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During migration, long-distance migratory songbirds may fly nonstop for days, whereas shorter-distance migrants complete flights of 6 to 10 h. Fat is the primary fuel source, but protein is also assumed to provide a low, consistent amount of energy for flight. However, little is known about how the use of these fuel sources differs among bird species and in response to flight duration. Current models predict that birds can fly until fat stores are exhausted, with little consideration of protein's limits on flight range or duration. We captured two related migratory species--ultra long-distance blackpoll warblers (Setophaga striata) and short-distance yellow-rumped warblers (Setophaga coronata)--during fall migration and flew them in a wind tunnel to examine differences in energy expenditure, overall fuel use, and fuel mixture. We measured fat and fat-free body mass before and after flight using quantitative magnetic resonance and calculated energy expenditure from body composition changes and doubly labeled water. Three blackpolls flew voluntarily for up to 28 h--the longest wind tunnel flight to date--and ended flights with substantial fat reserves but concave flight muscle, indicating that protein loss, rather than fat, may actually limit flight duration. Interestingly, while blackpolls had significantly lower mass-specific metabolic power in flight than that of yellow-rumped warblers and fuel use was remarkably similar in both species, with consistent fat use but exceptionally high rates of protein loss at the start of flight that declined exponentially over time. This suggests that protein may be a critical, dynamic, and often overlooked fuel for long-distance migratory birds. [ABSTRACT FROM AUTHOR]

Maternal effects can give newborns a head start in life by adjusting natal phenotypes to natal environments, yet their strength and adaptiveness are often difficult to investigate in natural populations. Here, we studied anticipatory maternal effects and their adaptiveness in common lizards in a seminatural experimental system. Specifically, we investigated how maternal environments (i.e., vegetation cover) and maternal phenotype (i.e., activity levels and body length) can shape offspring phenotype. We further studied whether such maternal effects influenced offspring survival in natal environments varying with respect to vegetation cover, conspecific density, and, consequently, maternal fitness. More active females from dense vegetation habitats produced bigger offspring than their less active counterparts, the contrary being true for sparse vegetation habitats. Moreover, females from dense vegetation habitats produced more active offspring and more active offspring survived better in dense vegetation habitats, resulting in greater maternal fitness through maternal effects. These results suggest adaptive anticipatory maternal effects, induced by vegetation structure and mediated by activity levels that may shape early-life prospects in natal environments. [ABSTRACT FROM AUTHOR]

Endocrine systems act as key intermediaries between organisms and their environments. This interaction leads to high variability in hormone levels, but we know little about the ecological factors that influence this variation within and across major vertebrate groups. We study this topic by assessing how various social and environmental dynamics influence testosterone levels across the entire vertebrate tree of life. Our analyses show that breeding season length and mating system are the strongest predictors of average testosterone concentrations, whereas breeding season length, environmental temperature, and variability in precipitation are the strongest predictors of within‐population variation in testosterone. Principles from small‐scale comparative studies that stress the importance of mating opportunity and competition on the evolution of species differences in testosterone levels, therefore, likely apply to the entire vertebrate lineage. Meanwhile, climatic factors associated with rainfall and ambient temperature appear to influence variability in plasma testosterone, within a given species. These results, therefore, reveal how unique suites of ecological factors differentially explain scales of variation in circulating testosterone across mammals, birds, reptiles, amphibians, and fishes. [ABSTRACT FROM AUTHOR]

Hormones control the major biological functions of stress response, growth, metabolism, and reproduction. In animals, these hormones show pronounced seasonality, with different set-points for different seasons. In humans, the seasonality of these hormones remains unclear, due to a lack of datasets large enough to discern common patterns and cover all hormones. Here, we analyze an Israeli health record on 46 million person-years, including millions of hormone blood tests. We find clear seasonal patterns: The effector hormones peak in winter-spring, whereas most of their upstream regulating pituitary hormones peak only months later, in summer. This delay of months is unexpected because known delays in the hormone circuits last hours. We explain the precise delays and amplitudes by proposing and testing a mechanism for the circannual clock: The gland masses grow with a timescale of months due to trophic effects of the hormones, generating a feedback circuit with a natural frequency of about a year that can entrain to the seasons. Thus, humans may show coordinated seasonal set-points with a winter-spring peak in the growth, stress, metabolism, and reproduction axes. [ABSTRACT FROM AUTHOR]

