Colour bands,dominance, and body mass regulation in male zebra finches (Taeniopygia guttata)

The arbitrary assignment of different coloured leg bands to zebra finches (Taeniopygia guttata) has profound effects on mate preference, reproductive success, mortality rates, parental investment and sex ratio. Choice chamber experiments indicate that the effect is mediated by altered attractiveness to members of the opposite sex. Effects on intrasexual dominance are more equivocal. We present two experiments which demonstrate significant effects of band colour on behavioural dominance (red bands are more dominant than light green bands) and the resulting diurnal pattern of gain in mass, fat, and seeds stored in the crop. Consistent with the literature on dominance and strategic regulation of body mass in other species, subordinate (green-banded) birds maintain higher fat reserves at dawn, but dominant (red-banded) birds show the highest overall daily mass gains. The lack of obvious effects of band colour on dominance in previous studies may lie in the degree to which food can be monopolized by particular individuals.     

The effect of season, sex and feeding style on home range area versus body mass scaling in temperate ruminants

Sex-specific estimates of the summer and winter home range area of 19 species of temperate ruminants were collated from the literature. It was predicted that there should be a shallower slope for the home range area against body mass relationship during winter than during summer, as large ruminants can meet more of their energy requirements from the fat reserves deposited during summer than small ruminants. Consequently, relatively large species do not need to range as widely during winter. There was a significant positive relationship between body mass and summer and winter home range area in both females and males. This relationship remained significant when analysed within feeding styles (browser, mixed feeder, grazer), except in mixed feeders in winter. As predicted, slope estimates were significantly lower during winter (b=0.59) than during summer (b=1.28), both before and after controlling for phylogeny. After controlling for phylogeny, browsers had a steeper slope (summer: b=1.48; winter: b=1.07) of the home range area against body mass relationship than did mixed feeders (summer: b=0.75; winter: b=-0.11) or grazers (summer: b=1.10; winter: b=0.34). There was no effect of sex after body mass was controlled for. The effect of season, sex and feeding style on the home range area versus body mass relationship in temperate ruminants is discussed.     

The winter fattening model: a test at low latitude using the Clamorous Reed Warbler

Small birds at high latitudes accumulate fat during the day so that they can survive long and cold winter nights. The winter fattening model suggests that birds increase their minimum (morning) mass in cold weather, build up their mass during the day, and then rely on the energy reserves so accumulated until the morning. While data from mid and high latitudes support this model, little is known about the strategies of birds inhabiting lower latitudes (< 40°N). We use an 18-year data set to investigate whether the winter fattening model holds in a mid-latitude (32°N) population of the Clamorous Reed Warbler Acrocephalus stentoreus . We show that morning mass and fat score vary as predicted by the winter fattening model. In addition, adults appear to be better adapted to long and cold winter nights than first-year birds. A long-term trend of increased body mass may be attributable to character release following reduced interspecific competition.     

Seasonal acclimatization to extreme climatic conditions by black-capped chickadees (Poecile atricapilla) in interior Alaska (64 degrees N).

Winters in interior Alaska (64 degrees N) are characterized by short photoperiod (5L : 19D) and chronic subfreezing temperatures. To determine if seasonal acclimatization of black-capped chickadees (Poecile atricapilla) at high latitude differs from that of conspecifics at lower latitudes, standard metabolic rates (SMR), metabolic response to low temperature (-30 degrees C), nocturnal hypothermia, body mass, fat reserves, and conductance were measured over two winters and one summer in three groups of seasonally acclimatized birds. Body mass and conductance did not vary with season, although furcular fat levels were higher in winter. Birds used nocturnal hypothermia when exposed to -30 degrees C in summer or winter. Although SMR did not vary seasonally, winter SMRs differed between the two winters of the study. Nocturnal hypothermia in summer and decreased SMR in response to extreme conditions may either reflect plasticity inherent to all populations of black-capped chickadees or may result from individual variation within this northern population.     

