First-year Birds Research Articles

Low juvenile survival threatens the Black Stork Ciconia nigra in northern Europe

Summary Detecting factors causing the decline of wildlife populations provides essential knowledge for their effective conservation. Populations of Black Stork Ciconia nigra are decreasing in northern Europe; however, there are no detailed analyses of its survival, which frequently is a key demographic parameter affecting population dynamics in long-lived species. We used long-term data from re-sighted colour-ringed birds and satellite-tracked birds to estimate age- and sex-specific survival in a rapidly declining Black Stork population in the Baltic region at the northern end of the European range. Apparent survival (0.89) among colour-ringed birds older than one year was not significantly different from the previously reported estimates in Central Europe and the estimated real survival of GPS-tracked birds (0.77). However, the apparent survival of first-year (1y) birds was only 0.04, which is remarkably lower than earlier estimates in Central Europe. The real survival of GPS-tracked 1y birds was somewhat higher (0.11), but still much lower than estimates in other long-lived species. Apparent survival was three times lower in 1y females (0.013) than 1y males (0.045); this could be explained in part by a higher mean natal dispersal of females (189.1 km), compared with that of males (72.0 km), as well as by sex-specific mortality due to poor foraging conditions. There were no significant differences in apparent survival between the male and female storks older than one year. To better address the population decline, further research is needed to determine the factors causing low survival in young Black Storks, including the roles of food availability and climate change.

Avian trematodes of central European corvids are heterogeneous regarding preferences for host species and age.

Corvids are highly adaptive birds that respond well to anthropogenic changes in their environment. Trematode communities of corvids were studied mainly in the 1950s through 1970s in regularly flooded parts of the Volga River delta in Russia; more recent studies and data from other regions where the corvids are in less contact with postflooding habitats are limited. Data for Corvus corax were lacking. Using our samples obtained from 1963 to 2023, we performed a large-scale analysis of trematode species composition and community structure in Corvus frugilegus, Corvus cornix, C. corax, Coloeus monedula, Pica pica, and Garrulus glandarius; all originated from the Czech Republic. We identified corvids as hosts of mutually overlapping component communities of only a few species of trematodes (Brachylecithum lobatum, Lyperosomum petiolatum, Lyperosomum longicauda, Tamerlania zarudnyi, Urogonimus macrostomus), with the presence of many rare and incidental findings of other trematode species. Only a few species used corvids as their core hosts (L. longicauda and B. lobatum). Trematode component communities in first-year birds included Prosthogonimus cuneatus, Prosthogonimus ovatus, Plagiorchis asperus, and Morishitium dollfusi due to an increased share of insects (intermediate hosts of Prosthogonimus and Plagiorchis) and snails (intermediate hosts of Morishitium) in the diet of juveniles. The trematode component communities of corvid species overlapped but were heterogeneous at the level of host individuals, likely reflecting differences in food sources related to the respective host ages and nesting sites.

Food on a plate: Wild geese maintain higher food intake rates on uniform winter cereals fields versus diverse grasslands

Spring staging Greater White-fronted Geese Anser albifrons have increasingly shifted from traditional diverse grassland fields to monocultures of winter cereals, causing conflict with farmers. To account for this transition, we tested two key predictions, controlling for goose age effects and sward height. Firstly, that cereal is better quality than grass (based on crude protein content). Secondly, that geese show higher peck rate and step rate on grassland than cereal, enabling them to compensate for lower, less selective intake rates there compared to the uniform, dense, high quality arable sward where all blades are equally of high profitability. Laboratory analyses showed that winter cereal had 27 % higher crude protein content than grass. Based on data extracted from video sequences of spring foraging geese in NE Poland, first-year birds (“immatures”) showed significantly higher peck rates and step rates than adults in all situations, likely reflecting their less efficient foraging abilities. Both age classes showed significantly higher peck rates on grass than winter cereal as predicted. Combining differential protein content and lamina length/dry weight relationships of grass versus cereal showed that geese obtained 17–33 % more protein from cereal lamina of the same length. At observed peck rates, this equated to a 6 % greater hourly crude protein intake rate on cereals compared to grass at lamina length 2.5 cm, increasing to 29 % difference at 12.5 cm. Hence, at longer swards, cereals become increasingly profitable for foraging geese over grass swards, despite the higher peck rates observed on grass which failed to compensate for lower lamina quality. We contend that these interactions explain the simultaneous attraction of cereal over grass swards in this study area and likely elsewhere and we discuss the management implications of these findings.

