Blue Tit Cyanistes Caeruleus Research Articles

How interacting anthropogenic pressures alter the plasticity of breeding time in two common songbirds.

Phenological adjustment is the first line of adaptive response of vertebrates when seasonality is disrupted by climate change. The prevailing response is to reproduce earlier in warmer springs, but habitat changes, such as forest degradation, are expected to affect phenological plasticity, for example, due to loss of reliability of environmental cues used by organisms to time reproduction. Relying on a two-decade, country-level capture-based monitoring of common songbirds' reproduction, we investigated how habitat anthropization, here characterized by the rural-urban and forest-farmland gradients, affected the average phenology and plasticity to local temperature in two common species, the great tit Parus major and the blue tit Cyanistes caeruleus. We built a hierarchical model that simultaneously estimated fledging phenology and its response to spring temperatures based on the changes in the proportion of juveniles captured over the breeding season. Both species fledge earlier in warmer sites (blue tit: 2.94 days/°C, great tit: 3.83 days/°C), in warmer springs (blue tit: 2.49 days/°C, great tit: 2.75 days/°C) and in most urbanized habitats (4 days for blue tit and 2 days for great tit). The slope of the reaction norm of fledging phenology to spring temperature varied across sites in both species, but this variation was explained by habitat anthropization only in the deciduous forest specialist, the blue tit. In this species, the responses to spring temperature were shallower in agricultural landscapes and slightly steeper in more urban areas. Habitat anthropization did not explain variation in the slope of the reaction norm in the habitat-generalist species (great tit), for which mean fledgling phenology and plasticity were correlated (i.e., steeper response in later sites). The effects of habitat change on phenological reaction norms provide another way through which combined environmental degradations may threaten populations' persistence, to an extent depending on species and on the changes in their prey phenology and abundance.

Population links between an insectivorous bird and moths disentangled through national-scale monitoring data.

Insects are key components of food chains, and monitoring data provides new opportunities to identify trophic relationships at broad spatial and temporal scales. Here, combining two monitoring datasets from Great Britain, we reveal how the population dynamics of the blue tit Cyanistes caeruleus are influenced by the abundance of moths - a core component of their breeding diet. We find that years with increased population growth for blue tits correlate strongly with high moth abundance, but population growth in moths and birds is less well correlated; suggesting moth abundance directly affects bird population change. Next, we identify moths that are important components of blue tit diet, recovering associations to species previously identified as key food sources such as the winter moth Operoptera brumata. Our work provides new evidence that insect abundance impacts bird population dynamics in natural communities and provides insight into spatial diet turnover at a national-scale.

Effects of competition and predation operating at individual and population levels: an overview of results from a long-term field experiment.

After an overview of the discussion about the existence of intra- and interspecific competition that illustrates the contradictory opinions I conclude that long-term field experiments are needed for firm conclusions. I discuss in some detail the role of two factors that limit population size of secondary cavity nesting birds e.g. territorial behavior and adequate cavities. This is followed by an overview of experimental long-term field studies in Belgium showing that intra- and interspecific competition in a great tit-blue tit system exists. By using nestbox configurations with high densities of nestboxes that differ in the diameter of their entrance hole in replicate study plots it is possible to manipulate the breeding densities of great tit Parus major and blue tit Cyanistes caeruleus independently, thereby varying the intensity of intra- and interspecific competition between these two coexisting species. When blue tit densities are experimentally increased local recruitment of great tits increases, and adult great tit post-breeding dispersal to other study plots decreases, implying that great tits use blue tit density to evaluate habitat quality and that high blue tit density results in heterospecific attraction. The reverse is not true. An experimental increase in great tit density leading to an increase in interspecific competition in a plot where blue tit density was already high leads to a decrease in blue tit nestling mass (illustrating interspecific competition for food), but to a gradual increase in blue tit body size. Both are primarily caused by an increase in the body size of immigrants (caused by intraspecific competition for protected roosting holes) in contrast to the control plot, where neither is observed. I also summarize behavioral, ecological and possible evolutionary effects of sparrowhawks on blue tits after sparrowhawks settled in an isolated study plot halfway through the study: adult survival substantially decreased for both sexes, but more for females that laid large clutches, leading to selection for females that laid a smaller clutch. This led to a change in the reproduction/survival life-history trade-off. Adult winter weights and nestling weights decreased, and the heaviest fledglings were selected against. Furthermore the frequency of polygyny increased. The long-term experiments also document the role of the use of public information and that species that compete can be attracted to sites in which competitor density is high.

