Turdus Merula Research Articles

Breeding success of passerine birds in the forest steppe of European Russia

In the period from 1985 to 2023, the breeding success of 15 bird species was studied in the Voronezh Nature Reserve (50°21ʹ-52°02ʹ N, 39°21ʹ-39°47ʹ E), where there has been no economic activity for 100 years. The plant cover consists of pine (32.3% of the total area), oak (29.3%), aspen (19.3%), birch (5.7%) and alder (5.2%) forests. 2004 nests were monitored. Low breeding success (25.4-27.9%, determined by the modified Mayfield method) was found in the Blackbird Turdus merula , the Song Thrush T. philomelos , the Finch Fringilla coelebs and the Greenfinch Chloris chloris. From 1.6 to 1.8 fledglings fly out for one breeding attempt. The average level of breeding success (38.7-50.4%) was found in the Common Chiffchaff Phylloscopus collybita , the Red-backed Shrike Lanius collurio , Redwing Turdus iliacus , Eurasian Blackcap Sylvia atricapilla , Garden Warbler S. borin and Hawfinch Coccothraustes coccothraustes . From 2.1 to3.4 fledglings fly out for one breeding attempt. A high level of breeding success (60.6-82.5%) was found in the Great Tit Parus major , the Common Redstart Phoenicurus phoenicurus , the Pied Flycatcher Ficedula hypoleuca , the Collared Flycatcher F. albicollis and the Spotted Flycatcher Muscicapa striata . From 3.7 to 7 fledglings fly out for one breeding attempt. Due to the increased pressure of nest predators, the breeding success of birds in the Voronezh Nature Reserve is often lower than in other areas. The greatest breeding success is typical for birds that place nests in hollows and other shelters. Breeding success is significantly lower in openly nesting species, especially in birds that begin nesting before the leaves bloom on trees and shrubs.

Trace element bioaccumulation in the plumage of common blackbirds (Turdus merula Linnaeus, 1758) from Agigea, Romania

The purpose of this research was to establish the baseline concentrations of thirteen trace elements (Cd, Co, Cr, Cu, Ni, Pb, Fe, Mg, Na, K, Sr, Ca, and Zn) in feathers of the common blackbird Turdus merula (n=9) at the Natura 2000 site “Marine Dunes from Agigea” (ROSCI0073). Both remiges and rectrices were pooled, and the quantification of trace elements was accomplished using two spectrometry analysis methods: high-resolution continuum source atomic absorption spectrometer with a graphite furnace (HR-CS GF-AAS) and flame atomic absorption spectrometer (FL-AAS). The concentration of Ca was the highest of the thirteen trace elements, registering at 209.9146±192.4098 µg·g-1 w.w., while Cd had the lowest concentration levels in feathers, 0.0243±0.0158 µg·g-1 w.w., respectively. However, the results obtained were significantly lower than those in the relevant literature. These findings suggest that the bioavailability of the analysed trace elements is minimal in our study area. Thus, it is imperative to conduct further research on the impact of these trace elements' accumulation and effects on avifauna in the Natura 2000 site “Marine Dunes from Agigea”.

A species-independent lateral flow microarray immunoassay to detect WNV and USUV NS1-specific antibodies in serum

Arboviruses such as West Nile Virus (WNV) and Usutu Virus (USUV) are emerging pathogens that circulate between mosquitoes and birds, occasionally spilling over into humans and horses. Current serological screening methods require access to a well-equipped laboratory and are not currently available for on-site analysis. As a proof of concept, we propose here a species-independent lateral flow microarray immunoassay (LMIA) able to quickly detect and distinguish between WNV Non-Structural 1 (NS1) and USUV NS1-specific antibodies. A double antigen approach was used to test sera collected from humans, horses, European jackdaws (Corvus monedula), and common blackbirds (Turdus merula). Optimization of the concentration of capture antigen spotted on the LMIA membrane and the amount of detection antigen conjugated to detector particles indicated that maximizing both parameters increased assay sensitivity. Upon screening of a larger serum panel, the optimized LMIA showed significantly higher spot intensity for a homologous binding event. Using a Receiver Operating Characteristics (ROC) curve, WNV NS1 LMIA results in humans, horses, and C. monedula showed good correlation when compared to “gold standard” WNV FRNT90. The most optimal derived sensitivity and specificity of the WNV NS1 LMIA relative to corresponding WNV FRNT90-confirmed sera were determined to be 96% and 86%, respectively. While further optimization is required, this study demonstrates the feasibility of developing a species-independent LMIA for on-site analysis of WNV, USUV, and other arboviruses. Such a tool would be useful for the on-site screening and monitoring of relevant species in more remote or low-income regions.