Winter food selection and exploratory behavior vary with natal territory characteristics in wild great tits

Differences in habitat characteristics experienced during rearing associate with variation in a range of behavioral phenotypes such as exploratory behavior, foraging behavior and food selection. The habitat-dependent selection hypothesis predicts that animals develop behavioral characteristics fitted to their rearing environment. Yet, little is known about how habitat characteristics during rearing shape how animals face winter conditions and adjust their winter foraging behavior. The aim of this study was to explore how fine-scale rearing habitat characteristics associate with exploratory behavior, food selection, and foraging performance during winter. For this, we measured habitat characteristics during the breeding season in territories of wild great tits (Parus major) and tested first-year juvenile birds that fledged from these territories for exploratory and foraging behavior at feeders during winter. We found evidence that faster explorers were raised in territories with lower quality habitat characteristics. In addition, fast exploring fledglings visited the feeders significantly more (total visits). Moreover, the rearing environment, via caterpillar availability and tree species composition, determined diet selection during winter in first-year birds. These results show support for the habitat-dependent selection hypothesis, since exploratory behavior as well as food selection during winter associate with habitat features of the rearing territories during development. This pattern can be caused either by the kinds of natural foods prevalent during rearing at these sites or because of intrinsic individual differences. Further experiments are needed to disentangle these two.Significance statementIndividuals vary in how they behaviorally adapt foraging and food selection strategies to the environmental conditions. A number of studies have shown that animals develop behavioral characteristics fitted to their rearing environment. However, how habitat characteristics during rearing shape the foraging strategy that animals use to face winter conditions is still unknown. We studied these links in yearling great tits using automated feeders that recorded their visits during winter. Fledglings with a higher exploratory score were born in territories with lower quality habitat characteristics and visited the feeders more. Furthermore, we found an association between caterpillar availability and tree species composition in the rearing territory of juveniles and their subsequent food selection in winter. Our study indicates that certain environmental conditions might favor the development of particular behaviors in birds and that early nutrition could shape food choice later in life.

Avian influenza overview March – April 2023

Between 2 March and 28 April 2023, highly pathogenic avian influenza (HPAI) A(H5Nx) virus, clade 2.3.4.4b, outbreaks were reported in domestic (106) and wild (610) birds across 24 countries in Europe. Poultry outbreaks occurred less frequently compared to the previous reporting period and compared to spring 2022. Most of these outbreaks were classified as primary outbreaks without secondary spread and some of them associated with atypical disease presentation, in particular low mortality. In wild birds, black-headed gulls continued to be heavily affected, while also other threatened wild bird species, such as the peregrine falcon, showed increased mortality. The ongoing epidemic in black-headed gulls, many of which breed inland, may increase the risk for poultry, especially in July-August, when first-year birds disperse from the breeding colonies. HPAI A(H5N1) virus also continued to expand in the Americas, including in mammalian species, and is expected to reach the Antarctic in the near future. HPAI virus infections were detected in six mammal species, particularly in marine mammals and mustelids, for the first time, while the viruses currently circulating in Europe retain a preferential binding for avian-like receptors. Since 13 March 2022 and as of 10 May 2023, two A(H5N1) clade 2.3.4.4b virus detections in humans were reported from China (1), and Chile (1), as well as three A(H9N2) and one A(H3N8) human infections in China. The risk of infection with currently circulating avian H5 influenza viruses of clade 2.3.4.4b in Europe remains low for the general population in the EU/EEA, and low to moderate for occupationally or otherwise exposed people.

Illegal killing associated with gamebird management accounts for up to three-quarters of annual mortality in Hen Harriers Circus cyaneus

