Breeding birds exhibit behaviours such as incubation and food provisioning, but proximate cues affecting the timing and duration of these behaviours remain poorly understood. In the Japanese Tit Parus cinereus minor, females incubate eggs and are provisioned by their mate. We report an unusual case of a female Japanese Tit incubating for at least 20 days without eggs, during which the female continuously interacted with its mate and was likely provisioned by him. We suggest that terminating incubation may require signals from chicks, and male provisioning may be triggered by female behaviours, such as incubation, begging displays or begging calls, rather than eggs. The development of a brood patch and nest building behaviours suggest elevated oestrogen levels in the female. Future research should explore proximate cues and hormonal regulation for these behaviours during breeding.
Successful mixed broods in hole-nesting passerines are relatively rare. Increased competition for nesting sites may result from environmental conditions that constrain the breeding period, bringing in contact species that would normally rarely interact. Meteorological conditions preceding the breeding period of 2024 could have delayed the reproduction of Eurasian Nuthatches Sitta europaea relative to Eurasian Blue Tits Cyanistes caeruleus in our study area. Here we report the first case of a successful mixed brood involving Eurasian Nuthatches and Blue Tits. On 4 May, we observed a Blue Tit hatchling in a Nuthatch nest. The Blue Tit, reared in the foster nest, had smaller tarsus and wing length relative to the average measures of all observed Blue Tit nestlings in 2024. However, its mass was in the normal range, and it fledged successfully, along with five Nuthatch ‘siblings’.
Territory quality is an important factor that influences male reproductive success, especially for polygynous species, in which only males with high-quality territories that provide sufficient resources for multiple females can achieve polygyny. Because males that establish territories earlier are more likely to obtain territories of higher quality, males of polygynous species are predicted to start territorial competition before the breeding season starts. I investigated the territory formation of a polygynous species, the Eurasian Wren Troglodytes troglodytes during winter at their breeding site in Japan. In this population, breeding sites are typically located in mountainous areas, and wrens are thought to migrate to lowlands in winter. However, I found that many males held winter territories at their breeding site and that most maintained their territories in the subsequent breeding season. In defending winter territories, wrens used specific calls instead of songs. It is possible that, despite the cost of territorial defence during winter, it is a strategy that allows males to secure access to high-quality breeding territories, thereby increasing their reproductive success.
Understanding how birds use stopover areas is essential for the effective conservation of migratory bird populations. Here, we evaluate the role of high altitude grasslands in the Central-Eastern Pyrenees as autumn stopover habitat for the Iberian population of the Red-backed Shrike Lanius collurio. Using data from a standardized mist-netting program (2010-2024), we analysed age related patterns in abundance, fuel load, fuel deposition rate and stopover duration. First-year birds were captured much more often (91.5%) and they did not have a longer stopover duration than adults. However, both age classes had low mean fuel load (0.0338 +/- 0.0536 SD, i.e. 3.4%) and a minimal fuel deposition rate, suggesting that the Pyrenees might not serve as a main refuelling site. Instead, the region may function as a transient area for the shrikes, particularly for first-year birds at the onset of their first migration. Despite the low fat accumulation, the high number of individuals using this area highlights its potential relevance. The mosaic of pastures and open habitats aligns with the shrikes' foraging preferences and may support a migration strategy based on short distance flights with low energy reserves. Given the ongoing population decline and habitat loss, preserving these herbaceous areas is critical to ensure safe passage for species like the Red-backed Shrike. Our findings underscore the need to protect not only key fuelling sites but also early-phase resting habitats along migratory flyways.
The Eurasian Skylark Alauda arvensis performs an aerial display flight to altitudes of over 100 metres while singing continuously for extended periods; a striking behaviour among avian aerial displays. Despite this conspicuous display, previous studies recorded only maximum altitudes and did not measure continuous flight trajectories. In this study, we used handheld laser rangefinders to obtain fine-scale and continuous altitude profiles of Eurasian Skylark song flights in Hokkaido, Japan. In total, we recorded 203 flights, of which 147 were complete from take-off to landing. Maximum altitude ranged from 10 to 179 m (mean = 73.6 m, median = 69.4 m), whereas flight duration ranged from 27 to 487 s (mean = 129.5 s, median = 98.0 s). Maximum altitude increased with flight duration but tended to plateau at approximately 150 m. Environmental variables (wind speed, temperature, time of day) showed no clear association with maximum altitude. Continuous recordings revealed three altitude-trajectory patterns: table-shaped (28 flights), mountain-shaped (46 flights) and wave-shaped (11 flights). Mountain-shaped flights were more frequent earlier in the morning, whereas wave-shaped flights occurred more often during longer-duration song flights. Taken together, our results demonstrate that skylark song flights are not confined to the conventional climb-level-descent pattern. By quantifying trajectories across entire display flights, this study provides a baseline for future research into the ecological and social significance of this behaviour.
