Individuals differ. While seemingly trivial, this insight has nevertheless led to paradigm shifts, as three key fields of organismal biology have seen marked changes in key concepts over the past few decades. In animal behaviour, it has become increasingly recognised that behavioural differences among individuals can be stable over time and across contexts, giving rise to the concept of animal personalities. In ecology, attention has similarly shifted towards variation in the ecological niches occupied by species, populations and individuals, giving rise to the concept of niche specialisation or individual niche variation. In evolutionary biology, where individual variation has always been central, there is a growing awareness of the complex and dynamic ways in which individuals interact with the environment to produce unique phenotypes. Additionally, recent theoretical and empirical research suggests that fitness landscapes are not only complex, with multiple fitness peaks, but might even be more accurately described as constantly shifting 'fitness seascapes', where the fitness peak that an individual can reach - whether local or global - depends on its genotype and its interaction with the environment. Moreover, the previous distinction between ecological and evolutionary timescales is being replaced by a more integrative view that recognises that evolution can occur on ecological timeframes. These shifting perspectives over the past two decades underscore the need for a more integrated conceptual framework that transcends disciplines. While in behaviour, ecology and evolution, the concept of individualisation has contributed to major scientific progress, sufficient cross-fertilisation is still lacking. Here, we propose a new conceptual unification: the individualised niche. By merging the niche concept with the fitness concept, new explanatory power for both ecological and evolutionary processes emerges.

Despite growing awareness of the importance of researcher diversity, barriers to inclusion and equity persist in science and at academic conferences. As hosts of the 37th International Ethological Congress, "Behaviour 2023", we studied gender disparities that unfold during question-and-answer (Q&A) sessions using observational and experimental behavioural data and surveys. We further used the surveys to investigate broader equity, diversity and inclusivity (EDI) issues at conferences in general. Attendees perceived as women asked fewer questions than those perceived as men because they raised their hands less often to ask questions, and not because they were chosen less often by the session host. Self-reports indicated that self-identified women felt more comfortable asking questions when their own gender was represented (in the audience, by the speaker, and/or by the host) and when the setting was smaller. However, this pattern was not reflected in the observational data as perceived women asked fewer questions regardless of the situation. We report potential reasons why women asked fewer questions using survey data, and experimentally tested whether we could reduce gender disparity in question-asking. Our results indicate that session hosts cannot mitigate the gender disparity in question-asking by actively selecting perceived women to start the Q&A session. We addressed further inclusivity barriers of underrepresented minorities beyond gender in a post-congress survey, which showed that underrepresented minorities did not have a more positive or negative congress experience but did perceive EDI issues as more severe. We conclude by providing recommendations for organising more inclusive scientific events.

Although variation in effect sizes and predicted values among studies of similar phenomena is inevitable, such variation far exceeds what might be produced by sampling error alone. One possible explanation for variation among results is differences among researchers in the decisions they make regarding statistical analyses. A growing array of studies has explored this analytical variability in different fields and has found substantial variability among results despite analysts having the same data and research question. Many of these studies have been in the social sciences, but one small “many analyst” study found similar variability in ecology. We expanded the scope of this prior work by implementing a large-scale empirical exploration of the variation in effect sizes and model predictions generated by the analytical decisions of different researchers in ecology and evolutionary biology. We used two unpublished datasets, one from evolutionary ecology (blue tit, Cyanistes caeruleus, to compare sibling number and nestling growth) and one from conservation ecology (Eucalyptus, to compare grass cover and tree seedling recruitment). The project leaders recruited 174 analyst teams, comprising 246 analysts, to investigate the answers to prespecified research questions. Analyses conducted by these teams yielded 141 usable effects (compatible with our meta-analyses and with all necessary information provided) for the blue tit dataset, and 85 usable effects for the Eucalyptus dataset. We found substantial heterogeneity among results for both datasets, although the patterns of variation differed between them. For the blue tit analyses, the average effect was convincingly negative, with less growth for nestlings living with more siblings, but there was near continuous variation in effect size from large negative effects to effects near zero, and even effects crossing the traditional threshold of statistical significance in the opposite direction. In contrast, the average relationship between grass cover and Eucalyptus seedling number was only slightly negative and not convincingly different from zero, and most effects ranged from weakly negative to weakly positive, with about a third of effects crossing the traditional threshold of significance in one direction or the other. However, there were also several striking outliers in the Eucalyptus dataset, with effects far from zero. For both datasets, we found substantial variation in the variable selection and random effects structures among analyses, as well as in the ratings of the analytical methods by peer reviewers, but we found no strong relationship between any of these and deviation from the meta-analytic mean. In other words, analyses with results that were far from the mean were no more or less likely to have dissimilar variable sets, use random effects in their models, or receive poor peer reviews than those analyses that found results that were close to the mean. The existence of substantial variability among analysis outcomes raises important questions about how ecologists and evolutionary biologists should interpret published results, and how they should conduct analyses in the future.

