The Woodpigeon Columba palumbus is a species generally increasing in numbers in most of its populations, including the urban population, which, two centuries after its emergence, is still expanding across the European Lowland. New for the species is a tendency to form dense breeding aggregations in suitable urban parks, with a corresponding slower increase in some other towns. This trend was driven by the presence of important nest predators, mostly Hooded Crows Corvus corone. Another factor involved was access to open farmland within the economic range of feeding flights. Nesting success (1^st brood) in urban habitats free of important predators was up to 50–77% but it fell to only 3–7% when predators appeared. Consequently, some urban populations of the Woodpigeon went into a phase of decline. In the farmland and secondary woods, the nesting success was also variable, ranging between 12 and 42% for unknown reasons. Safe urban populations produced 4–5 times more offspring per pair per season, yet their expansion was rather slow. Therefore, the urban overproduction may contribute to an increase in the total species abundance, owing to (deduced) overspill of recruits to the poorly reproducing subpopulation in the countryside. Alongside other factors such as amelioration of winter conditions and changes in agriculture, this would contribute to the documented growth of the whole population of the species. The shortage of firm data on the pristine breeding success (from extensive natural forests) remains the main obstacle to better understand the population dynamics of this migratory species.

Testosterone may affect many aspects of passerine maturation including the expression of plumage coloration and spring migration in adult birds. However, how the testosterone level changes during bird development is not well known. We compared the testosterone profile during juvenile development of a sexually dimorphic species, the Blackcap Sylvia atricapilla, and a monomorphic species, the Wood Warbler Phylloscopus sibilatrix. We first tested whether testosterone influences plumage coloration and increases at the onset of molt in males of the dimorphic but not the monomorphic species. We found that a testosterone level increase occurred in both sexes and species during later stages of molt, and thus was not related to male plumage coloration. We also investigated whether the increase in testosterone level coincides with juvenile dispersal. If testosterone affects dispersal behavior in these species, both sexes should show an elevated testosterone level during dispersal, but this increase should occur earlier in the Wood Warbler, which disperses earlier than the Blackcap. In juvenile Blackcaps, the increase in testosterone level occurred on the 43–68th day after hatching, while in Wood Warblers it occurred on the 32–36th day (i.e. 11–32 days earlier). The increase in testosterone level coincided with the onset of the post-juvenile dispersal in both species. This study provides the first direct evidence of a testosterone level increase during juvenile development in two free-living migratory birds. While not correlated with species plumage coloration, this increase might affect other aspects of behavior, e.g. juvenile dispersal.

In herbivores, habitat preference is influenced by resource availability, which is most evident in desert ecosystems. The desert puna is a South American environment dominated by grassy steppes with local grassy cushion plants associated with moist soil conditions, which form the habitat called ‘vegas'. In this environment, Puna Rhea Rhea tarapacencis has a strongly selective foraging strategy towards plant species that are in low abundance but that exhibit low contents of secondary compounds, fiber, or both. This contrasts with other generalist herbivores of arid environments, which prefer plant species with high fiber content and are highly abundant. We determined habitat use by Rheas in three habitat types: foothills, valley and vegas; and provided evidence of their feeding habitat preferences. From 2011 to 2014, we estimated density of birds and environmental variables such as total plant cover and abundance of total food, preferred foods and non-preferred foods. In particular, the density was estimated indirectly based on counting and collecting feces of the birds in transects. We analyzed the effect of the habitat type and environment variables on bird density; and compared the environmental variables among habitats. Puna Rheas used the three habitats, but fecal records were very scarce in vegas. The density was higher in foothills than in the valley (0.45 and 0.01 inds/km², respectively), increased with higher abundance of the preferred foods and declined with increased non-preferred foods. The foothills were preferred as they had the highest abundance of the preferred foods and the non-preferred foods were similarly abundant in foothills and valley. The vegas had the highest total plant cover and the lowest abundance of all food species consumed by the Rheas. Therefore, the abundance of preferred foods, which have the best nutritional quality, represents a good predictor of habitat preference and, possibly, an essential resource during the life cycle of the Puna Rhea.

