Longer is fatter: body mass changes of migrant Reed Warblers (Acrocephalus scirpaceus) staging at Eilat,Israel

Ecological barriers are the riskiest phases of the annual migrations for migratory birds. Comparatively little field data exists pertaining to the ability of migratory birds to prepare for the challenges of crossing ecological barriers, or their ability to recuperate afterward. Migrating Reed Warblers (Acrocephalus scirpaceus) were captured in Eilat, Israel, during their spring and autumn migrations. Data on spring and autumn body masses, their inter-annual variation, and the pattern of body mass increase were analysed. The birds show a significant inter-annual variation in their body mass and body condition index in both seasons, which is consistent with the data from other sites and for other passerine species. During stopovers, mass gain occurred in both seasons. Birds in poor initial condition, and those that stop over for a longer period of time, gained more body mass faster. In spring, but not in autumn, the progress of the season was also an important factor; late-arriving birds gained more fuel faster. The average rate of fuel gain was 0,157g·day^?1 ± 0.018 SE.     

Respiration,oxygen consumption and heart rate in some birds during rest and flight

Summary Pulmonary ventilation (tidal volume, frequency) and oxygen content of expired air were measured in separate flights for 3 species of birds — Evening Grosbeak (Hesperiphona vespertina), Ring-billed Gull (Larus delawarensis), and Black Duck (Anas rubripes). Heart rate was measured in flight or immediately after landing in 12 species.Respiratory frequency and tidal volume were greater in flight than during rest. As the O₂ content of expired air did not change appreciably, the increase in O₂ consumption was similar to the increase in ventilation and averaged more than 10 times basal. The influence of body weight on metabolism during flight was similar to that previously observed under basal conditions.Heart rates during flight (10 species), immediately after landing (12 species), and maximal rates from various authors (15 species) were in close agreement, and were 2–4 times as high as during rest. The heart rate decreased with increasing body weight according to the equation HR_f=25.1 BW^–0.16 (HR per sec, BW in g). In flight there was much less variation and there was a smaller decrease with increasing weight than during rest. Although the estimated stroke volume and heart size appear larger in birds, the ratio of these functions was similar to that in mammals.Issued as N.R.C.C. No. 11094.The valuable technical assistance of Mr. B. Mackenzie and Mr. R. Charbonneau made this study possible. We are also indebted to Dr. Doris Jensen of McMaster University for providing facilities for tests on ring-billed gulls.     

Even a mild spell of cold weather affects feeding in migrating redheaded buntings

We investigated whether a climatic change in temperature affected daily food intake in migrating male redheaded buntings. Groups of adult male birds (n = 18) were photoinduced into migratory phenotype under increasing spring daylengths (NDL); as the birds began to exhibit night restlessness, Zugunruhe, these were allocated into groups, either with ambient (NDL, variable daily temperature: maximum – 29–44 °C and minimum – 16–33 °C; for food intake (six birds) and activity recording, six birds) until 2 weeks after they concluded migration or with constant temperature (NDT, 22 ± 1 °C; for food intake (six birds)) conditions. As day length increased March onwards, daily food intake increased (hyperphagia) in NDL and NDT groups. However, hyperphagia was slower in NDT birds as compared to NDL birds, suggesting that altered ambient temperature affects daily food intake in migrating buntings. Another group of 12 birds were held under constant daylengths (12L:12D; EDT and constant temperature 22 ± 1 °C). Although the onset of Zugunruhe was delayed under EDT, the day of onset of Zugunruhe was taken as day 0. Daily food intake and body weight before and during migration of EDT birds were compared with that of NDT and NDL groups. Daily food intake and body weight increased in all migrating birds, but hyperphagia continued post-migration in NDT birds. The study suggests that constantly suboptimal temperature despite increasing daylength, NDT, appeared to affect feeding and body weight of migratory buntings as evident from continued hyperphagia and body weight gain, even after concluding migrating activity.     

