Low Wing Loading Research Articles

Morphological Divergence in an Insular Bat, Lasiurus cinereus semotus

1. Bats are the only terrestrial mammals to have reached isolated oceanic islands without human assistance. Despite the fact that the greatest evolutionary divergence would be expected on such islands, very few studies on the divergence of oceanic island fauna from their mainland counterparts have focused on bats. This study investigated divergence of the insular Hawaiian Hoary Bat, Lasiurus cinereus semotus, from its North American subspecies, L. c. cinereus. 2. Divergence in the Hawaiian Hoary Bat involved characters related to flight and feeding. 3. The Hawaiian bat has undergone a 45% reduction in body size with allometric responses in the size of its wings. These changes resulted in a combination of low wing loading (ratio of weight to wing area) with relatively long, narrow wings. The low wing loading permits slower and more manoeuvrable flight near vegetation, while the relatively long, narrow wings enable enduring flight in open areas. This increased flexibility in flight behaviour has allowed the Hawaiian bat to expand its foraging habitat to include open habitats similar to those of L. c. cinereus, and closed habitats that are not used by L. c. cinereus. 4. Divergence in characters related to feeding involved relative increases in size of the gape, size of the masseter muscle and the height of the coronoid process. These changes give the jaw more crushing power for more efficient processing of large and hard-bodied prey. This has enabled the Hawaiian bat to include large, and hard-bodied insects (not taken by L. c. cinereus) in its diet despite a marked reduction in body size.

Size-specific resource use in juvenile little brown bats, Myotis lucifugus (Chiroptera: Vespertilionidae): Is there an ontogenetic shift?

This paper correlates shifts in habitat use and diet with morphological transitions occurring during postpartum growth and development (ontogenetic niche) in little brown bats, Myotis lucifugus. Juveniles were captured in mist nets as they foraged in different microhabitats that were defined and quantified using "clutter indices" ranging from 0 (least cluttered) to 5 (most cluttered). I analyzed fecal samples from captured individuals to assess diet. Chi-squared analyses showed that there was a significant difference in habitat use and diet among juveniles captured in early, mid, and late July. Juveniles with smaller wings foraged in the least cluttered habitats, whereas juveniles with larger wings foraged in habitats with a high degree of clutter. Juveniles with larger wings were captured in all microhabitats, whereas those with smaller wings were captured predominantly in open microhabitats. Juveniles with relatively higher aspect ratios and lower wing loadings used a greater diversity of habitats than those with lower aspect ratios and higher wing loadings. In addition, differences in diet were significant and correlated with wing size. My results suggest resource partitioning between juveniles as a function of wing size. These data have important implications regarding how relative size among juveniles may effect intraspecific structuring of populations.

Wing Shape in Insectivorous Passerines Inhabiting New Guinea and Australian Rain Forests and Eucalypt Forest/Eucalypt Woodlands

AssTAcr.-Based on museum skins of 47 bird species in 17 genera, I evaluated the suppositions for members of various taxonomic groups in New Guinea and Australian rain forest compared to open eucalypt forest/eucalypt woodland that in rain forest birds compared to eucalypt forest/eucalypt woodland counterparts in each group: (1) outer primary 9 tends to be proportionately shorter; (2) secondary 1 is proportionally longer; and (3) the longest primary is more proximally placed relative to the body in its series. The postulations are largely confirmed. The results are presaged by the findings of earlier writers that species operating in confined spaces should have broad wings with rounded tips, with low wing loading conferring high manoeuvrability, and that distance flyers should have wings with long wingspans and pointed tips for economy of effort. Received 1 April 1993, accepted 4 September 1994. WHEN MEASURING SKINS of New Guinea and Australian tropical rain-forest insectivorous passerines, and eucalypt forest/woodland counterparts, I found regularly occurring differences in wing form. The former tended to have more rounded wings, with the outer primary 9 relatively short, while the longest primary in the series was placed more proximally than the others in its series relative to the body in the rain-forest species. Examples were found in foliage-gleaning warblers (Gerygone), whistlers (Pachycephala), ground-feeding robins, and several other groups, suggesting that a general habitat adaptation was operating, as has been shown for several body structures by Winkler and Leisler (1992). In this paper, I quantitatively explored this observation and postulated connection in a diverse set of ecomorphological types of birds. An early paper by Savile (1957) documented the occurrence of two alternative wing types in small birds-elliptical wings found in birds that lived in confined spaces, and wings characteristic of species that remain in the air for long periods. In the former group the wing is curved to increase negative pressure and, hence, lift above, with slotting of the tips serving to minimize turbulence and ensure uniform pressure over the entire surface. The result is high lift, as well as good control and manoeuvrability. By contrast, the high-speed wing has a lower camber, a slender tapering tip, a sweepback of the leading edge, and a short chord. These features reduce drag and conserve power.

