Natal legacies cause social and spatial marginalization during dispersal.

Early-life experiences can drive subsequent variation in social behaviours, but how differences among individuals emerge remains unknown. We combined experimental manipulations with GPS-tracking to investigate the pathways through which developmental conditions affect social network position during the early dispersal of wild red kites (Milvus milvus). Across 211 juveniles from 140 broods, last-hatched chicks-the least competitive-had the fewest number of peer encounters after fledging. However, when food supplemented, they had more encounters than all others. Using 4425 bird-days of GPS data, we revealed that this was driven by differential responses to competition, with less competitive individuals naturally spreading out into marginal areas, and clustering in central foraging areas when food supplemented. Our results suggest that early-life adversities can cause significant natal legacies on individual behaviour beyond independence, with potentially far-reaching consequences on the social and spatial structure of animal populations.

Winter Tracking Data Suggest that Migratory Seabirds Transport Per- and Polyfluoroalkyl Substances to Their Arctic Nesting Site.

Seabirds are often considered sentinel species of marine ecosystems, and their blood and eggs utilized to monitor local environmental contaminations. Most seabirds breeding in the Arctic are migratory and thus are exposed to geographically distinct sources of contamination throughout the year, including per- and polyfluoroalkyl substances (PFAS). Despite the abundance and high toxicity of PFAS, little is known about whether blood concentrations at breeding sites reliably reflect local contamination or exposure in distant wintering areas. We tested this by combining movement tracking data and PFAS analysis (nine compounds) from the blood of prelaying black-legged kittiwakes (Rissa tridactyla) nesting in Arctic Norway (Svalbard). PFAS burden before egg laying varied with the latitude of the wintering area and was negatively associated with time upon return of individuals at the Arctic nesting site. Kittiwakes (n = 64) wintering farther south carried lighter burdens of shorter-chain perfluoroalkyl carboxylates (PFCAs, C9-C12) and heavier burdens of longer chain PFCAs (C13-C14) and perfluorooctanesulfonic acid compared to those wintering farther north. Thus, blood concentrations prior to egg laying still reflected the uptake during the previous wintering stage, suggesting that migratory seabirds can act as biovectors of PFAS to Arctic nesting sites.

Spring arrival of the common cuckoo at breeding grounds is strongly determined by environmental conditions in tropical Africa.

Failure to adapt migration timing to changes in environmental conditions along migration routes and at breeding locations can result in mismatches across trophic levels, as occurs between the brood parasitic common cuckoo Cuculus canorus and its hosts. Using satellite tracking data from 87 male cuckoos across 11 years, we evaluate why the cuckoo has not advanced its arrival to the UK. Across years, breeding ground arrival was primarily determined by timing of departure from stopover in West Africa before northward crossing of the Sahara. Together with high population synchrony and low apparent endogenous control of this event, this suggests that a seasonal ecological constraint operating here limits overall variation in breeding grounds arrival, although this event was itself influenced by carry-over from timing of arrival into tropical Africa. Between-year variation within individuals was, in contrast, mostly determined by northward migration through Europe, probably due to weather conditions. We find evidence of increased mortality risk for (a) early birds following migration periods positively impacting breeding grounds arrival, and (b) late birds, possibly suffering energy limitation, after departure from the breeding grounds. These results help identify areas where demands of responding to global change can potentially be alleviated by improving stopover quality.

Distance doesn't matter: migration strategy in a seabird has no effect on survival or reproduction.

Migrating animals show remarkable diversity in migration strategies, even between individuals from the same population. Migrating longer distances is usually expected to be costlier in terms of time, energy expenditure and risks with potential repercussions for subsequent stages within the annual cycle. Such costs are expected to be balanced by increased survival, for example due to higher quality wintering areas or lower energy expenditure at lower latitudes. We compared reproductive parameters and apparent survival of lesser black-backed gulls (Larus fuscus) breeding in The Netherlands, whose winter range extends from the UK to West Africa, resulting in one-way migration distances that differ by more than 4500 km. Individuals migrating furthest arrived later in the colony than shorter distance migrants, but still laid in synchrony with the colony and consequently had a shorter pre-laying period. This shorter pre-laying period affected neither egg volumes nor hatching success. We found no relationship between migration distance and apparent survival probability, corresponding with previous research showing that annual energy expenditure and distance travelled throughout the year is similar across migration strategies. Combined, our results indicate an equal fitness payoff across migration strategies, suggesting there is no strong selective pressure acting on migration strategy within this population.

