Variation In Flight Performance Research Articles

Compensation for a costly ornament depends on the development of flight performance in stalk-eyed flies

Several species of stalk-eyed flies exhibit exaggerated sexual dimorphism where females favor males with longer eyespans. Longer eyespan increases a fly’s moment of inertia, and may, therefore, impact flight behavior and fitness, specifically maneuverability and predator evasion. However, these putative costs may be ameliorated by co-selection for compensatory traits, as flies with longer eyespans tend to have larger thoraces and wings, which allows them to perform turns similar to flies with shorter eyespans. Furthermore, the capacity to compensate for a potentially costly ornament may not be fixed across the life-history of the adult stage, as stalk-eyed flies achieve sexual maturity at 3-4 weeks of age, accompanied by significant growth of reproductive tissues and organs. Thus, growth of the abdomen and body mass over time may impose constraints on flight performance that may affect whether an adult reaches the age of reproductive viability. The purpose of this study was to investigate the flight performance of stalk-eyed flies and its relationship to body morphology and development. The flight performance of 1-to-30 day oldTeleopsis dalmanni(n=124) andDiasemopsis meigenii(n=83) were assessed by presenting normoxic, variable-density mixtures of heliox (O2, N2and He) in 10% increments ranging from air to pure heliox; the least-dense gas allowing flight represented maximal performance. Flight kinematics were analyzed using high-speed (5930fps) videography. Immediately following flight assessment, flies were euthanized, photographed, dissected and weighed. In both species, total body mass, thorax and abdominal mass increased across age. Wing kinematics and maximal flight capacity were associated with thorax mass, and increased with age as flies became heavier. Although flies with longer eyespans were indeed heavier, they had larger wings and thoraces; however, maximal flight capacity and kinematics were generally independent of eyespan. Thus, bearing long eye-stalks did not impair flight performance, nor did the increase in mass attributable to reproductive maturation. Instead, variation in flight performance appears associated with the development of the flight motor, and improved ratio of thorax-to-total mass, across age.

Sex-specific effects of wind on the flight decisions of a sexually dimorphic soaring bird.

In a highly dynamic airspace, flying animals are predicted to adjust foraging behaviour to variable wind conditions to minimize movement costs. Sexual size dimorphism is widespread in wild animal populations, and for large soaring birds which rely on favourable winds for energy-efficient flight, differences in morphology, wing loading and associated flight capabilities may lead males and females to respond differently to wind. However, the interaction between wind and sex has not been comprehensively tested. We investigated, in a large sexually dimorphic seabird which predominantly uses dynamic soaring flight, whether flight decisions are modulated to variation in winds over extended foraging trips, and whether males and females differ. Using GPS loggers we tracked 385 incubation foraging trips of wandering albatrosses Diomedea exulans, for which males are c. 20% larger than females, from two major populations (Crozet and South Georgia). Hidden Markov models were used to characterize behavioural states-directed flight, area-restricted search (ARS) and resting-and model the probability of transitioning between states in response to wind speed and relative direction, and sex. Wind speed and relative direction were important predictors of state transitioning. Birds were much more likely to take off (i.e. switch from rest to flight) in stronger headwinds, and as wind speeds increased, to be in directed flight rather than ARS. Males from Crozet but not South Georgia experienced stronger winds than females, and males from both populations were more likely to take-off in windier conditions. Albatrosses appear to deploy an energy-saving strategy by modulating taking-off, their most energetically expensive behaviour, to favourable wind conditions. The behaviour of males, which have higher wing loading requiring faster speeds for gliding flight, was influenced to a greater degree by wind than females. As such, our results indicate that variation in flight performance drives sex differences in time-activity budgets and may lead the sexes to exploit regions with different wind regimes.