The Ducted Tip—A Hydrofoil Tip Geometry With Superior Cavitation Performance

A novel hydrofoil design, consisting of a small diameter flow-through duct affixed to the tip, has been studied. The tip vortex cavitation inception index, σi, of this hydrofoil geometry is about a factor of 2 lower than that of a conventional rounded hydrofoil tip. This inception improvement comes with little associated performance penalty. For angles of attack greater than 8 deg the noncavitating lift-drag ratio is actually superior to that of an unducted hydrofoil of equal span, although with lower wing loadings the hydrofoil performance is diminished by application of the ducted tip. The ducted tip is effective at reducing the tip vortex inception index because, in contrast with the rounded tip, for which vorticity in the Trefftz plane is confined to a line, the ducted tip shed vorticity at the trailing edge is distributed over a line and circle. Distributing the vorticity in this fashion causes the trailing vortex to roll up less tightly, and hence have a higher core pressure and lower σi, than a conventional hydrofoil tip. It is also suspected that the interaction at the microscale level between the flow through the duct, and the flow around it, makes the vortex core size larger, and therefore σi smaller. The ducted tip design has many potential marine applications, including to ship and submarine propellers, submarine control fins, and ship rudders.

Evolutionary adaptation of contractile performance in muscle of ectothermic winter-flying moths

The temperature-sensitivity of muscle performance in a winter-flying ecotothermic moth (Operophtera bruceata) was examined and compared with that of a summer-flying endothermic hawkmoth (Manduca sexta). O. bruceata muscle contracted over a temperature range of 1­28 °C, whereas M. sexta muscle contracted at temperatures of 13­42.5 °C. Maximum (unloaded) contraction velocity (Vmax) was greater in O. bruceata over most of the range of temperatures where muscle from both species was excitable (3­4 lengths s-1 versus 0.6­3.6 lengths s-1 at 13­28 °C), but M. sexta muscle achieved a much higher Vmax at the temperature that this species maintains during flight (10 lengths s-1 at 40­42.5 °C). The capacity of O. bruceata muscle to generate tension was approximately twice that of M. sexta muscle (peak tetanic tension of 13.9 versus 7.0 N cm-2). This greater force-generating capacity in O. bruceata largely offset its lower shortening velocity, such that maximum instantaneous power output was equivalent in both species at temperatures below 35 °C (approximately 100­120 W kg-1). M. sexta muscle achieved instantaneous power outputs of up to 202 W kg-1 at temperatures of 40­42.5 °C. Muscle activation and deactivation (measured by times to peak tension and to half-relaxation during isometric twitches) were most rapid for O. bruceata at temperatures of 15­30 °C and for M. sexta at temperatures of 30­40 °C. Data for power output of flight muscle from these moths are combined with estimates of induced power required for flight in order to show how adaptations for thermal sensitivity of muscle power output interact with morphology (low wing-loading, high flight muscle ratio) to allow O. bruceata moths to fly at extremely low body temperatures, and to construct a model showing how the fecundity of flightless O. bruceata females would decline if they were to regain the ability to fly. Marginal flight over a narrow range of temperatures for O. bruceata females would require a 17 % reduction in fecundity; to fly over as large a range of temperatures as do males would require an 82 % reduction in fecundity.