Epigenetic-associated phenotypic plasticity of the ocean acidification-acclimated edible oyster in the mariculture environment.

For marine invertebrates with a pelagic-benthic life cycle, larval exposure to ocean acidification (OA) can affect adult performance in response to another environmental stressor. This carry-over effect has the potential to alter phenotypic traits. However, the molecular mechanisms that mediate "OA"-triggered carry-over effects have not been explored despite such information being key to improving species fitness and management strategies for aquafarming. This study integrated the genome-wide DNA methylome and transcriptome to examine epigenetic modification-mediated carry-over OA impacts on phenotypic traits of the ecologically and commercially important oyster species Crassostrea hongkongensis under field conditions. Larvae of C. hongkongensis were exposed to control pH 8.0 and low pH 7.4 conditions, mimicking near future OA scenario in their habitat, before being outplanted as post-metamorphic juveniles at two mariculture field sites with contrasting environmental stressors for 9 months. The larval carry-over OA effect was found to have persistent impacts on the growth and survival trade-off traits on the outplanted juveniles, although the beneficial or adverse effect depended on the environmental conditions at the outplanted sites. Site-specific plasticity was demonstrated with a diverse DNA methylation-associated gene expression profile, with signal transduction and the endocrine system being the most common and highly enriched functions. Highly methylated exons prevailed in the key genes related to general metabolic and endocytic responses and these genes are evolutionarily conserved in various marine invertebrates in response to OA. These results suggest that oysters with prior larval exposure history to OA had the ability to trigger rapid local adaptive responses via epigenetic modification to cope with multiple stressors in the field.

Immediate and carry-over effects of late-spring frost and growing season drought on forest gross primary productivity capacity in the Northern Hemisphere.

Forests are increasingly exposed to extreme global warming-induced climatic events. However, the immediate and carry-over effects of extreme events on forests are still poorly understood. Gross primary productivity (GPP) capacity is regarded as a good proxy of the ecosystem's functional stability, reflecting its physiological response to its surroundings. Using eddy covariance data from 34 forest sites in the Northern Hemisphere, we analyzed the immediate and carry-over effects of late-spring frost (LSF) and growing season drought on needle-leaf and broadleaf forests. Path analysis was applied to reveal the plausible reasons behind the varied responses of forests to extreme events. The results show that LSF had clear immediate effects on the GPP capacity of both needle-leaf and broadleaf forests. However, GPP capacity in needle-leaf forests was more sensitive to drought than in broadleaf forests. There was no interaction between LSF and drought in either needle-leaf or broadleaf forests. Drought effects were still visible when LSF and drought coexisted in needle-leaf forests. Path analysis further showed that the response of GPP capacity to drought differed between needle-leaf and broadleaf forests, mainly due to the difference in the sensitivity of canopy conductance. Moreover, LSF had a more severe and long-lasting carry-over effect on forests than drought. These results enrich our understanding of the mechanisms of forest response to extreme events across forest types.

Short- and long-term consequences of heat exposure on mitochondrial metabolism in zebra finches (Taeniopygia castanotis).

Understanding the consequences of heat exposure on mitochondrial function is crucial as mitochondria lie at the core of metabolic processes, also affecting population dynamics. In adults, mitochondrial metabolism varies with temperature but can also depend on thermal conditions experienced during development. We exposed zebra finches to two alternative heat treatments during early development: "constant", maintained birds at ambient 35 °C from parental pair formation to fledglings' independence, while "periodic" heated broods at 40 °C, 6 h daily at nestling stage. Two years later, we acclimated birds from both experiments at 25 °C for 21 days, before exposing them to artificial heat (40 °C, 5 h daily for 10 days). After both conditions, we measured red blood cells' mitochondrial metabolism using a high-resolution respirometer. We found significantly decreased mitochondrial metabolism for Routine, Oxidative Phosphorylation (OxPhos) and Electron Transport System maximum capacity (ETS) after the heat treatments. In addition, the birds exposed to "constant" heat in early life showed lower oxygen consumption at the Proton Leak (Leak) stage after the heat treatment as adults. Females showed higher mitochondrial respiration for Routine, ETS and Leak independent of the treatments, while this pattern was reversed for OxPhos coupling efficiency (OxCE). Our results show that short-term acclimation involved reduced mitochondrial respiration, and that the reaction of adult birds to heat depends on the intensity, pattern and duration of temperature conditions experienced at early-life stages. Our study provides insight into the complexity underlying variation in mitochondrial metabolism and raises questions on the adaptive value of long-lasting physiological adjustments triggered by the early-life thermal environment.