Soft microfluidic systems that capture, store, and perform biomarker analysis of microliter volumes of sweat, in situ, as it emerges from the surface of the skin, represent an emerging class of wearable technology with powerful capabilities that complement those of traditional biophysical sensing devices. Recent work establishes applications in the real-time characterization of sweat dynamics and sweat chemistry in the context of sports performance and healthcare diagnostics. This paper presents a collection of advances in biochemical sensors and microfluidic designs that support multimodal operation in the monitoring of physiological signatures directly correlated to physical and mental stresses. These wireless, battery-free, skin-interfaced devices combine lateral flow immunoassays for cortisol, fluorometric assays for glucose and ascorbic acid (vitamin C), and digital tracking of skin galvanic responses. Systematic benchtop evaluations and field studies on human subjects highlight the key features of this platform for the continuous, noninvasive monitoring of biochemical and biophysical correlates of the stress state. [ABSTRACT FROM AUTHOR]

Chronic changes in climate conditions may select for acclimation responses in terrestrial animals living in fluctuating environments, and beneficial acclimation responses may be key to the resilience of these species to global changes. Despite evidence that climate warming induces changes in water availability, acclimation responses to water restriction are understudied compared with thermal acclimation. In addition, acclimation responses may involve different modes, paces, and trade-offs between physiological and behavioral traits. Here, we tested the dynamical acclimation responses of a dry-skinned terrestrial ectotherm to chronic water restriction. Yearling common lizards (Zootoca vivipara) were exposed to sublethal water restriction during 2 mo of the summer season in laboratory conditions, then released in outdoor conditions for 10 additional months. Candidate behavioral (exploration, basking, and thermal preferences) and physiological (metabolism at rest and standard water loss rate) traits potentially involved in the acclimation response were measured repeatedly during and after water restriction. We observed a sequential acclimation response in water-restricted animals (yearlings spent less time basking during the first weeks of water deprivation) that was followed by delayed sex-specific physiological consequences of the water restriction during the following months (thermal depression in males and lower standard evaporative water loss rates in females). Despite shortterm negative effectsofwater restrictiononbodygrowth, annual growth, survival, and reproduction were not significantly different between water-restricted and control yearlings. This demonstrates that beneficial acclimation responses to water restriction involve both short-term flexible behavioral responses and delayed changes in thermal and water biology traits. [ABSTRACT FROM AUTHOR]

Global climate change is leading to decreased climatic predictability. Theoretical work indicates that changes in the climate's intrinsic predictability will affect population dynamics and extinction, but experimental evidence is scarce. Here, we experimentally tested whether differences in intrinsic precipitation predictability affect population dynamics of the European common lizard (Zootoca vivipara) by simulating more predictable (MP) and less predictable (LP) precipitation in 12 seminatural populations over 3 years and measuring different vital rates. A seasonal age-structured matrix model was parametrized to assess treatment effects on vital rates and asymptotic population growth (λ). There was a nonsignificant trend for survival being higher in MP than in LP precipitation, and no differences existed in reproductive rates. Small nonsignificant survival differences in adults explained changes in λ, and survival differences among age classes were in line with predictions from cohort resonance. As a result, λ was significantly higher in MP than in LP precipitation. This experimentally shows that small effects have major consequences on λ, that forecasted decreases in precipitation predictability are likely to exacerbate the current rate of population decline and extinction, and that stage-structured matrix models are required to unravel the aftermath of climate change. [ABSTRACT FROM AUTHOR]

