Chronic anthropogenic noise disrupts glucocorticoid signaling and has multiple effects on fitness in an avian community

Studies examining relationships among habitat disturbance, physiology, and fitness in wild animals often produce contradictory or inconclusive results, casting doubt on current conservation physiology predictive frameworks linking stress and fitness. We apply a new framework drawn from experimental systems utilizing chronic inescapable stressors to explore how noise, an environmental stimulus common to wildlife habitats worldwide, disrupts stress hormone signaling and impacts fitness. We utilize a natural experiment to show that chronic, anthropogenic noise reduced baseline corticosterone levels, increased acute corticosterone response, and, at highest amplitudes, negatively impacted multiple measures of fitness across three species of birds. Our work brings conservation physiology theory involving wild animals into needed alignment with recent theories based on chronic stress in laboratory studies. Anthropogenic noise is a pervasive pollutant that decreases environmental quality by disrupting a suite of behaviors vital to perception and communication. However, even within populations of noise-sensitive species, individuals still select breeding sites located within areas exposed to high noise levels, with largely unknown physiological and fitness consequences. We use a study system in the natural gas fields of northern New Mexico to test the prediction that exposure to noise causes glucocorticoid-signaling dysfunction and decreases fitness in a community of secondary cavity-nesting birds. In accordance with these predictions, and across all species, we find strong support for noise exposure decreasing baseline corticosterone in adults and nestlings and, conversely, increasing acute stressor-induced corticosterone in nestlings. We also document fitness consequences with increased noise in the form of reduced hatching success in the western bluebird (Sialia mexicana), the species most likely to nest in noisiest environments. Nestlings of all three species exhibited accelerated growth of both feathers and body size at intermediate noise amplitudes compared with lower or higher amplitudes. Our results are consistent with recent experimental laboratory studies and show that noise functions as a chronic, inescapable stressor. Anthropogenic noise likely impairs environmental risk perception by species relying on acoustic cues and ultimately leads to impacts on fitness. Our work, when taken together with recent efforts to document noise across the landscape, implies potential widespread, noise-induced chronic stress coupled with reduced fitness for many species reliant on acoustic cues.

Related papers:

title: Proximity to a high traffic road: glucocorticoid and life history consequences for nestling white-crowned sparrows.
abstract: Roads have been associated with decreased reproductive success and biodiversity in avian communities and increased physiological stress in adult birds. Alternatively, roads may also increase food availability and reduce predator pressure. Previous studies have focused on adult birds, but nestlings may also be susceptible to the detrimental impacts of roads. We examined the effects of proximity to a road on nestling glucocorticoid activity and growth in the mountain white-crowned sparrow (Zonotrichia leucophrys oriantha). Additionally, we examined several possible indirect factors that may influence nestling corticosterone (CORT) activity secretion in relation to roads. These indirect effects include parental CORT activity, nest-site characteristics, and parental provisioning. And finally, we assessed possible fitness consequences of roads through measures of fledging success. Nestlings near roads had increased CORT activity, elevated at both baseline and stress-induced levels. Surprisingly, these nestlings were also bigger. Generally, greater corticosterone activity is associated with reduced growth. However, the hypothalamic-pituitary-adrenal axis matures through the nestling period (as nestlings get larger, HPA-activation is greater). Although much of the variance in CORT responses was explained by body size, nestling CORT responses were higher close to roads after controlling for developmental differences. Indirect effects of roads may be mediated through paternal care. Nestling CORT responses were correlated with paternal CORT responses and paternal provisioning increased near roads. Hence, nestlings near roads may be larger due to increased paternal attentiveness. And finally, nest predation was higher for nests close to the road. Roads have apparent costs for white-crowned sparrow nestlings--increased predation, and apparent benefits--increased size. The elevation in CORT activity seems to reflect both increased size (benefit) and elevation due to road proximity (cost). Whether or not roads are good or bad for nestlings remains equivocal. However, it is clear that roads affect nestlings; how or if these effects influence adult survival or reproduction remains to be elucidated.

title: Noise pollution alters ecological services: enhanced pollination and disrupted seed dispersal
abstract: Noise pollution is a novel, widespread environmental force that has recently been shown to alter the behaviour and distribution of birds and other vertebrates, yet whether noise has cumulative, community-level consequences by changing critical ecological services is unknown. Herein, we examined the effects of noise pollution on pollination and seed dispersal and seedling establishment within a study system that isolated the effects of noise from confounding stimuli common to human-altered landscapes. Using observations, vegetation surveys and pollen transfer and seed removal experiments, we found that effects of noise pollution can reverberate through communities by disrupting or enhancing these ecological services. Specifically, noise pollution indirectly increased artificial flower pollination by hummingbirds, but altered the community of animals that prey upon and disperse Pinus edulis seeds, potentially explaining reduced P. edulis seedling recruitment in noisy areas. Despite evidence that some ecological services, such as pollination, may benefit indirectly owing to noise, declines in seedling recruitment for key-dominant species such as P. edulis may have dramatic long-term effects on ecosystem structure and diversity. Because the extent of noise pollution is growing, this study emphasizes that investigators should evaluate the ecological consequences of noise alongside other human-induced environmental changes that are reshaping human-altered landscapes worldwide.

title: A phantom road experiment reveals traffic noise is an invisible source of habitat degradation
abstract: Using landscape-scale traffic noise playbacks to create a “phantom road,” we find that noise, apart from other factors present near roads, degrades the value of habitat for migrating songbirds. We found that nearly one third of the bird community avoided the phantom road. For some bird species that remained despite noise exposure, body condition and stopover efficiency (ability to gain body condition over time) decreased compared with control conditions. These findings have broad implications for the conservation of migratory birds and perhaps for other wildlife, because factors driving foraging behavior are similar across animals. For wildlife that remains in loud areas, noise pollution represents an invisible source of habitat degradation. Decades of research demonstrate that roads impact wildlife and suggest traffic noise as a primary cause of population declines near roads. We created a “phantom road” using an array of speakers to apply traffic noise to a roadless landscape, directly testing the effect of noise alone on an entire songbird community during autumn migration. Thirty-one percent of the bird community avoided the phantom road. For individuals that stayed despite the noise, overall body condition decreased by a full SD and some species showed a change in ability to gain body condition when exposed to traffic noise during migratory stopover. We conducted complementary laboratory experiments that implicate foraging-vigilance behavior as one mechanism driving this pattern. Our results suggest that noise degrades habitat that is otherwise suitable, and that the presence of a species does not indicate the absence of an impact.

title: Anthropogenic noise weakens territorial response to intruder's songs
abstract: Noise pollution degrades natural acoustic conditions, potentially interfering with bird communication. However, exactly how noise impacts the ability of the signal receiver to detect and discriminate vocalizations from conspecifics remains understudied in field settings. We performed a natural experiment to determine the effect of noise pollution on the territory-defense behaviors of two emberizid sparrows exposed to carefully constructed playbacks of conspecific intruder songs. Although all birds reacted to the playbacks, response latency increased with noise levels. This suggests that noise interferes with signal reception and may indicate impaired signal discrimination. We place these results in the context of a receiver's “listening area” and the significant impact of noise pollution on this receiver-centric perceptual acoustic range. This work informs conservation efforts and provides a much needed field-based examination of the disruptive impact of noise pollution on behaviors directly related to reproduction and fitness.

title: Experimental exposure to urban and pink noise affects brain development and song learning in zebra finches (Taenopygia guttata)
abstract: Recently, numerous studies have observed changes in bird vocalizations—especially song—in urban habitats. These changes are often interpreted as adaptive, since they increase the active space of the signal in its environment. However, the proximate mechanisms driving cross-generational changes in song are still unknown. We performed a captive experiment to identify whether noise experienced during development affects song learning and the development of song-control brain regions. Zebra finches (Taeniopygia guttata) were bred while exposed, or not exposed, to recorded traffic urban noise (Study 1) or pink noise (Study 2). We recorded the songs of male offspring and compared these to fathers’ songs. We also measured baseline corticosterone and measured the size of song-control brain regions when the males reached adulthood (Study 1 only). While male zebra finches tended to copy syllables accurately from tutors regardless of noise environment, syntax (the ordering of syllables within songs) was incorrectly copied affected by juveniles exposed to noise. Noise did not affect baseline corticosterone, but did affect the size of brain regions associated with song learning: these regions were smaller in males that had been had been exposed to recorded traffic urban noise in early development. These findings provide a possible mechanism by which noise affects behaviour, leading to potential population differences between wild animals occupying noisier urban environments compared with those in quieter habitats.

title: Chronic industrial noise affects pairing success and age structure of ovenbirds Seiurus aurocapilla
abstract: 1Anthropogenic noise is rapidly increasing in wilderness areas as a result of industrial expansion. While many road studies have attempted to assess the effects of industrial noise on birds, conflicting factors such as edge effects often inhibit the ability to draw strong conclusions. 
2We assessed pairing success and age distribution of male ovenbirds Seiurus aurocapilla in the boreal forest of Alberta, Canada, in areas around noise-generating compressor stations compared with areas around habitat-disturbed, but noiseless, wellpads. This allowed us to control for edge effects, human visitation and other factors that are not controlled for in studies of noise generated by roads. Generalized estimating equations (GEE) were used to assess the impacts of noise on ovenbird pairing success, age structure and body morphology. 
3We found a significant reduction in ovenbird pairing success at compressor sites (77%) compared with noiseless wellpads (92%). These differences were apparent regardless of territory quality or individual male quality. Significantly more inexperienced birds breeding for the first time were found near noise-generating compressor stations than noiseless wellpads (48% vs. 30%). 
4While there are multiple proximate explanations for these results, the ultimate cause of the changes seems to be noise pollution. We hypothesize that noise interferes with a male's song, such that females may not hear the male's song at greater distances and/or females may perceive males to be of lower quality because of distortion of song characteristics. 
5Synthesis and applications. This work demonstrates that chronic background noise could be an important factor affecting bird populations. It can impact upon pairing success and age structure of passerines; in boreal Alberta this could pose a problem for certain species as energy development expands rapidly.

title: Shifting song frequencies in response to anthropogenic noise: a meta-analysis on birds and anurans
abstract: Anthropogenic noise has been shown to alter the transmission environment and distort acoustic signals, prompting vocalizing species to use compensatory mechanisms. Through a meta-analysis we investigated the relative importance of biological and contextual factors predisposing species to shift their singing/calling frequencies in response to anthropogenic noise. We gathered data from 36 studies, synthesizing information on more than 160 experiments and 60 bird and anuran species. To estimate the breadth of frequency shift, we calculated a standardized effect size using Hedges’ g. We fitted a multilevel linear mixed-effect model on g as the dependent variable weighted by its inverse variance, with typical frequency, body mass, experimental condition, and noise source type as independent terms. Our results reveal broader shifts in smaller bird species when compared with bigger species, an effect that was emphasized in the low-frequency component of the song spectrum. Birds increased their dominant frequencies when confronted to anthropogenic noise, whereas anurans were less prone to such shifts. Human-altered acoustic environments can be considered a novel selective force impelling change to the communication patterns of many vocalizing species.

title: Songs of the city: noise-dependent spectral plasticity in the acoustic phenotype of urban birds
abstract: Urbanization leads to homogenization of avian communities through local extinction of rare bird species and increasing numbers of the same common urban bird species over large geographical areas. Successful city birds often persist through some sort of behavioural plasticity that helps them survive and reproduce close to humans, in built-up areas, with all the typical urban feasts and hazards. In this review, I address whether behavioural plasticity of the acoustic phenotype can be an additional factor in explaining which species end up as urban survivors. Anthropogenic noise has been shown to negatively affect avian distribution and reproduction, especially for species that rely on relatively low-frequency songs for mediating territorial conflicts and attracting partners for mating. Spectral differences between songs of city and forest populations of the same species and correlations between individual song frequency use and local noise levels suggest that many successful city species shift song frequency upward under noisy urban conditions. Experimental evidence has confirmed the ability of several species to show rapid spectral adjustments as well as perceptual benefits of singing at higher frequency in noisy habitats. However, empirical evidence of fitness benefits for birds showing the ability and tendency of noise-dependent spectral adjustment is still lacking. Furthermore, depending on the species and the underlying mechanism for spectral change, there may also be fitness costs through a compromise on signal function. These two aspects are only two of many remaining avenues for future studies. The acoustic phenotype of urban birds provides a great model system to study fundamental processes such as causes and consequences of environmentally induced signal changes, ‘cultural assimilation’, and the relationship between phenotypic and genotypic evolution. Furthermore, the current and expected rate of urbanization remains high at a global scale, which will lead to further spread in time and space of artificially elevated noise levels. This should guarantee the continued interest of scientists, politicians and conservationists for many years ahead.

title: Experimental Chronic Noise Is Related to Elevated Fecal Corticosteroid Metabolites in Lekking Male Greater Sage-Grouse (Centrocercus urophasianus)
abstract: There is increasing evidence that individuals in many species avoid areas exposed to chronic anthropogenic noise, but the impact of noise on those who remain in these habitats is unclear. One potential impact is chronic physiological stress, which can affect disease resistance, survival and reproductive success. Previous studies have found evidence of elevated stress-related hormones (glucocorticoids) in wildlife exposed to human activities, but the impacts of noise alone are difficult to separate from confounding factors. Here we used an experimental playback study to isolate the impacts of noise from industrial activity (natural gas drilling and road noise) on glucocorticoid levels in greater sage-grouse (Centrocercus urophasianus), a species of conservation concern. We non-invasively measured immunoreactive corticosterone metabolites from fecal samples (FCMs) of males on both noise-treated and control leks (display grounds) in two breeding seasons. We found strong support for an impact of noise playback on stress levels, with 16.7% higher mean FCM levels in samples from noise leks compared with samples from paired control leks. Taken together with results from a previous study finding declines in male lek attendance in response to noise playbacks, these results suggest that chronic noise pollution can cause greater sage-grouse to avoid otherwise suitable habitat, and can cause elevated stress levels in the birds who remain in noisy areas.

