Population Of Blue Tits Research Articles

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.

Molecular epidemiology of malaria prevalence and parasitaemia in a wild bird population

Avian malaria (Plasmodium spp.) and other blood parasitic infections of birds constitute increasingly popular model systems in ecological and evolutionary host-parasite studies. Field studies of these parasites commonly use two traits in hypothesis testing: infection status (or prevalence at the population level) and parasitaemia, yet the causes of variation in these traits remain poorly understood. Here, we use quantitative PCR to investigate fine-scale environmental and host predictors of malaria infection status and parasitaemia in a large 4-year data set from a well-characterized population of blue tits (Cyanistes caeruleus). We also examine the temporal dynamics of both traits within individuals. Both infection status and parasitaemia showed marked temporal and spatial variation within this population. However, spatiotemporal patterns of prevalence and parasitaemia were non-parallel, suggesting that different biological processes underpin variation in these two traits at this scale. Infection probability and parasitaemia both increased with host age, and parasitaemia was higher in individuals investing more in reproduction (those with larger clutch sizes). Several local environmental characteristics predicted parasitaemia, including food availability, altitude, and distance from the woodland edge. Although infection status and parasitaemia were somewhat repeatable within individuals, infections were clearly dynamic: patent infections frequently disappeared from the bloodstream, with up to 26% being lost between years, and parasitaemia also fluctuated within individuals across years in a pattern that mirrored annual population-level changes. Overall, these findings highlight the ecological complexity of avian malaria infections in natural populations, while providing valuable insight into the fundamental biology of this system that will increase its utility as a model host-parasite system.

Variation in sleep behaviour in free-living blue tits, Cyanistes caeruleus: effects of sex, age and environment

Although sleep is fundamental for survival, not much is known about sleep behaviour in free-living animals and between-individual variation in sleep patterns has hardly been studied, except in humans. We analysed sleep behaviour in a free-living population of blue tits in southern Germany. We recorded individuals roosting in nestboxes between November and April using infrared-sensitive cameras. We investigated the following sleep parameters: time of entering and leaving the nestbox, sleep onset, awakening time, sleep duration, midpoint of sleep, latency to sleep and frequency and duration of nocturnal awakenings. Sleep onset, awakening time and sleep duration followed seasonal changes in daylength. Blue tits slept ca. 4.8 h longer in winter than in spring. During the night, birds woke up between 23 and 230 times, but this did not change seasonally. Local light conditions influenced awakening time: birds at brighter locations woke up earlier. Females slept on average 15 min longer per night than males and this sex difference became more pronounced in early spring. Although females spent a greater proportion of the night awake than males, they still slept more overall. First-year birds spent more time in the nestbox after waking up and left the nestbox later in the morning than older individuals. Repeatability estimates showed that individuals were consistent in their sleep behaviour over the 2-year study period. Our results indicate that sleep patterns are individual-specific traits in blue tits. We suggest that the observed sex difference in sleep duration is caused by sexual selection.

Combining capture–recapture data and pedigree information to assess heritability of demographic parameters in the wild

Quantitative genetic analyses have been increasingly used to estimate the genetic basis of life-history traits in natural populations. Imperfect detection of individuals is inherent to studies that monitor populations in the wild, yet it is seldom accounted for by quantitative genetic studies, perhaps leading to flawed inference. To facilitate the inclusion of imperfect detection of individuals in such studies, we develop a method to estimate additive genetic variance and assess heritability for binary traits such as survival, using capture-recapture (CR) data. Our approach combines mixed-effects CR models with a threshold model to incorporate discrete data in a standard 'animal model' approach. We employ Markov chain Monte Carlo sampling in a Bayesian framework to estimate model parameters. We illustrate our approach using data from a wild population of blue tits (Cyanistes caeruleus) and present the first estimate of heritability of adult survival in the wild. In agreement with the prediction that selection should deplete additive genetic variance in fitness, we found that survival had low heritability. Because the detection process is incorporated, capture-recapture animal models (CRAM) provide unbiased quantitative genetics analyses of longitudinal data collected in the wild.

