Extrapair paternity in insular African Blue Tits Cyanistes teneriffae is no less frequent than in continental Eurasian Blue Tits Cyanistes caeruleus

Birds breeding on islands often exhibit lower rates of extrapair paternity than their mainland counterparts, perhaps explained by low genetic variation, ‘slower’ life histories and reduced sexual selection in island populations. Extrapair paternity was apparent in 39% (12/19) of broods, and encompassed 15% (21/137) of nestlings, in a population of African Blue Tits Cyanistes teneriffae, in Tenerife, Canary Islands. There were no cases of intraspecific brood parasitism. The incidence of extrapair young lies in the upper range of that reported from mainland populations of the closely related Eurasian Blue Tit Cyanistes caeruleus. We conclude that there is no strong island effect on the genetic mating system in the Cyanistes species group but that extrapair paternity rates in Cyanistes are greater at southern latitudes.     

Blue Tits Cyanistes caeruleus breeding in a House Martin Delichon urbicum nest

This paper describes a breeding attempt by Blue Tits Cyanistes caeruleus in the nest of House Martins Delichon urbicum on the wall of a block of flats in Wroc?aw, Poland. Urban environments may provide novel competition and costs for breeding birds.     

Testosterone Reduces Promiscuity of Female Blue Tits (Cyanistes caeruleus): An Experimental Study

In many animal species, extra‐pair copulations (EPCs) are common and can increase fitness in both sexes. In males, EPCs can increase total reproductive output, whereas in females benefits of EPCs can be indirect through improving the genetic quality of their offspring. Males and females of many vertebrates show an increase in levels of the hormone testosterone (T) during the mating period. In males, T plays an important role in regulating mating behaviour including increasing their EPC rate. While much is known about the role of T in male mating behaviour, the role of T in female reproduction remains unclear. To study the influence of T on extra‐pair paternity rates in females in a field setting, we created three experimental groups of female blue tits (Cyanistes caeruleus): treated with either T, flutamide (Flu; an androgen receptor blocker) or empty implants before egg laying. Subsequently, we scored the number of extra‐pair offspring (EPO) in their broods. We also assessed the attractiveness of females treated with either T or Flu to males in mate choice trials in the laboratory. The overall proportion of EPO was lower for the T‐implanted group compared with the control group, whereas Flu had no effect. Given that males did not show a preference for Flu‐ vs. T‐treated females in the mate choice trials, it appears less likely that the reduction in EPO in the T‐implanted females was due to a reduction in their attractiveness. T levels may have negatively influenced EPO rate by affecting female within‐pair and/or extra‐pair mating behaviour. Future behavioural studies should investigate how elevated T levels reduce the number of EPO.     

Personality in Blue Tits (Cyanistes caeruleus) and its Effect on Their Breeding Success

In this study, we investigated whether blue tits (Cyanistes caeruleus) showed consistent variation in neophobia responses. The experiment represents a test of how personality, consistent individual differences in behaviour, may have fitness consequences. The experimental design consisted of a control observation followed by two neophobia tests, during which the parent's behaviour was recorded using the instantaneous sampling method. Blue tits showed consistent variation in neophobia responses, which was related to total offspring biomass, but not to mean offspring weight or fledging success. General linear mixed models analyses suggest that there may be ideal neophobia trait combinations in breeding pairs that maximise breeding success.     

Habitat structure modulates nestling diet composition and fitness of Blue Tits Cyanistes caeruleus in the Mediterranean region

Capsule: The nestling diet of Blue Tits Cyanistes caeruleus is influenced by parental effort and habitat type, and consequently has an impact on breeding success.

Aims: In a three-year study, we compared the nestling diet of Blue Tits in two Mediterranean forests (pinewood and oakwood) and tested its implications for breeding success.

Methods: Adults were captured at the nest to obtain morphological measurements, and provisioning behaviour was recorded when chicks were 11 days old. Nestling tarsus length and body mass were measured on day 13 after hatching.