Baseline corticosterone levels in spadefoot toads reflect alternate larval diets one year later.

Early-life environmental variation can influence later-life physiology, such as the regulation of glucocorticoids. However, characterizing the effects of environmental factors on hormone regulation can be hampered when assessing animals that are small and require destructive sampling to collect blood. Using spadefoot toads (genus Spea), we evaluated whether waterborne corticosterone (CORT) measures could be used as a proxy for plasma CORT measures, detect stress-induced levels of CORT, and detect larval diet-induced changes in CORT regulation after metamorphosed individuals were maintained for 1 year under common garden conditions. We found that waterborne CORT measures were correlated with plasma CORT measures and could be used to detect stress-induced levels of CORT. Further, larval diet type significantly influenced baseline plasma CORT levels 1-year post-metamorphosis: adults that had consumed live prey as larvae had higher plasma CORT levels than adults that had consumed detritus as larvae. However, waterborne measures failed to reflect these differences, possibly due to low sample size. Our study demonstrates the utility of the waterborne hormone assay in assessing variation in baseline and stress-induced CORT levels in adult spadefoots. However, resolving more subtle differences that arise through developmental plasticity will require larger samples sizes when using the waterborne assay.

Transfer of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and polychlorinated biphenyls (PCBs) from oral exposure into cow's milk - part II: toxicokinetic predictive models for risk assessment.

Understanding the transfer of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) as well as polychlorinated biphenyls (PCBs) from oral exposure into cow's milk is not purely an experimental endeavour, as it has produced a large corpus of theoretical work. This work consists of a variety of predictive toxicokinetic models in the realms of health and environmental risk assessment and risk management. Their purpose is to provide mathematical predictive tools to organise and integrate knowledge on the absorption, distribution, metabolism and excretion processes. Toxicokinetic models are based on more than 50 years of transfer studies summarised in part I of this review series. Here in part II, several of these models are described and systematically classified with a focus on their applicability to risk analysis as well as their limitations. This part of the review highlights the opportunities and challenges along the way towards accurate, congener-specific predictive models applicable to changing animal breeds and husbandry conditions.

Transfer of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and polychlorinated biphenyls (PCBs) from oral exposure into cow's milk - Part I: state of knowledge and uncertainties.

Polychlorinated dibenzo-para-dioxins (PCDDs) and dibenzofurans (PCDFs) (collectively and colloquially referred to as 'dioxins') as well as polychlorinated biphenyls (PCBs) are persistent and ubiquitous environmental contaminants that may unintentionally enter and accumulate along the food chain. Owing to their chronic toxic effects in humans and bioaccumulative properties, their presence in feed and food requires particular attention. One important exposure pathway for consumers is consumption of milk and dairy products. Their transfer from feed to milk has been studied for the past 50 years to quantify the uptake and elimination kinetics. We extracted transfer parameters (transfer rate, transfer factor, biotransfer factor and elimination half-lives) in a machine-readable format from seventy-six primary and twenty-nine secondary literature items. Kinetic data for some toxicologically relevant dioxin congeners and the elimination half-lives of dioxin-like PCBs are still not available. A well-defined selection of transfer parameters from literature was statistically analysed and shown to display high variability. To understand this variability, we discuss the data with an emphasis on influencing factors, such as experimental conditions, cow performance parameters and metabolic state. While no universal interpretation could be derived, a tendency for increased transfer into milk is apparently connected to an increase in milk yield and milk fat yield as well as during times of body fat mobilisation, for example during the negative energy balance after calving. Over the past decades, milk yield has increased to over 40 kg/d during high lactation, so more research is needed on how this impacts feed to food transfer for PCDD/Fs and PCBs.

