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Human-induced environmental changes, such as the introduction of invasive species, are driving declines in the movement of nutrients across ecosystems with negative consequences for ecosystem function. Declines in nutrient inputs could thus have knock-on effects at higher trophic levels and broader ecological scales, yet these interconnections remain relatively unknown. Here we show that a terrestrial invasive species (black rats, Rattus rattus) disrupts a nutrient pathway provided by seabirds, ultimately altering the territorial behaviour of coral reef fish. In a replicated ecosystem-scale natural experiment, we found that reef fish territories were larger and the time invested in aggression lower on reefs adjacent to rat-infested islands compared with rat-free islands. This response reflected changes in the economic defendability of lower-quality resources, with reef fish obtaining less nutritional gain per unit foraging effort adjacent to rat-infested islands with low seabird populations. These results provide a novel insight into how the disruption of nutrient flows by invasive species can affect variation in territorial behaviour. Rat eradication as a conservation strategy therefore has the potential to restore species interactions via territoriality, which can scale up to influence populations and communities at higher ecological levels.

Human-induced environmental changes, such as the introduction of invasive species, are driving declines in the movement of nutrients across ecosystems with negative consequences for ecosystem function. Declines in nutrient inputs could thus have knock-on effects at higher trophic levels and broader ecological scales, yet these interconnections remain relatively unknown. Here we show that a terrestrial invasive species (black rats, Rattus rattus) disrupts a nutrient pathway provided by seabirds, ultimately altering the territorial behaviour of coral reef fish. In a replicated ecosystem-scale natural experiment, we found that reef fish territories were larger and the time invested in aggression lower on reefs adjacent to rat-infested islands compared with rat-free islands. This response reflected changes in the economic defendability of lower-quality resources, with reef fish obtaining less nutritional gain per unit foraging effort adjacent to rat-infested islands with low seabird populations. These results provide a novel insight into how the disruption of nutrient flows by invasive species can affect variation in territorial behaviour. Rat eradication as a conservation strategy therefore has the potential to restore species interactions via territoriality, which can scale up to influence populations and communities at higher ecological levels.

Abstract Marine environments are subject to increasing disturbance events, and coral reef ecosystems are particularly vulnerable. During periods of environmental change, organisms respond initially through rapid behavioural modifications. Whilst mean population level modifications to behaviour are well documented, how these shifts vary between individuals, and the relative trade-offs that are induced, are unknown. We test whether the frequency and time invested in different behaviours varies both between and within individuals with varying resource availability. To do this, we quantify differences in four key behavioural categories (aggression, exploration, feeding and sociability) at two sites of different resource availability, using an obligate corallivore butterflyfish species (Chaetodon lunulatus). Individuals on a low resource site held larger territories, investing more time in exploration, which was traded off with less time invested on aggression, feeding and sociability. Repeatability measures indicated that behavioural differences between sites could plausibly be driven by both plasticity of behaviour within individuals and habitat patchiness within feeding territories. By combining population-level means, co-correlation of different behaviours and individual-level analyses, we reveal potential mechanisms behind behavioural variation in C. lunulatus due to differences in resource availability. Significance statement Using observational methods, we identify differences in the behaviour of an obligate corallivorous butterflyfish (Chaetodon lunulatus) between a high and a low resource site. We use a combination of density surveys, territory mapping and behavioural observation methods in a comparative analysis to relate behaviour directly to the environment in which it occurs. Bringing together insights from game theory and optimal foraging, we also use our results to highlight how understanding the correlations of different behaviours can inform our understanding of the extent to which behaviours are plastic or fixed. Furthermore, by considering how multiple behaviours are correlated, we move away from exploring individual behaviours in isolation and provide an in-depth insight into how differences in behaviour both between individuals and at the population level can affect responses to declining resource availability.

Identifying the environmental drivers of variation in fitness-related traits is a central objective in ecology and evolutionary biology. Temporal fluctuations of these environmental drivers are often synchronized at large spatial scales. Yet, whether synchronous environmental conditions can generate spatial synchrony in fitness-related trait values (i.e., correlated temporal trait fluctuations across populations) is poorly understood. Using data from long-term monitored populations of blue tits (Cyanistes caeruleus, n = 31), great tits (Parus major, n = 35), and pied flycatchers (Ficedula hypoleuca, n = 20) across Europe, we assessed the influence of two local climatic variables (mean temperature and mean precipitation in February–May) on spatial synchrony in three fitness-related traits: laying date, clutch size, and fledgling number. We found a high degree of spatial synchrony in laying date but a lower degree in clutch size and fledgling number for each species. Temperature strongly influenced spatial synchrony in laying date for resident blue tits and great tits but not for migratory pied flycatchers. This is a relevant finding in the context of environmental impacts on populations because spatial synchrony in fitness-related trait values among populations may influence fluctuations in vital rates or population abundances. If environmentally induced spatial synchrony in fitness-related traits increases the spatial synchrony in vital rates or population abundances, this will ultimately increase the risk of extinction for populations and species. Assessing how environmental conditions influence spatiotemporal variation in trait values improves our mechanistic understanding of environmental impacts on populations. birds, climate, clutch size, comparative analysis, fitness-related traits, fledgling number, phenology, spatial synchrony, timing of breeding, weather

Behavioural responses are often the first reaction of an organism to human-induced rapid environmental change (HIREC), yet current empirical evidence provides no consensus about the main environmental features that animals respond to behaviourally or which behaviours are responsive to HIREC. To understand how changes in behaviour can be predicted by different forms of HIREC, we conducted a meta-analysis of the existing empirical literature focusing on behavioural responses to five axes of environmental change (climate change, changes in CO2, direct human impact, changes in nutrients and biotic exchanges) in five behavioural domains (aggression, exploration, activity, boldness and sociability) across a range of taxa but with a focus on fish and bird species. Our meta-analysis revealed a general absence of directional behavioural responses to HIREC. However, the absolute magnitude of the effect sizes was large. This means that animals have strong behavioural responses to HIREC, but the responses are not clearly in any particular direction. Moreover, the absolute magnitude of the effect sizes differed between different behaviours and different forms of HIREC: Exploration responded more strongly than activity, and climate change induced the strongest behavioural responses. Model heterogeneities identified that effect sizes varied primarily because of study design, and the specific sample of individuals used in a study; phylogeny also explains significant variation in our bird model. Based on these results, we make four recommendations to further our understanding: 1) a more balanced representation of laboratory and field studies, 2) consideration of context dependency, 3) standardisation of the methods and definitions used to quantify and study behaviours and 4) consideration of the role for individual differences in behaviour. © 2021 Nordic Society Oikos. Published by John Wiley & Sons Ltd