The effects of latitude and day length on fattening strategies of wintering coal tits Periparus ater (L.): a field study and aviary experiment

1. Cyclic daily fattening routines are very common in wintering small wild birds, and are thought to be the consequence of a trade-off between different environmental and state-dependent factors. According to theory, these trajectories should range from accelerated (i.e. mass increases exponentially towards dusk) when mass-dependent predation costs are the most important cause of mortality risk, to decelerated (i.e. the rate of mass gain is highest at dawn and decreases afterward) when starvation is the greater risk. 2. We examine if geographically separate populations of coal tits, wintering in Scotland and central Spain under contrasting photoperiods, show differences in their strategies of daily mass regulation. We describe population differences in wild birds under natural conditions, and experimentally search for interpopulation variation in diurnal body mass increase under common, manipulated, photoperiod conditions (LD 9 : 15 h vs. 7 : 17 h), controlling for temperature, food availability, predator pressure and foraging arena. 3. Winter diurnal mass gain of wild coal tits was more delayed towards the latter part of the daylight period in central Spain (i.e. the locality with longer winter days) than in Scotland. In both localities, the pattern was linked to the average mass at dawn, with mass increasing more rapidly in lighter birds. However, under the controlled photoperiod situation the pattern of daily mass gain was similar in both populations. Diurnal body mass gain was more accelerated at the end of the day, and the increase in body mass in the first hour of the day was considerably lower under the long (9 h) than under the short (7 h) photoperiod in both populations. 4. Wintering coal tits show patterns of mass gain through the day that are compatible with current theories of the costs and benefits of fat storage, with birds at lower latitudes (with longer winter days) having a greater tendency to delay mass gain until late in the day. The experimental study revealed that these patterns are plastic, with birds responding directly to the photoperiod that they experience, suggesting that they are continually making fine-scale adjustments to energy reserves on the basis of both inherent (e.g. state-dependent) and extrinsic cues.     

Metabolic and thermoregulatory effects of photoperiod and melatonin on Peromyscus maniculatus acclimatization

A photoperiod-related seasonal rhythm in active period (scotophase), metabolic rate and core temperature was documented for animals held at 21.0 +/- 0.1 degrees C ambient; animals that were habituated to long nights (10:14LD) had a greater metabolic reserve than those held in summer photoperiods (14:10LD). While relative weights of gonads and sex accessory tissues of mice show typical "winter" regression, interscapular brown adipose tissue mass was unaffected by photoperiod; moreover, IBAT beta adrenergic responses under "winter" photoperiods did not differ from "summer" photoperiods in the absence of cold stimulus. Thermogenic efficiency, measured as the increment of active temperature level achieved per increment of active period metabolic effort, was highest for animals exposed to short photoperiods. Thermal conductance was reduced in animals exposed to short (10:14LD) photoperiods. Heat conservation and thermogenic response capacity was enhanced by melatonin treatment and short photoperiod.     

Consequences of load carrying by birds during short flights are found to be behavioral and not energetic

The doubly-labeled water technique and video were used to measure the effect of mass loading on energy expenditure and takeoff performance in zebra finches, Taeniopygia guttata, that were making routine (nonalarm) short flights. Finches that carried 27% additional mass did not expend more energy during flight than unloaded controls. Carrying additional mass, however, led to a reduced body mass and a decreased velocity during takeoffs (by 12%). Calculations of instantaneous mechanical power indicated that energy expended by unloaded and loaded finches at takeoff was similar, due to the observed decrease in velocity by mass-loaded finches and a lowering of their body mass. During routine short flights, zebra finches appear to maintain their metabolic power input and mechanical power output regardless of mass loading. Here, the costs of carrying additional mass during routine short flights were revealed to be behavioral and not energetic.     

Seasonal changes in the thermoenergetics of the marsupial sugar glider, Petaurus breviceps

Little information is available on seasonal changes in thermal physiology and energy expenditure in marsupials. To provide new information on the subject, we quantified how body mass, body composition, metabolic rate, maximum heat production, body temperature and thermal conductance change with season in sugar gliders (Petaurus breviceps) held in outdoor aviaries. Sugar gliders increased body mass in autumn to a peak in May/June, which was caused to a large extent by an increase in body fat content. Body mass then declined to minimum values in August/September. Resting metabolic rate both below and above the thermoneutral zone (TNZ) was higher in summer than in winter and the lower critical temperature of the TNZ occurred at a higher ambient temperature (Ta) in summer. The basal metabolic rate was as much as 45% below that predicted from allometric equations for placental mammals and was about 15% lower in winter than in summer. In contrast, maximum heat production was raised significantly by about 20% in winter. This, together with an approximately 20% decrease in thermal conductance, resulted in a 13 degrees C reduction of the minimum effective Ta gliders were able to withstand. Our study provides the first evidence that, despite the apparent lack of functional brown adipose tissue, sugar gliders are able to significantly increase heat production in winter. Moreover, the lower thermoregulatory heat production at most TaS in winter, when food in the wild is scarce, should allow them to reduce energy expenditure.     