Low variability and absence of phenotypic correlates of Clock gene variation in a great tit Parus major population

Studies of a range of taxa, including birds, have revealed latitudinal clines in allele length at the conserved Clock locus, a gene with known influences on behaviour and physiology. Such clines might reflect adaptation to seasonal variation, a suggestion supported by a recent within‐population analysis of blue tits Cyanistes caeruleus, which found associations between Clock genotype and timing of breeding in females. To test the generality of this pattern, we sequenced the polymorphic poly‐Q locus of the Clock gene in 521 female great tits Parus major, which were selected based on possession of extreme breeding phenotypes. In total, we identified five alleles with one allele accounting for 96% of allelic diversity in the sample set. Overall variability at the poly‐Q locus was very low, and the spatial distribution of Clock alleles across Wytham was highly homogenous. Our data further provide no evidence for a connection between Clock genotype and reproductive timing phenotype in female great tits; further, we found no effect of Clock genotype on reproductive success. Hence, these results are in contrast to the pattern found for the sympatric blue tit population inhabiting the same woodlands, suggesting that phenotypic effects of Clock are not general in passerine birds.

Experimental evidence for the role of calcium in eggshell pigmentation pattern and breeding performance in Blue Tits Cyanistes caeruleus

Previous studies have found strong relationships between calcium availability and eggshell pigmentation in the Great Tit (Parus major). According to the “structural function hypothesis”, protoporphyrins, the pigments responsible for reddish spots on speckled eggs, are deposited in those areas of the shell where calcium deposition is less intense. In the study reported here, which was carried out in three Blue Tit (Cyanistes caeruleus) populations in central Spain, we provide partial experimental support for the association between protoporphyrin eggshell pigmentation and shell thinning. Contrary to our expectations, we did not observe a decrease in the size and intensity of pigment spots for those eggs from calcium-supplemented nests. However, we did find that the provision of calcium-rich material during the egg-laying period led to a more wide distribution of pigment spots and reduced the proportion of eggs with defective shells (deviant pigmentation, dull and rough surface). When only the supplemented nests were considered in the analysis, within the same clutch we also detected differences in the spotting distribution between those eggs laid by female Blue Tits observed to have consumed calcium consumption on the day prior to laying and those observed not to have consumed calcium on the day prior to laying. Clutch size was not affected by the calcium supplementation. Female Blue Tits experimentally supplied with calcium-rich material had a shorter incubation period than control females, and they laid eggs with thicker shells. Eggshell thickness markedly affects the probability of hatching and could explain the lower proportion of unhatched late eggs found in supplemented nests in comparison with control ones. This study highlights the role of calcium in eggshell maculation and its effects on breeding performance of small passerines. We found the spotting distribution to be a good predictor of calcium deficiency. However, our results provide only mixed support for the “structural function hypothesis”: in our study populations, the thickness of the eggshell was intimately associated with calcium availability, but the relationship between calcium and protoporphyrin deposition remains far from clear.

Conclusive evidence for conspecific brood parasitism in the blue tit Cyanistes caeruleus: a reply to Griffith et al.

