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Copulations outside the pair bond are common among socially monogamous birds, but males differ in their extrapair siring success. A large body of research has focused on the ultimate causes and consequences of this variation, but the behavioural mechanisms underlying extrapair siring success remain poorly understood. Previous work showed that male songbirds that start singing earlier at dawn sire more extrapair offspring, suggesting that early morning activity influences the likelihood of obtaining extrapair copulations. However, this pattern may be confounded by male age, because adult males typically start singing earlier in the morning and have higher extrapair success than yearling males. We used data from an automated monitoring system to examine whether males' start and end of daily activity, that is, the time of exiting their roosting cavity in the morning and of entering their roost in the evening, relates to patterns of extrapair paternity in a population of blue tits, Cyanistes caeruleus. In line with previous work, we found that adult males emerged earlier from their roosting nestbox and had higher extrapair siring success than yearling males, whereas paternity loss was unaffected by age class and timing of activity. However, the effect of early emergence on paternity gain was not simply due to age, because earlier emerging males had higher extrapair success even after controlling for variation in age class. Males that ended their activity earlier in the evening were also more likely to sire extrapair offspring, independently of their age class. We discuss potential mechanisms that can explain how the timing of activity influences extrapair mating success and highlight the need for experimental manipulation of the timing of activity to test the causality of the reported relationship. [ABSTRACT FROM AUTHOR]

Leaving the nest is a key transition in the life of altricial birds, whereby fledging decisions should depend on multiple factors, including the risk of predation. High postfledging predation risk may favour fledging at a more advanced stage of development, if more developed fledglings are better at escaping predation, or together with others. While comparative studies have highlighted the role of predation risk for between-species variation in the timing of fledging, drivers of within-species variation in fledging behaviour remain largely unknown. We presented owl models near blue tit, Cyanistes caeruleus, nests during the first half of the day throughout the fledging period to simulate an increased risk of postfledging predation. Using an automated monitoring system, we then recorded the precise fledging times of 595 nestlings from 105 nests (52 predator-treated, 53 control nests). Contrary to our predictions, the predator presentations did not affect the age at which nestlings fledged, the time of day of fledging or other aspects of fledging behaviour. The tendency to fledge together with siblings was affected, but the effect was in the opposite direction to that expected, with nestlings exposed to the predator treatment being more likely to fledge alone. Parents visited predator-treated nests less often, but this effect diminished over the course of the morning. We suggest several explanations for why the behavioural responses to the predation risk manipulation were generally limited. • In altricial birds, the duration of the nestling period varies substantially. • Time of fledging may depend on relative risk of pre- and postfledging predation. • We presented owl models near blue tit nests to simulate increased predation risk. • The treatment did not affect the age or time of day at which nestlings fledged. • The treatment did affect other aspects of fledging and parental behaviour. [ABSTRACT FROM AUTHOR]

In altricial birds, leaving the nest is a key life history transition associated with a high risk of mortality. Studies of numerous species have shown that young typically fledge early in the day, and it is often asserted that early fledging is important for survival; however, evidence for this hypothesis is limited. We used an automated monitoring system to obtain precise fledging times of 1582 young blue tits, Cyanistes caeruleus , from 230 nests. As expected, nestlings primarily fledged early in the day (84% fledged before midday). However, we found no evidence that early fledging was associated with higher postfledging survival (i.e. recorded the following autumn or later). We propose two alternative explanations for the morning peak in fledging. Hypothesis 1 is that some offspring reach a developmental threshold for fledging overnight and leave the nest early the next day. This is supported by our observation that offspring that fledged early in the day tended to be more developed than those that fledged later in the day, that is, they were older and had a high body mass (measured at 14 days of age) for their fledging age. Hypothesis 2 is that the timing of fledging is related to parental provisioning behaviour. Our results do not support this hypothesis. Parents reduced their nest visit rate over the course of the day, but offspring did not fledge earlier when their parents decreased their visit rate more strongly with time of day. In conclusion, our results do not support the notion that the time of fledging affects survival but suggest a link with nestling development. • In altricial birds, nestlings typically fledge early in the day. • This is often assumed to improve survival, but with little supporting evidence. • We monitored the precise fledging times of 1582 blue tits from 230 nests. • Fledging time was not associated with the probability of local survival. • Instead, fledging time was related to the developmental stage of nestlings. [ABSTRACT FROM AUTHOR]

