Blue Tit Cyanistes Caeruleus Research Articles

Breeding Phenology of Blue Tits in Mediterranean Stone Pine Plantations: Effects of Nestboxes and Holm Oaks

Summary. Breeding phenology of blue tits in Mediterranean stone pine plantations: effects of nestboxes and holm oaks. A blue tit Cyanistes caeruleus population nesting in a Mediterranean stone pine plantation Pinus pinea in the Sierra Morena, Spain, was studied during 2007–2009. Nestboxes were distributed 50 m apart in a grid and territory size, territory location, number of Iberian holm oaks Quercus ilex in territories and number of conspecific neighbours were determined. Laying date, clutch size, hatching success, fledging success and fledgling mass were also recorded. Linear transects were carried out both within and outside the area where nestboxes were located. Over 50% of nestboxes remained unoccupied. The number of conspecific neighbours was positively associated with territory size. Occupied nestboxes had more holm oaks in their vicinity than did unoccupied nestboxes. Breeding success and fledgling mass were similar across territories although laying was earlier in larger territories and in those ...

Do secretions from the uropygial gland of birds attract biting midges and black flies?

Bird susceptibility to attacks by blood-sucking flying insects could be influenced by urogypial gland secretions. To determine the effect of these secretions on biting midges and black flies, we set up a series of tests. First, we placed uropygial gland secretions from blue tit Cyanistes caeruleus broods inside empty nest boxes while empty nest boxes without gland secretions were treated as controls. Blue tit broods, from which we had obtained uropygial secretions, were affected by biting midges and black flies. However, these insects were absent in nest boxes both with and without secretions from nestlings' uropygial glands. We subsequently tested for the effects of uropygial gland secretions from feral pigeons Columba livia monitoring the number of biting midges captured using miniature CDC traps. There was no significant difference in the number of biting midges captured. Overall, our results did not support a potential role of avian uropygial gland secretions in attracting biting midges and black flies.

Females call the shots: breeding dispersal and divorce in blue tits

In this paper, we study proximate causes and consequences of breeding dispersal and divorce in a Mediterranean blue tit Cyanistes caeruleus population. We attempt to evaluate the primacy of mate and territory quality in the decision making of birds. In females, the fidelity to their old territories was dependent on how they did in the previous year. We found differences in hatching success and fledging success between females that dispersed and those that did not. In particular, dispersal distance was negatively correlated with hatching success in the preceding breeding season. Dispersed females experienced a gain in terms of hatching success and increased productivity in comparison with those that retained their former mate. Both females and males improved the quality of their breeding site after dispersal. We also found evidence that divorce is adaptive for at least one pair member because adult females (but not juveniles) enhanced their breeding performance after the breakup. Such improvement was also observed when restricting the analyses to only those individuals that did not change territory, suggesting that these benefits not only accrue through the acquisition of better territories but advantages derived from pairing with a higher rank male (mate effects per se) could also be important. Our results suggest that 1) both dispersal and divorce can be regarded as adaptive decisions, 2) females play an active role in pair-bond maintenance, and 3) the intense competition for good nesting sites drives the observed high divorce rate (63%) reinforcing the view that breakups could be a side effect derived from the female’s attempt to improve their breeding place.

Nest ornamentation in blue tits: is feather carrying ability a male status signal?

In a wide range of animal taxa, males build elaborate mating structures to attract females. For instance, some bird species use their nests or display sites as nonbodily ornaments (extended phenotypes) in intersexual communication. Recently, it has been proposed that feather carrying constitutes a postmating sexual display. Here, evidence supporting this hypothesis is presented for a species in which such behavior had not been previously reported, the blue tit Cyanistes caeruleus. In our Mediterranean study populations, males carry feathers to the nest and place them outside the nest cup. Here, we show experimentally and by means of observational data that feather carrying by male blue tits induced their mates to increase their clutch size. In addition, males from ornamented nests fed their offspring at a higher rate than those from nests in which this behavior was not detected. Feather-carrying effort was positively associated with male tarsus length. On the other hand, females paired with males engaging in this activity reduced their feeding rates but obtained direct fitness benefits: Ornamented nests resulted in more fledged young with better body condition than those without feathers carried by males. In summary, this study suggests that male feather-carrying ability constitutes an honest signal of their parental quality and a good predictor of breeding success in these blue tit populations. Copyright 2011, Oxford University Press.