Sex, life history and morphology drive individual variation in flight performance of an insect parasitoid

1. The movement of organisms can be driven by multiple factors and has implications for fitness and the spatial distribution of populations. Insects spend a large proportion of their adult lives foraging by flying for resources; however, their capability and motivation to move can vary across individuals.2. The aims of this study were to examine interindividual and sex differences in flight performance and flight characteristics, using a flight mill bioassay, in Megarhyssa nortoni (Hymenoptera; Ichneumonidae), a parasitoid of the invasive woodwasp Sirex noctilio (Hymenoptera: Siricidae), one of the most important pests of pine afforestation worldwide. We also assessed the influence of morphological traits in combination with sex on flight and explored the cost of flight on longevity and mass loss.3. The results show a difference between sexes in flight characteristics and performance. Females show greater total distance flown than males, and have a better capacity to undergo sustained flight. Sexual size dimorphism was also found and it was noted that size positively affects distances travelled. Females have a longer life span than males, yet no differences were noted in longevity within sex between individuals that did not fly and those that flew. Age did not influence flight performance of females or impacted on post‐flight longevity. Females lost less body mass than males even after flying longer distances.4. These results suggest that sex‐specific behaviours probably govern flight abilities together with (and not only because of) morphological traits. The paper discusses sex‐specific life‐history strategies in parasitoids and their implications for biocontrol programmes.

Genomewide transcriptional signatures of migratory flight activity in a globally invasive insect pest.

Migration is a key life history strategy for many animals and requires a suite of behavioural, morphological and physiological adaptations which together form the ‘migratory syndrome’. Genetic variation has been demonstrated for many traits that make up this syndrome, but the underlying genes involved remain elusive. Recent studies investigating migration‐associated genes have focussed on sampling migratory and nonmigratory populations from different geographic locations but have seldom explored phenotypic variation in a migratory trait. Here, we use a novel combination of tethered flight and next‐generation sequencing to determine transcriptomic differences associated with flight activity in a globally invasive moth pest, the cotton bollworm Helicoverpa armigera. By developing a state‐of‐the‐art phenotyping platform, we show that field‐collected H. armigera display continuous variation in flight performance with individuals capable of flying up to 40 km during a single night. Comparative transcriptomics of flight phenotypes drove a gene expression analysis to reveal a suite of expressed candidate genes which are clearly related to physiological adaptations required for long‐distance flight. These include genes important to the mobilization of lipids as flight fuel, the development of flight muscle structure and the regulation of hormones that influence migratory physiology. We conclude that the ability to express this complex set of pathways underlines the remarkable flexibility of facultative insect migrants to respond to deteriorating conditions in the form of migratory flight and, more broadly, the results provide novel insights into the fundamental transcriptional changes required for migration in insects and other taxa.

Bumblebee flight performance in cluttered environments: effects of obstacle orientation, body size and acceleration.

Locomotion through structurally complex environments is fundamental to the life history of most flying animals, and the costs associated with movement through clutter have important consequences for the ecology and evolution of volant taxa. However, few studies have directly investigated how flying animals navigate through cluttered environments, or examined which aspects of flight performance are most critical for this challenging task. Here, we examined how body size, acceleration and obstacle orientation affect the flight of bumblebees in an artificial, cluttered environment. Non-steady flight performance is often predicted to decrease with body size, as a result of a presumed reduction in acceleration capacity, but few empirical tests of this hypothesis have been performed in flying animals. We found that increased body size is associated with impaired flight performance (specifically transit time) in cluttered environments, but not with decreased peak accelerations. In addition, previous studies have shown that flying insects can produce higher accelerations along the lateral body axis, suggesting that if maneuvering is constrained by acceleration capacity, insects should perform better when maneuvering around objects laterally rather than vertically. Our data show that bumblebees do generate higher accelerations in the lateral direction, but we found no difference in their ability to pass through obstacle courses requiring lateral versus vertical maneuvering. In sum, our results suggest that acceleration capacity is not a primary determinant of flight performance in clutter, as is often assumed. Rather than being driven by the scaling of acceleration, we show that the reduced flight performance of larger bees in cluttered environments is driven by the allometry of both path sinuosity and mean flight speed. Specifically, differences in collision-avoidance behavior underlie much of the variation in flight performance across body size, with larger bees negotiating obstacles more cautiously. Thus, our results show that cluttered environments challenge the flight capacity of insects, but in surprising ways that emphasize the importance of behavioral and ecological context for understanding flight performance in complex environments.