The breeding biology of the Pallid Swift was investigated in Iran, where the resident subspecies is Apus p. pallidus, for which no previous information was available. Main breeding parameters were found to be overall similar to European Pallid Swift populations studied so far. The percentage of second broods, mean clutch size, and reproductive success fall within the range found in the other studied colonies. The main difference to European populations is that in Iranian birds the whole breeding season is advanced by about 3 months, extending from February to June.
Globally, farmland birds have been on the decline. To understand or even halt these declines we need more knowledge on how birds use the agricultural landscape. While much is known already on habitat selection by farmland bird species during the day, we know very little about habitat selection by diurnally active birds and their behaviour during the night. This study focuses on the night-time behaviour and roosting habitat selection by Grey Partridges Perdix perdix. We investigated (1) the movements and distances travelled during the night-time, from the original roosting site to another site, (2) distances between roosting sites on consecutive nights and (3) roosting site habitats and temporal variability. We used GPS/GSM transmitters to collect data on night-time movement parameters and roost habitat use of 24 Grey Partridges (14 females and 10 males, 927 roosts) tagged in the years 2021-2022, primarily in Eastern Estonia. The results showed that on 422 nights (45.5% of cases), Grey Partridges moved from their original roosting site to another site during the nighttime for unknown reasons. They did not move far, males averaged 108 m and females averaged 70.4 m. The nocturnal movement of Grey Partridges did not depend on their sex. However, there was a statistically significant difference in the study periods, as night-time movement distances from January to March (mean: 155.0 +/- 264.0 m; +/- SD) were longer compared to night-time movement distances from April to June (44.9 +/- 98.8 m) and from July to August (24.3 +/- 56.7 m). Additionally, the nocturnal movements observed in July-August and October-November (84.6 +/- 101.0 m) were statistically different. The distance between the roosting sites did not depend on sex or on whether the individual was stationary or not in the previous night. Grey Partridges mostly selected winter cereal and winter oilseed rape fields and grassy habitats as roosting habitats. There were seasonal differences in roost habitat use.
This study describes the mesopelagic fish present in the diet of two sympatric storm petrels, the summer breeding Monteiro's Storm Petrel Hydrobates monteiroi and the winter breeding Band-rumped Storm Petrel H. castro. Prey species were identified based on otoliths obtained through stomach flushes. Fieldwork took place in 1998 and 1999 in three colonies of the Azores archipelago. 279 otoliths were found in 329 samples, corresponding to 8 fish orders, 11 families, 24 genera and 27 species. About one third of the otoliths (32%) could not be identified due to their eroded condition. Electrona risso was consistently the most abundant prey species in both years and for both seabird species. Myctophiformes, Argentiniformes and Beryciformes were present in the diet of the two storm petrel species. Gadiformes and Acropomatiformes were only present in the diet of Band-rumped Storm Petrel, while Perciformes, Trachichtyiformes and Stomiiformes were only present in the diet of Monteiro's Storm Petrel. Storm petrels are surface feeders and the mechanism by which they can access mesopelagic prey is unknown. The otolith analysis allowed us to identify new fish species that were not described before in the diets of these storm petrels. Although there has been one previous study on these storm petrels' diets, our study added 27 new prey species to the record. Mesopelagic fish are an important link between the components of the ocean food chain.
