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Apart from some species that reuse their nests regularly, the reuse of open nests is an uncommon phenomenon in the majority of species, especially the passerines. The interspecific reuse of open nests has rarely been described. Here I examine a case of such reuse in thrushes, specifically the reuse of a Fieldfare's (Turdus pilaris) nest by a Song Thrush (Turdus philomelos). A total of 14 Song Thrush nests with eggs were found in an orchard; more than half of these clutches were unsuccessful. Breeding success in the Song Thrush in the orchard was 29% for first clutches/broods and 60% for second clutches/broods. Eleven Fieldfare nests contained clutches: 87% of them were unsuccessful. Breeding success was as low as 14% in the case of first clutches/ broods, and no second clutches/broods were successful. Having reviewed the hypotheses relating to nest reuse, I consider that this case was not brought about by a lack of suitable nesting sites. It was, however, advantageous in that the time and costs of building a new nest were much reduced, given that the nesting territory was of high quality, and that the nesting season is short and breeding success low.

Animal movement and behaviour is fundamental for ecosystem functioning. The process of seed dispersal by frugivorous animals is a showcase for this paradigm since their behaviour shapes the spatial patterns of the earliest stage of plant regeneration. However, we still lack a general understanding of how intrinsic (frugivore and plant species traits) and extrinsic (landscape features) factors interact to determine how seeds of a given species are more likely to be deposited in some places more than in others. We develop a multi-species mechanistic model of seed dispersal based on frugivore behavioural responses to landscape heterogeneity. The model was fitted to data from three-years of spatially-explicit field observations on the behaviour of six frugivorous thrushes and the fruiting patterns of three fleshy-fruited trees in a secondary forest of the Cantabrian range (N Spain). With such model we explore how seed rain patterns arise from the interaction between animal behaviour and landscape heterogeneity. We show that different species of thrushes respond differently to landscape heterogeneity even though they belong to the same genus, and that provide complementary seed dispersal functions. Simulated seed rain patterns are only realistic when at least some landscape heterogeneity (forest cover and fruit abundance) is taken into account. The common and simple approach of re-sampling movement data to quantify seed dispersal produces biases in both the distance and the habitat at which seeds arrive. Movement behaviour not only affects dispersal distance and seed rain patterns but also can affect frugivore diet composition even if there is no built-in preference for fruiting species. In summary, the fate of seeds produced by a given plant species is strongly affected by both the composition of the frugivore assemblage and the landscape-scale context of the plant location, including the presence of fruits from other plants (from the same or different species).

During an intensive study of the urban population of the blackbird Turdus merula in Szczecin (1997–2023), four cases of surrogate copulation were observed in the blackbird and three in the fieldfare Turdus pilaris. In three cases, birds (blackbirds twice and fieldfare once) try to copulate with fledglings of their own species, and in all other cases, the birds try to copulate with moss and sticks. In three cases copulation, attempts were done by adult birds (two blackbirds and one fieldfare), and in four cases, it was a fledgling. The article describes seven surrogate copulations observed in blackbirds and fieldfares in light of hypotheses explaining this phenomenon.

For the first time, studies have been conducted aiming at the diversity of the oribatid mites (Oribatida) that inhabit the nests of open-nesting birds of the genus thrushes (Turdus), particularly fieldfare (T. pilaris Linnaeus, 1758) and redwing (T. iliacus Linnaeus, 1766), in the taiga forests of the European north-east. Long-term observations were carried out in the green belt of the city of Syktyvkar (N 61°40′ E 50°50′) in 2021–2025. Among 168 studied thrush nests (fieldfare—138, redwing—30), 1982 specimens of oribatid mites of 35 species from 33 genera and 26 families were found. The nests of thrushes contain a mixed fauna of oribatid mites, including the following: (a) Soil species that obviously enter the nest with building materials collected by birds from the soil surface. These are epigeic species such as Eupelops plicatus, Neoribates aurantiacus, and Chamobates pusillus; hemi-edaphic species such as Heminothrus peltifer; and euedaphic species such as Oppiella nova and Quadroppia quadricarinata. (b) Tree-dwelling species that have been recorded as inhabiting epiphytic lichens in the European north-east, such as Ameronothrus oblongus, Ceratoppia quadridentata, Oribatula propinqua, Trichoribates berlesei, and Diapterobates oblongus. (c) Eurybiont species such as Tectocepheus velatus, Scheloribates laevigatus, and Oribatula tibialis. An increase in the number and diversity of oribatid mites was noted in nests collected after the end of the nesting period and the flight of chicks compared to nests collected in the spring (overwintered nests).

