Effects of Light Intensity on the Flight Behaviour of Adult <Emphasis Type="Italic">Tirumala limniace</Emphasis> (Cramer) (Lepidoptera: Nymphalidae: Danainae)

Light intensity significantly affects insect flight behaviour. Mating of butterflies is significantly associated with flight frequency. However, no research has elucidated the effects of light intensity on butterfly flight. Thus, a clear understanding of the effects of light intensity on flight has significant theoretical implications for the cultivation and utilization of butterflies. We observed the flight behaviour of adult Tirumala limniace (Cramer) exposed to light intensities from 243 to 2240 lx and measured the frequency of flight, take-off rhythm, thoracic temperature excess (△T) when perching and flying, and the tendency for thoracic temperature to increase. Results showed that high-intensity light significantly increased flight activity, and males were more active than females under similar light intensities; strong light (1280–2240 lx) resulted in female and male butterflies taking flight earlier compared with weak light (243–864 lx); and a similar pattern was observed for flight duration, with flights by males being significantly longer than those by females at 864–2240 lx; △T of adults flying in strong light was significantly higher than in weak light, whereas the thoracic temperature of perching adults was similar to the air temperature. Compared with other light intensities, the equilibrium thoracic temperature of adults exposed to 2240 lx was higher, and the time to reach it was shorter; in addition, the △T and rate of thoracic temperature increase were higher and achieved more quickly, respectively. Thus, of the 243–2240 lx range, 2240 lx was the most optimal light intensity for adult T. limniace flight and captive rearing.     

Thermal physiological ecology of Colias butterflies in flight

Summary As a comparison to the many studies of larger flying insects, we carried out an initial study of heat balance and thermal dependence of flight of a small butterfly (Colias) in a wind tunnel and in the wild.Unlike many larger, or facultatively endothermic insects, Colias do not regulate heat loss by altering hemolymph circulation between thorax and abdomen as a function of body temperature. During flight, thermal excess of the abdomen above ambient temperature is weakly but consistently coupled to that of the thorax. Total heat loss is best expressed as the sum of heat loss from the head and thorex combined plus heat loss from the abdomen because the whole body is not isothermal. Convective cooling is a simple linear function of the square root of air speed from 0.2 to 2.0 m/s in the wind tunnel. Solar heat flux is the main source of heat gain in flight, just as it is the exclusive source for warmup at rest. The balance of heat gain from sunlight versus heat loss from convection and radiation does not appear to change by more than a few percent between the wings-closed basking posture and the variable opening of wings in flight, although several aspects require further study. Heat generation by action of the flight muscles is small (on the order of 100 m W/g tissue) compared to values reported for other strongly flying insects. Colias appears to have only very limited capacity to modulate flight performance. Wing beat frequency varies from 12–19 Hz depending on body mass, air speed, and thoracic temperature. At suboptimal flight temperatures, wing beat frequency increases significantly with thoracic temperature and body mass but is independent of air speed. Within the reported thermal optimum of 35–39°C, wing beat frequency is negatively dependent on air speed at values above 1.5 m/s, but independent of mass and body temperature. Flight preference of butterflies in the wind tunnel is for air speeds of 0.5–1.5 m/s, and no flight occurs at or above 2.5 m/s. Voluntary flight initiation in the wild occurs only at air speeds 1.4 m/s.In the field, Colias fly just above the vegetation at body temperatures of 1–2°C greater than when basking at the top of the vegetation. These measurements are consistent with our findings on low heat gain from muscular activity during flight. Basking temperatures of butterflies sheltered from the wind within the vegetation were 1–2°C greater than flight temperatures at vegetation height.     

Thoracic temperature,shivering, and flight in the monarch butterfly,Danaus plexippus (L.)

Summary Monarch butterflies, Danaus plexippus (L.), display a warm-up behavior characterized by wingstrokes of small amplitude. Thoracic temperature during this shivering and during fixed flight was measured by means of a smallbead thermistor inserted into the thorax. At ambient temperatures of 15–16°C, once shivering is initiated the thoracic temperature rises at a maximum rate of 1.3°C/min, and a thoracic temperature 4.0°C greater then ambient is produced (Table 1). Fixed flight at these low ambient temperatures results in a similar rate of increase in thoracic temperature, and a similar temperature excess is produced (Fig. 3). At ambient temperatures between 22 and 35°C the thoracic temperature of an animal starting to fly rises at a faster rate, 3.6°C/min, and reaches a greater excess, 7.9°C (Fig. 4). The wingbeat frequency of animals in fixed flight increases with increasing thoracic temperature (Fig. 2). In the absence of direct solar radiation, shivering typically occurs prior to flight at low ambient temperatures (13–17°C), and the resulting increase in thoracic temperature allows monarch butterflies to fly at these cool temperatures.I thank Miss Janice Ruppert and Mr. C. J. Doughty for their valuable technical assistance. The co-operation of the administrators of New Brighton Beach State Park in permitting me to collect in the park is appreciated. Financial support for this study was provided in part by a faculty research grant from the University of California.     