Previously we presented evidence for conspecific brood parasitism (CBP, the phenomenon of females depositing eggs into conspecific nests) in blue tits Cyanistes caeruleus. This evidence, from multiple nests, was based on the appearance of two eggs within a nest in a single day, sometimes for multiple consecutive days, one of which was always noticeably different in patterning compared to the rest of the eggs in the clutch (Vedder et al. 2007). However, based on the absence of molecular genetic evidence for CBP in a sample of 427 blue tit broods in Wytham Wood (Oxford, UK), despite the incidence of eggs with aberrant patterning, Griffith et al. (2009) suggested that our findings may have been misinterpreted and that the eggs we identified as parasitic and host may have been laid by the same female. Here we use molecular genetic data from two subsequent seasons, in conjunction with our previous criteria for identifying CBP, to provide unequivocal evidence of CBP in the blue tit and support for the validity of our previous criteria. In the breeding seasons of 2006 and 2007, we checked all occupied nestboxes in our study population (De Vosbergen, Groningen, the Netherlands) on a daily basis, and identified and numbered all newly laid eggs. Shortly prior to hatching, all eggs were digitally photographed and placed into separate compartments in incubators, such that each hatchling could be assigned to the specific egg it hatched from. Hatchlings were uniquely marked, returned to their original nest, and DNA sampled within 1 6 days of hatching. These nestlings were later genotyped for six microsatellite loci together with their putative parents (see Magrath et al. 2009 for a more detailed description of field and lab procedures). Examination of our daily laying records (n 2156 eggs at 188 nests) revealed two clear cases (both in 2006), in different nests, where two eggs appeared in a single day (on the 4th and 10th day of egg laying, respectively). In both cases, a single new egg had been recorded on the day before and after the appearance of the two eggs. Additionally, in both cases, the digital images showed that one of the two eggs was distinctly different in patterning compared to the other eggs in the clutch. In contrast to previous studies on blue tits, we were able to compare the genotypes of the hatchlings from specific eggs with the genotypes of the two provisioning parents. For both nestlings from eggs of distinct appearance, there was a mismatch at four of the six loci with the feeding female. We found no maternal mismatches with any of the other nestlings in the broods. At the nest where the two eggs appeared on the 10th day of laying, the genetic mother of the parasitic egg was identified as a secondary female (of a polygynous male that sired all her eggs). The day after the host nest was parasitized, the parasitic female started laying a clutch of 10 eggs in a nestbox two territories away from the host nest, which contained a nest that was completed weeks before (i.e. possibly deserted by a previous pair). The parasitic egg was also sired by the polygynous male but no other nestlings in the host nest were sired by this male. The other parasitic egg could not be assigned to a female or male that successfully reared a brood in our nestboxes, however this does not exclude the possibility that the genetic mother bred successfully in a natural cavity or outside the study area. The above scenario suggests a female in need of finding a nest to lay her eggs, but should, nevertheless, be classified as CBP because she increased her reproductive output without providing care for the nestling (Yom-Tov 1980). It also proves that females are capable of laying eggs in nests occupied by conspecifics and thus potentially unconstrained from using CBP as a strategy. Whether the behaviour has evolved as a conditional adaptive strategy, perhaps latently present in all females, or merely reflects an epiphenomenon of females preferring to lay their eggs in a nest instead of dumping them elsewhere, remains open to investigation. The extremely low frequency of CBP that we report here may suggest it to be an epiphenomenon, but recently a study on an Austrian population of blue tits found a relatively high frequency of nestlings with maternal microsatellite mismatches (15.4% of nests) throughout their study area, after nest sites were limited experimentally in part of the area (Jacot et al. 2009). Hence, although uncommon, CBP in blue tits may be a more frequent phenomenon than previously assumed (Kempenaers et al. 1995, Griffith et al. 2009), and there is need for caution when generalising findings across populations. Since it has

Chronic malaria infections increase family inequalities and reduce parental fitness: experimental evidence from a wild bird population

Avian malaria parasites (Plasmodium) occur commonly in wild birds and are an increasingly popular model system for understanding host-parasite co-evolution. However, whether these parasites have fitness consequences for hosts in endemic areas is much debated, particularly since wild-caught individuals almost always harbour chronic infections of very low parasite density. We used the anti-malarial drug Malarone to test experimentally for fitness effects of chronic malaria infection in a wild population of breeding blue tits (Cyanistes caeruleus). Medication caused a pronounced reduction in Plasmodium infection intensity, usually resulting in complete clearance of these parasites from the blood, as revealed by quantitative PCR. Positive effects of medication on malaria-infected birds were found at multiple stages during breeding, with medicated females showing higher hatching success, provisioning rates and fledging success compared to controls. Most strikingly, we found that treatment of maternal malaria infections strongly altered within-family differences, with reduced inequality in hatching probability and fledging mass within broods reared by medicated females. These within-brood effects appear to explain higher fledging success among medicated females and are consistent with a model of parental optimism in which smaller (marginal) offspring can be successfully raised to independence if additional resources become available during the breeding attempt. Overall, these results demonstrate that chronic avian malaria infections, far from being benign, can have significant effects on host fitness and may thus constitute an important selection pressure in wild bird populations.

Can eggs in a cavity be a female secondary sexual signal? Male nest visits and modelling of egg visual discrimination in blue tits

Eggshell colouration is thought to function as a female-specific secondary sexual trait. While tests of this idea are rapidly accumulating in cavity-nesting birds, some fundamental underlying assumptions remain rarely investigated: namely, can males see eggshell coloration and perceive colour differences between the eggs of different females? We tested these two key assumptions in a natural population of blue tits (Cyanistes caeruleus). Using transponders, we tracked male nest visits and found that all males visited their nest-boxes while eggs were present and often visually accessible. Interestingly, some males also visited neighbouring nests. We then tested whether birds could detect eggshell coloration using models of avian colour vision; models were performed with and without limitations on visual performance owing to dim light. Both models found that differences in eggshell brightness were often easier to discriminate than differences in colour; there was more contrast in white eggshell background between clutches than within and its contrast against nest background was repeatable within clutches, suggesting these features could act as signals. Yet, the detectability of these contrasts depended entirely on model assumptions of visual limitations. Consequently, we need a better understanding of underlying visual mechanisms in dim-light environments and behavioural discrimination experiments before confirming the signalling potential of eggshell coloration.

