Flight Capability Research Articles

Remex Growth and Body Mass of Mallards during Wing Molt

-We captured, banded (n = 4,129), and weighed (n = 809) Mallards (Anas platyrhynchos) during wing molt in western Poland. The condition of remex development was assessed (n = 3,421). We recaptured and remeasured 248 birds. The rate of remex growth in males (calculated by two methods) was 6.7 and 5.5 mm/day (P < 0.02). Males regained flight capability in 22-29 days, when remiges had reached 75-83% of final length. During the flightless period, males and females lost 12% of body mass. Birds whose flightless period was extended to replace only a few damaged quills continued to decline in body mass, which indicates that rate of mass loss was unrelated to costs of feather synthesis. We conclude that decrease of body mass is related to constraints on foraging time. We think this is a response to high exposure to predation during foraging. Reduction of flightlessness seems to be realized by a high growth rate of remiges, which was almost constant and independent of body mass. Received 24 August 1988, accepted 25 September 1989. LIKE other waterfowl, Mallards shed all their primaries and secondaries simultaneously, and are flightless during the period of wing molt. Flightless birds are more susceptible to predation, and movements are constrained. This situation influences habitat selection, antipredator behavior, foraging, and energy budget. Body mass decreases and body composition changes during flightlessness. Several hypotheses attempt to account for the changes in body mass. Hanson (1962) concluded that remex molt is a period of great nutritional stress for Canada Geese, and birds must catabolize body tissues to build feathers. Ankney (1979) argued that flightless geese can meet their nutrient requirements from the diet, and that maintenance of a superfluous reserve would be a waste of energy. Decreased body mass during molt may be adaptive, because it enabled birds to fly before completing growth of remiges, and this reduced the flightless period (Douthwaite 1976, Dean and Skead 1979, Owen and Ogilvie 1979, Bailey 1985, Austin and Fredrickson 1987, Sjoberg 1988). Young and Boag (1982) suggested that ducks may lose feeding opportunities as a result of secretive behavior. Douthwaite (1976) suggested that reserves accumulated before the molt make birds less vulnerable to food shortages where they would be exposed to predators. These hypotheses are not mutually exclusive, and Pehrsson (1987) suggested that limitation of foraging and use of body reserves minimalize exposure to predation and simultaneously shorten flightlessness. STUDY AREA AND METHODS This study was conducted in the floodplain of the River Warta at its confluence with the Odra River, western Poland (Majewski 1986). Flightless ducks concentrate in willow bushes (Salix spp.) surrounded by shallow water. The number of male Mallards that molt here reaches 25,000, many times greater than the number of local breeders. In 1981-1982 flightless Mallards were surrounded and driven into a net enclosure (Majewski 1981). Birds were banded (3,788 males and 341 females), weighed to the nearest 20 g (640 males and 169 females), and the ninth primary was measured to the nearest 1.0 mm (3,143 males and 278 females). The birds were then released. We recaptured 337 males and 13 females, typically after 3-9 days. Each was remeasured. Because most females were trapped late in the season, there were relatively few recaptures. We calculated the rate of remex growth from differences between lengths of the remiges divided by number of days between capture and recapture of each individual (n = 237). Birds with broken or pulled remiges were excluded, but some damage to remiges might have been overlooked. When caught for the first time, some birds shed their remiges, but regrowth was not yet visible. Recapture of these birds (n = 12) provided remex growth rates from the beginning of feather replacement. The remex length required to resume flight was established from the longest primaries among captured birds. We assumed that birds capable of flying could not be captured. We measured final length of the ninth primary in 18 males and 50 females caught or shot in other seasons. We estimated duration of flightlessness from the growth rate of remiges. Changes in body mass during molt were calculated 255 The Auk 107: 255-259. April 1990 This content downloaded from 207.46.13.101 on Sat, 08 Oct 2016 05:49:11 UTC All use subject to http://about.jstor.org/terms 256 PANEK AND MAJEWSKI [Auk, Vol. 107

Reproduction in the Space Environment

Long-duration space flight and eventual colonization of our solar system will require successful control of reproductive function and a thorough understanding of factors unique to space flight and their impact on gynecologic and obstetric parameters. Part II of this paper examines the specific environmental factors associated with space flight and the implications for human reproduction. Space environmental hazards discussed include radiation, alteration in atmospheric pressure and breathing gas partial pressures, prolonged toxicological exposure, and microgravity. The effects of countermeasures necessary to reduce cardiovascular deconditioning, calcium loss, muscle wasting, and neurovestibular problems are also considered. In addition, the impact of microgravity on male fertility and gamete quality is explored. Due to current constraints, human pregnancy is now contraindicated for space flight. However, a program to explore effective countermeasures to current constraints and develop the required health care delivery capability for extended-duration space flight is suggested. A program of Earth- and space-based research to provide further answers to reproductive questions is suggested.