Multiple responses to increasing spring temperatures in the breeding cycle of blue and great tits (Cyanistes caeruleus, Parus major)

Many bird species start laying their eggs earlier in response to increasing spring temperatures, but the causes of variation between and within species have not been fully explained. Moreover, synchronization of the nestling period with the food supply not only depends on first-egg dates but also on additional reproductive parameters including laying interruptions, incubation time and nestling growth rate. We studied the breeding cycle of two sympatric and closely related species, the blue tit Cyanistes caeruleus and the great tit Parus major in a rich oak-beech forest, and found that both advanced their mean first-egg dates by 11-12 days over the last three decades. In addition, the time from first egg to fledging has shortened by 2-3 days, through a decrease in laying interruptions, incubation time (not statistically significant) and nestling development time. This decrease is correlated with a gradual increase of temperatures during laying, suggesting a major effect of the reduction in laying interruptions. In both species, the occurrence of second clutches has strongly decreased over time. As a consequence, the average time of fledging (all broods combined) has advanced by 15.4 and 18.6 days for blue and great tits, respectively, and variance in fledging dates has decreased by 70-75%. Indirect estimates of the food peak suggest that both species have maintained synchronization with the food supply. We found consistent selection for large clutch size, early laying and short nest time (laying to fledging), but no consistent changes in selection over time. Analyses of within-individual variation show that most of the change can be explained by individual plasticity in laying date, fledging date and nest time. This study highlights the importance of studying all components of the reproductive cycle, including second clutches, in order to assess how natural populations respond to climate change.

Nest ectoparasites increase physiological stress in breeding birds: an experiment

Parasites are undoubtedly a biotic factor that produces stress. Heat shock proteins (HSPs) are important molecules buffering cellular damage under adverse conditions. During the breeding season, blue tit Cyanistes caeruleus (L.) adults are affected by blood parasites, nest-dwelling parasites and biting flies, potentially affecting their HSP-mediated responses. Here, we treated females with primaquine to reduce blood parasites and fumigated nests with permethrin to reduce nest-dwelling parasites to test whether these treatments affect HSP60 level during the breeding season. Medicated females, but not controls, had a significant reduction of the intensity of infection by Haemoproteus spp. blood parasites. However, final intensity of infection did not differ significantly between groups, and we did not find an effect of medication on change in HSP60 level. Fumigation reduced the abundance of nest-dwelling parasites (mites, fleas and blowfly larvae) and engorged biting midges in nests. Females breeding in non-fumigated nests increased HSP60 levels during the season more than those breeding in fumigated nests. Furthermore, the change in HSP60 level was positively correlated with the abundance of biting midges. These results show how infections by nest ectoparasites during the breeding period can increase the level of HSPs and suggest that biting midges impose physiological costs on breeding female blue tits. Although plausible, the alternative that biting midges prefer to feed on more stressed birds is poorly supported by previous studies.

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.

Context-dependent effects of parental effort on malaria infection in a wild bird population, and their role in reproductive trade-offs

Although trade-offs between reproductive effort and other fitness components are frequently documented in wild populations, the underlying physiological mechanisms remain poorly understood. Parasitism has been suggested to mediate reproductive trade-offs, yet only a limited number of parasite taxa have been studied, and reproductive effort-induced changes in parasitism are rarely linked to trade-offs observed in the same population. We conducted a brood size manipulation experiment in blue tits (Cyanistes caeruleus) infected with malaria (Plasmodium) parasites, and used quantitative PCR to measure changes in parasitaemia. In one of two years investigated, parasitaemia increased as a result of brood enlargement, and was also positively associated with two other indicators of reproductive effort: clutch size and single parenthood. These associations between both experimental and naturally varying reproductive effort and parasitaemia suggest that immune control of chronic malaria infections can be compromised when parents are working hard. Brood size manipulation significantly affected the number of independent offspring produced, which was maximised when brood size was unchanged. Moreover, when parents were infected with one of two common Plasmodium species, the shape of this trade-off curve was more pronounced, suggesting that parasitic infection may exacerbate the trade-off between quantity and quality of offspring. Although the involvement of parasites in survival costs of reproduction has received much attention, these results suggest their role in other commonly documented reproductive trade-offs, such as that between number and quality of offspring, warrants further study.