The causes and consequences of variation in the incubation regimes of oviparous animals remain unclear, despite having important fitness consequences. Avian incubation regimes can be shortened by parents initiating incubation prior to clutch completion or prolonged when there are gaps in the laying sequence. Here, we begin by quantifying variation in the incubation regimes of three populations of blue tits Cyanistes caeruleus from the UK and Poland before examining the consequences of such variation for their hatching and fledging success. We then investigate the mechanism causing such variation by exploring the impact of local weather conditions on incubation regimes. The difference between the expected and actual hatching dates of clutches was termed the “hatching deviation” and this showed considerable variation. Hatching deviation was negatively related to local temperature and clutch size. Hatching deviation affected hatching success and hatching deviation, temperature, wind speed and clutch size affected fledging success. Deviating from the expected laying and incubation regime caused lowered reproductive success. The most successful birds were those that were able to lay one egg per day and begin incubation upon clutch completion.

The phenology of many species shows strong sensitivity to climate change; however, with few large scale intra-specific studies it is unclear how such sensitivity varies over a species’ range. We document large intra-specific variation in phenological sensitivity to temperature using laying date information from 67 populations of two European songbirds covering a large part of their breeding range. Populations inhabiting deciduous habitats showed stronger phenological sensitivity compared with those in evergreen and mixed habitats. Strikingly, however, the lowest sensitivity was seen in populations that had experienced the greatest change in climate. Therefore, we predict that the strongest phenological advancement will not occur in those populations with the highest sensitivity. Our results show that to effectively assess the impact of climate change on phenology across a species range it will be necessary to account for intra-specific variation in phenological sensitivity, climate change exposure, and the ecological characteristics of a population.

Early theoretical models predicted that over evolutionary timescales, changes in effort by one biparental parent should result in incomplete compensation by the other. Empirical studies, however, report responses ranging from no compensation through to complete compensation which may mean that parents respond to each other's efforts over short time scales, as predicted by some recent theoretical models. Few studies have examined behavioural changes over short time periods which mimic the onset of reduced effort so we removed one blue tit (Cyanistes caeruleus) parent for 20 min during nestling provisioning. We then quantified the provisioning rates of both parents for 60 min 'pre-removal', the non-removed partner during the 20 min 'removal' period and both parents for 60 min 'post-removal'. When compared to pre-removal, both sexes reduced their provisioning rates during the removal stage and also during the post-removal stage. There were, however, sex-specific provisioning patterns in the hour after the parent was returned because after females were released, males began provisioning at a relatively high rate and then maintained that rate across the hour after removal whereas after males were released, females began provisioning at a low rate but significantly increased thereafter. There was no long term effect on offspring fitness, which probably reflects the short time parents were removed and so we conclude that parents with biparental care adjust their provisioning rates to successfully overcome very short term decreases in care.

Populations of Afro-Palearctic migrant birds have shown severe declines in recent decades. To identify the causes of these declines, accurate measures of both demographic rates (seasonal productivity, apparent survival, immigration) and environmental parameters will allow conservation and research actions to be targeted effectively. We used detailed observations of marked breeding birds from a ‘stronghold’ population of whinchats Saxicola rubetra in England (stable against the declining European trend) to reveal both on-site and external mechanisms that contribute to population change. From field data, a population model was developed based on demographic rates from 2011 to 2014. Observed population trends were compared to the predicted population trends to assess model-accuracy and the influence of outside factors, such as immigration. The sensitivity of the projected population growth rate to relative change in each demographic rate was also explored. Against expectations of high productivity, we identified low seasonal breeding success due to nocturnal predation and low apparent first-year survival, which led to a projected population growth rate (λ) of 0.818, indicating a declining trend. However, this trend was not reflected in the census counts, suggesting that high immigration was probably responsible for buffering against this decline. Elasticity analysis indicated λ was most sensitive to changes in adult survival but with covariance between demographic rates accounted for, most temporal variation in λ was due to variation in productivity. Our study demonstrates that high quality breeding habitat can buffer against population decline but high immigration and low productivity will expose even such stronghold populations to potential decline or abandonment if either factor is unsustainable. First-year survival also appeared low, however this result is potentially confounded by high natal dispersal. First-year survival and/or dispersal remains a significant knowledge gap that potentially undermines local solutions aimed at counteracting low productivity.

This is the peer reviewed version of the following article: Sutherland, W.J., Alvarez‐Castaneda, S.T., Amano, T., Ambrosini, R., Atkinson, P., Baxter, J.M., Bond, A.L., Boon, P.J., Buchanan, K.L., Barlow, J., Bogliani, G., Bragg, O.M., Burgman, M., Cadotte, M.W., Calver, M., Cooke, S.J., Corlett, R.T., Devictor, V., Ewen, J.G., Fisher, M., Freeman, G., Game, E., Godley, B.J., Gortazar, C., Hartley, I.R., Hawksworth, D.L., Hobson, K.A., Lu, M.‐L., Martin‐Lopez, B., Ma, K., Machado, A., Maes, D., Mangiacotti, M., McCafferty, D.J., Melfi, V., Molur, S., Moore, A.J., Murphy, S.D., Norris, D., van Oudenhoven, A.P., Powers, J., Rees, E.C., Schwartz, M.W., Storch, I. and Wordley, C. (2020), Ensuring tests of conservation interventions build on existing literature. Conservation Biology, 34: 781-783, which has been published in final form at https://doi.org/10.1111/cobi.13555. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. The attached file is the final approved author manuscript version, you are advised to consult the publisher’s version if you wish to cite from it.