Olfactory kin discrimination occurs in many animal taxa, but its potential contribution to commonly observed kin-biased behaviours in birds has rarely been tested. In a previous odour discrimination experiment, 7-day-old blue tit, Cyanistes caeruleus, nestlings showed stronger begging responses to olfactory cues from conspecific nestlings from other nests than from their own. The authors hypothesized olfaction to mediate kin-biased sibling competition in nests with varying relatedness due to extrapair paternity. In the present study, we aimed to test this hypothesis. We therefore replicated the previous experiment with a crucial modification: we cross-fostered two nestlings of each brood the day after hatching. This allowed us to test for olfactory kin discrimination when nestmates differed in relatedness (due to being cross-fostered) but not in familiarity. We ascertained the relatedness of nestlings using genetic parentage assignment. We preregistered our research plan with the Open Science Framework (OSF) to increase research transparency and reduce researcher degrees of freedom. We found that nestlings did not differ in their begging responses to related versus unrelated (cross-fostered) nestmates' odours, indicating that nestlings do not discriminate kin from nonkin odours when these are both familiar. Moreover, in an exploratory analysis, cross-fostered nestlings did not differ in survival or size from their non-cross-fostered nestmates shortly before fledging, indicating that the presence of unrelated individuals did not affect the distribution of parental care in the nest. In conclusion, we found no evidence for olfactory kin discrimination in begging blue tit nestlings. (c) 2025 The Authors. Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour. This is an open access article under the CC BY license (http://creativecommons.org/licenses/ by/4.0/).

Extra-pair paternity is prevalent in socially monogamous bird species with biparental care. Male extra-pair matings may coincide with paternal care provisioned to within-pair offspring. This may lead to a trade-off between obtaining additional fertilizations and securing offspring growth and survival through paternal care. In this pre-registered study, we manipulated the social environment of zebra finches to investigate how males trade off extra-pair mating versus providing paternal care. We compared paternal care provision between a social environment where two pairs bred together in a cage-resulting in an opportunity for extra-pair mating (Double-pair group)-to one with single breeding pairs (Single-pair group). We additionally measured plasma testosterone and corticosterone to identify hormonal correlates of male behavioral responses. To further increase the opportunity for extra-pair mating for the focal males from the Double-pair group we removed the male of the non-focal pair during chick rearing by the focal males. Contrary to our predictions, Double-pair males incubated more than Single-pair males. While we found substantial extra-pair paternity in the Double-pair group after removal of the non-focal males, male brood provisioning, chick growth and survival, and testosterone levels were not affected by the experimental increase in male extra-pair mating opportunity. Corticosterone levels were higher in Single-pair males between the first and replacement clutch. Refuting common assumptions, our findings provide no experimental evidence for a trade-off between extra-pair mating and paternal care. Males were able to pursue extra-pair fertilizations while they simultaneously secured the growth and survival of their within-pair offspring.