The flying Africans: extent and strength of the myth in the Americas

[First paragraph]The theme of human aerial flight permeates the mythology of Black America. Examples of the metaphor are found in major musical genres, myths and poetry in Black cultures that span the Caribbean and southern North America, embracing generations to testify to the depth of the cosmological and conscious projection of systems of flight escape and homeland return. While the theme of human flight does not occur in any significant proportion in West African mythology related themes of transformation and pursuit do appear. However, in African thought, witches and spirits possess the power of flight; a flight that can be blocked by the use of salt. The belief in spirit flight, ubiquitous in the Black diaspor of the New World, parallels that in African thought, but in the New World it is enlarged to include humans as possessors of the capability of flight.

Effect of Relative Humidity during Pupal Maturation on Subsequent Adult Eclosion and Flight Capability of the Melon Fly, Dacus cucurbitae COQUILLETT(Diptera : Tephritidae)

Effect of Relative Humidity during Pupal Maturation on Subsequent Adult Eclosion and Flight Capability of the Melon Fly, Dacus cucurbitae COQUILLETT(Diptera : Tephritidae)

Flight Behavior of Listronotus bonariensis (Coleoptera: Curculionidae) in the Waikato, New Zealand

The flight behavior of Listronotus bonariensis (Kuschel) in Waikato (New Zealand) pastures was studied by recording catches on aerial sticky traps and sampling ground populations; this was supported by dissection studies and laboratory experimentation. All flight activity in the field occurred between 25 August and 5 May. Flight phenology and intensity varied greatly between localities and years. Intensity was generally low, although occasional mass flights were observed. Sampled ground populations indicated that only a proportion of the weevils exhibited development of flight musculature and hence flight capability: the proportion of these “flight capable” weevils varied greatly from generation to generation. Field sampling and laboratory experimentation indicated partitioning of reproductive and dispersive effort among individuals in the population. Following emergence, some weevils became reproductive and others developed flight musculature before ovarian development and dispersal. The proportion of weevils in the latter category was highest in the field following peak emergence and was shown by laboratory experimentation to be increased by weevil crowding, particularly on unfavorable host plants. The laboratory experiments also indicated that alleviation of crowding resulted in degeneration of flight musculature and resumption of reproductive activity. Field sampling indicated overwintering in the pastures (summer breeding grounds) and no migration to adjacent potential hibernation sites. These results are discussed in relation to the climate of the Waikato and the dynamics of the populations.

Reproduction in the Space Environment

Long-duration space flight and eventual colonization of our solar system will require successful control of reproductive function and a thorough understanding of factors unique to space flight and their impact on gynecologic and obstetric parameters. Part II of this paper examines the specific environmental factors associated with space flight and the implications for human reproduction. Space environmental hazards discussed include radiation, alteration in atmospheric pressure and breathing gas partial pressures, prolonged toxicological exposure, and microgravity. The effects of countermeasures necessary to reduce cardiovascular deconditioning, calcium loss, muscle wasting, and neurovestibular problems are also considered. In addition, the impact of microgravity on male fertility and gamete quality is explored. Due to current constraints, human pregnancy is now contraindicated for space flight. However, a program to explore effective countermeasures to current constraints and develop the required health care delivery capability for extended-duration space flight is suggested. A program of Earth- and space-based research to provide further answers to reproductive questions is suggested.

Effect of Pinewood Nematode Density on Tethered Flight of Monochamus carolinensis (Coleoptera: Cerambycidae)

Monochamus carolinensis (Olivier) beetles infested with the pinewood nematode, Bursaphelenchus xylophilus , were tethered and flown upon emergence from host logs. The mean (±SD) number of nematodes carried per beetle was 7,933 (±16,997) with a mean flight time of 18.6 (±11.4) min. Larger beetles exhibited longer flights and carried more nematodes. The density of nematodes in the beetle had a slight negative influence on flight capability. The sex of the beetle had no effect on flight duration or the number of nematodes carried.