Thermoregulation in four species of tropical solitary bees: the roles of size,sex and altitude

Body temperatures during free flight in the field, warm-up rates during pre-flight warm-up, and temperatures during tethered flight are measured for four tropical solitary bee species at three sites of differing altitude in Papua New Guinea. All four species are capable of endothermic preflight warm-up; three species give slopes of thoracic temperature on ambient temperature of significantly less than 1, indicating regulation of thoracic temperature. In the kleptoparasitic Coelioxys spp. (Megachilidae) and Thyreus quadrimaculatus (Anthophoridae), warm-up rates and thoracic temperatures in flight are low by comparison with the two provisioning species Creightonella frontalis (Megachilidae) and Amegilla sapiens (Anthophoridae). In both C. frontalis and A. sapiens thoracic temperatures correlate positively and significantly with both ambient temperature and body mass. In A. sapiens, body mass increases with altitude; this can be interpreted as a response to lower ambient temperatures at higher altitude, an example of Bergmann's rule. In both A. sapiens and C. frontalis populations at higher altitude have higher thoracic temperatures independent of differences of body mass, suggestive of additional morphological or physiological adaptation to lower ambient temperatures. In A. sapiens there is no qualitative difference in body temperatures between males and females after controlling for body mass, while male C. frontalis have significantly lower thoracic temperatures than females of the species. This difference between A. sapiens and C. frontalis is discussed with reference to variation in mating systems found in the Apoidea.Abbreviations C.R.I. Christensen Research Institute - P.N.G. Papua New Guinea - SFT stable flight temperature - T _a ambient air temperature - T _ab abdominal temperature - T _dif the temperature difference between thorax and abdomen - T _ex thoracic temperature excess - VFT voluntary flight temperature     

Takeoff temperatures in Melitaea cinxia butterflies from latitudinal and elevational range limits: a potential adaptation to solar irradiance

1. This study provides evidence that a heliophilic butterfly, the Glanville fritillary (Melitaea cinxia) has adapted differently to environmental variation across latitudes and elevations. 2. In cool air, basking M. cinxia orient themselves perpendicular to the sun's rays to gain heat and take off. During flight, solar heating is reduced because orientation perpendicular to the sun is no longer possible and convective cooling occurs. Consequently, M. cinxia have been shown to suffer net heat loss in flight, even in full sunshine. When flight duration is restricted in this way, the takeoff temperature becomes an important thermal adaptation. 3. Using a thermal imaging camera, takeoff temperatures were measured in experimental butterflies. Butterflies from the northern range limit in Finland took flight at slightly hotter temperatures than butterflies from the southern limit in Spain, and much hotter than butterflies from the elevational limit (1900–2300 m) in the French Alps. Butterflies from low‐elevation populations in southern France also took off much hotter than did the nearby Alpine population. 4. These results suggest that the influence of elevation is different from that of latitude in more respects than ambient temperature. Values of solar irradiance in the butterflies' flight season in each region show that insects from the coolest habitats, Finland and the Alps, experienced similar solar irradiance during basking, but that Finns experienced much lower irradiance in flight. This difference may have favored Finnish butterflies evolving higher takeoff temperatures than Alpine butterflies that also flew in cool air but benefited from more intense radiant energy after takeoff.     

Sexual behaviour: female swift moth is not the aggressive partner

Observations on three naturally-occurring courtships of Hepialus show that sexual behaviour in these moths is similar to that of butterflies, with the male pursuing the female in flight and mating with her after she alights. Although the female appears to solicit courtship by flying past a hovering male, and although the male becomes flaccid immediately after copulation, it is not true that the female flies directly at the male and knocks him out of the air, as is widely held by moth-collectors.     