Clear-cuts and warming summers caused forest bird populations to decline in a southern boreal area

Land use and climate change are the main drivers of biodiversity change. However, their relative roles in the decline of biodiversity are still insufficiently known. Climate change is expected to be globally most pronounced in the boreal biome, where another key driver affecting boreal species is forestry. In NW Europe almost all forest land outside protected areas is subject to systematic forest management practices including clear-cutting, thinning and replanting. In addition, a human-caused increase in herbivores, such as ungulates, may affect the forest vegetation structure and thereby also bird species. We studied population changes of a bird community in a southern boreal area in Finland over a period of 30 years and related changes in the bird community concerning both land use and climate variables. During the study the total bird density declined by 26%, i.e., 1%/year. Long-distance migrants and residents declined the most, both by 44%, and short-distance migrants by 29%, while partial migrants increased by 29%. Clear-cuts were the most important variable explaining the decline in the total bird density and the density change of long-distance and short-distance migrants and residents. In addition, the higher summer mean temperature was related to the decline of the total bird density and short-distance migrants, which were also moderately negatively affected by the ungulate density. The increase in partial migrants was mostly due to an increase in the numbers of two bird species, the great tit Parus major and the blue tit Cyanistes caeruleus, which have benefitted from human actions in many ways. As a whole, the bird community did not recover to the level that prevailed before the clear-cuts in the study period. This indicates that recolonisation and the recovery rate by birds in maturing young stands cannot fully compensate for the loss of birds resulting from the clear-cuts. Forest management practices should adopt more biodiversity-friendly methods, such as continuous cover forestry, to better maintain populations of forest birds.

The phenology and clutch size of UK Blue Tits does not differ with woodland composition

The deciduous tree‐herbivorous caterpillar‐insectivorous bird food chain is a well‐studied system for investigating the impacts of climate change across trophic levels. To date, across Europe, most attention has focused on the impacts of increasing spring temperature on changes to phenology in Oak‐dominated (Quercus spp.) woodlands. Paridae species and Pied Flycatcher Ficedula hypoleuca are the most studied secondary consumers, all of which demonstrate an advancement in reproductive phenology with increases in spring temperature. Shifts in climate and phenology may also impact on reproductive investment in clutch size, and the effects of climate on phenology and clutch size may vary depending on woodland composition. To date, the effects of among‐habitat variation in phenology and reproductive investment have received little attention. Insectivorous birds inhabiting woodlands that differ in tree composition may differ in the timing of breeding, due to local tree leafing phenology acting as a cue for egg‐laying date and/or clutch size. Moreover, for most insectivorous birds, woodland composition within a territory is likely to be the main determinant of food availability for both adults and chicks. Consequently, if warming springs affect the temporal patterns of food availability differently across different woodland compositions, this may affect the optimal average local phenology for nesting birds. Here, using data from 34 long‐term (mean 15 years) nest monitoring sites across the UK, we investigate the effect of woodland tree composition and temperature on Blue Tit Cyanistes caeruleus first egg date (FED) and clutch size. We supplemented the nest monitoring data by quantifying woodland composition, at a site level, through modified point counts. We predict that birds breeding in woodlands with greater proportions of late‐leafing species, such as Oak and Ash Fraxinus excelsior, will breed later than those breeding in woodlands with greater proportions of early‐leafing species, such as Birch Betula spp. and Beech Fagus sylvatica. We found no evidence for differences in Blue Tit FED or clutch size in relation to the proportion of any of the tree species investigated, after controlling for temperature and latitude (FED: −3.4 and 2.2, clutch size: −0.4 and − 0.2 eggs for one‐unit increase in temperature and latitude, respectively). In recent decades and across all sites, clutch size has decreased as spring temperatures have increased, a strategy which could allow birds flexibly to adjust their breeding phenology such that nestling demand coincides with peak food availability. The lack of an effect of woodland composition on Blue Tit phenology suggests Blue Tits do not fine‐tune their reproductive phenology to the local tree composition. Whether this lack of evidence for phenological divergence is due to an absence of divergent selection on breeding phenology and clutch size or to gene flow is not clear.

