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The area of Coastal Dobrudzha in NE Bulgaria is well known for its richness of vagrants. A long-term research project was started at a location at Durankulak Lake, on the northern Black Sea Coast, aiming to obtain data on the characteristics of autumn migration of passerine birds and on the presence of vagrants there. A total of 20 mist nets with an overall length of 200 meters were set between August and October in two different habitats - reed bed and broad-leaved forest. In 2019, a total of 9344 birds of 84 species were caught and ringed. In 2020, the number of the birds caught increased to 13786 of 93 species. Vagrants such as dusky warbler (Phylloscopus fuscatus), yellow-browed warbler (Phylloscopus inornatus) and red-flanked bluetail (Tarsiger cyanurus) were captured in 2020. Detailed information about these findings is given in the present work.

Parasites trigger reactions in hosts, leading to suppressive resistance and/or tolerance, aiming to limit the parasitic costs. Both colonization by parasites and defense activation can induce varying amount of costs for the host. Understanding parasite-induced effects on host fitness crucially depends on assessing parasitic costs in specific wild host-parasite systems. To evaluate potential effects of blood parasite infection, we compared physiological traits of Common Buzzard nestlings Buteo buteo i) at different stages of infection and ii) with increasing levels of parasitemia (frequency of infected host cells) with Leucocytozoon toddi, a pathogen causing malaria-like conditions. We expected infection costs to appear from the onset of infection and during peak parasitemia, rather than when parasitemia was decreasing or in uninfected hosts. We found no difference in physiological traits among infection stages, indicating low immediate parasitic costs and pointing to infection tolerance in this ontogenic stage. Surprisingly, infection only led to decrease of host health during rare and particularly acute expressions of infection. Thus, Leucocytozoon toddi appears to typically display low virulence towards their hosts, during all stages of infection. Juveniles, as a relatively parasite-tolerant life-history stage, may enable parasite transmission in the population while avoiding infection-driven host mortality during this critical period.

Wildlife exposures to pest controlling substances have resulted in population declines of many predatory species during the past decades. Many pesticides were subsequently classified as persistent, bioaccumulative, and toxic (PBT) and banned on national or global scales. However, despite their risks for non-target vertebrate wildlife, PBT substances such as anticoagulant rodenticides (ARs) are still permitted for use in Europe and have shown to threaten raptors. Whereas risks of ARs are known, much less information is available on emerging agrochemicals such as currently used PPPs and medicinal products (MPs) in higher trophic level species. We expect that currently used PPPs are relatively mobile (vs. lipophilic) as a consequence of the PBT criteria and thus more likely to be present in aqueous matrices. We therefore analyzed blood of 204 raptor nestlings of three terrestrial (red kite, common buzzard, Montagu’s harrier) and two aquatic species (white-tailed sea eagle, osprey) from Germany. In total, we detected ARs in 22.6% of the red kites and 8.6% of the buzzards, whereas no Montagu’s harriers or aquatic species were exposed prior to sampling. ΣAR concentration tended to be higher in North Rhine-Westphalia (vs. North-Eastern Germany) where population density is higher and intense livestock farming more frequent. Among the 90 targeted and currently used PPPs, we detected six substances from which bromoxynil (14.2%) was most frequent. Especially Montagu’s harrier (31%) and red kites (22.6%) were exposed and concentrations were higher in North Rhine-Westphalia as well. Among seven MPs, we detected ciprofloxacin (3.4%), which indicates that risk mitigation measures may be needed as resistance genes were already detected in wildlife from Germany. Taken together, our study demonstrates that raptors are exposed to various chemicals during an early life stage depending on their sampling location and underpins that red kites are at particular risk for multiple pesticide exposures in Germany.