Reproductive cost of flight capability: a comparison of life history traits in wing dimorphic planthoppers

Abstract. 1. Reproductive costs associated with flight capability were evaluated in the wing dimorphic planthopper, Prokelisia dolus Wilson, by comparing the life history of traits of winged (macropterous) and flightless (brachypterous) females under controlled laboratory conditions.2. Macropters with large thoraces and fully developed wings maintain a greater investment in flight apparatus than brachypters with small thoraces and reduced wings.3. Associated with greater flight capability in the macropter of P.dolus are shorter adult life, decreased total fecundity, and delayed age at first reproduction compared to brachypterous females.4. Under field conditions where mortality is high, the difference in realized fecundity between the two wing forms living on similar resources is further exaggerated with the brachypter having the greater advantage.5. When the life history traits of the wing forms of P. dolus are compared with traits for nine other species of planthoppers, two similarities emerge. First, the preoviposition period of the macropterous wing form is always longer than that for the brachypter resulting in a reproductive delay. Second, most studies show that macropters are less fecund than brachypters.6. There is no general tendency among planthopper species for macropterous adults to live fewer days or develop more slowly as nymphs compared to their flightless counterparts.7. The reproductive delay and reduced fecundity of the volent wing form of planthoppers supports the notion that flight capability is costly and that phenotypic trade‐offs between flight and reproduction exist.

The European Spaceplane Hermes and Future Transportation Systems

AbstractThe way in which the Ariane-S Hermes space transportation system will give Europe an autonomous manned space flight capability is discussed, and the approach taken is outlined in some detail. The possibilities beyond Hermes are reviewed.

Dispersal Patterns of Western Gulls from Southeast Farallon Island

Abstract During 1978-1981 I studied age- and sex-related dispersal and foraging patterns of Western Gulls (Larus occidentalis) that breed on Southeast Farallon Island, California. Most adults were sedentary and foraged primarily on oceanic food during all seasons except autumn, when human refuse was of major importance. Autumn was the only period when adults did not maintain breeding territories, and also the time of primary molt when flight capabilities were reduced. During the breeding season many subadults moved north to areas where oceanic productivity is high. During autumn/winter most moved south to the Gulf of the Farallons/San Francisco Bay Area, where birds ate both oceanic food and refuse. Dispersal patterns of first-year gulls varied markedly between years, apparently as a result of annual differences in oceanic productivity. The consistency of movement patterns of other age classes resulted from an age-related increase in fidelity to foraging locations. This was most pronounced in adults. Most adults dispersed each year to the same site, and minimized competition by reducing concentrations at each location. Males were more sedentary than females, probably because they are responsible for securing and holding breeding territories.

Regulation of Migratory Flight by Juvenile Hormone Mimic and Inhibitor in the Western Corn Rootworm (Coleoptera: Chrysomelidae)

Adult mated and virgin females were dosed with a juvenile hormone (JH) agonist or antagonist to alter their intrinsic levels of juvenoid compounds. Of 468 females tested, 252 flew, and migratory flight behavior was observed in 145 (31%). No migratory flights were undertaken by untreated virgins. Females treated with juvenile hormone mimic (JHM) and inhibitor (AJH) flew both trivial and sustained flights that were significantly longer in duration and distance than those of controls, but age displacement of peak flight activity varied according to treatment and mating status. There seems to be a definitive window of migratory flight activity in the western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, that can be temporally displaced by JHM and AJH treatment. Ovarian development was negatively correlated with migratory flight activity, which substantiates the inverse relationship between flight and reproduction. JH moderates the considerable flight capabilities of the WCR, permitting adaptation of this species to a dynamic, agricultural ecosystem.

