Winter Energy Budget Research Articles

Winter condition, physiology, and growth potential of juvenile Antarctic krill

In recent years, substantial efforts have been made to understand the implications of climate change on Antarctic krill, Euphausia superba, because of their pivotal role in the Southern Ocean food web and in biogeochemical cycling. Winter is one of the least studied seasons in Antarctica and we have limited understanding about the strategies Antarctic krill use to survive the winter. In particular, data on the winter physiology and condition of juvenile Antarctic krill are severely lacking. From May to September (the austral autumn-winter) of 2019, we maintained juvenile Antarctic krill in large (1,330 L) aquarium tanks at Palmer Station, Antarctica and, at monthly time intervals, measured their physiology and condition. Each tank served as a “food environment scenario”, representing possible food environments the krill may encounter during winter along the Western Antarctic Peninsula. We found that, unlike adults, juvenile krill maintain relatively high respiration rates through the winter and respond positively to increased food concentrations by increasing their ingestion rates. Unlike larval krill, juveniles use lipid stores accumulated during the summer and autumn to sustain themselves through periods of starvation in the winter. We used our empirically derived measurements of physiology and condition to estimate the energy budget and growth potential of juvenile krill during the winter. We found that, given their comparatively high respiration rates, small juvenile krill (20 mg dry weight) would need to encounter food at concentrations of ~ 0.15 mg C L-1 daily to avoid loss of body carbon. Without sufficient lipid reserves, this value increases to ~ 0.54 mg C L-1, daily. The health of juvenile krill in the wintertime is dependent on their ability to accumulate lipid stores in the summer and autumn and to find sufficient food during the winter. Changes in food availability to Antarctic krill throughout the year may become problematic to juvenile krill in the future. Understanding the variability in the winter energy budget of juvenile Antarctic krill will allow us to improve population models that make assumptions on seasonal growth patterns.

Nocturnal torpor by superb fairy-wrens: a key mechanism for reducing winter daily energy expenditure.

Many passerine birds are small and require a high mass-specific rate of resting energy expenditure, especially in the cold. The energetics of thermoregulation is, therefore, an important aspect of their ecology, yet few studies have quantified thermoregulatory patterns in wild passerines. We used miniature telemetry to record the skin temperature ( Tskin) of free-living superb fairy-wrens ( Malurus cyaneus, 8.6 g; n = 6 birds over N = 7-22 days) and determine the importance of controlled reductions in body temperature during resting to their winter energy budgets. Fairy-wrens routinely exhibited large daily fluctuations in Tskin between maxima of 41.9 ± 0.6°C and minima of 30.4 ± 0.7°C, with overall individual minima of 27.4 ± 1.1°C (maximum daily range: 14.7 ± 0.9°C). These results provide strong evidence of nocturnal torpor in this small passerine, which we calculated to provide a 42% reduction in resting metabolic rate at a Ta of 5°C compared to active-phase Tskin. A capacity for energy-saving torpor has important consequences for understanding the behaviour and life-history ecology of superb fairy-wrens. Moreover, our novel field data suggest that torpor could be more widespread and important than previously thought within passerines, the most diverse order of birds.

The contribution of ice algae to the winter energy budget of juvenile Antarctic krill in years with contrasting sea ice conditions

AbstractKrill overwintering strategies vary with ontogeny and year; understanding this variability is essential to predicting how the species will respond to climate change in the future. Overwintering studies have focused on larval and adult krill, but we know little about how juvenile krill overwinter. The late winter diet of juvenile krill is important because it will determine their growth and development rates and consequently their reproductive potential the following spring. A diet rich in ice algae would promote growth and reproductive development. The Bransfield Strait (northern Antarctic Peninsula, AP) is an important overwintering ground for krill; it has been proposed this region offers a food-rich winter environment. We examined the contribution of ice algae to the energy budget of overwintering juvenile krill during 2 years with contrasting sea ice conditions. Grazing on ice algae contributed ∼146% to their winter energy budget in 2015, even though ice concentrations were ≤50% and consisted of newly formed pancake ice. However, when sea ice advanced late in the Bransfield Strait (2016), ice algae contributed significantly less (∼16%) to the winter energy budget of juvenile krill. Delayed sea ice advance may negatively affect growth and reproductive development of overwintering juvenile krill.