Guild Organisation and Morphology of High-Altitude Granivorous and Insectivorous Birds: Convergent Evolution in an Extreme Environment

This study was conducted in high-altitude alpine habitats of the Central Himalayas of Nepal. We studied altitudinal distribution, species diversity, niche segregation and morphology of members of two different guilds: granivorous and insectivorous song-birds, belonging to two phylogenetically distant tribes: cardueline finches and turdid chats. We test for convergences in general guild organisation, in niche differentiation patterns and in patterns of morphological change related to habitat, i.e. we tried to assess evolutionary convergence by comparing patterns of radiation within genera or similarly closely-related taxa of different groups within the same environment. Our data suggest convergence in guild properties at different levels from species diversity over niche segregation patterns to morphological traits. Firstly, species of both guilds were similarly arrayed with similar species diversity along the major habitat gradients from the lower alpine zone to the nival zone. Secondly, there were clear directional patterns of morphological change among unrelated genera in insectivorous and granivorous species. Species which occupied the highest altitude open areas were heavier, had longer and more pointed wings with lower wing loading, and longer claws than their lower altitude equivalents. In contrast, shrub-dwelling and ground-dwelling species utilising boulder fields and the understorey of alpine dwarf shrubs, tended to have longer tarsi and longer toes. Thirdly, convergence in general phenotype was expressed by overall morphological Euclidean distances (20 characters used), which, in several cases, were lowest between species pairs with distinct phylogenetic histories but with similar microhabitats. In particular, high-altitude species were less distant to other high-altitude species of different and similar ancestry and more distant to shrub species and vice versa. The among-guild convergences can be functionally linked to specific constraints imposed by habitat configurations and resource situations of the single tractions of the alpine habitat gradient. We therefore conclude that under the extreme alpine environmental conditions only a limited number of adaptive solutions are possible which fostered the observed patterns of convergence

How Convergent Is the American Redstart (Setophaga ruticilla, Parulinae) with Flycatchers (Tyrannidae) in Morphology and Feeding Behavior?

ABsTRAcr.-Possible convergence between the unique aerial-feeding American Redstart (Setophaga ruticilla) and the tyrannid flycatchers was considered using skeleton, external morphology, substrate use, and locomotory feeding movements. The redstart is a typical paruline in the broader functional units of forelimb, hindlimb, and body axis, as well as in proportionate lengths of the main axial elements of both the forelimb and hindlimb. It retains and utilizes the advantageous features of the wood-warblers, including the capacity to hop rapidly through the vegetation. To this it has added the long and broad bill, and long rictal bristes (adaptations for aerial feeding) of the tyrannids. The wing shape remains woodwarblerlike, but it is convergent with the flycatchers in its low wing loading. The tail is long, as in the flycatchers, for better aerial control, but is spread and, apparently, used to flush insects from vegetation, as in the specialized Australo-Papuan fantails (Rhipidura). The redstart is a unique adaptive and ecomorphological type among north American passerines. Received 30 March 1993, accepted 19 August 1993.

How a Long Tail and Changes in Mass and Wing Shape Affect the Cost for Flight in Animals

1. Relationships between foraging strategy, flight performance and wing shape in animals can be demonstrated with the use of aerodynamic theory. The optimal morphology is dictated not only by foraging behaviour and habitat selection but also by size of prey and migratory habits, as well as flight display. Here I demonstrate how changes in body size and structure of wings and tail affect the optimal flight speeds and power required to fly. 2. Long-tailed birds flying with their tails hanging downwards-backwards (e. g. widowbirds) are predicted to fly more slowly than short-tailed birds to save energy or to have larger wings (broader and/or longer wings giving lower wing loading) to compensate for increased tail drag during flight. Assuming that the tail length is five times as long in a long-tailed bird than in a short-tailed (normal) one, the minimum power and maximum range power would be about 30% higher in the long-tailed bird and the corresponding speeds about 40% slower. Ignoring wing inertial loads as a cost (inertial power) the corresponding percentages would become 16-18% higher powers and slower speeds. 3. I predict that members of a bird family that display in hovering or vertical take-off flights should not have elongated wings if wing inertia is important. In contrast to most other widowbird species, males of Jackson's widowbird (Euplectes jacksoni) do not have elongated wings (Anderson 1992), although they have particularly costly tails (Thomas 1993). This species has abandoned forward flight display and instead uses a vertical take-off and hovering flight display. Inertial costs appear to explain this result. 4. An increase in weight causes an increase in wing loading, which in turn requires higher flight speed for production of enough lift. A 50% increase in body mass (as fat, an egg or a fetus inside the body), would increase P mr and P mp by about 45-50% and V mr and V mp by about 20-25% (symbols defined in Fig. 1), when inertial power is taken to be zero. 5. A bird or bat carrying prey in the beak/mouth or claws should use about the same speed for minimization of flight costs as when flying without prey. 6. For low flight costs, and assuming a perfect elastic storage (zero inertial power), fast-flying species should benefit from short, narrow, high-aspect-ratio wings, hovering species should have long wings and slow-flying species should have larger wings (lower wing loadings) but with no particular demands on the aspect ratio. Ignoring inertial power the best flight economy is attained by the combination of a low wing loading (enabling slow flight) and high aspect ratio (Norberg & Rayner 1987; Norberg 1990). If we assume that inertial power is an important cost in hovering, a hovering animal should have short wings to minimize mechanical power