The real-time and carry-over effects of injustice on performance and service quality in a ridesharing driver scenario.

The nature of gig work and its growth have important implications for organizational justice theory. Aspects of gig work, including the transactional compensation arrangement, strict algorithmic rating system, and power asymmetry between drivers and customers, have implications for understanding how dimensions of distributive, informational, and interpersonal injustice manifest and impact job performance in the gig context. An understanding of this topic can inform justice theory more broadly and help explain inconsistent findings in the literature. Here, we report the results of two studies examining the unique effects of these respective dimensions of injustice on emotions and, ultimately, the driving performance and service quality in a ridesharing service context. In Study 1, we modeled the passenger-driver interaction of the ridesharing context using a driving simulator in a laboratory setting to differentiate the real-time and carry-over effects of specific dimensions of injustice. The results from 99 participants showed that perceptions of interpersonal injustice increased anger and unhappiness during the ride, in turn impairing driving and service performance. Antecedent-focused emotion regulation strategies (ERS) reduced felt unhappiness. Moreover, unexpectedly, perceived distributive injustice as caused by the customer rating had opposite (direct versus indirect) effects on service performance in the subsequent ride. Study 2 was an online simulation vignette scenario with 294 participants. The results replicated the findings of Study 1 and revealed two moderators of the unexpected distributive justice-performance relationship. Supplementary Information: The online version contains supplementary material available at 10.1007/s12144-022-04215-3.

Neural dissociation of the acoustic and cognitive representation of voice identity.

Recognising a speaker's identity by the sound of their voice is important for successful interaction. The skill depends on our ability to discriminate minute variations in the acoustics of the vocal signal. Performance on voice identity assessments varies widely across the population. The neural underpinnings of this ability and its individual differences, however, remain poorly understood. Here we provide critical tests of a theoretical framework for the neural processing stages of voice identity and address how individual differences in identity discrimination mediate activation in this neural network. We scanned 40 individuals on an fMRI adaptation task involving voices drawn from morphed continua between two personally familiar identities. Analyses dissociated neuronal effects induced by repetition of acoustically similar morphs from those induced by a switch in perceived identity. Activation in temporal voice-sensitive areas decreased with acoustic similarity between consecutive stimuli. This repetition suppression effect was mediated by the performance on an independent voice assessment and this result highlights an important functional role of adaptive coding in voice expertise. Bilateral anterior insulae and medial frontal gyri responded to a switch in perceived voice identity compared to an acoustically equidistant switch within identity. Our results support a multistep model of voice identity perception.

Differences in the temporal scale of reproductive investment across the slow-fast continuum in a passerine.

Life-history strategies differ with respect to investment in current versus 'future' reproduction, but when is this future? Under the novel 'temporality in reproductive investment hypothesis', we postulate variation should exist in the time frame over which reproductive costs are paid. Slow-paced individuals should pay reproductive costs over short (e.g. inter-annual) time scales to prevent reproductive costs accumulating, whereas fast-paced individuals should allow costs to accumulate (i.e. senescence). Using Fourier transforms, we quantify adjustments in clutch size with age, across four populations of blue tits (Cyanistes caeruleus). Fast populations had more prevalent and stronger long-term changes in reproductive investment, whereas slower populations had more prevalent short-term adjustments. Inter-annual environmental variation partly accounted for short-, but not long-term changes in reproductive investment. Our study reveals individuals differ in when they pay the cost of reproduction and that failure to partition this variation across different temporal scales and environments could underestimate reproductive trade-offs.

The relative influence of cross-seasonal and local weather effects on the breeding success of a migratory songbird.