Untersuchungen zur Jahresperiodik von Laubs?ngern. II

Zusammenfassung 17 Fitisse und 20 Zilpzalpe aus Südwestdeutschland wurden im Alter zwischen 6 und 11 Tagen aus dem Nest genommen und unter konstanter Tageslichtdauer aufgezogen. Ein Teil der Vögel lebte in einem 12:12-Stunden-Tag, der andere Teil in einem 18:6-Stunden-Tag. Alle Vögel wurden auf Gefiederentwicklung, Jugendmauser, Gewichtsentwicklung und Zugunruhe untersucht.Viele der unter natürlichen Lichtbedingungen beobachteten Vorgänge (Gwinner 1969) traten auch in photoperiodisch konstanten Bedingungen auf. Unterschiede zwischen den beiden Arten blieben im wesentlichen erhalten. Bei beiden Arten waren die Bedingungen des 12:12-Stunden-Tages der artgemäßen Ausprägung des Musters der Jugendentwicklung günstiger als die Bedingungen des 18:6-Stunden-Tages.Die Tageslichtdauer beeinflußte sowohl den zeitlichen Ablauf der untersuchten Vorgänge als auch das Ausmaß mancher Änderungen. Bei beiden Arten begannen und endeten viele Vorgänge im Kurztag früher als unter natürlichen Lichtbedingungen und unter natürlichen Lichtbedingungen früher als im Langtag.Die Tageslichtdauer kann die Jugendentwicklung so modifizieren, daß das Muster der einen Art unter einer Bedingung dem der anderen Art unter einer anderen Bedingung weitgehend entspricht.Die Ergebnisse zeigen, daß die untersuchten Vorgänge sowohl von endogenen Mechanismen als auch von der Tageslichtdauer kontrolliert werden.

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Investigations on annual rhythms in Warblers. IIThe effects of photoperiod on the development of plumage, body weight and migratory restlessness inPhylloscopus trochilus andPh. collybita

Summary 17 Willow Warblers and 20 Chiffchaffs were taken from their nests in southwest Germany and raised under constant photoperiodic conditions. Approximately one half of the birds of each species was kept in a 12-hr photoperiod (LD 12:12), the other half in an 18-hr photoperiod (LD 18:6). Plumage development, postjuvenile molt, and changes in body weight and migratory restlessness were investigated.The typical sequence of processes observed under natural photoperiodic conditions (Gwinner 1969) was also observed under constant photoperiodic conditions. Differences in the pattern of development between the two species were essentially maintained. The behaviour of birds kept in LD 12:12 reflected the natural pattern of behaviour better than that of birds kept in LD 18:6.The photoperiodic conditions modified the age of onset and end of the events investigated as well as their duration. The birds of both species initiated and terminated many events earlier in LD 12:12 than under natural light conditions and under natural light conditions earlier than in LD 18:6.The photoperiodic conditions may modify the sequence of events in such a way that the general pattern representative for one species under one particular photoperiod may be almost identical with the pattern of the other species under another photoperiod.It is concluded that the processes investigated are controlled by endogenous mechanisms as well as by photoperiod.

     

Oxygen consumption rates of adults and chicks during brooding in king quail (Coturnix chinensis)