Aggressive behaviours are commonly expressed in the competition for limited resources and influence the survival and reproduction of individuals. However, because of a predominant focus on male-male competition and aggression, the importance of female aggression remains much less understood. In this study, we quantified both female and male aggressiveness in breeding blue tits, Cyanistes caeruleus, in response to same-and opposite-sex territorial intruders. We asked whether behavioural responses to same-sex and opposite-sex intruders were different. Using taxidermic mounts and song playback, we simulated territorial intrusions by female or male conspecifics during the nest-building and egg-laying stages of breeding blue tit pairs. First, females showed overall stronger aggressive responses than males. Furthermore, females were similarly aggressive towards female and male intruders, while males were less aggressive towards females than males. These observations demonstrate a sex-specific territorial response. Second, we found repeatable variation in the aggressive responses of both females and males. Remarkably, aggressive responses towards mounts of different sexes were strongly positively correlated. This result suggests that the aggressive responses of individuals in intrasexual and intersexual conflicts reflect the same underlying behavioural trait. We discuss possible functional explanations for our findings. Our findings highlight the importance of female aggression in a biparental territorial species, warranting further investigations into the ecological costs and benefits of individual differences in aggressiveness in both females and males. (c) 2025 The Author(s). Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour. This is an open access article under the CC BY license (http://creativecommons.org/licenses/ by/4.0/).

Preen oil, the secretion of the uropygial gland, may be an important source of body odour in birds. By characterizing the chemical composition of preen oil, we can describe the olfactory phenotypes of birds and investigate whether odours could have a function in sexual signalling or other chemical communication. Here we analysed the preen oil of a wild passerine, the European Pied Flycatcher Ficedula hypoleuca, to find out whether it holds socially relevant information. We sampled both the female and male of breeding pairs during nestling rearing to test for sex differences and within-pair similarity. We additionally sampled the females during incubation to test for changes across breeding stages and for individual repeatability of chemical profiles. Pair mates had similar chemical profiles in comparison with other breeding adults. Furthermore, we found evidence for sex differences and for changes across breeding stages. Notably, the preen oil of females was more diverse and more volatile than that of males, and the preen oil secreted by females during incubation was more volatile than that secreted during nestling rearing. However, we found no evidence for individual repeatability of chemical profiles across breeding stages in females. Our results point towards a function of preen oil in sexual signalling, although other functions should not be excluded. Our study is a first step towards understanding the role of odours in the social life of an important avian model species used in the study of mate choice and sexual selection.

In humans, being more socially integrated is associated with better physical and mental health and/or with lower mortality. This link between sociality and health may have ancient roots: sociality also predicts survival or reproduction in other mammals, such as rats, dolphins, and non-human primates. A key question, therefore, is which factors influence the degree of sociality over the life course. Longitudinal data can provide valuable insight into how environmental variability drives individual differences in sociality and associated outcomes. The first year of life-when long-lived mammals are the most reliant on others for nourishment and protection-is likely to play an important role in how individuals learn to integrate into groups. Using behavioral, demographic, and pedigree information on 376 wild capuchin monkeys (Cebus imitator) across 20 years, we address how changes in group composition influence spatial association. We further try to determine the extent to which early maternal social environments have downstream effects on sociality across the juvenile and (sub)adult stages. We find a positive effect of early maternal spatial association, where female infants whose mothers spent more time around others also later spent more time around others as juveniles and subadults. Our results also highlight the importance of kin availability and other aspects of group composition (e.g., group size) in dynamically influencing spatial association across developmental stages. We bring attention to the importance of-and difficulty in-determining the social versus genetic influences that parents have on offspring phenotypes. RESEARCH HIGHLIGHTS: Having more maternal kin (mother and siblings) is associated with spending more time near others across developmental stages in both male and female capuchins. Having more offspring as a subadult or adult female is additionally associated with spending more time near others. A mother's average sociality (time near others) is predictive of how social her daughters (but not sons) become as juveniles and subadults (a between-mother effect). Additional variation within sibling sets in this same maternal phenotype is not predictive of how social they become later relative to each other (no within-mother effect).

Animals plastically adjust their physiological and behavioural phenotypes to conform to their social environment—social niche conformance. The degree of sexual competition is a critical part of the social environment to which animals adjust their phenotypes, but the underlying genetic mechanisms are poorly understood. We conducted a study to investigate how differences in sperm competition risk affect the gene expression profiles of the testes and two brain areas (posterior pallium and optic tectum) in breeding male zebra finches (Taeniopygia castanotis). In this pre-registered study, we investigated a large sample of 59 individual transcriptomes. We compared two experimental groups: males held in single breeding pairs (low sexual competition) versus those held in two pairs (elevated sexual competition) per breeding cage. Using weighted gene co-expression network analysis (WGCNA), we observed significant effects of the social treatment in all three tissues. However, only the treatment effects found in the pallium were confirmed by an additional randomisation test for statistical robustness. Likewise, the differential gene expression analysis revealed treatment effects only in the posterior pallium (ten genes) and optic tectum (six genes). No treatment effects were found in the testis at the single gene level. Thus, our experiments do not provide strong evidence for transcriptomic adjustment specific to manipulated sperm competition risk. However, we did observe transcriptomic adjustments to the manipulated social environment in the posterior pallium. These effects were polygenic rather than based on few individual genes with strong effects. Our findings are discussed in relation to an accompanying paper using the same animals, which reports behavioural results consistent with the results presented here.

