is more flexible than previously thought. Scops Owls bred exclusively in abandoned Eurasian Magpie Pica pica nests, which is unusual for this typically cavity-nesting species and was presumably caused by the lack of alternative sites. The distribution of Magpie nests might thus be the main driver of nest spacing and territorial behaviour of Scops Owls in this presumably nesting site limited population. However, the underlying cause of aggregation is unknown.

Recovery of ringed birds provides only a partial view of bird movements and may be complemented by using techniques such as molecular analyses. The White-throated Dipper Cinclus cinclus is a passerine restricted to mountain rivers, and considered sedentary in the Iberian Peninsula. The objective of this paper is to establish whether the displacement data found by molecular techniques match those obtained by ringing or not, and to infer if these displacements follow a defined route. 236 Dippers from 13 populations in the Iberian Peninsula were ringed and genotyped using microsatellite markers. The percentage of ringed Dippers that was subsequently recorded outside the sampling area was less than 3%, with most of the birds confined to the same river stretch. However, according to the genetic information presented here, 14.4% of the individuals had moved from their natal localities to other river basins, where they were subsequently trapped. Moreover, migrant Dippers travelled an average distance of 218 km (range 79–484), which is about ten times the distance estimated through ringing recoveries occurring in additional ringing data. The results of the genetic analysis revealed that Iberian Dippers move frequently between mountain ranges and suggest four potential routes for Dipper movements in the Iberian Peninsula. Molecular techniques thus complement the data obtained by ringing and provide new insights into the dispersion of this species.

Hornby's Storm Petrel Oceanodroma hornbyi is endemic to the Humboldt Current Region. Historically, little has been known about the location of the species' breeding sites or the size of its population. For these reasons, this species has been classified as ‘Data Deficient’ by IUCN, and it is difficult to know whether the species is threatened, and if so, what conservation actions may be necessary. As part of the project ‘Golondrinas del Desierto’ a search for the colonies of this species began in November 2013. It was known that the species breeds in the Atacama Desert, because some mummified individuals had been found there, and fledglings attracted by lights whilst on their way to the sea were found in nearby coastal cities. In this paper, we describe the first breeding site discovered for this species. This breeding location is 75 km from the shoreline, at 1100 meters above sea level, in the centre of the Atacama Desert, also known as the ‘absolute desert’. However, there is strong anthropogenic pressure on this desert due to the development of mines and solar energy projects. To protect these birds, it is important to estimate the breeding population size of the colony, search for new colonies and assess the threats to each of them, and to evaluate how many fledglings are drawn off course by lights into cities and industrial sites and how many die there.