Oxygen consumption rates were measured in chicks (0–7 days of age), and in non-brooding and brooding adults. Brooded chicks maintained a constant oxygen consumption rate at a chamber ambient temperature of 10–35°C (0–5 days of age: 2.95ml O₂·g^-1·h^-1 and 6–17 days of age: 5.80 ml O₂·g^-1·h^-1) while unbrooded chicks increased oxygen consumption rate at ambient temperature below 30°C to double the brooded oxygen consumption rate at 25 and 15°C for chicks < 5 days of age and>5 days of age, respectively. The massspecific oxygen consumption rate of breeding male and females (non-brooding) were significantly elevated within the thermoneutral zone thermal neutral zone (28–35°C) in comparison to non-breeding adults. Below the thermal neutral zone, oxygen consumption rate was not significantly different. The elevation in oxygen consumption rate of breeding quail was not correlated with the presence of broodpatches, which developed only in females, but is a seasonal adjustment in metabolism. Male and females that actively brooded one to five chicks had significantly higher oxygen consumption rate than non-brooding quail at ambient temperature below 30°C. Brooding oxygen consumption rate was constant during day and night, indicating a temporary suppression of the circadian rhythm of metabolism. Brooding oxygen consumption rate increased significantly with brood number, but neither adult body mass nor adult sex were significant factors in the relationship between brooding oxygen consumption rate and ambient temperature. The proportion of daylight hours that chicks were brooded by parents was negatively correlated with ambient temperature. After chicks were 5 days old brooding time was reduced but brooding oxygen consumption rate was unchanged. Heat from the brooding parent appeared to originate mainly from the apteria under the wings and legs rather than the broodpatch. The parental heat contribution to chick temperature regulation below the chicks' thermal neutral zone is achieved by increasing parental thermal conductance by a feedback control similar to that suggested for the control of egg temperature via the brood-patch. It is concluded that the brooding period is an energetic burden to parent quail, and the magnitude of the cost increases directly with brood number and inversely with ambient temperature during this period. The oxygen consumption rate of brooding parents was 5.80–6.90 ml O₂·g^-1·h^-1 (ambient temperature 10–15°C) at night and up to 5.10 ml O₂·g^-1·h^-1 (ambient temperature 18°C) during the day, which are 100 and 40% higher than non-brooding birds, respectively.Abbreviations bm body mass - SMR standard metabolic rate - T _a ambient temperature - T _b body temperature - I/O₂ oxygen consumption rate - C _wet wet thermal conductance - TNZ thermal neutral zone - ANOVA analysis of variance - ANCOVA analysis of covariance     

Influence du lindane sur le métabolisme respiratoire d'Asellus aquaticus L. Relation concentration — perturbation

The respiratory metabolism of Asellus aquaticus L. was investigated after short-term exposure to lindane poisoning at 15 °C. After 48 h, oxygen consumption was individually recorded with a polarographic method using a Clark electrode and a Copenhagen radiometer.The average oxygen consumption by poisoned individuals is higher than controls at concentrations lower than 8 µg·1^–1 but decreases to become lower than controls at higher dosages. If the metabolism of individuals is expressed as a function of weight, we find no significant correlation between weight and metabolism of poisoned Asellus, as opposed to controls. This result can be explained by the fact that poisoning intensity decreases with body weight at a given insecticide concentration, whereas metabolism increases as a function of weight. As a consequence there is apparently a lack of correlation between weight and metabolism amongst poisoned Asellus at dosages higher than 2 µg·1^–1. However, if metabolism is expressed as a metabolic ratio, a good correlation is observed between metabolism and weight of poisoned Asellus, the metabolic perturbation being significant at 4 µg·1^–1 and higher concentrations.These results prompt us to conclude that, during the initial step of intoxication, an increase of the oxygen consumption occurs under weak poisoning conditions, while higher concentrations of insecticide give rise to a decrease in metabolism.

     

Metabolic depression and Na+/K+ gradients in the aestivating Australian goldfields frog,Neobatrachus wilsmorei

During aestivation the metabolic rate of the Australian goldfields frog Neobatrachus wilsmorei was reduced by 80% from its standard metabolic rate. The in vitro rate of oxygen consumption of isolated muscle and skin from aestivating frogs was up to 50% lower than that of the non-aestivating frogs. This in vitro rate of oxygen consumption was maintained for 6–12 h, indicating an intrinsic metabolic depression of tissues during aestivation. Frogs became dehydrated during aestivation. Muscle, skin and liver also became dehydrated during aestivation, but brain and kidney did not. Na⁺ and K⁺ contents and extracellular space measurement for muscle indicated that ion gradients were maintained across the muscle cell membrane during aestivation. Increases in plasma concentrations of Na⁺ and K⁺ were matched with similar increases in muscle intracellular ion concentrations. Extracellular space measurements were unsuccessful in the other tissues, but K⁺ content in all tissues (per dry weight) was maintained during aestivation, and the concentration of plasma K⁺ did not increase above that which can be accounted for by dehydration, indicating that K⁺ gradients were maintained.Abbreviations bm body mass - DPM disintegrations per minute - dw dry weight - MR metabolic rate - vO₂ rate of oxygen consumption - ww wet weight     