Regional and seasonal flight speeds of soaring migrants and the role of weather conditions at hourly and daily scales

Given that soaring birds travel faster with supportive winds or in good thermal soaring conditions, we expect weather conditions en route of migration to explain commonly observed regional and seasonal patterns in the performance of soaring migrants. We used GPS‐loggers to track 13 honey buzzards and four Montagu's harriers for two to six migrations each. We determined how tailwinds, crosswinds, boundary layer height (a proxy for thermal convection) and precipitation affected hourly speeds, daily distances and daily mean speeds with linear regression models. Honey buzzards mostly travel by soaring while Montagu's harriers supplement soaring with flapping. Therefore, we expect that performance of harriers will be less affected by weather than for buzzards. Weather conditions explained between 30 and 50% of variation in migration performance of both species. Tailwind had the largest effect on hourly speeds, daily mean speeds and daily travel distances. Honey buzzards travelled significantly faster and farther, and Montagu's harriers non‐significantly faster, under better convective conditions. Honey buzzards travelled at slower speeds and shorter distances in crosswinds, whereas harriers maintained high speeds in crosswinds. Weather conditions varied between regions and seasons, and this variation accounted for nearly all regional and seasonal variation in flight performance. Hourly performance was higher than predicted at times when we suspect birds had switched to intermittent or continuous flapping flight, for example during sea‐crossings. The daily travel distance of Montagu's harriers was determined to a significant extent by their daily travel time, which differed between regions, possibly also due to weather conditions. We conclude with the implications of our work for studies on migration phenology and we suggest an important role for high‐resolution telemetry in understanding migratory behavior across entire migratory journeys.

Predictive Adaptive Responses: Condition‐Dependent Impact of Adult Nutrition and Flight in the Tropical ButterflyBicyclus anynana

The experience of environmental stress during development can substantially affect an organism's life history. These effects are often mainly negative, but a growing number of studies suggest that under certain environmental conditions early experience of such stress may yield individuals that are less sensitive to environmental stress later on in life. We used the butterfly Bicyclus anynana to study the effects of limited larval and adult food and forced flight on individual performance measured as reproduction and adult life span. Larvae exposed to food stress showed longer development and produced smaller adults. Thus, they were not able to fully compensate for the food deprivation during development. Females that experienced food stress during development did not increase tolerance for adult food limitation. However, females exposed to food stress during development coped better with forced flight compared with the control group. The apparent absence of costs of flight in poor-quality females may be a by-product of an altered body allocation, as females experiencing both food stress treatments had increased thorax ratios, compared with controls, and increased flight performances. The results reveal an important plasticity component to variation in flight performance and suggest that the cost of flight depends on an individual's internal condition.

Identification of Factors Influencing Flight Performance of Field-Collected and Laboratory-Reared, Overwintered, and Nonoverwintered Cactus Moths Fed with Field-Collected Host Plants

Environmental conditions during egg and larval development may influence the dispersal ability of insect pests, thus requiring seasonal adjustment of control strategies. We studied the longest single flight, total distance flown, and the number of flights initiated by wild Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae) to determine whether the flight performance of overwintered cactus moths with a prolonged feeding phase during development differs from nonoverwintered cactus moths. Pupae of field-collected and laboratory-reared moths were transported together from the United States to Switzerland, and flight mills were used to characterize the flight capacity of 24- to 48-h-old adults during their most active period of the diel cycle. The lack of seasonal variation in flight performance of those moths that developed under controlled environment but were fed with field-collected Opuntia cacti showed that seasonal changes in host plant quality did not affect flight. This consistent flight performance in the mass-reared laboratory population throughout the year is beneficial for sterile insect technique programs, which aim to limit the dispersal of this pest. For field-collected C. cactorum, the larger overwintered females performed similarly to nonoverwintered females, indicating that longer feeding time at lower temperature increases body size but does not influence female flight capacity. Young mated females had a similar flight capacity to unmated ones, suggesting that gravid females may play an important role in invading new habitats. For males, overwintering increased the proportion of long-distance flyers, suggesting that they are well-adapted to locate the more sparsely dispersed females in the spring.