Anuran vocalization is one of the most energetically expensive behaviors recorded in vertebrates. To sustain this behavior, circulating hormones in male frogs must act to promote calling behavior while mobilizing energy reserves. We hypothesize that this is accomplished through the actions of testosterone (T) and corticosterone (CORT). T is thought to elicit calling, while CORT mobilizes energy reserves. Eventually, high CORT concentrations and low energy reserves suppress calling behavior. We evaluated this hypothesis in light of the reproductive ecology of the Pig Frog, Lithobates grylio. Plasma samples from calling and non-calling males were collected during four months of the reproductive season. Calling males were shown to have significantly higher concentrations of circulating T and high body conditions. Conversely, non-callers exhibited elevated CORT and low body conditions. There was no correlation between the two hormones, but circulating T concentrations did decrease over the season. Lastly, we found that CORT is positively correlated with circulating glucose (in non-callers); this finding is supported by CORT's known role in gluconeogenesis. Taken together, these data indicate that circulating hormones and available energy reserves likely influence calling behavior in L. grylio. [ABSTRACT FROM AUTHOR]

Climatic change is expected to affect individual life histories and population dynamics, potentially increasing vulnerability to extinction. The importance of genetic diversity has been highlighted for adaptation and population persistence. However, whether responses of life-history traits to a given environmental condition depend on the genetic characteristics of a population remains elusive. Here we tested this hypothesis in the lizard Zootoca vivipara by simultaneously manipulating habitat humidity, a major climatic predictor of Zootoca’s distribution, and adult male color morph frequency, a trait with genome-wide linkage. Interactive effects of humidity and morph frequency had immediate effects on growth and body condition of juveniles and yearlings, as well as on adult survival, and delayed effects on offspring size. In yearlings, higher humidity led to larger female body size and lower humidity led to higher male compared to female survival. In juveniles and yearlings, some treatment effects were compensated over time. The results show that individual responses to environmental conditions depend on the population’s color morph frequency, age class, and sex and that these affect intra– and inter–age class competition. Moreover, humidity affected the competitive environment rather than imposing trait-based selection on specific color morphs. This indicates that species’ responses to changing environments (e.g., to climate change) are highly complex and difficult to accurately reconstruct and predict without information on the genetic characteristics and demographic structure of populations. [ABSTRACT FROM AUTHOR]

Despite a shared genetic architecture between males and females, sexual differences are widespread. The extent of this shared genetic architecture, reflected in the intersexual genetic correlation, has previously been correlated with the extent of phenotypic sexual dimorphism in shared traits. However, the magnitude of the difference in sex-specific additive genetic variances may also fuel sexual dimorphism. To explore the correlation between additive genetic variance dimorphism and phenotypic dimorphism, we conducted a literature search. We targeted traits expressed in both sexes and excluded sex-limited traits. The mean difference between the sexes in additive genetic variance was not significantly different from 0. However, the distribution of the sexual difference in additive genetic variance had a significant male-biased skew. This pattern persists even after removing traits explicitly related to reproduction. Furthermore, male traits had more residual and phenotypic variance than homologous female traits (as measured by both the mean and the skew), and this difference was not necessarily due to the difference between sexual traits and nonsexual traits. We found no evidence that sex chromosome system could explain sex differences in additive genetic, nonadditive genetic, or phenotypic variances. Finally, we found a significant correlation between the extent of sexual dimorphism in additive genetic variances and the extent of phenotypic sexual dimorphism. Understanding why traits have sex-specific patterns of variation awaits further investigation. [ABSTRACT FROM AUTHOR]

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Research on birds has long played an important role in ecological investigations, as birds are relatively easily observed, and their high metabolic rates and diurnal habits make them quite evidently responsive to changes in their environments. A mechanistic understanding of such avian responses requires a better understanding of how variation in physiological state conditions avian behavior and integrates the effects of recent environmental changes. There is a great need for sensor systems that will allow free-flying birds to interact with their environment and make unconstrained decisions about their spatial location at the same time that their physiological state is being monitored in real time. We have developed a miniature needle-based enzymatic sensor system suitable for continuous real-time amperometric monitoring of uric acid levels in unconstrained live birds. The sensor system was constructed with Pt/Ir wire and Ag/AgCl paste. Uricase enzyme was immobilized on a 0.7 mm sensing cavity of Nafion/cellulose inner membrane to minimize the influences of background interferents. The sensor response was linear from 0.05 to 0.6 mM uric acid, which spans the normal physiological range for most avian species. We developed a two-electrode potentiostat system that drives the biosensor, reads the output current, and wirelessly transmits the data. In addition to extensive characterization of the sensor and system, we also demonstrate autonomous operation of the system by collecting in vivo extracellular uric acid measurements on a domestic chicken. The results confirm our needle-type sensor system's potential for real-time monitoring of birds' physiological state. Successful application of the sensor in migratory birds could open up a new era of studying both the physiological preparation for migration and the consequences of sustained avian flight. [ABSTRACT FROM AUTHOR]