Predators are frequently victims of wildlife crime due to conflicts with human interests. Where predators are protected, killing may occur covertly and novel methods, including satellite tracking, are often required to assess population consequences. Wildlife crime persists in the British uplands, where raptors are illegally killed on moorland managed for Red Grouse Lagopus lagopus scotica shooting. To understand impacts on one such species, the Hen Harrier Circus cyaneus, we analysed data from 148 individuals tracked across Britain between 2014 and 2021. Using remotely sensed land-use data and continuous-time survival methods, we quantified survival rates, contributions of natural causes and illegal killing to mortality, and spatial and temporal associations between mortality and land managed for grouse shooting. Annual survival was low, especially among first-year birds (males: 14 %; females: 30 %), with illegal killing accounting for 27–43 % and 75 % of mortality in first-year and subadult (1-2 years) harriers respectively. Illegal killing is likely attributable to grouse moor management because i) a 10 % increase in grouse moor use resulted in a 43 % increase in mortality risk; ii) a strong overlap existed between mortality and grouse moor extent in 20 km squares, identifying hotspots of illegal killing in northern England and northeast Scotland; iii) death due to natural causes showed different spatial and temporal patterns; and iv) timing of mortality peaked around the shooting season and during breeding territory establishment. Governments have failed to reduce illegal killing of Hen Harriers and other raptors in Britain and our results emphasise that further legislative reform is needed to tackle this enduring criminality.

The Effect of Local Weather Conditions on American Kestrel (Falco sparverius) Reproduction

ABSTRACT American Kestrel (Falco sparverius) populations have been declining in North America during recent decades and potential causes, including climate change, currently are under investigation. Many studies of migratory birds have demonstrated the effects of climate change, including changes in local weather conditions and the increase in extreme weather, but the relationship between local weather and kestrel ecology in the northeastern United States has received little attention. We examined the relationship of local weather conditions and kestrel breeding performance in northwestern New Jersey between 1996 and 2016. We also obtained temperature, rainfall, and snowfall data from weather stations within or adjacent to our study area. We did not detect significant changes in climate over the study period, but we did find significant associations between local weather conditions and kestrel breeding performance. Warmer temperatures during the breeding season were significantly correlated with earlier nesting, and early nesting had significant positive correlations with clutch size, hatching rate, nestling survival, and nesting success (raising at least one young to fledging). We did not detect a significant relationship between rainfall and nesting variables, but snowfall during autumn was strongly related to kestrel breeding performance the following year. Compared to years when there was no snowfall in our study area the preceding autumn, kestrels breeding in years following autumn snow had significantly smaller clutches, lower hatching rates, lower nestling survival rate, and lower nesting success. Kestrels in our region are partial migrants; first-year birds generally migrate to southern wintering grounds while older birds may remain in the region, presumably in response to local conditions. We suggest that substantial snow during autumn may drive a larger percentage of adults to migrate south, as indicated by the greater number of kestrels counted at representative autumn hawk watch sites during years with substantial autumn snow. Our study concludes that variations in local weather conditions throughout the year can affect the breeding performance of American Kestrels, whether or not they are associated with climate change.

The using of data on the moult progress in the study of migration periods of the annual cycle of passerines

Using trapping and ringing of birds for studying the ecology and the demographic parameters of populations is necessary to determine as accurately as possible in which period of the annual cycle each individual was caught. The first-year passerine birds undergo juvenile migration (usually in form of postfledging dispersal) and postmoulting (autumn) migration in summer-autumn period. These stages of annual cycle are difficult to identify in trapping birds by calendar dates because the timing of migration seasons can significantly overlap in the same location. The study of moult at the Ladoga Ornithological Station made it possible to determine the states of plumage that mark juvenile and postmoulting migrations in first-year birds. The article presents two examples of the use of moult progress in the study of bird migrations. The first one is an analysis of the ratio of the terms of departure and passage in three long-distant and three short-distant migrants of passerines. It has been shown that the timing of the departure of local birds is earlier than the timing of the passage of other populations in all studied species, while the last local individuals in long-distance migrants are recorded long before the end of the passage of the species, and in short-distance migrants they can be found until its end. As another example, an analysis of long-term trends in the timing of summer-autumn movements in the Garden Warbler was performed. It is shown that for almost a fifty-year observation period, neither the timing of juvenile migration nor the timing of postmoulting migration of first-year birds has changed. At the same time, the timing of the spring passage of the species shifted to earlier. As a result, the duration of stay of the Garden Warbler in the Ladoga region has increased.

