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Species across a wide range of taxa and habitats are shifting phenological events in response to climate change. While advances are common, shifts vary in magnitude and direction within and among species, and the basis for this variation is relatively unknown. We examine previously suggested patterns of variation in phenological shifts in order to understand the cue–response mechanisms that underlie phenological change. Here, we review what is known about the mechanistic basis for nine factors proposed to predict phenological change (latitude, elevation, habitat type, trophic level, migratory strategy, ecological specialization, species’ seasonality, thermoregulatory mode, and generation time). We find that many studies either do not identify a specific underlying mechanism or do not evaluate alternative mechanistic hypotheses, limiting the ability of scientists to predict future responses to global change with accuracy. We present a conceptual framework that emphasizes a critical distinction between environmental (cue-driven) and organismal (response-driven) mechanisms causing variation in phenological shifts and discuss how this distinction can reduce confusion in the field and improve predictions of future phenological change.

Bioacoustic networks could vastly expand the coverage of wildlife monitoring to complement satellite observations of climate and vegetation. This approach would enable global-scale understanding of how climate change influences phenomena such as migratory timing of avian species. The enormous data sets that autonomous recorders typically generate demand automated analyses that remain largely undeveloped. We devised automated signal processing and machine learning approaches to estimate dates on which songbird communities arrived at arctic breeding grounds. Acoustically estimated dates agreed well with those determined via traditional surveys and were strongly related to the landscape's snow-free dates. We found that environmental conditions heavily influenced daily variation in songbird vocal activity, especially before egg laying. Our novel approaches demonstrate that variation in avian migratory arrival can be detected autonomously. Large-scale deployment of this innovation in wildlife monitoring would enable the coverage necessary to assess and forecast changes in bird migration in the face of climate change.

As global climate change progresses, the occurrence of potentially disruptive climatic events such as storms are increasing in frequency, duration and intensity resulting in higher mortality and reduced reproductive success. What constitutes an extreme climatic event? First we point out that extreme climatic events in biological contexts can occur in any environment. Focusing on field and laboratory data on wild birds we propose a mechanistic approach to defining and investigating what extreme climatic events are and how animals cope with them at physiological and behavioural levels. The life cycle of birds is made up of life-history stages such as migration, breeding and moult that evolved to match a range of environmental conditions an individual might expect during the year. When environmental conditions deteriorate and deviate from the expected range then the individual must trigger coping mechanisms (emergency life-history stage) that will disrupt the temporal progression of life-history stages, but enhance survival. Using the framework of allostasis, we argue that an extreme climatic event in biological contexts can be defined as when the cumulative resources available to an individual are exceeded by the sum of its energetic costs-a state called allostatic overload. This allostatic overload triggers the emergency life-history stage that temporarily allows the individual to cease regular activities in an attempt to survive extreme conditions. We propose that glucocorticoid hormones play a major role in orchestrating coping mechanisms and are critical for enduring extreme climatic events.This article is part of the themed issue 'Behavioural, ecological and evolutionary responses to extreme climatic events'.

Individuals at the forefront of a range shift are likely to exhibit phenotypic traits that distinguish them from the population breeding within the historic range. Recent studies have examined morphological, physiological and behavioral phenotypes of individuals at the edge of their range. Several studies have found differences in the hypothalamic-pituitary-adrenal (HPA) axis activity in response to acute restraint stress in individuals at the range limits. HPA axis activation leads to elevations in glucocorticoids that regulate physiology and behavior. Here we compare the hormonal profiles and morphometrics from Gambel's white-crowned sparrows (Zonotrichia leucophrys gambelii) breeding at the northern limit of the population's range to those birds breeding within the historic population range. Birds breeding at the northern limit experienced a harsher environment with colder temperatures; however, we found no differences in arthropod prey biomass between the northern limit and more southern (historic) sites. Males at the northern limit had higher body condition scores (mass corrected for body size) compared to individuals within the historic range, but no differences were found in beak and tarsus lengths, wing chord, muscle profile or fat stores. In males during the pre-parental stage, before breeding commenced, HPA axis activity was elevated in birds at the northern limit of the range, but no differences were found during the parental or molt stages. Females showed no differences in HPA axis activity during the parental stage. This study suggests that "pioneering" individuals at the limits of their breeding range exhibit physiology and morphology that are distinct from individuals within the historic range.