Oxygen consumption of a Chaoborus species from a neotropical reservoir (socuy reservoir,Venezuela)

Oxygen consumption of all four larval instars of a Chaoborus species from Socuy Reservoir in western Venezuela was studied under laboratory conditions at 25°C. On a logarithmic basis, oxygen consumption per organism increased as a smooth, linear function of body weight (0.49 power of body weight). Observed rates were lower than other Chaoborus species with comparable body weight at the same temperature. Oxygen consumption per unit weight decreased from smaller to large instar larvae. With the exception of instar I, values of oxygen consumption per unit weight were lower than values reported for other Chaoborus species. The results suggest that our species have low energy demands for maintenance, and are consistent with suggestions about high efficiency in use of energy in genus Chaoborus.     

Growth and oxygen consumption in embryonic and early postembryonic development of European pond turtle <Emphasis Type="Italic">Emys orbicularis</Emphasis> (Reptilia: Emydidae)

Experiments on developing eggs of European pond turtle (Emys orbicularis) demonstrated S-shaped changes in the rate of oxygen consumption and body weight during embryonic development. The rate of oxygen consumption and weight progressively increased within 70 days after hatching. During embryogenesis, the mass-specific rate of oxygen consumption decreased. After hatching, it increased but then decreased to a certain level, which remained constant to the end of the studied period. We observed unidirectional changes in the mass-specific rate of oxygen consumption and specific weight gain during embryonic development and this pattern was maintained after hatching. The coefficients of the allometric relationship between oxygen consumption and body weight were a = 0.33 and k = 0.52 during embryonic development and a = 0.17 and k = 0.89 during postembryonic development.Translated from Izvestiya Akademii Nauk, Seriya Biologicheskaya, No. 2, 2005, pp. 214–220.Original Russian Text Copyright © 2005 by Vladimirova, Alekseeva, Nechaeva.     

Effect of legume-based cropping systems on nitrogen mineralization potential of Vertisol

The quantity and patterns of net mineralization of soil nitrogen (N) were studied in Vertisols under different cropping systems in the semi-arid tropical areas. Eight cropping systems were selected; three contained pigeonpea (PP), one contained PP and cowpea (COP), and two contained chickpea (CP) as legume component crops, one included sequence cropping with nonlegumes during the rainy and postrainy seasons, and one system was kept fallow (F) during the rainy season and sown to sorghum (S) during the postrainy season. Cropping systems with PP as a component crop increased mineralizable N(N _o ) content two-fold in the soil compared with fallow + sorghum (F+S)–F+S system. The N mineralization rate constant (k) was not significantly affected by previous cropping history of the soil; however, a numerically higher rate constant was observed in the COP/PP intercrop, followed by sequential S+safflower (SF) system as compared to the other soils. Mineral N accumulation curves for six soils were more accurately described by the exponential model than the linear model. The active N fraction (N _o /N_tot %) varied between 8 and 16% for different systems and a direct relationship was observed between N _o /N_tot and total N for the soils under diverse cropping systems.ICRISAT JA (1638)     

Demographic and spatial responses of resident bird populations to the arrival of migratory birds within an urban environment

