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The role of the availability of calcium in limiting the breeding success and intensity of eggshell specking in birds remains unclear. Experimentally, we provided blue tits (Cyanistes caeruleus) and great tits (Parus major) in woodlands with underlying calcium-rich limestone or calcium-poor gritstone with calcium during the egg stage or during the entire reproductive period and examined their breeding success and eggshell speckling. When provided with calcium during the egg stage, experimental blue tits laid larger clutch sizes with higher clutch weights than controls, whilst experimental great tits had higher fledging success than controls. When provided with calcium throughout reproduction, there was no effect of treatment on blue tit reproductive success, but experimental great tits had higher hatching success and nestling masses than controls. Additional calcium during the egg stage resulted in experimental great tits, but not blue tits, laying less speckled eggs than controls, and additional calcium throughout reproduction led to experimental blue tits and great tits laying less speckled eggs than controls. The provision of calcium led to both species generally having higher levels of reproductive success and less speckled eggs than controls, irrespective of habitat geology, meaning that calcium availability does determine avian breeding success and eggshell specking.

Nestboxes are widely provided as nesting sites for hole-nesting birds, yet the relative contribution of nestbox characteristics and habitat quality in determining the occupancy rates and breeding success of birds remains unclear. We provided nestboxes in deciduous woodlands in England and examined if those nestboxes were erected in random orientations and whether the orientation of nestboxes and habitat quality, in the form of tree density, influenced their occupation by, and breeding success of, Blue Tits (Cyanistes caeruleus), Great Tits (Parus major) and Pied Flycatchers (Ficedula hypoleuca). We found that first, the nestboxes were erected non-randomly orientated towards the north and east, and away from the south and west. Second, the occupation rates of none of the species was related to nestbox orientation or tree density. Third, the breeding success of neither Blue Tits nor Great Tits varied with tree density but did vary with nestbox orientation. Blue Tit hatching success and fledging success was higher in nestboxes facing south than in other directions whilst in Great Tits, clutch sizes, hatching success and fledging success was higher in nestboxes facing south than nestboxes facing other directions. Our results suggest that nestbox characteristics, such as orientation, have more influence on the reproductive success of passerines than habitat quality. This further suggests that conservationists should orientate nestboxes southwards in order to maximise their benefit to birds in temperate climates during the breeding season.

The causes and consequences of interspecific variation in sex-specific contributions to animal parental care are relatively well understood during pregnancy or incubation and during offspring provisioning, but comparative patterns of sex-biased investment during nest-, den-, or other shelter-building have been almost completely overlooked. This is surprising because birthing shelters’ protective properties have important fitness consequences for both parents and offspring. Here, we address this gap in our knowledge by testing predictions concerning sex-specific contributions to avian nest building in more than 500 species of Western Palearctic birds in relation to the time available to breed and sex-specific reproductive effort, while also examining correlates with nesting site and nest structure. Using multivariate phylogenetic comparative and path analysis approaches, we found that, opposite to what had been predicted, species in which females build nests alone have shorter breeding seasons and breed at higher latitudes. In addition, species in which females lay larger clutch sizes and incubate eggs alone are more likely to have nests built by females alone, again countering predictions that reproductive contributions are not traded-off between the sexes. Finally, however, sex-specific nest building contributions were predictably related to nest site and structure, as species in which females built nests alone were more likely to have open cup nests relative to enclosed, domed nests of species in which both parents build. Our study provides important new insights, and generates several new questions for experimental research into the adaptive dynamics of sex-specific contributions prior or at the onset of parental care.

There is increasing concern about the burgeoning effects of discarded plastic on the earth's biodiversity. Quantifying the presence of plastic and other anthropogenic waste in the environment can be logistically and financially challenging, although it is possible that bird' nests can be used as bioindicators. Many birds in heavily modified terrestrial ecoystems, such as urban environments, incorporate plastic and other anthropogenic materials into their nests but our understanding of the presence of discarded plastic in nests in rural woodlands remains poor. Here, we show that plastic and other anthropogenic materials were present in 35 % of 325 pied flycatcher (Ficedula hypoleuca) nests from 17 rural woodlands throughout Great Britain, although the woodlands did vary in the amount of material incorporated into nests. Then, in an experimental test at one study site, where flycatchers were provided with a choice of two types of natural and two types of anthropogenic nest materials, they preferentially selected one natural and one anthropogenic material. In another test, the flycatchers were provided with plastic of four colours and overwhelmingly selected white and avoided orange, blue and yellow plastic. Although the flycatcher's selectivity for certain material types and colours preclude their nests being a reliable indicator of plastic in the environment, our study nonetheless demonstrates that bird species incorporate anthropogenic materials, such as plastic, into their nests in rural woodlands.