Host Cells of Leucocytozoon (Haemosporida, Leucocytozoidae) Gametocytes, with Remarks on the Phylogenetic Importance of This Character.

Leucocytozoon parasites remain poorly investigated in comparison to other haemosporidians. The host cell inhabited by their blood stages (gametocytes) remains insufficiently known. This study aimed to determine the blood cells inhabited by Leucocytozoon gametocytes in different species of Passeriformes and to test if this feature has a phylogenetic importance. We microscopically analyzed blood films stained with Giemsa from six different bird species and individuals and used PCR-based methods for parasite lineage identification. The DNA sequences obtained were applied for phylogenetic analysis. Leucocytozoon parasite from the song thrush Turdus philomelos (cytochrome b lineage STUR1), the blackbird Turdus merula (undetermined lineage), the garden warbler Sylvia borin (unknown lineage) inhabited erythrocytes, a parasite from the blue tit Cyanistes caeruleus (PARUS4) infects lymphocytes, while in the wood warbler Phylloscopus sibilatrix (WW6) and the common chiffchaff Phylloscopus collybita (AFR205) they were found inhabiting thrombocytes. Parasites infecting thrombocytes were closely related, while the parasites infecting erythrocytes were placed in three different clades, and the one found in lymphocytes was placed in a separate clade. This shows that the determination of host cells inhabited by Leucocytozoon parasites can be phylogenetically important and should be considered in future species descriptions. Noteworthy, phylogenetic analysis might be used for the prediction of which host cells parasite lineages might inhabit.

Helminth Community Structure of Tits Cyanistes caeruleus and Parus major (Paridae) during Their Autumn Migration on the Southern Baltic Coast.

The research problem undertaken in this study is to determine the scale of infection of Eurasian blue tit Cyanistes caeruleus and Great tit Parus major and the biological diversity of their internal parasites, helminths. The aim of the study is to gain new knowledge about the structure of the helminth communities of the Eurasian blue tit and Great tit on the southern coast of the Baltic Sea during autumn migration to their wintering grounds. Helminths of tits were collected in 2008-2012 on the southern coast of the Baltic Sea in Poland. PAST v. 2.11 software was used for the calculations. Barcoding DNA was used to identify trematodes initially classified based on morphological characters to the genera Leucochloridium and Urogonimus. Cestodes Anonchotaenia globata were recorded for the first time in Poland. The Eurasian blue tit is a new host in Poland for three species of helminths: cestode Monosertum parinum and filarial nematodes, Cardiofilaria pavlovskyi, and Diplotriaena henryi. The Great tit is a new host in Poland for trematode Urogonimus macrostomus, cestode A. globata and M. parinum, and filarial nematode Diplotriaena obtusa. The nematode C. pavlovskyi was the species most frequently recorded in both host species. A high degree of similarity was found between the component communities and infracommunities of helminths in Eurasian blue tit and Great tit. The new information provided in this study has increased our knowledge of the transmission of helminths in Central Europe.