Huddling reduces evaporative water loss in torpid Natterer's bats, Myotis nattereri

Periodic arousals during hibernation consume most of the winter energy budget for hibernating mammals. Evaporative water loss (EWL) is thought to affect the frequency of arousals and thus energy balance, and might have dramatic implications for over-winter survival and fitness. We hypothesized that huddling affects EWL and energy expenditure in torpid mammals. We tested this hypothesis using bats as a model and predicted that, during torpor, EWL and energy expenditure of huddling individuals would be lower than in individuals that are not in a huddle. We measured EWL and metabolic rate of torpid Myotis nattereri (Kuhl, 1817) huddling in groups or roosting individually. Evaporative water loss in huddling individual bats was almost 30% lower than in solitary animals (P=0.03), even after correcting for the effects of metabolic rate. Our results suggest that conservation of water is a substantial benefit underlying huddling by bats during hibernation. Ultimately, huddling could reduce the total cost of hibernation by reducing the number of expensive periodic arousals from torpor caused by the need to supplement water.

Effect of dietary fatty acids on metabolic rate and nonshivering thermogenesis in golden hamsters

Hibernating rodents prior to winter tend to select food rich in polyunsaturated fatty acids (PUFA). Several studies found that such diet may positively affect their winter energy budget by enhancing torpor episodes. However, the effect of composition of dietary fatty acids (FA) on metabolism of normothermic heterotherms is poorly understood. Thus we tested whether diets different in FA composition affect metabolic rate (MR) and the capacity for nonshivering thermogenesis (NST) in normothermic golden hamsters (Mesocricetus auratus). Animals were housed in outdoor enclosures from May 2010 to April 2011 and fed a diet enriched with PUFA (i.e., standard food supplemented weekly with sunflower and flax seeds) or with saturated and monounsaturated fatty acids (SFA/MUFA, standard food supplemented with mealworms). Since diet rich in PUFA results in lower MR in hibernating animals, we predicted that PUFA-rich diet would have similar effect on MR of normothermic hamsters, that is, normothermic hamsters on the PUFA diet would have lower metabolic rate in cold and higher NST capacity than hamsters supplemented with SFA/MUFA. Indeed, in winter resting metabolic rate (RMR) below the lower critical temperature was higher and NST capacity was lower in SFA/MUFA-supplemented animals than in PUFA-supplemented ones. These results suggest that the increased capacity for NST in PUFA-supplemented hamsters enables them lower RMR below the lower critical temperature of the thermoneural zone.

Winter Energetics of Female Indiana Bats Myotis sodalis

Understanding physiological limits and environmental optima is critical to developing protection strategies for endangered and threatened species. One theory to explain the decline in endangered Indiana bat Myotis sodalis populations involves increasing cave temperatures in winter hibernacula. Altered cave temperatures can raise metabolism and cause more arousals in torpid bats, both of which use more fat reserves. In addition, fluctuations in cave temperatures may cause additional arousals. Our objectives were to quantify the effect of temperature and fluctuations thereof on torpid metabolism and arousal frequency in this species. Female Indiana bats (n=36) were collected from caves just before hibernation, maintained in an environmental chamber that simulated hibernacula conditions, and had skin temperature recorded every 30 min throughout the winter. One environmental chamber containing bats (n=12) was sequentially set at 8°, 6°, and 4°C over the winter. The second chamber containing bats (n=12) experienced the same mean temperatures, but temperature fluctuated ±2°C on a regular basis. Torpor bouts were longest at 4°C and were not affected by temperature fluctuations. However, the temperature fluctuations appeared to cause longer arousals. Other bats (n=12) were individually placed in metabolic chambers to calculate oxygen consumption during torpor and during arousals. Torpid metabolism was affected by temperature; at 9°C, it was higher than at 7° or 5°C. Metabolism during arousals was not different among temperature treatments, but rates were almost 200 times higher than torpid metabolic rates. We calculated a winter energy budget and, from the energetic perspective, determined an optimum hibernation temperature (3°-6°C) for female Indiana bats. These findings suggest that hibernacula that provide these conditions deserve extra protection, although other factors in addition to energetics may play a role in temperature preferences.

