Brood division and transition to independence in Blackbirds Turdus merula

Blackbirds Turdus merula rearing young in the Botanic Garden, Oxford, were observed over three summers (1979–81). Between 0 and 10 days after fledging the young were divided between the parents so that each fed only certain fledglings and refused to feed others. This division was temporally stable. In broods where another nesting attempt followed, the male usually took responsibility for all the young, but in final broods they were divided fairly evenly. The probability of a fledgling surviving to independence declined as the number of young a parent fed increased; thus division should be favoured. However, if the female fed some young the inter-nest interval increased and the potential number of young that could be raised in that season was curtailed. This trade-off is examined by means of a model. After fledging the young improved in their ability to capture prey successfully and increased the size of the prey taken. At 15–24 days after fledging, self-feeding became more profitable than parental feeding and the young became fully independent. The timing of this transition is influenced by the parents, and it is suggested that by dividing the brood, parental feeding can be more carefully regulated so that finer control over the timing of independence is achieved.     

Changes in migration behaviour of Blackbirds Turdus merula from the Netherlands

Capsule Dutch Blackbirds from all regions had almost ceased migrating in the period between 1955 and 1990, probably as a result of climate change.     

Age‐specific reproduction and disposable soma in an urban population of Common Blackbirds Turdus merula

The mechanism of senescence is an important subject of current research, but our knowledge of the factors influencing the rate of ageing in naturally occurring populations remains rudimentary. Evolutionary theories of senescence predict that investment in reproduction in early life should come at the cost of reduced somatic maintenance and thus result in earlier or more rapid senescence. We use data on the complete reproductive histories of 431 Common Blackbirds (222 males and 209 females) collected during a 19‐year study of the ecology of an urban population of this species to test the main hypotheses addressing the issue of senescence. On average, the birds in this population survived for 3.7 (± 1.9 sd) years. Reproductive success in females peaked at the age of 4, but in males remained stable until the 5th year of life. We observed declines in reproductive success, indicative of senescence, after the peak years in both sexes. The mechanism of age‐related changes in the reproduction of females confirms the individual improvement and selective disappearance hypotheses. In the case of males, the increase in reproductive performance comes as a consequence of the disappearance of poor reproducers. The parental investment associated with early life fecundity (the first two breeding seasons in males and females) impairs the breeding success of females later on. Contrary to expectations, there was no negative impact of high early life fecundity on either mortality or lifespan. Individuals of both sexes with a high early life fecundity had a higher lifetime reproductive success than those in which early life fecundity was low. Hence, the most profitable strategy is to maximize reproductive effort in the early stages of life. This yields the highest lifetime reproductive success, despite the increased impact of senescence, especially in females. These results are consistent with the disposable soma hypothesis.     

No evidence of sex‐biased dispersal in an island population of Common Blackbirds Turdus merula

Natal dispersal has major consequences for the dynamics and genetic structure of populations. Female‐biased natal dispersal, otherwise the norm in birds, is overridden when the place to move is limited, as on isolated islands. This effect was confirmed for the fist time in a European study system, the Common Blackbird breeding on Heligoland Island. Spatially restricted and sexually uniform natal dispersal may be a prerequisite for successful establishment of populations on remote islands or isolated habitat fragments, and this could play a major role in speciation processes.     

宁夏六盘山发现乌鸫

正2011年5月6日,在甘肃省平凉市崆峒区柳湖公园(35°32′46″N,106°40′10″E,海拔1 294 m)内发现乌鸫(Turdusmerula)繁殖巢一个,巢营于一高大柳树上,巢距地面高4.2m,巢中4只雏鸟即将出飞。2016年5月15日,在宁夏回族自治区隆德县十八里铺村(35°61′02″N,106°06′91″E,海拔1 987 m)发现并记录到乌鸫雄性个体1只,生活环境为村庄。2018年5月25日,在该县黄家峡村(35°63′48″N,106°19′86″E,海拔223 0 m),     

The reproductive success of Blackbirds Turdus merula in relation to habitat structure and choice of nest site

The reproductive success of a population of Blackbirds Turdus merula occupying farmland and woodland was studied over 3 years to investigate the effects of habitat on breeding success. Territory distribution was patchy in both farmland and woodland; some areas were unoccupied, while other areas were occupied at variable densities. Habitat structure appeared to influence occupation: the index of habitat complexity ("cover score") was higher in occupied areas than in unoccupied areas and high-density territories had higher cover scores than low-density territories. However, habitat structure had no significant effect on reproductive success because the cover scores of territories where pairs were successful did not differ significantly from those of territories where there were no successful breeding attempts. There was no evidence of differential mortality rates in adults according to habitat. The height, bulk and exposure of c. 430 nests were measured to determine the effect of nest and nest-site characteristics on reproductive success. Nest exposure was the only feature that differed between successful and failed nests, successful nests being less exposed than failed nests. The major cause of breeding failure was nest predation, but the effect of nest exposure operated only during the laying and incubation period and not during the nestling period. The significance of habitat structure for variation in population densities between habitats is discussed.     