Test of the adaptiveness of sex ratio manipulation in a parasitoid wasp

In behavioral ecology it is generally assumed that behavior is adaptive. This assumption is tested here for sex ratio manipulation in response to host size in the parasitoid wasp Spalangia cameroni. Females produce a greater proportion of daughters on larger hosts. If this behavior is adaptive, it is not through a positive effect of host size on the fitness of daughters, as theory suggests and as found for other species. Females that developed on larger hosts were not more successful at drilling into hosts, were not more successful at interspecific competition for hosts, and did not have greater dispersal ability as measured by wing loading (weight/area of wing and thorax). The possibility that S. cameroni's sex ratio manipulation may be adaptive through a negative effect of host size on the fitness of sons cannot be ruled out. Relative to males from larger hosts, males from smaller hosts had lower wing loading and thus potentially greater dispersal ability. The actual effect of wing loading on fitness remains to be tested.

Seed Size and Dispersal Potential of Acer rubrum (Aceraceae) Samaras Produced by Populations in Early and Late Successional Environments

In order to determine if red maple dispersal potential or seed size change during secondary succession, samaras were collected from five populations located in early successional environments and five populations located in late successional environments. Wing loading ratios (samara mass—mg/samara area—cm2), which are inversely proportional to dispersal ability, were computed for all samaras, and seeds were excised from each samara and weighed. Samaras from the early successional red maples showed slightly but significantly lower wing loading ratios than those from the late successional environments. This result corresponds with the conclusions reached by several theoretical investigations of seed dispersal evolution that predict that recently founded populations will show greater dispersal abilities than more established populations. The earlier successional populations had slightly heavier seeds than the later successional populations, which suggests that the changes in community composition and dynamics that occur during this successional sequence do not select for heavier seeds in older red maple populations. Coefficients of variation for wing loading and seed size showed no consistent trends with successional stage, which indicates that variation in these characters does not decrease as succession proceeds.

Seed size and dispersal potential of Acer rubrum (Aceraceae) samaras produced by populations in early and late successional environments

In order to determine if red maple dispersal potential or seed size change during secondary succession, samaras were collected from five populations located in early successional environments and five populations located in late successional environments. Wing loading ratios (samara mass—mg/samara area—cm2), which are inversely proportional to dispersal ability, were computed for all samaras, and seeds were excised from each samara and weighed. Samaras from the early successional red maples showed slightly but significantly lower wing loading ratios than those from the late successional environments. This result corresponds with the conclusions reached by several theoretical investigations of seed dispersal evolution that predict that recently founded populations will show greater dispersal abilities than more established populations. The earlier successional populations had slightly heavier seeds than the later successional populations, which suggests that the changes in community composition and dynamics that occur during this successional sequence do not select for heavier seeds in older red maple populations. Coefficients of variation for wing loading and seed size showed no consistent trends with successional stage, which indicates that variation in these characters does not decrease as succession proceeds.