Contribution to ecological environmental factors and the occurrence of haemosporidians in birds in Zhongar Alatau National Park, Kazakhstan

In addition to the presence of a suitable host and vector, the prevalence of haemosporidians is influenced by several important factors, including the environmental conditions of the habitat, which depend on broader geographic characteristics. The aim of this study is to perform a preliminarily assessment of the distribution of blood parasites in birds from the mountainous area of Zhongar Alatau NP and to find potential new sites for research on their ecology in Kazakhstan. The results of this research constitute the first report on the occurrence of blood parasites from this area. A total of 58 birds, from the order Passeriformes and one individual from the order Caprimulgiformes, were examined during the study. The overall prevalence of infections caused by haemosporidian parasites (Haemoproteus, Leucocytozoon) was 18.6%. Neither the genus Plasmodium nor the presence of trypanosomes and microfilariae was detected in the birds examined. Three birds (5.1% prevalence) were infected with parasites of the genus Haemoproteus, in all eleven positive birds the analyses showed the presence of parasites of the genus Leucocytozoon (18.6% prevalence). The presence of parasites genus Haemoproteus was detected only in birds that were also infected with Leucocytozoon parasites. More infections with parasites of the genus Leucocytozoon are predicted due to the higher altitude and ecological factors at the capture sites, which are more favourable for the development of vectors of this genus. The species Haemoproteus majoris was detected in the host Emberiza cioides and species Haemoproteus minutus in host Turdus merula. Other species of this genus in the hosts Cyanistes cyanus and Turdus atrogularis were not determined. The species Leucocytozoon fringilinarum was detected in the hosts Cyanistes cyanus and Parus major, Leucocytozoon dubreuili was detected in Turdus atrogularis and Turdus merula. In the other host species Aegithalos caudatus, Emberiza cioides and Periparus aterus, it was not possible to dermine the species of the genus Leucocytozoon.

Survey of Tick-Borne Zoonotic Agents in Ixodes Ticks Carried by Wild Passerines during Postbreeding Migration through Italy

Recently, increasing attention has been posed on the role of migrating birds in the spread of ticks and indirectly of tick-borne pathogens (TBPs). Despite, Italy is considered a bridge between continental Europe and North Africa and a necessary path to connect Mediterranean countries, few studies have been conducted on ticks collected from birds migrating through this country and associated TBPs. The aims of this research were to estimate the infestation burden and identify tick species feeding on migratory birds, and perform a molecular screening for TBPs. During autumn migration (2019–2020), birds were inspected for ticks in a ringing station located in north-east Italy. Ticks were identified and screened for tick-borne encephalitis virus (TBEV), Borrelia burgdorferi sensu latu, Rickettsia spp., Ehrlichia spp., Neoehrlichia spp., Anaplasma phagocytophilum, and Bartonella spp. Ixodes ticks (n = 209) were feeding on 2.6% of passerines (88/3411). Most of these (208/209) were Ixodes ricinus, except one Ixodes frontalis. Eight bird species were infested: common blackbird, redwing, brambling, song thrush, common chaffinch, European robin, water pipit, and coal tit. Rickettsiales showed a low prevalence, from 1.4% of Ehrlichia spp., 4.3% of A. phagocytophilum, up to 7.2% of Rickettsia spp.. Borrelia burgdorferi s.l. had the highest prevalence, 54.6%, and several zoonotic genotypes were identified: B. garinii, B. valaisiana, B. afzeli, B. burgdorferi sensu stricto, and B. miyamotoi. All specimens were negative for TBEV and Bartonella spp.. Although the tick burden was generally low, most of the vectors (>60%) were positive for at least one pathogen, highlighting the relevance of a continuous monitoring of migrating birds as potential sources of pathogen dispersal.