Effects of Body Condition on Molting in Mallards

The effects of high and low protein food on molting in penned, wild-strain Mallards (Anas platyrhynchos) from southwestern Sweden were studied in 1979, 1980, and 1985. Body condition, as indicated primarily by lipid deposits, declined during the flightless period. This decline was probably more the result of a strategy to recover flight capability rapidly than the result of stress. By metabolizing stored lipids, birds may be able to seek refuge in habitats offering protection from predators, even if food in such habitats is scarce. During the flightless period, food quality did not affect the growth rate of the primary feathers. But when exposed to low protein food, even after recovering flight capability, birds, especially males, developed shorter wing feathers; this feather shortening may reduce their condition capacity, i.e., their capacity to increase body condition without reducing their flight capacity in late autumn. A lowered condition capacity could lead to decreased survival of the ducks when exposed to severe winter conditions. Female Mallards demonstrated a higher condition capacity than males, which may contribute to the more rapid recovery of female primaries. Since the final length of the primaries is affected by food quality during molting, wing length is probably not a variable suitable for use in a condition index.

F/A-18 Hornet reliability program: status report : Tommy W. Gordon. Proc. a. Reliab. Maintainab. Symp., 228 (1986)

Vespa velutina, also known as the Asian hornet, is considered as an invasive species out of its native zone. In particular, since it preys on honey bees, its recent progression in Europe could soon pose a significant risk to the local apiculture activity. European beekeepers are therefore investigating adapted control strategies, including V. velutina nest destruction. Unfortunately, nest location pinpointing generally follows a manual process which can prove tedious, time-consuming and inaccurate. In this article, we propose the use of a network of micro aerial vehicles featuring autonomous and cooperative flight capabilities. We describe an adapted controlled mobility strategy and detail the design of our Virtual Force Protocol (VFP) which allows a swarm of vehicles to track and follow hornets to their nests, while maintaining connectivity through a wireless multi-hop communication route with a remote ground station used to store applicative data such as hornet trajectory and vehicle telemetry. In order to achieve the mission objectives with a minimum of vehicles, we identify through simulations appropriate value for the key parameters of VFP and discuss the obtained network performance.

The circadian flight activity of Aedes aegypti parasitized with the filarial nematode Brugia pahangi

ABSTRACT. The circadian flight activity of Aedes aegypti L. infected with the filarial parasite Brugia pahangi was recorded for 16 consecutive days using an acoustic actograph. The flight activity of uninfected control mosquitoes in a LD 12:12h regime rose to a maximum 3 days after bloodfeeding, then decreased slightly and remained steady for the duration of the experiment. The flight activity of parasitized mosquitoes was temporarily depressed for 2 days after feeding on a microfilariaemic cat; this was probably caused by the parasites migrating from the midgut to the flight muscles. As parasitic larvae grew within the flight muscles during days 3—6, the daily activity of all mosquitoes returned to control levels. On days 7—8 the activity of mosquitoes parasitized with thirteen or more larvae fell dramatically to approximately 10% of that of the controls; this change coincided with the emergence of the highly‐active infective stage larvae from the flight muscles. The presence of fewer larvae did not impair flight. Because of their reduced flight capability, heavily‐infected mosquitoes probably play little if any part in the transmission of filariasis.

Sexual Differences in the Thermoregulation of Thymelicus Lineola Adults (Lepidoptera: Hesperiidae)

Sexual differences in thermoregulation and activity under different weather conditions were observed in field populations of the European skipper, Thymelicus lineola. The proximal causes of these differences were studied under both field and laboratory conditions and their possible importance for the mating strategy of this species was examined. Males had a longer daily period of activity than did females, which was related to the ability of males to fly in cooler conditions than females. In the laboratory, in the absence of a radiant heat source, both sexes began basking at body temperatures of 19°—25°C. However, males were able to fly at body temperatures 3° lower than females, which we attribute to a lower wing loading in males. Male mass is 42—62% of female mass, while their wing area is 86% of that of females. This difference should theoretically allow males to fly with a lower wingbeat frequency, and hence, at a lower temperature, since wingbeat frequency is temperature dependent. The body temperature of both male and female dead T. lineola pinned in the basking position rose faster and to a higher level than that of individuals pinned in the resting position with the wings folded, when exposed to an artificial radiant heat source. The thoracic temperature of males at equilibrium was °4° higher than that of females, despite their smaller size. Males also had higher heating and cooling rates, particularly of the abdomen, which heated and cooled two to four times faster than the female abdomen. In the field, females spent more time basking than males, yet female and male thoracic temperatures did not differ significantly. However, abdominal temperatures, which were always lower than thoracic temperatures in both sexes, were higher in females than in males. As a result, the difference between thoracic and abdominal temperatures was smaller in females than in males. The greater thorax—abdomen temperature differential in males can be explained by their higher rate of abdominal cooling and lower incidence of basking. We suggest that these sexual differences reflect sexual selection favoring males that have superior flight capability in marginal weather conditions.