title: Effects of construction noise on behavior and cortisol levels in a pair of captive giant pandas (Ailuropoda melanoleuca)
abstract: Studies of the effects of ambient noise on animals have found variable results. A study was conducted at the Smithsonian's National Zoological Park to determine what effect short-term demolition work would have on the behavior and cortisol excretion of giant pandas. Behavioral and endocrine differences were examined during the presence and absence of demolition work being conducted on an adjacent exhibit complex. High frequency noise was significantly louder on work days compared to non-work days. Panda activity budgets differed significantly between work and post-work periods, although in different ways. The male's use of substrates and locations that might be associated with refuge or shelter changed during the study; the female did not show similar changes. He spent more time in the enclosure adjacent to the work site rather than a more distant enclosure during the demolition period whether work was occurring or not. The behavior of both animals was more often characterized as “restless” during, as opposed to before or after the work period. In general, cortisol excretion increased during the study in both animals but this was likely a seasonal effect in the male. In many cases, significant short-term increases in cortisol were temporally associated with certain kinds of construction noises or specific physiological events. Variability in cortisol secretion fluctuated during the study for both animals but in differing patterns. These results demonstrate that demolition noise was associated with behavioral and some physiological changes in giant pandas, and these changes were individual-specific. Zoo Biol 0:1–18, 2006.

title: Physiological and behavioural stress responses in cynomolgus macaques (Macaca fascicularis) to noise associated with construction work
abstract: The aim of the present study was to evaluate the behavioural and physiological responses to environmental disturbances (live and recorded dynamite explosions) in laboratory non-human primates in preparation for a future tunnel construction underneath our animal facility. In a pilot study (A) on 20 female Macaca fascicularis, a day of test blasts resulted in an increase in faecal cortisol and immunoreactive cortisol metabolites (CICM), and the animals reacted behaviourally with vertical flight and vocalizations. In a follow-up study (B), we assessed the impact of 10 days of exposure to recorded detonations on the behaviour and CICM in 16 M. fascicularis. In the latter study we introduced a predictive signal, serving as a conditional stimulus, to half of the animals. We found no significant effects of the noise in the Signal group; while the Control groups’ CICM values were affected. The behaviour was largely unaffected in the two groups. It was decided not to introduce a research moratorium on biomedical research planned to be conducted during the future tunnel construction, and that a conditional stimulus (‘warning signal’) will be used.

title: Evidence that ship noise increases stress in right whales
abstract: Baleen whales (Mysticeti) communicate using low-frequency acoustic signals. These long-wavelength sounds can be detected over hundreds of kilometres, potentially allowing contact over large distances. Low-frequency noise from large ships (20–200 Hz) overlaps acoustic signals used by baleen whales, and increased levels of underwater noise have been documented in areas with high shipping traffic. Reported responses of whales to increased noise include: habitat displacement, behavioural changes and alterations in the intensity, frequency and intervals of calls. However, it has been unclear whether exposure to noise results in physiological responses that may lead to significant consequences for individuals or populations. Here, we show that reduced ship traffic in the Bay of Fundy, Canada, following the events of 11 September 2001, resulted in a 6 dB decrease in underwater noise with a significant reduction below 150 Hz. This noise reduction was associated with decreased baseline levels of stress-related faecal hormone metabolites (glucocorticoids) in North Atlantic right whales (Eubalaena glacialis). This is the first evidence that exposure to low-frequency ship noise may be associated with chronic stress in whales, and has implications for all baleen whales in heavy ship traffic areas, and for recovery of this endangered right whale population.

title: Effects of experimentally elevated traffic noise on nestling white-crowned sparrow stress physiology, immune function and life history
abstract: Roads have been associated with behavioral and physiological changes in wildlife. In birds, roads decrease reproductive success and biodiversity and increase physiological stress. Although the consequences of roads on individuals and communities have been well described, the mechanisms through which roads affect birds remain largely unexplored. Here, we examine one mechanism through which roads could affect birds: traffic noise. We exposed nestling mountain white-crowned sparrows (Zonotrichia leucophrys oriantha) to experimentally elevated traffic noise for 5 days during the nestling period. Following exposure to traffic noise we measured nestling stress physiology, immune function, body size, condition and survival. Based on prior studies, we expected the traffic noise treatment to result in elevated stress hormones (glucocorticoids), and declines in immune function, body size, condition and survival. Surprisingly, nestlings exposed to traffic noise had lower glucocorticoid levels and improved condition relative to control nests. These results indicate that traffic noise does affect physiology and development in white-crowned sparrows, but not at all as predicted. Therefore, when evaluating the mechanisms through which roads affect avian populations, other factors (e.g. edge effects, pollution and mechanical vibration) may be more important than traffic noise in explaining elevated nestling stress responses in this species.

title: Fecal corticosterone levels in California spotted owls exposed to low-intensity chainsaw sound
abstract: The California spotted owl (Strix occidentalis occidentalis) is a focal management species in Sierra Nevada national forests. To protect the owl from human activity, the United States Forest Service has proposed guidelines that would prohibit timber harvest and road or trail construction within 400 m of active owl nest sites during the breeding season. To guide these efforts, we tested the physiological stress response of 9 nonbreeding wild male owls to the sound of a chainsaw operated 100 m from their roost site, using change in fecal corticosterone level (ng/g dry feces) as the response variable. We employed a cross-over experimental design to control for differences among individuals. Chainsaw exposure did not result in a detectable increase in fecal corticosterone level (F 1 , 7 =0.01, P=0.94). These findings corroborate results of a field study that suggested spotted owls can tolerate low-intensity human sound in their environment without eliciting a physiological stress response. However, activities producing chronic and intense noise (e.g., timber harvest, road construction), which might elicit such a response, were not simulated in our experiment. The effects of these activities on California spotted owls will require further research.

title: Traffic noise causes physiological stress and impairs breeding migration behaviour in frogs
abstract: Noise from human activities is increasing globally. We provide evidence that traffic noise increases glucocorticoid concentrations and impairs reproductive behavior in frogs. Since prolonged stress can compromise health, survival and reproduction, and because impaired reproductive behavior can reduce mating opportunities, these results suggest noise may contribute to amphibian declines.

title: Neuroendocrine and Behavioral Responses and Brain Pattern of c‐fos Induction Associated with Audiogenic Stress
abstract: The present study determined simultaneously the behavioural, neuroendocrine and regional brain activity, using semi‐quantitative analysis of c‐fos mRNA induction, produced by 30 min of auditory stimulation at different white noise intensities (background 60 dB, 70, 80, 90 and 105 dBA), in rats. Only the highest noise intensities (90 and 105 dB) significantly increased corticosterone release after 30 min stimulation. Behaviourally, the 105 dB noise condition reliably reduced overall activity, and moderate noise intensities (70 and 80 dB) increased sleeping time. Three distinct patterns of c‐fos mRNA induction were observed. First, following exposure to the experimental cages, a wide pattern of brain activation was obtained in experimental animals irrespective of noise intensity presentation, compared to the naive rats. Second, a number of auditory structures (cochlear nuclei, superior olivary complex, nuclei of the lateral lemniscus, inferior colliculus and the medial division of the medial geniculate body) displayed a clear intensity‐dependent increase in c‐fos induction. Third, compared to all other conditions, the stressed rats (90 and 105 dB conditions) displayed significantly higher c‐fos induction in relatively few areas. Particularly intense c‐fos induction was observed in the bed nucleus of the stria terminalis, especially its anterior medial and ventral aspects, the septohypothalamic nucleus, the ventral lateral septum, the ventral portion of the dentate gyrus, a number of hypothalamic nuclei including the lateral preoptic area, the medial preoptic nucleus and the paraventricular nucleus, the median raphe and the pedunculopontine tegmental nucleus. The involvement of a number of these structures in a specific audiogenic stress responsive circuit is discussed.

title: Effect of sound on the hypothalamic-pituitary-adrenal axis.
abstract: In the rat, the stress of exposure to continuous, high intensity sound (130 db, 220 cycles/sec) evoked a pattern of adrenocortical response consisting of an initial, immediate high rate of hormone secretion (determined in adrenal venous blood by chromatographic techniques), a subsequent period of depression of corticosterone output to normal or subnormal levels, and eventual return of hormone secretion to high levels. The period of suppressed corticosterone secretion appeared dependent upon the continuous presence of the stressor for a period of 12 hr. The data suggest that the depression of corticosterone secretion is due to inhibition of secretion of ACTH. Bilateral surgical destruction of the middle ear of the animals abolished the response pattern. After placement of bilateral lesions in the posterior hypothalamus, the resting rate of corticosterone secretion was significantly greater than normal and the response pattern was markedly attenuated.

title: The Influence of Social Hierarchy on Primate Health
abstract: Dominance hierarchies occur in numerous social species, and rank within them can greatly influence the quality of life of an animal. In this review, I consider how rank can also influence physiology and health. I first consider whether it is high- or low-ranking animals that are most stressed in a dominance hierarchy; this turns out to vary as a function of the social organization in different species and populations. I then review how the stressful characteristics of social rank have adverse adrenocortical, cardiovascular, reproductive, immunological, and neurobiological consequences. Finally, I consider how these findings apply to the human realm of health, disease, and socioeconomic status.

title: Chronic Subordinate Colony Housing Paradigm: A Mouse Model to Characterize the Consequences of Insufficient Glucocorticoid Signaling
abstract: Chronic, in particular chronic psychosocial, stress is a burden of modern societies and known to be a risk factor for numerous somatic and affective disorders (in detail referenced below). However, based on the limited existence of appropriate, and clinically relevant, animal models for studying the effects of chronic stress, the detailed behavioral, physiological, neuronal, and immunological mechanisms linking stress and such disorders are insufficiently understood. To date, most chronic stress studies in animals employ intermittent exposure to the same (homotypic) or to different (heterotypic) stressors of varying duration and intensity. Such models are only of limited value, since they do not adequately reflect the chronic and continuous situation that humans typically experience. Furthermore, application of different physical or psychological stimuli renders comparisons to the mainly psychosocial stressors faced by humans, as well as between the different stress studies almost impossible. In contrast, rodent models of chronic psychosocial stress represent situations more akin to those faced by humans and consequently seem to hold more clinical relevance. Our laboratory has developed a model in which mice are exposed to social stress for 19 continuous days, namely the chronic subordinate colony housing (CSC) paradigm, to help bridge this gap. The main aim of the current review article is to provide a detailed summary of the behavioral, physiological, neuronal, and immunological consequences of the CSC paradigm, and wherever possible relate the findings to other stress models and to the human situation.

title: Traffic noise drowns out great tit alarm calls
abstract: Anthropogenic noise is one of the fastest growing and most ubiquitous types of environmental pollution and can impair acoustic communication in a variety of animals . Recent research has shown that birds can adjust acoustic parameters of their sexual signals (songs) in noisy environments [2,3], yet we know little about other types of vocalizations. Anti-predator signals contain subtle information that is critical for avoiding predation , and failure to detect these calls [6,7] as a result of anthropogenic noise pollution could have large fitness consequences by negatively impacting survival. We investigated whether traffic noise impacts both the production and perception of avian alarm calls using a combination of lab and field experiments with great tits (Parus major), a songbird that frequently inhabits noise-polluted environments. In response to experimental noise manipulation in controlled laboratory conditions, great tits increased the amplitude, but not the frequency parameters, of their mobbing alarm calls (hereafter 'alarm calls'). Playback experiments conducted in the wild indicate that current levels of road traffic noise mask alarm calls, impeding the ability of great tits to perceive these critical signals. These results show that, despite the vocal adjustments used to compensate for anthropogenic noise, great tits are not able to restore the active space of their calls in even moderately noisy environments. Consequently, birds are likely to suffer from increased predation risk under noise, with likely effects on their behaviour, populations, and community dynamics in noise-polluted areas.

title: The costs of chronic noise exposure for terrestrial organisms.
abstract: Growth in transportation networks, resource extraction, motorized recreation and urban development is responsible for chronic noise exposure in most terrestrial areas, including remote wilderness sites. Increased noise levels reduce the distance and area over which acoustic signals can be perceived by animals. Here, we review a broad range of findings that indicate the potential severity of this threat to diverse taxa, and recent studies that document substantial changes in foraging and anti-predator behavior, reproductive success, density and community structure in response to noise. Effective management of protected areas must include noise assessment, and research is needed to further quantify the ecological consequences of chronic noise exposure in terrestrial environments.

title: Neurobiology of Interpreting and Responding to Stressful Events: Paradigmatic Role of the Hippocampus
abstract: The sections in this article are: 
 
 
1 
Physiological Stress Responses 
1.1 
What Systems Respond to Stressors? 
 
1.2 
Habituation and Sensitization 
 
1.3 
Psychosocial Stressors 
 
 
 