Long-distance migration allows many bird species to overcome the severe climatic changes that occur in seasonal environments. Migration is highly demanding, and given its cyclical nature, we currently know that it has substantial effects on the population parameters of migratory birds during both breeding and wintering seasons. However, the potential effects of the presence of migratory birds in their wintering grounds on populations of resident birds have remain largely unexplored. Here, we propose the hypothesis that migratory birds negatively affect the habitat occupancy and population abundance of resident birds because of the arrival of numerous individuals during the most limiting months of the year. Here, we studied different species of migratory and resident birds that coexist during winter in an urban ecological reserve located within Mexico City. We used single-species multiseason occupancy models, two-species occupancy models, and distance sampling techniques to evaluate changes in occupancy and population density of resident bird species during three consecutive winters. We found an aggregation pattern between two resident species (Psaltriparus minimus and Thryomanes bewickii) with three migratory warblers (Cardellina pusilla, Setophaga coronata and Setophaga townsendi). Thus, our results provide evidence of the formation of mixed-species flocks in our study area. We also conclude that resident birds experience different demographic and behavioral processes during winter that not necessarily result from interspecific interactions with migratory birds.     

Metabolic rate and cost of growth in juvenile pike (Esox lucius L.) and perch (Perca fluviatilis L.): the use of energy budgets as indicators of environmental change

Summary Energy budgets of juvenile pike and perch (weighing approximately 3 g) were determined in experiments lasting up to 4 days, by simultaneously measuring oxygen consumption, food consumption, and growth of individual fish. Although the basic pattern of energy allocation was identical in the two species, perch subjected to constant light (PEL) showed faster growth, higher assimilation and conversion efficiency, and higher oxygen consumption than perch subjected to a short daylength regime (PED). The efficiency with which food energy was converted into body mass was 39±5% in PED but 49±4% in PEL. However, the “work coefficient” (increment of body mass/post-prandial increase of oxygen consumption: mg · μmol O _inf2 ^sup−1 ) differed only insignificantly between the two groups of perch, indicating that the metabolic cost of growth was unaffected by the manipulation of experimental conditions. This identifies the higher assimilation efficiency, i.e. the increased flow of food energy into the tissues as being the cause of accelerated growth of perch under the constant-light regime. In both species the maximum feeding-induced metabolic rate was 4 times higher than the lowest preprandial rate. In perch (which were kept on low rations before the experiments) the post-prandial metabolic rate increased steadily from day to day during the 4-day experiments, so that on the last day the rate of oxygen consumption exceeded the rate on the first day by about 41%. This investigation provides further evidence that the allocation of metabolic energy in fish is based on a flexible strategy which responds sensitively to changes in both internal and external conditions.     

Use of Stable Isotope Methodology to Determine Natal Origins of Mallards at a Fine Scale Within the Upper Midwest

Abstract: Waterfowl managers often attempt to protect local breeding stocks of mallards (Anas platyrhynchos) from hunting pressure, but presently they cannot identify natal origins of birds shot during fall hunting seasons with certainty, unless recovered birds are banded before fledging. Accordingly, we examined whether stable isotope methodology could accurately delineate natal origins of mallards at a fine scale within the upper Midwest (USA). We determined δ¹³C, δD, and δ¹⁵N values from feather samples of 102 flightless mallard ducklings collected in Minnesota, North Dakota, South Dakota, and Wisconsin, USA, from 7 July to 9 September 2002. We detected inverse relationships between latitude and δ¹³C(R² = 0.223) and δD(R² = 0.210). We also detected a weak positive relationship between easterly shifts in longitude and δ¹³C(R² = 0.067) and a weak negative relationship between easterly shifts in longitude and δ¹⁵N(R² = 0.076). The ¹³C and deuterium values differed (P < 0.02) among states: North Dakota was most depleted in ¹³C, and South Dakota was least depleted in deuterium. Discriminant function analysis delineated natal origins of mallard ducklings in Minnesota, North Dakota, South Dakota, and Wisconsin with low-to-moderate accuracy (47%), whereas we predicted natal origins of ducklings among subregions (Prairie [ND, SD] vs. Great Lakes [MN, WI] states) with moderate accuracy (72%). We conclude that stable isotope methodology has a limited ability to determine natal origins of migratory birds along a longitudinal corridor at fine scales but that it improves across ecoregions. However, the ability of deuterium to determine natal origins of migratory birds may vary as hydrological conditions, within and among areas, change throughout time. Researchers should account for annual variation in deuterium found in surface waters when investigating natal origins of migratory birds that use food derived primarily from these waters.     

