Corsican Blue Tits Research Articles

Parasite intensity is driven by temperature in a wild bird

Increasing awareness that parasitism is an essential component of nearly all aspects of ecosystem functioning, as well as a driver of biodiversity, has led to rising interest in the consequences of climate change in terms of parasitism and disease spread. Yet empirical knowledge on the extent and ways in which climatic factors affect parasite prevalence and intensities remains scarce. In an 18-year, multi-site, correlative study we investigated the contributions of weather variables and other factors to spatio-temporal variation in infestation by blowfly parasitic larvae (Protocalliphora spp.) in nests of Corsican blue tits (Cyanistes caeruleus). We found that ambient temperature during the nestling stage is strongly and positively related to parasite load (number of parasites per chick), both across broods when controlling for year, and across years. In addition, annual mean parasite load also increased with minimal spring temperature, and decreased with increasing average temperature in the previous summer. There was no indication of a dependence of parasite dynamics on host dynamics in this system, likely due in part to the wide host range of blowflies that do not solely rely on blue tit hosts. This suggests a major effect of temperature during the blowfly life cycle, with potential implications for blowfly host interactions across their geographical range as climate keeps warming up. Finally, given that ambient temperature increases throughout the breeding season and that blowflies negatively affect survival and recruitment of blue tits, these results also mean that parasites, along with caterpillar availability, can drive selection for breeding date in this system.

Phenotypic plasticity drives phenological changes in a Mediterranean blue tit population.

Earlier phenology induced by climate change, such as the passerines' breeding time, is observed in many natural populations. Understanding the nature of such changes is key to predict the responses of wild populations to climate change. Genetic changes have been rarely investigated for laying date, though it has been shown to be heritable and under directional selection, suggesting that the trait could evolve. In a Corsican blue tit population, the birds' laying date has significantly advanced over 40years, and we here determine whether this response is of plastic or evolutionary origin, by comparing the predictions of the breeder's and the Robertson-Price (STS) equations, to the observed genetic changes. We compare the results obtained for two fitness proxies (fledgling and recruitment success), using models accounting for their zero inflation. Because the trait appears heritable and under directional selection, the breeder's equation predicts that genetic changes could drive a significant part of the phenological change observed. We, however, found that fitness proxies and laying date are not genetically correlated. The STS, therefore, predicts no evolution of the breeding time, predicting correctly the absence of trend in breeding values. Our results also emphasize that when investigating selection on a plastic trait under fluctuating selection, part of the fitness-trait phenotypic covariance can be due to within individual covariance. In the case of repeated measurements, splitting within and between individual covariance can shift our perspective on the actual intensity of selection over multiple selection episodes, shedding light on the potential for the trait to evolve.

Environmental heterogeneity and population differences in blue tits personality traits.

Environmental heterogeneity can result in spatial variation in selection pressures that can produce local adaptations. The pace-of-life syndrome hypothesis predicts that habitat-specific selective pressures will favor the coevolution of personality, physiological, and life-history phenotypes. Few studies so far have compared these traits simultaneously across different ecological conditions. In this study, we compared 3 personality traits (handling aggression, exploration speed in a novel environment, and nest defense behavior) and 1 physiological trait (heart rate during manual restraint) across 3 Corsican blue tit (Cyanistes caeruleus) populations. These populations are located in contrasting habitats (evergreen vs. deciduous) and are situated in 2 different valleys 25 km apart. Birds from these populations are known to differ in life-history characteristics, with birds from the evergreen habitat displaying a slow pace-of-life, and birds from the deciduous habitat a comparatively faster pace-of-life. We expected personality to differ across populations, in line with the differences in pace-of-life documented for life-history traits. As expected, we found behavioral differences among populations. Despite considerable temporal variation, birds exhibited lower handling aggression in the evergreen populations. Exploration speed and male heart rate also differed across populations, although our results for exploration speed were more consistent with a phenotypic difference between the 2 valleys than between habitats. There were no clear differences in nest defense intensity among populations. Our study emphasizes the role of environmental heterogeneity in shaping population divergence in personality traits at a small spatial scale.