Nuclear copies of mitochondrial genes (numts) are commonplace in vertebrate genomes and have been characterized in many species. However, relatively little attention has been paid to understanding their evolutionary origins and to disentangling alternative sources of insertions. Numts containing genes with intact mitochondrial reading frames represent good candidates for this purpose. The sequences of the genes they contain can be compared with their mitochondrial homologs to characterize synonymous to nonsynonymous substitution rates, which can shed light on the selection pressures these genes have been subjected to. Here, we characterize 25 numts in the Antarctic fur seal (Arctocephalus gazella) genome. Among those containing genes with intact mitochondrial reading frames, three carry multiple substitutions in comparison to their mitochondrial homologs. Our analyses reveal that one represents a historic insertion subjected to strong purifying selection since it colonized the Otarioidea in a genomic region enriched in retrotransposons. By contrast, the other two numts appear to be more recent and their large number of substitutions can be attributed to noncanonical insertions, either the integration of heteroplasmic mtDNA or hybridization. Our study sheds new light on the evolutionary history of pinniped numts and uncovers the presence of hidden sources of mitonuclear variation.

Avian haemosporidians are a common and widespread group of vector-borne parasitescapable of infecting most bird species around the world. They can negatively affect host conditionand fitness. Vultures are assumed to have a very low prevalence of these blood parasites, likelydue to their strong immunity; however, factors contributing to variation in host exposure andsusceptibility to haemosporidians are complex, and supporting evidence is still very limited. Weanalyzed blood samples collected from nestlings of three vulture species in Spain over 18 years,and used updated nested-PCR protocols capable of detecting all haesmosporidian cytochrome blineages typical for diurnal birds of prey (Accipitriformes). Similarly to previous studies, we foundlow haemosporidian prevalence in cliff-breeding species, withLeucocytozoonas the only representedblood parasite genus: 3.1% in griffon vultures (Gyps fulvus) (n= 128) and 5.3% in Egyptian vultures(Neophron percnopterus) (n= 114). In contrast, the tree-breeding cinereous vulture (Aegypius monachus)had a substantially higher prevalence: 10.3% (n= 146). By far the most common lineage in Spanishscavenging raptors was theLeucocytozoonlineage CIAE02. No effects of nestling age and sex, ortemporal trends in prevalence were found, but an effect of nest habitat (tree-nest vs. cliff-nest) wasfound in the griffon vulture. These patterns may be explained by a preference of vectors to foragein and around trees rather than on cliffs and wide open spaces. We found an apparent detrimentaleffect of haemosporidians on body mass of nestling cinereous vultures. Further research is needed toevaluate the pathogenicity of each haemosporidian lineage and their interaction with the immunesystem of nestlings, especially if compromised due to pollution with pharmaceuticals and infectionby bacterial and mycotic pathogens., Funds for the fieldwork were provided by the projects CGL2009-12753-C02-01/BOS,CGL2010-15726 and PID2019-109685GB-I00 of Spanish Ministry of Science and Innovation. This research was partially funded by a Marie Curie grant (PIEF-GA-2013-625883) to N.C.

The outcomes of ecological interactions fall along a continuum from cooperative (mutually beneficial) to antagonistic (detrimental to one or both parties). This applies at both interspecific (e.g. plant-animal interactions) and intraspecific levels (e.g. male-female interactions). Phenotypic variation among individuals is increasingly being recognised as an important factor in ecological processes, and trait variation in either interacting party may determine the outcome of the interaction, such as whether a symbiont provides net costs or benefits to their host, or whether two conspecifics decide to cooperatively forage or to compete over food. This systematic review investigates the role of intraspecific trait variation (‘ITV’) in determining the cooperative-antagonistic outcome of ecological interactions. Based on a literature collection of 95 empirical and theoretical publications meeting our inclusion criteria, we give an overview of the various mechanisms that can lead to shifts between antagonism and cooperation within or between species. We describe two broad classes of interrelated mechanisms that may drive shifts in outcomes. First, trait frequency effects occur when processes influencing a population’s composition of traits linked to cooperation or antagonism (e.g. aggressive personality types, cheater/exploiter phenotypes etc.) lead to net shifts in interaction outcome. Second, systemic variance effects occur when changes in the amount of ITV in the population (as opposed to the mean phenotype) is the factor driving shifts. Both heritable genetic differences among individuals and phenotypic plasticity are important sources of phenotypic variation. The specific mix of heritable vs. plastic ITV may determine whether a change from cooperative to antagonistic, or vice versa, is likely to be short-term (i.e. context-dependent) or lead to more persistent shifts (e.g. mutualism breakdown). To guide future research on this topic we describe knowledge gaps and divergences between empirical and theoretical literature, further highlighting the value of applying research synthesis methods in ecology and evolution.