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 eco-logical processes in the wild. Furthermore, 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 evolution-ary research based on long-term 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 year and a half since the establishment, SPI-Birds has recruited over 120 members, and currently hosts data on almost 1.5 million individual birds collected in 80 populations over 2,000 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 collab-oration and synthesis. We provide community-derived data and meta-data stand-ards and improve data integrity guided by the principles of Findable, Accessible, Interoperable and Reusable (FAIR), and aligned with the existing metadata lan-guages (e.g. ecological meta-data language)., The encouraging community involvement stems from SPI-Bird's decentralized ap-proach: 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 demogra-phy, etc.) will aid much-needed large-scale ecological data integration., The SPI-Birds have been supported by an NWO personal grant (grant number 016.Veni.181.054) to A.C., and a Research Council of Norway grant: 223257 (SFF-III) and 267511 (EVOCLIM).

Correlational selection is defined as selection for adaptive character combinations, and it therefore favours combinations of coevolved traits via phenotypic integration. Whereas the evolution of avian nest-building and egg-laying characteristics are well understood, their correlated dynamics remain overlooked. Here, we examined patterns of correlated evolution between nest, egg and clutch characteristics in 855 species of birds from 90 families, representing nearly 9% and 33% of avian species- and family-level diversity. We show that the ancestral state of birds’ nests was semi-open with nest sites having since become progressively more open over time. Furthermore, nest characteristics appear to have influenced egg-laying patterns in that while semi-open nests with variable clutch sizes were probably ancestral, clutch sizes have declined over evolutionary time in both open and closed nests. Ancestrally, avian eggs were also large, heavy and either elliptic or round, and there have been high transition rates from elliptic to round eggs in open nests and vice versa in closed nests. Ancestrally, both unpigmented (white) and pigmented (blue–brown) eggs were laid in open nests, although blue–brown eggs have transitioned more to white over time in open and closed nests, independently. We conclude that there has been a remarkable level of correlated evolution between the nest and egg characteristics of birds, which supports scenarios of correlational selection on both of these extended avian phenotypes.

Bespoke microsatellite marker panels are increasingly affordable and tractable to researchers and conservationists. The rate of microsatellite discovery is very high within a shotgun genomic data set, but extensive laboratory testing of markers is required for confirmation of amplification and polymorphism. By incorporating shotgun next‐generation sequencing data sets from multiple individuals of the same species, we have developed a new method for the optimal design of microsatellite markers. This new tool allows us to increase the rate at which suitable candidate markers are selected by 58% in direct comparisons and facilitate an estimated 16% reduction in costs associated with producing a novel microsatellite panel. Our method enables the visualisation of each microsatellite locus in a multiple sequence alignment allowing several important quality checks to be made. Polymorphic loci can be identified and prioritised. Loci containing fragment‐length‐altering mutations in the flanking regions, which may invalidate assumptions regarding the model of evolution underlying variation at the microsatellite, can be avoided. Priming regions containing point mutations can be detected and avoided, helping to reduce sample‐site‐marker specificity arising from genetic isolation, and the likelihood of null alleles occurring. We demonstrate the utility of this new approach in two species: an echinoderm and a bird. Our method makes a valuable contribution towards minimising genotyping errors and reducing costs associated with developing a novel marker panel. The Python script to perform our method of multi‐individual microsatellite identification (MiMi) is freely available from GitHub (https://github.com/graemefox/mimi).

Nest building is a taxonomically widespread and diverse trait that allows animals to alter local environments to create optimal conditions for offspring development. However, there is growing evidence that climate change is adversely affecting nest-building in animals directly, for example via sea-level rises that flood nests, reduced availability of building materials, and suboptimal sex allocation in species exhibiting temperature-dependent sex determination. Climate change is also affecting nesting species indirectly, via range shifts into suboptimal nesting areas, reduced quality of nest-building environments, and changes in interactions with nest predators and parasites. The ability of animals to adapt to sustained and rapid environmental change is crucial for the long-term persistence of many species. Many animals are known to be capable of adjusting nesting behaviour adaptively across environmental gradients and in line with seasonal changes, and this existing plasticity potentially facilitates adaptation to anthropogenic climate change. However, whilst alterations in nesting phenology, site selection and design may facilitate short-term adaptations, the ability of nest-building animals to adapt over longer timescales is likely to be influenced by the heritable basis of such behaviour. We urgently need to understand how the behaviour and ecology of nest-building in animals is affected by climate change, and particularly how altered patterns of nesting behaviour affect individual fitness and population persistence. We begin our review by summarising how predictable variation in environmental conditions influences nest-building animals, before highlighting the ecological threats facing nest-building animals experiencing anthropogenic climate change and examining the potential for changes in nest location and/or design to provide adaptive short- and long-term responses to changing environmental conditions. We end by identifying areas that we believe warrant the most urgent attention for further research.

We determined breeding season habitat preferences for a declining migrant grassland bird, the Whinchat Saxicola rubetra, using intensive, territory-scale habitat and invertebrate data, and independently gathered landscape-scale field survey and remotely sensed habitat data to determine whether the same habitat relationships were evident at both spatial scales. At the territory scale, low-elevation and a heterogeneous vegetation structure with a high density of perches and tussocks were the dominant features of occupied habitats. The landscape-scale model successfully predicted areas where breeding Whinchats were more likely to occur, and similar and consistent relationships with habitat features occurred at both spatial scales. However, plant species richness and topographic slope elicited different responses at different spatial scales, with steeper slopes and high plant species richness favoured at the landscape scale, whereas at the territory scale, low plant species richness was preferred and slope did not determine settlement. These differences reflect differences in the way the data were measured and extrapolated. This study identifies important attributes of lowland grassland habitats and landscapes for a stable population of breeding Whinchats, and the analysis shows the good predictive ability of remotely sensed data to model this species' distribution at larger spatial extents. Our findings provide methods for assessing habitat availability for this declining species and for managing habitats and landscapes to provide these essential elements.