An increase in the perceived risk of predation triggers many behavioural changes in prey species, which can have consequences for their reproductive success. Perceived predation risk may also influence investment in extrapair activities and, as a result, the frequency of extrapair paternity (EPP), but this possibility remains largely untested. Here we report on a study of a small passerine bird, the blue tit, Cyanistes caeruleus , in which we experimentally manipulated perceived predation risk by intermittently broadcasting predator calls throughout the breeding season. We found no evidence that the treatment affected two behavioural indices of extrapair activity (extrabox visits and the time of emergence from the nestbox in the morning during the fertile period) or the rate of EPP itself. The treatment also had no significant effect on clutch size, hatching success or most reproductive behaviours. However, nests in the predator playback treatment produced more fledglings, which was mainly due to a lower frequency of complete brood mortality. We discuss potential explanations for this finding, as well as for the lack of evidence for other effects of the predator playback treatment on blue tit reproductive behaviour. Several measures of reproductive performance suggest that the year in which the experiment took place was an unusually poor one and further work is therefore needed to assess the generality of our findings. • Perceived predation risk has been shown to affect breeding behaviour and success. • Perceived predation risk may similarly affect extrapair behaviour and success. • We played predator calls to a population of blue tits throughout the breeding period. • We found no significant effects on breeding behaviour or extrapair activity/paternity. • Nests exposed to predator calls had a lower incidence of complete brood mortality. [ABSTRACT FROM AUTHOR]

In species with parental care, offspring often solicit food through elaborate begging displays. Begging is thought to be a reflection of offspring need, but short-term fluctuations in begging do not necessarily provide reliable information. Parents thus have to adjust their provisioning behaviour to the changing demands of their offspring, while minimizing the costs of responding to unreliable information. We conducted two experiments with blue tits, Cyanistes caeruleus , in which we tested how parents respond to short-term and long-term changes in begging intensity. In the first experiment we investigated how parents respond to increased begging during a single nest visit. In the second experiment we investigated how parents respond to increased begging during every nest visit for 1 h. Parents did not return faster to the nest during the short-term manipulation. Contrary to our expectations, however, parents also did not return faster to the nest in response to long-term manipulation. Instead, parents spent more time in the nestbox during both the short-term and the long-term manipulation. Our results highlight that the general pattern of a positive parental response to increased begging may not be a universal one. Comparisons across species and populations may help reveal the factors underlying variation in parental responsiveness to begging. [ABSTRACT FROM AUTHOR]

The disruption of daily rhythms is one of the most studied ecological consequences of light pollution. Previous work showed that several songbird species initiated dawn song earlier in areas with light pollution. However, the mechanisms underlying this shift are still unknown. Individuals may immediately adjust their timing of singing to the presence of artificial light (behavioural plasticity), but the observed effect may also be due to phenotype-dependent habitat choice, effects of conditions during early life or micro-evolution. The main aim of this study was to experimentally investigate how males of four common passerine species respond to day-to-day variation in the presence of artificial night lighting in terms of the timing of singing. During two consecutive breeding seasons, we manipulated the presence of light throughout the night in a cyclic fashion in several naturally undisturbed forest patches. We show that individuals of all four species immediately and reversibly adjusted their onset of dawn singing in response to artificial light. The effect was strongest in the European robin, but relatively small in the blue tit, the great tit and the blackbird. The effect in the latter two species was smaller than expected from the correlational studies. This may be coincidence (small sample size of this study), but it could also indicate that there are longer-term effects of living in light-polluted urban areas on timing of dawn singing, or that birds use compensatory behaviours such as light avoidance. We found no evidence that our light treatment had carryover effects into the subsequent dark period, but robins progressively advanced their dawn singing during the light treatment. [ABSTRACT FROM AUTHOR]

Although capture, handling and marking of birds as well as taking samples from them are ubiquitous and, in most cases, unavoidable procedures in ornithological research, their immediate effects on the individuals remain largely unstudied. Here, we present data over 3 years from a long-term field study on the breeding biology of the blue tit. Parents were captured at the nest when feeding 9–11-day-old young. For all birds, we measured the time of their first visit to the nest after capture and could thus establish their latency of return to the nest. After capture, parents stayed away a surprisingly long time (average 4.2 h, up to 18 h) and nests were not visited by either parent for a duration that almost never occurred under natural conditions. Parental return latencies were strongly associated with previous captures. Birds caught, marked and sampled previously returned on average 4.4 h earlier than new birds. Still these birds took on average 1.9 h to return. Thus, capture itself can have strong effects on immediate behaviour. Once the birds returned to the nest, the time between nest visits was similar to that observed before capture, indicating that birds resumed normal feeding activities. Return latencies of parents and the time nests were left alone had no long-term effects on offspring or breeding success. We discuss possible causes of delayed parental return and methodological implications. [ABSTRACT FROM AUTHOR]

