European Blackbirds Turdus Merula Research Articles

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%.

The first case of successful polyterritorial polygyny in the European Blackbird Turdus merula

ABSTRACT This paper describes the first case of successful polyterritorial polygyny in the European Blackbird Turdus merula. It was detected in an intensively studied color-banded population of European Blackbirds in Szczecin (northwestern Poland).

Breeding biology of the European Blackbird Turdus merula in orange orchards

During two successive years (2013–2014), we studied the breeding ecology of the European Blackbird Turdus merula in Guelma province, north-east of Algeria. The study was carried out in orange orchards of the region. We investigated nest placement in the orange trees and determined the factors of reproductive failure at this study area. Nests were placed at low height (mean±SD=1.42±0.04m) and located near the trunk (mean±SD=0.61±0.04m). The breeding season occurred between mid-May and mid-June and the peak of egg laying took place during the first half of May. The mean clutch size was 2.96±0.05, density of breeding pairs was 0.83±0.30p/ha. The breeding success reported in the present study was higher than that recorded in other studies. Predation was the leading cause of nest failure of the population under investigation. The present study shows that the orange orchards appear to be the preferred breeding area for Blackbird population.

Campylobacter jejuni sequence types show remarkable spatial and temporal stability in Blackbirds

BackgroundThe zoonotic bacterium Campylobacter jejuni has a broad host range but is especially associated with birds, both domestic and wild. Earlier studies have indicated thrushes of the genus Turdus in Europe to be frequently colonized with C. jejuni, and predominately with host-associated specific genotypes. The European Blackbird Turdus merula has a large distribution in Europe, including some oceanic islands, and was also introduced to Australia by European immigrants in the 1850s.MethodsThe host specificity and temporal stability of European Blackbird C. jejuni was investigated with multilocus sequence typing in a set of isolates collected from Sweden, Australia, and The Azores.ResultsRemarkably, we found that the Swedish, Australian, and Azorean isolates were genetically highly similar, despite extensive spatial and temporal isolation. This indicates adaptation, exquisite specificity, and stability in time for European Blackbirds, which is in sharp contrast with the high levels of recombination and mutation found in poultry-related C. jejuni genotypes.ConclusionThe maintenance of host-specific signals in spatially and temporally separated C. jejuni populations suggests the existence of strong purifying selection for this bacterium in European Blackbirds.

Loss of migration and urbanization in birds: a case study of the blackbird (Turdus merula).

Many organisms have invaded urban habitats, although the underlying factors initially promoting urbanization remain poorly understood. Partial migration may facilitate urbanization because such populations benefit from surplus food in urban environments during winter, and hence enjoy reduced fitness costs of migratory deaths. We tested this hypothesis in the European blackbird Turdus merula, which has been urbanized since the 19th century, by compiling information on timing of urbanization, migratory status, and population density for 99 cities across the continent. Timing of urbanization was spatially auto-correlated at scales up to 600 km. Analyses of timing of urbanization revealed that urbanization occurred earlier in partially migratory and resident populations than in migratory populations of blackbirds. Independently, this effect was most pronounced in the range of the distribution that currently has the highest population density, suggesting that urbanization facilitated population growth. These findings are consistent with the hypothesis that timing of urbanization is facilitated by partial migration, resulting in subsequent residency and population growth.

Partitioning of Cd and Pb in the blood of European blackbirds (Turdus merula) from a smelter contaminated site and use for biomonitoring

Blood composition is commonly measured to assess exposure to and effects of metals on birds. In most of passerine species, only small volumes of blood may be sampled safely (<500μL), which limit the measure of several markers of health status and chemical residues. Here, we documented the partitioning of Cd and Pb in the blood of European Blackbirds Turdus merula in order to propose usable relationships between whole blood concentrations (for which toxicological benchmarks exist) and those measured in the erythrocytes. Sixty-two blackbirds were trapped along a pollution gradient (smelter of Metaleurop Nord, Northern France). Blood was sampled and Cd and Pb concentrations were measured both in whole blood and in the erythrocytes only. Birds coming from the most contaminated sites exhibited high residues for both Cd and Pb. We assessed that 73% and 99% of Cd and Pb, respectively, were associated to erythrocytes. Strong linear relationships, that were not influenced by neither the age nor the sex, were established between whole blood residues and those of erythrocytes for Cd and Pb (adj-R2=0.78 and 0.93, respectively). Present findings are promising to optimize the use of small blood samples in order to investigate several responses relative to wildlife health status.