We investigated how phenotypic plasticity induced by experimentally manipulated sperm competition risk is reflected in transcriptomic profiles of testes and two brain areas (posterior pallium and optic tectum) in breeding male zebra finches ( Taeniopygia guttata ). Based on an exceptionally large sample of 59 individual transcriptomes, we compared two experimental groups: males held in single pairs versus two pairs per breeding cage. We found tissue-specific differential gene expression in all three tissues at the level of gene co-expression network modules. The treatment affected multiple cellular functions in the testes, which can be associated with germ cell production and modification. Moreover, neural and glial brain cell changes indicate phenotypic adjustment of male zebra finch behaviour to the social environment. Finally, individual co-expression modules correlated with individual behavioural phenotypes and hormonal profiles. Our pre-registered study shows the importance of transcriptomic plasticity for phenotypic adjustment to male-male competition in zebra finches. Peter Korsten, Uwe Mayer and Tim Schmoll share the last authorship.

Individuals respond adaptively to their environment. Yet, they may differ in their responses even when confronted with the same environmental challenge. Several complementary conceptual frameworks suggest that within populations among-individual variation in life history strategies aligns not only with individuals' propensities to take risks across different situations but also with their sensitivity to variation in environmental cues. Risk-prone individuals, suggested to invest more in current reproduction at the cost of their future reproductive prospects, are predicted to be less sensitive to environmental variation than risk-averse individuals. We tested this prediction in a population of breeding blue tits, Cyanistes caeruleus, by confronting them with different levels of predation threat at their nests and recording their latency to resume brood provisioning after the removal of the predator stimulus. We presented taxidermic woodpecker, Dendrocopos major (a common brood predator) and sparrowhawk, Accipiter nisus (a common adult predator) mounts at each nest, respectively representing low and high levels of threat to adult blue tits. As a nonpredator control stimulus, we presented a blackbird, Turdus merula, mount. We found that on average parents took longer to resume provisioning after presentation of a sparrowhawk than a woodpecker or blackbird. Furthermore, individual latency responses across all threat levels taken together were repeatable. However, despite the population level plastic adjustment to the level of predation threat, we found no evidence for among-individual variation in plasticity. Instead, individual differences in responses were roughly maintained across all levels of threat. While our findings show that individuals differ in their level of risk taking, in the high-stakes and ecologically relevant context of predation risk during parental care, commonly held expectations about among-individual variation in behavioural plasticity were not met.

Hatching asynchrony is a frequent phenomenon in altricial birds and can lead to brood reduction due to sibling competition. There are a number of adaptive hypotheses to explain its occurrence, relating hatching asynchrony to sibling competition and timing of breeding. Incubation prior to clutch completion (early incubation) is the main cause of hatching asynchrony. We used temperature loggers inside the nests of breeding Blue Tits Cyanistes caeruleus to provide a detailed account of female incubation over most of the egg-laying period. We relate this early incubation to the time interval between clutch completion and hatching as well as hatching asynchrony. Our study shows the frequent occurrence of early incubation during the beginning of the laying period, with all females showing more early incubation towards clutch completion. At first, early incubation mostly occurs at night, but as egg laying progresses, it also occurs during the day. However, overall there was more nocturnal than diurnal early incubation. These results were obtained using two different methods for quantifying incubation from temperature profiles, which we compared and cross-validated in this study. Moreover, the amount of early incubation related negatively to the time between clutch completion and first hatching and positively to the extent of hatching asynchrony. While we did not directly investigate the mechanisms driving variation in early incubation, the exceptionally cold March/April period followed by a warm May in our study year may explain the comparatively great amounts of early incubation we observed. We hypothesise that spring temperatures may influence the amount of early incubation, with warmer springs resulting in more early incubation and consequently shorter times from clutch completion until first hatching as well as increased hatching asynchrony. Such a mechanism of adjustment of incubation time and hatching asynchrony may also be important for the adaptation of birds to climate change.