Results: Caterpillars constituted the largest proportion of nestling diet in both habitats, however, higher numbers and biomass of noctuid, as well as higher numbers of tortricid larvae, were provided to nestlings in the pinewood. Furthermore, females provided tortricids more often than males, whereas males supplied more geometrid larvae and spiders. We found a more generalist diet for nestlings raised in the pinewood. Also, a greater number of young fledged when their diet included more tortricids and was more generalist, and Blue Tit nestlings raised on a diet with a higher number of spiders were in better body condition.

Conclusion: Differences in nestling diet between habitat types contribute to explain variance in breeding performance and therefore demonstrate diverse foraging behaviour strategies among populations.     

The carotenoid-based plumage coloration of adult Blue Tits Cyanistes caeruleus correlates with the health status of their brood

The Blue Tit Cyanistes caeruleus is a passerine bird in which both sexes provide substantial care to the offspring and display conspicuous carotenoid-based plumage coloration. It has been shown that carotenoid-based coloration in birds reflects both individual quality and foraging ability. Because the body condition of nestlings usually depends on the capacity of their parents to feed them, I predicted that, independent of sex, those individuals with the most exaggerated carotenoid-based plumage coloration should raise offspring in better health. I found that although, in my study population, the smallest females were paired with the largest males, the brightest females were paired with the brightest and most intensely coloured males. I used body condition and T-cell-mediated immune response of nestlings as measures of their health status. Generalized mixed models showed that brighter and more-yellow adults reared offspring in better than average condition and immune response. Older males and smaller females were also able to raise offspring with better immune response. All these results suggest that the carotenoid-based plumage coloration of parents is somehow linked with individual quality, as it presents a significant and positive correlation with the health status of their growing chicks. Thus, the brightest and more intensely coloured individuals raised the healthiest offspring.     

Influence of fine-scale habitat structure on nest-site occupancy,laying date and clutch size in Blue Tits Cyanistes caeruleus

Most birds have specific habitat requirements for breeding. The vegetation structure surrounding nest-sites is an important component of habitat quality, and can have large effects on avian breeding performance. We studied 13 years of Blue Tit Cyanistes caeruleus population data to determine whether characteristics of vegetation structure predict site occupancy, laying date and number of eggs laid. Measurements of vegetation structure included the density of English Oak Quercus robur, European Beech Fagus sylvatica, and other deciduous, coniferous and non-coniferous evergreen trees, within a 20-m radius of nest-boxes used for breeding. Trees were further sub-divided into specific classes of trunk circumferences to determine the densities for different maturity levels. Based on Principal Component Analysis (PCA), we reduced the total number of 17 measured vegetation variables to 7 main categories, which we used for further analyses. We found that the occupancy rate of sites and the number of eggs laid correlated positively with the proportion of deciduous trees and negatively with the density of coniferous trees. Laying of the first egg was advanced with a greater proportion of deciduous trees. Among deciduous trees, the English Oak appeared to be most important, as a higher density of more mature English Oak trees was associated with more frequent nest-box occupancy, a larger number of eggs laid, and an earlier laying start. Furthermore, laying started earlier and more eggs were laid in nest-boxes with higher occupancy rates. Together, these findings highlight the role of deciduous trees, particularly more mature English Oak, as important predictors of high-quality preferred habitat. These results aid in defining habitat quality and will facilitate future studies on the importance of environmental quality for breeding performance.     

Experimental evidence for parental,but not parentally biased,favouritism in relation to offspring size in Blue Tits Cyanistes caeruleus

In species with biparental care, males and females share the benefits of investing in offspring but pay the costs individually. As a result of these evolutionary conflicts of interest between the sexes, it is expected that the two parents should follow different behavioural rules when providing food to the young. Such a discrepancy may be accentuated when parents have to choose between different subsets of offspring (e.g. large and small nestlings). We manipulated the degree of hatching asynchrony in Blue Tits Cyanistes caeruleus and quantified male and female feeding behaviour when nestlings were 7 and 10 days old. First, we tested for a difference in the role of the sexes during the nestling rearing period between experimentally asynchronous and synchronous control broods. We then used experimentally asynchronous broods to assess differences between the sexes in the pattern of food distribution in terms of number of feedings and prey types, between junior and senior siblings. When nestlings in experimental nests were 7 days old, females fed young more often than did males despite facing a trade‐off between brooding the smallest nestlings and bringing food to the nest. At this age, there was also a skew in food delivery in favour of senior siblings, whereas food was more evenly distributed across the brood when nestlings were 10 days old. We found no difference in how male and female Blue Tits distributed feeding visits among junior and senior nestlings. However, females fed the smallest nestlings with more spiders in comparison with their senior siblings. This could be related to their more suitable size relative to other prey types, their high content of essential nutrients, or both, and may represent a more cryptic form of parentally biased favouritism. We compare these findings with previous work on other species and discuss why parents did not feed junior siblings more frequently.     