In seasonal environments, fluctuating early-season weather conditions and short breeding windows limit reproductive opportunities such that breeding earlier or later than the optimum may be particularly costly. Given the risk of early-season energy limitations, time- and energy-based carry-over effects stemming from environmental conditions across the annual cycle may have pronounced consequences for breeding phenology and fitness. Generally, when and where environmental conditions are most influential are poorly understood, limiting our ability to predict the future of climate-sensitive populations. For an alpine-breeding, migratory population of horned lark Eremophila alpestris in northern British Columbia, Canada (54.8°N), we assessed how weather conditions across the annual cycle influenced clutch initiation date and offspring development. We also addressed how cross-seasonal effects on breeding parameters combine to influence reproductive fitness. With 12 years of breeding data and 3 years of migration data, we used a sliding window approach to identify points during the annual cycle when weather events most influenced breeding phenology and offspring development. Consequences for breeding success were assessed using nest survival simulations. Average clutch initiation date varied up to 11 days among years but did not advance from 2003 to 2019. Warmer temperatures at stopover and breeding sites advanced clutch initiation, but winter conditions had no effect. Sub-zero stopover temperatures carried over to prolong offspring development independent of clutch initiation date, potentially indicating energy-based carry-over effects acting on parental investment. Nest survival decreased with both later clutch initiation and prolonged offspring development such that females nesting earlier and fledging offspring at a younger age were up to 45% more likely to reproduce successfully. We demonstrate that stronger carry-over effects originated from environmental conditions closer to the breeding site in time and space, as well as the potential for energy-based mechanisms to link pre-breeding conditions to reproductive fitness. We also highlight the importance of extended stopovers for songbirds breeding in seasonal environments, particularly given that climatic conditions are becoming increasingly decoupled across stages of the annual cycle. Understanding the cross-seasonal mechanisms shaping breeding decisions in stochastic environments allows for more accurate predictions of population-level responses to climate change.

Les variations saisonnières de l'environnement, notamment due aux conditions climatiques changeantes en début de saison ainsi que la réduction de la période propice à l'accouplement contraint fortement les possibilités de reproduction. Dans ces conditions, s'accoupler avant ou après le moment optimal peut s'avérer particulièrement coûteux. Les effets de report (temporels et énergétiques) causés par ces variations environnementales peuvent avoir des conséquences notables sur la phénologie de la reproduction, et ultimement sur la valeur sélective des individus. Où et quand les effets des conditions environnementales sont le plus critiques reste encore méconnu, limitant notre capacité à prédire le futur des populations sensibles aux variations climatiques. Ici, nous avons évalué comment des conditions climatiques au cours de l'année influencent la date de ponte et le développement des oisillons dans une population migratrice d'Alouette hausse-col Eremophila alpestris se reproduisant en milieux alpin. Nous tirons profit de données issues de 12 ans de suivit de la reproduction et de 3 ans de suivit migratoire, et utilisons une approche dite de 'sliding window' pour identifier les moments du cycle annuel pour lequel le climat a eu le plus d'influence sur la phénologie de la reproduction et le développement des oisillons. La date moyenne de ponte s'avère variable d'une année à l'autre (certaine différence allant jusqu'à 11 jours), mais ne se décale pas sur la période de 2003 à 2019. Nos résultats montrent que des conditions climatiques plus chaudes lors des haltes migratoires ainsi que sur les sites de reproductions rendent la date de ponte plus précoces. Des températures négatives lors des haltes migratoires aussi ont pour conséquences un temps de développement des oisillons plus long, et ceci indépendamment de la date de ponte. Cela suggère des effets de report, notamment énergétique, affectant l'investissement des parents. Nos résultats montrent que la survie au nid diminue lorsque la date de ponte est plus tardive ou que le temps de développement des oisillons est rallongé. De cette manière, les femelles commençants la nidification plus tôt et pour qui les oisillons quittent le nid plus tôt ont 45% plus de chance de se reproduire avec succès. Nous démontrons que des conditions environnementales proche du site de reproduction (que ce soit dans le temps ou dans l'espace) cause un fort effet de report, et suggérons un possible mécanisme reliant les conditions climatiques pré-reproductives au succès reproducteur. De plus, nous mettons en lumière l'importance des haltes migratoires prolongées pour la reproduction des passereaux en environnement saisonnier, particulièrement du fait que les conditions climatiques sont de plus en plus découplées au cours des les étapes du cycle annuel. Une meilleure compréhension des mécanismes inter-saisonniers influençant les décisions de reproduction en environnement stochastique permettrait de mieux prédire les réponses des populations aux changements climatiques.