Identification of Factors Influencing Flight Performance of Field-Collected and Laboratory-Reared, Overwintered, and Nonoverwintered Cactus Moths Fed with Field-Collected Host Plants

Environmental conditions during egg and larval development may influence the dispersal ability of insect pests, thus requiring seasonal adjustment of control strategies. We studied the longest single flight, total distance flown, and the number of flights initiated by wild Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae) to determine whether the flight performance of overwintered cactus moths with a prolonged feeding phase during development differs from nonoverwintered cactus moths. Pupae of field-collected and laboratory-reared moths were transported together from the United States to Switzerland, and flight mills were used to characterize the flight capacity of 24- to 48-h-old adults during their most active period of the diel cycle. The lack of seasonal variation in flight performance of those moths that developed under controlled environment but were fed with field-collected Opuntia cacti showed that seasonal changes in host plant quality did not affect flight. This consistent flight performance in the mass-reared laboratory population throughout the year is beneficial for sterile insect technique programs, which aim to limit the dispersal of this pest. For field-collected C. cactorum, the larger overwintered females performed similarly to nonoverwintered females, indicating that longer feeding time at lower temperature increases body size but does not influence female flight capacity. Young mated females had a similar flight capacity to unmated ones, suggesting that gravid females may play an important role in invading new habitats. For males, overwintering increased the proportion of long-distance flyers, suggesting that they are well-adapted to locate the more sparsely dispersed females in the spring.

Sex-specific development of avian flight performance under experimentally altered rearing conditions

Numerous studies have examined predation risk resulting from the costs of impaired flight performance associated with many key life-history stages such as reproduction and migration. Interestingly, although avian nestlings experience multiple resourcebased physiological trade-offs and undergo considerable morphological and physiological changes during postnatal development, there is no data available on how nestlings manage the competing demands of growth and the development of flight ability at this critical life-history stage. We examined numerous morphological traits to determine which are responsible for variation in flight performance in juvenile European starlings (Sturnus vulgaris), a sexually size-dimorphic passerine. We then manipulated maternal quality during chick rearing (via feather clipping) to examine sex-specific sensitivity of fledgling flight performance to the quality of the rearing environment. Results suggest that the mechanics underlying variation in juvenile flight performance are relatively simple, being principally determined by the ratio of pectoral muscle mass to body mass (BM) and the surface area of the wings. Interestingly, although the maternal quality manipulation decreased BM and structural size in daughters, only the flight performance of sons was negatively affected. Our results suggest that a survival-related trait can be significantly affected in the larger sex when raised under stressful conditions. Furthermore, measuring only BM and structural size may not be sufficient in understanding how the sexes are affected by stressful rearing conditions in sexually size-dimorphic species. Key words: development, escape performance, european starling, flight ability, predation risk, sexual size dimorphism. [Behav Ecol]

Natural Variation in Flight Performance Is Related to Timing of Breeding in Tree Swallows (Tachycineta bicolor) in New York

Natural Variation in Flight Performance Is Related to Timing of Breeding in Tree Swallows (Tachycineta bicolor) in New York

Natural Variation in Flight Performance is Related to Timing of Breeding in Tree Swallows (Tachycineta Bicolor) in New York

AbstractIn many avian species, including Tree Swallows (Tachycineta bicolor), females that lay eggs earlier in the season have higher fitness. It has been hypothesized that nonheritable variation in individual quality could explain how variation in laying date persists in the face of this apparently directional selection. Previous experimental work on Tree Swallows has suggested that natural variation in flight ability enables early-laying females to attain feeding rates high enough to support egg production on earlier, sparser food than later-laying females. We tested that hypothesis with standardized flights through a 9.75-m flight-performance test tunnel. One group of female swallows was tested at the height of the breeding season on 28 May regardless of their nesting phenology; another group was tested on the 11th day of incubation. Average acceleration in the tunnel was negatively correlated with clutch initiation date for the females tested on 28 May. Daily variation in ambient environmental conditions had strong effects on swallow flight performance in the tunnel, and no relationship was observed in the day-11 birds. Because natural variation in foraging performance is correlated with variation in female Tree Swallows' clutch initiation dates, flight ability appears to be a key element of individual quality in this species.