Migratory birds face numerous challenges as they travel to and from their wintering grounds. Their ability to overcome these obstacles depends on their physical fitness, energy reserves and migration strategy. During migration, birds often need flight interruptions in vegetated areas which play a crucial role for migrants heading to wintering quarters or flying back to breeding areas. For the migratory raptor, the Western Marsh Harrier Circus aeruginosus a particularly difficult challenge is crossing the Sahara Desert. In this region, the birds encounter areas with lack of vegetation and harsh atmospheric conditions. To understand their behaviour in such an unfavourable environment, we studied the migratory patterns of Marsh Harriers in the Sahara Desert using GPS/GSM telemetry from 2019 to 2023. We examined flight interruptions within an hourly resolution and unique stop sites in hyper-arid areas of the Sahara Desert and enhanced the dataset with Normalised Difference Vegetation Index (NDVI), land cover data, U (velocity of the east-west) and V (velocity of the north-south) wind components and sunrise and sunset times. We explored the timing of the daytime flight interruptions used by Marsh Harriers and described the selection of sites with emphasis on the NDVI. Marsh Harriers preferred areas with higher NDVI and increased distance between unique stop sites. We also found increased density of flight interruptions during late afternoon and tendency for flight interruptions in the vicinity of consecutive night roost. Flight interruptions were also affected by wind conditions. Our study, made possible by advanced GPS/GSM technology and remote sensing data, provides new insights into the use of unique stop sites by Marsh Harriers during migration over the Sahara Desert. It underlines the importance of scarce vegetation during the Sahara crossing for the Marsh Harrier and helps to explain the selection of areas within a harsh environment used for breaks of a short duration. Our findings open the door for further investigation of Marsh Harrier behaviour during migration through harsh environments.
Eurasian Woodcock Scolopax rust/cola perform a distinctive courtship display known as 'roding', in which male Woodcock travel over large areas of woodland and other suitable breeding habitats in search of females. Observations of roding provide the only practical basis for breeding season surveys of Woodcock, although our existing understanding of roding is derived from a very small number of studies. To provide more representative assessments of roding range size, i.e. the geographic area covered by a displaying male Woodcock, this study analysed fine-scale GPS data collected by tracking Woodcock during their courtship flights. Different methods for estimating roding range size are compared: minimum convex polygons, localised convex hulls and Brownian bridge kernels. Mean estimates of daily roding range size, produced using data from 16 tagged individuals, varied from 0.41-2.00 km2 depending on the method used, with the two most congruous methods suggesting averages of 1.11 km2 or 1.29 km2. The results presented here generally support the existing interpretation of roding as a lek-like system in which mating is determined by male-male competition and female mate selection. Roding ranges were somewhat larger than those provided by previous assessments and we recorded some individuals that made roding movements on a scale far exceeding any previous estimates. The results appear to lend cautious support to existing interpretations of roding count data but raise questions about how woodland size and connectivity may influence display behaviour and thus survey results.
In birds, chick survival to fledging is a commonly used index of reproductive success and challenges during the prefledging period can predict performance at subsequent life stages. Prefledging survival of Common Tern chicks was studied at a North American breeding colony in 1989-2022 (4647 chicks in 32 years) to elucidate the relative importance of factors influencing chick survival and interactions between them. Study plots were fenced so that surviving chicks could be followed to fledging age. Mean productivity during the study was lower than at other coastal North American colonies and the main cause of chick mortality was starvation. Chick survival was related most strongly to hatch date and hatching order. Survival was highest among the earliest-hatched chicks and showed a curvilinear decline with increasing hatch date. Within a brood, first-hatched chicks were more than twice as likely to survive as second-hatched chicks and over 11 times more likely to survive than third-hatched chicks. To a lesser extent, chick survival depended on brood size, being higher in larger broods during 'good' years but lower in larger broods in 'poor' years. These results indicate that studies of chick survival or productivity need to consider hatch date (which may be an index of parental quality). Survival of second-hatched (B-)chicks showed the most variability, so that this parameter may serve as a single index of reproductive performance. Annual colony-wide productivity was correlated with mean clutch size earlier in the same year.
In a previous analysis of data collected on the primary wing moult of adult Snow Buntings Plectrophenax nivalis in High Arctic northeast Greenland (72 degrees N) in 1972, it was estimated from linear regression that the moult duration was 28 days. This method is now considered inappropriate and has been superseded by the Underhill-Zucchini method to analyse primary moult. The revised estimates are as follows: mean start date was 21 +/- 5.9 July (+/- SD), the mean duration was 31 days and the mean completion date was 21 August. Therefore, this revised estimate of 31 days still means that the Snow Bunting is the fastest moulting passerine known to date. This speed of moult is symptomatic of an adaptation to a northerly breeding distribution when breeding, moult and preparation for migration are compressed into the short summer of the High Arctic.