Variable temperature regimes and wetland salinity reduce performance of juvenile wood frogs.

On a changing planet, amphibians must respond to weather events shifting in frequency and magnitude, and to how those temperature and precipitation changes interact with other anthropogenic disturbances that modify amphibian habitat. To understand how drastic changes in environmental conditions affect wood frog tadpoles, we tested five temperature manipulations, including Ambient (water temperatures tracking daily air temperatures), Elevated (+ 3 °C above ambient), Nightly (removal of nightly lows), Spike (+ 6 °C above ambient every third week), and Flux (alternating ambient and + 3 °C weekly) crossed with Low Salt (specific conductivity: 109-207 µS-cm) and High Salt (1900-2000 µS-cm). We replicated each of the ten resulting treatments four times. High-salinity conditions produced larger metamorphs than low-salinity conditions. Tadpole survival was reduced only by the Spike treatment (P = 0.017). Elevated temperatures did not shorten larval periods; time to metamorphosis did not differ among temperature treatments (P = 0.328). We retained 135 recently metamorphosed frogs in outdoor terrestrial enclosures for 10 months to investigate larval environment carryover effects. Juvenile frogs grew larger in low-density terrestrial enclosures than high density (P = 0.015) and frogs from Ambient Low Salt larval conditions grew and survived better than frogs from manipulated larval conditions. Frogs from High Salt larval conditions had lower survival than frogs from Low Salt conditions. Our results suggest that anthropogenic disturbances to larval environmental conditions can affect both larval and post-metamorphic individuals, with detrimental carryover effects of high-salinity larval conditions not emerging until the juvenile life stage.

Prehatching temperatures drive inter-annual cohort differences in great tit metabolism.

Basal metabolic rate (BMR) constitutes the lowest metabolic rate in a resting animal and is, therefore, considered to reflect the energetic cost of maintenance in endotherms. BMR is a reversible plastic trait that changes with environmental and ecological circumstances, albeit being heritable and susceptible to selection. Inter-individual variation within populations of small birds is substantial, and while many of the drivers of such variation have been identified, many remain unexplained. We studied winter BMR variation of juveniles over a 15-year period in a wild population of great tits Parus major at the northern border of their distribution. BMR during winter consistently changed between years, even after controlling for environmental factors, suggestive of a non-reversible developmental plasticity shaping the adult metabolic phenotype. BMR in cohorts of wintering great tits varied among winters as a response to minimum ambient temperatures experienced early in life, during the prehatching period. This developmental plasticity might be adaptive if temperatures experienced by growing embryos would metabolically prime them to an environment that they will likely encounter in future life. However, in line with a more unpredictable future climate, the risk of phenotype-environment mismatch is likely to lead to certain cohorts being poorly adapted to prevailing winter conditions, resulting in wider annual fluctuations in population size.

A note on point estimation and interval estimation of the relative treatment effect under a simple crossover design.

To increase power or reduce the number of patients needed for a parallel groups design, the crossover design has been often used to study treatments for noncurable chronic diseases. However, in the presence of carry-over effect caused by treatments, the commonly-used estimator which ignores the carry-over effect leads to a biased estimator for estimating the treatment effect difference. A two-stage test approach aimed to address carry-over effect proposed was found to be potentially misleading. In this paper, we propose a weighted average of the commonly-used estimator and an unbiased estimator that uses only the first period of the data. We derive an optimal weight that minimizes the mean squared error (MSE) and its modified estimator. We apply Monte Carlo simulation to evaluate the performance of the proposed estimators in a variety of situations. In the simulations, we examine the estimated MSE (EMSE), percentile interval length, and coverage probability calculated from the percentile intervals among considered estimators. Simulation results show that our proposed weighted average estimator and its modified estimator lead to smaller EMSEs on average comparing to the two commonly used estimators. The coverage probabilities using our proposed estimators are reasonably close to the nominal confidence level and the interval lengths are shorter comparing to the use of the unbiased estimator that uses only the first period of the data. We apply an example that was to evaluate the efficacy of two type of bronchodilators for asthma treatment to demonstrate the use of the proposed estimators.