Broodedness, not latitude, affects the response of reproductive timing of birds to food supplementation

IntroductionMultiple food supplementation experiments during the pre-laying period have shown that the availability of additionalfood at this time can advance laying date (laydate) and/orincrease the number and/or quality of the eggs laid (Nageret al. 1997). It would therefore appear that food is a lim-iting factor at this critical time of year, although the extentof this limitation varies between years, locations, andspecies (Nager et al. 1997). Svensson (1995) and Dhondtet al. (2002) showed that the response to supplementaryfeeding depends on the number of clutches a female usu-ally lays in a season: single-brooded bird species onlyrespond weakly to supplementary feeding whereas multi-brooded species respond more strongly. In two recentpapers, Schoech and Hahn (2007, 2008) documented alatitude effect on responses to supplemental feeding andconcluded that birds advance laying in response to feedingmore as the distance from the equator decreased. If theseauthors are correct, this is indeed an important observationas it suggests that birds would be more food limited in thepre-breeding season closer to the equator than furthernorth.In this paper I re-analyze the dataset used by Schoechand Hahn in order to test if latitude, number of broods, orboth influence the effect of supplemental feeding on lay-date. The response to food supplementation has beenmeasured in four species at three or more latitudes, makingit possible to determine if latitudinal variation of theresponse to supplemental food can be confirmed withinsingle species, which is a stronger test than that in which allspecies are combined. If latitude drives the response tosupplemental food, the differences between control birdsand birds provided with additional food should be largest inpopulations furthest south (closest to the equator). If thenumber of clutches a species usually lays in a season drivesthe response, the effect of food supplementation should notvary systematically with latitude.Materials and methodsTo explore to what extent broodedness influences theresponse to supplemental food, I added this information tothe dataset Schoech and Hahn (2008) provided in theirElectronic Supplementary Material (see Electronic Sup-plementary Material of this article). For the within-speciescomparison, I added results on food supplementationexperiments in the Corsican Blue Tit Cyanistes caeruleus(Bourgault et al. 2009). Single-brooded species very rarelylay a second clutch after having fledged a first brood (13species); double-brooded species often lay a second clutchafter having raised a first brood successfully (8 species);triple-brooded species often lay three clutches or more perseason (3 species). I assigned species to a category

Seasonal variation in diet quality: antioxidants, invertebrates and blue tits Cyanistes caeruleus

Breeding success is often dictated by the degree to which parents can synchronize the maximum food requirements of offspring to the peak in abundance of invertebrate prey. Less studied is how the nutritional quality of individual diet items impacts on breeding. In the present study, we assessed the abundance and antioxidant concentrations of arboreal arthropods from oak woodland and provisioning behaviour of the blue tit Cyanistes caeruleus. Dietary antioxidants are important during development because they defend against oxidative stress. Operophtera caterpillars, Erannis caterpillars, and spiders contained significantly different levels of individual carotenoids and a-tocopherol. Concentrations of lutein and b-carotene in Operophtera caterpillars did not vary seasonally, although concentrations of zeaxanthin declined and a-tocopherol increased with date. Blue tit broods hatched later in the season received significantly fewer caterpillars and more spiders per chick compared to earlier broods. Reflecting changes in prey composition, blue tit nestling plasma showed decreases in zeaxanthin and increases in a-tocopherol with date. Thus, processes that shift the timing of breeding in birds and/or prey composition are likely to alter antioxidant intake and thus potentially influence the oxidative stress status of animals. The data obtained in the present study suggest a mechanism by which environmental change as a result of human activities could influence the health and fitness of individuals in natural populations. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99, 708–717. ADDITIONAL KEYWORDS: a-tocopherol – carotenoids – caterpillars – neonatal nutrition – oxidative stress – spiders.

Age and sex dimorphism in the Canary Blue Tit Cyanistes teneriffae teneriffae on the island of Tenerife, Canary Islands

The Canary Blue Tit Cyanistes teneriffae has recently been split off from the Common Blue Tit Cyanistes caeruleus as a separate species. Live biometrics from across the entire distribution on the island of Tenerife (subspecies teneriffae teneriffae) are reported. Results suggest that first-year birds had similar bill shape to adults but differed in wing length, tarsus, tail and mass, being smaller on average. A high degree of sexual size dimorphism is reported, males being on average larger than females for wing length, bill length, bill depth and tarsus. A classification tree between the sexes showed that wing length and bill depth were the most important variables and correctly classified males in all occasions (i.e. male = wing length > 62.5 mm; bill depth > 3.7 mm, 100% correctly classified) but for practical sexing in the field it is recommended to use wing length as a reliable sexing criterion (wing length > 62.5 = male, 96% correctly classified). This high degree of sexual size dimorphism observed suggests a high sexual selection in the Canary Blue Tit.