Seasonal decline in provisioning effort and nestling mass of Blue Tits Cyanistes caeruleus: experimental support for the parent quality hypothesis

A common feature of many birds breeding in seasonal environments is that fitness‐related parameters such as nestling mass or survival decline as the breeding season progresses. Consequently, there is a tendency for early breeders to have better reproductive performance than individuals breeding later in the season. This variation could be caused by factors associated with the date of laying, such as changing environmental conditions (date hypothesis), or by differences in parental quality between early and late breeders (parent quality hypothesis). To evaluate the relative importance of both hypotheses, we manipulated hatch dates of Blue Tits Cyanistes caeruleus by exchanging clutches with different incubation stages and assessed the impact on nestling mass, nestling diet and provisioning rates. Mean nestling mass declined significantly over the season. This was the combined result of differences in parental quality, which dominated in the early part of the season, and the influence of hatching date (date effect per se), which prevailed later in the season. Nestling diet composition was apparently uninfluenced by the manipulation, suggesting that deteriorating food supplies are the primary reason for the seasonal variation in the nestling diet. Counter to the date hypothesis, delayed parents did not feed their young less than control pairs did, but in fact exhibited higher provisioning rates. Our results suggest that in this population, parental quality seems to constrain post‐hatching reproductive performance and such intrinsic limitations may help to explain why certain individuals breed later.     

Pair bond and breeding success in Blue Tits Parus caeruleus and Great Tits Parus major

Data from 939 nests of the Blue Tit Parus caeruleus and 1008 nests of the Great Tit P. major from nestboxes provided in superabundance in mixed forest study sites between 1976 and 2001 were analysed to examine the effects of mate retention on breeding success and the relationship between mate fidelity and site fidelity. Most birds retained their former partner (76% in Great Tits and 65% in Blue Tits). The probability of a pair divorcing was affected by male age in Great Tits, divorce being more likely in pairs with first‐year males. Great Tit pairs breeding together for a second season bred earlier, but had no higher breeding success than pairs breeding together for the first time. In Blue Tits laying date and start of incubation tended to be earlier in pairs breeding together for a second season, but hatching and fledging dates were not earlier than in other pairs. Great Tit pairs breeding together for two consecutive seasons bred earlier in the second season than in the first, but breeding success did not differ significantly between years. In both species, breeding performance did not differ between pairs that divorced after a season and pairs that stayed together. Thus breeding success did not determine whether a pair divorced or bred together again. Neither Blue Tits nor Great Tits improved their breeding performance through divorce. Blue Tit females even had fewer fledglings in the year after divorce than in the year before. Mate retention affected breeding site fidelity. Blue Tit females had greater breeding dispersal distances between consecutive years when re‐mating than when breeding again with the same mate. In Great Tits both males and females dispersed more when re‐mating than when retaining the former partner, suggesting that mate retention increased the chance of retaining the breeding site. In both species, breeding dispersal distances did not differ between pairs that divorced and pairs in which one mate disappeared. Because no major advantage of mate retention was evident, we suggest that mate retention evolved under different conditions than those found in study sites with high breeding densities and a superabundance of artificial nesting sites.     