Associations in mixed-species foraging groups are common in animals, yet have rarely been explored in the context of collective behaviour. Despite many investigations into the social and ecological conditions under which individuals should form groups, we still know little about the specific behavioural rules that individuals adopt in these contexts, or whether these can be generalized to heterospecifics. Here, we studied collective behaviour in flocks in a community of five species of woodland passerine birds. We adopted an automated data collection protocol, involving visits by RFID-tagged birds to feeding stations equipped with antennae, over two winters, recording 91 576 feeding events by 1904 individuals. We demonstrated highly synchronized feeding behaviour within patches, with birds moving towards areas of the patch with the largest proportion of the flock. Using a model of collective decision making, we then explored the underlying decision rule birds may be using when foraging in mixed-species flocks. The model tested whether birds used a different decision rule for conspecifics and heterospecifics, and whether the rules used by individuals of different species varied. We found that species differed in their response to the distribution of conspecifics and heterospecifics across foraging patches. However, simulating decisions using the different rules, which reproduced our data well, suggested that the outcome of using different decision rules by each species resulted in qualitatively similar overall patterns of movement. It is possible that the decision rules each species uses may be adjusted to variation in mean species abundance in order for individuals to maintain the same overall flock-level response. This is likely to be important for maintaining coordinated behaviour across species, and to result in quick and adaptive flock responses to food resources that are patchily distributed in space and time. [ABSTRACT FROM AUTHOR]

Offspring provisioning and nest defence are important forms of parental care. In birds, parents that engage in nest defence behaviour have to interrupt nestling provisioning with potentially harmful consequences for offspring growth and condition. To maximize fitness, parents should trade off optimal levels of offspring provisioning versus nest defence, but relatively little is known about how parents allocate their time between these two activities and how parental decisions to postpone provisioning vary as a function of the intensity of nest predation risk. We found that pairs of blue tits, Cyanistes caeruleus, adjusted parental care behaviours according to perceived immediate risk levels by switching from offspring provisioning to nest defence. In the presence of a direct nest predation threat, parents interrupted offspring provisioning for longer than in response to a novel object close to the nest, but still gradually resumed provisioning activity, probably because of a decrease in perceived predation risk over time. By increasing their provisioning effort once the immediate threat had diminished, parents compensated at least partly for the lost provisioning opportunities during high-risk situations. Hence, by adaptively adjusting the temporal trade-off between different parental care behaviours according to the perceived risk, blue tits are presumably able to mitigate potential negative long-term consequences of interruptions in provisioning during high-risk situations for offspring growth and condition. [ABSTRACT FROM AUTHOR]

Blue tits are famous for the ‘milk bottle’ innovation, which emerged at numerous sites across Britain in the early 20th century. However, overall we still know little about the factors that foster or hinder the spread of innovations, or of the impact of individual differences in behaviour on social transmission. We used a two-action and control experimental design to study the diffusion of innovation in groups of wild-caught blue tits, and found strong evidence that individuals can use social learning to acquire novel foraging skills. We then measured six individual characteristics, including innovative problem solving, to investigate potential correlates of individual social-learning tendency. Consistent with a hypothesis of common mechanisms underlying both processes, we found evidence for a relationship between social learning and innovativeness. In addition, we observed significant age- and sex-biased social learning, with juvenile females twice as likely to acquire the novel skill as other birds. Social learning was also more likely in subordinate males than dominant males. Our results identify individual variation and transmission biases that have potential implications for the diffusion of innovations in natural populations. [ABSTRACT FROM AUTHOR]

Social learning is widely used among vertebrates to acquire information about a variable environment. We conducted a study of social learning in the wild which involved cross-fostering eggs of blue tits, Cyanistes caeruleus, to nests of great tits, Parus major, and vice versa. This allowed us to quantify the consequences of being reared in a different social context but in an environment otherwise natural to the birds. We studied choice of nest site by offering to the local recruits either a small or a large nestbox. Most blue tits bred in small nestboxes, whereas most great tits used the large boxes. Size of the natal nestbox affected subsequent box choice. In addition, in blue tits, more cross-fostered birds than controls nested in large nestboxes, with an opposite result for cross-fostered great tits. Apparently, as a consequence of sexual misimprinting on their foster parents, the cross-fostered young used members of the foster species as models for subsequent nest site choice. Such social copying may apply broadly to other types of behaviours and not only to the choice of nest site. This study demonstrates both vertical and horizontal transmission of nest site preference of two vertebrates in the wild. Future studies should try to find out how animals balance the use of personal experience with the information socially acquired. [Copyright &y& Elsevier]