Morphometry of black grouse Lyrurus tetrix L. and hazel grouse Tetrastes bonasia L. from the north of the Arkhangelsk Region, Russia

Body weight and lengths of the wing, tail, tarsus, and beak were measured in 139 black grouse (BG) Lyrurus tetrix (Linnaeus, 1758) and 318 hazel grouse (HG) Tetrastes bonasia (Linnaeus, 1758) captured in the north of the Arkhangelsk Region (Russia) in 1990–2006. Almost all the estimates are within the average range of the parameters for Northern Europe (Norway – Komi Republic). Sexual dimorphism in BG was revealed for all traits except the wing length; dimorphism by tail length in Northern Europe appears to be growing from east to west. Size dimorphism in HG is inexplicit and, apparently, minimal in spring; females before and during egg-laying are heavier than males. In young BG, the dimensional growth of tarsi in males and females is completed in the 2nd-3rd months since birth, that of beak – in the 3rd-4th month, that of tail and wings – in the 4th-5th months. In HG, these processes are shorter: tarsi and beak – in the 2nd month, wings and tail – in the 3rd-4th months. Tail and beak lengths and body weight showed the greatest variation in both species, while wings and tarsi were the most stable parts of their bodies. Tarsus was also utterly independent of the other four traits, while wing length correlated with tail length and body weight (BG) or tail length only (HG). The age-related variation patterns for studied traits and correlations between them indicate the likelihood of migration processes, especially for BG. The arrival of first-year birds of both species in study area from August to May-June is hardly probable, but their emigration may take place. Part of the size variation in adult birds is apparently due to arrivals from outside.

The fate of rescued Manx Shearwaters following grounding

Manx Shearwaters Puffinus puffinus, like other procellariiform seabirds, spend most of their lives at sea and are encountered on land only when breeding at colonies or if they are grounded due to unfavourable weather conditions or exposure to artificial light. Here, we used historical ringing data to explore the age class structure and spatial patterns of Manx Shearwater groundings and examined ringing and recovery data to identify records of post-grounding survival for first-year and adult birds. We noted 35 cases, out of 6,381 ringed grounded shearwaters, where a bird went on to be recaptured, including two individuals that were later recorded as having successful breeding attempts. While this constitutes only a small number of birds confirmed to have survived following grounding, it is likely to be a considerable underestimate of survival considering the low probability of recapturing a surviving shearwater. Finally, we found that a greater proportion of grounded birds were first-years compared to adult shearwaters, and that adults were found to be grounded further away from colonies than first-year birds. This may be indicative of differential impacts of light pollution at different life stages.

Eurasian Woodcock monitoring in Hungary between 2009–2021

To preserve the traditional spring hunting of the Eurasian Woodcock (Scolopax rusticola) in Hungary while also assuring its sustainability, a monitoring program was maintained with the coordination of the Hungarian Hunters’ National Association. The program's primary goal was to estimate the size of the migrating population in the country based on synchronised census data and track its long-term changes. The program was maintained successfully with national coverage in the last 13 years, and it was based on synchronised roding surveys performed weekly, 12 times each spring. The observers used standardised paper forms to record the number of contacts (Woodcocks seen and/or heard). Hunting of Woodcock between 2010–2021 was only allowed for the monitoring program participants with strict regulation and obligatory sample collection from each bird. The primary purpose of sample collection was to assess the sex- and age structure of the population and to evaluate their trends. According to the results, no significant trend could be observed either in the population size or the sex- and age composition between 2009 and 2021. The proportion of males was above 75% each year, while the proportion of first-year birds and adults was almost identical in the annual hunting bags. The measure of harvesting was meagre compared to the size of the population, and it had no significant, detectable impact.

Annual captures and low apparent survival rates in two tit species in western Hungary

AbstractAdult and juvenile survival are important factors affecting the population dynamics of small passerines. Understanding variation in the population dynamics and survival rates is critical for ecological studies and nature conservation. The aim of this study was to investigate the annual capture-recapture, apparent survival and capture probabilities of the Blue TitCyanistes caeruleusand the Great TitParus majoroccurring in western Hungary. Data from 8,628 Blue Tits and 7,727 Great Tits came from a constant-effort ringing scheme, using three ringing periods, spanning 24 years (1998 to 2021). The annual captures did not show a significant linear trend from 1998 to 2021 in the study site for both tit species. The temporal variation of annual captures and the annual capture-recapture proportions of different ages and sexes of the tit species were similar. This indicated that the migration strategies of these two partial migrant species did not differ significantly. According to the best standard Cormack-Jolly-Seber model, apparent survival of first-year birds was lower than that for adults. The CJS model selection for the dataset indicated that the time and sex had no effect on apparent survival probabilities for both tit species. Capture probability in the juvenile groups was not significantly higher than that in the adult groups for both species.