Orb-web visibility: the influence of insect flight behaviour and visual physiology on the evolution of web designs within the Araneoidea

Ecological differentiation among spiders that build orb-webs depends on the ability of webs both to absorb the kinetic energy of prey impact and to intercept prey (web visibility). Analyses of Diptera flying near webs show that Drosophila melanogaster Meigen avoids high-fibre-density orb-webs sooner than they avoid low-fibre-density webs. From analyses of the flight potential and visual capabilities of D. melanogaster, Trichoporosopon digitatum (Rondani) and Culex quinquesfasciatus Say, it seems surprising that orb-webs capture any prey at all. The thin diameter and refractive properties of web silks give spider webs a translucent quality that greatly reduces visibility. Web suspension in low- and diffuse-light environments, as well as against visually confused backgrounds, decreases one of the most important visual cues for prey, contrast between the web and its background. Among spiders that capture prey which are characterized by specialized visual and flight capabilities, oscillating webs and three-dimensional webs may enhance web capture effectiveness. Web oscillation and the static distortion of the plane of some orb-webs allow webs to ‘escape’ from the range of visual resolution of potential prey.

The All-Electric Fighter Airplane Flight Control Issues, Capabilities, and Projections

The prime issues raised in any all-electric airplane discussion are (1) is the electric power system as reliable and trustworthy as a hydraulic power system; (2) can electromechanical flight control actuators perform satisfactorily, i.e., can the performance match that of hydraulic actuators; (3) can redundant electromechanical actuation systems (EMAS) be designed to equal the flight safety reliability of dual tandem hydraulic actuators; and (4) can satisfactory solutions be found or developed for dissipating the heat generated in actuators and power controllers. The first question should be inconsequential since it is assumed that the all-electric aircraft will be equipped with a fly-by-wire (FBW) flight control system (FCS) which is already dependent upon an uninterrupted supply of electrical power. Design studies and hardware already developed show that the answer to question (2) is that EMAS outperform hydraulic actuators, particularly under load. The answer to question (3) is not as clear primarily because the issue has not been addressed in any depth. As posed the answer must be yes, but with the proviso that the weight might be greater than currently predicted. Studies have shown that we can cope with the heat dissipation issue addressed in question (4) in the case of motors and inverter/power controllers. The projections regarding usage of EMAS and the future of the all-electric airplane must be based on the type of vehicle (small subsonic transport, large transport, or military tighter) and the economics involved.

The flight maintenance mechanism in the cockroachPeriplaneta americana L.