Adverse weather conditions are expected to result in impaired nestling development in birds, but empirical studies have provided equivocal support for such a relationship. This may be because the negative effects of adverse weather conditions are masked by parental effects. Globally, ambient temperatures, rainfall levels and wind speeds are all expected to increase in a changing climate and so there is a need for a better understanding of the relationship between weather conditions and nestling growth. Here, we describe a correlative study that examined the relationships between local temperatures, rainfall levels and wind speeds and the growth of individual blue tit (Cyanistes caeruleus) nestlings in relation to their hatching order and sex. We found that changes in a range of morphological characters were negatively related to both temperature and wind speed, but positively related to rainfall. These patterns were further influenced by the hatching order of the nestlings but not by nestling sex. This suggests that the predicted changes in local weather conditions may have complex effects on nestling growth, but that parents may be able to mitigate the adverse effects via adaptive parental effects. We therefore conclude that local weather conditions have complex effects on avian growth and the implications for patterns of avian growth in a changing climate are discussed.

Feathers are a widely used nesting material and whilst they may serve to provide thermoregulatory benefits, to repel ectoparasites and/or act as a sexual signal, their exact function remains unclear. Here, we describe a two-part study that examined the function of feathers in Blue Tit ( Cyanistes caeruleus) nests. In the first part, we supplemented (experimental) Blue Tit nests with individually-marked feathers during nest building and incubation, and examined the fate of those feathers: remain in the original nestbox; removed ( i.e. lost); or moved to neighbouring nestbox. Parents’ responses to them and their reproductive success was compared with unsupplemented (control) pairs. Blue Tits at experimental nests generally removed the feathers provided during nest building but generally kept the feathers provided during incubation, providing no support for a thermoregulatory function of feather nest constituents; they retained feathers more often when ambient temperatures were higher later in the spring. As ectoparasite load did not differ between experimental and control nests, feathers appeared to function primarily as sexual signals. We suggest that males during nest building generally removed additional feathers because their introduction mimicked another male attempting to cuckold the resident male. In the second part of the study, we searched for evidence of conspecific nest prospecting and nest material theft by placing individually-marked feathers into the two nestboxes neighbouring each experimental nestbox used in the first part of the study, again both during nest building and incubation. We found no evidence of nest material theft or therefore of conspecific nest prospecting, even when one or both of the neighbouring nestboxes were empty. This suggests that feather availability is not limiting and we conclude that feathers serve primarily as a sexual signal in Blue Tits. However, we were unable to provide any evidence of nest material theft and studies that film both of the parents’ responses to the feathers would be useful.

The energetic costs associated with nest construction are becoming increasingly apparent, yet we still know remarkably little about how those costs affect parental care during the subsequent egg laying, incubation, nestling provisioning and fledgling stages of reproduction. Here we describe a study where we provided experimental pairs of Blue Tits ( Cyanistes caeruleus) with supplementary food throughout the nest-building period and then quantified nest characteristics, incubation behaviours and nestling provisioning rates at experimentally fed and unfed control nests. We have already reported that experimental females built heavier nests than unfed females and here we extend that study by showing that whilst hatching asynchrony and brood sizes at hatching did not differ between treatments, males at experimental nests provisioned their offspring at significantly higher rates than did males at control nests. As female provisioning rates did not differ significantly between treatments, total parental provisioning rates were higher at experimental nests, although brood sizes and the mass of nestlings at pre-fledging did not differ between treatments. This implies that when the energetic costs of nest construction were indirectly reduced via the provision of supplementary food, females responded by constructing larger nests. Females did not alter their incubation or provisioning behaviours but males did increase their provisioning rates. Unfortunately, our experimental design means that we are unable to disentangle the relative contributions of the provision of supplementary food and the size of the female-built nest in causing male provisioning rates to be higher at experimental nests. In summary, our study suggests that the energetic costs of nest construction are carried over into future stages of reproduction in a sex-specific and complex manner.

Parent-offspring conflict over the supply of parental care results in offspring attempting to exert control using begging behaviours and parents attempting to exert control by manipulating brood sizes and hatching patterns. The peak load reduction hypothesis proposes that parents can exert control via hatching asynchrony, as the level of competition amongst siblings is determined by their age differences and not by their growth rates. Theoretically, this benefits the parents by reducing both the peak load of the offspring's demand and their overall demand for food and benefits the offspring by reducing the amplification of their competition. However, the peak load reduction hypothesis has only received mixed support. Here, we describe an experiment where we manipulated the hatching patterns of domesticated zebra finch Taeniopygia guttata broods and quantified patterns of nestling begging and parental feeding effort. There was no difference in the begging intensity of nestlings raised in asynchronous or experimentally synchronous broods, yet parental feeding effort was lower when provisioning asynchronous broods and particularly so when levels of nestling begging were low. Further, both parents acted in unison, as there was no evidence of parentally biased favouritism in relation to hatching pattern. Therefore, our study provided empirical support for the prediction that hatching asynchrony reduces the feeding effort of parents, thereby providing empirical support for the peak load reduction hypothesis.

© 2014 The Authors. Nests are structures built to support and protect eggs and/or offspring from predators, parasites, and adverse weather conditions. Nests are mainly constructed prior to egg laying, meaning that parent birds must make decisions about nest site choice and nest building behavior before the start of egg-laying. Parent birds should be selected to choose nest sites and to build optimally sized nests, yet our current understanding of clutch size-nest size relationships is limited to small-scale studies performed over short time periods. Here, we quantified the relationship between clutch size and nest size, using an exhaustive database of 116 slope estimates based on 17,472 nests of 21 species of hole and non-hole-nesting birds. There was a significant, positive relationship between clutch size and the base area of the nest box or the nest, and this relationship did not differ significantly between open nesting and hole-nesting species. The slope of the relationship showed significant intraspecific and interspecific heterogeneity among four species of secondary hole-nesting species, but also among all 116 slope estimates. The estimated relationship between clutch size and nest box base area in study sites with more than a single size of nest box was not significantly different from the relationship using studies with only a single size of nest box. The slope of the relationship between clutch size and nest base area in different species of birds was significantly negatively related to minimum base area, and less so to maximum base area in a given study. These findings are consistent with the hypothesis that bird species have a general reaction norm reflecting the relationship between nest size and clutch size. Further, they suggest that scientists may influence the clutch size decisions of hole-nesting birds through the provisioning of nest boxes of varying sizes.

