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The species-specific and age-related autumn migration strategies of the sedge, reed and great reed warbler were investigated at stopover sites between central Europe and north-eastern Africa during autumn. Adult reed warblers accumulated larger fat reserves than juveniles and consequently were able to cover longer distances from most stopover sites. Juvenile sedge warblers, on the other hand, left Europe with significantly larger fat reserves than adults as opposed to the populations migrating along the western route. Both juvenile and adult great reed warblers were potentially able to make long flights without refuelling from the northern part of the Mediterranean region onwards. It was the proximity of large ecological barriers that had the most prominent influence on the potential flight distances of adult and juvenile Acrocephalus warblers during their southward migration. In reed and sedge warblers, the differences in mean flight distances covered by adults and juveniles were the largest (ca. 600 km) just before the crossing of the Mediterranean Sea, but smaller (ca. 200 and 400 km, respectively) in front of the Sahara Desert. Juvenile and adult great reed warblers were potentially able to cover 1660 km from Turkey, which was also supported by very low numbers of individuals caught at the Egyptian ringing sites. The results of this study carried out in the key regions of the eastern European–African flyway documented that migration strategies differed between adults and juveniles of three long-distance migrant species, yet this variation depended on the migration stage and the proximity of natural ecological barriers.

Abstract How blood parasite infections influence the migration of hosts remains a lively debated issue as past studies found negative, positive, or no response to infections. This particularly applies to small birds, for which monitoring of detailed migration behavior over a whole annual cycle has been technically unachievable so far. Here, we investigate how bird migration is influenced by parasite infections. To this end, we tracked great reed warblers (Acrocephalus arundinaceus) with multisensor loggers, characterized general migration patterns as well as detailed flight bout durations, resting times and flight heights, and related these to the genus and intensity of their avian haemosporidian infections. We found migration distances to be shorter and the onset of autumn migration to be delayed with increasing intensity of blood parasite infection, in particular for birds with Plasmodium and mixed‐genus infections. Additionally, the durations of migratory flight bout were prolonged for infected compared to uninfected birds. But since severely infected birds and particularly birds with mixed‐genus infections had shorter resting times, initial delays seemed to be compensated for and the timing in other periods of the annual cycle was not compromised by infection. Overall, our multisensor logger approach revealed that avian blood parasites have mostly subtle effects on migratory performance and that effects can occur in specific periods of the year only.

The great reed warbler Acrocephalus arundinaceus is a common migrant through the Western Palearctic. However, its migration strategy, especially the spatiotemporal pattern of accumulation and utilisation of energy stores en route, is poorly known. Using ringing data collected at distant stopover sites located from Central Europe to Asia Minor, we observed that pattern in juvenile great reed warblers migrating along the eastern European flyway in autumn. We analysed body condition and stopover duration and estimated potential flight ranges for this species, taking into account two large ecological barriers – the Mediterranean Sea and the Sahara Desert – which it crosses during its southward migration. In Central and South-Eastern Europe the seasonal trends in body condition were similar and non-linear, with low values in August (i.e., during intensive migration of Acrocephalidae), and then a significant increase from the beginning of September until the end of the month. Estimated potential flight ranges showed that individuals migrating through Central and South-Eastern Europe might generally reach only the northern coast of the Mediterranean Sea. On the other hand, those flying from Asia Minor were able to reach the northern edge of the Sahel zone, crossing two large ecological barriers without refuelling. Therefore, it seems that great reed warblers change their autumn strategy en route: first, they migrate in short steps with low energy reserves through continental Europe; and then, after intensive refuelling before the Mediterranean Sea, they reach sub-Saharan Africa in a long flight. Based on the analysis of ringing data from several stopover sites, we show the complex pattern of how a long-distance migratory species accumulates and utilises its energy stores en route.

Background: Ixodid ticks are widely studied due to their epidemiological and epizootic importance. It is of great value to know vertebrate host preferences of ticks in order to understand their ecological relationships and distribution. Earlier studies report birds as important hosts of Ixodid tick and a total of 136 ticks species have been frequently found in birds worldwide. However, only few studies related to host preferences of ticks among wild birds in Bulgaria were conducted till now. Aim: To obtain new data on the host preferences of ixodid ticks among wild birds at three locations in Bulgaria. Material and methods: The study was conducted between 2010 – 2020 in three sites in Bulgaria – Biological Experimental Station Kalimok (Silistra region), near Brodilovo village (Burgas region), and the city of Sofia (city park). The birds were caught by mist nets and inspected for ticks. Ticks found were removed by fine tweezers or a special removal tool for ectoparasites. Tick identification was based on external morphological characteristics. Results: A total of 2419 individual birds belonging to 78 species were examined. Of these, 70 individuals (16 species) carried ticks, thus representing 2.9% infestation rate. A total of 262 ticks were collected and identified as: Ixodes ricinus, Hyalomma marginatum, Haemaphysalis punctata, Hae. concinna, Hae. sulcata and two specimens could only be identified to the genus Haemaphysalis. Ixodes ricinus was the most commonly encountered tick (224/262), predominantly nymphs, followed by Hyalomma marginatum (27/262). The highest prevalence of tick infestation was observed among the Eurasian Blackbird, Turdus merula (28.6%), followed by the common nightingale, Luscinia megarhynchos (12.9%) and the common chaffinch, Fringilla coelebs (11.3%). These three bird species harboured the majority of ticks on their heads – some single individuals were infested by 10 up to 25 ticks per bird. Conclusion: Ixodes ricinus was found as the predominant tick species in this study. Nymphs were the most frequently observed stage. Infesting both birds and humans, this tick species has the potential to spread local tick-borne infections.