Genetics of personalities: no simple answers for complex traits

Identifying the genes that underlie phenotypic variation in natural populations, and assessing the consequences of polymorphisms at these loci for individual fitness are major objectives in evolutionary biology. Yet, with the exception of a few success stories, little progress has been made, and our understanding of the link between genotype and phenotype is still in its infancy. For example, although body length in humans is largely genetically determined, with heritability estimates greater than 0.8, massive genome-wide association studies (GWAS) have only been able to account for a very small proportion of this variation (Gudbjartsson et al. 2008). If it is so difficult to explain the genetics behind relatively 'simple' traits, can we envision that it will at all be possible to find genes underlying complex behavioural traits in wild non-model organisms? Some notable examples suggest that this can indeed be a worthwhile endeavour. Recently, the circadian rhythm gene Clock has been associated with timing of breeding in a wild blue tit population (Johnsen et al. 2007; Liedvogel et al. 2009) and the Pgi gene to variation in dispersal and flight endurance in Glanville fritillary butterflies (Niitepold et al. 2009). A promising candidate gene for influencing complex animal personality traits, also known as behavioural syndromes (Sih et al. 2004), is the dopamine receptor D4 (DRD4) gene. Within the last decade, polymorphisms in this gene have been associated with variation in novelty seeking and exploration behaviour in a range of species, from humans to great tits (Schinka et al. 2002; Fidler et al. 2007). In this issue, Korsten et al. (2010) attempt to replicate this previously observed association in wild-living birds, and test for the generality of the association between DRD4 and personality across a number of European great tit populations.

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.

Heritability of resting metabolic rate in a wild population of blue tits

We report the first study with the aim to estimate heritability in a wild population, a nest box breeding population of blue tits. We estimated heritability as well as genetic and phenotypic correlations of resting metabolic rate (RMR), body mass and tarsus length with an animal model based on data from a split cross-fostering experiment with brood size manipulations. RMR and body mass, but not tarsus length, showed significant levels of explained variation but for different underlying reasons. In body mass, the contribution to the explained variation is mainly because of a strong brood effect, while in RMR it is mainly because of a high heritability. The additive variance in RMR was significant and the heritability was estimated to 0.59. The estimates of heritability of body mass (0.08) and tarsus length (0.00) were both low and based on nonsignificant additive variances. Thus, given the low heritability (and additive variances) in body mass and tarsus length the potential for direct selection on RMR independent of the two traits is high in this population. However, the strong phenotypic correlation between RMR and mass (0.643 +/- 0.079) was partly accounted for by a potentially strong, although highly uncertain, genetic correlation (1.178 +/- 0.456) between the two traits. This indicates that the additive variance of body mass, although low, might still somewhat constrain the independent evolvability of RMR.

Phenotypic correlates of Clock gene variation in a wild blue tit population: evidence for a role in seasonal timing of reproduction

The timing of reproduction in birds varies considerably within populations and is often under strong natural selection. Individual timing within years is dependent on a range of environmental factors in addition to having an additive genetic basis. In vertebrates, an increasing amount is known about the molecular basis for variation in biological timing. The Clock gene includes a variable poly-glutamine (poly-Q) repeat influencing behaviour and physiology. Recent work in birds, fish and insects has demonstrated associations between Clock genotype and latitude across populations, which match latitudinal variation in breeding time. In this study, we investigated the phenotypic correlates of variation in Clock genotype within a single blue tit Cyanistes caeruleus population over two successive breeding seasons. In females, but not in males, we observed a general trend for birds with fewer poly-Q repeats to breed earlier in the season. Incubation duration was shorter in both females and males with fewer repeats at the polymorphic Clock locus. Poly-Q Clock allele-frequency was homogenously distributed within the study population and did not exhibit any consistent environment-related variation. We further tested for effects of Clock genotype on reproductive success and survival, and found that females with fewer poly-Q repeats produced a higher number of fledged offspring. Our results therefore suggest that (i) selection in females, but not in males, for fewer poly-Q repeats may be operating, (ii) the across-population associations in timing of breeding involving this locus could be linked to variation within populations, and (iii) the Clock gene might be involved in local adaptation to seasonal environments.