Nest size is positively correlated with fledging success in Corsican Blue Tits (Cyanistes caeruleus) in an insular oak-dominated habitat mosaic

Avian nests function to provide a safe environment for parents, eggs and nestlings. Positive associations between nest size and other components of breeding performance are expected in two conditions. First, larger nests protect nest occupants better against environmental fluctuations (e.g., weather) than smaller nests. This implies that nest size is a determinant of survival in nest occupants. Second, if reproduction is physically costly, “stronger” parents are expected to be able to build both larger nests and rear more offspring. Here we present the findings of a 17-year correlative nest box study in Corsican Blue Tits (Cyanistes caeruleus ogliastrae) that examined the associations between nest size and different aspects of breeding success. We found that females with larger nests produced more fledglings, but did not produce more hatchlings or heavier nestlings than females with smaller nests. The analyses involving nest size controlled for other female characteristics (first-egg date, clutch size, female age) and environmental factors (oak habitat type, weather during the nestling stage) which we assumed could influence aspects of breeding success. Our findings concerning associations between the size of the nest and breeding success differ from those reported in previous studies in other geographic regions, perhaps because the costs that are associated with reproduction or the local environmental conditions that influence breeding performance are population specific. Our correlative study illustrates that avian studies of niche construction may benefit from long-term multi-factor investigations.

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

Context-dependent Changes in the Weighting of Environmental Cues That Initiate Breeding in a Temperate Passerine, the Corsican Blue Tit (Cyanistes caeruleus)

ABSTRACT. Birds use local environmental cues to fine-tune the timing of egg laying such that the nestling period normally coincides with the local peak in food availability. Ambient temperature, vegetation phenology, and insect phenology are often considered the most likely cues, but no previous studies have explicitly compared and partitioned their relative effects. We used confirmatory path analyses and a long-term study of Blue Tits (Cyanistes caeruleus) to identify and measure the relative weighting of the causal paths that link laying date to spring phenology and temperature in deciduous and evergreen oak forests on Corsica. Path analysis showed that the effects of temperature and vegetation phenology vary between forest types and season. In deciduous oak forest, where females lay eggs early in spring, phenology of vegetation or insects sets the laying date. In evergreen oak forest, where breeding occurs later in the season, females shift from a predominantly phenology-based cue system to a predomina...

Spring vegetation phenology is a robust predictor of breeding date across broad landscapes: a multi-site approach using the Corsican blue tit (Cyanistes caeruleus)

The regulation of reproductive schedules is an important determinant of avian breeding success. In heterogeneous environments, the optimal breeding period may fluctuate temporally across habitats, often on a spatial scale much shorter than the average dispersal range of individuals. The synchronisation of reproductive events with the most favourable period at a given site therefore involves the integration of a suite of fine-scale environmental signals which contain information about future breeding conditions. In this study, we monitored clutch initiation date of blue tits (Cyanistes caeruleus) breeding in a wide range of environmental conditions (altitude, temperature regimes, habitat type) in Corsica (France) to understand the role of spring temperature and leafing phenology on the precise fine-tuning of egg laying on a local scale. Timing of breeding in blue tits was strongly correlated with phenology of the dominant vegetation (r(2) = 0.87). In contrast, spring temperature was not as robust a predictor of the timing of breeding, because a large part of the residual variation in egg-laying date was accounted by differences (ca. 2 weeks) in the development of the vegetation between habitat types (evergreen vs. deciduous oak forests). Female blue tits therefore appear to use the environmental variable (vegetation phenology) that is most closely linked to the future production of insect prey in order to accurately time laying over the entire spatio-temporal breeding landscape.

Why do Corsican Blue Tits Cyanistes caeruleus ogliastrae not use nest boxes for roosting?

We compared winter roosting behaviour of Blue Tits Cyanistes caeruleus in the mainland of southern France and on the island of Corsica in small-holed nest boxes. While in southern France Blue Tits use nest boxes for roosting, Corsican Blue Tits do not. We suggest that this behaviour is innate because Corsican wild-caught as well as F1 and F2 birds born in captivity do not use nest boxes in aviaries even when kept adjacent to mainland tits that sleep in boxes. We suggest that the cost/benefit balance differs between mainland France and Corsica: in Corsica, the costs of roosting in the canopy are less than in mainland France because (1) predators, e.g. owls, are rare in Corsica while abundant on the mainland, (2) the permanent evergreen foliage of the dominant tree in Corsica, the holm oak, could be preferred to nest boxes which are not risk-free, and (3) the costs of using cavities for roosting could be higher in Corsica because of increased mammal predator pressure and higher ectoparasite load than on the mainland.