We studied ontogenetic shifts in sexual dimorphism and female reproduction in the Reeves's Butterfly Lizard, Leiolepis reevesii (Agamidae), from Hainan, southern China. The smallest reproductive female was 84 mm snout-vent length (SVL). The largest female and male were 136 mm and 166 mm SVL, respectively. Sexual dimorphism in head size and tail size was evident in adults, with adult males having larger heads and longer tails than did adult females of the same SVL. Head size relative to SVL was greatest in hatchlings and smallest in adults, with juveniles in between. Tail length relative to SVL was shorter in hatchlings than in juveniles and adults but did not differ between juveniles and adults. Females produced a single clutch of 2-8 eggs per breeding season stretching from mid-April to mid-July. Clutch size, egg mass, and clutch mass were all positively related to female SVL. Egg mass was negatively correlated with clutch size when holding female SVL constant, and egg length was negatively correlated with egg width when holding egg mass constant. Larger females increased reproductive output primarily through production of more and larger eggs (and hence heavier clutches). Males are the larger sex in L. reevesii presumably because (1) the selective pressure toward increased male size is strong; (2) the selective pressure toward increased female size is comparatively low; and (3) somatic growth is more likely to be constrained by reproduction in smaller females because of a negative correlation between relative clutch mass and SVL. [ABSTRACT FROM AUTHOR]

Past studies have suggested a fundamental difference in testosterone concentrations between tropical and northern latitude male birds, with the convention being that males in the tropics express much lower levels of testosterone. However, recent comparative studies have shown that tropical males with a short and synchronous breeding season (i.e. a breeding season typical of northern species) express maximum testosterone levels similar to those of northern latitude birds. Here, we ask the converse: do northern latitude songbirds that express a defining life-history characteristic typical of the tropics, i.e. year-round territoriality, have an annual testosterone profile similar to that of tropical songbirds? For the few year-round territorial species for which data are available, we found that seasonal testosterone profiles and seasonal maxima in plasma testosterone were similar between males of tropical and non-tropical species. For example, males of both groups expressed seasonal maxima during the period when females were fertile, and testosterone levels at this time were similar. In contrast, this and other studies show that species with seasonal territories typically express maximum testosterone levels earlier in the breeding cycle, when territories are first being established. Taken together, we suggest that specific life-history traits may play a more important role in determining testosterone profiles of tropical and non-tropical birds than breeding latitude and encourage further studies to allow for more formal comparisons. [ABSTRACT FROM AUTHOR]

The challenge hypothesis was proposed as a mechanism for vertebrates to optimize their testosterone titers by upregulating testosterone during periods of aggressive competition. Here we test key predictions of the challenge hypothesis in an independently evolved endocrine system: juvenile hormone (JH) in a social insect. We assess how social conflict influences JH titers in Polistes dominulus wasps. Aggressive conflict was produced by removing the queen from some colonies (experimental) and a low-ranked worker from other colonies (control). Queen removal produced competition among workers to fill the reproductive vacancy. Workers upregulated their JH titers in response to this social conflict; worker JH titers were higher in queenless than in queenright colonies. Furthermore, JH titers were associated with an individual's ability to dominate rivals; the worker that took over as the replacement queen had a substantially higher JH titer than did other workers. Finally, JH titers were positively associated with aggression in queenless colonies, but there was no relationship between JH and aggression in stable, queenright colonies. Overall, these results match key predictions of the challenge hypothesis and parallel much of the work on testosterone in vertebrates. Social modulation of hormone titers is not confined to a particular endocrine system but is likely to be an adaptive feature of endocrine systems across diverse taxa. [ABSTRACT FROM AUTHOR]

