Helen Chmura

• PhD
• Research Ecologist at US Forest Service

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...

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 en...

Climate warming is rapid in the Arctic, yet impacts to biological systems are unclear because few long-term studies linking biophysiological processes with environmental conditions exist for this data-poor region. In our study spanning 25 years in the Alaskan Arctic, we demonstrate that climate change is affecting the timing of freeze-thaw cycles i...

Background Each spring and fall billions of songbirds depart on nocturnal migrations across the globe. Theory suggests that songbirds should depart on migration shortly after sunset to maximize their potential for nightly flight duration or to time departure with the emergence of celestial cues needed for orientation and navigation. Although captiv...

Purpose of Review Climate change will continue to alter spatial and temporal variation in fire characteristics, or pyrodiversity. The causes of pyrodiversity and its consequences for biological communities are emerging as a promising research area with great potential for understanding and predicting global change. We reviewed the literature relate...

The regulation of seasonality has been an area of interest for decades, yet global climate change has created extra urgency in the quest to understand how sensory circuits and neuroendocrine control systems interact to generate flexibility in biological timekeeping. The capacity of temperature to alter endogenous or photoperiod-regulated neuroendoc...

Many animals adjust the timing of seasonal events, such as reproduction, molt, migration, and hibernation, in response to interannual variation and directional climate-driven changes in temperature. However, the mechanisms by which temperature influences seasonal timing are relatively under-explored. Seasonal timing involves retrograde signaling in...

Hibernation involves prolonged intervals of profound metabolic suppression periodically interrupted by brief arousals to euthermy, the function of which is unknown. Annual cycles in mammals are timed by a photoperiodically-regulated thyroid-hormone-dependent mechanism in hypothalamic tanycytes, driven by thyrotropin (TSH) in the pars tuberalis (PT)...

Shifts in the timing of cyclic seasonal life-history events are among the most commonly reported responses to climate change, with differences in response rates among interacting species leading to phenological mismatches. Within a species, however, males and females can also exhibit differential sensitivity to environmental cues and may therefore...

Birds engage in diverse life cycle stages across the year that are often defined by distinct changes in physiology, morphology and behaviour. These life cycle stages, such as reproduction, molt, and migration, reflect the seasonal characteristics of the diverse habitats in which birds live. This chapter reviews the diversity of annual schedules fro...

Corticosterone affects physiology and behavior both during normal daily processes but also in response to environmental challenges and is known to mediate life history trade-offs. Many studies have investigated patterns of corticosterone production at targeted times of year, while ignoring underlying annual profiles. We aimed to understand the annu...

Social interactions can shape daily activity patterns, and this is an area of growing research interest. The propensity for individuals to be active at certain times of day may structure interactions with competitors and potential mates, influencing fitness outcomes. Aspects of daily activity such as timing of activity onset and offset exhibit with...

Numerous studies of spring migration have discovered that environmental conditions experienced on the wintering grounds and/or during vernal migration itself can have “carry-over effects” altering timing or success of the subsequent breeding season. Few studies have evaluated whether breeding and pre-basic molt have carry-over effects on autumn mig...

Ultimate factors such as food availability and weather create optimal windows of time for birds to reproduce. However, within a given year, birds must rely upon proximate environmental information such as photoperiod, food, temperature, social cues, and other factors to anticipate when that window will occur and prepare physiologically for breeding...

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...

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...

In this mini-review, we discuss how biologging technology can be used to detect, understand, and forecast species' responses to climate change. We review studies of phenology, thermal biology, and microhabitat selection as examples to illustrate the utility of a biologging approach in terrestrial and aquatic species. These examples show that biolog...

1. Rapid warming has facilitated an increase in deciduous shrub cover in arctic tundra. Because shrubs create a cooler microclimate during the growing season, shrub cover could modulate the effects of global warming on the phenology and activity of ectotherms, including arthropods. This possibility was explored here using two dominant arthropod gro...

Severe weather events are increasing worldwide because of climate change. To cope with severe weather events, vertebrates rely on the stress response which is activated by the hypothalamic-pituitary-adrenal (HPA) axis to adjust physiology and behavior. Previous studies have detailed changes in baseline concentrations of the stress hormone corticost...