Influence of nest box design and nesting material on ectoparasite load for four woodland passerines

ABSTRACT Capsule Abundance of haematophagous ectoparasites in woodland passerine nests is influenced by complex interactions between nest box design, bird species, amount of nesting material and nest composition. Aims To analyse ectoparasite abundance relative to nest box design (old wooden nest boxes present for over 2 years versus new wooden nest boxes of the same dimensions vs deep wooden nest boxes designed to reduce predation risk) and bird species (Blue Tit Cyanistes caeruleus, Great Tit Parus major, Pied Flycatcher Ficedula hypoleuca and Eurasian Nuthatch Sitta europaea). The potential influence of amount of nesting material and nest composition was also studied. Methods After fledging, nests were collected from nest boxes. Ectoparasites and nest materials were identified and quantified. Generalized linear modelling was used to examine the influence of nest box design, bird species, amount of nest material and nest composition on ectoparasite loads. Akaike’s Information Criterion was used to select optimal models. Results Abundance of Hen Fleas Ceratophyllus gallinae and parasitic Blowfly Protocalliphora was significantly higher for deep nest boxes than nest boxes of standard dimensions. Old nest boxes had significantly higher loads than new nest boxes, despite thorough cleaning between breeding seasons. Hen Flea abundance was highest in Eurasian Nuthatch nests. Blowfly abundance was highest in Pied Flycatcher nests. Abundances of both fleas and blowfly were positively related to nest mass and amount of animal hair in the nest, and, for parasitic Blowfly, were negatively related to the amount of tree bark. Conclusion Ectoparasite load depends not only on bird species but also nest box design and nesting material. We recommend: (1) nest boxes are regularly replaced to reduce parasite load; (2) deep nest boxes are not used as the large nests constructed not only remove anti-predator benefits of eggs/chicks being harder to reach but are also associated with high haematophagous ectoparasite loads.

Autumn fueling behavior in passerines in relation to migratory distance and daylength.

Songbirds have evolved diverse strategies to cope with seasonality, including long-, medium-, and short-distance migration. There is some evidence that birds with a longer migration distance deposit fuel faster. However, most studies focus on long-distance migrants. Comparisons between species with different migration distances are necessary to broaden our understanding of fueling capacity in migratory birds. We present maximum fuel deposition rates of five songbird species migrating along the southeast coast of Sweden in autumn with migration distances ranging from long (neotropical migrant) to short (partial/irruptive migrant) (Willow Warbler Phylloscopus trochilus, Lesser Whitethroat Curruca curruca, Common Chiffchaff P.collybita, European Robin Erithacus rubecula, and Blue Tit Cyanistes caeruleus). The birds were fed ad libitum in captivity and were exposed to either extended or natural daylength. All species ceased to increase in mass when they reached a certain fuel load, generally corresponding to migration distance, despite unlimited access to food and ample time for foraging. Blue Tits, Willow Warblers, and Lesser Whitethroats had the highest fuel deposition rates with extended daylength (19%, 20%, and 20%, respectively), and about 13% with natural daylength, which is comparable to the highest rates found in migratory songbirds in nature. European Robins and Common Chiffchaffs that winter in the temperate Mediterranean had the lowest fuel deposition rates (12% and 12% with extended daylength, respectively). Our results suggest that the long- and short-distance migrants in this study have developed an extreme capacity for rapid refueling for different reasons; speedy migration to distant wintering grounds or winter survival in Scandinavia. This study contributes to our current knowledge of maximum fuel deposition rates in different species and the limitations posed by daylength. We highlight the need for future studies of species with different migration strategies in order to draw broad conclusions about fueling strategies of migratory birds.