Fasting endurance and cold resistance without hypothermia in a small predatory bird: the metabolic strategy of Tengmalm's owl,Aegolius funereus

The energetic adaptations of non-breeding Tengmalm's owls (Aegolius funereus) to temperature and fasting were studied during the birds' autumnal irruptions in western Finland. Allometric analysis (including literature data and two larger owl species measured in this study) indicates that the basal metabolic rate of owls is below the mean level of non-passerine birds. However, the basal metabolic rate of the 130-g Tengmalm's owl (1.13 W) is higher than in other owls of similar size. This is probably related to its northern distribution and nomadic life history. Relative to its size, Tengmalm's owl has excellent cold resistance due to effective insulation (lower critical temperature +10°C, minimum conductance 0.19 mW·cm^-2·°C^-1). Radiotelemetric measurements of body temperature showed that the level of body temperature is lower than for birds in general (39.4°C at zero activity) and that the amplitude of the diurnal cycle is also low (0.2–0.6°C). In contrast to many other small birds, Tengmalm's owls do not enter hypothermia during a 5-day fast at thermoneutrality or in cold. Moreover, while the metabolic rate per bird shows the expected mass-dependent decrease, the mass-specific rate decreases only slightly during the fast. In line with this, there was no decrease in the plasma triiodothyronine concentration during the fast in the owl, whereas a dramtic drop was observed in the pigeon and Japanese quail that were used as a reference. Despite this, the owl has an excellent capacity for fasting because of its ability to accumulate extensive fat depots and its low overall metabolic rate. Fasting reduced evaporative water loss to 50% of that in the fed state. Calculations show that the oxygen consumption observed in fasting birds would involve a production of metabolic water barely sufficient to compensate for evaporative water loss. The threat of dehydration may thus set a limit to the decrease in metabolic rate in fasting owls (owls rely totally on water either ingested with food or produced metabolically). We conclude that the metabolic strategy in Tengmalm's owl is largely dictated by an evolutionary pressure for fasting endurance. With the restrictions set by small body size and water economy, this bird has apparently taken these adaptations to an extreme. The constraints that preclude hypothermia, which could increase the capacity for fasting even more, remain unknown.Abbreviations BM body mass - BMR basal metabolic rate - EWL vaporative water loss - MR metabolic rate - T₃ triiodothyronine - T _a ambient temperature - T _b body temperature - VO₂ oxygen consumption     

Migratory Orientation of Blackcaps (Sylvia atricapilla): Population-specific Shifts of Direction during the Autumn

The population-specific orientation of two groups of blackcaps (Sylvia atricapilla), one from southwest Germany, the other from easternmost Austria, was studied outdoors in Emlen funnels. We investigated whether a seasonal shift in the migratory direction — as expected for the Austrian birds from ringing recoveries — occurs under experimental conditions and in a seasonally constant magnetic field. The West German birds, for which no shift was expected, oriented southwest during the entire season. The Austrian birds oriented southeast in October and southsouthwest in November. The clockwise shift by about 60° occurred within a 10-day period. The results indicate that in this species seasonal changes of migratory direction are probably based on an endogenous program, occur without the birds actually migrating and are independent of changes in the magnetic field. Our results provide further evidence that directional shifts in Sylvia warblers may be controlled by a different mechanism than in pied flycatchers (Ficedula hypoleuca).     

Migrating Birds as Dispersal Vehicles for West Nile Virus

Whereas migrating birds have been implicated in the spread of West Nile virus (WNV), there is no direct evidence of birds actively migrating while infectious. The role of birds in WNV dispersal is difficult to assess in the field. However, this role can be evaluated experimentally because birds in migratory disposition display increased locomotor activity or restlessness under captive conditions. We tested the following hypotheses: (1) migrating passerine birds continue to exhibit migratory activity while infectious with WNV and (2) the migratory state of the individual affects the magnitude of viremia. We examined the migratory activity of two neoarctic-neotropical passerine migrants, Swainson’s thrush (Catharus ustulatus) and gray catbird (Dumetella carolinensis), during acute WNV infection. All gray catbirds and six of nine Swainson’s thrushes exhibited migratory activity while infectious. Moreover, migratory status did not appear to influence viremia titers, as might be expected if individuals were immunosuppressed during migration. Therefore, we demonstrate that migrating passerine birds are potential dispersal vehicles for WNV.     