The European laurel <i>Laurus nobilis</i> berries in the diet of the blackbird <i>Turdus merula</i>

The feeding activity of frugivorous birds is influenced by the selection criteria for berry size. European laurel (Laurus nobilis), a dioecious species with high lipid and protein content in its berries, is dispersed by blackbird (Turdus merula). This study aimed to investigate the relationship between berry size and feeding behavior of blackbird. Field data was collected in a botanical park near Rome (Italy) and included seed collection, observation of regurgitation events, and bird population surveys. The volume and shape index of berries and seeds were measured, and statistical analyses were performed. The results showed a positive linear correlation between berry and seed volume. Blackbird selectively consumed larger berries, resulting in a higher percentage of pericarp as an energy resource. The birds exhibited a bimodal strategy, feeding on both large ellipsoidal and large round berries, which had a higher percentage of pericarp. The shape index of berries and seeds showed a significant difference between the control collection and those consumed by blackbird. The findings suggest a case of coevolution, with the plant optimizing seed dispersal by offering berries of different sizes to accommodate the feeding behavior of blackbird. This study provides insights into the ecological relationship between frugivorous birds and plants, highlighting the role of berry size in seed dispersal strategies.

Factors affecting fledglings survival in urban population of European blackbirds in Szczecin (NW Poland)

The first-year survival alters population growth rates and viability in birds, however this period remains the least-studied of the avian life stages. Here we present results of the 19 years of study of fledglings apparent survival of urban population of European blackbird Turdus merula in Szczecin (NW Poland). We checked for possible influence on survival of several factors, including parental traits, such as parental age, their previous breeding experience, natal brood size, presence of another brood in a given breeding season and the time gap between clutches of a particular pair. Moreover, we incorporate into our analysis fledging’s hierarchy in the brood, its fledging time in the breeding season, temperature and precipitation during the first months of life. We also investigated changes in the apparent survival over 19 years. We found that the individual’s hierarchy in the nest, and the day of fledging had the strongest influence on the apparent survival, with heavier birds fledged earlier in the season surviving better. Increase in parental age and previous breeding experience of the pair could result in enhanced survival. Surprisingly increased precipitation lowered fledglings’ survival. During the 19 years of the study fledglings’ apparent survival dropped about 10%.

Morishitium polonicum (Machalska, 1980) is a junior synonym of Morishitium dollfusi (Timon-David, 1950) (Trematoda: Cyclocoeliidae).

Species of the genus Morishitium Witenberg, 1928 are parasites of the body cavity, air sacs, and lungs of birds. At least 14 species are considered valid, but molecular confirmation of their status is lacking. Here, we provide the first molecular data on Morishitium dollfusi isolated from their type host Pica pica, compared them with previously reported molecular data from Morishitium polonicum isolated from their type and paratype hosts, Turdus merula and Turdus philomelos, and performed extensive measurements of 511 individuals of Morishitium spp. across a broad host spectrum, at multiple infection intensities, and year-round. We analyzed the molecular phylogenetics of Morishitium spp. adults isolated from bird hosts of Czech origin and provide comparative measurements of the analyzed specimens. Based on the molecular examination of morphologically identified specimens of M. dollfusi and M. polonicum (CO1, ND1, and ITS2 markers), we propose synonymization of Morishitium dollfusi (Timon-David, 1950) with Morishitium polonicum (Machalska, 1980) (isolates of European origin). The three markers were either identical (CO1, ITS2) or formed haplotypes shared by the two species (ND1). Morphological analyses revealed a continuum of key identification features for the two above-named species, although we used specimens matching the original descriptions and isolated them from the type hosts. Therefore, Morishitium polonicum is a junior synonym of Morishitium dollfusi. Attention is needed regarding the status of East Asian isolates identified previously as M. polonicum (or M. polonicum malayense). The molecular analysis revealed that these isolates form a distinct clade, and further research is needed to produce data allowing the likely separation of the malayense clade as a separate species.