Importance of feeding ecology to the reproductive success of Blackbirds Turdus merula nesting in rural habitats

The feeding ecology of Blackbirds Turdus merula breeding in contiguous woodland and farmland habitats was studied over three years. The aim of the study was to investigate how reproductive success was influenced by nestling diet and the provisioning rates of parents feeding nestlings. Parental provisioning rates increased with brood size, and consequently individual nestlings were no lighter in larger broods. None of the environmental factors measured had strong effects on parental provisioning rate. The nestling diet was dominated by caterpillars and earthworms, the former occurring in a short period in the middle of the breeding season. The availability of earthworms was higher in woodland and was dependent on rainfall in farmland. Nestling mass and provisioning rates were marginally higher under predominantly earthworm diets. Nestling mass increased with rainfall in farmland only, and was higher in farmland than in woodland or woodland-edge, although it is doubtful whether this result is of any significance for fledgling survival. Overall, Blackbirds were able to provision their nestlings adequately throughout the breeding season across a range of conditions. There was no evidence to suggest that reproductive success was constrained by aspects of feeding ecology within the natural range of brood size.     

Long-Term Effects of Chronic Light Pollution on Seasonal Functions of European Blackbirds (Turdus merula)

Light pollution is known to affect important biological functions of wild animals, including daily and annual cycles. However, knowledge about long-term effects of chronic exposure to artificial light at night is still very limited. Here we present data on reproductive physiology, molt and locomotor activity during two-year cycles of European blackbirds (Turdus merula) exposed to either dark nights or 0.3 lux at night. As expected, control birds kept under dark nights exhibited two regular testicular and testosterone cycles during the two-year experiment. Control urban birds developed testes faster than their control rural conspecifics. Conversely, while in the first year blackbirds exposed to light at night showed a normal but earlier gonadal cycle compared to control birds, during the second year the reproductive system did not develop at all: both testicular size and testosterone concentration were at baseline levels in all birds. In addition, molt sequence in light-treated birds was more irregular than in control birds in both years. Analysis of locomotor activity showed that birds were still synchronized to the underlying light-dark cycle. We suggest that the lack of reproductive activity and irregular molt progression were possibly the results of i) birds being stuck in a photorefractory state and/or ii) chronic stress. Our data show that chronic low intensities of light at night can dramatically affect the reproductive system. Future studies are needed in order to investigate if and how urban animals avoid such negative impact and to elucidate the physiological mechanisms behind these profound long-term effects of artificial light at night. Finally we call for collaboration between scientists and policy makers to limit the impact of light pollution on animals and ecosystems.     

Avian haematozoan parasites and their associations with mosquitoes across Southwest Pacific Islands

The degree to which haematozoan parasites can exploit a range of vectors and hosts has both ecological and evolutionary implications for their transmission and biogeography. Here we explore the extent to which closely related mosquito species share the same or closely related haematozoan parasites, and examine the overlap in parasite lineages with those isolated from avian hosts, Zosterops species, sampled across the same study sites. Mosquito samples were collected and analysed (14 species, n = 804) from four islands in Vanuatu and the main island of New Caledonia. Using polymerase chain reaction, 15.5% (14/90) of pooled mosquito (thoracic) samples showed positive amplifications. Subsequent phylogenetic analysis of the cytochrome b gene identified four genetically distinct Plasmodium and two Haemoproteus lineages from these samples, five of which were identical to parasite lineages (n = 21) retrieved from the avian hosts. We found that three Plasmodium lineages differing by a maximum of 0.9% sequence divergence were recovered from different species and genera of mosquitoes and two Haemoproteus lineages differing by 4.6% sequence divergence were carried by 10 distantly related (11-21% divergent) mosquito species. These data suggest a lack of both cospeciation and invertebrate host conservatism. Without experimental demonstration of the transmission cycle, it is not possible to establish whether these mosquitoes are the biological vectors of isolated parasite lineages, reflecting a limitation of a purely polymerase chain reaction-based approach. Nonetheless, our results raise the possibility of a new transmission pathway and highlight extensive invertebrate host shifts in an insular mosquito-parasite system.     

Divorce and its consequences in the Common Blackbird Turdus merula

An urban population of Common Blackbirds Turdus merula was studied between 1995 and 1998 in the Botanic Garden in Bonn, Germany. The number of breeding pairs varied from 32 to 39 per breeding season. Mean divorce rate (pair separation with remating of at least one of the partners) between two breeding seasons was 19.3% and 5.1% within breeding seasons. The number of fledglings produced per breeding season, of pairs which subsequently divorced, was significantly lower than that of pairs that stayed together. Females, but not males, produced more fledglings in the season after divorce than with their former mates the year before, and as many as females of the same age in stable pair bonds. The increase in reproductive success was thus unlikely to be due to age effects. Nestling mass correlated positively with offspring survival to the following year. Females had heavier nestlings after divorce than in their former pair bond. There was no difference in nestling mass for males before and after divorce. The data were used to test the predictions of several hypotheses to explain divorce. Because divorce was more likely after low reproductive success in the previous year, and only females benefited, the findings best support the 'better option' hypothesis.     