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

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.

Weather conditions affect animals in many different ways. Variation in temperature, rainfall, wind, and other environmental variables can have an impact at a range of temporal and spatial scales and at every level from individual behavior to species distributions. The interactions between these variables may be particularly important but are often overlooked. Hence, understanding how animals respond to weather conditions is a fundamental topic in evolution, ecology, and conservation, especially in a time of major environmental change.Birds are an ideal group in which to investigate these relationships because they occur in almost every ecosystem across the globe, exploit a wide variety of food resources and often move between vastly different environments during their annual life cycle. Most recent research has focused on the impact of climate change and extreme weather events, but even small-scale variation in weather conditions may influence avian behavior, life history, physiology, and morphology. Assessing how birds respond to variation in weather, and the fitness consequences this brings, therefore plays a crucial role in a number of active research areas, including:(1) identifying the selective pressures that may have led to trait evolution;(2) predicting how birds will respond to environmental change; and(3) developing successful conservation measures for threatened species.This timely Research Topic builds on the symposium The Effects of Weather on Birds held at the 2019 European Ornithologists’ Union Congress at Cluj-Napoca, Romania. It will bring together articles from a range of disciplines to offer valuable and synthesized insights into the relationship between weather and birds. In doing so, it will link together broader themes such as adaptation, phenotypic plasticity, life history evolution, population dynamics, and migration, while also increasing our knowledge on the potential impacts of climate change.We welcome contributions on any aspect of the weather and how it affects the behavior or ecology of birds. Articles may be original research papers, comparative analyses, reviews or perspectives.

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.

Birds' eggs exhibit a small amount of interspecific diversity in terms of their colors and patterning but considerable variation occurs at the intraspecific level. Here, we examined the contributions of habitat geology, first egg dates, clutch sizes and year in determining intraspecific variation in the intensity of speckling patterns on the eggs of Blue Tits Cyanistes caeruleus and Great Tits Parus major breeding in deciduous woodlands with underlying calcium-rich limestone and calcium-poor gritstone rock types in northwest England. Eggshell speckling patterns varied significantly in relation to habitat geology, with both species laying more heavily speckled eggs in woodlands with gritstone rock types than in woodlands with limestone rock types, even though the weights of laying females and the availability of aerial invertebrates never differed between the two habitat geology types. Meanwhile, there was no variation in eggshell speckling patterns in both species in relation to first egg dates,...

The arid and semi-arid zones of Australia are characterized by highly variable and unpredictable environmental conditions which affect resources for flora and fauna. Environments which are highly unpredictable in terms of both resource access and distribution are likely to select for a variety of adaptive behavioral strategies, intrinsically linked to the physiological control of behavior. How unpredictable resource distribution has affected the coevolution of behavioral strategies and physiology has rarely been quantified, particularly not in Australian birds. We used a captive population of wild-derived zebra finches to test the relationships between behavioral strategies relating to food access and physiological responses to stress and body condition. We found that individuals that were in poorer body condition and had higher peak corticosterone levels entered baited feeders earlier in the trapping sequence of birds within the colony. We also found that individuals in poorer body condition fed in smaller social groups. Our data show that the foraging decisions which individuals make represent not only a trade-off between food access and risk of exposure, but their underlying physiological response to stress. Our data also suggest fundamental links between social networks and physiological parameters, which largely remain untested. These data demonstrate the fundamental importance of physiological mechanisms in controlling adaptive behavioral strategies and the dynamic interplay between physiological control of behavior and life-history evolution.

The zebra finch is a common model organism in neuroscience, endocrinology, and ethology. Zebra finches are generally considered opportunistic breeders, but the extent of their opportunism depends on the predictability of their habitat. This plasticity in the timing of breeding raises the question of how domestication, a process that increases environmental predictability, has affected their reproductive physiology. Here, we compared circulating steroid levels in various "strains" of zebra finches. In Study 1, using radioimmunoassay, we examined circulating testosterone levels in several strains of zebra finches (males and females). Subjects were wild or captive (Captive Wild-Caught, Wild-Derived, or Domesticated). In Study 2, using liquid chromatography-tandem mass spectrometry (LC-MS/MS), we examined circulating sex steroid profiles in wild and domesticated zebra finches (males and females). In Study 1, circulating testosterone levels in males differed across strains. In Study 2, six steroids were detectable in plasma from wild zebra finches (pregnenolone, progesterone, dehydroepiandrosterone (DHEA), testosterone, androsterone, and 5α-dihydrotestosterone (5α-DHT)). Only pregnenolone and progesterone levels changed across reproductive states in wild finches. Compared to wild zebra finches, domesticated zebra finches had elevated levels of circulating pregnenolone, progesterone, DHEA, testosterone, androstenedione, and androsterone. These data suggest that domestication has profoundly altered the endocrinology of this common model organism. These results have implications for interpreting studies of domesticated zebra finches, as well as studies of other domesticated species.