Aromatic plants in blue tit Cyanistes caeruleus nests: no negative effect on blood-sucking Protocalliphora blow fly larvae

Nesting birds use several behavioural or physiological defence mechanisms against parasites. On Corsica, female blue tits Cyanistes caeruleus incorporate fresh fragments of a limited number of aromatic plants in the nest cup, from the end of nest construction until fledging. Some of these plants negatively affect bacterial growth and host location by blood-sucking mosquitoes in laboratory conditions. In natural populations, Corsican blue tit chicks are exposed to the highest levels of blood-sucking ectoparasitic blow flies Protocalliphora spp. reported in Europe. These ectoparasites can have severe negative effects on chick development and survival probabilities, especially when food constraints are elevated. Here we investigated in several natural Corsican blue tit populations the hypothesis that aromatic plants brought to the nest have anti-blow fly effects during the chick-rearing stage. We predicted that: 1) the amount of aromatic plants should be negatively related to blow fly infestation intensity across nests, 2) experimental addition of aromatic plants in nests should reduce blow fly infestation intensity, and 3) nestlings should be in better physical condition in nests where aromatic plants were experimentally added. No significant relation was found between amount of aromatic plants in nests and blow fly infestation intensity. Experimental addition of aromatic plants did not reduce blow fly infestation intensity and did not affect the chick phenotypic parameters we measured. We conclude that aromatic plants in blue tit nests are not used as a defence against ectoparasitic Protocalliphora blow flies in our study population.

Common paths link food abundance and ectoparasite loads to physiological performance and recruitment in nestling blue tits

Summary 1Identifying how selection shapes life-history traits by causally relating environment to phenotype, performance and fitness has often proven elusive due to limitations of classical analysis methods, which only identify covariance in traits, and to the difficulties in experimentally manipulating environment to expose cause and effect in wild populations. 2In an approach resembling the experimental method common to all modern research, structural equation modelling can not only identify covariance in traits, but also test hypotheses of direct and indirect causal paths that tie environment to phenotypes and fitness through natural selection. Here, we use novel confirmatory path analyses and a long-term study of Corsican blue tits to analyse the interactions between environmental variables (prey abundance and ectoparasite load), phenotypic traits (mass and haematocrit), physiological performance (aerobic capacity) and nestling recruitment. 3Our analyses show that an antagonistic interaction between ectoparasites and food abundance sets tissue development and oxygen carrying capacity of blood at fledging, and that identical paths link these variables to physiological performance and recruitment. 4This study suggests that metabolic capacity at fledging may be important in determining subsequent recruitment and unmasks subtle fitness costs of an ectoparasite.

Early seasonal development of brain song control nuclei in male blue tits

In songbirds, the seasonal growth of the song system is generally thought to be controlled by the spring increase in plasma levels of testosterone and/or related changes in singing activity. Here we report an extremely early seasonal growth (before February) of the song control nuclei HVC and RA in Corsican blue tits ( Parus caeruleus) indicating that the vernal development of these nuclei occurs well before the vernal increase in plasma testosterone, testes size and song activity. The development of HVC and RA occurred simultaneously in two populations that are known to breed consistently 1 month apart as an adaptation to heterogeneous landscapes (predominance of broad-leaved deciduous versus evergreen oak trees). The unidentified environmental and/or physiological cues controlling the plasticity in the song system must therefore differ, at least in part, from those affecting other morphological and physiological traits controlling reproduction.

The effect of habitat quality on foraging patterns, provisioning rate and nestling growth in Corsican Blue Tits Parus caeruleus

Many bird species face seasonal and spatial variation in the availability of the specific food required to rear chicks. Caterpillar availability is often identified as the most important factor determining chick quality and breeding success in forest birds, such as tits Parus spp. It is assumed that parents play an important role in mediating the effect of environment on chick development. A reduction in prey availability should therefore result in increased foraging effort to maintain the amount of food required for optimal chick development. To investigate the capacity of adults to compensate for a reduction in food supply, we compared the foraging behaviour of Blue Tits Parus caeruleus breeding in rich and poor habitats in Corsica. We monitored the foraging effort of adults using radiotelemetry. We also identified and quantified prey items provided to nestlings by using a video camera mounted on the nest. We found that the mean travelling distance of adults was twice as great in the poor habitat as it was in the rich. Despite the marked difference in foraging distance, the proportion of optimal prey (caterpillars) in the diet of the chicks and the total biomass per hour per chick did not differ between the two habitats. We argue that relationships between habitat richness, offspring quality and breeding success cannot be understood adequately without quantifying parental effort.