The species-specific and age-related autumn migration strategies of the sedge, reed and great reed warbler were investigated at stopover sites between central Europe and north-eastern Africa during autumn. Adult reed warblers accumulated larger fat reserves than juveniles and consequently were able to cover longer distances from most stopover sites. Juvenile sedge warblers, on the other hand, left Europe with significantly larger fat reserves than adults as opposed to the populations migrating along the western route. Both juvenile and adult great reed warblers were potentially able to make long flights without refuelling from the northern part of the Mediterranean region onwards. It was the proximity of large ecological barriers that had the most prominent influence on the potential flight distances of adult and juvenile Acrocephalus warblers during their southward migration. In reed and sedge warblers, the differences in mean flight distances covered by adults and juveniles were the largest (ca. 600 km) just before the crossing of the Mediterranean Sea, but smaller (ca. 200 and 400 km, respectively) in front of the Sahara Desert. Juvenile and adult great reed warblers were potentially able to cover 1660 km from Turkey, which was also supported by very low numbers of individuals caught at the Egyptian ringing sites. The results of this study carried out in the key regions of the eastern European–African flyway documented that migration strategies differed between adults and juveniles of three long-distance migrant species, yet this variation depended on the migration stage and the proximity of natural ecological barriers. [ABSTRACT FROM AUTHOR]

Abstract European Turtle Doves (Streptopelia turtur) are long‐distance migrants and have experienced a population decline of more than 78% since 1980. Their conservation depends on refined knowledge of breeding origins and population connectivity. Feathers collected at stopover sites, but molted at breeding grounds, provide an opportunity to assign birds to potential regions of origin using tissue stable hydrogen isotope values and relate those to a European feather hydrogen isoscape. Here, 101 feather samples from 13 different breeding countries were analyzed to calibrate the European hydrogen isoscape and 101 feather samples from Spanish, Italian, Maltese, Greek, and Bulgarian stopovers were assigned to potential regions of origin. The assigned range of origin for all 101 individuals grouped together agreed with known distribution patterns. Bulgarian samples were mostly assigned to Russian areas. Possible origins of Greek, Italian, Maltese, and Spanish samples ranged from central to southern Europe. Individual assignments highlighted four broad regions of origin, corresponding to a cool/humid to hot/dry temperature gradient. Proportions of birds assigned to these regions varied among birds sampled at different stopover sites. Therefore, our results provide important information about population connectivity and may be useful to evaluate possible influences of hunting on Turtle Dove populations.

Abstract Background Over the past decade, the miniaturisation of animal borne tags such as geolocators and GPS-transmitters has revolutionized our knowledge of the whereabouts of migratory species. Novel light-weight multi-sensor loggers (1.4 g), which harbour sensors for measuring ambient light intensity, atmospheric pressure, temperature and acceleration, were fixed to two long-distance migrant bird species - eurasian hoopoe (Upupa epops) and great reed warbler (Acrocephalus arundinaceus). Using acceleration and atmospheric pressure data recorded every 5 and 30 min, respectively, we aimed at reconstructing individual diurnal and seasonal patterns of flight activity and flight altitude and thereby, at describing basic, yet hitherto unknown characteristics of migratory flight behaviour. Furthermore, we wanted to characterise the variability in these migration characteristics between individuals, species and migration periods. Results The flight duration from breeding to sub-Saharan African non-breeding sites and back was more variable within than between the species. Great reed warblers were airborne for a total of 252 flight hours and thus, only slightly longer than eurasian hoopoes with 232 h. With a few exceptions, both species migrated predominantly nocturnally - departure around dusk and landing before dawn. Mean flight altitudes were higher during pre- than during post-breeding migration (median 1100 to 1600 m a.s.l.) and flight above 3000 m occurred regularly with a few great reed warblers exceeding 6000 m a.s.l. (max. 6458 m a.s.l.). Individuals changed flight altitudes repeatedly during a flight bout, indicating a continuous search for (more) favourable flight conditions. Conclusions We found high variation between individuals in the flight behaviour parameters measured – a variation that surprisingly even exceeded the variation between the species. More importantly, our results have shown that multi-sensor loggers have the potential to provide detailed insights into many fundamental aspects of individual behaviour in small aerial migrants. Combining the data recorded on the multiple sensors with, e.g., remote sensing data like weather and habitat quality on the spatial and temporal scale will be a great step forward to explore individual decisions during migration and their consequences.