European barn owl chicks ( Tyto alba) show a body mass overshoot prior to fledging that has been predicted to serve as an energy reservoir during periods of stochastic food availability. However, the composition of the mass overshoot has heretofore not been directly examined in nestlings of this or any other species displaying a body mass overshoot during growth (e.g., raptors and seabirds). To experimentally determine whether the overshoot in body mass in juvenile European barn owls ( Tyto alba) may act as an energy reservoir, we compared the body composition of owl chicks raised on an ad libitum diet to those fed a restricted diet designed to eliminate the overshoot. Chicks raised on the two diets were also compared for differences in maturation of diverse functions (e.g., locomotion) and tissues (e.g., skeletal development). Contrary to expectations, our results on body composition in juvenile barn owls indicate that the mass overshoot prior to fledging is primarily comprised of an increased water compartment. Thus, we suggest that the mass overshoot in owls (and possibly in other species) does not serve as an energy reservoir but, rather, may function as an insurance against dehydration when hot in-nest conditions force chicks to rely on evaporative cooling: temperatures in barn owl nests can reach up to 43°C. We found no significant differences in maturation indexes between diet treatments at the time of fledging [ABSTRACT FROM AUTHOR]

The authors examine dominance and subordination in the social psychology, political science, and biology literatures. Using Summers and Winberg (2006) as a guide, the authors suggest that extreme dominance or subordination phenotypes—including social dominance orientation and right-wing authoritarianism—are determined by an organism's genetic predispositions, motivations, stress responses, and long-term hormone release and uptake states. The authors offer hypotheses about the likely neurochemical profiles for each of these extreme dominance and subordination phenotypes and suggest two designs that begin to test these hypotheses. [ABSTRACT FROM AUTHOR]

The "challenge hypothesis" posits that when established social orders are challenged, plasma testosterone (T) in socially monogamous breeding male birds will temporarily increase to facilitate aggressive responses. However, not all birds conform to predictions. To expand upon past findings, we examined effects of direct territorial challenge on T levels in the blue tit (Cyanistes caeruleus). We found that simulated territorial intrusions caused a decline in plasma T during both territory establishment and laying/incubation. Conversely, corticosterone (CORT) levels dramatically increased. We also examined challenged blue tit males for levels of corticosterone-binding globulin (CBG), a carrier molecule that displays affinity for both CORT and T in birds. Although the CBG showed increased occupation by CORT during challenge, effects were not accompanied by a significant increase in the unbound T fraction. Thus, competitive hormone interactions on the CBG do not seem sufficient to explain changes in circulating T levels. To place our results within the context of past findings, we compared all socially monogamous birds tested to date for plasma levels of T during situational territorial intrusion experiments. We found that birds raising only one brood per season (e.g., the blue tit) consistently show no increase in plasma T but instead show elevations in circulating CORT. Thus, we suggest that single-broodedness plays an important role in determining patterns of hormone change and should be considered in future discussions of hormone-behavior interactions. [ABSTRACT FROM AUTHOR]

To elucidate the developmental aspects of the evolution of sexual size dimorphism (SSD), an understanding of the sex-specific ontogeny of body size is critical. Here, we evaluate the relative importance of genetic and environmental determinants of SSD in juvenile common lizards ( Lacerta vivipara). We examined the prenatal and post-natal effects of population density and habitat humidity on SSD, as well as the maternal effects of food availability, corticosterone level, humidity and heat regime during gestation. Analyses indicated strong prenatal and post-natal plasticity in body size per se and yielded three main results with respect to SSD. First, SSD in juvenile common lizards matches qualitatively the SSD observed in adults. Secondly, SSD was influenced by none of the prenatal factors investigated here, suggesting poor sex-biased maternal effects on offspring size. Thirdly, SSD was sensitive to post-natal habitat humidity, which positively affected growth rate more strongly in females than in males. Thus, natural variation in SSD in juvenile common lizards appears to be primarily determined by a combination of sex-biased genetic factors and post-natal conditions. We discuss the possibility that viviparity may constrain the evolution of sex-biased maternal effects on offspring size. [ABSTRACT FROM AUTHOR]