Phenotypic plasticity as a cause and consequence of population dynamics.

Predicting complex species-environment interactions is crucial for guiding conservation and mitigation strategies in a dynamically changing world. Phenotypic plasticity is a mechanism of trait variation that determines how individuals and populations adapt to changing and novel environments. For individuals, the effects of phenotypic plasticity can be quantified by measuring environment-trait relationships, but it is often difficult to predict how phenotypic plasticity affects populations. The assumption that environment-trait relationships validated for individuals indicate how populations respond to environmental change is commonly made without sufficient justification. Here we derive a novel general mathematical framework linking trait variation due to phenotypic plasticity to population dynamics. Applying the framework to the classical example of Nicholson's blowflies, we show how seemingly sensible predictions made from environment-trait relationships do not generalise to population responses. As a consequence, trait-based analyses that do not incorporate population feedbacks risk mischaracterising the effect of environmental change on populations.

Human activity shapes the wintering ecology of a migratory bird.

Human behavior profoundly affects the natural world. Migratory birds are particularly susceptible to adverse effects of human activities because the global networks of ecosystems on which birds rely are undergoing rapid change. In spite of these challenges, the blackcap (Sylvia atricapilla) is a thriving migratory species. Its recent establishment of high-latitude wintering areas in Britain and Ireland has been linked to climate change and backyard bird feeding, exemplifying the interaction between human activity and migrant ecology. To understand how anthropogenic influences shape avian movements and ecology, we marked 623 wintering blackcaps at 59 sites across Britain and Ireland and compiled a dataset of 9929 encounters. We investigated visitation behavior at garden feeding sites, inter-annual site fidelity, and movements within and across seasons. We analyzed migration tracks from 25 geolocators fitted to a subset of individuals to understand how garden behavior may impact subsequent migration and breeding. We found that blackcaps wintering in Britain and Ireland showed high site fidelity and low transience among wintering sites, in contrast to the itinerant movements characteristic of blackcaps wintering in their traditional winter range. First-winter birds showed lower site fidelity and a greater likelihood of transience than adults. Adults that frequented gardens had better body condition, smaller fat stores, longer bills, and rounder wingtips. However, blackcaps did not exclusively feed in gardens; visits were linked to harsher weather. Individuals generally stayed at garden sites until immediately before spring departure. Our results suggest that supplementary feeding is modifying blackcap winter ecology and driving morphological evolution. Supplemental feeding may have multifaceted benefits on winter survival, and these positive effects may carry over to migration and subsequent breeding. Overall, the high individual variability in blackcap movement and foraging ecology, and the flexibility it imparts, may have allowed this species to flourish during rapid environmental change.

Birds of different morphs use slightly different strategies to achieve similar reproductive performance following heatwave exposure.

Responses to extreme climatic events may differ between individuals of distinct morphs which differ in life-history strategies, resulting in climate change 'winners' and 'losers' within species. We examined the reproductive performance and carry-over effects on offspring of black- and red-headed Gouldian finches Erythrura gouldiae after exposure to simulated heatwaves of moderate or severe intensity. We expected black-headed pairs' reproductive performance to decline after the severe heatwave because only the condition of black-headed females deteriorates during such a heatwave. Supporting the fact that Gouldian finches of different morphs use alternative reproductive strategies, we found that black-headed females initiated egg-laying a month earlier than red-headed females after experiencing a severe heatwave. We also found that this severe heatwave resulted in shorter spermatozoa in males irrespective of their morph. Despite these effects associated with heatwave intensity, the overall reproductive performance of both morphs was not affected by this factor, which was possibly due to an increased nestling provisioning rate by parents after exposure to the severe heatwave. However, offspring still bore the cost of parental exposure to the severe heatwave, as they showed a reduced condition (lower plasma antioxidant capacity and transient lower breathing rate) and higher oxidative damage (at least in fledglings with black-headed parents). These results suggest that inter-morph phenotypic variability in the Gouldian finch does not result in clear differences in reproductive performance following heatwave exposure, despite basal phenotypic differences between morphs. Whether animals using alternative reproductive strategies are, in the end, differently affected by climate changes will likely depend on the capacity of their offspring to recover from altered developmental conditions.