Wintertime radiation and energy budget along an urbanization gradient in Montreal, Canada

AbstractThis study reports on the radiation and energy balance of three sites (rural, suburban, and urban) located along an urbanization gradient in the Montreal, QC, region for two winters (December–March) with contrasting snow regimes. The urban and suburban sites had similar albedo which was about half that at the rural site during the snow‐cover period. Temporal variability in albedo was attributable to the presence of snow on rooftops at the urban site and to a site‐specific response to cloudiness at the suburban site. As compared to the suburban site, the urban site showed higher albedo inducing lower net radiation (Q*) which was compensated for by greater anthropogenic heat flux (QF), so that the urban site had highest total available energy (Q* + QF). Hourly QF estimates were a significant term in the winter energy budget analysis. QF was dominated by building heating at both urbanized sites, while vehicular traffic contributed to rush hour peaks. Daytime total available energy was mostly dissipated as sensible heat flux (QH) at the beginning of the winter season and mostly stored (ΔQS) towards the end of the winter at both urbanized sites. Daytime energy partitioning into QH and ΔQS was correlated with air temperature with no significant differences between urbanized sites. On a daily time scale, available energy was mostly stored before noon and dissipated as QH in the afternoon at both urbanized sites. Urbanized sites showed differences in diurnal variability of QH and ΔQS occurring in the afternoon and evening. Latent heat flux (QE) was low throughout winter and accounted for 10% of the total available energy during daytime at the urbanized sites. Water vapour emissions showed intra‐urban differences in their response to wintertime climatic conditions. Copyright © 2010 Royal Meteorological Society

Energy conservation in hibernating endotherms: Why “suboptimal” temperatures are optimal

Many endotherms use facultative heterothermic responses of torpor or hibernation to conserve energy during periods of low energy availability. A common assumption when estimating winter energy budgets is that endotherms should hibernate at the ambient temperature ( T a) that minimizes torpid metabolic rate (TMR) and maximizes the duration of torpor bouts. However, previous studies of the energetic benefits of hibernation have assumed constant T a within hibernacula. Here we use an individual-based energetic model to estimate overwinter energy expenditure of mammals hibernating at T as that vary temporally. We show that, in accordance with the principles of Jenson's inequality, hibernators can conserve energy by selecting microclimates warmer than the single T a value that minimizes TMR ( T min). As temporal variation in T a increases, endotherms should choose microclimates with mean T as progressively warmer than T min. Further, as thermal conductance decreases, as it does with increasing body mass and use of social thermoregulation, the mean T a that minimizes overwinter energy expenditure approaches, but never equals, T min. We suggest that the commonly held assumption of stable microclimates in hibernacula has skewed the interpretation of the optimal expression of hibernation for energy conservation. Our results contradict much of the accepted understanding of hibernation energetics and add to a growing body of literature proposing that hibernating at a T a warmer than T min is optimal.