 
2 
Plasticity and Adaptation in the Central Nervous System: Hippocampus 
2.1 
Role of the Hippocampus in Behavioral and Neuroendocrine Adaptation 
 
2.2 
Plasticity of the Hippocampus 
 
 
 
 
3 
Hippocampal Neuronal Morphology is Altered by Hibernation, Chronic Stress, and Aging 
3.1 
Pharmacological Manipulations of Dendritic Atrophy 
 
3.2 
Mechanism of Dendritic Atrophy and Role of Adrenal Steroids 
 
3.3 
Hippocampal Neuronal Damage Resulting from Chronic Stress and Aging 
 
3.4 
Structural Changes in the Human Hippocampus 
 
3.5 
Stress Effects on Cognitive Performance in Rodents and Humans 
 
3.6 
Life-Long Implications of Stressful Experiences 
 
 
 
 
4 
The Price of Adaptation: Allostasis and Allostatic Load 
4.1 
Definitions 
 
4.2 
Anticipation and Behavior in Allostatic Load 
 
4.3 
Four Types of Allostatic Load 
 
4.4 
Individuals versus Groups 
 
4.5 
Measurement of Allostatic Load 
 
 
 
 
5

title: Neurocircuitry of stress: central control of the hypothalamo–pituitary–adrenocortical axis
abstract: Integration of the hypothalamo-pituitary-adrenal stress response occurs by way of interactions between stress-sensitive brain circuitry and neuroendocrine neurons of the hypothalamic paraventricular nucleus (PVN). Stressors involving an immediate physiologic threat ('systemic' stressors) are relayed directly to the PVN, probably via brainstem catecholaminergic projections. By contrast, stressors requiring interpretation by higher brain structures ('processive' stressors) appear to be channeled through limbic forebrain circuits. Forebrain limbic sites connect with the PVN via interactions with GABA-containing neurons in the bed nucleus of the stria terminalis, preoptic area and hypothalamus. Thus, final elaboration of processive stress responses is likely to involve modulation of PVN GABAergic tone. The functional and neuroanatomical data obtained suggest that disease processes involving inappropriate stress control involve dysfunction of processive stress pathways.

title: The concept of allostasis in biology and biomedicine
abstract: Living organisms have regular patterns and routines that involve obtaining food and carrying out life history stages such as breeding, migrating, molting, and hibernating. The acquisition, utilization, and storage of energy reserves (and other resources) are critical to lifetime reproductive success. There are also responses to predictable changes, e.g., seasonal, and unpredictable challenges, i.e., storms and natural disasters. Social organization in many populations provides advantages through cooperation in providing basic necessities and beneficial social support. But there are disadvantages owing to conflict in social hierarchies and competition for resources. Here we discuss the concept of allostasis, maintaining stability through change, as a fundamental process through which organisms actively adjust to both predictable and unpredictable events. Allostatic load refers to the cumulative cost to the body of allostasis, with allostatic overload being a state in which serious pathophysiology can occur. Using the balance between energy input and expenditure as the basis for applying the concept of allostasis, we propose two types of allostatic overload. Type 1 allostatic overload occurs when energy demand exceeds supply, resulting in activation of the emergency life history stage. This serves to direct the animal away from normal life history stages into a survival mode that decreases allostatic load and regains positive energy balance. The normal life cycle can be resumed when the perturbation passes. Type 2 allostatic overload begins when there is sufficient or even excess energy consumption accompanied by social conflict and other types of social dysfunction. The latter is the case in human society and certain situations affecting animals in captivity. In all cases, secretion of glucocorticosteroids and activity of other mediators of allostasis such as the autonomic nervous system, CNS neurotransmitters, and inflammatory cytokines wax and wane with allostatic load. If allostatic load is chronically high, then pathologies develop. Type 2 allostatic overload does not trigger an escape response, and can only be counteracted through learning and changes in the social structure.

title: Physiological stress in ecology: lessons from biomedical research.
abstract: Increasingly, levels of the 'stress hormones' cortisol and corticosterone are being used by ecologists as indicators of physiological stress in wild vertebrates. The amplitude of hormonal response is assumed to correlate with the overall health of an animal and, by extension, the health of the population. However, much of what is known about the physiology of stress has been elucidated by the biomedical research community. I summarize five physiological mechanisms that regulate hormone release during stress that should be useful to ecologists and conservationists. Incorporating these physiological mechanisms into the design and interpretation of ecological studies will make these increasingly popular studies of stress in ecological settings more rigorous.

title: Chronic stress in free-living European starlings reduces corticosterone concentrations and reproductive success.
abstract: Chronic increases in stress hormones such as glucocorticoids are maladaptive, yet studies demonstrating a causal relationship among chronic stress, increases in glucocorticoid concentrations, and subsequent fitness costs in free-living animals are lacking. We experimentally induced chronic psychological stress in female European starlings (Sturnus vulgaris) by subjecting half of the females at our study site to a chronic stress protocol consisting of 4, 30 min stressors (loud radio, predator calls, a novel object, or predator decoys including a snake, rat, and owl) administered in random order daily for 8 days after clutch completion. Experimental females were captured at the end of the chronic stress protocol (9 days after the onset of the chronic stress protocol), and unstressed control females were captured at the same stage of the nesting cycle. Chronically stressed females had lower baseline corticosterone (CORT, the avian glucocorticoid) concentrations and lower reproductive success than unstressed females. Furthermore, surviving nestlings in experimentally stressed broods showed sensitization of the CORT response to acute stress, which is a physiological change that could persist to adulthood. Attenuation of baseline CORT concentrations in adult females is contrary to the general assumption that elevated CORT concentrations indicate stress, suggesting that more research is necessary before CORT concentrations can be used to accurately assess chronic stress in field studies.

title: The effect of chronic psychological stress on corticosterone, plasma metabolites, and immune responsiveness in European starlings.
abstract: Although increases in glucocorticoid concentrations during acute stress are believed to help animals survive stressful events, chronic changes in glucocorticoid concentrations can alter metabolism and lead to disease. We studied the effect of chronic psychological stress on corticosterone (CORT), corticosterone binding globulin (CBG), glucose, and triglyceride concentrations as well as immune responsiveness to a T-cell mitogen challenge in European starlings, Sturnus vulgaris. To induce chronic stress we used a chronic stress protocol consisting of five stressors (loud radio, cage tapping, cage rolling, human voice, and bag restraint) administered in random order for 30 min for 4 times/day over 18 days. Total CORT decreased throughout the chronic stress period, which parallels a previous study with starlings. CBG capacity did not significantly change with chronic stress, thus free CORT followed the same pattern of attenuation as total CORT during chronic stress. Despite the change in regulation of CORT release, daytime glucose and triglyceride concentrations did not change with chronic stress. In addition, immune responsiveness in chronically stressed and unstressed birds was similar. Our results, together with a previous study using a similar CSP in European starlings, suggest that starlings physiologically dampen the HPA axis during chronic psychological stress to avoid pathology associated with chronically augmented CORT concentrations such as hyperglycemia and impaired immune function.

title: Noninvasive Physiological Measures of Disturbance in the Northern Spotted Owl
abstract: The Northern Spotted Owl ( Strix occidentalis caurina ) continues to decline across its entire range at a rate exceeding 4% per year, with a 1% annual acceleration (Burnham et al. 1994). One possible factor impeding its recovery is the lack of adequate measures that reflect the impact of habitat disturbance on this species (Hanson et al. 1993). Measures of reproductive success between individual owl sites and areas are critical to evaluating long-term effects of management in species such as the Northern Spotted Owl. The considerable time-span from nesting to fledging, however, makes it difficult to pinpoint individual factors associated with nest failure among the myriad sources of disturbance over the course of the breeding season. At the least, large numbers of breeding pairs and considerable time are required to use reproductive success to index such disturbance impacts. More immediate measures of disturbance could complement measures of reproductive success, providing a proactive tool to guide adaptive management in a manner that does not compromise owl survivorship and reproduction. We demonstrate that noninvasive hormone measurements of physiological stress in feces could provide an objective, readily accessible and cost effective means of quantifying impacts of disturbance in Northern Spotted Owls that can directly address pivotal conservation questions surrounding this and other listed species. It is well-documented that physiological stress occurs in response to environmental pressure and affects resistance to disease, survival, and reproduction negatively in a variety of species (Moberg 1985; Munck et al. 1984; Wingfield & Farner 1993). Until recently, however, the application of physiological stress measures to free-ranging threatened or endangered species has been severely limited by the invasiveness of sample collection procedures such as repeated capture and blood withdrawal. Fecal steroid measures provide an ideal alternative to serum measures because they are relatively easy to collect longitudinally, without disturbing study subjects. Results illustrate that fecal stress hormone disturbance measures can be used as a proactive management tool, enabling the industry and wildlife managers to optimize the tradeoffs between resource utilization and proliferation of species at risk.

title: Snowmobile activity and glucocorticoid stress responses in wolves and elk
abstract: The effect of human activities on animal populations is widely debated, particularly since a recent decision by the U.S. Department of the Interior to ban snowmobiles from national parks. Immunoassays of fecal glucocorticoid levels provide a sensitive and noninvasive method of measuring the physiological stress responses of wildlife to disturbances. We tested for associations between snowmobile activity and glucocorticoid levels in an elk (Cervus elaphus) population in Yellowstone National Park and wolf (Canis lupus) populations in Yellowstone, Voyageurs, and Isle Royale national parks. For wolves, comparisons among populations and years showed that fecal glucocorticoid levels were higher in areas and times of heavy snowmobile use. For elk, day-to-day variation in fecal glucocorticoid levels paralleled variation in the number of snowmobiles after we controlled for the effects of weather and age. Also for elk, glucocorticoid concentrations were higher in response to snowmobiles than to wheeled vehicles after we controlled for the effects of age, weather, and number of vehicles. Despite these stress responses, there was no evidence that current levels of snowmobile activity are affecting the population dynamics of either species in these locations.

title: Predators as stressors? Physiological and reproductive consequences of predation risk in tropical stonechats (Saxicola torquata axillaris)
abstract: Tropical birds usually lay smaller clutches and are less likely to initiate a second brood than their temperate–zone relatives. This reduction in annual fecundity is generally explained as an adaptation either to higher rates of nest predation or to a more limited food supply concurrent with higher adult survival in the tropics. However, the physiological parameters associated with lower annual fecundity in tropical birds have not been well investigated. We compared the annual fecundity, behaviour and a number of physiological parameters of stonechat parents feeding fledged juveniles in territories with and without fiscal shrikes, a predator on adult and fledged birds. Stonechat pairs in territories with shrikes were less likely to initiate a second brood and delayed successive broods compared to pairs in territories without shrikes. After fledging of their young, males showed a greater propensity than females to initiate distraction calls after a human intrusion into their territory and, therefore, invested more in the defence of their young. In territories with shrikes stonechat males had higher initial plasma corticosterone levels and lower body conditions than males in territories without shrikes, suggesting that they were chronically stressed. In contrast, the females from both types of territory had low initial plasma corticosterone levels. We conclude that shrike presence might account for the delay in initiation of a second brood and the reduction in the tendency to initiate a second brood. Whether these effects are mediated by the elevated levels of corticosterone remains to be demonstrated.

title: When Not Enough Is Too Much: The Role of Insufficient Glucocorticoid Signaling in the Pathophysiology of Stress-Related Disorders
abstract: Previous theories have emphasized the role of excessive glucocorticoid activity in the pathology of chronic stress. Nevertheless, insufficient glucocorticoid signaling (resulting from decreased hormone bioavailability or reduced hormone sensitivity) may have equally devastating effects on bodily function. Such effects may be related in part to the role of glucocorticoids in restraining activation of the immune system and other components of the stress response, including the sympathetic nervous system (SNS) and corticotropin-releasing hormone (CRH).  The literature on neuroendocrine function and glucocorticoid-relevant pathologies in stress-related neuropsychiatric disorders, including posttraumatic stress disorder and major depression, was reviewed.  Although not occurring together, both hypocortisolism and reduced responsiveness to glucocorticoids (as determined by dexamethasone challenge tests) were reliably found. Stress-related neuropsychiatric disorders were also associated with immune system activation/inflammation, high SNS tone, and CRH hypersecretion, which are all consistent with insufficient glucocorticoid-mediated regulation of stress hyperresponsiveness. Finally, antidepressants, a mainstay in the treatment of stress-related disorders, were regularly associated with evidence of enhanced glucocorticoid signaling.  Neuroendocrine data provide evidence of insufficient glucocorticoid signaling in stress-related neuropsychiatric disorders. Impaired feedback regulation of relevant stress responses, especially immune activation/inflammation, may, in turn, contribute to stress-related pathology, including alterations in behavior, insulin sensitivity, bone metabolism, and acquired immune responses. From an evolutionary perspective, reduced glucocorticoid signaling, whether achieved at the level of the hormone or its receptor, may foster immune readiness and increase arousal. Emphasis on insufficient glucocorticoid signaling in stress-related pathology encourages development of therapeutic strategies to enhance glucocorticoid signaling pathways.