Plasma corticosterone increases in association with migratory flight in the red knot Calidris canutus islandica, suggesting that corticosterone may promote migratory activity and/or energy mobilization in this species. This hypothesis is supported by general effects of glucocorticoids, which include stimulation of locomotion and the mobilization of energy depots. We experimentally examined the role of elevated corticosterone levels in the migratory red knot by comparing foraging behavior, flight frequency, and plasma metabolites between vehicle-injected controls and birds treated with RU486, an antagonist to the genomic low-affinity glucocorticoid receptor (GR). We predicted that RU486 treatment would interfere with energy mobilization. However, we expected no effects on flight activity because recent studies suggest that glucocorticoids affect locomotion through a nongenomic receptor. Finally, because glucocorticoids exert permissive effects on food intake, we postulated that RU486 treatment in the red knot would interfere with feeding. Results were consistent with the latter prediction, suggesting that the GR participates in the promotion of hyperphagia, the intense feeding state that is characteristic of the migratory condition. RU486 treatment did not affect flight frequency, suggesting that corticosterone may support migratory activity through a receptor other than the GR. Energy metabolism (as determined through plasma metabolites) was also unaffected by RU486, possibly because energetic demands experienced by captive birds were low. [ABSTRACT FROM AUTHOR]

We relate variation in the timing of arrival by migrating birds breeding at northerly latitudes to individual differences in the prior accumulation of energy stores. Balancing starvation risks early in the season against the almost universal declining trend in reproductive prospects with advancing date is seen as an individual decision with fitness consequences. We review three studies implicating events at the staging sites or in winter in setting the individual migratory schedule. Climate change influences the timetable of a pied flycatcher ( Ficedula hypoleuca) population breeding in The Netherlands and wintering in West Africa, followed since 1960. Mean air temperature in the period mid April-mid May (arrival and laying) increased and laying date advanced by 10 days. Still, in recent years most birds did not lay early enough to maximise fitness (determined by recruitment and parental survival) whereas many parents achieved this goal in 1980–1985. As the flycatchers have not started to arrive earlier, some ecological constraint further upstream is postulated (possibly the hurdle of the crossing of Sahara and Mediterranean). The ability to follow individual migrants provides a second avenue to assess the fitness implications of migratory schedules. Thus, brightly coloured male bar-tailed godwits ( Limosa lapponica) captured in the Dutch Wadden Sea (the intermediate staging site linking a West African wintering area with breeding sites in arctic Russia) and traced with miniature radio-transmitters did not depart early. The ‘best’ males (with bright breeding plumage) were picked up by the listening stations in Sweden 650 km further along the migratory route ten days later than the paler individuals. If early arrival confers the competitive advantage of prior occupancy but increases mortality, the ‘best’ males may be able to afford arriving later and thus avoid some of the survival costs. Return rate of the ‘bright’ males to the staging site in later seasons was indeed higher than for the ‘pale’, early males. Intensive observation of pink-footed geese ( Anser brachyrhynchus) fitted with coded neck-collars substantiate the tight relationship between energy stores (fat) accumulated up to final departure from the final staging site (Vesterålen, N. Norway) en route to the nesting grounds (Spitsbergen) and subsequent success. The breeding outcome of individual parents (accompanied by juveniles or not) could be related to observations of body condition before departure (visual ‘abdominal profile index’). Recently, perceived conflicts with agriculture have resulted in widespread harassment by humans. The geese have: drastically shortened their stay on the Vesterålen, fail to achieve the body condition usual a decade ago and reproductive output has fallen. Although the geese are currently pioneering new staging sites, an adequate alternative has not materialised, underlining the critical role of the final take-off site. [ABSTRACT FROM AUTHOR]

Summary 1. In several migrant bird species it has now been established that refuelling is typified not only by fat deposition, but also by changes in lean body protein. The body composition of a long-distance migratory shorebird, the Bar-tailed Godwit Limosa lapponica taymyrensis , was examined on a stopover site in spring to evaluate changes in lean dry mass of organ and muscle tissue over the period of refuelling. 2. It was hypothesized that tissues which support long-distance flight would hypertrophy and reach peak size towards the end of refuelling, i.e. immediately before the 4500-km bout of flight to Arctic breeding grounds. In contrast, it was hypothesized that tissues involved in digestion would initially hypertrophy, but then atrophy during the final stages of stopover, so that wing loading during long-distance flight would be minimized. 3. Flight muscles of godwits steadily increased in lean dry mass during refuelling and reached peak size in birds preparing to depart the stopover site – possibly in an effort to maximize power output. 4. In contrast, the lean dry mass of stomach, liver, kidneys and intestines of godwits increased only during the early stages of refuelling, indicating a quick initial growth of organs involved in the support of refuelling activities. Additionally, in birds readying for departure, the intestines no longer differed in size from those of recent arrivals, suggesting a reduction in size of digestive tissues prior to flight. 5. Such changes in body composition appear consistent with those found in another shorebird and in a grebe preparing for a bout of migratory flight, suggesting a common pattern in allocation of lean body mass in at least some migratory species during fuelling. [ABSTRACT FROM AUTHOR]