Avian influenza viruses are predominantly associated with waterfowl and shorebirds, and are rarely detected in other avian hosts in nature. In 2021, an H1N1 virus was isolated from a Fieldfare Turdus pilaris in Zaporizhzhia Oblast, Ukraine. A phylogenetic analysis revealed that all eight gene segments belonged to the Eurasian low-pathogenic avian influenza lineages. The highest nucleotide identity of the HA gene was observed with viruses detected in Georgia, Sweden, and Ukraine (99.11%), while the NA gene showed the greatest identity to viruses from Western Europe (99.14–99.57%). Genetic analysis of the HA cleavage site showed a sequence (PSIQSR↓GLF) that contained a single basic amino acid. No deletions were detected in the stalk region of NA gene, and no specific mutations in PB2 protein were found. However, several amino acid substitutions were identified in the HA gene (D204E, S207T, and D239G) that may affect the binding affinity to specific antibodies. The occurrence of this virus in a wild, seemingly healthy thrush indicate that additional surveillance in poorly studied ecological groups such as Passeriformes is warranted.

Background Species of Plasmodium (Haemosporida, Plasmodiidae) are remarkably diverse haemoparasites. Information on genetic diversity of avian malaria pathogens has been accumulating rapidly, however exo-erythrocytic development of these organisms remains insufficiently addressed. This is unfortunate because, contrary to Plasmodium species parasitizing mammals, the avian malaria parasites undergo several cycles of exo-erythrocytic development, often resulting in damage of various organs. Insufficient knowledge on the exo-erythrocytic development in most described Plasmodium species precludes the understanding of mechanisms of virulence during avian malaria. This study extends information on the exo-erythrocytic development of bird malaria parasites. Methods A roadkill fieldfare (Turdus pilaris) was sampled in Switzerland and examined using pathologic, cytologic, histologic, molecular and microbiologic methods. Avian malaria was diagnosed, and erythrocytic and exo-erythrocytic stages of the parasite were identified using morphologic characteristics and barcode DNA sequences of the cytochrome b gene. The species-specific characteristics were described, illustrated, and pathologic changes were reported. Results An infection with Plasmodium matutinum lineage pLINN1 was detected. Parasitaemia was relatively low (0.3%), with all erythrocytic stages (trophozoites, meronts and gametocytes) present in blood films. Most growing erythrocytic meronts were markedly vacuolated, which is a species-specific feature of this parasite's development. Phanerozoites at different stages of maturation were seen in leukocytes, macrophages, and capillary endothelial cells in most organs examined; they were particularly numerous in the brain. Like the erythrocytic meronts, growing phanerozoites were markedly vacuolated. Conspicuous exo-erythrocytic development and maturation in leucocytes suggests that this fieldfare was not adapted to the infection and the parasite was capable to escape from cellular immunity. Conclusions This is the first report of exo-erythrocytic development of the malaria parasite lineage pLINN1 during single infection and the first report of this lineage in the fieldfare. The findings of multiple phanerozoites in brain, skeletal muscle, and eye tissue in combination with signs of vascular blockage and thrombus formation strongly suggest an impaired vision and neuromuscular responsiveness as cause of the unexpected collision with a slowly moving car. Further studies on exo-erythrocytic stages of haemosporidian parasites are pivotal to understand the true level of populational damage of avian malaria in wild birds.

Facultative migration is thought to be influenced by food and weather, with birds remaining in northern areas if food is abundant and weather conditions are benign, but migrating south when food is scarce and weather is harsh. However, the relative importance of these two factors has rarely been tested with long-term data, and effects of weather are poorly documented. Here, I assess whether winter numbers of the Fieldfare (Turdus pilaris) and the Redwing (T. iliacus) in southern Norway during the period 1980–2020 varied in relation to the abundance of an important source of winter food (rowanberries, Sorbus aucuparia) and indices of winter harshness (North Atlantic Oscillation index, temperature, duration of snow cover). Two regions with contrasting winter harshness (western Norway with a maritime climate, eastern Norway with a continental climate) were compared. Winter numbers of Fieldfare in both regions, and Redwing in eastern Norway, were highest in years with high rowanberry abundance. Weather had mixed influence on thrush winter numbers, but interacted with rowanberry abundance in several cases so that small numbers of thrushes occurred with the combination of low rowanberry abundance and harsh weather. Such interactions occurred both in eastern and western Norway, and for both species, including for the Redwing in western Norway. In conclusion, facultative migration was strongly related to food availability with large numbers wintering in years with large rowanberry crops, and with additional effects of harsh weather working in concert with low rowanberry abundance to reduce wintering numbers to low levels in some years.