A crowd-sourced genomic project to assess hybrid content in a rare avian vagrant (Azure Tit Cyanistes cyanus (Pallas, 1770))

The aim of this study was to correlate plumage variation with the amount of genomic hybrid content in hybrids between Azure Tits Cyanistes cyanus (Pallas, 1770) and European Blue Tit Cyanistes caeruleus (Linnaeus, 1758), by re-sequencing the genomes of museum specimens of non-hybrids and presumed hybrids with varying plumages. The project was funded by crowdsourcing and initiated when two presumed Azure Tits, observed by hundreds of Swedish birdwatchers, were rejected as hybrids based on minor plumage deviations assumed to indicate hybrid contents from the European Blue Tit. The results confirm that hybrids with intermediate plumages, so called Pleske’s Tits, are first generation hybrids (F1 hybrids). Individuals, whose plumages are similar to Azure Tits, but assessed as hybrids based on minor plumage deviations, are all backcrosses but vary in their degree of hybrid content. However, some individuals morphologically recognized as pure Azure Tits expressed similar degrees of hybrid content. The results indicate that: (1) hybrid content may be widespread in Azure Tits in the western part of its habitat distribution; (2) plumage deviation in backcrosses is not linearly correlated with the genetic degree of hybrid origin; and (3) all Azure Tits observed in Europe outside its natural distribution may have some degree of hybrid origin. We therefore suggest that it is very difficult to phenotypically single out hybrids beyond first generation backcrosses. We argue that decreased sequencing costs and improved analytical tools open the doors for museomic crowd-sourced projects that may not address outstanding biological questions but have a major interest for lay citizens such as birdwatchers.

The effects of a decade of agri‐environment intervention in a lowland farm landscape on population trends of birds and butterflies

Abstract Declines in farmland biodiversity remain evident despite over three decades of research and implementation of agri‐environment schemes (AES). Although positive effects of AES are often demonstrated locally or in the short term, studies exploring longer term trends in biodiversity often show contradictory results. Evidence for the potential of AES to drive beneficial changes in populations remains sparse, especially for mobile taxa such as birds and butterflies. We analysed the abundance of 12 widespread bird and 9 butterfly species from a 10‐year study of AES intervention in a farmland landscape in southern England. We compared estimates of annual population growth rates from our study landscape with rates derived from large‐scale national monitoring schemes in equivalent landscapes without substantial AES. Species trends in our study landscape were frequently stable or increasing, in contrast to concurrent declining trends in equivalent landscapes without AES. These differences were significant for total abundance of granivorous species and for chaffinch Fringilla coelebs, blue tit Cyanistes caeruleus and great tit Parus major individually. For butterflies, differences in trends were significantly more positive for gatekeeper Pyronia tithonus and green‐veined white Pieris napi, while small white P. rapae showed a trend that was significantly more negative in our study landscape. Synthesis and applications. Our results demonstrate that, for some bird and butterfly species, the higher abundances associated with areas of AES uptake within a typical commercial farmland landscape can co‐occur with positive or stable population trends over long time scales and that these trends can show significant differences from those in equivalent landscapes without substantial AES interventions. Our results suggest that previously observed inconsistencies in AES benefits may in part reflect a lack of long‐term studies with accurate data on AES uptake and quality (i.e. successful implementation and management). Our results, thus, affirm the importance of delivering and monitoring high‐quality AES options if the design and implementation of the next generation of AES is to achieve significant benefits for biodiversity.

A Mixed Brood of Coal Tits Periparus ater and Blue Tits Cyanistes caeruleus in Central Portugal

Mixed-species broods appear to be an uncommon phenomenon in altricial birds. In secondary hole-nesting birds, such as tits (Paridae), mixed-species clutches occur as a consequence of facultative interspecific brood parasitism or as a byproduct of nest takeover. Here, we report a case of a mixed-species brood composed of one Coal Tit Periparus ater and three Blue Tit Cyanistes caeruleus nestlings that was successfully raised by a Blue Tit pair. The foreign Coal Tit nestling received more food than its Blue Tit nestmates, possibly resulting in a larger tarsus length compared to other Coal Tit nestlings from a regular single-species brood in the same forest.