The specific roles of corticosterone in promotion of avian migration remain unclear even though this glucocorticosteroid is elevated in many migrating bird species. In general, glucocorticosteroids promote metabolic homeostasis and may elicit ef-fects on feeding and locomotion. Because the migratory stages of refueling and flight are characterized by distinct behaviors and physiology, the determination of corticosterone levels during each stage should help identify potential processes in which corticosterone is involved. We measured baseline levels of corticosterone in bar-tailed godwits (Limosa lapponica) during two distinct stages of migration: (1) immediately after arrival at a false stopover site just short of the Wadden Sea and (2) through-out the subsequent 4-wk refueling period on the Wadden Sea. Plasma corticosterone was higher in arriving than in refueling birds. In addition, corticosterone increased with size-corrected body mass during the refueling phase, suggesting that corticosterone rises as birds prepare to reinitiate flight. Therefore, elevated corticosterone appears associated with migratory flight... [ABSTRACT FROM AUTHOR]

Environmental changes can propagate through food webs in complex ways via trophic cascades. In the North American Arctic, hyperabundant populations of geese are causing significant habitat change and the resulting trophic cascades are known to impact plant and invertebrate communities. However, the potential impacts on other tundra‐nesting birds are not fully understood. Here, we evaluate the impacts of light geese (Snow Geese, Chen caerulescens, and Ross' Goose, Chen rossii) populations on other tundra‐nesting birds, using count data collected during bird surveys conducted at varying distances from light goose colonies across the Canadian Arctic. From a dataset of 920 12–16 ha plots distributed across the Canadian Arctic, we identified 527 that were within 200 km of the mapped extent of known light goose colonies. After accounting for regional variation, we demonstrate that densities of most Cover‐Nesting Shorebirds and passerines are depressed in the vicinity of light goose colonies. We suggest that these trends are the results of the combined effects of goose‐induced changes in habitat and predator–prey interactions. These direct and indirect effects of light geese could be contributing to the declines experienced by some tundra‐nesting bird populations in parts of their range. Ongoing climate‐related changes to habitat, predators, and arthropods could interact with this effect of geese to further alter the suitability of tundra habitats for Arctic‐breeding birds, in additive or even unanticipated ways. [ABSTRACT FROM AUTHOR]

The complexity of the physiological phenotype currently prevents us from identifying an integrative measure to assess how the internal state and environmental conditions modify life‐history strategies. In this article, it is proposed that shorter telomeres should lead to a faster pace‐of‐life where investment in self‐maintenance is decreased as a means of saving energy for reproduction, but at the cost of somatic durability. Inversely, longer telomeres would favor an increased investment in soma maintenance and thus a longer reproductive lifespan (i.e., slower pace‐of‐life). Under this hypothesis, telomere dynamics could be such an integrative mediator, which will assemble the information about oxidative stress levels, inflammation status and stress reactivity, and relate this information to the potential lifespan of the organism and its pace‐of‐life strategy. The signaling function of telomere dynamics can also reach over generations, a phenomenon in which the telomere lengths of gametes would provide a channel through which offspring would receive information about their environment early in their development, hence increasing the possibilities for developmental plasticity. Telomeres are regions of non‐coding DNA at the end of eukaryotic chromosomes that shorten at each cell division, resulting in shorter telomeres in older organisms. Under the telomere messenger hypothesis, telomeres would gather information about the environmental factors that cause oxidative damage, inflammation, and physiological stress within the organism, and relate this information to the lifespan of the organism and its pace‐of‐life strategy. [ABSTRACT FROM AUTHOR]