title: A short review on the psychoneuroimmunology of posttraumatic stress disorder: From risk factors to medical comorbidities
abstract: Posttraumatic stress disorder (PTSD) is a serious and debilitating condition with a prevalence rate of approximately 8% in the United States. Given the number of veterans returning from conflicts around the globe with PTSD, and the substantial number of civilians experiencing traumas, new perspectives on the biology of PTSD are needed. Based on the concept that PTSD is a disorder of stress response systems, numerous studies have suggested changes in hypothalamic-pituitary-adrenal (HPA) axis and sympathetic-adrenal-medullary (SAM) system function in patients with PTSD. Given that both glucocorticoids and catecholamines exert powerful effects on the immune system, it is surprising that relatively few studies have examined immune changes in patients with PTSD. Moreover, patients with PTSD are known to have increased rates of comorbidity with somatic disorders that involve immune and inflammatory processes. Patients with PTSD have been found to exhibit a number of immune changes including increased circulating inflammatory markers, increased reactivity to antigen skin tests, lower natural killer cell activity, and lower total T lymphocyte counts. Studies with humans and rodents suggest that certain proinflammatory cytokines are able to induce neurochemical and behavioral changes that resemble some key features of PTSD. This short article reviews immune alterations in PTSD, and considers possible mechanisms by which such changes may be related to neuroendocrine alterations and medical comorbidities of PTSD.

title: A new view on hypocortisolism
abstract: Low cortisol levels have been observed in patients with different stress-related disorders such as chronic fatigue syndrome, fibromyalgia, and post-traumatic stress disorder. Data suggest that these disorders are characterized by a symptom triad of enhanced stress sensitivity, pain, and fatigue. This overview will present data on the development, mechanisms and consequences of hypocortisolism on different bodily systems. We propose that the phenomenon of hypocortisolism may occur after a prolonged period of hyperactivity of the hypothalamic-pituitary-adrenal axis due to chronic stress as illustrated in an animal model. Further evidence suggests that despite symptoms such as pain, fatigue and high stress sensitivity, hypocortisolism may also have beneficial effects on the organism. This assumption will be underlined by some studies suggesting protective effects of hypocortisolism for the individual.

title: Immunization with a heat-killed preparation of the environmental bacterium Mycobacterium vaccae promotes stress resilience in mice
abstract: The hygiene, or “old friends,” hypothesis proposes that lack of exposure to immunoregulatory microorganisms in modern urban societies is resulting in an epidemic of inflammatory disease, as well as psychiatric disorders in which chronic, low-level inflammation is a risk factor. An important determinant of immunoregulation is the microbial community occupying the host organism, collectively referred to as the microbiota. Here we show that stress disrupts the homeostatic relationship between the microbiota and the host, resulting in exaggerated inflammation. Treatment of mice with a heat-killed preparation of an immunoregulatory environmental microorganism, Mycobacterium vaccae, prevents stress-induced pathology. These data support a strategy of “reintroducing” humans to their old friends to promote optimal health and wellness. The prevalence of inflammatory diseases is increasing in modern urban societies. Inflammation increases risk of stress-related pathology; consequently, immunoregulatory or antiinflammatory approaches may protect against negative stress-related outcomes. We show that stress disrupts the homeostatic relationship between the microbiota and the host, resulting in exaggerated inflammation. Repeated immunization with a heat-killed preparation of Mycobacterium vaccae, an immunoregulatory environmental microorganism, reduced subordinate, flight, and avoiding behavioral responses to a dominant aggressor in a murine model of chronic psychosocial stress when tested 1–2 wk following the final immunization. Furthermore, immunization with M. vaccae prevented stress-induced spontaneous colitis and, in stressed mice, induced anxiolytic or fear-reducing effects as measured on the elevated plus-maze, despite stress-induced gut microbiota changes characteristic of gut infection and colitis. Immunization with M. vaccae also prevented stress-induced aggravation of colitis in a model of inflammatory bowel disease. Depletion of regulatory T cells negated protective effects of immunization with M. vaccae on stress-induced colitis and anxiety-like or fear behaviors. These data provide a framework for developing microbiome- and immunoregulation-based strategies for prevention of stress-related pathologies.

title: Effect of chronic psychosocial stress-induced by subordinate colony (CSC) housing on brain neuronal activity patterns in mice
abstract: Chronic subordinate colony (CSC) housing has been recently validated as a murine model of chronic psychosocial stress which induces alterations of stress-related parameters including decreased body-weight gain and an increased level of anxiety in comparison with single housed control (SHC) mice. By using immunohistochemical immediate early gene (IEG) mapping we investigated whether CSC housing causes alterations in neuronal activation patterns in limbic areas including the amygdala, hippocampus, septum and the periaqueductal gray (PAG) and hypothalamic paraventricular nucleus (PVN). While CSC housing increased basal Zif-268 expression in the nucleus accumbens shell compared to SHC, IEG responses to subsequent open arm (OA) exposure were attenuated in the ventral and intermediate sub-regions of the lateral septum, parvocellular PVN and the dorsal CA3 region of the hippocampus of CSC compared with SHC mice. In contrast, a potentiated c-Fos response in CSC mice was observed in the dorsomedial PAG after OA exposure. Confirming previous findings obtained on the elevated plus-maze, an enhanced anxiety-related behavior in CSC compared with SHC mice was also observed during OA exposure. In order to investigate the appropriate control conditions for CSC housing, group housed control (GHC) mice were additionally included in the behavioral testing. Interestingly, GHC as well as CSC mice showed significantly less risk assessment/exploratory behavior during OA exposure compared with SHC mice indicating that group housing itself is stressful for mice and not an adequate control for the CSC paradigm. Overall, CSC housing is an ethologically relevant chronic psychosocial stressor which results in an elevated sensitivity to a subsequent novel, aversive challenge. However, the CSC-induced increase in anxiety-related behavior was accompanied by differences in neuronal activation, compared with SHC, in defined sub-regions of brain areas known to be involved in the processing of emotionality and stress responses.

title: Identifying hormonal habituation in field studies of stress.
abstract: Habituation is a term commonly used to explain a decrement in response intensity to a repeated stimulus or set of stimuli. In the stress literature, hormonal habituation is often used to describe a situation where an individual has learned to perceive a repeated stressor as innocuous, and thus the intensity of the release of hormonal stress mediators reduces over time. Consequently, a habituated individual is not considered stressed. There are, however, situations where an individual may be chronically stressed despite a reduction in the response intensity of hormonal stress mediators to a repeated stimulus. These alternative explanations are rarely considered in field studies even though a false conclusion that an individual has habituated (i.e., is not stressed) may lead to false conclusions regarding the animal's overall physiology and health. The present paper provides four alternative explanations for an observed attenuation in the response of hormonal stress mediators to a repeated stimulus or set of stimuli which lead to six criteria that define habituation in a field context. Furthermore, we propose four diagnostic tests to help distinguish hormonal habituation from these alternative explanations in field studies. These tests will help identify hormonal habituation in free-living animals and prevent potential problems of falsely describing an individual or population of individuals as habituated.

title: Chronic psychosocial stress results in sensitization of the HPA axis to acute heterotypic stressors despite a reduction of adrenal in vitro ACTH responsiveness
abstract: Although chronic psychosocial stress is often accompanied by changes in basal hypothalamo-pituitary-adrenal (HPA) axis activity, it is vital for a chronically-stressed organism to mount adequate glucocorticoid (GC) responses when exposed to acute challenges. The main aim of the present study was to test whether this is true or not for the chronic subordinate colony housing (CSC, 19 days) paradigm, an established and clinically relevant mouse model of chronic psychosocial stress. As shown previously, CSC mice are characterized by unaffected morning and decreased evening plasma corticosterone (CORT) levels despite enlarged adrenals, suggesting a maladaptive breakdown of adrenal functioning. Plasma CORT levels, determined by repeated blood sampling via jugular vein catheters, as well as relative right adrenal CORT content were increased in CSC compared with single-housed control (SHC) mice in response to acute elevated platform (EPF, 5min) exposure. However, in vitro stimulation of adrenal explants with physiological and pharmacological doses of ACTH revealed an attenuated responsiveness of both the left and right adrenal glands following CSC, despite mRNA and/or protein expression of melanocortin 2 receptor (Mc2r), Mc2r accessory protein (MRAP), and key enzymes of steroidogenesis were not down-regulated. Taken together, we show that chronic psychosocial stressor exposure impairs in vitro ACTH responsiveness of both the left and right adrenal glands, whereas it increases adrenal responsiveness to an acute heterotypic stressor in vivo. This suggests that an additional factor present during acute stressor exposure in vivo rescues left and right adrenal ACTH sensitivity, or itself acts as CORT secretagogue in chronically stressed CSC mice.

title: The honesty of bird song: multiple constraints for multiple traits
abstract: The function of bird song is closely linked to sexual selection. A fundamental question regarding the evolution of sexually selected male signals is how their honesty is maintained. The neural space required for storing a large song repertoire size has traditionally been identified as a key constraint. However, it is often forgotten that bird song is a multifaceted behaviour, and that the different characters that comprise it have specific costs. Recent research has revealed the existence of new constraints, such as social aggression or learning opportunities, which limit the expression of several song characteristics. We review the existing evidence for each of these constraints, revealing some major gaps in our knowledge of this fascinating biological system.

title: The mixed-species chorus as public information: túngara frogs eavesdrop on a heterospecific
abstract: Multispecies choruses represent a promising but uninvestigated forum for public information. Although frogs exposed to a potential predator call more readily in the presence of conspecific calls than in their absence, none are known to make comparable use of heterospecific calls. To test for heterospecific eavesdropping, we isolated calling male tungara frogs (Physalaemus pustulosus), presented them with a potential predator, and recorded their responses to playbacks of 1 of 4 stimuli: calls of a conspecific, a sympatric heterospecific (Leptodactylus labialis), an allopatric congener (Physalaemus enesefae), or silence. We found that males called more in response to the L. labialis call than to either the silent stimulus or the P. enesefae call. In contrast, the P. enesefae call did not result in significantly more calling than the silent stimulus. The conspecific call was the most effective at promoting calling. The data indicate that tungara frogs selectively attend to the call of a heterospecific. We hypothesize that such heterospecific eavesdropping contributes to the emergent behavior of mixed-species choruses.

title: Information Exploitation By Downy Woodpeckers in Mixed-Species Flocks
abstract: Downy woodpeckers (Picoides pubescens) benefit from foraging in mixed-species winter flocks by decreasing their vigilance level and increasing their feeding rate. I investigated one mechanism, auditory cues, downy woodpeckers use to obtain information on the presence of other flock members and potential predators. Experiments with predator models and with recorded alarm calls and contact calls from flock members yielded the following results. Downy woodpeckers use the contact calls of other flock members to assess the presence of flocks members. Woodpeckers foraging alone but with the recorded contact calls of flock members showed lower vigilance levels and higher feeding rates than woodpeckers foraging alone with no recordings or with the control recordings. Woodpeckers respond to the other species' alarm calls as an indication of potential predators and also to their contact calls as an all clear signal afterwards. Downy woodpeckers decreased their vigilance levels and resumed foraging faster when the contact calls followed the presentation of predator models or alarm calls than when these were presented alone.

title: When the birds go unheard: highway noise disrupts information transfer between bird species
abstract: Highway infrastructure and accompanying vehicle noise is associated with decreased wildlife populations in adjacent habitats. Noise masking of animal communication is an oft-cited potential mechanism underlying species loss in sound-polluted habitats. This study documents the disruption of between-species information transfer by anthropogenic noise. Titmice and chickadees broadcast specific calls to alert kin of predator threats, and sympatric vertebrates eavesdrop on these alarm calls to avoid predators. We tested if tufted titmouse alarm call eavesdropping by northern cardinals is disrupted by road noise. We broadcast recorded alarm calls to cardinals in natural areas near and far from highways. Cardinals reliably produced predator avoidance responses in quiet trials, but all birds in noisy areas failed to respond, demonstrating that highway noise is loud enough to disrupt this type of survival-related information via masking or cognitive distraction. Birds in family Paridae are abundant, highly social and vocal residents of woodlands across the Holarctic whose alarm calls are used by many species to mediate predation risks. Our work suggests that communication network disruption is likely to be widespread, and could help explain the pattern of reduced biodiversity near roadways.

title: Eavesdropping on the neighbours: fledglings learn to respond to heterospecific alarm calls
abstract: Young birds and mammals suffer from a high risk of predation, and should be under strong selection for early response to cues indicating danger, including the alarm calls of other species. Despite this prediction, there has been little investigation of the development of response by young animals to heterospecific alarm calls, and none on fledgling birds. Previous studies have suggested that learning is important in the recognition of heterospecific alarm calls in adult birds, but when learning occurs is unknown. We examined the responses of fledgling white-browed scrubwrens, Sericornis frontalis, at three ages to playback of the aerial alarm calls of the sympatric superb fairy-wren, Malurus cyaneus, and New Holland honeyeater, Phylidonyris novaehollandiae. Fairy-wren and scrubwren alarm calls are acoustically similar, while honeyeater alarm calls are distinct, but adult scrubwrens respond to both. Recently fledged scrubwrens responded strongly to conspecific alarm calls, but weakly to heterospecific alarm calls. By contrast, only 2 weeks after leaving the nest most fledglings responded to fairy-wren and honeyeater alarm calls similarly to conspecific alarm calls. However, fledglings in territories without honeyeaters ignored honeyeater alarm calls. Three weeks later, fledglings on all territories responded to all heterospecific alarm calls, an identical response to that of their parents. These results demonstrate that fledglings can quickly develop appropriate responses to heterospecific alarm calls, and present strong evidence that response is learned over a microgeographical scale.