Colonisation of urban environments is associated with reduced migratory behaviour, facilitating divergence from ancestral populations

How individuals colonising novel environments overcome the diverse suite of new selection pressures is a fundamental question in ecology and evolution. Urban environments differ markedly from the rural ones that they replace and successful colonisation of urban areas may therefore require local adaptation and phenotypic/genetic divergence from ancestral populations. Such a process would be facilitated by limited dispersal to and from the novel habitat. Here we assess divergence in migratory behaviour between seven pairs of urban and rural European blackbird Turdus merula populations along a 2800 km transect across Europe. This former forest specialist is now amongst the most abundant urban birds across most of its range. We use a stable isotope approach due to the lack of sufficient ringing data from multiple urban populations, and compare hydrogen isotopic ratios of tissues grown in the breeding (feathers) and wintering areas (claws) to derive an index of long distance migratory behaviour. We find a tendency for urban blackbirds to be more sedentary than rural ones at all sites and this divergence is particularly strong at the north‐eastern limit of our transect, i.e. in Estonia and Latvia. These urban populations are those that have been established most recently (from the late 1930s to 1950s) implying that urbanisation can promote rapid ecological divergence. The increased sedentary behaviour of urban birds could promote further ecological divergence between rural and urban populations, such as the earlier breeding of urban blackbirds, and in some cases may contribute to their previously documented genetic divergence.

Population processes in European Blackbirds Turdus merula: a state–space approach

Understanding the demographic processes driving populations is critical in formulating effective management plans. State–space models offer an appealing framework in which to construct models to examine temporal and spatial variation in population dynamics, as they make efficient use of the varied sources of data available. We develop a Bayesian state–space model of the population dynamics of European Blackbird Turdus merula using data collected as part of the British Trust for Ornithology’s Integrated Population Monitoring programme. Previous models of similar data have concentrated on simultaneous estimation of abundance and survival parameters and we extend this approach by incorporating the direct estimation of brood size and nesting success. We show that annual population change is most correlated with adult survival, but that population processes appear to differ in eastern and western regions of Britain which themselves differ markedly in their landscape composition.

Sexual dimorphism of egg size in the European Blackbird Turdus merula

Recently, a number of studies have shown that female birds are able to control the sex of their progeny at the stage of the gamete. There is also some evidence that females adjust their investment in offspring depending on the sex of the embryo during egg formation. Differential maternal investment to the eggs depending on their sex is usually interpreted as an adaptive strategy, by which females can increase competitive abilities of the smaller sex, or preferentially invest towards the sex with the potentially higher fitness returns. Here, we studied variation in egg size in relation to embryo sex and laying order in the European Blackbird Turdus merula. We found male and female eggs to differ in size, with larger eggs containing male embryos, as well as a significant interaction between embryo sex and laying order. This interaction resulted from the fact that egg size increased with the laying sequence among eggs bearing females but did not change with laying order among eggs bearing males. There was no relationship between offspring sex and the laying sequence within a clutch. We suggest that sexual dimorphism in egg size recorded in the European Blackbird may reflect favouritism of the sex which may give higher fitness returns.

Investigator activities reduce nest predation in blackbirds Turdus merula

The effect of investigator perturbance has been traditionally considered detrimental for avian nesting success in terms of enhanced nest predation. This conclusion was however based on a taxonomically biased group of species and, thus, the study of that effect in additional species was essential for reaching a more firm conclusion. Furthermore, although it has been suggested that the effect of nest visiting could also depend on nest predator community, no study has so far tested this hypothesis yet. Trying to detect possible influence of nest‐visiting rates and predator community on nesting success we visited European blackbird Turdus merula nests at two different experimental rates in two populations that considerably differ in the composition of their nest predator communities and natural nest predation rates. Contrary to the traditional ideas, our results not only show that investigator disturbance significantly reduces nest predation, but also that this reduction is maintained in both populations despite the difference in the community of nest predators. We discuss these findings and suggest that predators, especially mammals, might avoid places disturbed by investigators.