Carotenoid-based coloration correlates with the hatching date of Blue Tit Cyanistes caeruleus nestlings

Carotenoid-based coloration occurs predominantly in adult birds, yet in some species from the family Paridae, this trait is also present at the nestling stage. One of the factors proposed to affect the expression of this trait in immature birds is hatching date. Here, using the avian tetrahedral colour space model, we examined the influence of hatching date on the breast carotenoid-based plumage coloration of the Blue Tit Cyanistes caeruleus nestlings. Because Blue Tits are sexually dichromatic, we also investigated the potential interaction between hatching date and sex that could arise from differences in condition dependence of this trait between males and females. We found a positive relationship between UV chroma of breast feathers and hatching date. The amount of UV reflectance is thought to be negatively related to carotenoid content in feathers. The observed increase of UV chroma through the breeding season might therefore be caused by a seasonal decline in the availability and quality of Lepidoptera larvae – the main source of carotenoids in food of the Tits. We also observed a sex difference in the relationship between brightness of breast feathers (achromatic, structural component) and hatching date, which in males was negative and in females not significant. Our study provides further evidence that the timing of breeding is related to the expression of nestling carotenoid-based coloration, a potentially meaningful element of offspring–parent communication, and suggests a sex-specific effect of hatching date on its structural component.     

The effects of season,sex, age and weather on population-level variation in the timing of activity in Eurasian Blue Tits Cyanistes caeruleus

All birds sleep and many do so in a specific location, the roost. Thus, every day each individual needs to decide when to go to (enter) and leave the roosting place. This determines the timing of activity, a trait shaped by both natural and sexual selection. Despite its importance in a variety of contexts, including foraging, predation, mating success and parental care, variation in the timing of activity has rarely been studied. Here, we describe this variation in a population of Eurasian Blue Tits Cyanistes caeruleus roosting in nestboxes using data collected over 7 years. We investigate seasonal changes in the start and end of activity and assess to what extent these parameters are sex- and age-specific and affected by weather. We show that the start of activity is relatively constant in relation to sunrise during winter but undergoes drastic changes during the breeding season. The end of activity is markedly later relative to sunset in mid-winter and is also strongly influenced by breeding behaviour. Females generally start their activity later and end it earlier than males. The duration of daily activity is shorter during periods of rain and longer when temperatures are relatively high for the time of year.     

Non-territorial nightingales prospect territories during the dawn chorus

Male songbirds usually sing when they have occupied a territory, but the territory prospecting of non-territorial males is more elusive and has been rarely studied. Here, we simulated newly arriving, non-territorial males by translocating unmated male nightingales (Luscinia megarhynchos) to our study site. We show that territory prospecting of translocated males was largely confined to the hour before sunrise. The radio-tagged males made extensive excursions visiting several singing males at dawn, but after dawn they remained stationary outside occupied territories. As in many other songbird species, dawn was also the time when resident males sang the most. These results suggest that nonterritorial male nightingales use the dawn chorus to assess singing residents or territory occupancy. For resident males, dawn singing may be important to announce territory occupancy to prospecting males and may thus play a role in territory maintenance.     

Sexual dimorphism and growth trade‐offs in Blue Tit Cyanistes caeruleus nestlings

The outcome of sibling competition for food is often determined by variation in body size within the brood and involves trade‐offs; traits that enhance competitive ability within the nest may be developed at the expense of traits that enable effective flight at fledging, or vice versa. We quantified growth of skeletal, body mass and feather traits in male and female Blue Tit Cyanistes caeruleus nestlings. Males were significantly heavier, had longer tarsi and tended to have greater head–bill lengths than females, whereas females were similar to males in wing flight feather growth. These differences in growth may result from sexual differences in selection of the traits. Females are likely to prioritize feather growth to facilitate synchronized fledging with the rest of the brood, and to enhance escape from predators. We suggest that males are heavier and develop longer tarsi because body size is an important determinant of male reproductive success.     

The effect of old age on the reproduction of Great Tits Parus major and Blue Tits P. caeruleus

The results from two data sets show that in Great Tits Parus major and Blue Tits P. caeruleus reproduction is influenced by age. In both species, laying dates become earlier while clutch- and brood-size increase between the ages of 1 and 2, but there is no change in nesting success or post-fledging juvenile survival. Great Tits aged 5 or older are 'old' in that laying starts later and nesting success, brood-size and post-fledging juvenile survival decrease. Blue Tits become 'old' 1 year earlier than Great Tits: females aged 4 or older lay later, have a lower nesting success and smaller brood-size, and their young show a decreased post-fledging survival. The effect on laying date, in the Blue Tit, becomes apparent only for females aged 6 and older. It is concluded that ageing in small passerines is to be expected more generally, but that no extrapolations can be made as to the timing of the effect from one species to another.