Adaptive latitudinal variation in Common Blackbird Turdus merula nest characteristics

Nest construction is taxonomically widespread, yet our understanding of adaptive intraspecific variation in nest design remains poor. Nest characteristics are expected to vary adaptively in response to predictable variation in spring temperatures over large spatial scales, yet such variation in nest design remains largely overlooked, particularly amongst open‐cup‐nesting birds. Here, we systematically examined the effects of latitudinal variation in spring temperatures and precipitation on the morphology, volume, composition, and insulatory properties of open‐cup‐nesting Common Blackbirds’ Turdus merula nests to test the hypothesis that birds living in cooler environments at more northerly latitudes would build better insulated nests than conspecifics living in warmer environments at more southerly latitudes. As spring temperatures increased with decreasing latitude, the external diameter of nests decreased. However, as nest wall thickness also decreased, there was no variation in the diameter of the internal nest cups. Only the mass of dry grasses within nests decreased with warmer temperatures at lower latitudes. The insulatory properties of nests declined with warmer temperatures at lower latitudes and nests containing greater amounts of dry grasses had higher insulatory properties. The insulatory properties of nests decreased with warmer temperatures at lower latitudes, via changes in morphology (wall thickness) and composition (dry grasses). Meanwhile, spring precipitation did not vary with latitude, and none of the nest characteristics varied with spring precipitation. This suggests that Common Blackbirds nesting at higher latitudes were building nests with thicker walls in order to counteract the cooler temperatures. We have provided evidence that the nest construction behavior of open‐cup‐nesting birds systematically varies in response to large‐scale spatial variation in spring temperatures.     

Distribution and abundance patterns of a newly colonizing species in Tunisian oases: the Common Blackbird Turdus merula

We investigated distribution and abundance patterns of a recently arrived species in the oases of southern Tunisia: the Common Blackbird Turdus merula . In this system, we expected that the vegetation structure and geographical locations of oases would have played an important part in shaping the patterns of oasis occupancy and local abundance. Using data collected at 53 oases during two breeding seasons, we found that Blackbird occurrence in a given oasis depended mainly on its presence at neighbouring oases. However, vegetation structure did not prove to be a relevant predictor of Blackbird occurrence. Within occupied oases, local abundance was associated with vegetation structure, namely with the diversity and abundance of the two lowest vegetation layers: fruit trees and herbaceous plants. The presence of Blackbirds at neighbouring oases was not found to account for local abundance. Overall, our results suggest that the distribution and abundance of this newly colonizing species in the southern Tunisian oasis system are influenced by processes acting at two different spatial scales. Landscape-scale processes (i.e. dispersal and colonization from nearby occupied oases) are likely to play an important role in shaping the pattern of oasis occupancy, whereas local-scale factors seem to be more relevant in determining the abundance of locally established populations.     

Effects of sex and sampling site on the relative proportion of pesticides in uropygial gland secretions of European Blackbirds (Turdus merula)

Dichlorodiphenyltrichloroethane (DDT) is a pesticide that was commonly used for decades worldwide. The use of DDT was banned in the 1970s and 1980s in Europe because of its high toxicity and persistence in the environment, bioaccumulation in living organisms and biomagnification through food webs. However, monitoring using both invasive and non-invasive methods has routinely reported the occurrence of DDT metabolites such as dichlorodiphenyldichloroethylene (DDE) in wild birds, providing valuable information about the exposure to pesticides and potential differences between species and over time. Here, we analysed the relative proportion of DDE in the uropygial gland secretions of European Blackbirds Turdus merula from two localities in southern Spain. Given the negative effects of this pollutant on animal immunity, we also tested for associations between the prevalence of haemosporidians and the relative proportion of DDE in their secretions. Relative proportions of DDE varied between sampling sites and were higher in females than in males, regardless of their age. In spite of the potential immunosuppressive effect of DDE, haemosporidian infection was not associated with DDE presence.     

江西吉安乌鸫的繁殖生态研究

2009～2010年对江西省吉安地区乌鸫Turdus merula的繁殖进行了调查研究,结果表明:当地乌鸫的营巢时间在3月9日至16日,产卵时间是3月18日至26日,平均窝卵数5.14(4～6)枚(n=14),平均卵大小29.71 mm×21.16 mm,平均卵重6.63 g(n=71).孵卵和暖巢主要由雌鸟承担,但雄鸟也有暖巢行为,孵化率为65.83%,育雏期13～15 d,离巢率高达100%.与高海拔的乌鸫相比,当地乌鸫产大窝小卵,这一特征保证了大窝雏数和高离巢率,繁殖对策属于r-选择.     

Some correlates of density in an urban Blackbird Turdus merula population

Capsule Blackbird density within a town is related to the proportion of gardens, open space and housing density within individual developments.