Strategic diel regulation of body mass in European robins

Stochastic dynamic programming (SDP) is a computational technique that has been used to model daily routines of foraging in small birds. A diurnal bird must build up its fat reserves towards dusk in order to avoid starvation during the night, when it cannot feed. However, as well as the benefits of avoiding starvation, storing fat imposes costs such as an increased predation risk and higher flight and metabolic costs. There is therefore an optimal level of fat reserves for a bird to reach at dusk in order to survive overnight without being left with excessive fat reserves at dawn. I tested a prediction common to all SDP models of daily foraging routines, that a bird will attempt to reach this level at dusk, regardless of its fat reserves the previous dawn. I provided supplementary food to manipulate the fat reserves at dawn of free-living European robins, Erithacus rubecula. Diurnal changes in body mass (a reliable estimate of fat reserves) were then monitored remotely. Robins provided with an ad libitum food supply reached almost exactly the same body mass at dusk, regardless of their body mass at dawn, supporting the prediction that birds attempt to reach a target level of reserves at dusk. Copyright 2000 The Association for the Study of Animal Behaviour.     

Seasonal variation in body composition and morphology of adult muskrats in central Saskatchewan, Canada

We quantified seasonal variation in body composition and morphology of adult muskrats ( Ondatra zibethicus ) inhabiting freshwater marsh environments in central Saskatchewan, Canada. The study areas were characterized by long and cold winters extending over six months during which muskrats were restricted to foraging under ice. A total of 162 adult muskrats were collected during nine sampling periods across the year. The large accumulation of fat reserves (16% of body mass) during winter and the concurrent decline in protein mass suggested a reduced maintenance requirement associated with the presence of energy-rich food resources. Dietary fibre content increased significantly during mid-summer and was manifested by changes in gut morphology. Mobilization of fat reserves during summer months by both sexes reflected high energetic demands for reproduction. Males depleted fat reserves soon after spring break-up, while near-exhaustion of fat reserves in females occurred 4–6 weeks later, during lactation. Pregnant females contained significantly greater fat and protein reserves compared to non-pregnant and lactating females. The dynamics of body reserves in muskrats should be viewed as an integral part of the sex-specific life-history traits of this important herbivore species of marsh environments.     

Role of melanocortin in the long-term regulation of energy balance: lessons from a seasonal model

Siberian hamsters express photoperiod-regulated seasonal cycles of body weight and food intake, providing an opportunity to study the role of melanocortin systems in regulating long-term adaptive changes in energy metabolism. These hamsters accumulate intraperitoneal fat reserves when kept in long summer photoperiods, but show a profound long-term decrease in food intake and body weight when exposed to a short winter photoperiod. Icv administration of a MC3/4-R agonist (MTII) potently suppresses food intake in hamsters in both the obese and lean state, indicating the potential for melanocortin systems to regulate energy metabolism in the hypothalamus of the Siberian hamster. Icv treatment with the melanocortin antagonist SHU9119 increases food intake in both seasonal states. Moreover, hamsters bearing neurotoxic lesions, which destroy the majority of POMC expressing neurons in the arcuate nucleus are still able to show seasonal regulation of body weight. These studies in a seasonal model substantiate the view that endogenous melanocortin systems exert a tonic inhibition of food intake in mammals. The observations that this melanocortin tone occurs to a similar extent in both an anabolic state induced by a long day photoperiod, and in a catabolic state induced by a short day photoperiod, suggests that alterations in endogenous melanocortin tone are not the primary cause of the lipolysis, weight-loss and hypophagia which characterize the establishment of the short day-induced overwintering state.     