A preliminary study of the winter roosting behaviour of four woodland passerines

ABSTRACT Capsule Radio-tracking of four woodland passerine species reveals variation in winter roost site selection within and between species. Aims To evaluate methods for studying winter roosting behaviour in woodland passerines and to collect preliminary data on intra- and inter-specific differences in roost site characteristics and spatial arrangement. Methods Ten woodland birds (three Eurasian Blackbirds Turdus merula, three Dunnocks Prunella modularis, two Great Tits Parus major and two European Robins Erithacus rubecula), were fitted with a tail-mounted Lotek PicoPip AG337 VHF radio tag (January to March 2022). Tagged birds were located by triangulation, and nightly winter roost locations identified and characterized. A geographic information system was used to quantify roost site fidelity, roosting height and types of habitats used. Results Manual tracking of birds with radio tags is a cost effective and appropriate method for studying passerine winter roosting behaviour. Sample sizes were too small to allow exploration of significant differences between sites, age and sex. European Robins showed the greatest site fidelity in relation to between-night roost positions, with Eurasian Blackbird, Great Tit and Dunnock being more variable in the sites chosen between nights. Eurasian Blackbird and Great Tit roost sites were generally higher above the ground (up to 6 m), compared to European Robins and Dunnocks (all sites less than 4 m above the ground). Eurasian Blackbirds varied the most in the number of habitats used for roost sites, and European Robins showed the least variation. Only three out of 11 habitat types (bramble Rubus sp, laurel Prunus sp. and Sycamore Acer pseudoplatanus with Ivy Hedera helix) were used by more than one species as a roosting habitat. Conclusion Further research should focus on: (1) habitat use in relation to relative availability; (2) increasing samples sizes to allow comparison of factors such as age, sex and sites; (3) the impact of supplementary feeding on roosting behaviour; (4) quantifying the thermal properties of roost sites.

Immune challenge reduces daily activity period in free-living birds for three weeks.

Non-lethal infections are common in free-living animals and the associated sickness behaviours can impact crucial life-history trade-offs. However, little is known about the duration and extent of such sickness behaviours in free-living animals, and consequently how they affect life-history decisions. Here, free-living Eurasian blackbirds, Turdus merula, were immune-challenged with lipopolysaccharide (LPS) to mimic a bacterial infection and their behaviour was monitored for up to 48 days using accelerometers. As expected, immune-challenged birds were less active than controls within the first 24 h. Unexpectedly, this reduced activity remained detectable for 20 days, before both groups returned to similar activity levels. Furthermore, activity was positively correlated with a pre-experimental index of complement activity, but only in immune-challenged birds, suggesting that sickness behaviours are modulated by constitutive immune function. Differences in daily activity levels stemmed from immune-challenged birds resting earlier at dusk than control birds, while activity levels between groups were similar during core daytime hours. Overall, activity was reduced by 19% in immune-challenged birds and they were on average almost 1 h less active per day for 20 days. This unexpected longevity in sickness behaviour may have severe implications during energy-intense annual-cycle stages (e.g. breeding, migration, winter). Thus, our data help to understand the consequences of non-lethal infections on free-living animals.

The Effect of Seasons on Total Antioxidant Capacity (TAC), Total Oxidant Capacity (TOC) and OSI (Oxidative Stress Index) Levels in Free-Living Blackbirds (Turdus merula) in Nature

The Effect of Seasons on Total Antioxidant Capacity (TAC), Total Oxidant Capacity (TOC) and OSI (Oxidative Stress Index) Levels in Free-Living Blackbirds (Turdus merula) in Nature

Seasonal variation in the diurnal activity pattern of Eurasian blackbirds (Turdus merula) in the forest

Camera traps are increasingly used to estimate the density of animals as well as their activity patterns. As camera traps allow monitoring of animals over long periods of time without disturbance, they are especially useful to observe changes in diurnal activity patterns over time. In ornithology, camera trapping is still in its infancy. To our knowledge, no study has yet investigated the activity pattern of a songbird over the full annual cycle. We used camera traps in the Rammert, a small mountainous forest area near Rottenburg in Southwest Germany to monitor the diurnal activity pattern of forest-dwelling Eurasian blackbirds (Turdus merula). As the activity level of animals is known to be affected by day light, we used double-anchoring transformation of day times to account for the variation in sunrise and sunset across the different seasons. By generating activity models, we investigated the pattern of blackbird activity during the four seasons of the year and compared the patterns of male and female birds, respectively. A significant difference between a unimodal activity pattern in spring and a bimodal pattern for the rest of the year was found which might be related to breeding and territorial behaviour in spring. Moreover, we observed that the activity pattern of males and females overlapped greatly but still showed some variation in the number and timing of density peaks.

Tendon-Derived Mesenchymal Stem Cells (TDSCs) as an In Vitro Model for Virological Studies in Wild Birds.