The effect of urbanisation on avian morphology and latitudinal gradients in body size

Urban areas occupy a large and growing proportion of the earth. Such sites exhibit distinctive characteristics relative to adjacent rural habitats, and many species have colonised and now successfully exploit urban habitats. The change in selection pressures as a result of urbanisation has led to trait divergence in some urban populations relative to their rural counterparts, but studies have generally been local in scale and the generality of differentiation thus remains unknown. The European blackbird Turdus merula is one of the commonest urban bird species in the Western Palearctic, but populations vary substantially in the length of time they have been urbanised. Here we investigate patterns of morphological variation in European blackbirds occupying 11 paired urban and rural habitats across much of the urbanised range of this species and spanning 25° of latitude. First, we assessed the extent to which urban and rural blackbirds are differentiated morphologically and the consistency of any differentiation across the range. Paired urban and rural Blackbird populations frequently exhibited significant morphological differences, but the magnitude and direction of differentiation was site dependent. We then investigated whether the nature of latitudinal gradients in body‐size differed between urban and rural populations, as predicted by differences in the climatic regimes of urban and rural areas. Blackbird body‐size exhibited strong latitudinal gradients, but their form did not differ significantly between urban and rural habitats. The latitudinal gradient in body size may be a consequence of Seebohm's rule, that more migratory populations occurring at high latitudes have longer wings. We conclude that while there can be substantial morphological variation between adjacent urban and rural bird populations, such differentiation may not apply across a species’ range. Locality specific differentiation of urban and rural blackbirds may arise if the selection pressures acting on blackbird morphology vary in an inconsistent manner between urban and rural habitats. Alternatively, phenotypic divergence could arise in a stochastic manner depending on the morphological traits of colonists, through founder effects.

Clutch Size, Nest Predation, and Distribution of Avian Unequal Competitors in a Patchy Environment

I studied reproductive success, nest predation, and most productive clutch size of seven passerine bird species (Barn Swallow Hirundo rustica, Great Tit Parus major, European Blackbird Turdus merula, Yellowhammer Emberiza citrinella, House Sparrow Passer domesticus, Chaffinch Fringilla coelebs, Black billed Magpie Pica pica) breeding in a patchy environment of tree lots in a matrix of farmland. Habitat patches of 0.07—3.61 ha consistent primarily of elm Ulmus glabra and various other deciduous trees, a thick undergrowth of bushes, primarily elder Sambucus nigra, and herbs. Clutch size of all species was independent of habitat patch size even after controlling for time of breeding and age of breeding birds, but brood size at fledging increased with increasing patch size for the Great Tit, European Blackbird, Yellowhammer, Chaffinch, and Black—billed Magpie, but not far the Barn Swallow and House Sparrow. The frequency of nest predation decreased with increasing size of habitat patches in the open—nesting European Blackbird, Yellowhammer, Chaffinch, and Black—billed Magpie, but not in the hole— or the semi—hole nesters. Brood size of Great Tit, European Blackbird, Yellowhammer, Chaffinche, and Black—billed Magpie increased with increasing patch size even after excluding nests suffering from nest predation. The most productive clutch size measured as the second—order polynomial regression of brood size at fledging on clutch size differed in relation to habitat patch size for the Great Tit, European Blackbird, Yellowhammer, Chaffinch, and Black—billed Magpie, but not for the Barn Swallow and House Sparrow, suggesting that there is no unique optimal clutch size in the first five species. A decreasing fraction of yearling breeding birds was found with increasing patch size in the Great Tit, European Blackbird, Yellowhammer, and Chaffinch, but not in the Barn Swallow and House Sparrow, Habitat patches differed in quality with respect to absolute food abundance and nest predation risks, and territorial species relying nearly exclusively on food resources found within patches or suffering from intense nest predation followed an ideal despotic distribution, while colonial species relying on food resources outside patches followed an ideal free distribution for unequal competitors.