A deeper understanding of the processes underlying the distribution of animals in space is crucial for both basic and applied ecology. The Common buzzard (Buteo buteo) is a highly aggressive, territorial bird of prey that interacts strongly with its intra- and interspecific competitors. We propose and use random matrix theory to quantify the strength and range of repulsion as a function of the buzzard population density, thus providing a novel approach to model density dependence. As an indicator of territorial behaviour, we perform a large-scale analysis of the distribution of buzzard nests in an area of $300$ square kilometres around the Teutoburger Wald, Germany, as gathered over a period of $20$ years. The nearest and next-to-nearest neighbour spacing distribution between nests is compared to the two-dimensional Poisson distribution, originating from uncorrelated random variables, to the complex eigenvalues of random matrices, which are strongly correlated, and to a two-dimensional Coulomb gas interpolating between these two. A one-parameter fit to a time-moving average reveals a significant increase of repulsion between neighbouring nests, as a function of the observed increase in absolute population density over the monitored period of time, thereby proving an unexpected yet simple model for density-dependent spacing of predator territories. A similar effect is obtained for next-to-nearest neighbours, albeit with weaker repulsion, indicating a short-range interaction. Our results show that random matrix theory might be useful in the context of population ecology., Comment: 13 pages, with many figures; revised and slightly enlarged version

The gut microbiome is an integral part of a species’ ecology, but we know little about how host characteristics impact its development in wild populations. Here, we explored the role of such intrinsic factors in shaping the gut microbiome of northern elephant seals during a critical developmental window of six weeks after weaning, when the pups stay ashore without feeding. We show that the early-life gut microbiome is already substantially different in male and female pups, even though males and females cannot yet be distinguished morphologically. Sex and age both explain around 15% of the variation in gut microbial beta diversity, while microbial communities sampled from the same individual show high levels of similarity across time, explaining another 40% of the variation. Only a small proportion of the variation in beta diversity is explained by health status, but healthy individuals have a greater microbial alpha diversity than their non-healthy peers. Across the post-weaning period, the elephant seal gut microbiome is highly dynamic. We found evidence for several colonisation and extinction events as well as a decline in Bacteriodes and an increase in Prevotella, a pattern that has previously been associated with the transition from nursing to solid food. Lastly, we show that genetic relatedness is correlated with gut microbiome similarity in males but not females, again reflecting substantial early sex-differences. Our study represents a naturally diet-controlled and longitudinal investigation of how intrinsic factors shape the early gut microbiome in a species with extreme sex differences in morphology and life history.

Background Selecting high-quality habitat and the optimal time to reproduce can increase individual fitness and is a strong evolutionary factor shaping animal populations. However, few studies have investigated the interplay between land cover heterogeneity, limitation in food resources, individual quality and spatial variation in fitness parameters. Here, we explore how individuals of different quality respond to possible mismatches between a cue for prey availability (land cover heterogeneity) and the actual fluctuating prey abundance. Results We analyse timing of breeding and reproductive success in a migratory population of Eurasian kestrels (Falco tinnunculus) breeding in nest-boxes, over a full three-year abundance cycle of main prey (voles), and consider several components of individual quality, including body condition, blood parasite infection, and genetic diversity (n = 448 adults) that act on different time scales. Older individuals, and kestrel parents in higher body condition started egg-laying earlier than younger birds and those in lower body condition. Additionally, egg-laying was initiated earlier during the increase and decrease phases (2011 and 2012) than during the low phase of the vole cycle (2013). Nestling survival (ratio of eggs that fledged successfully) was higher in early nests and in heterogeneous landscapes (i.e., mosaic of different habitat types), which was evident during the increase and decrease phases of the vole cycle, but not during the low vole year. Conclusions We found a strong positive effect of landscape heterogeneity on nestling survival, but only when voles were relatively abundant, whereas a difference in the timing of breeding related to territory landscape heterogeneity was not evident. Therefore, landscape heterogeneity appeared as the main driver of high reproductive performance under favourable food conditions. Our results show that landscape homogenization linked to agricultural intensification disrupts the expected positive effect of vole abundance on reproductive success of kestrels.