Management of fat reserves and food caches in tufted titmice (Parus bicolor) in relation to unpredictable food supply

In the temperate zone, permanent-resident birds and mammalsthat do not hibernate must survive harsh winter conditions oflow ambient temperature, long nights, and reduced food levels.To understand the energy management strategy of food-hoardingbirds, it has been hypothesized that such birds respond to increasedstarvation risk by increasing the number of their hoards ratherthan by increasing their fat reserves and that they cache earlyin the day and retrieve their caches later to achieve fat reservesnecessary to survive the night We tested these hypotheses byobserving the responses in captivity of a caching bird, thetufted titmouse (Parus bicolor), to the combined influencesof reduced predictability of food and naturally occurring ambienttemperature and photoperiod. When the food supply was unpredictable,birds significantly increased both internal fat reserves atdusk and external food caches. Initially leaner birds tendedto increase their fat reserves to a greater extent and initiallyfatter birds tended to cache more food and to fly significantlyless. Half the birds also increased their dawn and mean dailybody mass. All birds tended to forage, gain body mass, and cachefood at significantly lower rates in the morning and at significantlyhigher rates in the evening. Cache retrieval showed the oppositetrend, with birds retrieving most of their caches in the morning.Our results do not support the hypothesis that caching birdsincrease caching rate but not body mass under an unpredictablefood regime. Instead fat reserves and food caches are both importantcomplementary sources of energy in food-hoarding birds. Energymanagement by wintering birds occurs in response to a numberof biotic and abiotic factors acting simultaneously; thus futuremodels must incorporate independent variables in addition tothe state of the food supply and time of day     

Effects of feeding time constraints on body mass regulation and energy expenditure in wintering dunlin (Calidris alpina)

We examined the effects of time-restricted feeding on regulationof body mass and activity energy expenditure in captive winteringdunlin (Calidris alpina) held in outdoor aviaries at TomalesBay, California. In the first of two experiments, we comparedbirds under 24 h : 24 h (fasting : ad libitum feeding) foodrestriction with controls under continuous ad libitum feeding. In the second experiment, we compared birds under 24 h : 6 h: 12 h : 6 h (fasting : ad libitum : fasting : ad libitum)food restriction with birds under 24 h : 24 h food restriction.We estimated total energy expended on activities from dailymass balance using an additive model based on measures of grossenergy intake, thermoregulation, basal metabolism, and a sensitivity analysis of gross utilization efficiency and energy densityof reserve body tissue. Dunlin under 24 h : 24 h food restrictionovercompensated for body mass lost while fasting, increasingtheir body mass relative to controls fed ad libitum. Dunlinunder 24 h : 6 h : 12 h : 6 h food restriction were unable to recover body mass lost during the first fasting day. Whenallowed to feed, food-restricted birds reduced the amount ofenergy spent on being active and increased food intake andenergy storage relative to controls, but when forced to fast,they increased their activity energy expenditure. These patterns suggest winter body mass regulation consistent with the behaviorsof free-living dunlin in winter.     

The effect of seasonal food restriction on activity, metabolism and torpor in the South African hedgehog (Atelerix frontalis)

Twelve South African hedgehogs (Atelerix frontalis) were subjected to nine-week experimental protocol comprising four weeks of simulated summer conditions (14L: 10D and 25 °C), and transition week followed by four weeks of simulated winter conditions (10L: 14D and 15 °C).
Six control hedgehogs, with access to food ad libitum throughout the experiment, did not increase their energy intake during winter yet retained stable body mass. Six experimental hedgehogs, of similar body size, experienced restricted diet during the last three weeks of each season. These hedgehogs displayed significantly lower energy intake than controls during food restriction and lost approximately 7% of their body weight in both seasons, although this weight loss was not significant.
Both groups displayed lower digestive efficiencies in winter, together with decline in activity. However, there remained no significant effect of food restriction on these parameters.
Neither control nor experimental hedgehogs displayed torpor during summer and, whilst both groups became torpid in winter, the duration of torpor was significantly longer in experimental hedgehogs following food restriction.
Analysis of fluctuations in body mass suggest that experimental hedgehogs supplemented their restricted diet with energy derived from body reserves during both seasons. However, the ability of this species to modify the duration of torpor in response to additional energetic stress indicates that A. frontalis can control its energetic expenditure in order to limit the depletion of body reserves.     