Organisms interact with their environments in various ways. We present a conceptual framework that distinguishes three mechanisms of organism-environment interaction. We call these NC3 mechanisms: niche construction, in which individuals make changes to the environment; niche choice, in which individuals select an environment; and niche conformance, in which individuals adjust their phenotypes in response to the environment. Each of these individual-level mechanisms affects an individual's phenotype-environment match, its fitness, and its individualized niche, defined in terms of the environmental conditions under which the individual can survive and reproduce. Our framework identifies how individuals alter the selective regimes that they and other organisms experience. It also places clear emphasis on individual differences and construes niche construction and other processes as evolved mechanisms. The NC3 mechanism framework therefore helps to integrate population-level and individual-level research.

Various aspects of sociality in mammals (e.g., dyadic connectedness) are linked with measures of biological fitness (e.g., longevity). How within- and between-individual variation in relevant social traits arises in uncontrolled wild populations is challenging to determine but is crucial for understanding constraints on the evolution of sociality. We use an advanced statistical method, known as the ‘animal model’, which incorporates pedigree information, to look at social, genetic, and environmental influences on sociality in a long-lived wild primate. We leverage a longitudinal database spanning 20 years of observation on individually recognized white-faced capuchin monkeys ( Cebus capucinus imitator ), with a multi-generational pedigree. We analyze two measures of spatial association, using repeat sampling of 376 individuals (mean: 53.5 months per subject, range: 6–185 months per subject). Conditioned on the effects of age, sex, group size, seasonality, and El Niño–Southern Oscillation phases, we show low to moderate long-term repeatability (across years) of the proportion of time spent social (posterior mode [95% Highest Posterior Density interval]: 0.207 [0.169, 0.265]) and of average number of partners (0.144 [0.113, 0.181]) (latent scale). Most of this long-term repeatability could be explained by modest heritability ( h 2 social : 0.152 [0.094, 0.207]; h 2 partners : 0.113 [0.076, 0.149]) with small long-term maternal effects ( m 2 social : 0.000 [0.000, 0.045]; m 2 partners : 0.000 [0.000, 0.041]). Our models capture the majority of variance in our behavioral traits, with much of the variance explained by temporally changing factors, such as group of residence, highlighting potential limits to the evolvability of our trait due to social and environmental constraints.

Success in sperm competition is an important determinant of male fitness in mating systems with female multiple mating. Thus, sperm competition risk represents a key dimension of the male social environment to which individual males are expected to adaptively adjust their reproductive phenotype. Such adaptive phenotypic adjustment we here refer to as male social niche conformance. In this pre-registered study, we investigated how male zebra finches, Taeniopygia guttata, adjust their behavior to sperm competition risk. We experimentally manipulated the opportunity for extra-pair mating to create two levels of sperm competition risk: 1) Single-pair, no sperm competition risk; 2) Double-pair, sperm competition risk. We compared male courtship, mate guarding, copulation rates, and aggression between the treatment groups. To identify hormonal correlates of male behavioral adjustment, we measured plasma testosterone and corticosterone levels before and after the social treatment started. Contrary to our pre-registered predictions, males from the Double-pair treatment group decreased courtship rates compared to those from the Single-pair group, and Double-pair males responded less aggressively towards intruders than Single-pair males. Testosterone levels decreased over the breeding cycle, but social treatment had no effect on either testosterone or corticosterone levels. Our results indicate that male zebra finches do not intensify courtship or competitive reproductive behaviors, or upregulate key hormones when another breeding pair is present. Although we found no evidence for the predicted adaptive behavioral responses to sperm competition risk, we show that male zebra finches plastically adjust their behavior to their social environment.