The evolution and maintenance of conspicuous phenotypic polymorphisms has challenged evolutionary ecologists for centuries. Polymorphisms in pleiotropic cascades or genetic linkage may lead to correlations of life history traits such as immunity, parasite infection levels, pigmentation and lifetime reproductive success. The common buzzard Buteo buteo is a bird of prey occurring in several plumage morphs, which differ in pigmentation and in the prevalence, infection intensity and clone composition of their most common blood parasite, as well as in ectoparasite infestation levels. Buzzard morphs are heritable and exhibit a heterozygote advantage where intermediates have higher lifetime reproductive success (LRS). We explored the hypothesis that the differences in pigmentation also correspond to differences in immunity. We hence compared an inducible adaptive and an innate constitutive immune response between the buzzard plumage morphs. The increase of specific anti-tetanus antibodies after vaccination was explained by the morph of the nestling's mother and was highest in offspring of intermediate mothers. Additionally, nestlings with higher humoral response were less infected with blood parasites and, if infected, harboured a lower genetic diversity of these parasites. The phytohaemagglutinin-induced skin swelling, a complex of cellular inflammatory responses, was lowest in intermediate nestlings. The higher LRS of intermediate buzzards suggests that the cellular immunity is an inferior fitness determinant compared to humoral immunity. The strength of immune responses was not linear along the melanisation gradient, indicating that there is most likely no simple genetic correlation between immune responses and plumage morphs.

Persistent plumage colour polymorphism occurs in around 3.5% of bird species, with raptors showing a disproportionately high frequency of such polymorphisms. The genus Buteo has more polymorphic species than any other raptor genus (15 polymorphic species out of 25). These polymorphisms are interesting from an evolutionary perspective, because they are heritable and hence a good model for understanding mechanisms preserving genetic variation. For evolutionary models, it is important to assess whether discrete morphs exist or whether variation is more continuous. Using image analysis, we show that in Common Buzzards Buteo buteo variation is continuous and unimodal, ranging from very dark to very light individuals. Previous studies on Common Buzzards have used a classification with three discrete morphs. We compared this classification with a seven-scale morph classification used in our study. We used photographs of the same individuals taken at different ages. Even though the plumage gets somewhat darker from juvenile to adult age, morph type did not change substantially.

Long-term genetic data from intensively monitored natural populations are important for understanding how effective population sizes (N-e) can vary over time. We therefore genotyped 1622 common buzzard (Buteo buteo) chicks sampled over 12 consecutive years (2002-2013 inclusive) at 15 microsatellite loci. This data set allowed us to both compare single-sample with temporal approaches and explore temporal patterns in the effective number of parents that produced each cohort in relation to the observed population dynamics. We found reasonable consistency between linkage disequilibrium-based single-sample and temporal estimators, particularly during the latter half of the study, but no clear relationship between annual N-e estimates ((N) over cap (e)) and census sizes. We also documented a 14-fold increase in (N) over cap (e) between 2008 and 2011, a period during which the census size doubled, probably reflecting a combination of higher adult survival and immigration from further afield. Our study thus reveals appreciable temporal heterogeneity in the effective population size of a natural vertebrate population, confirms the need for long-term studies and cautions against drawing conclusions from a single sample.