Migratory connectivity describes to which degree different breeding populations have distinct (non‐overlapping) non‐breeding sites. Uncovering the level of migratory connectivity is crucial for effective conservation actions and for understanding of the evolution of local adaptations and migratory routes. Here we investigate migration patterns in a passerine bird, the great reed warbler Acrocephalus arundinaceus, over its wide Western Palearctic breeding range using geolocators from Spain, Sweden, Czech Republic, Bulgaria and Turkey. We found moderate migratory connectivity: a highly significant spatial structure in the connections between breeding and sub‐Saharan non‐breeding grounds, but at the same time a partial overlap between individual populations, particularly along the Gulf of Guinea where the majority of birds from the Spanish, Swedish and Czech populations spent their non‐breeding period. The post‐breeding migration routes were similar in direction and rather parallel for the five populations. Birds from Turkey showed the most distinctive migratory routes and sub‐Saharan non‐breeding range, with a post‐breeding migration to east Africa and, together with birds from Bulgaria, a previously unknown pre‐breeding migration over the Arabian Peninsula indicating counter‐clockwise loop migration. The distances between breeding and sub‐Saharan non‐breeding sites, as well as between first and final sub‐Saharan non‐breeding sites, differed among populations. However, the total speed of migration did not differ significantly between populations; neither during post‐breeding migration in autumn, nor pre‐breeding migration in spring. There was also no significant relationship between the total speed of migration and distance between breeding and non‐breeding sites (neither post‐ nor pre‐breeding) and, surprisingly, the total speed of migration generally did not differ significantly between post‐breeding and pre‐breeding migration. Future challenges include understanding whether non‐breeding environmental conditions may have influenced the differences in migratory patterns that we observed between populations, and to which extent non‐breeding habitat fluctuations and loss may affect population sizes of migrants.

Abstract: Blood parasite infections have been shown to influence behavioural traits of their avian hosts, in particular activity level and boldness. Following the hypothesis that a mixed infection by different [...]

Abstract Long‐term shifts in vegetation phenology generally follow the pattern of global warming. Yet, topographical complexity and biome diversity cause uneven spatial trends in the phenological response of vegetation to climate change. If phenology changes similarly along migration routes, individuals may adequately respond by shifting the whole migration schedule to still time life history with local phenological events. On the contrary, phenological shifts that differ in direction or magnitude between sites can enhance the risk of mistiming, resulting in reduced survival and reproductive success and eventually population declines. We identified the direction and magnitude of long‐term shifts in vegetation phenology along avian migration routes, using remotely sensed vegetation data over 29 yr (1982–2010) to estimate the risk of mistiming for different sets of assumptions concerning cues and adaptability of migration timing. For this study, we used individual series of non‐breeding, spring stopover and breeding sites (determined by light‐level geolocation) of three European populations of Luscinia megarhynchos (Common Nightingale), an insectivorous Palearctic long‐distance migrant. The breeding populations in France, Italy, and Bulgaria are representatives for populations migrating on the western, central, and eastern flyway toward sub‐Saharan Africa. The direction and magnitude of phenological shifts differed between migration stages and across flyways and under most sets of assumptions, the resulting risk of mistiming was higher in the Western compared to Central and Eastern flyway. We emphasize that estimates for the risk of mistiming as resulting from phenological shifts highly depend on the cues that migrants use to time migratory progression and on the adaptive potential of the particular migratory species to react to phenological shifts.

Population genetic structure was studied in paddyfield warblers Acrocephalus agricola breeding in NE Bulgaria, SE Russia and S Kazakhstan. We were particularly interested in the degree of genetic differentiation and gene flow of the Bulgarian population due to its geographical isolation, recent origin and unique migratory strategy. Analyses of mitochondrial DNA (mtDNA) showed that there was no divergence between Bulgarian and Russian populations (FST = 0.007), whereas those in Kazakhstan differed significantly from the European breeding populations (Russia: FST = 0.058; Bulgaria: FST = 0.114). The degree of differentiation between populations at nuclear markers (five microsatellite loci; FST ≈ 0) was weaker than for mtDNA. We suggest that this relatively weak differentiation over the range of this species reflects a recent postglacial expansion, and results from mismatch distribution analyses and Fu’s FS tests are in agreement. Preservation of small and geographically isolated populations which may contain individuals with unique adaptive traits, such as the studied Bulgarian population of paddyfield warbler, is valuable for the long-term conservation of expanding migratory bird species [Current Zoology 57 (1): 63–71, 2011].