title: Responses by breeding birds to heterospecific song and mobbing call playbacks under varying predation risk
abstract: We conducted a playback experiment to study the effect of predation risk on the attraction of forest passerines to heterospecific territory songs and mobbing calls during the breeding season. The experiment consisted of five treatments, which were played at different distances from the nests of sparrowhawks, Accipiter nisus: the territory song and mobbing calls of the willow tit, Parus montanus, and of the redwing, Turdus iliacus, with classical music as a control. Song may indicate the absence of predators whereas mobbing indicates a potential danger. We assumed that predation risk increases with decreasing distance to a hawk's nest. Therefore, we predicted that the correlation between the number of species attracted and increasing predation risk would be positive for song and negative for mobbing calls. We also examined the effect of body mass on the species' responses. In general, song and mobbing calls attracted more species than the control. For both willow tit and redwing treatments, mobbing calls elicited the strongest response and these attracted more species the lower the predation risk. Attraction to territory songs, however, did not vary in relation to predation risk. Small bird species (<20 g) showed increasing attraction to mobbing calls with decreasing risk, but large bird species did not. Out results suggest that birds exploit heterospecific signals in their decision making but under the constraints of predation risk.

title: Traffic noise reduces foraging efficiency in wild owls
abstract: Anthropogenic noise has been increasing globally. Laboratory experiments suggest that noise disrupts foraging behavior across a range of species, but to reveal the full impacts of noise, we must examine the impacts of noise on foraging behavior among species in the wild. Owls are widespread nocturnal top predators and use prey rustling sounds for localizing prey when hunting. We conducted field experiments to examine the effect of traffic noise on owls’ ability to detect prey. Results suggest that foraging efficiency declines with increasing traffic noise levels due to acoustic masking and/or distraction and aversion to traffic noise. Moreover, we estimate that effects of traffic noise on owls’ ability to detect prey reach >120 m from a road, which is larger than the distance estimated from captive studies with bats. Our study provides the first evidence that noise reduces foraging efficiency in wild animals, and highlights the possible pervasive impacts of noise.

title: Acoustic environments matter: Synergistic benefits to humans and ecological communities.
abstract: Protected areas are critical locations worldwide for biodiversity preservation and offer important opportunities for increasingly urbanized humans to experience nature. However, biodiversity preservation and visitor access are often at odds and creative solutions are needed to safeguard protected area natural resources in the face of high visitor use. Managing human impacts to natural soundscapes could serve as a powerful tool for resolving these conflicting objectives. Here, we review emerging research that demonstrates that the acoustic environment is critical to wildlife and that sounds shape the quality of nature-based experiences for humans. Human-made noise is known to affect animal behavior, distributions and reproductive success, and the organization of ecological communities. Additionally, new research suggests that interactions with nature, including natural sounds, confer benefits to human welfare termed psychological ecosystem services. In areas influenced by noise, elevated human-made noise not only limits the variety and abundance of organisms accessible to outdoor recreationists, but also impairs their capacity to perceive the wildlife that remains. Thus soundscape changes can degrade, and potentially limit the benefits derived from experiences with nature via indirect and direct mechanisms. We discuss the effects of noise on wildlife and visitors through the concept of listening area and demonstrate how the perceptual worlds of both birds and humans are reduced by noise. Finally, we discuss how management of soundscapes in protected areas may be an innovative solution to safeguarding both and recommend several key questions and research directions to stimulate new research.

title: Costs of fear: behavioural and life-history responses to risk and their demographic consequences vary across species.
abstract: Behavioural responses to reduce predation risk might cause demographic 'costs of fear'. Costs differ among species, but a conceptual framework to understand this variation is lacking. We use a life-history framework to tie together diverse traits and life stages to better understand interspecific variation in responses and costs. We used natural and experimental variation in predation risk to test phenotypic responses and associated demographic costs for 10 songbird species. Responses such as increased parental attentiveness yielded reduced development time and created benefits such as reduced predation probability. Yet, responses to increased risk also created demographic costs by reducing offspring production in the absence of direct predation. This cost of fear varied widely across species, but predictably with the probability of repeat breeding. Use of a life-history framework can aid our understanding of potential demographic costs from predation, both from responses to perceived risk and from direct predation mortality.

title: Sound settlement: noise surpasses land cover in explaining breeding habitat selection of secondary cavity-nesting birds.
abstract: Birds breeding in heterogeneous landscapes select nest sites by cueing in on a variety of factors from landscape features and social information to the presence of natural enemies. We focus on determining the relative impact of anthropogenic noise on nest site occupancy, compared to amount of forest cover, which is known to strongly influence the selection process. We examine chronic, industrial noise from natural gas wells directly measured at the nest box as well as site-averaged noise, using a well-established field experimental system in northwestern New Mexico. We hypothesized that high levels of noise, both at the nest site and in the environment, would decrease nest box occupancy. We set up nest boxes using a geospatially paired control and experimental site design and analyzed four years of occupancy data from four secondary cavity-nesting birds common to the Colorado Plateau. We found different effects of noise and landscape features depending on species, with strong effects of noise observed in breeding habitat selection of Myiarchus cinerascens, the Ash-throated Flycatcher, and Sialia currucoides, the Mountain Bluebird. In contrast, the amount of forest cover less frequently explained habitat selection for those species or had a smaller standardized effect than the acoustic environment. Although forest cover characterization and management is commonly employed by natural resource managers, our results show that characterizing and managing the acoustic environment should be an important tool in protected area management.

title: Coupling of dispersal and aggression facilitates the rapid range expansion of a passerine bird
abstract: Behaviors can facilitate colonization of a novel environment, but the mechanisms underlying this process are poorly understood. On one hand, behavioral flexibility allows for an immediate response of colonizers to novel environments, which is critical to population establishment and persistence. On the other hand, integrated sets of behaviors that display limited flexibility can enhance invasion success by coupling behaviors with dispersal strategies that are especially important during natural range expansions. Direct observations of colonization events are required to determine the mechanisms underlying changes in behavior associated with colonization, but such observations are rare. Here, we studied changes in aggression on a large temporal and spatial scale across populations of two sister taxa of bluebirds (Sialia) to show that coupling of aggression and dispersal strongly facilitated the range expansion of western bluebirds across the northwestern United States over the last 30 years. We show that biased dispersal of highly aggressive males to the invasion front allowed western bluebirds to displace less aggressive mountain bluebirds. However, once mountain bluebirds were excluded, aggression of western bluebirds decreased rapidly across consecutive generations in concordance with local selection on highly heritable aggressive behavior. Further, the observed adaptive microevolution of aggression was accelerated by the link between dispersal propensity and aggression. Importantly, our results show that behavioral changes among populations were not caused by behavioral flexibility and instead strongly implicate adaptive integration of dispersal and aggression in facilitating the ongoing and rapid reciprocal range change of these species in North America.

title: Anthropogenic noise is associated with reductions in the productivity of breeding Eastern Bluebirds (Sialia sialis).
abstract: Although previous studies have related variations in environmental noise levels with alterations in communication behaviors of birds, little work has investigated the potential long-term implications of living or breeding in noisy habitats. However, noise has the potential to reduce fitness, both directly (because it is a physiological stressor) and indirectly (by masking important vocalizations and/or leading to behavioral changes). Here, we quantified acoustic conditions in active breeding territories of male Eastern Bluebirds (Sialia sialis). Simultaneously, we measured four fitness indicators: cuckoldry rates, brood growth rate and condition, and number of fledglings produced (i.e., productivity). Increases in environmental noise tended to be associated with smaller brood sizes and were more strongly related to reductions in productivity. Although the mechanism responsible for these patterns is not yet clear, the breeding depression experienced by this otherwise disturbance-tolerant species indicates that anthropogenic noise may have damaging effects on individual fitness and, by extraction, the persistence of populations in noisy habitats. We suggest that managers might protect avian residents from potentially harmful noise by keeping acoustically dominant anthropogenic habitat features as far as possible from favored songbird breeding habitats, limiting noisy human activities, and/or altering habitat structure in order to minimize the propagation of noise pollution.

title: Aggressive behavior by Western Bluebirds (Sialia mexicana) varies with anthropogenic disturbance to breeding habitat
abstract: Human population growth has resulted in more frequent interactions between humans and wildlife, making it increasingly important to understand how anthropogenic disturbance affects animal populations. A number of recent studies on birds have shown that individuals experiencing high levels of disturbance are frequently more aggressive than conspecifics living in less disturbed areas. Our study asked whether heterospecific aggression varied in Western Bluebirds (Sialia mexicana) breeding in artificial nest boxes over a gradient of human disturbance in the Okanagan Valley of British Columbia, Canada. Unlike most previous studies, which have investigated effects of high disturbance (urbanization), our study focused on sites with lower rates of human disturbance, including ranch lands, vineyards, and recreational trails. Using decoys and playback, we measured the response of bluebird pairs to a simulated territory intrusion by one of two heterospecifics: a competing cavity nester, the House Wren (Troglodytes aedon), and a non-competing species, the American Goldfinch (Spinus tristus). We asked whether this response varied with the level of human disturbance experienced by the pair, and also whether aggression was correlated with female flight initiation distance (FID; a measure of boldness), local density of boxes in a territory, and presence of neighboring cavity-nesters. Overall, aggression was significantly higher towards the competitor stimulus (wren) than the non-competitor (goldfinch). Aggression towards the wren model did not change with disturbance level; however, aggression towards the goldfinch model increased significantly in more disturbed areas. Female FID did not vary across disturbance categories, but was correlated with aggression towards the wren, where individuals that responded more aggressively had marginally larger FIDs (i.e., behaved less boldly). Female FID was not correlated with aggression towards the goldfinch. Birds nesting in territories with more boxes tended to be more aggressive towards the wren, and birds nesting in territories with one or more box-nesting neighbors were significantly more aggressive towards the wren than birds without neighbors. Neither of these factors was correlated with aggression towards the goldfinch. Thus, the predicted association between disturbance and aggression was detected only in response to the non-competitor species (goldfinch), whereas aggression towards the competitor species (wren) varied with territory quality and number of competitors. Our study shows that variation in low levels of anthropogenic disturbance may be associated with behavioral effects in bird populations, and serves as a reminder that different factors may influence the expression of aggression in different contexts.

title: Detection and discrimination of natural calls in masking noise by birds: estimating the active space of a signal
abstract: We tested the ability of birds to detect and discriminate natural vocal signals in the presence of masking noise using operant conditioning. Masked thresholds were measured for budgerigars, Melopsittacus undulatus, and zebra finches, Taeniopygia guttata, on natural contact calls of budgerigars, zebra finches and canaries, Serinus canaria. Thresholds increased with increasing call bandwidth, the presence of amplitude modulation and high rates of frequency modulation in calls. As expected, detection thresholds increased monotonically with background noise level. Call detection thresholds varied with the spectral shape of noise. Vocal signals were masked predominantly by noise energy in the spectral region of the signals and not by energy at spectral regions remote from the signals. In all cases, thresholds for discrimination between calls of the same species were higher than thresholds for detection of those calls. Our data provide the first opportunity to estimate distances over which specific communication signals may be effective (i.e. their ‘active space’) using masked thresholds for the signals themselves. Our results suggest that measures of peak sound pressure level, combined with the spectrum level of noise within the frequency channel having the greatest signal power relative to background noise, give the most similar results for estimating a signal’s maximum communication distance across a variety of sounds. We provide a simple model for estimating likely detection and discrimination distances for the signals tested here.  2003  on behalf of The Association for the Study of Animal Behaviour.

title: Boat noise reduces acoustic active space in the lusitanian toadfish Halobatrachus didactylus
abstract: Anthropogenic noise is considered of global concern since increasing ocean background noise due to human activities is impacting aquatic lifeforms. One of the most prevalent anthropogenic noise sources are boat engines. Although motorboat traffic has increased in the last decades, the impact of boat noise on the communication of aquatic animals is still poorly known. Impact of boat noise on the communication active space of a vocal teleost, the Lusitanian toadfish (Halobatrachus dydactilus), was tested. To achieve this goal a comparison between the maximum distance a fish can perceive the conspecific advertisement signal – the boatwhistle, before and after embedding the acoustic signal in boat noise, using the AEP technique, was made. Noise from two different types of boat, a small motorboat and a ferryboat, was used. At about 2 m water depth, active space ranged between 6 and 13 m, depending on boatwhistle spectral characteristics. Noise from the small motorboat and from the ferry boat reduced the commun...

title: Anthropogenic noise impairs owl hunting behavior
abstract: Emerging evidence indicates that anthropogenic noise has highly detrimental impacts on natural communities; however, the effects of noise on acoustically specialized predators has received less attention. We demonstrate experimentally that natural gas compressor station noise impairs the hunting behavior of northern saw-whet owls ( Aegolius acadius ). We presented 31 wild-caught owls with prey inside a field-placed flight tent under acoustic conditions found 50–800 m (46–73 dBA) from a compressor station. To assess how noise affected hunting, we postulated two hypotheses. First, hunting deficits might increase with increasing noise—the dose–response hypothesis. Secondly, the noise levels used in this experiment might equally impair hunting, or produce no impact—the threshold hypothesis. Using a model selection framework, we tested these hypotheses for multiple dependent variables—including overall hunting success and each step in the attack sequence (prey detection, strike, and capture). The dose–response hypothesis was supported for overall hunting success, prey detection, and strike behavior. For each decibel increase in noise, the odds of hunting success decreased by 8% (CI 4.5%–11.0%). The odds of prey detection and strike behavior also decreased with increasing noise, falling 11% (CI 7%–16%) and 5% (CI 5%–6%), respectively. These results suggest that unmitigated noise has the potential to decrease habitat suitability for acoustically specialized predators, impacts that can reverberate through ecosystems.