Usefulness of coarse grain data on forest management to improve bird abundance models

We tested the use of coarse grain data on forest management systems to improve habitat suitability models in predicting distribution and abundance of five bird species, nesting in broadleaf forests in Lombardy (Italy). They were the long‐tailed tit Aegithalos caudatus, marsh tit Poecile palustris, blue tit Cyanistes caeruleus, wood nuthatch Sitta europaea and short‐toed tree‐creeper Certhia brachydactyla. Bird data were collected from 4552 point counts from 1992 to 2002. To model the habitat suitability for each species, we used generalized linear models with negative binomial distribution and log link function. Environmental predictors were land‐use fractional covers, forest isolation, elevation, slope, aspect, and coarse grain data on forest management systems aggregated for administrative provinces. They were selected by a stepwise procedure based on the Bayesian Informative Criterion. Predictors on forest management system were useful to improve model fit for all cavity‐nesting species, which was also shown to be affected by forest isolation. The long‐tailed tit, which is not an obligate cavity nester, did not exhibit any preference with respect either to forest management or isolation.

Bird ringing in Britain and Ireland in 2009

This is the 73rd annual report of the British Trust for Ornithology's Ringing Scheme, covering data received and work carried out in 2009. Much of the research carried out during the year looked at ways to improve the analysis of ringing data to understand population change. This included producing survival rates from the Constant Effort Sites (CES) scheme for the first time and further developing methods of analysing our demographic data sets in an integrated manner. Research was also undertaken on the biometric data to investigate how individual condition responds to long‐term environmental change. CES data suggested that the low productivity in 2007 and 2008, combined with one of the coldest winters since 1995/96 for residents, contributed to reduced adult numbers in 2009 in many species. There were significant decreases in Wren Troglodytes troglodytes, Sedge Warbler Acrocephalus schoenobaenus, Reed Warbler A. scirpaceus, Blackcap Sylvia atricapilla, Lesser Whitethroat S. curruca, Willow Warbler Phylloscopus trochilus, Long‐tailed Tit Aegithalos caudatus, Blue Tit Cyanistes caeruleus, Great Tit Parus major, Treecreeper Certhia familiaris, Chaffinch Fringilla coelebs, Greenfinch Carduelis chloris and Reed Bunting Emberiza schoeniclus. However, a good breeding season, for both residents and migrants, resulted in significantly higher productivity for 15 species, but significantly lower for Willow Tit Poecile montana, compared to the long‐term mean (1983–2007). Data for 104 Retrapping Adults for Survival studies were submitted, covering 39 species, three quarters of which are Birds of Conservation Concern. The total number of birds ringed (935,867) was the highest ever recorded, and was over 10% higher than the mean of the previous five years. However, the total number of pulli ringed in 2009 (179,712) was only 5% higher than the preceding five‐year mean, while that of fully grown birds (756,155) was over 13% higher. The recovery total (14,643) was also high. However, this is partly due to changes in the way that records of colour‐ringed and other specially marked birds are stored. The number of recoveries of foreign‐ringed birds (1,314) was higher than the mean of the preceding five years, although this figure is influenced by varying response times of different ringing schemes. Recovery details for 250 individual birds are given in the final section of the report. They include movements that confirm suspected or known migration patterns, unexpected movements and longevity records.

Effects of competition on great and blue tit reproduction: intensity and importance in relation to habitat quality

1. In studies on the effect of competition in plant communities two terms are used to describe its effects: the absolute reduction in growth of an individual as a consequence of the presence of another one is called intensity, while the relative impact of competition on an individual as a proportion of the impact of the whole environment is called importance. One school of thought is that the role of competition remains constant across productivity gradients, while the other is that it decreases with increasing severity. J.B. Grace (1991. A clarification of the debate between grime and tilman. Functional Ecology, 5, 583-587.) suggested that the apparent contradiction might be solved if we acknowledge that the two schools are discussing different aspects of competition: the intensity of competition might remain constant while its importance declines with increasing severity. 2. There are no studies that compare intensity and importance of competition in bird populations between areas that differ in quality or productivity and hence it is not possible to make predictions how intensity or importance of competition would vary between them. 3. I compared variation in intensity and importance of competition of three demographic variables between five plots that differ strongly in quality for great Parus major L. and blue tit Cyanistes caeruleus (L.). 4. Both intensity and importance of competition are larger in great than in blue tit populations meaning that the effect of competition on demographic variables is stronger in great than in blue tits and that the contribution of competition to variation in these variables is relatively higher in great than in blue tits. 5. Intensity of competition is higher in low quality than in high quality plots for both species, a result not expected from studies in plant communities. 6. Importance of competition varies strongly between plots. It is larger in oak-dominated plots than in mixed deciduous plots. 7. In birds breeding density increases with habitat quality but is limited by territorial behaviour. As a result competition for food is reduced in high quality habitats resulting in a reduction of competition intensity in high quality sites in which birds breed at high densities. 8. It can be predicted that in studies of territorial species density dependent effects on reproduction are more likely to be detected in low quality sites explaining in part differences in results between studies.