Telomere length and telomere shortening predict survival in many organisms. This raises the question of the contribution of genetic and environmental effects to variation in these traits, which is still poorly known, particularly for telomere shortening. We used experimental (cross‐fostering) and statistical (quantitative genetic “animal models”) means to disentangle and estimate genetic and environmental contributions to telomere length variation in pedigreed free‐living jackdaws (Corvus monedula). Telomere length was measured twice in nestlings, at ages 4 (n = 715) and 29 days (n = 474), using telomere restriction fragment (TRF) analysis, adapted to exclude interstitial telomeric sequences. Telomere length shortened significantly over the nestling period (10.4 ± 0.3 bp day–1) and was highly phenotypically (rP = 0.95 ± 0.01) and genetically (rG > 0.99 ± 0.01) correlated within individuals. Additive genetic effects explained a major part of telomere length variation among individuals, with its heritability estimated at h2 = 0.74 on average. We note that TRF‐based studies reported higher heritabilities than qPCR‐based studies, and we discuss possible explanations. Parent–offspring regressions yielded similar heritability estimates for mothers and fathers when accounting for changes in paternal telomere length over life. Year effects explained a small but significant part of telomere length variation. Heritable variation for telomere shortening was low (h2 = 0.09 ± 0.11). The difference in heritability between telomere length (high) and telomere shortening (low) agrees with evolutionary theory, in that telomere shortening has stronger fitness consequences in this population. Despite the high heritability of telomere length, its evolvability, which scales the additive genetic variance by mean telomere length, was on average 0.48%. Hence, evolutionary change of telomere length due to selection is likely to be slow.

Individuals differ. This seemingly trivial statement has nevertheless led to paradigm shifts, as three different fields of organismal biology have seen a marked change in key concepts over the past few decades. In animal behaviour, it has increasingly been realised that behavioural differences among individuals can be stable over time and across contexts, giving rise to the concept of animal personalities. In ecology, an increasing focus is likewise on the considerable variation in the ecological niche realised by species, populations, and individuals, giving rise to the concept of niche specialisation or individual niche variation. In evolutionary biology, where individual variation has always been central, there is an increasing awareness of the complexity with which individuals interact with the environment in producing unique phenotypes. Recent theoretical and empirical work has highlighted that the fitness landscape is rather complex, with multiple fitness peaks. It depends on the individual with its genotype, in interaction with its specific environment, which local or global fitness peak is attainable. Over the past 15 years, the need for more integrated conceptual frameworks transcending disciplines has been voiced ever more strongly. Whereas initially the ecological time scale was deemed to be fundamentally different from the evolutionary one, this notion has recently been replaced by a more integrative one, where evolution can indeed happen over ecological time scales. While in each of the three fields behaviour, ecology, and evolution, the concept of individualisation has contributed to major scientific progress, sufficient cross-fertilisation is lacking. Here, we propose a new level of conceptual unification: the individualised niche. By merging the niche concept with the fitness and animal personality concepts, new explanatory power for both ecological and evolutionary processes emerges.

The existence of among-individual variation in behaviour within populations is poorly understood. Recent theory suggests that fine-scale individual differences in investment into current versus future reproduction may lead to a ‘slow-fast’-pace-of-life continuum, also referred to as the ‘pace-of-life-syndrome’ (POLS) hypothesis. According to this idea, individuals are predicted to differ in their level of risk-taking, which may drive among-individual variation and covariation of behaviours. Consistent individual differences in aggression, an ecologically relevant and potentially risky behaviour, have been reported across the animal kingdom. Here we test whether such individual differences in aggression are a manifestation of underlying differences in risk-taking. In a wild blue tit ( Cyanistes caeruleus ) population, we used standard behavioural tests to investigate if male territorial aggressiveness and risk-taking during breeding are positively related. At the start of breeding, we simulated conspecific territorial intrusions to obtain repeated measures of male aggressiveness. Subsequently, we measured male risk-taking as their latency to resume brood provisioning after presenting two different predators at their nest: human and sparrowhawk, a common predator of adult songbirds. First, we found substantial repeatability for male aggressiveness ( R = 0.56 ± 0.08 SE). Second, while males took longer to resume provisioning after presentation of a sparrowhawk mount as compared to a human observer, risk-taking was repeatable across these two predator contexts ( R = 0.51 ± 0.13 SE). Finally, we found no evidence for a correlation between male aggressiveness and risk-taking, thereby providing little support to a main prediction of the POLS hypothesis. Significance statement Consistent, and often correlated, individual differences in basal behaviours, such as aggression, exploration and sociability, are found across the animal kingdom. Why individuals consistently differ in their behaviour is poorly understood, as behavioural traits would seem inherently flexible. The ‘pace-of-life syndrome’ (POLS) hypothesis proposes observed behavioural variation to reflect differences in risk-taking associated with individual reproductive strategies. We tested this idea in a wild blue tit population by investigating whether individual males that were more aggressive toward territorial intruders also took more risk when provisioning their nestlings under a threat of predation. While we found consistent individual differences in both aggressiveness and risk-taking, these behaviours were not significantly correlated. Therefore, our study demonstrates among-individual variation in ecologically relevant behaviours in wild blue tits but provides little support for the POLS hypothesis.