1. In order to find the receptors that maintained flight in the cockroachPeriplaneta americana a wind tunnel was used (Fig. 1A). 2. After removal of the antennal flagella prolonged flight was not possible. However, sticking of cut antenna restored flight capability (Table 2a, b). These data showed that for maintenance of cockroach flight antennal flagella were needed as levers acting on pedicel receptors: chordotonal sensilla (including the chordotonal sensilla of Johnston's organ) and sensilla campaniformia. 3. In the laminar airstream passive antennal vibration caused by the wing motor activity was absent and the observed antennal movements in flight were evoked only by antennal muscle activity. Fixation of active antennal movements by immobilization the head-scapus and scapus-pedicel joints leads to cessation of flight. Therefore, pedicel receptors are capable to maintain the cockroach flight only if active antennal movements in the airstream are present. 4. The frequency of active antennal movements with amplitude of more than 1 mm is in the cause of 3–10 Hz (Fig. 3B). Each of these active movements like at instantaneous cessation of\(\bar 1\)1 and\(\overline 1 \overline 1 \)1 antennal joints evoked lash (passive deflection) of its flagellum relatively to the pedicel. To estimate low-amplitude passive deflexions which are defined by high-amplitude active movements due to the inertia, ‘sail-property’ and weight of the flagellum a mathematical model was developed. This model describes the displacements of the cockroach flagellum which are evoked by the active movements in the airstream of different velocity. 5. The application of the constructed mathematical model showed that at active antennal movements in the air current velocity of 1.5–2 m/s (minimum velocity at which the cockroach flight was possible) the angle determined by the flagellum weight (its ‘sagging’) was compensated and the angle of flagellum displacement relative to the pedicel at the active movements upward was increased by 1.5–2 times as compared with the same angles at the same antennal movements in still air (Fig. 4). It seems clear that just the redistribution of the load on the pedicel receptors was that mechanical stimulus which periodically acting with frequency of active antennal movements of 3–10 Hz led to alterate the mosaic of excitation of differently located in pedicel chordotonal and campaniform sensilla (functional asymmetry of the system of pedicel receptors) and ultimate maintenance of prolonged flight. 6. Microelectrode recording of electrical activity of the pedicel sensilla showed that three functional types of receptors (phasic-tonic receptors with slow and incomplete adaptation, phasic-tonic receptors with fast and complete adaptation and phasic receptors) were revealed. These receptors perceived the changes in amplitude (starting from 20–30 μm), the frequency (up to 50 Hz, Fig. 6), the flagellum movement velocity as well as they had directional sensitivity. (The sector of the maximal sensitivity was 90–135° in most receptors.) Thus, redistribution of the load in flight from the ventral to dorsal side of the pedicel evoked electrical activity of a definite group of receptors. The sectors of maximal sensitivity of these receptors were dorsally orientated. 7. The pedicel mechanoreceptors' responses in the cockroach head ganglia went over into the descending interneurons of three functional types including the phasic-tonic type with slow incomplete adaptation, the phasic-tonic type with fast and complete adaptation and phasic interneurons. In the cockroach brain the chiasma of the nervous tracts provides receiving the information about the flagellum deflexion to the left and right sides of the prothoracic ganglia. Interneurons were not able to respond for a long time to flagellum vibration, if its frequency exceeded 10 Hz (Fig. 8). Thus, it was evident that electrical activity maintaining the cockroach flight consisted of the impulse bursts of the pedicel receptors and related interneurons at each deflection of the flagellum with regard to the pedicel at the active antennal movements in the air current.

Spontaneous, field tested and tethered flight in healthy and infected Magicicada septendecim L.

Flight capabilities of healthy and fungus infected Magicicada septendecim L. (Homoptera: Cicadidae) were compared using 3 complementary techniques: 1) observations of spontaneous flights, 2) field-tested flights, and 3) tethered flights in which endurance was measured. Spontaneous flight distances are much lower than those obtained on field tested fliers. While healthy individuals flew significantly greater distances than did individuals bearing conidia or resting spores of the fungus, Massospora cicadina Peck, the two groups-healthy versus conidia and resting spores pooled-did not differ in flight speed or flight endurance. The magnitude of each of the 3 flight indicators is much lower than those of most dispersing insects, suggesting that this periodical cicada species is a relatively poor disperser.Nevertheless, and contrary to the results of one published study, cicadas flew long distances in single flights, also they often took many flights. Our data help to explain how periodical cicadas can invade new, sometimes distant, habitat each generation. Since infected individuals have both the speed and the endurance of healthy individuals, we conclude that the conspicuous absence of the fungus from early successional, manmade, and second growth habitat is due either to the inability of resting spores of this fungus to survive in recently plowed or fertilized soils or to an intrinsic aversion to flight of infected individuals.

Effects of Duration and Intensity of Sifting Pupae of Various Ages on Adult Eclosion and Flight Capability of the Mediterranean Fruit Fly (Diptera: Tephritidae)

Laboratory-reared pupae of Ceratitis capitata (Wiedemann) (medfly), held at 21.1°C, were agitated at intensities of 10 to 50 rpm for various time periods in a simulated rotary sifting device at 3, 4, 5, 6, 7, and 11 days of age, and subsequent effects on adult eclosion and flight capability were determined. Eclosion rates decreased with increasing agitation intensity or duration, and the rates of decrease were nearly similar for 3- to 7-day-old pupae, but less for 11-day-old pupae. The occurrence of nonfliers also increased as the intensity and duration of agitation were increased, but there were differences in sensitivity among ages, with 5-day-old pupae being most sensitive, followed by 4-,3-, and 6-day-old pupae, whereas 7- and 11-day-old pupae were unaffected. The production of nonflying medflies depends upon the intensity and duration of the agitation, but only during the critical period of development.