Habitat quality as a predictor of spatial variation in blue tit reproductive performance: a multi-plot analysis in a heterogeneous landscape

Vertebrate studies have rarely investigated the influence of spatial variation in habitat richness on both short-term (breeding) and long-term (offspring recruitment) reproductive performance using simultaneously multi-patch, multi-habitat type and multi-year approaches at landscape level. Here we present results of such an approach using the influence of two oak tree (Quercus ilex, Q. humilis) species on reproductive performance in Corsican blue tits (Parus caeruleus ogliastrae) as a model system. We found that blue tits breeding in rich broad-leaved deciduous patches consistently laid eggs earlier in the season, and produced larger clutches and more fledglings of higher quality, than those breeding in poor evergreen patches. Also, parents, especially males, were in better physical condition in the broad-leaved deciduous than in the evergreen patches. Surprisingly, estimates of long-term effects of reproduction, such as recruitment rates of locally born offspring, did not differ between the two habitat types. Our results suggest that short-term breeding performance and phenotypic quality of both chicks and parents do not necessarily provide reliable information about contributions to following generations at a scale larger than that of the local study plot. Differences in reproductive performance between the two oak habitat types could not be attributed to density-dependent effects, differences in levels of nest predation, or differences in age structure of the birds. We suggest that habitats that are optimal for breeding are not necessarily optimal for survival after the breeding season.

Asynchronous hatching in a blue tit population: a test of some predictions related to ectoparasites

Although much attention has been devoted to understanding the adaptive value of size hierarchies within broods of altricial birds, current hypotheses are the subject of much debate. Recently it has been suggested that parasites could play a role in promoting the establishment and maintenance of a nestling size hierarchy within broods. For example, the "tasty chick hypothesis" stipulates that the last-hatched chick in asynchronously hatching clutches would have the least efficient immune system, resulting in subsequent parasite aggregation on this chick and hence reducing parasitic pressure on the other chicks of the brood. From data collected during four breeding seasons and after experimental removal of the last-hatched chick, we tested three predictions based on variation in chick body characters within broods in a Corsican blue tit (Parus caeruleus ogliastrae) population exposed to high levels of ectoparasites (Protocalliphora spp.). None of the predictions were fully supported and alternative explanations could not be excluded. In particular, there was no evidence for aggregation of parasites on the last-hatched chick or for a beneficial role of this chick with respect to the others, be it "tasty" or not. Thus, our results are not consistent with the hypothesis that mechanisms responsible for size hierarchies within broods have evolved to alleviate the negative effect of parasites on the fitness of their host.

Aromatic plants in bird nests as a protection against blood-sucking flying insects?

The nest protection hypothesis suggests that some of the fresh plant material, brought by some bird species to their nests, contain secondary compounds that repel parasites or mask the chemical cues that parasites use to find the host. Corsican blue tits (Paruscaeruleus) bring pieces of several species of aromatic plants to the nest at dusk, suggesting a protection against nocturnal agents such as blood-sucking flying insects. The potential repellent or masking effect of these aromatic plant species, alone or in mixture, was experimentally investigated in the mosquito Culexpipiens, using domestic chicks as bird hosts. Aromatic plants had a repellent effect against mosquitoes, although a masking effect could not be ruled out. The plant mixture was the most efficient, although some aromatic plants had a significant effect when used individually. These results are discussed in the context of the nest-protection hypothesis and of the impact of flying blood-sucking insects on bird behaviour and life history traits.

High divorce rates in Corsican blue tits: how to choose a better option in a harsh environment