Does avian winter fat storage integrate temperature and resource conditions? A long‐term study

Theoretical models of short‐term avian behaviour suggest that small birds adaptively balance the ecological costs and benefits of winter fat to maximize survival probability. When low starvation risk eliminates benefit but not cost of fat, birds are leaner than when under high starvation risk. Most models focus on single factors affecting starvation risk and subsequent choice of adaptive body mass; however, in complex environments, more than one factor affects starvation risk. To test for multiple interacting factors affecting fat reserves, long‐term geographical data on winter fat in a ground‐feeding finch, the dark‐eyed junco Junco hyemalis were analyzed. Two measures of fat were used: (1) visible subcutaneous fat class, and (2) body mass residuals left after age, sex and wing length effects were factored out. Site means for fat measures were obtained from juncos visiting supplemental feeding sites in midwest and northwest North America. In backward elimination regression of fat class, the temperature‐snowfall interaction term and its constituent variables, proximate temperature (averaged over capture day and the preceding ten days) and snowfall (frequency over the same time interval) were significant explanators of variation. Snowfall frequency is considered to be a surrogate measure of resource deterioration. The interaction term, also found in backward regression of body mass residuals, showed that as temperature declined at low snowfall frequency, less fat was deposited than when temperature declined at high snowfall frequency. Thus, in a recently cold environment suggesting relatively high resource predictability, perceived starvation risk is low, and less costly fat is needed to reduce starvation risk compared to a cold and unpredictable resource environment. The analysis of mass residuals also yielded a significant effect of daylength, suggesting an underlying fattening programme independent of proximate environmental conditions. A longitudinal study of junco fat stores indicated that individual environmental responses contributed significantly to midwinter fat peaks. These results agree with predictions of a synergistic model of adaptive fat regulation in small birds by suggesting that a ground‐feeding bird may maximize winter survival probability by integrating multiple environmental factors affecting starvation risk.     

Evidence for a trade-off between growth and body reserves in northern white-tailed deer

We contrasted patterns of growth and accumulation of body reserves in autumn between two high-density (HD) white-tailed deer populations facing winters of different severity and length. Both populations occurred in the absence of effective predators and suffered from some forage competition based on reduced body masses. A third population living at low density (LD) and confronting long and severe winters (SW) served to distinguish the influence of food competition and winter severity on growth and body reserves. We estimated body components (water, protein, fat and ash) of deer during the first half of November and compared growth patterns between sexes and regions. HD-SW males continuted growth to an older age than HD males facing short and mild winters (MW) but females of both regions reached adult body mass at the same age. LD-SW deer exhibited a growth pattern similar to that of HD-SW animals but were the heaviest and the largest, suggesting that growth patterns are related to winter harshness (or length of the growing season) and that final body size is related to forage competition in summer. Sexual dimorphism became evident at an older age in the HD-SW population than in the HD-MW population, demonstrating that winter harshness does not affect immature males and females in the same manner. Fawns from the HD-SW population had proportionally longer legs and a higher percentage of body fat. Adaptations of immature deer to long and severe winters suggest that survival during the first winter represents the most critical step in the life span of northern white-tailed deer.     

In vivo and in vitro effects of oestradiol-17β on lipid metabolism in Notemigonus crysoleucas

The effects of oestradiol-17β on the gonosornatic index, liver size, hepatic and body lipid levels in the cyprinid teleost, Notemigonus crysoleucas , were investigated. Administration of oestradiol to female TV. crysoleucas during the gonadal preparatory and prespawning seasons stimulates increases in ovarian size. During the early spawning season oestradiol therapy results in a reduction of ovarian gonosomatic index. Oestrogen treatment of males causes a suppression of testicular growth. In female fish exposed to long (15-5L/8-5D) or intermediate (12L/12D) photoperiods oestradiol increases body fat reserves. At short photoperiods (9L/15D) oestrogen treatment of females results in body fat store depletion Low doses deplete and high doses of oestradiol increase body lipid reserves in male fish. The hepatosomic index increases in both male and female fish following oestrogen treatment. Oestradiol therapy during the gonadal preparatory season, but not during the prespawning season, increases total liver lipids. The in vitro effects of oestradiol on liver lipid and carbohydrate metabolism were also examined. Under the conditions used in these experiments, lipid depletion was observed in liver slices incubated with or without oestradiol. Pretreatment of fish with oestradiol before liver tissue was removed drastically reduced in vitro lipid depletion. Oestradiol retards the gluconeogenesis and glycogenesis seen in liver slices incubated in a hormone-free medium.     