Migration Patterns and Recorded Emigration of the Great Cormorant Phalacrocorax carbo sinensis in the Largest French Colony of Lac de Grand-Lieu: Density-Dependent Factors Operating at Different Time and Geographical Scales

The number of wintering Great Cormorants Phalacrocorax carbo sinensis in France has strongly increased since the 1970s, mainly due to the protection of the ‘continental’ sinensis subspecies in countries north of France. This increase has led to the establishment of a pioneering inland breeding colony in western France, while previously only the largely marine ‘Atlantic’ P. c. carbo subspecies occurred on the Channel coast. The marine subspecies was attracted and bred in this new inland settlement of sinensis, which rapidly became the largest colony in France. This paper analyses the migration pattern of birds from this colony by analysis of the dispersal of colour-ringed birds between 1989 and 2008. Interestingly, besides a classic south-west migration pattern, birds from this colony also displayed a pattern heading north-east, up to countries such as The Netherlands, from where the founders (sinensis) of this colony probably originated. Sightings and recoveries revealed that about 25% of the adults and 19% of the first-year birds headed north-east. Due to this north-east migration direction, the overall annual dispersal point was located only 50 km south-west of the colony, although in December and January this midpoint was located about 320 km south-west of the colony. The birds largely avoided Brittany, presumably to avoid competition with individuals of the carbo subspecies, and the main wintering areas of sinensis from other colonies, both in France (east, centre and south) and in Spain. Over the years 1989–2008, in the breeding period, the mean dispersal distance was shorter for adults than for young birds (54 km vs. 144 km, respectively) but in winter adult birds migrated further than young ones (305 km vs. 221 km, respectively). The mean annual dispersal distance in winter varied from 106 km to 527 km (all age-classes taken together). Migratory distance was not related to mean winter temperature. For adults, dispersal distance correlated with the annual number of breeding pairs in the Grand-Lieu colony between 1990 and 2003, but not between 2004–2008. Emigration (breeding in another colony) was recorded up to 2011 to 11 inland colonies and one coastal colony (founded more recently than Grand-Lieu), nine of them in France, two in Spain and one in The Netherlands. Annual emigration rate was negatively related to colony size in Grand-Lieu. The study points to the existence of density-dependent effects on distribution patterns of Cormorants outside the breeding season but also suggests connectivity and interaction among colonies that are hundreds of kilometres apart.

Body mass and geographic distribution determined the evolution of the wing flight-feather molt strategy in the Neornithes lineage

The evolutionary history of many organisms is characterized by major changes in morphology and distribution. Specifically, alterations of body mass and geographic distribution may profoundly influence organismal life-history traits. Here, we reconstructed the evolutionary history of flight-feather molt strategy using data from 1,808 Neornithes species. Our analysis suggests that the ancestral molt strategy of first-year birds was partial or entirely absent, and that complete wing flight-feather molt in first-year birds first evolved in the late Eocene and Oligocene (25–40 Ma), at least 30 Myr after birds first evolved. Complete flight-feather molt occurred mainly at equatorial latitudes and in relatively low body mass species, following a diversification of body mass within the lineage. We conclude that both body mass and geographic distribution shaped the evolution of molt strategies and propose that the evolutionary transition towards complete juvenile molt in the Neornithes is a novel, relatively late adaptation.

Experimental manipulation of photoperiod influences migration timing in a wild, long-distance migratory songbird.

Previous laboratory studies have demonstrated the role of photoperiod in cueing the migration timing of small land birds; however, how migration timing of young birds in wild environments develops in relation to these cues have rarely been investigated. Such investigations can make important contributions to our developing understanding of the phenotypic plasticity of migration timing to new conditions with climate change, where changes in the timing of nesting may expose juvenile birds to different photoperiods. We investigated the impact of manipulating photoperiod during nestling development in a long-distance migratory songbird on the timing of post-breeding movements in the wild. Using programmable lighting installed in the nest-boxes of purple martins (Progne subis), we exposed developing nestlings, from hatch to fledge date, to an extended photoperiod that matched the day length of the summer solstice in Manitoba, Canada. We found that birds with a simulated, earlier photoperiod had a longer nesting period and later fledge and autumn departure dates than control group birds. This study demonstrates the phenotypic plasticity of first-year birds to the ontogenetic effect of their hatch date in the formation of the timing of their first post-breeding movements. Further, we discuss how these results have implications for the potential use of assisted evolution approaches to alter migration timing to match new conditions with climate change.