Weight Loading and Reproductive Status Affect the Flight Performance of Pieris napi Butterflies

Weight-induced mobility reductions can have dramatic fitness consequences and winged animals are especially sensitive to the trade-off between mass and locomotion. Data on how natural weight fluctuations influence a flying insect’s ability to take off are scarce. We therefore quantified take-off flight ability in Pieris napi butterflies in relation to reproductive status. Take-off flight ability (velocity and take-off angle) under suboptimal temperature conditions was recorded with a 3D-tracking camera system and was predicted to decrease with relatively larger weight loads. Our results show that relatively larger weight loads generally reduce flight speed in male butterflies and lower take-off angles in females. However, despite having a lower wing loading, mated male butterflies flew slower than unmated males. Our study suggests that retention of weight loads associated with reproduction impairs insect flight performance.     

Flight morphology of Neotropical butterflies: palatability and distribution of mass to the thorax and abdomen

Summary We test whether palatability of Neotropical butterflies is associated with distribution of mass to the thorax and abdomen. Thoracic mass is predominantly muscle mass, whereas abdominal mass includes organs of digestion, food storage, and reproduction. To escape from predation, butterflies palatable to the rufous-tailed jacamar (Galbula ruficauda) use fast, erratic flight, whereas unpalatable butterflies have defensive chemicals and slow, regular flight patterns. We adjusted for effects of phylogeny and report partial correlations for two levels of analysis: 1) comparisons among-lineage means, which test for correlations between traits of distantly related lineages, and 2) comparisons among deviations from lineage means (or within lineages), which test for correlations between traits of more closely related species.Among lineages for both males (n=10 lineages) and females (n=9), palatability and thoracic mass were positively correlated, whereas palatability and abdominal mass were negatively correlated. An inverse correlation between thoracic and abdominal mass is a consequence of the two segments composing 75% of the total body mass. Predation, indexed by palatability, may select for increased flight speed and thoracic mass at the expense of the abdomen, but relative flight speed and thoracic mass were not significantly correlated.Within lineages (n=45 species for each sex), thoracic mass was uncorrelated with palatability in both sexes. Relative flight speed correlated positively with thoracic mass and negatively with body mass. Palatability and abdominal mass were negatively correlated for males but not females. Hence differences between the sexes in mass distribution suggest differences in reproductive constraints and predation stress.     

Thermal biology of flight in a butterfly: genotype,flight metabolism,and environmental conditions

Knowledge of the effects of thermal conditions on animal movement and dispersal is necessary for a mechanistic understanding of the consequences of climate change and habitat fragmentation. In particular, the flight of ectothermic insects such as small butterflies is greatly influenced by ambient temperature. Here, variation in body temperature during flight is investigated in an ecological model species, the Glanville fritillary butterfly (Melitaea cinxia). Attention is paid on the effects of flight metabolism, genotypes at candidate loci, and environmental conditions. Measurements were made under a natural range of conditions using infrared thermal imaging. Heating of flight muscles by flight metabolism has been presumed to be negligible in small butterflies. However, the results demonstrate that Glanville fritillary males with high flight metabolic rate maintain elevated body temperature better during flight than males with a low rate of flight metabolism. This effect is likely to have a significant influence on the dispersal performance and fitness of butterflies and demonstrates the possible importance of intraspecific physiological variation on dispersal in other similar ectothermic insects. The results also suggest that individuals having an advantage in low ambient temperatures can be susceptible to overheating at high temperatures. Further, tolerance of high temperatures may be important for flight performance, as indicated by an association of heat‐shock protein (Hsp70) genotype with flight metabolic rate and body temperature at takeoff. The dynamics of body temperature at flight and factors affecting it also differed significantly between female and male butterflies, indicating that thermal dynamics are governed by different mechanisms in the two sexes. This study contributes to knowledge about factors affecting intraspecific variation in dispersal‐related thermal performance in butterflies and other insects. Such information is needed for predictive models of the evolution of dispersal in the face of habitat fragmentation and climate change.     