The ecological and evolutionary interface of hummingbird flight physiology.

The hovering ability, rapidity of maneuvers and upregulated aerobic capacity of hummingbirds have long attracted the interest of flight biologists. The range of intra- and interspecific variation in flight performance among hummingbirds, however, is equally impressive. A dominant theme in hummingbird evolution is progressive invasion of higher-elevation habitats. Hypobaric challenge is met behaviorally through compensatory changes in wingbeat kinematics, particularly in stroke amplitude. Over evolutionary time scales, montane colonization is associated with increases in body mass and relative wing area. Hovering ability has been well-studied in several North American hummingbird taxa, yet the broad range of interspecific variation in hummingbird axial and appendicular anatomy remains to be assessed mechanistically. Such varied features as tail length, molt condition and substantial weight change due to lipid-loading can dramatically alter various features of the flight envelope. Compared with our present knowledge of hovering performance in hummingbirds, the mechanics of forward flight and maneuvers is not well understood. Relationships among flight-related morphology, competitive ability and foraging behavior have been the focus of numerous studies on tropical and temperate hummingbirds. Ecologists have hypothesized that the primary selective agents on hummingbird flight-related morphology are the behaviors involved in floral nectar consumption. However, flight behaviors involved in foraging for insects may also influence the evolution of wing size and shape. Several comparisons of hummingbird communities across elevational gradients suggest that foraging strategies and competitive interactions within and among species vary systematically across elevations as the costs of flight change with body size and wing shape.

Assessing the aerodynamic effects of tail elongations in the house martin ( Delichon urbica ): implications for the initial selection pressures in hirundines

Of the three species of hirundine that breed sympatrically across the U.K., one, the barn swallow, has outer tail feathers elongated into streamers, whereas the other two species, the house martin and the sand martin, do not. The tail streamer of the barn swallow is regarded as a classic example of a sexually selected trait. Recent evidence, however, has suggested that streamers may have evolved largely through natural selection for enhanced flight performance and increased maneuverability. We tested the hypotheses that small streamers (1) increase performance in turning flight, but (2) decrease performance in flight variables related to velocity. We manipulated the lengths of house martin outer tail feathers and measured changes in their free-flight performance, using stereo-video to reconstruct the birds" three-dimensional flight paths. Five flight variables were found to best describe individual variation in flight performance. Of these five, the three variables determining maneuverability predicted that flight performance would be optimized by a 6- to 10-mm increase in the length of the outer tail feathers. In contrast, for mean velocity and mean acceleration, extension of the outer tail feathers appears to have a detrimental effect on flight performance. We suggest that the initial selection pressure for streamers in ancestral short-tailed "barn swallows" was via natural selection for increased maneuverability. In addition, we propose that the benefits of increased maneuverability have differed between hirundines in the past, such that the cost of increasing the length of the outer tail feather has, to date, outweighed the benefits of doing so in streamerless hirundines.

The effect of tail streamer length on aerodynamic performance in the barn swallow

The elongated tail of the male barn swallow (Hirundo rustica) is regarded as one of the classic examples of a male trait exaggerated by female choice. However, recently a hypothesis has been proposed suggesting that the streamers, or elongated outer tail feathers, may aid aerodynamic performance through the Norberg mechanism, providing lift at slow speeds and high angles of attack when the tail is fully spread. The possibility exists that the tail streamer has evolved under natural selection, sexual selection, or a combination of both selection pressures. We tested these three hypotheses by reducing the streamer length of free-flying swallows and measuring their aerodynamic performance, using stereo-video. Measurements of flight performance were made from the digitized three-dimensional flight paths. Five flight variables best described the individual variation in flight performance. Four of these five parameters—mean velocity, mean curvature, maximum agility, and mean rate change of curvature in the XY plane—had significant second-order polynomial relationships with tail streamer manipulation. The first and second principal components (from principal components analysis of the flight variables) also showed similar relationships with streamer manipulation. The combination of a curvilinear relationship between flight performance and streamer length and an aerodynamic optimum between 0 and 20 mm reduction is only predicted if both natural and sexual selection have been acting on streamer morphology. Our data therefore suggest that sexual selection has extended streamer length by around 10 mm beyond its aerodynamic optimum. We suggest that both natural and sexual selection have been important in shaping tail morphology in the barn swallow, and the relative importance of both selection pressures is discussed. Key words: barn swallows, flight performance, Hirundo rustica, maneuverability, natural selection, Norberg mechanism, sexual selection. [Behav Ecol 11: 228–238 (2000)]

Are Rooster Crows Honest Signals of Fighting Ability?

