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.     

Survival of suburban blackbirds Turdus merula varies seasonally but not by sex

Survival is a key demographic parameter in bird populations yet remarkably little is known about the seasonal pattern of survival. Mortality may increase as a result of breeding behaviour, harsh environmental conditions, resource limitation or any combination of these; knowing which is important for understanding the ecology of population change. We analyse an intensive ten-year colour marking programme of European blackbirds Turdus merula to estimate seasonal and sex-specific survival rates. The annual survival rate (0.67) was similar to that produced from analyses of dead recoveries across Britain, but within year variation was significant. Survival rates were lowest during the early part of the breeding period and highest in the autumn, but there was little difference between the sexes. Understanding this pattern of variation is important in interpreting both life-history variation and the mechanisms of population 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.     

Comparative behavioural responses of silvereyes (Zosterops lateralis) and European blackbirds (Turdus merula) to secondary metabolites in grapes

Secondary metabolites in fruit are compounds that are not directly associated with plant growth; some are directly related to plant reproductive processes, specifically seed protection and dispersion. There is a complex and species‐specific interaction between these plant compounds and their avian seed dispersers. To determine whether two important secondary metabolites in wine grapes – tannins and colour pigments – might be important cues to two of the avian species that forage on wine grapes, and how species‐specific this interaction might be, comparative field experiments were run with Australasian silvereyes (Zosterops lateralis) and European blackbirds (Turdus merula). Both species were offered a glucose/fructose artificial nectar with increasing concentrations of grape tannins. In a second experiment, they were offered both green and purple artificial grapes where only the colour differed. Both species showed aversion to tannins; silvereyes appeared to have greater tolerance than blackbirds of tannin concentrations above 5%. In summer no preference was shown between green and purple coloured artificial grapes, but in late autumn blackbirds took only purple grapes whereas silvereyes pecked mostly at green. Links between tannin for seed protection and colour signals to birds are discussed. Colour may cue the two species to different species‐specific aspects of fruit nutritive value.     

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.     

Vertical transmission of feather lice between adult blackbirds Turdus merula and their nestlings: a lousy perspective

There is limited information about the natural history of the transmission of feather lice (Phthiraptera) from parent birds to their young. This article therefore examines the transmission of 4 species of feather lice from parent blackbirds to their nestlings in an English population, and addresses questions formulated from the perspective of the lice. The lice that disperse onto the several young in the nest were mostly found on the larger chicks, those with higher survival prospects. The lice dispersing to chicks were overwhelmingly nymphs, which cannot be sexed morphologically, and so the prediction that the adult lice dispersing would be disproportionately female, potential founders of a new population, was only supported for the most numerous species, Brueelia merulensis. There was no evidence that louse dispersal to chicks was density dependent and more likely when the parents were more heavily infested. Finally, I predicted that lice might aggregate on female blackbirds, which undertake more brooding, to increase their chance of transmission to nestlings. For 1 louse species, B. merulensis, prevalence, but not louse intensity, was higher on female than male blackbirds. For 2 other louse species, Philopterus turdi and Menacanthus eurysternus, no differences between male and female blackbirds were detected.     

Age-dependent changes in biometrics indicate senescence in the European Blackbird Turdus merula

Capsule: A 19-year study of European Blackbirds Turdus merula confirms that senescence is associated with a decrease in condition measured by wing length but bills become progressively longer with age.

Aims: To explore the correlations between biometrics of Blackbirds and age, to identify possible links with senescence.

Methods: During the 19 years of the study, 801 birds of known age were measured: 431 males and 370 females, aged from 2 to 10 years. Among these 91 males and 50 females were retrapped at least one moult later. For each bird, there were at least one set of measurements when fully grown.

Results: Wing length increased until the sixth year of life after which it started to decrease. An increase in bill length throughout the lifetime was found in both sexes.

Conclusion: Changes in wing length correspond with an earlier study of this population suggesting the onset of senescence after the fifth to sixth calendar year of life.     

Large-scale spatial variation in the breeding performance of song thrushes Turdus philomelos and blackbirds T. merula in Britain

1.  Spatial variation in breeding performance is of critical importance in understanding the large-scale distribution and abundance of living species, and in understanding species conservation. We studied the large-scale spatial variation in reproductive output of two species of declining British bird, the song thrush Turdus philomelos and the blackbird Turdus merula .
2.  We developed a method to predict spatial variation in reproductive output. Brood size and nest failure rates during the incubation and nestling periods were related to environmental factors using generalized linear models. Predicted values obtained from these models were combined to give values of number of fledglings produced per nesting attempt for 10-km squares throughout Britain.
3.  We observed substantial spatial variation in reproductive output for both species; the component that varied most was nest failure rate during incubation. We were more successful in relating environmental factors to spatial variation in reproductive output for song thrush than for blackbird.
4.  Reproductive output in both species was affected mainly by factors that vary on a small spatial scale. Nest failure rate during incubation increased significantly where corvids were more abundant, suggesting a role for avian nest predators in determining spatial variation in reproductive output.
5.  Our approach can be extended readily to other species of birds, to other taxonomic groups and to finer spatial scales. Such models could be used to evaluate the implications of current and proposed wider countryside management for spatial variation in breeding performance. Evaluations based on breeding success as well as numbers are likely to be more robust than those based solely on abundance.     

Comparative behavior of free-ranging blackbirds (Turdus merula) and silvereyes (Zosterops lateralis) with hexose sugars in artificial grapes

In order to detect bird responses to sugar parameters of ripening grapes, artificial grapes containing controlled concentrations of hexose sugars were offered to free-range blackbirds (Turdus merula) and silvereyes (Zosterops lateralis). Time-lapse video was used to observe the two species of birds feeding on grapes presented on a novel two-tier bird-table. The comparative interest displayed by the birds for grapes of varying concentrations of hexose sugars, and the time spent feeding by each species were analyzed statistically, to discover the level of sugar concentration in grapes that is attractive to these birds. Blackbirds exhibited a preference for high sugar concentration, while silvereyes preferred grapes with a lower concentration. Blackbird visits were much shorter than those of silvereyes and they took whole grapes whereas silvereyes pecked. Differences in behavior of the two species are discussed and the assumption that all frugivorous birds are attracted to fruit for similar reasons is challenged. It may be that differences in digestive glucose absorption processes underlie the observed difference in behavioral responses of the two species.     

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),     

An Experimental Study of Prey-attack Behavior in the European Blackbird Turdus m. merula L

The experiments reported in this paper are designed to investigate the features of insect prey that may influence the orientation of first attack in the European blackbird. Three types of stimulus cues are considered: motion, morphological characters, and color patterns. The ontogeny of prey-handling techniques and the specific manipulatory activities involved in the breaking-up of insect prey are dealt with. The role of learning in the development of preyattack behavior is demonstrated. This study deals only with the preparation of food for selffeeding.     

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.     

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.     

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.