We investigate which hypothesis, the “better mate hypothesis” or the “better territory hypothesis” best explains the unusually high divorce rate (59%) in a population of blue tits (Parus caeruleus) living in a sclerophyllous habitat characterised by severe environmental constraints (trophic, parasitic, climatic) on the island of Corsica, France. Using data from the breeding seasons 1985–1998 and from a brood size experiment (1990–1993) we examined the causes of divorce and their consequences on breeding performance, mate assortment and territory choice. Breeding performance had no significant effect on whether birds re‐united or divorced in the next breeding season. Re‐uniting pairs did better than divorced females and the latter improved their breeding performance compared to prior to divorce, but this was mainly due to age and territory effects. There were no differences in male performance depending on whether they re‐united or divorced. The age combination of pairs did not differ between re‐uniting and divorcing pairs, but mate assortment changed after divorce with males re‐mating more often with older partners than females. Manipulation of brood size showed a trend for birds with enlarged broods to divorce more. Pairs responded significantly to territory quality by divorcing more often in poor than in good breeding sites. Both faithful pairs and male divorcees had shorter breeding dispersal distances than female divorcees. Divorce rates were determined by the large differences in quality among breeding sites. Males, whatever their status, usually retained their previous territory whereas divorced females moved significantly longer distances and improved their breeding site. Moving to a better territory after divorce benefits only females which appear to be the choosing sex in the decision to divorce. This study strongly supports the “habitat mediated hypothesis” and we suggest that the large observed intraspecific variation in the magnitude of divorce rates in many species of birds is mostly determined by habitat characteristics.

Aromatic herbs in Corsican blue tit nests: The ‘Potpourri’ hypothesis

This study reports that Corsican blue tit (Parus caeruleus ogliastrae) nests contain between one to five aromatic herb species between the onset of egg laying till the chicks’ finished growth 13 d after hatching. An herb removal experiment during the chick stage shows that blue tits bring fresh aromatic material 1–5 d after herb removal. Nests with a series of distinct odour classes easily perceived by humans have never been reported in birds. A new ‘Potpourri’ hypothesis is proposed that may explain the functional significance of this behaviour.

Food Handling Time of Blue Tit Chicks: Constraints and Adaptation to Different Prey Types

Extensive literature shows that lepidopteran larvae constitute the most important component of the diet of nestling tits (Parus spp.). In Blue Tits Parus caeruleus, breeding is usually timed to match the nestling stage to the period when caterpillars are most abundant. This is true even in places where caterpillars are not very numerous and many alternative prey types have to be used. in a study of a Corsican Blue Tit P. c. ogliastrae population, characterised by the extensive use of non-caterpillar prey, we compared some aspects of the behaviour of nestlings when fed caterpillars, grasshoppers and spiders. The expectation deduced from ecological and behavioural literature that nestlings should be best able to swallow caterpillars was confirmed. Chick prey handling time could be ranked from caterpillars (the shortest time), through spiders to grasshoppers (the longest time). Handling time increased exponentially with prey size within each prey category and was to some extent subject to variation between broods. Consequently, the behaviour of nestlings provides new support for the idea that Blue Tits are best adapted to eating caterpillars and that mechanical constraints prevent them from using very big prey items, especially non-caterpillar prey, and that this is likely to affect their choice of prey. Such constraints may be less strict in Great Tits Parus major because of their larger body size.

Water Content of Prey of Nestling Blue Tits in a Corsican Habitat

Caterpillars are important prey for tits (Parus spp.), including Corsican blue tits. It is hypothesized that the low abundance of water-rich caterpillars in combination with high temperatures, especially at the end of the breeding season, cause problems of water balance for the nestlings in the Corsican population. Tits were expected to prefer feeding their young with water-rich prey. The three most important groups of prey (caterpillars [82.8% water], grasshoppers [78.9%] and spiders [69.1%]) differ significantly in water content. The water content of grasshoppers was much higher than expected from the literature. From previous studies it was known that, apart from caterpillars (20-60% of the prey items), tits prefer feeding their nestlings with spiders (26-40%) rather than with grasshoppers (5-17%). This unexpected result is discussed within the framework of a cost-benefit analysis of prey choice, mainly with respect to prey availability.

Nestling diet variation in an insular Mediterranean population of blue tits Parus caeruleus: effects of years, territories and individuals.

Mediterranean evergreen forests of Corsica are characterized by relatively high species diversity of arthropods with low population densities. Food is never superabundant for Corsican blue tits Parus caeruleus. This study focused on the composition of the food of blue tit nestlings and especially on two main components, caterpillars and spiders. The nestling diet was studied for two years using 8-mm cameras that automatically took photographs of adult birds with food. The diet was composed of c. 50% caterpillars and c. 30% spiders. There were between-year and between-individual differences in these proportions. In both years of the study the proportion of caterpillars declined during the course of the breeding season. Individual and time effects on prey sizes were also observed. Pairs and individuals were fairly constant in the proportions of prey over the feeding period. Different food items were not brought in runs. These findings suggest that strong food limitation exists on Corsica, which can considerably influence life-history traits of the blue tit.