The experimental provision of calcium increases the reproductive success of passerine birds

Abstract The role of the availability of calcium in limiting the breeding success and intensity of eggshell specking in birds remains unclear. Experimentally, we provided blue tits (Cyanistes caeruleus) and great tits (Parus major) in woodlands with underlying calcium-rich limestone or calcium-poor gritstone with calcium during the egg stage or during the entire reproductive period and examined their breeding success and eggshell speckling. When provided with calcium during the egg stage, experimental blue tits laid larger clutch sizes with higher clutch weights than controls, whilst experimental great tits had higher fledging success than controls. When provided with calcium throughout reproduction, there was no effect of treatment on blue tit reproductive success, but experimental great tits had higher hatching success and nestling masses than controls. Additional calcium during the egg stage resulted in experimental great tits, but not blue tits, laying less speckled eggs than controls, and additional calcium throughout reproduction led to experimental blue tits and great tits laying less speckled eggs than controls. The provision of calcium led to both species generally having higher levels of reproductive success and less speckled eggs than controls, irrespective of habitat geology, meaning that calcium availability does determine avian breeding success and eggshell specking.

Bird populations most exposed to climate change are less sensitive to climatic variation

The phenology of many species shows strong sensitivity to climate change; however, with few large scale intra-specific studies it is unclear how such sensitivity varies over a species’ range. We document large intra-specific variation in phenological sensitivity to temperature using laying date information from 67 populations of two co-familial European songbirds, the great tit (Parus major) and blue tit (Cyanistes caeruleus), covering a large part of their breeding range. Populations inhabiting deciduous habitats showed stronger phenological sensitivity than those in evergreen and mixed habitats. However, populations with higher sensitivity tended to have experienced less rapid change in climate over the past decades, such that populations with high phenological sensitivity will not necessarily exhibit the strongest phenological advancement. Our results show that to effectively assess the impact of climate change on phenology across a species’ range it will be necessary to account for intra-specific variation in phenological sensitivity, climate change exposure, and the ecological characteristics of a population.

The interactive effect of ambient temperature and brood size manipulation on nestling body mass in blue tits: an exploratory analysis of a long-term study

BackgroundRelatively few studies have examined the interactive effects of ecological factors on physiological responses in wild animals. Nearly all of them have been short-term investigations that did not include experimental manipulations, limiting our ability to understand how climate change will affect natural populations. Using a 10-year brood size manipulation experiment in wild blue tits (Cyanistes caeruleus), we quantified the impact of weather conditions and brood competition on the body mass and structural size (tarsus length) of nestlings just prior to leaving the nest.ResultsWe found that variation in nestling body mass on day 14 after hatching was explained by an interactive effect between average ambient temperature experienced during nestling period and brood size treatment. Specifically, in control broods nestling body mass was correlated with temperature in a non-linear manner (concave) with the vertex point (maximum body mass) at ca. 13 °C. In contrast, in enlarged broods nestling body mass permanently increased (also non-linearly) as temperature advanced.ConclusionsOur results highlight the importance of considering the effects of brood rearing conditions alongside other environmental factors experienced during growth while investigating early-life environmental effects on body condition.

Adaptive final (last-laid) eggs in the Eurasian Blue Tit Cyanistes caeruleus

Adaptive final (last-laid) eggs in the Eurasian Blue Tit Cyanistes caeruleus

Turn taking is not restricted by task specialisation but does not facilitate equality in offspring provisioning

Sexual conflict arises when two individuals invest in their common offspring because both individuals benefit when their partner invests more. Conditional cooperation is a theoretical concept that could resolve this conflict. Here, parents are thought to motivate each other to contribute to provisioning visits by following the rules of turn taking, which results in equal and efficient investment. However, parents have other tasks besides provisioning, which might hinder taking turns. To investigate restrictions by other care tasks and whether turn taking can be used to match investment, we manipulated brooding duration in female blue tits (Cyanistes caeruleus) during the early nestling phase by changing nest box temperature. As expected, females subjected to cold conditions brooded longer than females under warm conditions. Yet, contrary to our prediction, females had similar visit rates in both treatments, which suggests that females in the cold treatment invested more overall. In addition, the females’ turn taking level was higher in the more demanding cold condition (and the calculated randomised turn taking levels of females did not differ), hence females don’t seem to be restricted in their turn taking strategy by other care tasks. However, males did not seem to match the females’ turn taking levels because they did not adjust their visit rates. Thus, level of turn taking was not restricted by an other sex-specific task in females and did not facilitate a greater investment by their male partners.