Various studies have reported that extrapair young outperform their within-pair half-siblings in fitness-relevant traits, suggesting indirect benefits of extrapair copulations for females. Recent studies, however, suggest that potential confounding maternal effects such as laying and hatching order may have been overlooked. In this study on blue tits, Cyanistes caeruleus, we investigated fledging behaviour, a potentially fitness-relevant trait, in relation to the paternity status of the offspring. We tested whether extrapair young differed from within-pair young in fledging order per se and after we controlled for hatching order, a potential confounding maternal effect. We found that male, but not female, extrapair young fledged earlier than their within-pair nestmates. This effect was partly mediated by the higher body mass of extrapair young, which is a major determinant of fledging order independent of paternity status. However, even when we controlled for body mass, a correlate of hatching order, male extrapair young still fledged earlier than their same-sex half-siblings, indicating that male extrapair nestlings may be at an advantage over their siblings. [Copyright &y& Elsevier]

Social and intrasexual competition for access to food, territory and reproduction is a major selection force acting on male phenotypes. In contrast, its evolutionary consequences for female phenotypes, especially female ornamentation, have been overlooked. Because fighting is costly for individuals, physical indicators of status that are correlated with aggressiveness or fighting ability are predicted to evolve. Under the badge of status hypothesis, individuals are predicted to attack unknown rivals that present signals of similar size or intensity more vigorously than dissimilar rivals. We used blue tits, Cyanistes caeruleus, to test whether UV/blue and yellow coloration mediates female aggression. We exposed territorial birds to two female blue tit decoys during nest building: one had a UV/blue crown with an enhanced UV signal (UV+) and the other had a reduced UV signal (UV−). We found that resident females with higher UV signal more often landed on the cage containing the UV+ decoys whereas females with a lower UV signal more often landed on the cage containing the UV− decoys. This result suggests that UV/blue crown coloration is a badge of status and supports the hypothesis that female–female competition can generate or maintain female ornamentation. Resident females with darker yellow chests also attacked the decoys with greater intensity. Previous studies suggest that brighter yellow females invest more in reproduction and consequently could be more sexually attractive. So, this last result may be explained by a higher motivation of darker yellow females or a trade-off between aggressiveness and female investment in reproduction. [Copyright &y& Elsevier]

The study of the genetic consequences of dispersal is a central topic in evolutionary, conservation and behavioural research. However, few studies have simultaneously considered dispersal movements from marked individuals and contemporary patterns of gene flow. We analysed the link between dispersal behaviour and gene flow in four populations of blue tits with different degrees of connectivity. For this purpose, we monitored four breeding patches and used genotypic and capture–mark–recapture data to study the genetic consequences of dispersal at different spatial scales. Data on natal dispersal movements revealed that both males and females dispersed less than expected under a random pattern of settlement at the two large spatial scales considered: the whole study area and the two main localities. However, natal dispersal distance was lower than expected under random settlement within natal patches in males whereas an opposite pattern was found for females. Accordingly, microsatellite data revealed limited gene flow between the localities studied and an isolation-by-distance pattern of genetic structure that was particularly strong at the large spatial scale (i.e. considering geographically distant breeding patches). Finally, the strong male philopatry was reflected by a stronger genetic structure and a lower admixed ancestry in this sex. Overall, we found evidence that restricted dispersal and fragmentation may have both contributed to reduce interpopulation gene flow at different spatial scales in a forest species and that there is concordance between genetic studies and those based on capture–mark–recapture. [Copyright &y& Elsevier]

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. 4.8h 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 15min 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. [ABSTRACT FROM AUTHOR]