Parental investment in reproduction is generally limited by the availability of food and so avian life-history research has generally focused on the brood rearing phase, when food requirements are greatest. Only relatively recently has the focus extended to the incubation phase and, even more recently, to the nest-building phase where there is now observational, comparative and experimental evidence that avian nest building is an energetically and temporally expensive activity. This review emphasises that nest construction is energetically expensive and we suggest that such costs should be incorporated into avian life-history research.

The ecological and evolutionary consequences of variation in behaviour between individuals are well studied, yet the causes of such variation remain poorly understood. Parents can generally exert a great deal of influence on the early life of their offspring, so one possibility is that the mode of parental investment determines subsequent offspring behaviours. In birds, hatching asynchrony occurs when females begin incubation prior to clutch completion, and the subsequent hatching regime creates phenotypic disparities between early and late-hatched offspring. By experimentally manipulating hatching patterns in zebra finches, Taeniopygia guttata, we examined the influence of hatching asynchrony on subsequent exploratory behaviour during adulthood. Late-hatched birds from asynchronous broods explored the novel environment more than their siblings which hatched earlier or came from synchronous broods, although there were no differences in exploratory behaviour towards a novel object. Additionally, females were bolder towards a novel object than were males, independently of hatching regime, but there were no sex differences in exploration of the novel environment. Our results support the idea that both hatching asynchrony and sex have previously underappreciated influences on offspring behaviours, and highlight the importance of variation in parental investment in generating and maintaining behavioural variation.

Our understanding of fundamental organismal biology has been disproportionately influenced by studies of a relatively small number of ‘model’ species extensively studied in captivity. Laboratory populations of model species are commonly subject to a number of forms of past and current selection that may affect experimental outcomes. Here, we examine these processes and their outcomes in one of the most widely used vertebrate species in the laboratory – the zebra finch (Taeniopygia guttata). This important model species is used for research across a broad range of fields, partly due to the ease with which it can be bred in captivity. However despite this perceived amenability, we demonstrate extensive variation in the success with which different laboratories and studies bred their subjects, and overall only 64% of all females that were given the opportunity, bred successfully in the laboratory. We identify and review several environmental, husbandry, life-history and behavioural factors that potentially contribute to this variation. The variation in reproductive success across individuals could lead to biases in experimental outcomes and drive some of the heterogeneity in research outcomes across studies. The zebra finch remains an excellent captive animal system and our aim is to sharpen the insight that future studies of this species can provide, both to our understanding of this species and also with respect to the reproduction of captive animals more widely. We hope to improve systematic reporting methods and that further investigation of the issues we raise will lead both to advances in our fundamental understanding of avian reproduction as well as to improvements in future welfare and experimental efficiency.

Marie Vaugoyeau [et al.], The increase in size of human populations in urban and agricultural areas has resulted in considerable habitat conversion globally. Such anthropogenic areas have specific environmental characteristics, which influence the physiology, life history, and population dynamics of plants and animals. For example, the date of bud burst is advanced in urban compared to nearby natural areas. In some birds, breeding success is determined by synchrony between timing of breeding and peak food abundance. Pertinently, caterpillars are an important food source for the nestlings of many bird species, and their abundance is influenced by environmental factors such as temperature and date of bud burst. Higher temperatures and advanced date of bud burst in urban areas could advance peak caterpillar abundance and thus affect breeding phenology of birds. In order to test whether laying date advance and clutch sizes decrease with the intensity of urbanization, we analyzed the timing of breeding and clutch size in relation to intensity of urbanization as a measure of human impact in 199 nest box plots across Europe, North Africa, and the Middle East (i.e., the Western Palearctic) for four species of hole-nesters: blue tits (Cyanistes caeruleus), great tits (Parus major), collared flycatchers (Ficedula albicollis), and pied flycatchers (Ficedula hypoleuca). Meanwhile, we estimated the intensity of urbanization as the density of buildings surrounding study plots measured on orthophotographs. For the four study species, the intensity of urbanization was not correlated with laying date. Clutch size in blue and great tits does not seem affected by the intensity of urbanization, while in collared and pied flycatchers it decreased with increasing intensity of urbanization. This is the first large-scale study showing a species-specific major correlation between intensity of urbanization and the ecology of breeding. The underlying mechanisms for the relationships between life history and urbanization remain to be determined. We propose that effects of food abundance or quality, temperature, noise, pollution, or disturbance by humans may on their own or in combination affect laying date and/or clutch size., E. Barba acknowledges funding of project CGL2013-48001-C2-1-P (Spanish Ministry of Science and Innovation).

Recent studies are documenting the extent to which the mass and construction of bird nests varies between individuals and locations. In the Blue Tit ( Cyanistes caeruleus) and Great Tit ( Parus major), temperatures experienced by females during nest construction are inversely related to nest mass. Moreover, Mainwaring et al. ( Journal of Biogeography, 2012) showed that nests constructed at high latitude are heavier and better insulated than nests built by conspecifics in the south. Although mean spring temperature was used as a proxy for latitude in the Mainwaring et al. study, it remains untested whether individual birds build nests in response to a narrower range of temperatures experienced at the start of the breeding season. Our study showed that irrespective of latitude nest mass, and in particular nest cup mass, of Blue Tits and Great Tits was significantly affected by the temperature experienced by the birds for the seven days preceding clutch initiation. Similar results were seen with the insulatory properties of nests. The potential impact of variation in nest construction and insulation on subsequent incubation and chick-rearing behaviour is discussed.

Hatching asynchrony can have profound short-term consequences for offspring, although the long-term consequences are less well understood. The purpose of this study was to examine the long-term consequences of hatching asynchrony for offspring fitness in birds. Specifically, we aimed to test the hypothesis that hatching asynchrony increases the sexual attractiveness and fecundity, respectively, of early-hatched male and female zebra finch, Taeniopygia guttata (Vieillot, 1817) offspring. Mate-choice trials comparing male nestlings with the same parents, but that were reared in asynchronous or experimentally synchronous broods, revealed no female preference in relation to hatching regime. We did however find strong evidence that, as adults, late-hatched males were more attractive to females than siblings that had hatched earlier. Meanwhile, we found a weak trend towards early-hatched females depositing more carotenoids and retinol in the egg yolk than late-hatched or synchronously hatched females, although there were no differences in terms of clutch characteristics or the deposition of a-tocopherol or ?-tocopherol in the egg yolk. Therefore, we found that the beneficial long-term consequences of hatching asynchrony were sex specific, being accrued by late-hatched male nestlings and by early-hatched female nestlings. Consequently, we conclude that the long-term consequences of hatching asynchrony are more complex than previously realised. (c) 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106, 430438.