Nest decoration: birds exploit a fear of feathers to guard their nest from usurpation.

Many species of birds incorporate feathers into their nest as structural support and to insulate the eggs or offspring. Here, we investigated the novel idea that birds reduce the risk of nest usurpation by decorating it with feathers to trigger a fear response in their rivals. We let prospecting birds choose between a dyad of nest-boxes in the wild, both containing some nest materials, but where one had a few white feathers and the other had none. All three species of cavity-nesting birds studied, the pied flycatcher Ficedula hypoleuca, the blue tit Cyanistes caeruleus, and the tree swallow Tachycineta bicolor, hesitated to enter boxes with white feathers. A similar avoidance of white feathers was found when the alternative nest-box of a dyad held black feathers. However, the birds readily collected white feathers that we placed in front of their nest-box, showing the fear of such feathers was context-dependent. We suggest that naive prospecting birds may perceive feathers in nests as the result of a predation event, and that owners decorate nests with bright feathers that can be seen from the opening to deter others from entering.

A non‐destructive approach to collect nest material data using photographs

The materials that birds use to build their nests have a profound effect on nest quality and consequently on the builder’s reproductive success. Given that the common method to quantify nest materials by dismantling nests takes time and limits study species, we developed a non‐destructive and much quicker method for quantifying nest materials using nest photographs. Using our photographic method, the proportions of the main materials in 45 Blue Tit Cyanistes caeruleus and 20 Dartford Warbler Sylvia undata nests, including grass, heather and moss, matched those found by dismantling the nests, but the proportions of rarer animal‐derived materials differed between the two methods. Provided that there is an initial calibration with the dismantling method, the photographic method offers two key advantages: a reduction in the time it takes to quantify the major components of nests, and application to previously inaccessible data, including museum collections. Together, these advantages encourage further study of nesting materials and enable a better understanding of avian nest diversification.

Experimental manipulation of cavity temperature produces differential effects on parasite abundances in blue tit nests at two different latitudes.

Although different predictive models forecast that climate change will alter the distribution and incidence of parasitic diseases, few studies have investigated how microclimatic changes may affect host-parasite relationships. In this study, we experimentally increased the temperature inside nest boxes of the blue tit Cyanistes caeruleus during the nestling period at two different latitudes (central Spain and central Germany) to determine its effect on parasite abundance. The two localities have contrasting climate conditions: the southern one in Spain is warmer and drier than the northern one in Germany. Consistent with this, we observed that the parasitic fauna in nests at the two localities differs. The flea species Ceratophyllus gallinae was more abundant in the northern locality, while the blowfly species Protocalliphora azurea and biting midge species of the genus Culicoides were more abundant in the southern one, as were blood parasites. Moreover, dermanyssid mites and blackflies (Simuliidae) were observed only in the southern locality. The temperature inside nest boxes was increased using heat mats placed underneath the nest material during the nestling period (day 3 to day13 post-hatching). Compared with control nests, the average temperature in heated nests increased by 2.24 °C and 1.35 °C at night in Spain and Germany, respectively. Consequently, the average relative humidity in heated versus control nests decreased 4.93 and 0.82 units in Spain and Germany, respectively. The abundance of blowfly pupae in the heated nests was significantly lower than that of control nests at both localities. The abundance of larval fleas was also lower in the heated nests, but only at the Spanish locality. Infection by the blood parasites Haemoproteus/Plasmodium was higher in males attending the heated nests in Germany, and the control nests in Spain. Moreover, both male body mass and nestling wing length were negatively related to the abundance of larval fleas. In conclusion, our results indicate that increased temperature at the nestling stage may affect the fitness of blue tits by altering parasite prevalence rates.