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.

Species’ geographic ranges and range limits are thought to be determined by climate, and across climatic gradients the morphology of populations varies non-randomly. Ecogeographic rules seek to characterise such variation, with Bergmann’s rule positing that organisms inhabiting colder environments are typically larger-bodied than those inhabiting warmer environments. While Bergmann’s rule has been supported across a range of taxonomic groups, how organisms’ behaviour may moderate its effect remains unclear. Here we investigate whether conformity to Bergmann’s rule among birds of the Western Palearctic varies in relation to nest design and migratory behaviour, using phylogenetic comparative analyses. We test predictions using data on nest structure and location, migration, body mass, latitudinal distribution, annual mean temperature and phylogenetic relatedness for a sample of >500 species. We find that conformity to Bergmann’s rule depends strongly on migratory behaviour: non-migratory species breeding at colder, more northerly latitudes are larger-bodied, while body mass is unaffected by climate in short- and long-distance migrants. Among non-migratory species, conformity to Bergmann’s rule depends, further, on nest design: species with more open nests, who are thus most exposed to adverse climatic conditions while breeding, conform most strongly to Bergmann’s rule. Our findings suggest that enclosed nesting and migration allow smaller bodied species to breed in colder environments than their body size would otherwise allow. Therefore, we conclude that organisms’ behaviour can strongly affect exposure to environmental selection pressures.

SJR would like to thank his undergraduate (Connor Barnes, Clare Davies, Emily Elwell, Corrie Grafton, Jacob Haddon, Claire Herlihy, Derek Law, Eleanor Leanne, Holly Mynott, Penny-Serena Pratt, Anna Smith, Peter Tasker, Alison Wildgoose, Amy Williams and Daniel Woodward) and postgraduate (Richard Bufton, Dan Hunt, Victoria Pattison-Willits and Jen Smith) ‘nest’ students, and Charles Deeming, who have all provided new insights about urban nests over the last few years. MCM thanks Charles Deeming, Tom Martin, Bret Tobalske and Blair Wolf for useful discussions on the topic of urban nesting birds. PS would like to thank the participants of the ‘Human-Raptor Interactions—From Conservation Priorities to Conflict Mitigation’ symposium, Arjun Amar, Daniel Berkowic, Shane McPherson and Steve Redpath for the useful discussions on the topic of urban conservation regarding human–wildlife conflicts. JDI-Á would like to thank Olivia Sanllorente for providing interesting discussions on the topic and her constant support. Finally, we all thank Dan Chamberlain and an anonymous reviewer for helpful comments that improved the manuscript significantly., The world is urbanising rapidly, and it is predicted that by 2050, 66% of the global human population will be living in urban areas. Urbanisation is characterised by land-use changes such as increased residential housing, business development and transport infrastructure, resulting in habitat loss and fragmentation. Over the past two decades, interest has grown in how urbanisation influences fundamental aspects of avian biology such as life-history strategies, survival, breeding performance, behaviour and individual health. Here, we review current knowledge on how urbanisation influences the nesting biology of birds, which determines important fitness-associated processes such as nest predation and community assembly. We identify three major research areas: (i) nest sites of birds in urban areas, (ii) the composition of their nests, and (iii) how these aspects of their nesting biology influence their persistence (and therefore conservation efforts) in urban areas. We show that birds inhabiting urban areas nest in a wide variety of locations, some beneficial through exploitation of otherwise relatively empty avian ecological niches, but others detrimental when birds breed in ecological traps. We describe urban-associated changes in nesting materials such as plastic and cigarette butts, and discuss several functional hypotheses that propose the adaptive value and potential costs of this new nesting strategy. Urban areas provide a relatively new habitat in which to conserve birds, and we show that nestboxes and other artificial nest sites can be used successfully to conserve some, but not all, bird species. Finally, we identify those subject areas that warrant further research attention in the hope of advancing our understanding of the nesting biology of birds in urban areas.

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.

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.