title: Research, part of a Special Feature on Effects of Roads and Traffic on Wildlife Populations and Landscape Function Impacts of Traffic Noise and Traffic Volume on Birds of Roadside Habitats
abstract: Roadside habitats are important for a range of taxa including plants, insects, mammals, and birds, particularly in developed countries in which large expanses of native vegetation have been cleared for agriculture or urban development. Although roadside vegetation may provide suitable habitat for many species, resident animals can be exposed to high levels of traffic noise, visual disturbance from passing vehicles, and the risk of collision with cars and trucks. Traffic noise can reduce the distance over which acoustic signals such as song can be detected, an effect known as acoustic interference or masking. Studies from the northern hemisphere show that the singing behavior of birds changes in the presence of traffic noise. We investigated the impact of traffic noise and traffic volume on two species of birds, the Grey Shrike-thrush (Colluricincla harmonica) and the Grey Fantail (Rhipidura fuliginosa), at 58 roadside sites on the Mornington Peninsula, southeastern Australia. The lower singing Grey Shrike-thrush sang at a higher frequency in the presence of traffic noise, with a predicted increase in dominant frequency of 5.8 Hz/dB of traffic noise, and a total effect size of 209 Hz. In contrast, the higher singing Grey Fantail did not appear to change its song in traffic noise. The probability of detecting each species on a visit to a site declined substantially with increasing traffic noise and traffic volume, with several lines of evidence supporting a larger effect of traffic noise. Traffic noise could hamper detection of song by conspecifics, making it more difficult for birds to establish and maintain territories, attract mates and maintain pair bonds, and possibly leading to reduced breeding success in noisy roadside habitats. Closing key roads during the breeding season is a potential, but untested, management strategy to protect threatened bird species from traffic noise and collision with vehicles at the time of year when they are most vulnerable to their impacts. Other management options include reducing the speed and/or volume of traffic on such roads to an acceptably low level. Ours is the first study to investigate the effect of traffic noise on the singing behavior of birds in the southern hemisphere.

title: The Sound of Danger: Threat Sensitivity to Predator Vocalizations, Alarm Calls, and Novelty in Gulls
abstract: The threat sensitivity hypothesis predicts that organisms will evaluate the relative danger of and respond differentially to varying degrees of predation threat. Doing so allows potential prey to balance the costs and benefits of anti-predator behaviors. Threat sensitivity has undergone limited testing in the auditory modality, and the relative threat level of auditory cues from different sources is difficult to infer across populations when variables such as background risk and experience are not properly controlled. We experimentally exposed a single population of two sympatric gull species to auditory stimuli representing a range of potential threats in order to compare the relative threat of heterospecific alarm calls, conspecific alarms calls, predator vocalizations, and novel auditory cues. Gulls were able to discriminate among a diverse set of threat indicators and respond in a graded manner commensurate with the level of threat. Vocalizations of two potential predators, the human voice and bald eagle call, differed in their threat level compared to each other and to alarm calls. Conspecific alarm calls were more threatening than heterospecfic alarm calls to the larger great black-backed gull, but the smaller herring gull weighed both equally. A novel cue elicited a response intermediate between known threats and a known non-threat in herring gulls, but not great black-backed gulls. Our results show that the relative threat level of auditory cues from different sources is highly species-dependent, and that caution should be exercised when comparing graded and threshold threat sensitive responses.

title: Interspecific response to playback of bird song.
abstract: Responses to bird song have usually only been studied at the intraspecific level. I experimentally tested whether playback of the song of the black wheatear Oenanthe leucura in an area in S Spain resulted in responses from conspecifics as well as heterospecific birds by comparing the numbers of individuals singing before and after playback. The number of singing male black wheatears increased considerably, but also the number of singing males of five other passerine species increased significantly. The heterospecific response to playback may be due (1) to interspecific territoriality, (2) to black wheatear song signalling the absence of predators, or (3) to heterospecifics confusing the species-identity of the singer. The second alternative is considered more likely, since an ecologically wide array of species increased their song rate following playback. The conspicuous dawn (and dusk) chorus of bird song may be augmented by social facilitation due to the singing of conspecifics as well as heterospecifics.

title: Immune function and survival of great tit nestlings in relation to growth conditions
abstract: Life history theory predicts a trade-off between number and quality of offspring. Reduced quality with increasing brood size may arise from a decrease in body condition or in immunocompetence that would be important in fighting off virulent parasites by immunologically naive offspring. We tested the effect of rearing conditions on immune function of nestling great tits (Parus major) by reducing or increasing broods by two hatchlings. In the middle of the nestling period (on day 8), nestlings from enlarged broods developed lower T cell responses [as measured from the cutaneous swelling reaction to injection with phytohaemagglutinin (PHA)] and tended to have lower total leukocyte and lymphocyte concentrations in their peripheral blood than nestlings from reduced broods. Brood size manipulation affected the PHA response of nestlings most strongly in small clutches, suggesting that nestling immune function was dependent on their parents’ condition, as estimated by original clutch size. Intra-brood differences in nestling mortality were unrelated to immune parameters, but nestlings in broods without mortality had a stronger PHA response, higher concentration of lymphocytes and higher body mass on day 15 than nestlings in broods with mortality. These results support the prediction that the immune function of altricial birds is affected by rearing conditions, and that growth and immune parameters are related to inter-brood differences in nestling survival.

title: Behavioural consequences of two chronic psychosocial stress paradigms: Anxiety without depression
abstract: Chronic stress, in particular chronic psychosocial stress, is a risk factor in the aetiology of various psychopathologies including anxiety- and depression-related disorders. Therefore, recent studies have focussed on the development of social-stress paradigms, which are believed to be more relevant to the human situation than non-social-stress paradigms. The majority of these paradigms have been reported to increase both anxiety- and depression-related behaviour in rats or mice. However, in order to dissect the mechanisms underlying anxiety or depression, animal models are needed, which specifically induce one, or the other, phenotype. Here, we study both short- (1d after stressor termination) and long-term (4d or 7d after stressor termination) behavioural and physiological consequences of two well-validated chronic psychosocial stress models: social-defeat/overcrowding (SD/OC) and chronic subordinate colony housing (CSC). We demonstrate that SD/OC and CSC result in different physiological alterations: SD/OC more strongly affecting body-weight development, whereas CSC more strongly affects adrenal and pituitary morphology. Both stressors were shown to flatten circadian locomotor activity immediately after stress termination, which normalized 7d later in SD/OC group but reversed to hyperactivity during the dark phase in the CSC group. Importantly, neither stress paradigm resulted in an increase in depression-related behaviour as assessed using the forced swim test, tail suspension test and saccharin preference test at any time-point. However, both stress paradigms lead to an anxiogenic phenotype; albeit with different temporal profiles and not towards a novel con-specific (social anxiety). CSC exposure elevates anxiety-related behaviour immediately after stressor termination, which lasts for at least 1 wk. In contrast, the anxiogenic phenotype only develops 1 wk after SD/OC termination. In conclusion, both models are unique for uncovering the molecular underpinnings of anxiety-related behaviour without conflicting depression-based alterations.

title: A framework for understanding ecological traps and an evaluation of existing evidence.
abstract: When an animal settles preferentially in a habitat within which it does poorly relative to other available habitats, it is said to have been caught in an "ecological trap." Although the theoretical possibility that animals may be so trapped is widely recognized, the absence of a clear mechanistic understanding of what constitutes a trap means that much of the literature cited as support for the idea may be weak, at best. Here, we develop a conceptual model to explain how an ecological trap might work, outline the specific criteria that are necessary for demonstrating the existence of an ecological trap, and provide tools for researchers to use in detecting ecological traps. We then review the existing literature and summarize the state of empirical evidence for the existence of traps. Our conceptual model suggests that there are two basic kinds of ecological traps and three mechanisms by which traps may be created. To this point in time, there are still only a few solid empirical examples of ecological traps in the published literature (although those few examples suggest that both types of traps and all three of the predicted mechanisms do exist in nature). Therefore, ecological traps are either rare in nature, are difficult to detect, or both. An improved library of empirical studies will be essential if we are to develop a more synthetic understanding of the mechanisms that can trigger maladaptive behavior in general and the specific conditions under which ecological traps might occur.

title: Increased amplitude and duration of acoustic stimuli enhance distraction
abstract: Extraneous sounds have a variety of effects on animals; they may interfere with communication, cause physical harm, increase wariness, influence settlement decisions, or they may cause distractions in ways that increase vulnerability to predation. We designed a study to investigate the effects of changing both the amplitude and duration of an acoustic stimulus on distraction in a terrestrial hermit crab (Coenobita clypeatus). In experiment 1, we replicated the key findings from a field result: crabs hid more slowly in response to a silent visual stimulus when we simultaneously broadcast a white noise than they did when in a silent condition. In experiment 2, we altered the noise duration and found that a long noise generated greater latencies to hide than a short noise. In experiment 3, we increased the noise amplitude and found that hide latency increased with higher-intensity auditory stimuli. These experiments demonstrate a variety of stimulus factors that influence distraction. Our results suggest that prey animals could be in greater danger from predators when in an environment with auditory distractions.

title: Anthropogenic noise affects risk assessment and attention: the distracted prey hypothesis
abstract: Many studies have focused on the effects of anthropogenic noise on animal communication, but only a few have looked at its effect on other behavioural systems. We designed a playback experiment to test the effect of noise on predation risk assessment. We found that in response to boat motor playback, Caribbean hermit crabs (Coenobita clypeatus) allowed a simulated predator to approach closer before they hid. Two hypotheses may explain how boat noise affected risk assessment: it masked an approaching predator's sound; and/or it reallocated some of the crabs' finite attention, effectively distracting them, and thus preventing them from responding to an approaching threat. We found no support for the first hypothesis: a silent looming object still got closer during boat motor playbacks than during silence. However, we found support for the attentional hypothesis: when we added flashing lights to the boat motor noise to further distract the hermit crabs, we were able to approach the crabs more closely than with the noise alone. Anthropogenic sounds may thus distract prey and make them more vulnerable to predation.

title: A Framework for Understanding Noise Impacts on Wildlife: An Urgent Conservation Priority
abstract: Anthropogenic noise is an important environmental stressor that is rapidly gaining attention among biologists, resource managers, and policy makers. Here we review a substantial literature detailing the impacts of noise on wildlife and provide a conceptual framework to guide future research. We discuss how several likely impacts of noise exposure have yet to be rigorously studied and outline how behavioral responses to noise are linked to the nature of the noise stimulus. Chronic and frequent noise interferes with animals' abilities to detect important sounds, whereas intermittent and unpredictable noise is often perceived as a threat. Importantly, these effects can lead to fitness costs, either directly or indirectly. Future research should consider the range of behavioral and physiological responses to this burgeoning pollutant and pair measured responses with metrics that appropriately characterize noise stimuli. This will provide a greater understanding of the mechanisms that govern wildlife responses...

title: Differential post-fledging survival of great and coal tits in relation to their condition and fledging date
abstract: 1 We present a multivariate model of the post-fledging survival of juvenile great and coal tits (Parus major L., P. ater L.) in relation to chick body condition and timing of breeding. Radio-telemetry and colour marks were used to track tit families during 20 days from fledging, that is, the period of post-fledging dependence. Data on 342 chicks of 68 broods were obtained. 
2 Forty-seven per cent of juveniles died during the observation period, predation being the main cause of mortality. In the first 4 days after fledging the mortality rate was 5–10% per day. 
3 Survival of juveniles was positively correlated with fledging mass. Furthermore, survival strongly decreased during the season. In the second half of June, mortality was five times the rate of mid-May. The differential survival resulted in selection for both early fledging and high fledging mass. Juvenile condition was less important for survival in birds that had fledged early in the season. Their survival rates exceeded 70% in all weight classes, whereas in late broods only the heaviest individuals survived equally well. The survival of birds fledging both late and in poor condition was below 20%. Thus, selection for high fledging mass was much stronger in the late season than in early broods. 
4 We conclude that the impact of predation after leaving the nest results in selection for early breeding and, particularly in the late season, for high fledging mass. This may explain why the earliest broods have been found to produce most recruits into the breeding population even if they did not profit from maximum food availability during the nestling period. On the other hand, energetic limitations may constrain the begin of egg laying in adult birds. Thus, counteracting evolutionary responses to the seasonal development of food availability (the caterpillar peak) and to the risk of post-fledging mortality (the peak in post-fledging mortality) may have focused the period of optimal reproduction to a narrow time-window.

title: How robins find worms
abstract: An understanding of diet selection in animals requires knowledge of not only what animals eat in relation to what is available, but also how they perceive the foods available to them. Birds use auditory, visual, olfactory and possibly vibrotactile cues to find prey, but vision is the predominant mode of prey detection. In a series of controlled experiments in an aviary, four American robins, Turdus migratoriusfound buried mealworms in the absence of visual, olfactory and vibrotactile cues, suggesting that they could use auditory cues to locate the prey. They also had significantly reduced foraging success when auditory cues were obscured by white noise. These results conflict with the only other experimental study of foraging in American robins, which concluded that they foraged using visual clues alone.