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Diurnal variation in flight performance and hence potential predation risk in small birds

The speed and agility with which small birds can take flight are crucial in determining whether or not they will survive an attack by a predator. Theoretical models of bird flight predict that these aspects of performance will be influenced by variations in body mass; recent influential models of optimal foraging routines and energy storage are based on the resulting assumption that predation risk is mass-dependent. Small birds show slight but very consistent changes in body mass during the course of a day, being lightest at dawn and heaviest at dusk. Here we show for the first time that this natural diurnal variation in mass has a highly significant and disproportionate impact on flight performance: individual zebra finches were over 30% slower at dusk than at dawn, despite being less than 7% heavier. These results are in close agreement with predictions from flight mechanical theory, but the consequent mass-dependent diurnal variation in predation risk is predicted to be far greater than previously thought.

VARIATION IN BODY SIZE AND FLIGHT PERFORMANCE IN MILKWEED BUGS (ONCOPELTUS).

In this paper we report observations on variation in flight performance and body size among tropical, temperate, and island milkweed bugs (Oncopeltus: Hemiptera: Lygaeidae). This is one of a series of papers on life history variation in Oncopeltus; photoperiodism is discussed in Dingle et al. (1980) and size dependent timing of metamorphosis in Blakley and Goodner (1978). Other papers are in preparation. The distribution of these bugs throughout much of the Western Hemisphere (Slater, 1964) allows comparison, both within and among species, of the selective forces acting on life histories. Various species occur in tropical and temperate regions and on islands throughout the Caribbean on milkweeds (Asclepiadaceae) and occasionally on plants of related families. One species, Oncopeltus fasciatus, is a long distance migrant to temperate North America (Dingle, 1968a et seq.), while the remainder are confined to the tropics and subtropics. General discussions of the ecology of these insects may be found in Blakley (1977), Dingle (1968a et seq.), Evans (1979), Ralph (1976, 1977), Root and Chaplin (1976), and Sauer and Feir (1973); a summary is included in Dingle et al. (1980) which also gives collecting sites for the populations discussed here. Migratory physiology is reviewed by Rankin (1978). All species discussed in this paper belong to the subgenus Erythrischius (Slater, 1964). We found that flight performance differed considerably among species and populations of Oncopeltus. Dispersal abilities of insects vary with habitat (Southwood, 1962; Dingle, 1972), and many species occurring in isolated habitats, including islands, are apterous or brachypterous (Carlquist, 1974; Vepsaldinen, 1978). There are, however, only a few studies (e.g., Rose, 1972) which demonstrate that relatively shorter (as opposed to functionless) wings actually lead to reduced flight and none, so far as we know, demonstrating reduced flight in cases where it would be expected, for example, on islands, but where there is no obvious alteration in wing structure. In this report we demonstrate that reduced flight can occur with no apparent changes in wing morphology. Body size has attracted considerable attention from evolutionary biologists. It is easy to measure, and it is associated with a number of other characteristics from life history statistics (Pianka, 1970; Stearns, 1976; Blueweiss et al., 1978) to an array of morphological and physiological traits (summarized by Pyke, 1978). Despite much effort by ecologists and others, however, the adaptive significance of body size is not well understood, and indeed there seems to be no general agreement on the most important selective factors (Pyke, 1978). Body size is also frequently influenced by proximate environmental conditions such as food availability, so that analysis is complex. Regardless of such phenotypic variability, the heritability of body size differences is more often assumed than demonstrated so that their adaptive nature falls short of proof. In this study we demonstrate heritable differences in body size between bugs of island 1 Present address: Institute for Behavioral Genetics, University of Colorado, Boulder, Colorado 80309.