Advanced breeding dates in relation to recent climate warming in a Mediterranean montane population of Blue Tits Cyanistes caeruleus

Trends in the onset of breeding, clutch size and numbers of hatchlings and fledglings are examined for a Mediterranean montane population of Blue Tits (Cyanistes caeruleus) subject to recent warming in springtime monitored during 20 years. Blue Tits advanced their breeding dates in relation to mean air temperatures in April and, as a consequence, laid larger clutches. However, increases in the numbers of hatchlings and fledged young over time were not statistically significant after accounting for variables of influence. The entire breeding season seems to have been displaced towards earlier dates by adjusting breeding time to increased temperatures in prebreeding time, to which Blue Tits have been more responsive than Pied Flycatchers (Ficedula hypoleuca) in the same area. The alternative hypothesis, that interference competition with Pied Flycatchers for nestboxes and caterpillars, the main common food base of nestlings, has been the driving force behind the advancement of laying of the Blue Tit population, was not supported. However, the significant advance of breeding dates in Blue Tits has not been sufficient to overcome the precipitous decline in reproductive fitness with the advancement of the season.

Egg patterning is not a reliable indicator of intraspecific brood parasitism in the blue tit Cyanistes caeruleus

A recent study reported the incidence of intraspecific brood parasitism (IBP) in the blue tit, based on differences in pigmentation between eggs within clutches and the appearance of multiple eggs within a nest in a single day. Here we present data from another population of blue tits Cyanistes caeruleus in which we show that such evidence is not necessarily indicative of IBP. As in many other studies of birds, we found that the patterning and degree of pigmentation on eggs is individually highly characteristic of a female. As in the previous study of blue tits, a minority of clutches (about 3% of 904 clutches) contained one, two or three eggs that were distinctly different from the other eggs in the clutch, either in size or patterning, but not both. Molecular genetic analyses of parentage in a sample of these clutches with suspected IBP demonstrated unequivocally that all eggs within each clutch had in fact been laid by a single female, in all cases the social parent. We also found no evidence of IBP from paternity analyses of a sample of 3,529 offspring from 427 broods in this population, adding to previous evidence of the absence of IBP in this species. These findings cast doubt on the utility of purely observational approaches to provide evidence of intraspecific brood parasitism; our study suggests that egg morphology and records of laying patterns are inadequate to enable the identification of IBP.

Maternal Effects Contribute to the Superior Performance of Extra-Pair Offspring

The explanation for extra-pair mating in female birds remains poorly understood and contentious [1-7]. Several leading hypotheses propose that females benefit indirectly by enhancing the genetic quality of their offspring, through good genes or genetic compatibility effects [1, 8, 9]. Supporting this idea, recent studies have identified a range of fitness-related traits for which extra-pair offspring (EPO) are superior to their within-pair (WP) half-siblings [10-21]. However, such performance differences may result from nongenetic maternal effects if EPO are positioned earlier in the laying order and benefit from the advantages of earlier hatching [22, 23]. Here we show that EPO are larger, heavier, and more likely to fledge than their WP half-siblings in a population of blue tits, Cyanistes caeruleus. However, extra-pair paternity declined markedly with laying order, resulting in EPO generally hatching earlier. After correcting for variation in hatch time, none of the observed disparities between EPO and their WP half-siblings remained significant. These findings indicate that phenotypic comparisons between maternal half-siblings must consider potential hatching-order effects and suggest that the evidence for genetic benefits from extra-pair copulation may be less compelling than currently accepted. Moreover, the overrepresentation of EPO early in the laying order may help explain female extra-pair mating.