Genotypic and environmental effects on flight activity and oviposition in the Glanville fritillary butterfly

Adverse environmental conditions constrain active flight and thereby limit reproduction in most insects. Butterflies have evolved various adaptations in order to thermoregulate, allowing females to search for nectar and to oviposit under unfavorable thermal conditions. We studied experimentally and with observational data the effect of low ambient temperatures experienced in the morning on the timing of oviposition and clutch size in the Glanville fritillary butterfly (Melitaea cinxia). Comparisons were made between individuals with different forms of the gene Pgi, encoding the glycolytic enzyme phosphoglucose isomerase, since naturally segregating variation at Pgi is known to be correlated with flight metabolic rate, flight performance, and fecundity. Experiencing low temperature in the morning delayed the initiation of oviposition and decreased clutch size. We used a thermal image camera to measure the thoracic surface temperature of butterflies immediately after voluntary flight. Single nucleotide polymorphism at Pgi was associated with thoracic temperature at low ambient temperatures. This has consequences for reproduction because females that are able to fly at lower ambient temperatures generally initiate oviposition earlier in the afternoon, when the environmental conditions are most favorable and the average egg clutch size is generally largest. These results suggest that variation in physiological and molecular capacity to sustain active flight at low ambient temperature has significant fitness-related consequences in insects.     

Synchronous Crepuscular Flight of Female Asian Gypsy Moths: Relationships of Light Intensity and Ambient and Body Temperatures

Female gypsy moths (Lymantria dispar) of Asian heritage studied in central Siberia and Germany exhibit a highly synchronous flight at dusk, after light intensity falls to about 2 lux. This critical light intensity sets the timing of flight behaviors independent of ambient temperature. Flight follows several minutes of preflight wing fanning during which females in Germany and those from a laboratory colony (derived from Siberian stock) raised their thoracic temperatures to 32–33°C at ambient temperatures of 19–22°C. Thoracic temperature of females in free flight exceeded the air temperature (19–22°C) by approximately 11–13°C. The duration of wing fanning was strongly dependent on ambient temperature. In Germany, where ambient temperatures at dusk ranged between 21 and 25°C, females wing fanned for only 2.1 ± 0.2 (SE) min; in the much colder temperatures prevalent at dusk in Bellyk, central Siberia (11–13°C), females spent 11.2 ± 0.6 min in preflight wing fanning. The majority (80%) of mated and even virgin females initiated flight during the evening of the day they eclosed. However, in Bellyk, a small proportion (12%) of females wing fanned for an extended time but then stopped, whereas others (8%) never wing fanned and, therefore, did not take flight. Females also were capable of flight when disturbed during the daylight hours in Germany where the maximal temperature was high (27–30°C), but not in Siberia, where temperatures peaked at only 17–19°C. However, Siberian females were able to propel themselves off the tree on which they were perched by executing several vigorous wing flicks when approached by the predaceous tettigoniid, Tettigonia caudata.     

Effect of local weather on butterfly flight behaviour,movement, and colonization: significance for dispersal under climate change

Recent climate change is recognized as a main cause of shifts in geographical distributions of species. The impacts of climate change may be aggravated by habitat fragmentation, causing regional or large scale extinctions. However, we propose that climate change also may diminish the effects of fragmentation by enhancing flight behaviour and dispersal of ectothermic species like butterflies. We show that under weather conditions associated with anticipated climate change, behavioural components of dispersal of butterflies are enhanced, and colonization frequencies increase. In a field study, we recorded flight behaviour and mobility of four butterfly species: two habitat generalists (Coenonympha pamphilus; Maniola jurtina) and two specialists (Melitaea athalia; Plebejus argus), under different weather conditions. Flying bout duration generally increased with temperature and decreased with cloudiness. Proportion of time spent flying decreased with cloudiness. Net displacement generally increased with temperature. When butterflies fly longer, start flying more readily and fly over longer distances, we expect dispersal propensity to increase. Monitoring data showed that colonization frequencies moreover increased with temperature and radiation and decreased with cloudiness. Increased dispersal propensity at local scale might therefore lower the impact of habitat fragmentation on the distribution at a regional scale. Synergetic effects of climate change and habitat fragmentation on population dynamics and species distributions might therefore appear to be more complex than previously assumed.     

Thermoregulatory physiology of the carpenter bee,Xylocopa varipuncta

Summary The carpenter beesXylocopa varipuncta maintain thoracic temperatures of 33.0°C to 46.5°C during continuous free flight from 12°C to 40°C. Since the thoracic temperature excess is not constant (decreasing from 24°C at low air temperatures to 6°C at high) the bees are thermoregulating. We document physiological transfer of relatively large amounts of heat to the abdomen and to the head during pre-flight warm-up and during artificial thoracic heating. Most of the temperature increase of the head is due to passive conduction, while that of the abdomen is due to active physiological heat transfer despite a series of convolutions of the aorta in the petiole that anatomically conform to a counter-current heat exchanger. Although the thermoregulatory mechanisms during flight are far from clarified, our data suggest that thermoregulation involves a strong reliance on active convective cooling through increased flight speed.     