title: Natal Dispersal of Great Tits in a Patchy Environment
abstract: The importance of dispersal for population genetics, population dynamics, and conservation biology is well established. We studied natal dispersal of Great Tits between Wytham Wood (high-quality habitat), and hedgerows and small woodlands within 2 km of Wytham Wood (the "surrounding area"; low-quality habitat). We (1) quantified the exchange of birds between these habitats, and (2) evaluated whether there was phenotypic variation between dispersing and philopatric birds. Only 6% of immigrants in Wytham were born in the surrounding area, and only 5% of emigrant recruits from Wytham bred in the surrounding area. This indicates that most nonphilopatric birds dispersed >2 km, considerably farther than expected. The effect of sex on dispersal depends on the scale on which it is studied: females dispersed longer distances than males, but the exchange of birds between woodlands was not sex biased. The proportion of immigrants among breeding birds was similar for both sexes, confirming the latter result. Dispersing and philopatric birds did not differ in hatch date, but birds that hatched in the surrounding area and dispersed into Wytham had greater nestling mass than those that did not. This effect was not found in Wytham, suggesting that there is an interaction between phenotypic quality and habitat quality with respect to dispersal: birds of high phenotypic quality disperse when they are born in low-quality habitat. As a result, birds breeding in Wytham (high-quality) had greater mass as nestlings than birds breeding in the surrounding area (low-quality). To our knowl- edge, this is the first demonstration that conditions during early development have an affect on the quality of the environment in which a bird subsequently reproduces.

title: Is clutch size in birds affected by environmental conditions during growth?
abstract: Only environmental conditions occurring at the time of breeding have been shown to affect clutch size in birds, even though conditions experienced during growth are known to affect body size or egg size. We show here that environmental conditions experienced during early life can affect clutch size in captive zebra finches (Taeniopygia guttata) and wild great tits (Parus major). Not only do factors outside the immediate breeding season affect clutch size, but clutch size control mechanism is permanently influenced by conditions experienced during ontogeny.

title: Nest Predation Risk and Growth Strategies of Passerine Species: Grow Fast or Develop Traits to Escape Risk?
abstract: Different body components are thought to trade off in their growth and development rates, but the causes for relative prioritization of any trait remains a critical question. Offspring of species at higher risk of predation might prioritize development of locomotor traits that facilitate escaping risky environments over growth of mass. We tested this possibility in 12 altricial passerine species that differed in their risk of nest predation. We found that rates of growth and development of mass, wings, and endothermy increased with nest predation risk across species. In particular, species with higher nest predation risk exhibited relatively faster growth of wings than of mass, fledged with relatively larger wing sizes and smaller mass, and developed endothermy earlier at relatively smaller mass. This differential development can facilitate both escape from predators and survival outside of the nest environment. Tarsus growth was not differentially prioritized with respect to nest predation risk, and instead all species achieved adult tarsus size by age of fledging. We also tested whether different foraging modes (aerial, arboreal, and ground foragers) might explain the variation of differential growth of locomotor modules, but we found that little residual variation was explained. Our results suggest that differences in nest predation risk among species are associated with relative prioritization of body components to facilitate escape from the risky nest environment.

title: Behavioral Responses Associated with a Human-Mediated Predator Shelter
abstract: Human activities in protected areas can affect wildlife populations in a similar manner to predation risk, causing increases in movement and vigilance, shifts in habitat use and changes in group size. Nevertheless, recent evidence indicates that in certain situations ungulate species may actually utilize areas associated with higher levels of human presence as a potential refuge from disturbance-sensitive predators. We now use four-years of behavioral activity budget data collected from pronghorn (Antilocapra americana) and elk (Cervus elephus) in Grand Teton National Park, USA to test whether predictable patterns of human presence can provide a shelter from predatory risk. Daily behavioral scans were conducted along two parallel sections of road that differed in traffic volume - with the main Teton Park Road experiencing vehicle use that was approximately thirty-fold greater than the River Road. At the busier Teton Park Road, both species of ungulate engaged in higher levels of feeding (27% increase in the proportion of pronghorn feeding and 21% increase for elk), lower levels of alert behavior (18% decrease for pronghorn and 9% decrease for elk) and formed smaller groups. These responses are commonly associated with reduced predatory threat. Pronghorn also exhibited a 30% increase in the proportion of individuals moving at the River Road as would be expected under greater exposure to predation risk. Our findings concur with the ‘predator shelter hypothesis’, suggesting that ungulates in GTNP use human presence as a potential refuge from predation risk, adjusting their behavior accordingly. Human activity has the potential to alter predator-prey interactions and drive trophic-mediated effects that could ultimately impact ecosystem function and biodiversity.

title: A consensus endocrine profile for chronically stressed wild animals does not exist.
abstract: Given the connection between chronic stress and health, there has been a growing emphasis on identifying chronically stressed wild animals, especially in relation to anthropogenic disturbances. There is considerable confusion, however, in how to identify chronically stressed wild animals, but the most common assumption is that measures of glucocorticoid (GC) function will increase. In an attempt to determine an "endocrine profile" of a chronically stressed wild animal, this review collected papers from the literature that measured baseline GC, stress-induced GC, measures of integrated GC, negative feedback, hypothalamic-pituitary-adrenal axis sensitivity, and/or body weight in chronically stressed animals. The collected studies encompassed laboratory and field studies, numerous diverse species, and multiple techniques for inducing chronic stress. Each paper was ranked according to its relevance to wild animals and scored as to whether the measured response increased, decreased, or stayed the same after exposure to chronic stress. The analyses uncovered so much variation between studies that the literature does not support a generalized endocrine profile in how wild animals respond to chronic stress. The common predictions appear to be based almost entirely on theoretical models rather than empirical data. The three most important variables affecting GC responses were the stressors used to induce chronic stress, the potential for those stressors to induce habituation, and the taxon of the focal species. The best approach for identifying a chronically stressed population appears to be documentation of changes at multiple levels of GC regulation, but the direction of the change (increase or decrease) may be relatively unimportant compared to the fact that the response changes at all. The conclusion is that a consistent, predictable, endocrine response to chronic stress, regardless of the protocol used to induce chronic stress and the species under study, does not exist.

title: Short Telomeres in Depression and the General Population Are Associated with a Hypocortisolemic State
abstract: The hypothalamic-pituitary-adrenal (HPA) axis plays a central role in stress regulation, and leukocyte telomere length (TL) has been suggested to represent a cumulative measure of stress. Depression is intimately related with stress and frequently exhibits a dysregulated HPA axis. We aimed to study the relationships between TL and biological and psychological facets of stress in recurrent major depressive disorder and controls.



Leukocyte TL was measured in 91 subjects with recurrent major depressive disorder and 451 control subjects. Stress was assessed from both a biological perspective, by assessing HPA axis function with a weight-adjusted very-low-dose dexamethasone suppression test (DST), and a psychological perspective, with self-report questionnaires.



TL was shorter among patients compared with control subjects (277 base pairs, p = .001). Overall, short TL was associated with a hypocortisolemic state (low post-DST cortisol and high percentage of cortisol reduction after the DST) among both patients and control subjects but more pronounced among patients. This state, which was overrepresented among patients, was characterized by high familial loading of affective disorders among patients (p = .001) and high C-reactive protein levels among control subjects (p = .040). TL was also inversely associated with stress measured with the Perceived Stress Questionnaire (r(s) = -.258, p = .003).



Short TL is associated with depression and hypocortisolism. Because hypocortisolism has been shown to develop from chronic stress exposure, our findings corroborate the concept of TL as a cumulative measure of stress and provide novel insights into the detrimental role of stress in depressive illness and the general population.

title: Hormones, brain and stress.
abstract: The stress system orchestrates body and brain responses to the environment. This action exerted by the mediators of the stress system has two modes of operation. The immediate response mode driven by corticotropin-releasing hormone (CRH) organises via CRH-1 receptors the behavioural, sympathetic and hypothalamic-pituitary-adrenal (HPA) responses to a stressor. In the other - slower - mode, which facilitates behavioural adaptation, the urocortins acting through CRH-2 receptors seem prominent. Corticosteroid hormones secreted by the adrenal cortex are implicated in both modes through their high affinity type 1 (mineralocorticoid receptors - MR) and lower affinity type 2 (glucocorticoid receptors - GR) receptors that are co-localised in limbic neural circuitry. Current data suggest that MR controls in specific afferents the threshold or sensitivity of the fast CRH-1 driven stress system mode and thus prevents disturbance of homeostasis, while GR facilitates its recovery by restraining in these very same circuits stress responses and by mobilising energy resources. In preparation for future events GR facilitates behavioural adaptation and promotes storage of energy. The balance in the two stress system modes is thought to be essential for cell homeostasis, mental performance and health. Imbalance induced by genetic modification or chronic stressors changes specific neural signalling pathways underlying psychic domains of cognition and emotion, anxiety and aggression. This Yin-Yang stress concept is fundamental for genomic strategies to understand the mechanistic underpinning of cortisol-induced stress-related disorders such as i.e. severe forms of depression and co-morbid diseases.

title: Stress, Adaptation, and Disease: Allostasis and Allostatic Load
abstract: Adaptation in the face of potentially stressful challenges involves activation of neural, neuroendocrine and neuroendocrine‐immune mechanisms. This has been called “allostasis” or “stability through change” by Sterling and Eyer (Fisher S., Reason J. (eds): Handbook of Life Stress, Cognition and Health. ), and allostasis is an essential component of maintaining homeostasis. When these adaptive systems are turned on and turned off again efficiently and not too frequently, the body is able to cope effectively with challenges that it might not otherwise survive. However, there are a number of circumstances in which allostatic systems may either be overstimulated or not perform normally, and this condition has been termed “allostatic load” or the price of adaptation (McEwen and Stellar,  1993; ). Allostatic load can lead to disease over long periods. Types of allostatic load include (1) frequent activation of allostatic systems; (2) failure to shut off allostatic activity after stress; (3) inadequate response of allostatic systems leading to elevated activity of other, normally counter‐regulated allostatic systems after stress. Examples will be given for each type of allostatic load from research pertaining to autonomic, CNS, neuroendocrine, and immune system activity. The relationship of allostatic load to genetic and developmental predispositions to disease is also considered.

title: The role of inflammation in depression: from evolutionary imperative to modern treatment target
abstract: Crosstalk between inflammatory pathways and neurocircuits in the brain can lead to behavioural responses, such as avoidance and alarm, that are likely to have provided early humans with an evolutionary advantage in their interactions with pathogens and predators. However, in modern times, such interactions between inflammation and the brain appear to drive the development of depression and may contribute to non-responsiveness to current antidepressant therapies. Recent data have elucidated the mechanisms by which the innate and adaptive immune systems interact with neurotransmitters and neurocircuits to influence the risk for depression. Here, we detail our current understanding of these pathways and discuss the therapeutic potential of targeting the immune system to treat depression.

title: Mapping the extent of noise on a national scale using geospatial models
abstract: Because many wildlife habitats, geological processes, and anthropogenic impacts occur on a regional scale, acoustical analyses must encompass a similar extent. Geospatial sound modeling incorporates spatial representations of biological, geophysical, climatic, and anthropogenic factors to assess expected contributions to the existing sound pressure level from both anthropogenic and natural sources. This method enables mapping of sound pressure levels at national scales. The models do not directly apply the physics of sound propagation or characteristics of individual sound sources. Instead, long-term sound pressure level measurements from hundreds of sites across the contiguous United States were used to train regression models to predict acoustic conditions. This talk will focus on the implications of the resulting acoustic maps of the contiguous United States. In addition, noise and the relationship to light pollution will be considered.

title: Noise Pollution Changes Avian Communities and Species Interactions
abstract: Humans have drastically changed much of the world's acoustic background with anthropogenic sounds that are markedly different in pitch and amplitude than sounds in most natural habitats. This novel acoustic background may be detrimental for many species, particularly birds. We evaluated conservation concerns that noise limits bird distributions and reduces nesting success via a natural experiment to isolate the effects of noise from confounding stimuli and to control for the effect of noise on observer detection biases. We show that noise alone reduces nesting species richness and leads to different avian communities. Contrary to expectations, noise indirectly facilitates reproductive success of individuals nesting in noisy areas as a result of the disruption of predator-prey interactions. The higher reproductive success for birds within noisy habitats may be a previously unrecognized factor contributing to the success of urban-adapted species and the loss of birds less tolerant of noise. Additionally, our findings suggest that noise can have cascading consequences for communities through altered species interactions. Given that noise pollution is becoming ubiquitous throughout much of the world, knowledge of species-specific responses to noise and the cumulative effects of these novel acoustics may be crucial to understanding and managing human-altered landscapes.

title: Synchrony does not explain extrapair paternity rate variation in northern or southern house wrens
abstract: Rates of extrapair paternity (EPP) vary widely among and within bird species, and 2 hypotheses suggest that this variation is driven by variation in breeding synchrony. These hypotheses make contradictory predictions, and each has some support from field studies, but the general relationship between EPP and synchrony remains unclear. We investigated EPP in relation to population-wide and local breeding synchrony in 2 populations of house wrens (Troglodytes aedon)--a migratory northern temperate (New York, USA) and a sedentary southern temperate (Buenos Aires, Argentina) population--that differ in numerous life-history traits. The northern population had significantly higher EPP rates and modestly but significantly higher local breeding synchrony. Population-wide breeding synchrony did not differ between populations. The proportion of extrapair young within a nest was not related to the nest's population-wide or local synchrony index in either population. These results suggest that across divergent life histories in this species, breeding synchrony does not account for within-population variation in EPP.