Aromatic plants in nests of the blue tit Cyanistes caeruleus protect chicks from bacteria

Several bird species add fresh fragments of plants which are rich in volatile secondary compounds to their nests. It has been suggested, although never tested, that birds use fresh plants to limit the growth of nest microorganisms. On Corsica, blue tits (Cyanistes caeruleus) incorporate fresh fragments of aromatic plants into their nests. These plants do not reduce infestation by nest ectoparasites, but have been shown to improve growth and condition of chicks at fledging. To understand the mechanisms underlying such benefits, we experimentally tested the effects of these plants on the bacteria living on blue tits. Aromatic plants significantly affected the structure of bacterial communities, in particular reducing bacterial richness on nestlings. In addition, in this population where there is a strong association between bacterial density and infestation by blood-sucking Protocalliphora blow fly larvae, these plants reduced bacterial density on the most infested chicks. Aromatic plants had no significant effect on the bacteria living on adult blue tits. This study provides the first evidence that fresh plants brought to the nests by adult birds limit bacterial richness and density on their chicks.

Rearing environment effects on immune defence in blue tit Cyanistes caeruleus nestlings

Rearing conditions may influence ontogeny and functioning of the immune system. Activation of different mechanisms involved in host disease resistance and their internal regulation can be affected by intrinsic and extrinsic factors influencing development. I investigated how rearing environment can influence associations between humoral and cellular constituents of immune defence in nestling blue tits (Cyanistes caeruleus). The ability to mount a cell-mediated immune response was estimated as a hypersensitivity reaction to phytohaemagglutinin, and the ontogeny of humoral immunity was determined by assessing circulating levels of total IgG in 15-day-old nestlings. Heterogeneity in rearing conditions was evoked by placing nest-boxes in areas differing in habitat structural characteristics, and examining natural variation in nest ectoparasite infestations, hatching date, brood size and brood sex-ratio. Habitat characteristics, parasitism and hatching date may shape associations between different components of the immune system in developing birds. I discuss the effects of rearing conditions on the interaction between different arms of the immune system and the implications for understanding negative correlations within the immune system at the individual and brood level.

Bird ringing in Britain and Ireland in 2008

This is the 72nd annual report of the British Trust for Ornithology's Ringing Scheme, covering work carried out, and data received, in 2008. Research carried out in 2008 included developing methods to combine ringing data with data from other monitoring schemes to detect the causes of population change. This approach was used for Song Thrush Turdus philomelos data, confirming the findings of previous analyses that the population decline observed over the last thirty years is primarily related to first‐year survival. Constant Effort Site data suggested that low productivity in 2007 contributed to reduced adult numbers during 2008 for many species, including significant decreases in Blackcap Sylvia atricapilla, Willow Warbler Phylloscopus trochilus, Blue Tit Cyanistes caeruleus and Bullfinch Pyrrhula pyrrhula. However, there were significant increases in numbers of adult Long‐tailed Tits Aegithalos caudatus and Chiffchaffs Phylloscopus collybita. As in 2007, the 2008 breeding season was poor, with 11 of the 25 core species monitored by the Scheme showing significantly lower productivity compared to the long‐term average (1983–2007). In contrast to 2007, many of the species faring worst were residents, including Blackbird Turdus merula, Song Thrush and Great Tit Parus major. Data for 92 Retrapping Adults for Survival studies were submitted, covering 34 species, more than half of which are of conservation concern. The total number of birds ringed (835,326) was 2% lower than the mean of the previous five years. This reduction may have been influenced by the poor breeding season in 2008; the total number of pulli ringed in 2008 (161,846) was 6% lower than the preceding five‐year mean, while that of fully grown birds (673,480) showed no change. The recovery total (15,164) was the highest in over 15 years; however, this is partly due to changes in the way that records of colour‐ringed and other specially marked birds are stored, which led to an inflation of the 2008 total. The number of recoveries of foreign‐ringed birds (1,192) was higher than the mean of the preceding five years, although this figure is influenced by response times of different ringing schemes, which vary from year to year. Recoveries of 230 individual birds are presented in the final section of the report. They include unexpected movements, movements that confirm suspected or known migration patterns, and longevity records.