Local Individual Preferences for Nest Materials in a Passerine Bird

BackgroundVariation in the behavioural repertoire of animals is acquired by learning in a range of animal species. In nest-building birds, the assemblage of nest materials in an appropriate structure is often typical of a bird genus or species. Yet plasticity in the selection of nest materials may be beneficial because the nature and abundance of nest materials vary across habitats. Such plasticity can be learned, either individually or socially. In Corsican populations of blue tits Cyanistes caeruleus, females regularly add in their nests fragments of several species of aromatic plants during the whole breeding period. The selected plants represent a small fraction of the species present in the environment and have positive effects on nestlings.Methodology/Principal FindingsWe investigated spatiotemporal variations of this behaviour to test whether the aromatic plant species composition in nests depends on 1) plant availability in territories, 2) female experience or 3) female identity. Our results indicate that territory plays a very marginal role in the aromatic plant species composition of nests. Female experience is not related to a change in nest plant composition. Actually, this composition clearly depends on female identity, i.e. results from individual preferences which, furthermore, are repeatable both within and across years. A puzzling fact is the strong difference in plant species composition of nests across distinct study plots.Conclusions/SignificanceThis study demonstrates that plant species composition of nests results from individual preferences that are homogeneous within study plots. We propose several hypotheses to interpret this pattern of spatial variation before discussing them in the light of preliminary results. As a conclusion, we cannot exclude the possibility of social transmission of individual preferences for aromatic plants. This is an exciting perspective for further work in birds, where nest construction behaviour has classically been considered as a stereotypic behaviour.

Condition‐dependent genetic benefits of extrapair fertilization in female blue tits Cyanistes caeruleus

In many socially monogamous birds, both partners perform extrapair copulations (EPC). As this behaviour potentially inflicts direct costs on females, they are currently hypothesized to search for genetic benefits for descendants, either as 'good' or 'complementary' genes. Although these hypotheses have found some support, several studies failed to find any beneficial consequence of EPC, and whether this behaviour is adaptive to females is subject to discussion. Here, we test these two hypotheses in a natural population of blue tits by accounting for the effect of most parameters known to potentially affect extrapair fertilization. Results suggest that female body mass affected the type of extrapair genetic benefits obtained. Heavy females obtained extrapair fertilizations when their social male was of low quality (as reflected by sexual display) and produced larger extrapair than within-pair chicks. Lean females obtained extrapair fertilizations when their social mate was genetically similar, thereby producing more heterozygous extrapair chicks. Our results suggest that mating patterns may be condition-dependent.

Long-term effects of nestling condition on blood parasite resistance in blue tits (Cyanistes caeruleus)

Little is know about whether the conditions experienced during ontogeny affect resistance to parasites later in life in wild animals. Here, we used a population of blue tits ( Cyanistes caeruleus (L., 1758)) to investigate to what extent conditions experienced during the nestling stage could explain the ability to control blood parasite ( Haemoproteus majoris (Laveran, 1902)) infections 1 year later. Although short-term effects may be expected based on the well-known sensitivity of the immune system to current conditions, it is less known whether this translates into a permanent alteration of parasite resistance. By relating nestling condition (measured as body mass or size-corrected body mass) at the beginning and end of the nestling stage to parasite intensity of individual recruiting birds 1 year later, we indeed found significant positive effects of both early and late nestling condition on the long-term ability to control parasites. These results indicate that parasites may be important as a mechanistic explanation for the trade-off between number and quality of offspring. It further points to the potential relevance for maternal effects in host–parasite interactions.

The Abundance and Suitability of Tree Cavities and Their Impact on Hole-Nesting Bird Populations in Beech Forests of NE Iberian Peninsula

The availability and suitability of tree cavities for hole-nesting birds were surveyed in three beech wood types (mature, cleared and coppice forests) in the North east of the Iberian Peninsula. We sampled the occupation of cavities and the abundance of hole-nesting birds. We also tested experimentally with tit nest boxes whether the lack of suitable nest-holes may limit the abundance of secondary cavity-nesters. We surveyed hole-nesting birds before and after nest box provision. Trunk and branch cavities (25.9%) were significantly more abundant in mature woods, and are correlated with the density of secondary occupants. Stump and root cavities (74.1%) were more abundant in coppice forests. Shortage of big diameter's (> 45 cm DBH) and good bearing trees explained the lack of cavities in managed forests. Only small proportion of available cavities was used by birds (5.5%). All occupied cavities were placed in trunk (5.5%) and presented smaller diameter entrances than the whole availability of cavities. Nest boxes occupation rate was higher in the plots where suitable nest holes were scarce (managed woods), and consequently it brought an increase on both Great Tit and Blue Tit populations. These two species populations were favoured from the next breeding season after the provision of nest boxes, but not in mature stands nor in control sites (with no nest boxes). Therefore, results show that suitability of cavities rather than availability determines secondary hole-nesting bird abundance in managed forests.