Migratory birds have evolved the ability to accumulate fat reserves to fuel their migratory journeys. However, increased fuel load leads to an increased body mass, which is expected to impair flight performance and increase predation risk. Results of previous research are contradictory, with some studies reporting detrimental effects of fat load on flight performance, while others showing no such influences. Furthermore, no studies have investigated the relationship between fat load and flight performance in obligate aerial insectivores, which are known to accumulate only moderate fat loads while migrating overland and not crossing wide ecological barriers such as oceans or deserts. In this study we investigated the inter-individual variation in short-term flight performance (flight manoeuvrability, velocity and acceleration) in juvenile Barn Swallows Hirundo rustica in relation to fat load in Poland (central Europe), during the initial stages of autumn southward migration. We evaluated individual swallow fat loads by means of a Total Body Electrical Conductivity (TOBEC) scanner. In order to evaluate short-term flight performance in a standardised manner we used flight tunnels. We controlled statistically for the independent effect of wing morphology, which can be expected to influence flight performance. Juvenile fat loads were on average 7.5% (range 0.2–20.5) of lean body mass, but we found no negative effect of the fat mass on short-term flight performance traits. Individuals with larger fat mass reached higher velocity compared to leaner ones, which is in line with theoretical expectations. However, fat mass did not significantly predict flight manoeuvrability or acceleration. The results indicate that relatively small fat loads accumulated by juvenile Barn Swallows during overland migration do not impair short-term flight performance.

In tropical forests many forest-dwelling non-aquatic passerines build nests by forest streams. It has been proposed that this behavior protects the nest from predators. However, this hypothesis has been rarely tested, and relevant aspects of the relationships between nesting birds and forest streams are to be studied. Firstly, it is not clear whether tropical forest understory passerines can indeed select stream banks for nest construction, as researchers often use forest streams as pathways, which could cause the false impression that nests of certain species are more frequently found near water. Secondly, it is expected that if birds select stream banks for nest construction, they will choose nest spots with characteristics that could increase nest survival. We studied nest site selection in two Atlantic Forest birds: the Blue Manakin Chiroxiphia caudata and the Star-throated Antwren Rhopias gularis. Nests were searched near and far from water, and a number of stream characteristics, including width, depth, water speed and water sound were compared between nest sites and random sites chosen upstream or downstream. Finally, we addressed whether stream variables could explain nest daily survival rate (DSR). Nests of both species were found only near or over water, and the average DSR was 0.975 for the Blue Manakin and 0.972 for the Star-throated Antwren. Our results provided support for the "aqua-phobic nest predator hypothesis", since we found a positive correlation between DSR and stream depth for the Star-throated Antwren and a negative correlation between nest distance from water and DSR for the Blue Manakin. However, stream parameters were not among the main variables explaining nest site selection along streams. This suggests that partial isolation provided by forest streams may reduce nest predation and can drive these species to use stream banks for nesting. The main predators of Blue Manakin nests were birds (80% of filmed predation events), whereas nests of Star-throated Antwren were preyed upon mostly by mammals (54.5% of the records).