The group of haemosporidian parasites is of general interest to basic and applied science, since several species infect mammals, leading to malaria and associated disease symptoms. Although the great majority of haemosporidian parasites appear in bird hosts, as in the case of Leucocytozoon buteonis, there is little genomic information about genetic aspects of their co-evolution with hosts. Consequently, there is a high need for parasite-enrichment strategies enabling further analyses of the genomes, namely without exposure to DNA-intercalating dyes. Here, we used flow cytometry without an additional labelling step to enrich L. buteonis from infected buzzard blood. A specific, defined area of two-dimensional scattergramms was sorted and the fraction was further analysed. The successful enrichment of L. buteonis in the sorted fraction was demonstrated by Giemsa-staining and qPCR revealing a clear increase of parasite-specific genes, while host-specific genes were significantly decreased. This is the first report describing a labelling-free enrichment approach of L. buteonis from infected buzzard blood. The enrichment of parasites presented here is free of nucleic acid-intercalating dyes which may interfere with fluorescence-based methods or subsequent sequencing approaches.

1. The habitat heterogeneity (HHH) and individual adjustment (IAH) hypotheses are commonly proposed to explain a decrease in reproduction rate with increasing population density. Higher numbers of low-quality territories with low reproductive success as density increases lead to a decrease in reproduction under the HHH, while more competition at high density decreases reproduction across all territories under the IAH. 2. We analyse the influence of density and habitat heterogeneity on reproductive success in eight populations of long-lived territorial birds of prey belonging to four species. Sufficient reliability in distinguishing between population-wide, site-specific and individual quality effects on reproduction was granted through the minimal duration of 20 years of all data sets and the ability to control for individual quality in five of them. 3. Density increased in five populations but reproduction did not decrease in these. Territory occupancy as a surrogate of territory quality correlated positively with reproductive success but only significantly so in large data sets with more than 100 territories. 4. Reproductive success was always best explained by measures of territory quality in multivariate models. Direct or delayed (t-1) population density entered very few of the best models. Mixed models controlling for individual quality showed an increasing reproductive performance in older individuals and in those laying earlier, but measures of territory quality were also always retained in the best models. 5. We find strong support for the habitat heterogeneity hypothesis but weak support for the individual adjustment hypothesis. Both individual and site characteristics are crucial for reproductive performance in long-lived birds. Proportional occupancy of territories enables recognition of high-quality territories as preferential conservation targets.

Characteristics of soaring birds' spring migration over inland SE Bulgaria We investigated the scale and characteristics of spring migration of soaring birds in Bourgas district, SE Bulgaria during three 5-day periods in March (27th-31st), April (20th-24th) and May (12th-16th) 2008. Simultaneous counts were carried out from six observation points in two separate areas (Karnobat and Sredets), located 24.5 km and 37.3 km inland from the Black Sea coast, respectively. In total, 31,049 soaring birds of at least 27 species were counted, by far the most numerous being the White Stork Ciconia ciconia (23,358 ind.), followed by the Lesser Spotted Eagle Aquila pomarina (3,112 ind.). In Karnobat area, situated farther from the Black Sea coast, the total number of soaring migrants (21,231) was more than two-fold higher than in Sredets area (9,818). Overall, there was a significant difference in flock size and flight altitude within separate area (i.e. among observation points) as well as between the two observation areas and the three 5-day periods. However, there was a substantial variance in factors significantly affecting the flock size and flight altitude among most numerous individual species. In general, birds passed at much higher altitude above Karnobat area (mean flight altitude 208.3 m ± 6.4) compared to Sredets area (mean flight altitude 130.5 m ± 4.4). In both observation areas, northern direction was the most commonly observed flight direction (46.3% of all recorded flight directions). The highest numbers of soaring migrants passed in the late afternoon, between 15.00 and 18.00 hrs - 11,554 individuals (43.0% of all birds counted). The study confirmed that the front of Western Black Sea migration route, or "Via Pontica" as part of the Mediterranean/Black Sea Flyway in SE Bulgaria, is rather wide, since the magnitude of inland migration in Bourgas district can be compared with that along the Black Sea coast, at least during spring migration. Both observation areas qualify as Important Bird Areas (IBA) of European importance according to the several BirdLife International criteria. We recommend that any new wind farms built should avoid the area of Hisar Hill south of Karnobat and the NW parts of Sredets Municipality.