title: Fat provisioning in winter impairs egg production during the following spring: a landscape-scale study of blue tits.
abstract: 1. Provisioning of garden birds is a growing phenomenon, particularly during winter, but there is little empirical evidence of its true ecological impacts. One possibility is that winter provisioning could enhance subsequent breeding performance, but this seems likely to depend on the types of nutrients provided. For example, whereas effects of macronutrients such as fat are unlikely to be carried over to influence breeding in small passerines, micronutrients such as dietary vitamin E (an antioxidant) may be stored or have lasting health benefits. 2. Here, we examine the carry-over effects of winter food supplements on egg production in wild populations of blue tits (Cyanistes caeruleus). Over three consecutive years, birds were provisioned with fat, fat plus vitamin E or remained unfed (controls). 3. The provision of fat in winter resulted in smaller relative yolk mass in larger eggs and reduced yolk carotenoid concentrations in early breeders. However, these effects were not seen in birds provisioned with fat plus vitamin E. Lay date, clutch size, egg mass and yolk vitamin E concentrations were not significantly affected by winter provisioning treatment. 4. Our results indicate that winter provisioning can have important downstream consequences, in particular affecting investment in egg production several weeks or months later. 5. Provisioning is widely applied to support garden bird populations and for the conservation management of endangered species. However, our results challenge the assumption that such practices are always beneficial at the population level and emphasize how the ecological impacts can depend on the specific nutritional profile of provisioned foods.

title: Stress in a conservation context: A discussion of glucocorticoid actions and how levels change with conservation-relevant variables
abstract: Over the past few decades, there has been a steep increase in the number of conservation-related field studies that measure glucocorticoid hormones (corticosterone or cortisol) as a marker for stress. Endocrine tools show great potential for informing conservation, however interpretation of results is often complicated. This paper reviews the role of glucocorticoids for non-physiologists, evaluates select applications of glucocorticoid measures to conservation field studies, and proposes a theoretical model to focus future research. Because levels of glucocorticoids typically increase in response to challenge and sometimes predict mortality or decrease reproduction, it is often assumed that high levels of glucocorticoids indicate stress. However, literature review suggests that glucocorticoid measures fail to change consistently in a predictable manner with adverse conditions and do not always show a linear correlation with survival or reproductive success. Inconsistencies relate in part to methodological problems but also have a physiological basis. We propose that relationships between (1) glucocorticoids and fitness and (2) glucocorticoids and disturbance may be more log quadratic rather than linear. We hope these models will be useful in generating predictions for future studies and resolving the inconsistencies that currently complicate interpretation for conservation endocrinologists.

title: Collecting baseline corticosterone samples in the field: is under 3 min good enough?
abstract: Evaluating corticosterone (CORT) responses to stress in free-living vertebrates requires knowing the unstressed titers prior to capture. Based upon laboratory data, the assumption has been that samples collected in less than 3 min of capture will reflect these unstressed concentrations. This assumption was tested for six species using samples collected from 945 individuals at 0-6 min after capture. Samples were from five avian species trapped at multiple times of year and one reptilian species, comprising a total of 14 different data sets for comparisons. For seven of 14 data sets, including five species, there was no significant increase in corticosterone titers within 3 min of capture. In six of the 14 data sets, corticosterone titers increased significantly after 2 min, and in one data set, the increase started at 1.5 min. In all seven of the cases showing an increase before 3 min, however, corticosterone titers from the time of increase to 3 min were significantly lower than titers after 30 min of restraint stress. These results indicate a high degree of confidence for these species that samples collected in less than 2 min reflect unstressed (baseline) concentrations, and that samples collected from 2-3 min also will likely reflect baseline concentrations but at worst are near baseline.

title: In search of relationships between the acute adrenocortical response and fitness.
abstract: The assumption that the acute response to stress is adaptive is pervasive in the literature, but there is little direct evidence regarding potential positive fitness consequences of an acute stress response. If acute glucocorticoid (GC) elevation increases lifetime reproductive success (fitness), in what contexts does this occur, and through what combination of effects on annual reproductive output and interannual survival? Here we examine the framework under which most comparative acute GC studies fall, evaluate the commonalities of those studies in the light of expected fitness effects, and suggest methods to better examine the potentially beneficial effects of the acute GC response for free living animals. An overwhelming majority of papers from this area examine environmental-physiological-social effects on GC reactivity. Fewer evaluate intermediate performance measures (fitness proxies). We could only find 11 that directly examine GC effects on reproductive output and survival. The environment-GC-performance papers suggest that greater GC reactivity favors self-maintenance behavior (survival) at the expense of current reproduction. However, the two studies that directly address GC reactivity and fitness (2 of the 11) find the opposite effect (greater GC reactivity predicts lower annual survival). We suggest that it is time to move past simple evaluation of factors regulating GC secretion. These studies will be much richer and informative if researchers include performance and fitness measures. We especially support incorporating and testing ideas of context dependency, coping strategies, and possible fluctuating selection pressures when considering the fitness benefits of the acute GC response.

title: Season and migration alters the corticosterone response to capture and handling in an Arctic migrant, the white-crowned sparrow (Zonotrichia leucophrys gambelii).
abstract: The Gambel's race of white-crowned sparrow (Zonotrichia leucophrys gambelii) migrates each year from their wintering grounds in the Southwestern United States to the Arctic to breed. Associated with this migration is a change in both the nonstressed and the stress-induced levels of circulating plasma corticosterone. Birds were captured at two sites on their wintering grounds (New Mexico and Arizona). Although stress-induced corticosterone levels were elevated at each site compared to nonstressed levels, there were no differences between wintering sites. These were also similar to levels in birds caught in Washington state during fall migration. In contrast, nonstressed corticosterone values were greatly elevated in birds on their breeding grounds in Alaska and similar to stress-induced levels in wintering birds. Corticosterone levels rose even further in response to the stress of capture and handling in breeding birds. These augmented corticosterone levels during breeding were not associated with weather. Both nonstressed and stress-induced corticosterone levels were similar in birds caught on their breeding grounds on two different years, one with temperatures during mid-May of approximately 0 degree C during a snow storm and the other with temperatures in the mid-20s. These results suggest that seasonal physiological changes, and not local conditions, underlie seasonal changes in corticosterone levels. Furthermore, birds caught in Washington state during spring migration had intermediate levels of both nonstressed and stress-induced corticosterone. Corticosterone release may function differently during spring and fall migrations.

title: EXOGENOUS TESTOSTERONE AND THE ADRENOCORTICAL RESPONSE IN DARK-EYED JUNCOS
abstract: Hormonal manipulations with implants allow examination of the costs and benefits of behaviors and physiologic states mediated by a given hormone. As a part of on- going research into the effects of the steroid hormone testosterone (T) in Dark-eyed Juncos (Junco hyemalis), we measured the corticosterone (B, a steroid hormone secreted by the ad- renal in response to stress ) response to the stress of capture and handling in males treated with T (T-males) and in control males (C-males). Although B may be essential for energy mobilization, chronic or repeated exposure to elevated levels of B can have many negative effects. Because T mediates many behaviors that may increase the likelihood that an indi- vidual will encounter stressors, we predicted that plasma B would rise more rapidly in T- males than in controls. In the first few minutes post-capture, the increase in B levels was significantly higher in T-males than in controls. B levels in samples collected 10, 30, and 60 min post-capture were consistently higher in T-males than in C-males; however, the differ- ence was not statistically significant. Because previous work has shown that T-males reduce their parental contribution, we compared females that were mated to T-males and C-males (hereafter T- and C-females). B levels of T-females increased sharply in the first few minutes post-capture, whereas in C-females they did not; however, the responses were not statisti- cally different. Males had higher initial levels and a greater B-response to stress than females when data were compared irrespective of treatment. Our results suggest that the behaviors or physiological changes induced by T are potentially costly and that such costs may in part be incurred through elevated B. Received 25 November 1997, accepted 5 May 1998. IN MOST NORTH-TEMPERATE BIRDS, circulating levels of testosterone (T) in males are elevated during the sexual phase of the breeding season

title: Measures of physiological stress: a transparent or opaque window into the status, management and conservation of species?
abstract: We discuss the methodological issues associated with measuring stress hormones in wild animals. We discuss five questions that we think should be considered about the use of stress hormone measurements in conservation physiology. We present a meta-analysis showing that human activities consistently increase stress hormone levels across vertebrates.

title: Assessing baseline stress physiology as an integrator of environmental quality in a wild avian population: Implications for use as a conservation biomarker
abstract: Stress hormones (i.e., glucocorticoids such as corticosterone and cortisol) have been widely proposed as biomarkers of habitat quality and disturbance. However, there is growing evidence that baseline glucocorticoid (GC) levels are highly context-dependent, potentially confounding their utility for inferring population-level disturbance depending on the life history stage and the duration, severity, and type of environmental change being measured. Determining which aspects of an organism's environment are consistently reflected by baseline GC levels is therefore of paramount importance to establishing how they may be best suited to conservation monitoring goals. We investigated the relationship between baseline GC levels and three extrinsic (food availability, inter-specific nest competition, intra-specific competition) and two intrinsic (reproductive investment, body condition) environmental contexts in breeding female tree swallows (Tachycineta bicolor) at two reproductive stages. We combined this with a manipulation of energetic demand (i.e., a decrease in foraging profitability) to determine whether baseline GCs reflect the extrinsic or intrinsic environment when females are faced with an unexpected disturbance. Baseline GC levels were not reflective of any environmental component in control females, regardless of reproductive stage. However, levels increased and were reflective of a decrease in body mass when females were challenged during the offspring provisioning period. Our findings suggest that baseline GCs may not always be indicative of the environmental contexts we associate with variation in habitat quality, particularly when individuals are operating within their expected energetic demand. In a conservation sense, baseline GCs may be more valuable in reflecting unexpected perturbations, which could limit their applicability as sensitive, predictive biomarkers across a diversity of systems.

title: The consequences of clutch size for incubation conditions and hatching success in starlings
abstract: 1. Starling (Sturnus vulgaris) clutches were manipulated so that sibling eggs were incubated within either natural-sized clutches, or clutches that had been experimentally enlarged but were still within the natural range of variation. Thus the consequences of incubated clutch size for hatching success were investigated. 
 
2. Eggs incubated within enlarged clutches hatched less successfully than eggs incubated within natural-sized clutches, suggesting that clutch size affects the conditions experienced by embryos during incubation. 
 
3. Eggs incubated in enlarged clutches may have hatched poorly because clutch enlargement altered nest microclimate, causing increased water loss during the incubation period. 
 
4. There was no evidence that enlargement altered nest microclimate by energetically constraining parents from incubating effectively. Instead, intrinsic physical properties of enlarged clutches affected clutch temperature directly. 
 
5. Parents that had incubated experimentally enlarged clutches subsequently fledged fewer chicks than control parents, suggesting that constraints imposed during incubation may influence the optimal number of eggs that parents should lay. 
 
6. Future studies should investigate whether parents laying naturally large clutches can minimize the problems of incubating many eggs by adaptively tailoring the shape and composition of their eggs to their expected clutch size.

title: NOISE AND HUMAN PERFORMANCE, A PSYCHOPHYSIOLOGICAL APPROACH
abstract: A theoretical approach is developed for the study of the effects of noise on human performance which takes into account the psychological factors of distraction and habituation and the physiological factors of auditory adaptation and bodily arousal. Two experiments designed to test theoretical predictions suggested that the approach is reasonable. Distraction studied in terms of changes in ambient noise levels was found to be a function of the amount of change. When adaptation of the ear is controlled by use of on-off sound sequences, ignoring distraction, performance is directly related to the on-off ratio early in exposure and inversely related to the ratio later in exposure. At all sound ratios performance in noise is better than in quiet. When distraction is taken into account, these results are influenced by the differences in rate and amount of adaptation of loudness and rate of habituation to distraction so that at any given time performance may seem to be decreased, increased or unaffected.

title: Parsimonious Mixed Models
abstract: The analysis of experimental data with mixed-effects models requires decisions about the specification of the appropriate random-effects structure. Recently, Barr, Levy, Scheepers, and Tily, 2013 recommended fitting `maximal' models with all possible random effect components included. Estimation of maximal models, however, may not converge. We show that failure to converge typically is not due to a suboptimal estimation algorithm, but is a consequence of attempting to fit a model that is too complex to be properly supported by the data, irrespective of whether estimation is based on maximum likelihood or on Bayesian hierarchical modeling with uninformative or weakly informative priors. Importantly, even under convergence, overparameterization may lead to uninterpretable models. We provide diagnostic tools for detecting overparameterization and guiding model simplification.

title: Uninformative Parameters and Model Selection Using Akaike's Information Criterion
abstract: As use of Akaike's Information Criterion (AIC) for model selection has become increasingly common, so has a mistake involving interpretation of models that are within 2 AIC units (ΔAIC ≤ 2) of the top-supported model. Such models are <2 ΔAIC units because the penalty for one additional parameter is +2 AIC units, but model deviance is not reduced by an amount sufficient to overcome the 2-unit penalty and, hence, the additional parameter provides no net reduction in AIC. Simply put, the uninformative parameter does not explain enough variation to justify its inclusion in the model and it should not be interpreted as having any ecological effect. Models with uninformative parameters are frequently presented as being competitive in the Journal of Wildlife Management, including 72% of all AIC-based papers in 2008, and authors and readers need to be more aware of this problem and take appropriate steps to eliminate misinterpretation. I reviewed 5 potential solutions to this problem: 1) report all model...