The Turquoise-fronted Amazon Amazona aestiva is one of the most extensively poached species as a result of illegal trade in Brazil. Reintroduction programs have been increasingly used in the management of these animals in captivity. Several preparatory procedures should be carried out during the pre-release period to characterize the group of animals and subsequently increase the success of reintroduction programs. The most important procedures are temperament assessment and environmental enrichment training, which is expected to influence the behavior of the released birds. This study aimed to assess the temperament of the amazons in captivity and its influence on a reintroduction program. The temperaments of 50 parrots were classified from shy to bold and monitored during five phases of activity throughout the study: environmental enrichment training in captivity, a period of acclimatization in an aviary placed in the release area, the offer of fruit from the release region, dependence on the aviary after it was opened, and post-release food supplementation. Once the animals were released, they were monitored for 18 months. Temperament assessment supported the reintroduction project, because through this information it was possible to predict the individual behaviors of reintroduced animals when dealing with environmental challenges. The purpose of the pre-release environmental enrichment training was to encourage individual amazons to increase exploratory behaviors, and was effective in enhancing the natural behavior of the species and reducing stereotypies. Animals classified as shy required a longer intervention period to achieve the same results since they exhibited greater dependence on the aviary and, consequently, took longer to explore the release area. In the medium term, no significant difference was observed between shy and bold parrots in their departure after opening the aviary, use of supplementary feeding, or survival. Therefore, the activities performed prior to release adequately promoted similar habituation conditions for both profiles.

Birds associated with steppe and pseudosteppe habitats are one of the most threatened avian communities in Europe, given their recent decline due to agriculture intensification and land abandonment. Large-scale conversion of natural and rural areas into irrigated farmlands is ongoing in North Africa, but the effects of this habitat modification on steppe bird species are not investigated. In this study, we investigated the breeding biology of the Eurasian Stone-curlew nesting in grazed steppes and irrigated farmlands in south-western Morocco. Breeding data were collected during 2017 and 2018 breeding seasons on 59 nests. Egg volume was significantly higher in grazed steppes than in irrigated farmlands (37.3 ± 2.30 cm³ vs 35.1 ± 2.11 cm³, average ± SD), possibly due to greater food availability in the former habitat. On the other hand, daily nest survival over the incubation period did not differ between habitats and it was quite high (0.85 [95% CI: 0.71–0.93]) also when compared to the data available for other regions. These results suggest that birds nesting in protected areas characterized by traditional pastoralism might find better conditions for reproduction which allow them to lay larger eggs. In addition, the ongoing process of agricultural intensification in the area does not seem to affect the likelihood of nest failure. Our data add to the few available pieces of evidence regarding the effect of breeding habitat on the reproductive biology of the Stone-curlew in the southern range of its distribution. Further data are needed in order to understand the conservation implication of our findings and, in particular, how the observed variability of egg size might affect chick quality and survival.

Why foraging animals sometimes leave patches before consuming all available food items is a key question in behavioural ecology. Abandoning some food would appear to be disadvantageous, yet optimal foraging theory demonstrates that this sometimes optimises energy intake rates. Crossbills Loxia are specialist avian granivores that forage on seeds within the cones of many species of conifer in the northern hemisphere. They often abandon a few seeds within cones they have fed upon. We assessed whether seeds left within Scots Pine Pinus sylvestris cones by foraging crossbills were of lower mass or in particular positions within the cone. Crossbills foraged on long cones which have more seeds per cone and heavier seeds, but avoided the longest cones, which typically have thicker scales that require more energy to open. Cones dropped by foraging crossbills contained over four seeds per cone, representing approximately one fifth of those originally present. Crossbills left mostly small or empty seeds (< 2 mg), whereas the average mass of seeds from intact cones sampled from the canopy was 3.6 mg. Infrequently, single seeds of high mass (> 4 mg) were left behind, perhaps mistakenly overlooked during foraging. Such apparent preferential foraging on heavier seeds is probably advantageous, because of the higher energy reward per seed. To directly discriminate between seeds prior to extraction would reduce energy expenditure in foraging. This raises the question of how crossbills could attain this favourable outcome. While cones scales were closed an external cue would be required. After cone scale dehiscence, seeds would be visible to crossbills, allowing them to discriminate visually among seeds and selectively extract heavier seeds, leaving lighter seeds behind within the cone. Dropping cones when few seeds are encountered or as seed mass declines towards the distal scales could be additional components of crossbill foraging strategy.