AROUSAL PATTERNS, METABOLIC RATE, AND AN ENERGY BUDGET OF EASTERN RED BATS (LASIURUS BOREALIS) IN WINTER

Abstract Eastern red bats (Lasiurus borealis) will move into leaf litter during cold bouts of winter, and because temperatures fluctuate at these roosts, our 1st goal was to quantify winter arousals in response to ambient temperature (Ta). Additionally, we measured changes in metabolism and body temperature (Tb) during hibernation and arousals at various Ta. Using these data, we estimated winter energy budgets. Bats were captured during autumn of 2003 and 2004 in southwestern Missouri and kept in environmental chambers simulating natural conditions. We assessed torpor bout duration using temperature-sensitive data-loggers within environmental chambers at 15°C, 10°C, 5°C, and 2°C. Metabolic rate during torpor was assessed within metabolic chambers at 15°C, 10°C, 5°C, 1°C, and −5°C. Examination of our data suggests that torpor bout duration was not affected by sex and it was inversely related to Ta down to 2°C. Metabolic rate during torpor was not affected by sex but it did vary with Ta. Tb of hibernating b...

Winter habitat relationships of deer and elk in the temperate interior mountains of British Columbia

Recent work has examined ultimate factors limiting deer (Odocoileus spp.) and elk (Cervus elaphus) populations during winter, such as temperature and forage, but there has been inadequate examination of the influence of snow, especially in concert with foraging decisions. We examined deer and elk habitat selection on winter range in the temperate mountains of southeastern British Columbia. The life histories of radiocollared mule deer (O. hemionus) and elk included seasonal elevational migrations (1,000–1,400 m) and long-distance movements (up to 50–63 km, respectively). Late-winter, deep-snow habitat is limited in wet, mountainous environs and may explain the relatively low densities of ungulates present. Snow-track transects conducted during late winter suggested that deer (mule deer and white-tailed deer [O. virginianus] combined) avoided areas with >40 cm of snow and elk areas with >50 cm. Late-winter snow depth was positively related to elevation and negatively related to slope and solar radiation (hours/day), all of which can be obtained from existing databases and used to map relative late-winter snow depth. The snow-depth model can be used to map potential winter range regardless of current vegetation cover. During late winter deer selected older forests and stands with greater amounts of Douglas-fir (Pseudotsuga menziesii) in the overstory in forested sites. Older stands probably were selected because they had lower snow depths, while mature Douglas-fir trees offered more litterfall forage than other tree species. In contrast, elk selection among forested stands was weak, which suggested that forested stands were not preferred portions of their late-winter habitat. Track data during late winter confirmed that both deer and elk also used areas with low canopy cover, likely to acquire browse. We demonstrated that it is possible to map potential winter range using topographic variables as surrogates for relative snow depth, and we present a model applicable to portions of the temperate interior mountains. We suggest it is important to consider both forage production and snow interception in habitat management because winter energy budgets are a balance between nutrient intake and cost of locomotion.

Periodic arousal from hibernation is necessary for initiation of immune responses in ground squirrels.

Golden-mantled ground squirrels (Spermophilus lateralis) undergo seasonal hibernation during which core body temperature (T(b)) values are maintained 1-2 degrees C above ambient temperature. Hibernation is not continuous. Squirrels arouse at approximately 7-day intervals, during which T(b) increases to 37 degrees C for approximately 16 h; thereafter, they return to hibernation and sustain low T(b)s until the next arousal. Over the course of the hibernation season, arousals consume 60-80% of a squirrel's winter energy budget, but their functional significance is unknown and disputed. Host-defense mechanisms appear to be downregulated during the hibernation season and preclude normal immune responses. These experiments assessed immune function during hibernation and subsequent periodic arousals. The acute-phase response to bacterial lipopolysaccharide (LPS) was arrested during hibernation and fully restored on arousal to normothermia. LPS injection (ip) resulted in a 1-1.5 degrees C fever in normothermic animals that was sustained for > 8 h. LPS was without effect in hibernating squirrels, neither inducing fever nor provoking arousal, but a fever did develop several days later, when squirrels next aroused from hibernation; the duration of this arousal was increased sixfold above baseline values. Intracerebroventricular infusions of prostaglandin E(2) provoked arousal from hibernation and induced fever, suggesting that neural signaling pathways that mediate febrile responses are functional during hibernation. Periodic arousals may activate a dormant immune system, which can then combat pathogens that may have been introduced immediately before or during hibernation.