Evidence for seasonal changes in population structure of Reed Buntings (Emberiza schoeniclus) in the Lake Neusiedl Region: a stable-isotope approach

Migrating species and populations are affected by conditions existing across large geographical scales. The degree to which populations mix at stop-over sites and wintering grounds is variable and can involve important fitness consequences. Thus, the link between breeding and wintering grounds and seasonal shifts in population structure are important to understand population demographics, local adaption and diversification patterns. This work aims to infer migration patterns and population connectivity in the Reed Bunting (Emberiza schoeniclus) community of a Ramsar-designated wetland, Lake Neusiedl, Seewinkel, Austria. Stable isotope markers (hydrogen, δ2H, carbon, δ13C) in feathers were analyzed to assign individuals to a specific breeding or natal area. Based on the geographic assignment, birds were compared with respect to their ecomorphological traits and their habitat selection (large reed bed versus more open habitat at shore of an alkaline lake) during winter to assess potential ecological differences and possibly associated morphological divergence. Stable isotope data revealed that the local Reed Bunting community undergoes seasonal changes in population structure. Three different populations that vary in their δ2H signature and to some extent in morphological characteristics as well as in δ13C values were identified. Indications for differential migration related to age and/or sex were additionally found, since males and females as well as first-year birds and adults showed remarkable differences in their traits and feather isotope values. δ2H values diverged significantly between these groups in both age and sex classes and birds with highest feather δ2H values were considered to represent the local breeding population at Lake Neusiedl and possibly also Reed Buntings from close surroundings. Moreover, this group had the highest δ13C values in first-year individuals as well as in adults. In both sex classes, the assignment of Reed Buntings to different populations was ultimately possible due to differences in bill shape with residents being characterized by more massive bills than individuals belonging to populations visiting the study area only during migration or for wintering. During winter, beak shape and feather δ2H and δ13C values differed significantly between birds caught in the reed stand of Lake Neusiedl and those captured near the salt pan, hence, indicating differential habitat selection among co-occurring populations during winter. These findings suggest that morphological attributes, such as bill shape and size as well as linked adaptations to different food sources play a decisive role for niche segregation among wintering populations. The results provide evidence that different populations mix during migration and during winter at Lake Neusiedl and the extent to which they are specialized to a specific habitat varied.

Sex, age, molt strategy, and migration distance explain the phenology of songbirds at a stopover along the East Asian flyway

Sex- and age-specific differences in the timing of migration are widespread among animals. In birds, common patterns are protandry, the earlier arrival of males in spring, and age-differential migration during autumn. However, knowledge of these differences stems mainly from the Palearctic-African and Nearctic-Neotropical flyways, while detailed information about the phenology of migrant birds from the East Asian flyway is far scarcer. To help fill parts of this gap, we analyzed how migration distance, sex, age, and molt strategy affect the spring and autumn phenologies of 36 migrant songbirds (altogether 18,427 individuals) at a stopover site in the Russian Far East. Sex-differential migration was more pronounced in spring than in autumn, with half of the studied species (6 out of 12) showing a protandrous migration pattern. Age-differences in migration were rare in spring but found in nearly half of the studied species (11 out of 25) in autumn. These age effects were associated with the birds’ molt strategy and the mean latitudinal distances from the assumed breeding area to the study site. Adults performing a complete molt before the onset of autumn migration passed the study site later than first-year birds undergoing only a partial molt. This pattern, however, reversed with increasing migration distance to the study site. These sex-, age-, and molt-specific migration patterns agree with those found along other flyways and seem to be common features of land bird migration strategies.Significance statementThe timing of animal migration is shaped by the availability of resources and the organization of annual cycles. In migrant birds, sex- and age-differential migration is a common phenomenon. For the rarely studied East Asian flyway, we show for the first time and based on a large set of migrant songbirds that earlier migration of males is a common pattern there in spring. Further, the timing and extent of molt explained age-differential migration during autumn. Adults molting their complete plumage at the breeding area before migration showed delayed phenology in comparison to first-year birds, which perform only a partial molt. This pattern, however, reversed with increasing migration distance to the study site. Since our results agree with the general patterns from the other migration flyways, similar drivers for differential migration may act across different flyway systems, provoking a similar evolutionary response.