Intermittent feeding in a migratory omnivore: digestion and body composition of American black duck during autumn

Birds fast intermittently during weather disturbances and migration. We tested responses of black duck to lost feeding days during autumn mass gain. Nine adult males were fed a pelleted diet (1.5% fat, 15.8% protein, and 18.3% neutral detergent fiber) and caged indoors during September and October (12 h light; 17 degrees -24 degrees C) to measure balances over 14 d when fed ad lib. each day and fasted intermittently for 2 d wk(-1) (short fast) or 4 d wk(-1) (long fast). Body mass (1,081 g), body water content, and metabolizable intakes of energy and protein were maintained as daily intakes of dry matter increased to 1.65 (short fast) and 2.35 (long fast) times the unfasted level. Intermittent feeding reduced metabolizability of dry matter, energy, protein, and acid detergent fiber. Concentrations of Mn provided similar estimates of metabolizability to direct measures in unfasted birds but underestimated measures of birds on long fasts. Fasting regimes continued outdoors for 9 wk when temperatures declined to -9 degrees C. Birds on short fasts were heavier (1,373 vs. 1,241 g) and fatter (159 vs. 58 g) than those on long fasts, while body water (894 g) and protein (316 g) were similar between groups after 5 wk. Birds on long fasts subsequently gained mass when fed daily, but those on short fasts lost mass when fed each day. Omnivorous waterfowl combine ingestive and digestive flexibility with plasticity of body lipid to contend with uncertain food availability.     

The effect of brief light pulses on the photoperiodic reaction in the Djungarian hamsterPhodopus sungorus

Summary The effects of brief light pulses on photoperiodic reaction were examined in male Djungarian hamsters (Phodopus sungorus). Half of the animals came from long photoperiods and, accordingly, were in physiological summer state with large and functional testes. The other half had lived in short natural photoperiods before and was in physiological winter condition with involuted testes. These animals were exposed to long (LD 168) or to short (LD 816) photoperiods, or to short photoperiods in which the 16 h of darktime were interrupted by 1 min of light each night, either 4, 8 or 12 h after light off.Light pulses at midnight had the same effect as long photoperiods, they maintained gonadal size and activity or caused rapid recrudescence. If the light pulses were applied 4 or 12 h after light-off, however, a marked difference in effect ensued, depending on previous state and light regime. In animals coming from long photoperiods, these schedules induced regression, while in hamsters coming from short photoperiods the same schedules stimulated recrudescence, though significantly less than full long photoperiods or schedules with light-interruptions at midnight. Changes in body weight and pelage colour closely paralleled the changes in gonadal state.     

Vulnerability to severe weather and regulation of body mass of Icelandic and British Redshank Tringa totanus

During severe weather, Redshanks suffer the heaviest mortality amongst all the shorebird species wintering around the North Sea coasts of the British Isles. An earlier study had suggested that this resulted from a failure to accumulate sufficient body fat reserves before mid-winter. Detailed field studies in northeast England between 1993 and 1995 of seasonal changes in body mass, and in estimated lean and fat masses, of two races of Redshank, both of which winter in the same estuary, were accompanied by similar studies of small numbers held in captivity with unlimited food. After differences in body size were allowed for, there were no differences in body composition and its seasonal pattern of change in birds of the Icelandic and British races. Body mass changes in wild birds paralleled those in captives between November and March, and mid-winter levels were not limited by food supply; indeed they were slightly higher in a winter with lower prey densities. It is concluded that Redshanks regulate body mass and, indirectly, fat reserves at levels set by a trade-off between the risks of predation and starvation. Unlike most other shorebird species, they take very small prey in relation to their body size and hence must feed for long periods during each tidal cycle to achieve their daily energy intake needs. Thus they have little scope to extend their feeding time during severe weather, which also forces them to feed on ice-free exposed coastal habitats where wind chill cannot be avoided. Both factors lead to more rapid depletion of fat reserves than in other species which have higher energy intake rates or lower total daily requirements.