Daily torpor in the gray mouse lemur (Microcebus murinus) in Madagascar: energetic consequences and biological significance

Patterns and energetic consequences of spontaneous daily torpor were measured in the gray mouse lemur (Microcebus murinus) under natural conditions of ambient temperature and photoperiod in a dry deciduous forest in western Madagascar. Over a period of two consecutive dry seasons, oxygen consumption (VO₂) and body temperature (T _b) were measured on ten individuals kept in outdoor enclosures. In all animals, spontaneous daily torpor occurred on a daily basis with torpor bouts lasting from 3.6 to 17.6 h, with a mean torpor bout duration of 9.3 h. On average, body temperatures in torpor were 17.3±4.9°C with a recorded minimum value of 7.8°C. Torpor was not restricted to the mouse lemurs’ diurnal resting phase: entries occurred throughout the night and arousals mainly around midday, coinciding with the daily ambient temperature maximum. Arousal from torpor was a two-phase process with a first passive, exogenous heating where the T _b of animals increased from the torpor T _b minimum to a mean value of 27.1°C before the second, endogenous heat production commenced to further raise T _b to normothermic values. Metabolic rate during torpor (28.6±13.2 ml O₂ h^–1) was significantly reduced by about 76% compared to resting metabolic rate (132.6±50.5 ml O₂ h^–1). On average, for all M. murinus individuals measured, hypometabolism during daily torpor reduced daily energy expenditure by about 38%. In conclusion, all these energy-conserving mechanisms of the nocturnal mouse lemurs, with passive exogenous heating during arousal from torpor, low minimum torpor T _bs, and extended torpor bouts into the activity phase, comprise an important and highly adapted mechanism to minimize energetic costs in response to unfavorable environmental conditions and may play a crucial role for individual fitness. Received: 8 July 1999 / Accepted: 3 December 1999     

Rates of oxygen consumption by Thais (Nucella) Lapillus (L.)

Oxygen consumption by Thais varied seasonally with higher values in summer than in winter. This seasonal difference was due in part to the effects of temperature and in part to those of feeding. During feeding, rates of oxygen consumption were high, but declined in the period between meals. There was little evidence of acclimation of oxygen consumption to changes in temperature; low (winter) rates of consumption were more sensitive to increases in temperature than were high (summer) rates. A polynomial expression, including terms for temperature and ‘time since last meal’, was derived for the constant a′ in the allometric equation relating oxygen consumption (_o2) to dry body weight: _o2 = a′.W^0.511.     

Temperature regulation in a burrow-nesting tropical seabird,the Wedge-tailed Shearwater (Puffinus pacificus)

Summary At low air temperatures (2.3–13.9°C), Wedge-tailed Shearwaters (Puffinus pacificus) shivered and their oxygen consumption increased to as much as 283% of the mean value (0.77 ml O₂/g·h) within the thermoneutral zone of air temperature (23–34°C). The minimal thermal conductance of the tissues and plumage was similar to the value predicted from the body mass (320.5 g). The oxygen consumption of the birds within their thermoneutral zone was lower than predictions based on body mass. At elevated air temperatures, the shearwaters panted at respiratory frequencies as high as 260 respirations/min; maximal respiratory frequencies were not invoked until the birds had become hyperthermic. During exposure to a hot environment, the oxygen consumption of the birds increased and in most instances the shearwaters were not able to lose heat equivalent to their concurrent metabolic heat production.Symbols and abbreviations BMR basal metabolic rate - C _total total thermal conductance - f respiratory frequency - TEWL total evaporative water loss - T _st stomach temperature - T _re rectal temperature