Intraguild predation (IGP) is a commonly recognized mechanism influencing the community structure of predators, but the complex interactions are notoriously difficult to disentangle. The mesopredator suppression hypothesis predicts that a superpredator may either simultaneously repress two mesopredators, restrain the dominant one and thereby release the subdominant mesopredator, or elicit different responses by both mesopredators. We show the outcome arising from such conditions in a three-level predator assemblage (Eurasian eagle owl Bubo bubo L., northern goshawk Accipiter gentilis L. and common buzzard Buteo buteo L.) studied over 25 years. In the second half of the study period, the eagle owl re-colonized the study area, thereby providing a natural experiment of superpredator introduction. We combined this set-up with detailed GIS analysis of habitat use and a field experiment simulating intrusion by the superpredator into territories of the subdominant mesopredator, the buzzard. Although population trends were positive for all three species in the assemblage, the proportion of failed breeding attempts increased significantly in both mesopredators after the superpredator re-colonized the area. We predicted that superpredator-induced niche shifts in the dominant mesopredator may facilitate mesopredator coexistence in superpredator-free refugia. We found significant changes in nesting habitat choice in goshawk, but not in buzzard. Since competition for enemy-free refugia and the rapid increase in population density may have constrained niche shifts of the subdominant mesopredator, we further predicted behavioural changes in response to the superpredator. The field experiment indeed showed a significant increase in aggressive response of buzzards towards eagle owl territory intrusion over the course of 10 years, probably due to phenotypic plasticity in the response towards superpredation risk. Overall, our results show that intraguild predation can be a powerful force of behavioural change, simultaneously influencing habitat use and aggressiveness in predator communities. These changes might help to buffer mesopredator populations against the negative effects of intraguild predation.

Avian time-activity budgets are known to be affected by many environmental factors. The aim of this study was to examine whether roosting times of common ravens Corvus corax are affected by inclement weather conditions in response to increased energy demands. The study was conducted at a communal roost of ravens in Thuringia, Germany, from August 2003 to January 2005. The number of roosting ravens fluctuated substantially, ranging from zero individuals in summer to 574 in winter. During the entire study period, a composting facility served as the main feeding ground for roosting ravens. There, the feeding-to-resting ratio did not depend on flock size, indicating the ravens were not food limited. Ravens arrived at the preroost and the roost later relative to sunset on cloudless evenings and on days with shorter length of daylight. Weather conditions measured as ambient temperature, wind speed, and cumulative daily precipitation had no effect on arrival times at the preroost and the roost. Likewise, moonlight did not affect roosting times. Apparently, flexible time-activity budgets resulting from a superabundant food supply may have enabled ravens to moderate the effects of environmental conditions on arrival times at the preroost and the roost.

Parasite transmission strategies strongly impact host–parasite co-evolution and virulence. However, studies of vector-borne parasites such as avian malaria have neglected the potential effects of host relatedness on the exchange of parasites. To test whether extended parental care in the presence of vectors increases the probability of transmission from parents to offspring, we used high-throughput sequencing to develop microsatellites for malaria-like Leucocytozoon parasites of a wild raptor population. We show that host siblings carry genetically more similar parasites than unrelated chicks both within and across years. Moreover, chicks of mothers of the same plumage morph carried more similar parasites than nestlings whose mothers were of different morphs, consistent with matrilineal transmission of morph-specific parasite strains. Ours is the first evidence of an association between host relatedness and parasite genetic similarity, consistent with vector-mediated parent-to-offspring transmission. The conditions for such ‘quasi-vertical’ transmission may be common and could suppress the evolution of pathogen virulence.

Density-dependent reproduction is commonly explained by either the habitat heterogeneity (HHH) or individual adjustment (IAH) hypothesis. Under the HHH, high quality territories are assumed to be occupied first. At higher density, occupation of low-quality territories increases due to lower availability of high-quality territories, which reduces mean reproductive success. Alternatively, the IAH assumes that increased competition at higher densities reduces reproductive success in all territories. For birds of prey, HHH plays an important role in territorial species, and IAH in socially breeding species. To test the generality of this hypothesis, we studied the mechanism behind density dependence in raven Corvus corax, a long-lived passerine bird, using long-term population data from a large number of territories. Population density decreased reproduction, which was explained by increased usage of low quality territories at higher density, supporting the HHH. Density reduced reproduction in low quality territories, but not in high and intermediate quality territories. We additionally compared the explanatory power of different models describing brood size, representing IAH, HHH, or a combination of both. The best model represented a combination of both hypotheses, in which the effect of density depended on territory quality. Our conclusion that both IAH and HHH are supported can be explained by the biology of ravens, where territorial adults not only experience interference competition with other territorial adults, but also with social groups of juveniles and floaters. We conclude that the relative importance of IAH and HHH may depend on variation in territory quality and social structure.