Species' ranges are shifting rapidly with climate change, altering the composition of biological communities and interactions within and among species. Hybridization is among the species interactions that may change markedly with climate change, yet it is understudied relative to others. We used non‐invasive genetic detections to build a maximum entropy species distribution model and investigate the factors that delimit the present and future ranges of American marten (Martes americana) and Pacific marten (Martes caurina) in a contact zone in the Northern Rockies. We found that climate change will decrease the suitable habitat predicted for both species, as well as the amount of overlap in predicted suitable habitat between the species. Interestingly, predicted suitable habitat for Pacific marten extended further north in the study region than our genetic detections for the species, suggesting that biotic factors, such as interactions with American marten, may affect the realized range of this species. Our results suggest that future work investigating the interactions among biotic and abiotic factors that influence hybrid zone dynamics is important for predicting the futures of these two species in this area under climate change. Climate change is altering the distributions of species worldwide, including those of hybridizing species. We use species distribution models, built from non‐invasive genetic detections of marten species, to show that the distributions of American marten and Pacific marten in the Northern Rockies of the United States will be differentially affected by climate change. [ABSTRACT FROM AUTHOR]

Thyroid hormones (TH) are key regulators of metabolism that could play an important role in altering physiology and energy allocation across life-history stages. Here, we examine seasonal TH dynamics from 345 plasma samples collected from 134 free-living arctic ground squirrels (Urocitellus parryii (Richardson, 1825)) across three consecutive years (2014-2016). We also examine whether unbound levels of triiodothyronine (free [T.sub.3]) in plasma are correlated with total [T.sub.3] levels and total thyroxine ([T.sub.4]) levels, and whether fecal [T.sub.3] metabolite levels correlate with plasma TH levels. We found significant differences in plasma TH levels across stages of the annual cycle, but these differences were highly inconsistent across years. However, within a given time period, pregnant females had lower free [T.sub.3] levels compared with lactating females. We also found that although free [T.sub.3] was correlated with both total [T.sub.3] and total [T.sub.4] in plasma, fecal [T.sub.3] was not positively correlated with plasma TH levels. Given the lack of consistent differences across life-history stages, we suggest environmental heterogeneity may be the primary driver of TH dynamics, masking any potential endogenous seasonal rhythms in TH secretion. We urge caution in the use of fecal [T.sub.3] metabolites as a proxy for circulating levels and encourage further research to understand the observed discrepancy. Key words: Urocitellus parryii, arctic ground squirrel, fecal hormones, reproductive state, thyroid, thyroxine, triiodothyronine. Les hormones thyroidiennes (HT) sont des regulateurs cles du metabolisme qui pourraient jouer un important role dans la modulation de la physiologie et de l'allocation d'energie durant les differentes etapes du cycle de vie. Nous examinons la dynamique saisonniere des HT de 345 echantillons de plasma preleves de 134 spermophiles arctiques (Urocitellus parryii (Richardson, 1825)) vivant en liberte sur trois annees consecutives (2014-2016). Nous tentons aussi de determiner si les concentrations de triiodothyronine libre ([T.sub.3] libre) dans le plasma sont correlees aux concentrations totales de [T.sub.3] et aux concentrations totales de thyroxine ([T.sub.4]), et si les concentrations fecales de metabolites de [T.sub.3] sont correlees aux concentrations plasmiques des HT. Nous relevons des differences significatives des concentrations plasmiques des HT entre les differentes etapes du cycle annuel, mais ces differences sont fortement incoherentes d'une annee a l'autre. Cependant, sur une periode de temps donnee, les femelles gestantes presentent des concentrations de [T.sub.3] libre plus faibles que les femelles en lactation. Nous constatons egalement que, si la [T.sub.3] libre est correlee a la [T.sub.3] totale et a la [T.sub.4] totale dans le plasma, la [T.sub.3] fecale n'est pas positivement correlee aux concentrations plasmiques des HT. Au vu de l'absence de difference coherente entre les differentes etapes du cycle biologique, nous proposons que l'heterogeneitedumilieu pourrait etreleprincipal facteurdemodulationdeladynamique des HT, masquant tout rythme saisonnier endogene eventuel de la secretion des HT. Nous pronons la prudence dans l'utilisation de metabolites fecaux de la [T.sub.3] comme variable substitutive des concentrations en circulation et encourageons la realisation de travaux visant a expliquer l'incoherence observee. [Traduit par la Redaction] Mots-cles : Urocitellus parryii, spermophile arctique, hormones fecales, etat reproducteur, thyroide, thyroxine, triiodothyronine., Introduction Physiological and behavioral flexibility allows free-living vertebrates to cope with environmental heterogeneity, including predictable seasonal changes and unpredictable challenges. Adjustments of physiology and behavior to environmental conditions are often [...]