For pollination via mutualism to occur, both the plant and the pollinator must be present at the same time, specifically during the plant's flowering. Migrating birds may act as pollinators for different plant species that flower at different times of the year, and in different places thousands of kilometres apart. The insectivorous palearctic warbler Lesser Whitethroat Curruca curruca winters in eastern Sahel where it is found to be a major visitor on flowering Sahelo-Sudanian Maerua crassifolia trees (Capparaceae). The peak flowering of M. crassifolia occurs in January, in the middle of Sahel's dry season. Lesser White-throats use the eastern Mediterranean flyway during spring migration towards their breeding sites all over Europe. Bird migration was monitored for 12 years, in three different sites in the Dead Sea Valley, c. 1200 km north of the Sahel. These sites hold a disjunct, relict and northernmost part of the world distribution of Sudanian flora. Specifically, the Ein Gedi oasis, holds dozens M. crassifolia trees. In this study it is shown that in the Dead Sea Valley (1) the Lesser Whitethroat is a potential major pollinator of M. crassifolia while consuming nectar and picking pollen from the flowers on its feathers, (2) the peak migration of Lesser Whitethroats and the peak flowering of M. crassifolia coincide in the beginning of April and (3) the Lesser Whitethroat prefers stopover sites with flowering M. crassifolia trees. These findings suggest that mutualism exists between the Lesser Whitethroat and M. crassifolia, in different seasons and in different biogeographical regions. In addition, these findings suggest a possible adjustment of M. crassifolia flowering time, on an edge of its distribution range, to the phenology of its migrating pollinators.
The extent to which geographical features like coastlines and mountain ranges funnel migrating birds depends on the seasonal context and direction of migration. Near Batumi, in the Republic of Georgia, the eastern Black Sea coast and Lesser Caucasus funnel over one million raptors through a 10-20 km wide coastal strip every autumn. The funnelling effect of the Lesser Caucasus appears much less evident for northbound migrants. Yet historical data suggest tens of thousands of raptors pass through the region in spring. To elucidate the composition and timing of spring raptor migration we conducted full-season migration surveys near Batumi in 2019, 2020 and 2022. In total, we recorded 33 species and, on average, counted 542,161 raptors (range: 455,799-618,848) annually. The bulk of the spring passage consisted of Black Kite Milvus migrans (239,649 +/- 22,547 SD) and Steppe Buzzard Buteo buteo vulpinus (194,029 +/- 102,702). The most diverse and intense spring migration occurred from late March through mid-April when the median passage date of 12 of 15 common species (>100 individuals/year) occurred. Species with longer autumn migration periods tended to have longer spring migration periods, and most species had a longer migration period in spring than in autumn, likely due to larger age differences in timing during spring. Species' abundance was up to an order of magnitude lower in spring than in autumn, consistent with a weaker bottleneck-effect in spring. Nevertheless, our results confirm the eastern Black Sea coast as a principal spring flyway and help redraw the map of East African-Eurasian migration for several Palearctic raptors. Our data provides a baseline for detecting changes in raptor migration through short-term surveys and can help plan migration-based conservation and research at Batumi in spring.
Same-sex parenting is known in many species, including seabirds, but is rarely reported in burrow-nesting seabirds. This study shares the first documented case of two female Black-vented Shearwaters Puffinus opisthomelas forming a pair, observed on Natividad Island, Mexico, where most of the population breeds. Our findings reveal that two females have co-occupied the same burrow, successfully raising three chicks in 2017, 2019 and 2023. Although it is unclear exactly how the eggs were fertilized, this case demonstrates that same-sex pairs can be as reproductively successful as male-female pairs, suggesting a cooperative breeding strategy. The stability of this pairing and their reproductive success point to the possibility that same-sex pairs might play a more sig-nificant role in the breeding dynamics of Black-vented Shearwater. We believe this record adds to the evidence of the evolutionary significance of same-sex behaviours in seabirds, offering new insights into the reproductive dynamic of this species.