Differences in the Diets of Juvenile and Adult Hoary Bats, Lasiurus cinereus

The diets of hoary bats ( Lasiurus cinereus ) within the first 2 weeks post-fledging were studied by means of fecal analysis. Results were compared to the diet of adult hoary bats within the same area. Juvenile bats consumed significantly fewer Odonata than did adults. Chironomidae (Diptera) were the major contributor to the diet of juveniles during the 1st week of flight, but were a negligible component in the diet of older juveniles or adults. Due to a lack of experience, juveniles likely have poor handling skills of larger insects. However, lower wing loading and greater maneuverability may make small prey more available to juveniles.

Echolocation, flight morphology and foraging strategies of some West African hipposiderid bats

We studied echolocation call structure, flight morphology and feeding behaviour of three hipposiderid bats (Asellia tridens, Hipposideros caffer and H. ruber: Chiroptera: Hipposideridae) in The Gambia during the wet season (July‐August). All three species emitted brief CF/FM echolocation calls. In A. tridens CF (constant frequency) frequencies between 108 and 122 kHz were recorded. This variation was caused mainly by sex and age difference in call frequencies: juveniles used lower frequencies than did adults, and males were lower in frequency than females. Among adults, CF frequency was related to forearm length in a polynomial manner. Asellia tridens is unusual for a microchiropteran in that males are larger than females: nevertheless this species follows the typical trend for bats using CF components in their calls in that males call at lower frequencies than do females. The spread in frequencies noted for A. tridens in group flight was not caused primarily by individual shifting their frequencies when flying in a group compared with when flying alone. Three bats were flown separately and then together in a small room. The hypothesis that bats shift emitted frequencies in group flight to minimize confusing their own echoes with those from conspecifies was not supported. Rather, we suggest each bat has a personal CF frequency determined by sex, age and size, and that the variation created by these factors reduces confusion with other bats' echoes during group flight. Bats of the genus Hipposideros were separated into two groups by discriminant analysis on flight morphology. The two groups showed little overlap of CF frequencies used in echolocation. Bats identified as H. ruber called with CF resting frequencies between 121 and 136 kHz, while H. caffer used 128–153 kHz. Our results support the classification of these bats into two sibling species. We compared the flight performance of A. tridens and H. ruber by flying bats through obstacle courses: H. ruber had a lower wing loading and was able to negotiate more complex arrays of obstacles than could A. tridens. In the wild, H. ruber fed in more cluttered situations than did A. tridens. Both species were feeding mainly on Coleoptera during the study period, and in H. ruber individuals with higher aspect ratios and longer wingspans tended to eat more months than did bats with broader and shorter wings.

The invasive potential of Australian banksias in South African fynbos: A comparison of the reproductive potential ofBanksia ericifoliaandLeucadendron laureolum

AbstractSeveral taxa of the Australian Proteaceae have invaded South African fynbos and require costly management programmes to bring under control.Banksiaspp. have been introduced only recently to fynbos regions. The invasive potential ofBanksia ericifolia(Proteaceae) was investigated by comparing its recruitment potential with that of an indigenous proteaceous shrub,Leucadendron laureolum. Both species are overstorey shrubs that are killed by fire and rely on canopy‐stored seeds (serotiny) for recruitment. Eight year oldB. ericifoliashrubs produced an average of 16 500 seeds per plant, which is thirty times more than the average of 570 seeds produced by 10 year oldL. laureolumshrubs. The seed bank ofB. ericifoliawas not only larger than that ofL. laureolum(1098 vs 525 viable seeds m−2projected canopy cover), but also considerably larger than that described for the species in its native environment (200–330 seeds m−2in a 9 year old stand north of Sydney).Leucadendron laureoleumreleased most of its seed a few days after the cones were burnt, whereas seed release inB. ericifoliawas spread over 12 weeks. The seeds ofB. ericifoliahad lower wingloading and fall rates thanL. laureolumand were dispersed over greater distances. The relative seedling growth rates of the two species were very similar (0.03 g per day), but below‐ground biomass was greater and proteoid roots were more developed inB. ericifoliaseedlings than inL. laureolumafter 100 days. Four year oldB. ericifoliaplants growing in the field had attained over twice the height of indigenous pro‐teoids and accumulated up to 10 times the fresh biomass ofL. xanthoconus, a species which is ecologically similar toL. laureolum. The Bioclimatic Prediction System (BIOCLIM) was used to create a bioclimatic profile ofB. ericifoliaand identify climatically suitable areas in the Cape Province. Results show that its potential distribution covers most fynbos areas in the southwestern Cape. It is concluded thatB. ericifoliahas the potential to be highly invasive in fynbos.