Body temperatures in free-flying pigeons

We examined the relationship between body temperature (T_b) of free flying pigeons and ambient water vapor pressure and temperature. Core or near core T_b of pigeons were measured using thermistors inserted into the cloaca and connected to small transmitters mounted on the tail feathers of free flying tippler pigeons (Columba livia). Wet and dry bulb temperatures were measured using modified transmitters mounted onto free-flying pigeons. These allowed calculation of relative humidity and hence water vapor pressure at flight altitudes. Mean T_b during flight was 42.0 ± 1.3 °C (n = 16). Paired comparisons of a subset of this data indicated that average in-flight T_b increased significantly by 1.2 ± 0.7 °C (n = 7) over that of birds at rest (t = −4.22, P < 0.05, n = 7) within the first 15 min of takeoff. In addition, there was a small but significant increase in T_b with increasing ambient air (T_a) when individuals on replicate flights (n = 35) were considered. Inclusion of water vapor pressure into the regression model did not improve the correlation between body temperature and ambient conditions. Flight T_b also increased a small (0.5 °C) but significant amount (t = 2.827, P < 0.05, n = 8) from the beginning to the end of a flight. The small response of T_b to changing flight conditions presumably reflects the efficiency of convection as a heat loss mechanism during sustained regular flight. The increase in T_b on landing that occurred in some birds was a probable consequence of a sudden reduction in convective heat loss. Accepted: 2 February 1999     

温度对甜菜夜蛾飞行能力的影响

温度对甜菜夜蛾飞行能力有显著的影响（P<0.05）。在16～32℃内,成虫均能进行正常的飞行活动。24℃下的成虫飞行能力最强,在15 h的吊飞飞行中,成虫飞行距离最远（37.14 km）、飞行速度最快（0.87 m/s）、飞行时间最长（11.73 h）。温度低于２０℃或高于２８℃时,其飞行能力均显著降低。甜菜夜蛾在不同温度下飞行时对主要能源物质（甘油三酯）的利用效率不同。在较适宜的温度下,尽管成虫飞行消耗的甘油三酯较多,但单位飞行距离所消耗的甘油三酯却较少,即利用效率较高,表明成虫飞行能源物质利用效率的不同是导致其在不同温度下飞行能力产生差异的主要原因之一。     

Cold adaptation across the elevation gradient in an alpine butterfly species complex

1. Temperature acts as a major factor on the timing of activity and behaviour in butterflies, and it might represent a key driver of butterfly diversification along elevation gradients. Under this hypothesis, local adaptation should be found along the elevation gradient, with butterflies from high elevation populations able to remain active at lower ambient temperature than those from low elevation. 2. The warming-up rate and the thoracic temperature at take-off of 123 individuals of the Alpine butterfly species complex Coenonympha arcania – C. macromma – C. gardetta were recorded in controlled conditions. 3. Warming-up rate increased with elevation in C. arcania: high-elevation males of C. arcania were able to warm up more quickly compared to low-elevation ones. 4. High-elevation C. gardetta had a darker underwing pattern than low-elevation ones. This high-elevation species was significantly smaller (lower weight and wing surface) than the two other species and had a faster warming-up rate. 5. This study's results suggest that the ability to warm up quickly and to take flight at a high body temperature evolved adaptively in the high-altitude C. gardetta and that low temperature at high altitude may explain the absence of C. arcania, while the hybrid nature of C. macromma is probably the explanation of its elevation overlap with both the other species and its local replacement of C. gardetta.     

Dispersal in the Glanville fritillary butterfly in fragmented versus continuous landscapes: comparison between three methods

1. Habitat fragmentation may lead to natural selection on dispersal rate and other life‐history traits. Both theoretical analyses and empirical studies suggest that habitat fragmentation may select either for increased or decreased dispersal depending on the traits of the species and the characteristics of the landscape. 2. Dispersal and movement rates in Glanville fritillary butterflies (Melitaea cinxia) originating from a continuous landscape in China and from a highly fragmented landscape in Finland were compared using three different methods. 3. The methods included replicated mark‐release‐recapture (MRR) experiments conducted in the natural environments in China and Finland, tracking with harmonic radar of captive‐reared but free‐flying butterflies in a common environment in the field, and replicated common garden experiments in a large outdoor population cage. 4. The results were largely consistent, showing that butterflies from the more continuous landscape in China had a lower movement rate than butterflies originating from the fragmented landscape in Finland. Butterflies originating from newly‐established populations in Finland moved significantly longer distances than butterflies originating from old populations in Finland or from China, demonstrating significant intra‐specific variation in dispersal rate in Finland. These results are consistent with model predictions for the Glanville fritillary. 5. The tracking experiment revealed a result that would have been impossible to obtain with MRR experiments: movement rate was influenced by a significant interaction between population origin (China vs. Finland) and ambient air temperature.     