While the effect of weather on reproduction has been studied for many years in avian taxa, the rapid pace of climate change in arctic regions has added urgency to this question by changing the weather conditions species experience during breeding. Given this, it is important to understand how factors such as temperature, rain, snowfall, and wind af...

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 d...

In 2007, a fire burned over 100 000 ha along the Anaktuvuk River in Alaska, causing widespread ecological disturbance. Despite efforts to understand ecosystem recovery, little is known about higher trophic levels. Here, we present qualitative findings from a preliminary bird survey of the burn scar region, conducted in 2014, at three sites represen...

Arctic regions are warming rapidly, with extreme weather events increasing in frequency, duration, and intensity just as in other regions. Many studies have focused on how shifting seasonality in environmental conditions affects vegetation phenology, while far fewer have examined how the breeding phenology of arctic fauna responds. We studied two s...

To time reproduction optimally, birds have evolved diverse mechanisms by which they respond to environmental changes that help them anticipate and prepare for the breeding season. While residents initiate reproductive preparation and breed in the same geographic location, migrant birds simultaneously prepare for breeding and migration far from thei...

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...

Both internal and environmental factors influence the trade-offs animals make between foraging and antipredator vigilance. However, few studies examine both internal and environmental factors simultaneously, preventing us from drawing inferences about their relative importance during foraging. We capitalized on a long-term study of yellow-bellied m...

The effects of climate change are more acute in the Arctic than any other region, and as such, arctic tundra wildlife habitats are changing in ways that are not yet well understood. Remote sensing tools are capable of assessing dynamics in wildlife-habitat associations over a wide range of spatial scales and in a variety of ecosystems. As already w...

Climate change is causing rapid shifts in temperature while also increasing the frequency, duration, and intensity of extreme weather. In the northern hemisphere, the spring of 2013 was characterized as extreme due to record high snow cover and low temperatures. Studies that describe the effects of extreme weather on phenology across taxa are limit...

Birds breeding at high latitudes can be faced with extreme weather events throughout the breeding season. In response to environmental perturbations, vertebrates activate the hypothalamic-pituitary-adrenal (HPA) axis and synthesize corticosterone, which promotes changes in behavior and physiology to help the animal survive. The parental care hypoth...

Raising nestlings to fledging is energetically demanding for songbirds, requiring parents to balance several major tradeoffs. Nestling growth rates are highly susceptible to variation in environmental conditions and parental investment, and highly variable environments with short breeding seasons such as the Arctic magnify these tradeoffs. Arctic-n...

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–...

Hematocrit is an easily measured parameter that can be used to assess changes in oxygen carrying capacity necessitated by fluctuations in metabolic demands. Most hematocrit studies draw conclusions from changes in hematocrit that occur over a small sampling interval without an understanding of the variation that exists across the annual cycle. Whit...

Breeding Bird Survey (BBS) data from 1993-2012 indicating total number of Gambel’s white-crowned sparrows observed along 20-mile transect conducted on the James Dalton Highway, Alaska. South Fork Koyukuk is located south of the Brooks Range, Dietrich River is in the Brooks Range, and Roche Mountonee and Sagavanirktok Department of Transportation ar...

Mean daily wind speed during the breeding season of white-crowned sparrows at the historic range (gray) and range limit (black) located along the James Dalton Highway, Alaska. The timing of pre-parental (PP), parental (P), and molt (M) stages are indicated by the horizontal lines at the top of each graph. Wind speeds were significantly higher at ev...

A species’ range can be thought of as a manifestation of the ecological niche in space. Within a niche, evolution has resulted in traits that maximize fitness. Across millennia, natural oscillations in temperature have caused shifts in the geographic location of appropriate habitat and with corresponding changes in species’ ranges. Contemporary cli...

Annual schedules of reproduction, migration, and plumage molt evolve to cope with varying environmental predictability, and respond to environmental cues for timing and coordination. Species' schedules may include many or few distinct phenotypic stages; more stages increase tolerance of environmental extremes but decrease temporal flexibility. Prox...

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 r...

This literature review consists of two major sections. The first is a broad scan of the published literature to identify major trends in the development of the field of climate adaptation. This survey was based on queries of the Web of Science, a comprehensive online bibliographic database, and focuses on what can be referred to as self-identified...