Climate warming is affecting the Arctic in multiple ways, including via increased dominance of deciduous shrubs. Although many studies have focused on how this vegetation shift is altering nutrient cycling and energy balance, few have explicitly considered effects on tundra fauna, such as the millions of migratory songbirds that breed in northern regions every year. To understand how increasing deciduous shrub dominance may alter breeding songbird habitat, we quantified vegetation and arthropod community characteristics in both graminoid and shrub dominated tundra. We combined measurements of preferred nest site characteristics for Lapland longspurs ( Calcarius lapponicus) and Gambel's White-crowned sparrows ( Zonotrichia leucophrys gambelii) with modeled predictions for the distribution of plant community types in the Alaskan arctic foothills region for the year 2050. Lapland longspur nests were found in sedge-dominated tussock tundra where shrub height does not exceed 20 cm, whereas White-crowned sparrows nested only under shrubs between 20 cm and 1 m in height, with no preference for shrub species. Shrub canopies had higher canopy-dwelling arthropod availability (i.e. small flies and spiders) but lower ground-dwelling arthropod availability (i.e. large spiders and beetles). Since flies are the birds' preferred prey, increasing shrubs may result in a net enhancement in preferred prey availability. Acknowledging the coarse resolution of existing tundra vegetation models, we predict that by 2050 there will be a northward shift in current White-crowned sparrow habitat range and a 20-60% increase in their preferred habitat extent, while Lapland longspur habitat extent will be equivalently reduced. Our findings can be used to make first approximations of future habitat change for species with similar nesting requirements. However, we contend that as exemplified by this study's findings, existing tundra modeling tools cannot yet simulate the fine-scale habitat characteristics that are critical to accurately predicting future habitat extent for many wildlife species. [ABSTRACT FROM AUTHOR]

The acute-phase response (APR) is an adaptive emergency life-history stage, wherein vertebrates exhibit fever and anorexia to survive an infection. However, induced immune responses are energetically costly, and sick animals may reduce physical activity to compensate. Tests of this predicted energetic trade-off in free-ranging animals are rare due to difficulties in measuring individual physiology and behaviour under immune challenge in natural settings. However, recent advances in biologging technology now make such studies possible. We surgically implanted heart rate/temperature loggers in free-ranging adult male Arctic ground squirrels, fitted the squirrels with collar-mounted accelerometers and light/temperature loggers, and injected animals with lipopolysaccharide (LPS) to simulate an immune challenge. LPS-injected squirrels exhibited approximately 1°C overnight fevers accompanied by slightly elevated (10 bpm) heart rates; LPS-injected squirrels also spent 19% less of their time aboveground the following day and reduced overall movement by 40% compared with saline-injected controls. Thus, we found support for an energetic trade-off between functional immune responses (fever and anorexia) and lethargic sickness behaviour within the APR of a free-ranging mammal. Moreover, our results suggest animal-borne devices can play an important role in future studies of vertebrate immunity and disease dynamics.