The use of wild animals in research is complicated due to the capture and housing conditions, as well as to legal aspects, making it difficult to develop in vivo and in vitro models for the study of pathologies that affect these species. Here we validate an in vitro model of tendon-derived mesenchymal cells (TDSC) from Eurasian blackbird (Turdus merula) cadaveric samples. Through the expression of surface markers and the ability to differentiate into multiple lineages, the nature of the cells was confirmed. We then evaluated Mesenchymal Stem Cells (MSCs) as an infection model for the Usutu Flavivirus. To this aim, blackbird TDSCs were compared to Vero E6 cells, commonly used in Flavivirus studies. Both cells showed permissiveness to USUV infection as confirmed by immunocytochemistry. Moreover, TDSCs exhibited replication kinetics similar to, although slightly lower than, Vero E6, confirming these cells as a pertinent study model for the study of the pathogenesis of USUV. In this work, we isolated and characterized tendon-derived mesenchymal stem cells, which represent an interesting and convenient in vitro model for the study of wildlife species in laboratories.

Internal Architecture Differentially Affects Thermal Insulation in the Walls of Common Blackbird Turdus merula Nests

Nest construction may result in niche creation by the bird, i.e., modification of the immediate environment in terms of temperature or humidity. Here thermal insulation of nests of the Common Blackbird Turdus merula was investigated using a heat source placed inside the cup. The temperature profile of the nest wall was recorded using thermistors placed at different positions in the nest wall. Temperatures were affected by the layers in the wall with the grass cup lining and mud cup offering more insulation than the outer wall. Thermal conductance of the wall of Common Blackbird nests was relatively high compared to other reports for this variable in other passerine species from Australia. Variation among Common Blackbird nests in terms of temperature differences across layers, and thermal conductance overall, correlated with the thickness of the grass cup lining. Thermal insulation provided by a nest wall is dependent on the thicknesses and types of materials used in each part of the wall. Previous studies using nest deconstruction have demonstrated that the various layers in a wall have differing thermal characteristics. This is the first report of clear differences in the temperature profile across the different parts of the intact nest wall. Whether this pattern is also observed in nests of other species requires further investigation. The placement of different materials within the nest wall by the bird is not a random process and the results support the idea that the avian nest is involved in niche creation.

Adoption and feeding of fieldfare nestlings and fledglings by European blackbird.

Interspecific adoption is an intriguing topic in behavioral and evolutionary ecology. As it is a rare phenomenon, seldom documented in the literature, reports of interspecific adoption based on solid data are particularly valuable. A long-term and extensive monitoring programme involving a local population of European blackbirds (Turdus merula, hereafter blackbird) has yielded, among other things, observations of alloparental behavior exhibited by blackbirds toward fieldfare (Turdus pilaris) nestlings (a single nest, the first-ever record) and fledglings (12 cases in all). We discuss the observations in the context of the available literature.

Energetics and fuel use vary with migration strategy across populations of Common Blackbirds

Abstract Seasonal migration is a physiologically demanding endeavour that animals prepare for by finding and storing energy. Species and populations vary in their tendencies to migrate and the energetic demands of migration likely determine the degree and type of preparation that different animals undergo. Birds fuel their migratory flight using stored fat. Previous work has suggested that in addition to being energetically dense, certain lipids like polyunsaturated fatty acids (PUFAs) may be particularly efficient fuels that are preferentially mobilized for flight or serve may additional functions, such as modulating membrane fluidity or stimulating gene expression as ligands, during long‐distance migratory flight. Using a series of behavioural and metabolic experiments in a partial transplant aviary setting of Common Blackbirds (Turdus merula) populations that range from being fully migratory to partially migratory to sedentary, we asked how migratory restlessness (Zugunruhe), weight gain and oxidation of stearic acid (18:0), oleic acid (18:1n‐9), linoleic acid (18:2n‐6) and alpha linolenic acid (18:3n‐3; ALA) varied with migratory mode and season. We found no population‐level differences in the timing of Zugunruhe. However, before migration, a greater proportion of individuals from fully migratory populations exhibited weight gain and migratory restlessness, as well as increased oxidation of PUFAs. After Zugunruhe, only individuals from migratory populations showed reduced PUFA oxidation. All populations showed increased oxidation of saturated fat after Zugunruhe. Our results demonstrate that certain migratory traits, like the timing of Zugunruhe are expressed similarly across populations in response to local environmental conditions, while other traits, like lipid oxidation, can vary among populations. Read the free Plain Language Summary for this article on the Journal blog.

Host Cells of Leucocytozoon (Haemosporida, Leucocytozoidae) Gametocytes, with Remarks on the Phylogenetic Importance of This Character.