To investigate the ecological significance of personality, researchers generally measure behavioural traits in captivity. Whether behaviour in captivity is analogous to behaviour in the wild, however, is seldom tested. We compared individual behaviour between captivity and the wild in blue tits, Cyanistes caeruleus. Over two winters, 125 blue tits were briefly brought into captivity to measure exploratory tendency and neophobia using variants of standard personality assays. Each was then released, fitted with a passive integrated transponder. Using an electronic monitoring system, we then recorded individuals'' use of feeders as they foraged in the wild. We used variation in the discovery of new feeders to score 91 birds for exploratory tendency in the wild. At eight permanent feeding stations, 78 birds were assayed for neophobia in the wild. Behavioural variation in the captive personality trials was independent of permanent (e.g. sex) and nonpermanent (e.g. condition or weather) sources of between-individual variation at capture. Individual exploratory tendency and neophobia were consistent and repeatable in captivity, and analogous traits were repeatable in the wild; thus all constituted personality traits in the blue tit. Exploratory tendency and neophobia were not correlated with each other, in either the captive or the wild context. Therefore they are independent traits in blue tits, in contrast to many species. Finally, exploratory tendency and neophobia measured in captivity positively predicted the analogous traits measured in the wild. Reflecting differences in the use of feeding opportunities, personality in captivity therefore revealed relevant differences in foraging behaviour between individuals. [Copyright &y& Elsevier]

Laboratory studies suggest that young birds prefer to learn conspecific songs over songs from heterospecifics. However, field studies have shown that many species copy heterospecific song. We cross-fostered pied flycatchers, Ficedula hypoleuca, to nests of blue tits, Cyanistes caeruleus, and great tits, Parus major, in the field. Recent studies have shown that species recognition is genetically determined in pied flycatchers. However, we found that most cross-fostered males included song types from the foster species in their repertoire, with an even stronger effect if reared with heterospecific nestmates. Furthermore, in cross-fostered males frequency range and syllable number per strophe were intermediate between control flycatchers and the foster species. The results contrast with those obtained when blue tits and great tits are cross-fostered in the field; the tits not only adopt songs from the foster species but, in contrast to the flycatchers, they also become sexually imprinted on it. Vocal mimicry may include a cost of reduced species recognition, but this cost may be minimized by also keeping a large proportion of conspecific song in the repertoire. Our finding highlights the importance of early experience for song acquisition, showing that altered social-rearing conditions may cause a mixed choice of song tutors. Depending on different proximate mechanisms, song used in mate choice may more readily respond to environmental change than mate choice itself. Changes in song by learning may thus serve as an essential first step in hybridization and speciation processes. [Copyright &y& Elsevier]

In resource defence mating systems, males monopolize a resource that is of primary importance for breeding females. For secondary cavity nesters, the availability of suitable nesting sites is important in determining the strength of intrasexual competition, whereby phenotypic and behavioural traits will be favoured that enable individuals to gain access to these sites. The traits that are important in male competition may additionally affect mate choice decisions and a female''s investment in the current brood. In a field study on blue tits, Cyanistes caeruleus, we increased intrasexual competition by experimentally limiting nest sites in experimental plots and compared these plots to control plots. Birds breeding in experimental plots did not differ phenotypically from birds in control plots. However, females that bred in the nest site-limited plots fed their offspring at a higher rate than control females. This result indicates that increased competition for limited resources led to more investment in current reproduction, either because successful females were of higher intrinsic quality or because they adjusted their investment in relation to superior territory or male characteristics. [Copyright &y& Elsevier]

For altricial birds, detailed studies of parental care include egg incubation, brooding and chick feeding, all of them being crucial to offspring survival. Few studies have explored nest building and maintenance from this perspective, although the nest is the first environment experienced by hatchlings. On Corsica, blue tits, Cyanistes caeruleus, incorporate fresh fragments of several species of aromatic plants in the nest cup throughout the nesting period, and replenish the nest with fresh fragments of the same plant species quickly after experimental removal. In this study, we experimentally tested whether aromatic plants used by blue tits affect the growth and condition of nestlings. Because we expected the effects of plants to depend on environmental conditions, we tested this hypothesis both in enlarged and in control broods. Aromatic plants positively affected chick mass gain in enlarged broods. Chicks in nests containing aromatic plants also had higher haematocrit levels. In addition, in 1 of the 2 study years, feathers developed faster in aromatic-treated nests than in nests where aromatic plants had been replaced by a neutral nest material (moss). However, no significant effect of aromatic plants on chick body size at fledging was found. We propose several hypotheses on the proximal mechanisms whereby aromatic plants affect chick growth and condition. [Copyright &y& Elsevier]