Meteorological factors affecting refueling of European Robin (Erithacus rubecula) during migrations.

Weather ultimately affects avian migration. The significance of meteorological variables is relatively well known for flights of migrants and for departure/landing decisions at stopover sites. Success of migration greatly depends on storage of fat and body mass gain at stopovers; however, the influence of weather on refueling at stopovers is surprisingly poorly studied. We tested the hypothesis that body mass change of European Robins during their migratory stopovers is affected by meteorological factors (air temperature, precipitations, surface wind speed), along with other ecological variables. We used data on body mass change in 9743 individuals (5147in spring and 4587 in the fall) captured and recaptured within the same day on the Courish Spit of the Baltic Sea in 1994-2003. Fuel deposition rate in Robins was positively associated with air temperature and with higher amount of precipitation. Wind speed did not influence the refueling efficiency of our study species. Also, fuel deposition rate of Robins was affected by age (higher in adults than in first-year birds), negatively influenced by the number of conspecifics at stopover, influenced by the progress of the season (negatively in spring and positively in fall), and negatively influenced by initial energy reserves of migrants, when birds in poor energy condition were more likely to gain weight than birds with large fuel stores. This study shows that refueling of Robins on migration stopovers is substantially affected by meteorological factors that should be taken in to account for comprehensive understanding of stopover ecology and migration strategy of songbird migrants.

Emerging helminthiases of song thrush (Turdus philomelos) in Central Europe.

Turdus philomelos is a common Western Palearctic thrush species of forests and agricultural landscapes, where it relies on the presence of hedgerows, patches of trees, and shrubs. In the present study, we address long-term changes in component communities of trematodes in T. philomelos across the timespan of over half a century. Based on our preliminary observations, we hypothesized that component communities of trematodes in T. philomelos in the study area are more diverse and species-rich compared with several decades ago. In the 1961-2019, we performed full-body necropsies of T. philomelos, which originated from the southern Czech Republic, and examined them for the presence of trematodes. We compared the trematode species richness and diversity of the analyzed component communities. The number of trematode species per host steadily increased in time in adult females and males. In juveniles, the highest numbers of trematode species per host were reached already in 1961-1990, then dropped and slowly raised up again in the latter time periods. The newly accumulated evidence suggests that trematodes with intermediate hosts previously restricted to T. philomelos wintering grounds increased in abundance in the study area. Some of them (Morishitium polonicum, Psilotornus confertus) sporadically appeared in juveniles or first-year birds, from which they were previously completely absent. Some of the spreading species, such as Lutztrema attenuatum, are present in high prevalence and high intensities of infection. Yet unknown part of observed changes could be related to changes in food composition; however, direct evidence for changes in T. philomelos diet is lacking despite clear evidence for a decline in earthworms in agricultural landscapes.

Migratory behaviour and survival of Great Egrets after range expansion in Central Europe.

Great Egret Ardea alba is one of few Western Palearctic species that underwent a rapid range expansion in the recent decades. Originally breeding in central and eastern Europe, the species has spread in northern (up to the Baltic coast) and western (up to the western France) directions and established viable breeding populations throughout almost entire continent. We monitored one of the first Great Egrets colonies established in Poland to infer migratory patterns and survival rates directly after range expansion. For this purpose, we collected resightings from over 200 Great Egret chicks marked between 2002–2017 in central Poland. Direction of migration was non-random, as birds moved almost exclusively into the western direction. Wintering grounds were located mainly in the western Europe (Germany to France) within 800–950 km from the breeding colony. First-year birds migrated farther than adults. We found some, although relatively weak, support for age-dependent survival of Great Egrets and under the best-fitted capture-recapture model, the estimated annual survival rate of adults was nearly twice higher than for first-year birds (φad = 0.85 ± 0.05 vs. φfy = 0.48 ± 0.15). Annual survival rate under the constant model (no age-related variation) was estimated at φ = 0.81 ± 0.05. Our results suggest that Great Egrets rapidly adapted to novel ecological and environmental conditions during range expansion. We suggest that high survival rate of birds from central Poland and their western direction of migration may facilitate further colonization processes in western Europe.