Sexual size dimorphism results in asymmetric sibling competition, and nestlings of the smaller sex are expected to prioritise the development of those morphological characters that maximise effective sibling competition. In this study, we test the prediction that female Blue Tit Cyanistes caeruleus nestlings, which are smaller than males, preferentially develop relative gape area in a trade-off against growth of mass and head-bill length. We found that whilst male nestlings were heavier, female and male nestlings had similar head-bill lengths, but females had relatively larger gape areas. Therefore, female nestlings were investing relatively more resources in gape area than males because of their overall smaller body size, presumably because gapes are an integral part of the process used by nestlings to solicit food from their parents.

Family conflicts over parental care result in offspring attempting to exert control using solicitation behaviours, whilst the parents are potentially able to retaliate through provisioning rules. However, the evolutionary interests of one parent may not necessarily support the evolutionary interests of the other parent, and such conflicts of interest may be expressed in how the two parents allocate the same form of parental care to individual offspring. Theory suggests that such parentally biased favouritism is a universally predicted outcome of evolutionary conflicts of interest, and empirical evidence suggests that parentally biased favouritism occurs in relation to offspring size and solicitation behaviours. However, unequivocal empirical evidence of parentally biased favouritism in relation to offspring sex is absent, due to being strongly confounded by sex differences in size and solicitation behaviours. Here, we present strong evidence for parentally biased favouritism in relation to offspring sex in zebra finches (Taeniopygia guttata), independent of the effects of chick size and begging intensity. Mothers preferentially provisioned sons over daughters, whilst fathers showed no bias, meaning that sons received more food than daughters. Parentally biased favouritism in relation to offspring sex facilitates parental control over evolutionary conflicts of interest and is probably more widespread than previously realised.

The composition and dynamics of the gastrointestinal bacterial communities in birds is determined by both host-specific and environmental exposure factors yet these are poorly understood. We selected the zebra finch, Taeniopygia guttata, as the host species to examine the diversity and temporal stability of the faecal microflora in a bird, owing to its importance as a model organism in avian ecology, neuroscience and evolution studies. The stability of the gut bacterial community of individual male and female zebra finches was assessed through repeat faecal sampling via culture and temperature gradient gel electrophoresis and partial sequencing of PCR-amplified eubacterial 16S rRNA gene products. Nineteen bacterial genera were detected across all samples (n = 99), with each bird carrying on average six operational taxonomic units. Using a novel statistical approach, we showed that bacterial assemblages and community richness varied between individual birds but remained stable over time within individuals. Neither the composition nor richness of bacterial communities differed significantly between the sexes. Our results show that zebra finches housed together under controlled conditions show consistent variation between individuals in their gut microflora that is not attributable to differences in host exposure to environmental microbial sources. Future studies could usefully explore the origin of this individual-specific variation and its consequences for host fitness and sexual selection.

The outcome of sibling competition for food is often determined by variation in body size within the brood and involves trade-offs; traits that enhance competitive ability within the nest may be developed at the expense of traits that enable effective flight at fledging, or vice versa. We quantified growth of skeletal, body mass and feather traits in male and female Blue Tit Cyanistes caeruleus nestlings. Males were significantly heavier, had longer tarsi and tended to have greater head-bill lengths than females, whereas females were similar to males in wing flight feather growth. These differences in growth may result from sexual differences in selection of the traits. Females are likely to prioritize feather growth to facilitate synchronized fledging with the rest of the brood, and to enhance escape from predators. We suggest that males are heavier and develop longer tarsi because body size is an important determinant of male reproductive success.

The Australian zebra finch, Taeniopygia guttata, is a widely used model organism, yet few studies have compared domesticated and wild birds with the aim of examining its relevance as an evolutionary model species. Domestic and wild broods hatch over approximately 4 and 2 days, respectively, which is important given that nestlings can fledge after as little as 12 days, although 16–18 days is common. We aimed to evaluate the extent to which the greater hatching asynchrony in domestic stock may effect reproductive success through greater variance in size hierarchies, variance in within-brood growth rates, and partial brood mortality. Therefore, by simultaneously controlling brood sizes and experimentally manipulating hatching intervals in both domesticated and wild birds, we investigated the consequences of hatching intervals for fledging success and nestling growth patterns, as well as trade-offs. Fledging success was similarly high in domestic and wild broods of either hatching pattern. Nonetheless, between-brood analyses revealed that domestic nestlings had significantly higher masses, larger skeletal characters, and longer wings than their wild counterparts, although wild nestlings had comparable wing lengths at the pre-fledging stage. Moreover, within-brood analyses revealed only negligible differences between domestic and wild nestlings, and larger effects of hatching order and hatching pattern. Therefore, despite significant differences in the hatching intervals, and the ultimate size achieved by nestlings, the domestication process does not appear to have significantly altered nestling growth trade-offs. The present study provides reassuring evidence that studies involving domesticated zebra finches, or other domesticated model organisms, may provide reasonable adaptive explanations in behavioural and evolutionary ecology.

Maternal and environmental effects can profoundly influence offspring phenotypes, independent of genetic effects. Within avian broods, both the asymmetric post-hatching environment created by hatching asynchrony and the differential maternal investment through the laying sequence have important consequences for individual nestlings in terms of the allocation of resources to body structures with different contributions to fitness. The purpose of this study was to evaluate the relative importance of post-hatching environmental and maternal effects in generating variation in offspring phenotypes. First, an observational study showed that within blue tit, Cyanistes caeruleus, broods, late-hatched nestlings allocated resources to tarsus development, maintained mass gain and head-bill growth and directed resources away from the development of fourth primary feathers. Second, a hatching order manipulation experiment resulted in nestlings from first-laid eggs hatching last, thereby allowing comparison with both late and early-hatched nestlings. Experimental nestlings had growth patterns which were closer to late-hatched nestlings, suggesting that within-brood growth patterns are determined by post-hatching environmental effects. Therefore, we conclude that post-hatching environmental effects play an important role in generating variation in offspring phenotypes.