Ecomorphology of Insectivorous Bats: A Test of Predictions Using Two Morphologically Similar Species

Wing morphology and echolocation call design have been used to make predictions regarding habitat—use and resource partitioning in insectivorous bats. Species with very different morphologies and/or calls forage in different habitats or in different ways. However, bat communities contain many morphologically similar species, which would be predicted to overlap ecologically. We tested the reliability of such predictions and assumptions by investigating the habitat use and diet of two similar species, the little brown bat (Myotis lucifugus) and the long—legged bat (Myotis volans), in southern Alberta, Canada. We recorded the echolocation calls of free—flying individuals and measured wing morphology. The echolocation calls of the two species overlapped in design, although on average the calls of M. volans were shorter and had higher maximum frequency than those of M. lucifugus. Both species had low wing loading and aspect ratio although M. lucifugus had significantly higher values than did M. volans and was thus expected to forage in areas with less environmental clutter. Field observations did not substantiate this, however. We assessed the foraging ecology of the bats by: (1) monitoring species—specific echolocation calls of free—flying individuals, (2) capturing bats in mist—nets set in various habitats, (3) observing the foraging behavior of light—tagged individuals, and (4) assessing the diet from fecal samples. There was no evidence of temporal partitioning of resources by the two species, but some spatial partitioning occurred. Although individuals of both species generally fed in open areas, M. lucifugus foraged primarily low over water while M. volans fed high above the ground and along cliff edges. Neither fed consistently in cluttered areas despite wing and echolocation call designs that should permit such behavior. Despite the overlap in foraging areas, the diets of the two species differed significantly. Myotis volans ate primarily lepidopterans while M. lucifugus ate a wider variety of prey, including dipterans, lepidopterans, and coleopterans. Our results suggest that there are several levels at which morphology influences the ecology of insectivorous bats. Large differences may influence foraging—habitat choice by restricting some species to certain habitats. At another level, however, we suggest that small differences influence prey availability rather than habitat availability. Bats may select habitats based on the distribution of suitable prey rather than due to direct limitations imposed by morphology or echolocation call design.

Influence of wing and tail morphology on the duration of song flight in skylarks

Song flight, which is an aerial song display especially used by many open country bird species, is expected to be energetically very costly. Any morphological adaptation reducing the magnitude of this cost thus would be favored by selection. Male skylarks Alauda arvensis perform frequent song flights during a period of nearly half the year. Skylarks are sexually size dimorphic in most body traits, but particularly in wing area and wing span, which is absolutely and relatively larger in males than in females. Wing loadings, aspect ratios, and flight costs therefore are smaller in males than in females. I investigated the effect of wing area and aspect ratio on the duration of the song flights of individual birds by timing their duration before and after an experimental manipulation of wing area. Male skylarks were caught, ringed, and released (control I), had the tips of their wing feathers cut (control II), or had the tips of their wing feathers reduced by approximately 10 mm. There were no statistically significant differences in morphology or duration of songs between treatment groups before experimental treatments. However, males having the tips of their wing feathers reduced by ca. 10 mm performed only greatly abbreviated song flights. Original wing loading and aspect ratio also affected the duration of song flights, since male skylarks with low wing loadings and high aspect ratios performed longer song flights than did males with high wing loadings and low aspect ratios. This was the case both before and after experimental treatment. Wing area is suggested to reflect the ability of individual skylarks to invest in morphological structures allowing an increased song output.