Behavioral Energetics of Overwintering in the Rifleman, Acanthisitta-Chloris

The role of behavioural adjustments in meeting increased daily energy requirements in winter was investigated in rifleman, Acanthisitta chloris, inhabiting lowland forest in South I., New Zealand, by comparing their population density, time-activity budget and foraging behaviour in autumn and winter. Rifleman foraged for 83% of daytime in both seasons. The combined effects on the birds' winter energy budget of increased thermoregulation costs and the shorter daylength for foraging were at least partly offset by an estimated 23-29% decrease in the amount of energy expended daily on activity and a 78% increment in prey caught per day. The reduced energy expenditure on activity resulted from rifleman spending less time on expensive flying and more time roosting. The increase in prey capture rate may have stemmed from a 35% seasonal reduction in the birds' population density and reduced prey mobility at lower ambient temperatures. Marked sexual size dimorphism was not reflected in gender differences in activity budgeting or prey capture rate, but the sexes differed in their relative use of foraging substrates. Rifleman showed few seasonal changes in daily activity rhythm or microhabitat use. The behavioural energetic overwintering tactics of rifleman are compared with those of other Australasian and north temperate zone land-birds.

Winter Energy Budgets and Cost of Arousals for Hibernating Little Brown Bats, Myotis lucifugus

Winter Energy Budgets and Cost of Arousals for Hibernating Little Brown Bats, Myotis lucifugus

The Bioenergetics of Hibernation in the Eastern Garter Snake Thamnophis sirtalis sirtalis

Body composition changes during hibernation were measured for garter snakes maintained in a laboratory hibernaculum and snakes from a natural hibernaculum in Wisconsin. Laboratory animals were maintained at 4 C, 24-h darkness (DD), for 165 days, the period of natural hibernation. Twelve randomly selected individuals were assayed at the beginning and end of natural hibernation and for every 6 wk of simulated hibernation. The final laboratory assay was performed concurrently with field emergence. Glycogen and proteins from liver and muscle tissues were utilized by both laboratory and field snakes during hibernation. Muscle catabolism of these substrates accounted for 76.5%-78.7% of the total winter energy budget. No change was observed in total body weight, liver weight, tissue lipid content, fat-body weights, organic matter, inorganics, or water content. The similarity between energy budgets for field (0.45 cal/ g/day) and laboratory (0.42 cal/g/day) hibernating snakes indicates that natural hibernation was closely simulated.

Winter energy budget simulation for a latitudinal transect along the east coast of the Americas

This paper continues the application of a physically-based model, comprising a combination of a solar transmission section and a slope energy budget portion [2]. The changing energy budget components (net radiation, conduction, sensible, and latent heat fluxes) occurring at the various slope angles (0 and 90 degrees) and orientations (south-, west-, and north-facing) were systematically examined in the context of two contrasting environments along a latitudinal transect of the east coast of the Americas. As before, the response of the energy budget components were systematic and orderly on a latitudinal basis accompanied by a great diversity among the energy budgets of different slopes and orientations at any particular latitude.

The role of ice and snow in lake heat budgets

Methods of precisely calculating the latent heat terms for snow and ice in the winter energy budget of lakes are presented. The ice term is normally overestimated and the snow term underestimated by existing methods.

The Digestion and Intake of Winter Foods by Wild Ptarmigan in Alaska

This paper describes a method for measuring the digestibility, metabolizable energy, and daily intake of foods eaten by wild ptarmigan in winter, using the magnesium which occurs naturally in the food as a digestibility marker. This method has already been tested on captive Red Grouse (Lagopus lagopus scoticus) (Moss and Parkinson 1972). Further laboratory tests with captive Rock Ptarmigan (Lagopus mutus) are now presented together with winter energy budgets of free-living Willow (Lagopus lagopus), Rock, and White-tailed (Lagopus leucurus) Ptarmigan in Alaska.