Hatching asynchrony results in age and size hierarchies within broods, and the subsequent asymmetric competition among siblings has important consequences for nestlings' fitness. In this study, we compare the growth of Barn Swallow (Hirundo rustica) nestlings in relation to their order of hatching. The aim was to test the prediction that early-hatched nestlings develop differently from late-hatched nestlings, which should be under greater pressure to trade investment in growth in favor of traits important to simultaneous fledging. Early-hatched nestlings were always larger than late-hatched nestlings, but when the age difference was taken into account, the two classes of nestling gained mass and head-bill length in similar ways, including having similar asymptotes, as predicted by nonlinear curve models. For wing length, however, late-hatched nestlings reached the inflection point of growth sooner than early-hatched nestlings, and although scaled rates of wing growth were similar, early-hatched ...

Nest building requires parental investment and we should expect to find trade-offs between building and other behaviours or demands. For example, species breeding in temperate zones face the seasonal shift from spring to summer and might alter their nest construction in relation to environmental conditions as the season progresses. We quantified seasonal variation in the length of the nest building period, nest mass, composition, Hen Flea Ceratophyllus gallinae abundance and egg production in nestbox breeding Blue Tits Cyanistes caeruleus. The nest building period decreased seasonally, possibly indicating individual adjustment of optimal time of reproduction. Despite this, there was no seasonal trend in overall nest mass, although nest composition did change. The mass of the nests' moss base and Hen Flea abundance showed no seasonal variation, but there was a seasonal decline in the mass of the cup lining material, suggesting that female Blue Tits selectively adjust the cup lining component of their nests to reflect increasing ambient temperatures in order to create an optimal microclimate for the developing embryos and nestlings.

Among bird species where only one parent constructs the nest, the “sexual display hypothesis” predicts that building behaviour and the structure of the completed nest is a post-pairing, sexually selected signal that informs the non-builder of her/his partner's quality and/or willingness to invest in reproduction. Moreover, the “differential allocation hypothesis” predicts that an individual's investment in parental behaviours, such as nest building, will vary in relation to the partner's quality. These hypotheses were examined in the socially monogamous, hole-breeding Blue Tit, a species in which the female alone builds nests. Parental quality was quantified by recording body size, feather mite load and age. The weight of nests was found to correlate positively with female head-bill length and feather mite load, but not with any indicators of male quality. This result is in accordance with the “sexual display” hypothesis, and demonstrates that nest size could be a form of intra-specific communic...

Unlike many other polygynous passerine species, female Corn Buntings Miliaria calandra apparently do not suffer costs by pairing polygynously, yet it is unclear whether this is because polygynous males hold the highest quality territories or because pairing with polygynous males is unimportant in determining female reproductive success. Male Corn Buntings on North Uist, Scotland, consistently defended territories which contained nesting habitat, and females often foraged outside male territories when provisioning nestlings. Females showed strong preferences for nesting in uncultivated land, and 80% of nests were under Hogweed Heracleum sphondylium, possibly because this provided cover against predation and the weather. When provisioning nestlings, females showed strong preferences for foraging in cereal crops, probably because this habitat provided better food resources and/or better cover from predators. Males were unpaired or paired with one to three females per breeding season, but variation in territory size or vegetation composition did not explain differences in the number of females paired with individual males. We suggest that when females neither gain benefits nor suffer costs by breeding polygynously, and males do not differ greatly in the areas of habitat selected, polygyny can arise through random female settlement within the nesting habitat.

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.

In altricial birds, nestlings usually respond to the sound and appearance of the provisioning adults by begging for food when the adults arrive at the nest. Nestlings can, however, also beg incorrectly on hearing misleading sounds in the environment and fail to beg when the adult arrives. This study uses the blue tit Cyanistes caeruleus to test the hypotheses that nestling begging strategies are influenced by the reliability of the stimulus to beg, and that nestling motivational state affects the response to different stimuli. Here, we show experimentally that nestling hunger strongly influences the response to stimuli that vary in their reliability. While hunger increases begging rate, it also increases the likelihood that nestlings will beg when the parent is absent. This is in agreement with both the predictions of signal detection theory and recent empirical work on other species. We found, however, no evidence that age-related perceptual constraints influence the begging response of ten day old nestlings to different stimuli.

Evolutionary conflicts of interest between family members are expected to influence patterns of parental investment. In altricial birds, despite providing the same kind of parental care, patterns of investment in different offspring can differ between parents, a situation termed parentally biased favoritism. Previous explanations for parentally biased favoritism have received mixed theoretical and empirical support. Here, we test the prediction that in blue tits, Cyanistes caeruleus, females bias their food allocation rules to favor the smallest offspring during the nestling stage. By doing so, females could increase the subsequent amount of paternal care supplied by their partner during the fledging period, as a previous study showed that males feed the largest fledglings. When size differences within the brood are less pronounced, all offspring will require similar amounts of postfledging care, and thus, the male parent will lose the advantage of caring for the largest offspring that are closest to independence. In this study, we controlled the hunger of the smallest and largest nestlings in the brood and compared the food allocation rules of the 2 parents. We found that the male parent had a stronger preference than the female to feed the closest nestlings and made no distinction between nestlings based on size, whereas the female provisioned small hungry nestlings more when they were at intermediate distances from her. These differences in parental food allocation rules are consistent with predictions based on sexual conflict over postfledging parental investment. Copyright 2007, Oxford University Press.