In order to describe the influence of Pleistocene glaciations on the genetic structure and demography of a highly mobile, but specialized, passerine, the Savi's Warbler (Locustella luscinioides), mitochondrial DNA sequences (ND2) and microsatellites were analysed in c.330 individuals of 17 breeding and two wintering populations. Phylogenetic, population genetics and coalescent methods were used to describe the genetic structure, determine the timing of the major splits and model the demography of populations. Savi's Warblers split from its sister species c.8 million years ago and have two major haplotype groups that diverged in the early/middle Pleistocene. One of these clades originated in the Balkans and is currently widespread, showing strong evidence for population expansion; whereas the other is restricted to Iberia and remained stable. Microsatellites agreed with a genetic break around the Pyrenees, but showed considerable introgression and a weaker genetic structure. Both genetic markers showed an isolation-by-distance pattern associated with the population expansion of the eastern clade. Breeding populations seem to be segregated at the wintering sites, but results on migratory connectivity are preliminary. Savi's Warbler is the only known migratory bird species in which Iberian birds did not expand beyond the Pyrenees after the last glaciation. Despite the long period of independent evolution of western and eastern populations, complete introgression occurred when these groups met in Iberia. Mitochondrial sequences indicated the existence of refugia-within-refugia in the Iberian Peninsula during the last glacial period, which is surprising given the high dispersal capacity of this species. Plumage differences of eastern subspecies seemed to have evolved recently through natural selection, in agreement with the glacial expansion hypothesis. This study supports the great importance of the Iberian Peninsula and its role for the conservation of genetic variation.

Pleistocene glacial cycles play a major role in diversification and speciation, although the relative importance of isolation and expansion in driving diversification remains debated. We analysed mitochondrial DNA sequence data from 15 great reed warbler (Acrocephalus arundinaceus) populations distributed over the vast Eurasian breeding range of the species, and revealed unexpected postglacial expansion patterns from two glacial refugia. There were 58 different haplotypes forming two major clades, A and B. Clade A dominated in Western Europe with declining frequencies towards Eastern Europe and the Middle East, but showed a surprising increase in frequency in Western and Central Asia. Clade B dominated in the Middle East, with declining frequencies towards north in Central and Eastern Europe and was absent from Western Europe and Central Asia. A parsimonious explanation for these patterns is independent postglacial expansions from two isolated refugia, and mismatch distribution analyses confirmed this suggestion. Gene flow analyses showed that clade A colonised both Europe and Asia from a refugium in Europe, and that clade B expanded much later and colonised parts of Europe from a refugium in the Middle East. Great reed warblers in the eastern parts of the range have slightly paler plumage than western birds (sometimes treated as separate subspecies; A. a. zarudnyi and A. a. arundinaceus, respectively) and our results suggest that the plumage diversification took place during the easterly expansion of clade A. This supports the postglacial expansion hypothesis proposing that postglacial expansions drive diversification in comparatively short time periods. However, there is no indication of any (strong) reproductive isolation between clades and our data show that the refugia populations became separated during the last glaciation. This is in line with the Pleistocene speciation hypothesis invoking that much longer periods of time in isolation are needed for speciation to occur.

The great reed warbler Acrocephalus arundinaceus is a common migrant through the Western Palearctic. However, its migration strategy, especially the spatiotemporal pattern of accumulation and utilisation of energy stores en route, is poorly known. Using ringing data collected at distant stopover sites located from Central Europe to Asia Minor, we observed that pattern in juvenile great reed warblers migrating along the eastern European flyway in autumn. We analysed body condition and stopover duration and estimated potential flight ranges for this species, taking into account two large ecological barriers – the Mediterranean Sea and the Sahara Desert – which it crosses during its southward migration. In Central and South-Eastern Europe the seasonal trends in body condition were similar and non-linear, with low values in August (i.e., during intensive migration of Acrocephalidae), and then a significant increase from the beginning of September until the end of the month. Estimated potential flight ranges showed that individuals migrating through Central and South-Eastern Europe might generally reach only the northern coast of the Mediterranean Sea. On the other hand, those flying from Asia Minor were able to reach the northern edge of the Sahel zone, crossing two large ecological barriers without refuelling. Therefore, it seems that great reed warblers change their autumn strategy en route: first, they migrate in short steps with low energy reserves through continental Europe; and then, after intensive refuelling before the Mediterranean Sea, they reach sub-Saharan Africa in a long flight. Based on the analysis of ringing data from several stopover sites, we show the complex pattern of how a long-distance migratory species accumulates and utilises its energy stores en route. [ABSTRACT FROM AUTHOR]