While it is universally recognised that environmental factors can cause phenotypic trait variation via phenotypic plasticity, the extent to which causal processes operate in the reverse direction has received less consideration. In fact individuals are often active agents in determining the environments, and hence the selective regimes, they experience. There are several important mechanisms by which this can occur, including habitat selection and niche construction, that are expected to result in phenotype-environment correlations (i.e. non-random assortment of phenotypes across heterogeneous environments). Here we highlight an additional mechanism - intraspecific competition for preferred environments - that may be widespread, and has implications for phenotypic evolution that are currently underappreciated. Under this mechanism, variation among individuals in traits determining their competitive ability leads to phenotype-environment correlation; more competitive phenotypes are able to acquire better patches. Based on a concise review of the empirical evidence we argue that competition-induced phenotype-environment correlations are likely to be common in natural populations before highlighting the major implications of this for studies of natural selection and microevolution. We focus particularly on two central issues. First, competition-induced phenotype-environment correlation leads to the expectation that positive feedback loops will amplify phenotypic and fitness variation among competing individuals. As a result of being able to acquire a better environment, winners gain more resources and even better phenotypes - at the expense of losers. The distinction between individual quality and environmental quality that is commonly made by researchers in evolutionary ecology thus becomes untenable. Second, if differences among individuals in competitive ability are underpinned by heritable traits, competition results in both genotype-environment correlations and an expectation of indirect genetic effects (IGEs) on resource-dependent life-history traits. Theory tells us that these IGEs will act as (partial) constraints, reducing the amount of genetic variance available to facilitate evolutionary adaptation. Failure to recognise this will lead to systematic overestimation of the adaptive potential of populations. To understand the importance of these issues for ecological and evolutionary processes in natural populations we therefore need to identify and quantify competition-induced phenotype-environment correlations in our study systems. We conclude that both fundamental and applied research will benefit from an improved understanding of when and how social competition causes non-random distribution of phenotypes, and genotypes, across heterogeneous environments.

The integration and synthesis of the data in different areas of science is drastically slowed and hindered by a lack of standards and networking programmes. Long-term studies of individually marked animals are not an exception. These studies are especially important as instrumental for understanding evolutionary and ecological processes in the wild. Further, their number and global distribution provides a unique opportunity to assess the generality of patterns and to address broad-scale global issues (e.g. climate change). To solve data integration issues and enable a new scale of ecological and evolutionary research based on long-terms studies of birds, we have created the SPI-Birds Network and Database (www.spibirds.org) – a large-scale initiative that connects data from, and researchers working on, studies of wild populations of individually recognizable (usually ringed) birds. Within a year of the establishment, SPI-Birds counts 120 members working on more than 80 populations, with data concerning breeding attempts of almost a million individual birds over a 1700 cumulative years, and counting. SPI-Birds acts as a data hub and a catalogue of studied populations. It prevents data loss, secures easy data finding, use and integration, and thus facilitates collaboration and synthesis. We provide community-derived data and meta-data standards and improve data integrity guided by of Findable, Accessible, Interoperable, and Reusable (FAIR), and aligned with the existing metadata languages (e.g. ecological meta-data language). The encouraging community involvement stems from SPI-Bird's decentralized approach: research groups retain full control over data use and their way of data management, while SPI-Birds creates tailored pipelines to convert each unique data format into a standard format. We outline the lessons learned, so that other communities (e.g. those working on other taxa) can adapt our successful model. Creating community-specific hubs (such as ours, COMADRE for animal demography, etc.) will aid much-needed large-scale ecological data integration.