Avian parents initially provide their offspring with resources such as food and protection from predators but the offspring then undergo a period of transition from dependency to independence. That transition represents a crucial period of an individual’s life as their inexperience in simultaneously searching for food and avoiding predators’ means that the risks of mortality are higher than during other periods of their life. Unfortunately, our understanding of the transition to independence has lagged behind other life history stages due to the logistical challenges associated with tracking individuals after they have left the relatively safe confines of the nest. However, recent technological advances that have enabled individuals to be tracked remotely have dramatically increased our understanding of the process by which offspring acquire independence. First, interspecific studies of birds have demonstrated that the offspring of species that suffer both high levels of nest predation and ectoparasite-induced nestling mortality leave the nest comparatively sooner than the offspring of species that suffer lower levels of nest predation and ectoparasite-induced nestling mortality. Second, intraspecific studies have become much more prevalent in recent years as new technologies have been used to show that between-brood or litter variation in the timing of independence is influenced by predation risk, ectoparasite-induced nestling mortality and parent-offspring conflict over the provision of care. Further studies have shown that within-brood variation in the timing of independence also occurs as a result of both genetic effects such as parentage and offspring sex, and parental effects such as hatching asynchrony, that result in inequalities between siblings. In summary, there is considerable variation in the process by which avian offspring acquire independence at the interspecific and intraspecific levels. However, whilst we have a reasonable understanding of the causes of such variation, our understanding of the consequences of such variation is less developed and deserves further research.

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.

Most bird species construct nests of some form in which to lay eggs and raise offspring. Traditionally, behaviours associated with the location and design of birds’ nests were thought to be innate and inflexible, which is at least partly due to the paucity of research examining nest building behaviours. There is increasing evidence, however, that there are multiple points at which birds make decisions concerning their nest: where to build, what to build and which material to use. Nest structure is determined by a number of factors including natural selection, sexual selection, ectoparasite avoidance and environmental adjustment. The choice of nest site and materials may be affected by a bird’s own experience or by the experience of conspecifics. A bird may also learn at least some aspects of nest building from observing others. For such a key component of reproduction, it is perhaps surprising that there is rather little known about the causes and consequences of variation in nest structure and almost nothing about building itself.

Nest building is a taxonomically widespread behaviour that consists of the construction of a suitable receptacle with collected materials for the incubation of eggs and sometimes for the raising of offspring. The use of specific nest materials has important fitness consequences for avian parents and offspring because they help to determine the thermal, parasitic and bacterial environment within nests and may also influence parental investment via intraspecific signalling. However, we presently know very little about the process by which nest materials are selected from the wider environment and specifically, it is unclear whether wild birds randomly or non-randomly select nest materials in relation to their local availability. Here, we report an experiment in which we provided experimental pairs of pied flycatchers (Ficedula hypoleuca) with wool, feathers and deer hair - commonly used nest materials found in their woodland habitats - close to their nests during the nest building period whilst control pairs were not provided with any materials. We found that females at experimental nests showed very clear preferences for deer hair, whilst almost completely avoiding the wool and feathers, thereby demonstrating that females exhibited very strong preferences for certain nest materials but not others. We therefore conclude that birds select nest materials in a non-random manner and do not simply use the materials most commonly available to them.

Bird populations are often limited by the availability of suitable nesting sites and nestboxes are commonly provided with the explicit intention of increasing the availability of nesting sites. However, birds also regularly nest on man-made structures such as houses, uninhabited buildings such as barns and factories, bridges, metal pipes in fences and pylons that are not intentionally provided for breeding birds. Such man-made structures are widely used as nesting sites by a range of birds and their primary advantage is that they often provide nesting sites in areas where they are limiting. However, the primary disadvantages of such structures are that they sometimes act as ecological traps by attracting birds to nest in suboptimal areas, the nesting birds sometimes negatively impact other species and their temporary nature means that they can be dismantled and hence, lost as nesting sites very quickly. Despite such potential drawbacks, the evidence suggests that man-made structures provide suitable nesting sites for a range of bird species globally, and I urge practitioners to use such structures more widely as a conservation tool for conserving endangered birds.