Leucocytozoon parasites remain poorly investigated in comparison to other haemosporidians. The host cell inhabited by their blood stages (gametocytes) remains insufficiently known. This study aimed to determine the blood cells inhabited by Leucocytozoon gametocytes in different species of Passeriformes and to test if this feature has a phylogenetic importance. We microscopically analyzed blood films stained with Giemsa from six different bird species and individuals and used PCR-based methods for parasite lineage identification. The DNA sequences obtained were applied for phylogenetic analysis. Leucocytozoon parasite from the song thrush Turdus philomelos (cytochrome b lineage STUR1), the blackbird Turdus merula (undetermined lineage), the garden warbler Sylvia borin (unknown lineage) inhabited erythrocytes, a parasite from the blue tit Cyanistes caeruleus (PARUS4) infects lymphocytes, while in the wood warbler Phylloscopus sibilatrix (WW6) and the common chiffchaff Phylloscopus collybita (AFR205) they were found inhabiting thrombocytes. Parasites infecting thrombocytes were closely related, while the parasites infecting erythrocytes were placed in three different clades, and the one found in lymphocytes was placed in a separate clade. This shows that the determination of host cells inhabited by Leucocytozoon parasites can be phylogenetically important and should be considered in future species descriptions. Noteworthy, phylogenetic analysis might be used for the prediction of which host cells parasite lineages might inhabit.

Apoptosis in Usutu virus-associated encephalitis in naturally infected Eurasian blackbirds (Turdus merula)

Apoptosis in Usutu virus-associated encephalitis in naturally infected Eurasian blackbirds (Turdus merula)

Low level of extra-pair paternity in an urban population of blackbirds

We studied extra-pair paternity in a socially monogamous bird, the European Blackbird (Turdus merula). The research was conducted in an urban park in Poland. We obtained genetic samples from 36 broods (123 nestlings) of 21 unique pairs. The proportion of broods with some extra-pair nestlings was 17.1% (6 broods), and overall, 13.1% (16 nestlings) of all nestlings were sired by extra-pair males. In one brood (2.8% of all the investigated broods), we found one egg laid by a female which did not have her own territory in the study area (brood parasitism). These figures are relatively low compared to other closely related passerines. We suggest that mate guarding in the studied population may effectively prevent females from engaging in extra-pair activity, and in the case of females, divorce and serial polygamy are better strategies for enhancing the genetic quality and genetic diversity of their offspring than infidelity.

The pathology of co-infection with Usutu virus and Plasmodium spp. in naturally infected Eurasian blackbirds (Turdus merula)

Usutu virus (USUV) is a mosquito-borne zoonotic flavivirus causing mortality in Eurasian blackbirds (Turdus merula) in Europe. In dead blackbirds, avian malaria co-infection due to mosquito-borne hemosporidians (e.g., Plasmodium spp.) has been reported. In humans, a similar co-infection of a flavivirus, Dengue virus, and Plasmodium spp. is causing increased severity of clinical disease. Currently, the effects of co-infection of arboviruses and hemosporidians in blackbirds remain unclear. This study investigates the rate of USUV and Plasmodium spp. co-infection in found-dead blackbirds (n = 203) from 2016 to 2020 in the Netherlands. Presence of Plasmodium spp. was evaluated by cytology (43/203; 21,2%), histopathology (94/186; 50,5%) and qPCR (179/203; 88,1%). The severity of histological lesions in USUV and Plasmodium spp. co-infected dead blackbirds (121/203; 59,6%) were compared with those in Plasmodium spp. single-infected cases. Additionally, since no knowledge is present on the infection rate on live birds and mosquitoes in the Netherlands, a small group of live blackbirds (n = 12) and selected in the field-collected mosquito pools (n = 96) in 2020 were tested for the presence of Plasmodium spp. The latter was detected in the tested live blackbirds by qPCR (8/10; 80%), and cytology (3/11; 27,3%) and in the mosquito pools by qPCR (18/96; 18,7%). For this study, co-infection between USUV and Plasmodium spp. was observed only in the dead blackbirds. The high Plasmodium spp. presence, associated with lower lesions score, in single infected found dead birds suggest a predominantly smaller pathogenic role as single agent. On the other hand, the higher histological lesion scores observed in USUV and Plasmodium spp. co-infected birds suggests a major pathogenic role for the virus or an increased severity of the lesions due to a possible interplay of the two agents.