Visual ground pattern modulates flight speed of male Oriental fruit moth Grapholita molesta

Insects flying in a horizontal pheromone plume must attend to visual cues to ensure that they make upwind progress. Moreover, it is suggested that flying insects will also modulate their flight speed to maintain a constant retinal angular velocity of terrestrial contrast elements. Evidence from flies and honeybees supports such a hypothesis, although tests with male moths and beetles flying in pheromone plumes are not conclusive. These insects typically fly faster at higher elevations above a high‐contrast ground pattern, as predicted by the hypothesis, although the increase in speed is not sufficient to demonstrate quantitatively that they maintain constant visual angular velocity of the ground pattern. To test this hypothesis more rigorously, the flight speed of male oriental fruit moths (OFM) Grapholita molesta Busck (Lepidoptera: Tortricidae) flying in a sex pheromone plume in a laboratory wind tunnel is measured at various heights (5–40 cm) above patterns of different spatial wavelength (1.8–90°) in the direction of flight. The OFM modulate their flight speed three‐fold over different patterns. They fly fastest when there is no pattern in the tunnel or the contrast elements are too narrow to resolve. When the spatial wavelength of the pattern is sufficiently wide to resolve, moths fly at a speed that tends to maintain a visual contrast frequency of 3.5 ± 3.2 Hz rather than a constant angular velocity, which varies from 57 to 611° s^?1. In addition, for the first time, it is also demonstrated that the width of a contrast pattern perpendicular to the flight direction modulates flight speed.     

Ambient temperature affects free-flight performance in the fruit fly Drosophila melanogaster

To gain insight into how temperature affects locomotor performance in insects, the limits of flight performance have been estimated in freely flying fruit flies Drosophila melanogaster by determining the maximum load that a fly could carry following take-off. At a low ambient temperature of 15 °C, muscle mechanical power output matches the minimum power requirements for hovering flight. Aerodynamic force production rises with increasing temperature and eventually saturates at a flight force that is roughly equal to 2.1 times the body mass. Within the two-fold range of different body sizes, maximum flight force production during free flight does not decrease with decreasing body size as suggested by standard aerodynamic theories. Estimations of flight muscle mechanical power output yields a peak performance of 110 W kg⁻¹ muscle tissue for short-burst flight that was measured at an ambient temperature of 30 °C. With respect to the uncertainties in estimating muscle mechanical power during free flight, the estimated values are similar to those that were published for flight under tethered flight conditions. Accepted: 5 January 1999     

Respiratory water loss during rest and flight in European Starlings (Sturnus vulgaris)

Respiratory water loss in Starlings (Sturnus vulgaris) at rest and during flight at ambient temperatures (T(amb)) between 6 and 25 degrees C was calculated from respiratory airflow and exhaled air temperature. At rest, breathing frequency f (1.4+/-0.3 Hz) and tidal volume Vt (1.9+/-0.4 ml) were independent of T(amb), but negatively correlated with each other. Mean ventilation at rest was 156+/-28 ml min(-1) at all T(amb). Exhaled air temperature (T(exh)) at rest increased with T(amb) (T(exh) = 0.92.T(amb)+12.45). Respiratory water loss at rest averaged 0.18+/-0.09 ml h(-1) irrespective of T(amb). In flying Starlings f was 4.0+/-0.4 Hz and independent of T(amb). Vt during flight averaged 3.6+/-0.4 ml and increased with T(amb) (Vt = 0.06.T(amb)+2.83) as, correspondingly, did ventilation. T(exh) during flight increased with T(amb) (T(exh) = 0.85.T(amb)+17.29). Respiratory water loss during flight (average REWL(f) = 0.74+/-0.22 ml h(-1)) was significantly higher than at rest and increased with T(amb). Our measurements suggest that respiratory evaporation accounts for most water loss in flying Starlings and increases more than cutaneous evaporation with rising ambient temperature.