The effect of changing climatic conditions on wild populations has been the subject of much recent research. Most attention has been on the direct effects of climate changes on species of lower trophic levels and on the negative consequences of climate change. However, a deeper understanding of how climate change affects apex predators is vital, as they are keystone species that have a disproportionate effect on ecosystems. Studying survival in an apex predator requires individual-based data from long-term studies and is complicated by the integration of climatic effects on lower trophic levels. Here we assess how climate affects the survival of the Common Buzzard Buteo buteo. We analysed the survival of 670 males and 669 females over the period 1989-2011, during which time our study population quadrupled. We used mark-recapture survival analysis of individual resightings of breeding adults to identify the environmental factors best explaining survival. A decrease in the North Atlantic Oscillation (NAO) index increased survival to an extent that largely explains the population increase. This might be caused by higher Common Vole Microtus arvalis survival in drier conditions and under snow cover. Buzzard survival appeared to increase more for males than for females, possibly due to the males' higher sensitivity to winter food availability resulting from their smaller body mass. However, we also found that the effect of NAO strongly depended on the area in which individuals lived, especially for females. This may have been caused by the recolonization of Eagle Owls Bubo bubo in some parts of our study area. This study suggests that climatic changes can have complex effects on species of higher trophic levels via an interaction with their prey.

Polymorphic genes involved in the conserved molecular signalling of circadian and circannual clocks may play important roles in governing the timing of breeding and dispersal and thereby affect fitness in vertebrates. However, relatively few studies have explored associations between phenological candidate genes and behaviour, and these are somewhat biased towards particular taxonomic groups such as passerine birds and salmonid fish. Consequently, we assayed microsatellite polymorphisms within the exonic and 3' untranslated regions of the regulatory genes CLOCK, NPAS2, ADCYAP1 and CREB1 in the common buzzard (Buteo buteo), a polymorphic raptor species with three plumage morphs that differ in key life history traits including lifetime reproductive success. In contrast to studies of passerines, CLOCK poly-glutamine (poly-Q) was found to be monomorphic in 976 common buzzard nestlings as well as in three other Buteo species. Moreover, none of the candidate genes were significantly associated with fledging dates, although intermediately melanized females were found to lay earlier on average than light or dark morph individuals, and their offspring carried longer ADCYAP1 alleles. In contrast, all three candidate genes explained significant variation in one or more measures of juvenile buzzard dispersal (resighting probability, timing of dispersal and distance dispersed). Our findings contribute towards a broader body of work on the adaptive significance of CLOCK polymorphism, while also building upon previous studies that have documented links between ADCYAP1 variability and the timing of migration.

Correlations between heterozygosity and fitness are frequently found but rarely well understood. Fitness can be affected by single loci of large effect which correlate with neutral markers via linkage disequilibrium, or as a result of variation in genome-wide heterozygosity following inbreeding. We explored these alternatives in the common buzzard, a raptor species in which three colour morphs differ in their lifetime reproductive success. Using 18 polymorphic microsatellite loci, we evaluated potential genetic differences among the morphs which may lead to subpopulation structuring and tested for correlations between three fitness-related traits and heterozygosity, both genome wide and at each locus separately. Despite their assortative mating pattern, the buzzard morphs were found to be genetically undifferentiated. Multilocus heterozygosity was only found to be correlated with a single fitness-related trait, infection with the blood parasite, Leucocytozoon buteonis, and this was via interactions with vole abundance and age. One locus also showed a significant relationship with blood parasite infection and ectoparasite infestation. The vicinity of this locus contains two genes, one of which is potentially implicated in the immune system of birds. We conclude that genome-wide heterozygosity is unlikely to be a major determinant of parasite burden and body condition in the polymorphic common buzzard.