In socially monogamous species with a resource-based mating system, mate choice and territory choice cannot easily be separated. We studied the occurrence and consequences of postbreeding dispersal and divorce in a population of blue tits breeding in nestboxes. Dispersal was defined relative to the spatial position of territories estimated as Dirichlet tiles. Although more than 80% of males and females changed nestbox between breeding seasons, only 3% of males and 25% of females moved to a new territory. Settlement following postbreeding dispersal was driven by habitat quality: dispersing females ended up in territories with higher clutch size expectancy. Dispersed females (both widowed and divorced) reared more fledglings than resident ones, suggesting that dispersal is adaptive. Our results suggest that even at relatively small spatial scales and in continuous habitats, postbreeding dispersal may be driven by habitat quality gradients. Across all years, 53% of surviving pairs divorced. We assessed the effects of mate change independently of territory quality, by restricting analyses to resident individuals that, after divorce, shared a part of their former territory or settled in its close vicinity. Reproductive success increased for males after divorce, but decreased for females. It did not change for reunited pairs in subsequent seasons. Paternity loss or gain through extrapair copulations, and hence overall siring success, did not differ between divorced and reunited males, either before divorce or pair re-formation, or in the year after. After divorce, males but not females paired with larger, presumably higher-quality partners. The results support the better option hypothesis and suggest that males, but not females, may benefit from divorce. However, our results are also compatible with the alternative hypothesis that divorce is driven by female–female competition, whereby a dominant female evicts the former mate. [Copyright &y& Elsevier]

Species recognition may be learned through imprinting early in life. Imprinting has normally been studied under highly unnatural conditions in the laboratory. We tested whether species recognition mediated through imprinting is individually modifiable in a field setting where great tits, Parus major, have been artificially cross-fostered to blue tits, Cyanistes caeruleus, and vice versa. We have shown previously that cross-fostered birds have deviant species recognition, in terms of both mate choice and aggressive responses towards rivals. Natural interactions among conspecifics and heterospecifics are common in these populations, potentially giving cross-fostered birds scope for relearning their species identity. We tested whether species recognition may change with experience during adulthood by comparing the aggressive response of cross-fostered birds and controls of different ages towards caged intruders. When breeding, cross-fostered birds responded aggressively towards same-sex individuals of their heterospecific foster species, while unmanipulated controls responded mainly towards conspecifics. We found that the aggressive response decreased with age at similar rates in both treatments and in both species. Moreover, there was no effect of age on the relative response towards conspecifics and heterospecifics in either treatment. Hence, we found no evidence that the species recognition behaviour towards same-sex individuals is shifted towards conspecifics with age in interspecifically cross-fostered birds. We conclude that species recognition is irreversible once it has been established in free-living great tits and blue tits. This is the first study to investigate the stability of species recognition in the field. [Copyright &y& Elsevier]

Despite the fact that in many bird species offspring are provisioned by two parents, few studies to date have examined the implications of biparental care for offspring solicitation behaviour. Male and female parents can differ in their potential value to individual offspring if they follow different allocation rules and/or have different provisioning rates. If such differences occur, offspring should use different rules when soliciting to the male and female parent. This study looked at how the begging behaviour of nestling blue tits, Cyanistes caeruleus, is influenced by their hunger, size and by the sex of the provisioning adult. Nestling hunger was manipulated across size ranks, using periods of hand feeding or food deprivation. While nestling hunger influenced all aspects of nestling begging behaviour, nestling size and the sex of the provisioning adult only affected the position of nestlings in the nest cup. When hungry, nestlings moved closer to the male parent and the largest nestlings in a brood primarily obtained the closest positions. This may be the result of offspring responding to a difference between the sexes in parental food allocation rules. [Copyright &y& Elsevier]

Research on the costs of nest reuse is central to understanding the population ecology and evolution of cavity-nesting birds. We explored the consequences of nest reuse by offering blue tits three types of nestboxes in which to breed: nestboxes with an old nest (O), empty nestboxes (E) and nestboxes with an old nest fumigated with insecticide (F). The experimental groups differed in ectoparasitism level: the O nestboxes had the most and the F nestboxes the fewest ectoparasites. Blue tits using nestboxes that contained old nests from the previous season paid a cost caused by the presence of nest ectoparasites: both reproductive success and female body mass at the end of the nestling period were reduced. Haematozoan infections in females also increased with the level of ectoparasitism. The costs of nest reuse would be reduced in areas and/or seasons with few ectoparasites, as shown by the results from the group with fumigated old nests. [Copyright &y& Elsevier]