Fires can strongly change the vegetation structure and the availability of resources for wildlife, but fire suppression has long affected the natural role of fire in shaping boreal ecosystems in northern Europe. Recently, wildfires have increased in frequency, possibly due to global warming. In contrast to the boreal systems in North America, there have been few studies on responses of wildlife to wildfires in northern Europe. Based on the findings from North America, we predict that responses of wildlife to wildfire vary among wildlife species: where mammalian herbivores, such as moose Alces alces and mountain hare Lepus timidus, will be attracted to burnt areas following an increase in food availability, other species, such as reindeer Rangifer tarandus, are negatively impacted due to fire reducing their preferred food. We then tested our predictions by contrasting wildlife utilization of sites that burnt by wildfire in 2006 with nearby unburnt control sites in three areas in northern Sweden. To measure wildlife utilization, we used 72 camera traps, equally divided between the burnt and control sites, with two placement strategies: random and on wildlife trails. The cameras recorded 27 mammal and bird species during summer 2018. Species assemblage differed between burnt and control sites. Fieldfare Turdus pilaris used burnt sites more than control sites, while pine marten Martes martes and western capercaillie Tetrao urogallus used control sites more than burnt sites. We however did not find support for a positive effect of past forest fires on any of the observed wild mammals. We discuss how, due to the impact of forestry, forage‐rich habitat may not be as limiting in Scandinavia as in the North‐American context, potentially leading to recently burnt sites being less attractive to herbivores such as moose.

In most passerines, parent birds clean their nests. Egg shells, fecal sacs, and dead nestlings, as well as foreign objects, for example, leaf and twig debris, as they appear, are usually removed from nests in one or another way. If, for one reason or another (nest predation, inclement weather, starvation etc.), all offspring die, parents abandon the nest with egg or/and nestling remains. Finding one or another nest empty and intact before the earliest possible fledging date, observers who monitor nests usually attribute the failure to predation. Camera traps placed at 148 Fieldfare (Turdus pilaris) nests in 2016–2020 to study nest predation in Moscow City, Russia documented two cases of sanitation (by females) of entire and almost entire (all but one dead nestling) broods of dead nestlings that had died due to inclement weather. This information is one of the very few, probably the second, and for Eurasian species probably the first published evidence of such a behaviour in passerines. In addition, eight cases of removal by parents of the traces of predation were recorded immediately or soon after (within 0.1–4.2 h) complete depredation of nest contents: eating at the nest or the removal by parents of egg shells, remains of egg contents, as well as feathers lost by parents as a result of predator attacks, an active or passive elimination of disturbances in the lining of the nest cup. Complete or partial “concealment of evidence” by parents occurred in about every four depredated nests, including those in which predators did not leave any “evidence.” The removal by parents of all evidence of clutch/brood failure that had happened for any reason, not only due to predation, was recorded in approximately every third nest from which all offspring disappeared without a trace before the earliest possible fledging date. These behaviours of parents could possibly be considered as bringing them to the point of absurdity, “by inertia,” a sequence of stereotypic actions to maintain cleanliness, as well as the lining of the nest. An observation was also made of a female adding lining material to the nest cup (re-lining) on top of a dead, ca. 7-day old nestling from the failed previous brood and then laying a replacement clutch. All these cases are interesting not only because they provide new information on parental behaviour in the Fieldfare. These “strange behaviours” are also a potential source of bias when studying nest predation and signs left by different predatory species with traditional methods for monitoring the nests, with neither video monitoring nor automatic photography. Furthermore, it must not be excluded that, under some circumstances, even estimates of the relative frequency of different causes of nest failure can be biased due to these behavioural curiosities. That is why it is important to know how many and how frequently do bird species show similar behaviours.

Sindbis virus (SINV) is a mosquito-borne bird virus that occasionally causes human disease in Fennoscandia, suggested to have cyclic 7-year intervals between outbreaks. Reliable data on human infections in Sweden is however lacking. Here we investigated the SINV antibody prevalence among birds in a Swedish area endemic to SINV to scrutinize if a cyclic variation in antibody prevalence is present in the natural host of SINV. Serum from birds were sampled in the summers of 2002-2004 and 2009 in the floodplains of the River Dalälven in central Sweden, with 2002 and 2009 representing hypothesized years of SINV outbreaks. A total of 963 birds from 52 species (mainly passerines) were tested for the presence of SINV antibodies using a plaque reduction neutralization test. The highest SINV antibody prevalence was found in Turdidae species, specifically Fieldfare, Redwing and Song thrush in which more than 70% of sampled individuals had antibodies to SINV in 2009. The SINV antibody prevalence significantly varied between years with 2% in 2002, 8% in 2003, 14% in 2004 and 37% in 2009. Antibodies were found equally often in hatchlings and in adults and increased from early to late in the season. Clearly, the SINV antibody prevalence was not elevated in the bird hosts in the predicted outbreak year 2002, thus solid evidence of a cyclic occurrence of SINV in Sweden is still lacking.