Due to their falling cost, unmanned aerial vehicles, often called drones, are increasingly used as a tool in bird research and conservation. However, behavioural responses of birds to flying drones are still not well understood, for example do birds recognize drones as predators, as benign, or as neutral elements? How do they react to drones? We answered these questions and described the behaviour of birds toward drones during a study with White Stork Ciconia ciconia in north-eastern Poland. We used a small quadrocopter and noted flight initiation distances (FID) of adult storks on nests and behavioural reactions of their young towards drones. During nest inspections by drone, adult White Storks showed FIDs of between 1 and 20 metres, but occasionally did not even flush during drone approaches. FID was mainly affected by breeding stage, but some storks even ignored the working drones close to the nest (14%). Birds that escaped from the nest at the egg stage, returned to it on average within 23 seconds. The most common reactions of young White Storks to the drone were scaring (42%) and akinesis (34%). The rapid return of adult storks to the nest, even when scared away, shows that drones are not an highly invasive tool for examining their breeding outputs, even during the most sensitive period, i.e. egg stage. We believe that drones will soon become an important and common tool in research of the White Stork for determining breeding success and examining nests for hazards, e.g. waste, strings or electrocution risk. Our research can be a useful guide to researchers for predicting stork behaviour during inspection of their nests in the near future.

Incubation of eggs and nestlings is energetically costly and may be affected by the amount of thermal insulation the surrounding nest provides. In many small passerine species, animal-derived materials, i.e., feathers and hair, are often used in the nest lining where, presumably, their lower thermal conductance offers better insulation. A previous study that involved partial deconstruction of thrush nests revealed that different parts of the nest confer different levels of insulation. The present study examined the insulatory values of Common Chaffinch Fringilla coelebs nests because of the high proportion of animal-derived materials in their cup lining but not the outer nest. Insulatory values and cooling rates of temperature loggers inside the cup were determined for whole nests and then only the cup lining. There were no significant relationships between nest measurements and measures of thermal insulation. However, removal of the outer nest wall reduced the insulatory value by around 10% despite the cup lining being less than half the thickness of the complete nest wall and the cup lining being only a third of the total nest mass. Differential placement of animal-derived materials within the cup lining of Common Chaffinch nests means that the birds seem to be able to confer a high level of insulation without expending too much energy searching for a large mass of particular nest materials.

Citizen science (i.e. monitoring or research schemes with volunteer participation in data collection) is becoming an increasingly used tool that may yield reliable estimates of species distribution ranges. In 2017 and 2018, we assessed the fine-grain distribution and habitat use of the Middle Spotted Woodpecker in the Basque Country (N Spain) by combining two citizen science approaches: opportunistic observations gathered from internet collaborative databases, and standardised records collected by volunteers trained with a species-specific fieldwork protocol. Six out of the thirty-four opportunistic observations were located out of previously known distribution ranges. Because the reliability of those observations was difficult to assess, opportunistic observations should be validated to avoid false positives. As for the species-specific approach, Middle Spotted Woodpecker occurrence was examined by conducting itineraries with point counts and audio-stimulation, sampled twice during the pre-breeding season, in 95 UTM units of 1 km². Woodpeckers were recorded in 29 of those units. In combination with recent species-specific studies, our results show that Middle Spotted Woodpeckers occurred mainly in a core, continuous range (69 positive units in and around the Izki forest) and in two smaller ranges (6 units in Montes de Vitoria and 5 units in Sierra de Entzia). Out of previously known distribution ranges, the species-specific approach showed that woodpecker occurrence was negatively affected by the distance to the core Izki forest and, to a lesser extent, positively influenced by the tree basal area of the forest stand. While the species-specific fieldwork approach allowed to improve the delineation of distribution ranges and the assessment of habitat use, the opportunistic approach pointed out to overlooked ranges but showed limited efficacy to assess the fine-grain distribution of the Middle Spotted Woodpecker.