Very little is known about the normal gastrointestinal flora of wild birds, or how it might affect or reflect the host’s life-history traits. The aim of this study was to survey the species richness of bacteria in the faeces of a wild population of blue tits Cyanistes caeruleus, and to explore the relationships between bacterial species richness and various life-history traits, such as age, sex and reproductive success. Using PCR-TGGE, 55 operational taxonomic units (OTUs) were identified in blue tit faeces. DNA sequencing revealed that the 16S rRNA gene was amplified from a diverse range of bacteria, including those that shared closest homology with Bacillus licheniformis, Campylobacter lari, Pseudomonas spp. and Salmonella spp. For adults, there was a significant negative relationship between bacterial species richness and the likelihood of being detected alive the following breeding season; bacterial richness was consistent across years but declined through the breeding season; and breeding pairs had significantly more similar bacterial richness than expected by chance alone. Reduced adult survival was correlated with the presence of an OTU most closely resembling C. lari; enhanced adult survival was associated with an OTU most similar to Arthrobacter spp. For nestlings, there was no significant change in bacterial species richness between the first and second week after hatching, and nestlings sharing the same nest had significantly more similar bacterial richness. Collectively, these results provide compelling evidence that bacterial species richness was associated with several aspects of the life-history of their hosts.

Parents should allocate parental investment in relation to the expected reproductive value of their offspring. We used a cross-fostering experiment to see whether factors influencing offspring reproductive value (brood size, nestling sex, age or paternity) were related to parental investment in nest defence in the blue tit, Cyanistes caeruleus. Although brood size and the incidence of extrapair paternity did not influence the nest defence behaviour of parents, we found a significant difference in the way male and female parents responded to the experimental change in sex ratio of the brood; the nest defence response of males was faster at nests with an increased proportion of sons, but the response of females was unrelated to changes in brood sex ratio. Furthermore, there was no relation between the original sex ratio of the brood, before manipulation, and the nest defence response of the male, indicating that paternal investment in this behaviour was a direct response to the manipulated brood sex ratio.

Although most (>90%) species of birds have biparental care, little is known about the consequences of such care for offspring behaviour and fitness-related traits. We examined the effect of biparental care on chick growth and begging behaviour in zebra finches, by comparing biparental broods with uniparental broods in which the male parent was removed and the brood size halved to control for potential parental workload. Differences in patterns of growth and begging behaviour between treatments therefore resulted from the difference in (1) the number of parents providing care and/or (2) the number of chicks per brood. Collaborating parents did not appear to act in concert and fed chicks independently of each other's feeding bouts. Broods reared by two parents were fed more frequently than those fed by one, and because biparental feeding bouts were less predictably spaced in time with less food available for each chick per feeding bout, competition was greater than in broods reared by single parents. Furthermore, chicks in biparental broods sustained an additional cost of begging: they had to beg almost twice as hard as chicks reared by single parents to receive a given amount of food, and they received less food per chick. Despite these effects, they grew faster. Growth rate may depend not just on the amount of food available but also on the frequency and predictability with which it is delivered, and, in particular, it reflects an adaptive response to competition for the available resources.

1. Maternal diet can significantly influence the quality and size of eggs, and this may, in turn, influence the fitness of offspring. In this study, we show how antioxidants (vitamin E compounds and carotenoids) in the diet of female zebra finches influence the concentrations of antioxidants in their eggs. Antioxidants are biochemicals derived from the diet, which reduce damage to cell membranes caused by the free radicals produced during normal metabolism and growth. 2. Females were given either a seed-only or a seed + rearing food diet prior to egg laying. The seed + rearing food diet was more enriched with carotenoids, but had lower amounts of less effective antioxidants, such as γ-tocopherol. Eggs were collected as they were laid, then analysed to determine the concentrations of antioxidants using high-performance liquid chromatography. 3. Females in the two food groups had similar rates of food consumption and laid similar sized clutches. Females on the seed-only diet produced eggs of similar mass to that of females on the seed + rearing food diet. 4. The concentrations of the most effective antioxidant (α-tocopherol) were higher in the eggs of females from the seed-only group and, for both food groups, concentrations decreased with successively laid eggs within clutches. The concentration of carotenoids in egg yolks did not differ between food treatments, but also decreased with successive eggs. Less effective antioxidants were relatively under-represented in eggs in relation to their availability in food, and were deposited in similar overall amounts between the two food treatments, and independently of laying sequence. 5. Our results indicate that egg size is not necessarily an accurate guide to egg quality, especially when comparing between clutches of different females or across species. Females may be able to adjust egg composition to influence offspring quality variation within broods, possibly traded-off against their personal use of antioxidants, their future reproductive success, control over sibling competition within their brood and/or brood reduction.

Parental care is often costly1; hence, in sexually reproducing species where both male and female parents rear their offspring (biparental care), sexual conflict over parental investment can arise2. Such conflict occurs because each care-giver would benefit from withholding parental investment for use with another partner, leading to a reduction in the amount of care given by one parent at the expense of the other3,4,5. Here we report experiments to explore the prediction from theory that parents rearing offspring alone may provide greater parental investment than when rearing offspring together with a partner3,5. We found that when the number of offspring per parent, and hence the potential workload, were kept constant, offspring received a greater per capita parental investment from single females than from both parents working together, and that males reared by single mothers were more sexually attractive as adults than their biparentally reared siblings. This difference between single- and two-parent families is due to a reduction in care provided by females when they care together with a male, rather than laziness by males or differences in the begging behaviour of chicks, supporting the claim that sexual conflict in biparental care can reduce the quality of offspring raised3,5.

This study examined the seasonal partitioning of nitrogen (N) between plants and soil microorganisms on a mountain plateaux (Carex bigelowii—Racomitrium lanuginosum heath) in the Scottish Highlands. Specifically, we determined whether there is a temporal relationship between the abundance of dominant soil fauna, soil nitrogen availability, and the partitioning of N between microbes and plants. We found that soil microorganisms and plant tissue of Carex contain similar portions of the total N pool, but that this N partitioning varies greatly over the growing season. At the onset of plant growth in May, the microbial N pool was at its lowest (1.8% of total N), and available N was sequestered by the severely N-limited microbial biomass. At this time, plant N requirement appears to have been met by the use of internal reserves of N in roots. Significant net mineralisation of N was not detected until microbial demands for N had been satisfied in June. Peak rates of N mineralisation corresponded to maximal plant biomass and shoot N content of Carex in July, whereas microbial sequestration of N was found to be most intense in late season when plant demands had subsided after senescence. Although microbial biomass was lowest in early season, we find no convincing evidence to support the notion that microbial competition for N is limited at this time. The patterns of N partitioning that we describe are likely to have implications for the retention of N in these high mountain ecosystems.