Aeroelastic characteristics of a highly flexible aircraft

This paper describes an aeroelastic analysis performed on a human-powered aircraft. The structural characteristics of this aircraft (namely, very flexible wings, high aspect ratio, and low wing loadings) are typical of proposed high-altitude long-endurance aircraft. Because of these unique features, the aircraft exhibits uncommon aeroelastic characteristics. The structural dynamics of the airplane are obtained from a finite element model. In an assumed mode approach, a subset of the natural mode shapes is used to calculate the quasisteady and unsteady generalized modal forces using a two-dimensional strip model, which includes unsteady drag and leading-edge suction forces. The aeroelastic model predicts the airplane to be stable (at both sea level and high altitude), except for a mildly unstable phugoid mode. The results indicate that unsteady aerodynamics are significant for this type of aircraft and that the flexibility of the aircraft must be included to correctly model the dynamics for control purposes. A final conclusion is that the aircraft dynamics are highly dependent on the flight conditions (flight speed and altitude). d,D e J k,K Nomenclature = area of span station i • parasite drag coefficient = slope of lift curve = aerodynamic moment about the aerodynamic center at zero angle of attack = half chord (ct/2) at span station i - damping, damping matrix = Oswald's efficiency factor

Sex and Age Dimorphism in the Barn Owl and a Test of Mate Choice

I investigated sex and age dimorphism and the possible effect of body size on mate choice in a northern Utah population of the Barn Owl (Tyto alba). In all characters measured (body mass; length of body, tarsus, foot, tail, and wing; and wing area), females averaged larger than males, but the ranges of these values overlapped considerably. Females were significantly larger than males in all characters except wing chord and tail length. Males had significantly lower wing loading than females. Lower wing loading could contribute to more efficient foraging by males and thus support hypotheses that partitioning of reproductive duties between the sexes may play an important role in reversed sexual dimorphism. Adults and immatures did not differ in size. I found no evidence to support the hypothesis that females choose small males as mates.

Aerial Displaying and Flying Ability of Chatham Island SnipeCoenocorypha pusillaand New Zealand SnipeC. aucklandica

SummaryMiskelly, C.M. (1990). Aerial displaying and flying ability of Chatham Island Snipe Coenocorypha pusilla and New Zealand Snipe C. aucklandica Emu 90, 28–32.Chatham Island Snipe Coenocorypha pusilla and New Zealand Snipe C. aucklandica were studied intensively during one and six breeding seasons respectively, and observations of aerial displays and related behaviours recorded. Chatham Island Snipe gave three types of acoustic aerial displays. The displays were performed only at night. Type 1 was a strident monosyllabic call, also given in several contexts on the ground. Type 2 was a series of disyllabic calls identical to a common territorial display given on the ground. Type 3 began with a series of disyllabic calls and ended with a non-vocal ‘roar’ considered homologous to the ‘drumming’ displays of Gallinago snipes. Evidence for non-vocal acoustic displaying by three subspecies of New Zealand Snipe is discussed. The intensively studied Snares Island Snipe C. aucklandica huegeli was not seen to give aerial displays. Chatham Island Snipe were flushed significantly more frequently and flew further than Snares Island Snipe, and had significantly lower wing-loadings. The aerial displays of Chatham Island Snipe were similar to descriptions of aerial displays of the ‘Chubbia’ snipes of South America: Cordilleran Snipe Gallinago stricklandii, Andean Snipe G. jamesoni and Imperial Snipe G. imperialis.

Bats and Gaps: Microchiropteran Community Structure in a Queensland Rain Forest

We examined how a community of insectivorous bats in upland rain forest differentially used closed canopy areas and artificial gaps produced by selective logging. Bat foraging activity was monitored at paired canopy and gap sites using ultrasonic detection equipment. The data supported the prediction that gap use was related to morphology and bat species were classifiable as closed canopy specialist, gap specialists, and gap incorporators. Closed canopy specialists were species with low aspect ratio and wing loading, whereas gap specialists had high values for these two measures. Gap incorporators, which used both canopy areas and gaps, were intermediate in morphology. The closed canopy species were presumed to forage more readily in a cluttered environment. In this community there were no strict gap specialists, but instead the gap specialists were also recorded in other, more open habitats. The community consisted of two distinct subcommunities: four species in closed canopy areas and five in gaps. Three other species were incorporators, but the incorporation rate was very low; only 8% of the activity in gaps and 27% in closed canopy areas was due to these species. There was no relation between patterns of gap use and gap vegetation cover or age up to 6 yr, suggesting that exclusion of gap specialists from a regenerating gap is a slow process. There is tight phenetic packing in the two subcommunities, indicating that vegetation structure is more important than competition in constraining the structure of this community.