Blood parasites of migrating yellow wagtails of two subspecies--Motacilla flava feldegg and Motacilla flava flava-were studied on a sample of 473 birds caught in spring and autumn periods in Bulgaria. We controlled eight "migration waves" (flocks captured in different evenings) of yellow wagtails for four parameters--average body mass, average fat level, average wing length, and average prevalence of different hematozoan species. Gametocytes or meronts of a total of six species of hematozoa belonging to three genera were identified-Haemoproteus motacillae, Haemoproteus anthi, Plasmodium relictum, Plasmodium subpraecox, Plasmodium cathemerium, and Tryponosoma avium. Mixed infections were detected in 31 cases, of which 14 were of H. anthi/H. motacillae type. Parasite species composition was similar in the two studied subspecies of M. flava. We did not find any significant differences in the overall infection prevalence or number of infecting parasites between M. f. flava and M. f. feldegg. Parasite prevalence and the number of co-infecting parasites in spring were much higher than in fall. Season had a strong influence on the prevalence of H. anthi and H. motacillae, and for both, there was a marginally significant interaction between subspecies and season, but not a season-independent influence of subspecies. Males of M. f. feldegg had a significantly higher overall blood parasite prevalence and prevalence of H. anthi than females. Sex-related differences in the prevalence of other parasites were not significant. Migration waves of yellow wagtails differed in overall infection status and in H. motacillae prevalence, but not for H. anthi prevalence. We also found significant differences in fat score, weight, and wing length between the studied migration waves of the yellow wagtails. Fat scores of birds infected with different hematozoa were lower compared with those of the non-infected birds. This only marginally was true for body weight and was not the case for wing length. Overall, infected birds were in worse condition (estimated as the residual weight after regression with wing length) compared with the non-infected birds, but after controlling for seasonal effects, the differences in condition appeared to be due to migration season and did not significantly differ between infected and non-infected birds caught in the same season.

Melanin is one of the major pigments of vertebrates and has many suggested functions. Although it is supposed to have an antipathogenic effect, its relationship to infection with ecto- and endoparasites largely remains to be examined. The common buzzard Buteo buteo occurs in three eumelanin morphs which differ in their lifetime reproductive success. We examined the distribution of the blood-sucking ectoparasite Carnus haemapterus and the blood parasite Leucocytozoon toddi among buzzard nestlings and related parasite infection to the morph of the host and its parents. We controlled the effect of melanin morph on parasites for the potentially confounding total leukocyte numbers, heterophil : lymphocyte ratio (H : L ratio), age, sex, hierarchical rank within the brood and annual food availability. Blood parasite prevalence was lower in offspring of intermediately coloured males. This pattern was apparent during high and low food availability, and although this result did not remain under intermediate vole densities, it could contribute to observed fitness differences in male buzzards. In contrast, carnid fly score increased with darkness of the host plumage. However, among chicks infected with the blood parasite, Leucocytozoon infection intensity decreased with plumage darkness. The two parasite species may exert selection pressures in opposite directions on melanism of their host. Therefore, buzzards with intermediate amounts of melanin may prosper as they are sufficiently protected against endoparasites, but not too attractive for ectoparasites. Parasites could help explain the persistence of colour polymorphism in their buzzard host.

Blood parasite prevalence in two related warbler species (Acrocephalus arundinaceus and A. scirpaceus) was studied at three Bulgarian sites that differed mainly in altitude and weather. The prevalence of Haemoproteus, the most common parasite genus, was significantly lower at the highest altitude site (730 m above sea level, asl). Such a pattern was not found in ectoparasite-transmitted Hepatozoon. This can be explained with worsening conditions for the development of free-flying vectors with altitude and suggests loosening of the host-parasite conflict at higher breeding sites. The total heamatozoan prevalence was significantly higher in great reed warbler, compared with reed warbler especially as regards Haemoproteus parasites.