Interspecific cross-fostering affects mate guarding behaviour in great tits (Parus major)

Mate guarding is thought to decrease the likelihood of cuckoldry and, hence, increase the fitness of guarding males. Mate guarding is costly for males and must be traded off with other fitness-enhancing behaviours. Over several years, we have cross-fostered great tits ( Parus major ) to blue tits ( Cyanistes caeruleus ) and this experimental treatment has influenced the mate and rival recognition of cross-fostered birds. Here we show that cross-fostered great tit males mate guard their females less than do control great tits, regardless of whether the cross-fostered males were mated to great tit females or cross-fostered blue tit females. Cross-fostered great tit males sang more and interacted more frequently with blue tit males than did controls. Females paired to males of the two groups did not differ in the extent to which they initiated movements away from their mates. We conclude that the altered species-assortative behaviour resulting from interspecific cross-fostering influences mate guarding in great tit males, probably by cross-fostered males increasing investment in territorial behaviour at the expense of mate guarding, and/or by cross-fostered males mate guarding less due to a reduced affinity for their female. Such trade-offs may have a general significance for mate guarding species.

Eggshell pigmentation pattern in relation to breeding performance of blue tits Cyanistes caeruleus

1. We test the consequences, in terms of breeding success and parental effort, of eggshell pigmentation pattern in a hole-nesting bird, the blue tit Cyanistes caeruleus that lays eggs asymmetrically speckled with reddish spots (maculated eggs). 2. We assess the effect of distribution of spots (pigment 'spread') and spot size and pigment intensity (pigment 'darkness') on eggshell physical properties and breeding parameters concerning nestling condition, investment of parents in offspring care and reproductive output in two different habitat types: a deciduous oakwoodland and an evergreen forest. 3. Blue tit clutches with more widely distributed spots showed a thicker eggshell, a shorter incubation period, a lesser amount of mass loss per day and a higher hatching probability than those with spots forming a 'corona' ring. While eggs with larger and darker (more pigment intensity) spots showed a thicker eggshell and a shorter incubation period. In the light of 'signal function hypothesis', these egg traits may reflect female health status and, consequently, this could affect male parental effort. 4. Here we show supports for some of the necessary assumptions of this hypothesis. We found a positive relationship between egg pigment 'spread' and male but not female provisioning rates per day. On the other hand, pigment 'darkness' of blue tits' clutches was positively related to female tarsus length, while pigment 'spread' was positively related to clutch size, male body mass and nestling tarsus length. Our study shows that eggshell pigment 'spread' can be used as an indicator of clutch quality. Further investigations are needed to understand the role of calcium availability as possible causal agent of deviant eggs and its relation to the maculation phenomenon.

Sparrowhawk Accipiter nisus presence and winter bird abundance

The decline and subsequent re-colonisation of the Sparrowhawk Accipiter nisus in the UK has allowed an examination of its potential impacts on passerine abundance through analysis of long-term garden bird monitoring data. Weekly counts in gardens in winter have been collected annually since the early 1970s, a period when Sparrowhawks were initially rare but recolonised to a point in the 1990s when they were recorded in the majority of gardens. Change in bird count from year-to-year for 10 common prey species from up to 483 survey sites were analysed in relation to Sparrowhawk re-colonisation, the number of feeding units per site (e.g. bird tables, hanging bird feeders) and, for a subset of the data, minimum temperature. Year-to-year change increased with Sparrowhawk re-colonisation in Great Tit Parus major, Blue Tit Cyanistes caeruleus and Collared Dove Stretopelia decaocto, but decreased in Starling Sturnus vulgaris, Chaffinch Fringilla coelebs and Greenfinch Carduelis chloris. Positive associations may suggest a behavioural response to predators, or an attraction of predators to increased prey caused by confounding effects of improvement in site quality. The significant negative effects detected suggest that there is a temporal matching between increased predation pressure and decreases in bird abundance for certain species. However, there was no strong evidence that Sparrowhawk re-colonisation was linked to long-term declines in population size.