Although personality has been well studied in a wide range of species, relatively few studies have assessed if behavior in standardized captive tests is predictive of behavior in the wild. We captured wild zebra finches around 2 breeding colonies and assayed their exploratory behavior with a novel environment test. The birds’ foraging behavior in the wild was also measured with the use of a passive integrated transponder tag system to monitor their use of feeders that were periodically moved around the colonies to assess exploratory behavior and sociality. During the same period, individuals’ reproductive success was monitored at the nest-boxes being used in this area. We found that our measures of sociality, wild, and captive exploration were repeatable, but contrary to our predictions, exploration in the novel environment test was not significantly correlated with exploration of feeders in the wild. We failed to find a predicted negative relationship between exploration and sociality, instead finding a significant positive correlation between exploration in the novel environment and sociality. Finally, we found little evidence that any of our measured personality traits influenced reproductive success at the colony, either individually or when the interactions between the personalities of both members of the pair were taken into account. The only exception was that highly exploratory males (assayed with wild feeder behavior) were more likely to make breeding attempts than less exploratory males. Our results suggest that researchers should use caution when using tests such as the classic novel environment test to make inferences about personality in wild populations.

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.

Hatching asynchrony is widespread in birds laying clutches containing multiple eggs, yet is seemingly paradoxical as the age and size hierarchies result in asymmetric sibling competition and low survival prospects for late-hatched nestlings. We examined the causes of variation in hatching asynchrony between broods of zebra finch, Taeniopygia guttata, in three environments: domesticated, captive wild and wild free-living. We found that broods of both domesticated and wild birds taken into captivity hatched more asynchronously than wild free-living broods. This was directly attributable to both male and female parents of domesticated and captive wild broods initiating incubation as soon as the first egg was laid as opposed to when the clutch was virtually complete in wild free-living broods. Wild free-living birds that were transferred to captive environments immediately switched to the incubation onset behaviour seen in domesticated birds, thereby demonstrating a previously unsuspected level of intraspecific plasticity in incubation behaviour. This finding suggests that something about the captive environment is driving the early onset of incubation and contributing to an elevated level of hatching asynchrony in captive birds. Across all populations and environments males contributed almost equally to incubation, and the onset of incubation by males was highly coordinated with that of their partner.

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).

Standardized long-term multi-plot investigations of variation in nest size in free-ranging model species are rare, despite their value for understanding how the environment influences plastic traits such as nest size. Here, we report the results of an 18-yr descriptive study of nest size in first clutches produced by secondary-cavity nesting great tits (Parus major) and blue tits (Cyanistes caeruleus) in the Mediterranean, whilst also taking individual (lay-date, clutch size, age, species) and environmental characteristics (e.g. weather, oak habitat, region) into account. Nests of both species were built in relatively small standardized boxes erected in habitat patches that differed in the presence of the dominant oak species which was either summergreen deciduous or evergreen sclerophyllous. Nest size showed strong differences between species, and also in relation to environmental factors. Great tits built smaller nests than blue tits, Corsican birds had larger nests than mainland ones, nests tended to be larger in evergreen oak-habitat, and larger nests were built during drier weather. None of the individual-specific traits most often considered in long-term studies (lay-date, clutch size, and female age) were related to nest size in either species. Experimental approaches will be required to identify the underlying mechanisms that caused the observed phenotypic diversity for nest size in our study system.

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.

Active conservation has often been successful in reversing or arresting population declines of endangered species. However, examples of Critically Endangered species recovering in the absence of human intervention are extremely rare. We censused the Raso lark, a single-island endemic of the Cape Verdes archipelago, annually from 2001 to 2010. Between 2004 and 2010, the world population grew from 65 to 470 individuals. This remarkable increase occurred without conservation intervention, but correlated strongly and positively with rainfall. Because of this population increase, the mean age of birds reduced and the population shifted from male skew, a consequence of higher male survival, towards one where the sexes were more equally represented. This study illustrates the dramatic effect that natural changes in climatic conditions may have on the recovery of endangered species. However, the current favourable situation may not persist, and we suggest a translocation to another Cape Verdean island be urgently considered. We conclude that temporal trends in the population dynamics of endangered populations need to be considered when planning and implementing species recovery plans.

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.

The advantages and disadvantages of breeding in nestboxes are well known, whilst the merits of roosting in nestboxes during the non-breeding season remain poorly understood. Here I review the advantages and disadvantages of using nestboxes as roosting sites during the non-breeding season. The main advantage of nestboxes is that they increase the number of cavities available for roosting and birds gain considerable thermal benefits and energy savings, when compared to congeners roosting outside of cavities. However, the main disadvantage is that roosting birds are widely targeted by detrimental ectoparasites, and birds actively avoid nestboxes where ectoparasites are abundant. Meanwhile, there is insufficient evidence to make any firm conclusions as to whether roosting in nestboxes increases or decreases predation risk and this is an area, which warrants further research. Consequently, there is a great deal of variation in the quality of individual nestboxes as roosting sites, and interspecific competition...