Human activities, including resource exploitation, coastal development and tourism, are prominent threats to waterbirds. Ensuring undisturbed habitats thus remains a conservation priority, especially in densely populated areas in Europe. Eurasian Spoonbills Platalea l. leucorodia are emblematic migratory waterbirds that have shown a strong recovery in European protected areas, including the Dutch Wadden Sea that is now the species' main European stronghold. However, this recovery has stalled, and while breeding colonies are strictly protected, visual observations suggest Spoonbills shift space use throughout their summer residency period, notably after breeding, into areas that may not be adequately protected. Focusing on a major breeding area in the eastern Wadden Sea, on the island of Schiermonnikoog, we used GPS-loggers with behavioural sensors to track 31 Eurasian Spoonbills over an 11-year period to describe space use and activity budgets from May to September. Using dynamic Brownian Bridge Movement Models to describe utilization distributions (UD), we delineated four key zones for this population and described substantial changes in their home range (95% UD), vital areas (75% UD) and core areas (50% UD) throughout the breeding and post-breeding periods. Key zones differed in intensity of use and function (based on activity budgets) throughout the summer residency period. Males and females exhibited distinct space use patterns, which converged into one key zone after breeding, namely the intertidal mudflats of Lutjewad, on the coast of the province of Groningen, used for moulting, pre-migratory flight fuelling and potentially as an information and social hub. The attractiveness of Lutjewad for Spoonbills might be linked to low levels of human disturbance at this site, which could be threatened by existing plans for major infrastructure developments. Overall, Spoonbills spent much of their summer residency period outside their strictly protected colonies, in key zones that are protected as N2000-sites, National Park or Natural World Heritage sites. However, additional measures may be needed in these areas to shield Spoonbills from human disturbance for extended periods.
In the last part of the twentieth century the House Sparrow Passer domesticus population started to decline in The Netherlands. To investigate whether there is a difference in yearly growth factor between urban and rural areas we estimated for two local House Sparrow populations, one suburban (in Leek) and one rural population (in Terheijl), the life history parameters, reproduction and survival. The mean (+/- SE) number of broods per year was (Leek vs. Terheijl): 1.202 +/- 0.039 and 1.463 +/- 0.043 and the mean number of fledglings per adult per brood 1.294 +/- 0.033 and 1.744 +/- 0.033. The analysis of survival data was performed with half-year-periods resulting in yearly survival estimates of juveniles of 0.325 and 0.395 and of adults of 0.442 and 0.487, for Leek and Terheijl, respectively. Based on these life history values a matrix population model for these populations was developed. Due to the different population growth factors of the two populations, we developed a metapopulation model in which we included a dispersal flow of juveniles from the (thriving) rural population to the surrounding environment, i.e. partly to sub-urban Leek. A simplified version was fitted to long term population estimates in Leek and Terheijl. This resulted in a dispersal of 48.5% of the juveniles from Terheijl. From this percentage leaving Terheijl only 19% should reach the population in Leek. These estimates resulted in a yearly growth of the metapopulation of 0.6% and thus the seemingly stable population numbers that are observed in Leek and Terheijl. More insights into this local source-sink relationship could help create awareness of the dependence of seemingly viable House Sparrow populations in (sub)urban areas on dispersal of juveniles from rural areas.
The post-fledging dependence period is a poorly known life stage of birds. In particular, knowledge of the interactions of fledged birds with unrelated con specifics is scarce. In territorial species, entering a foreign territory poses risks to a juvenile bird associated with the likely aggressive response of the territory owner. In this work, I explored the early movements of fledged Eurasian Scops Owls in a densely-packed neighbourhood characterized by small and contig u ous territories. To detect, identify, and track juvenile owls, I combined visual monitoring and spectrographic analysis of their vocalisations, which exhibited individually distinctive features. Juvenile owls entered foreign territories about five days after fledging and came in contact with neighbouring adults. The neighbouring adults never attacked the juveniles. Instead, they attacked the adults that were escorting and feeding those juveniles. During those interactions, they called at an acoustic frequency lower than that of the calls they gave on other occasions. Thus, territorial Scops Owls perceived juveniles differently from adults. The results emphasize an overlooked aspect of the early life of Scops Owls, when repeated interactions with other individuals can potentially influence their movement and possibly dispersal. Furthermore, the adults that attend a brood are likely to incur a cost of aggregation, in terms of the risk of being injured during conflicts with their neighbours.
Hybridization is an important factor in bird evolution. Distinguishing between hybrids and phenotypically aberrant individuals of one of the parental species can be challenging. Here, we use DNA sequencing of loci on chromosomes 2 and Z and the mitochondrial DNA to establish the status of a putative hybrid Azure Tit Cyanistes cyanus X Blue Tit Cyanistes caeruleus caught in Belgium in 2021. The genotype at each of these loci was a perfect match to Blue Tit. We therefore conclude that the bird was a genetically pure Blue Tit, despite its plumage being intermediate between Azure Tit and Blue Tit. We suggest records of Pleske's Tit lacking DNA information should be treated with caution.
