The dawn flight of the gold swift Hepialus hecta: predator avoidance and the integration of complex lek behaviour (Lepidoptera,Hepialidae)

Predator pressure is a considerable evolutionary force. The evening twilight flight of species in the family Hepialidae Swift moths has been attributed to the moths (which have no hearing and so cannot detect bats) flying in a bat/bird free window. Several species deploy elaborate lek behaviour in this period. The expected flight in the dawn twilight is little reported, except in the non‐leking Hepialus (Korscheltellus) gracilis. A detailed study of the dawn flight in the leking species Hepialus (Phymatopus) hecta shows that it is less extensive than the evening lek flight (both in duration and in the number of moths participating), is confined to a much narrower window around sunrise, involves no reproductive behaviour, and functions only to re‐locate the members of copulating pairs and sessile displaying males from the emergent ground vegetation to less conspicuous roosting sites. Compilation of individual biographies over the 24‐h cycle permits a full construction of the diel activity in time and space. It consists of two twilight flight periods, separated by prolonged roosting during the hours of darkness and daylight. The moths use almost the whole available range of roosting sites, from the base of the ground vegetation to the tree canopy, and cyclically leave and re‐enter the lek site from these positions. The copulating posture and position avoid mammalian predators, and facilitate escape from spiders and wasps by the efficient use of a dead drop. The narrowness of the dawn flight is attributed to the need for this prolonged but conspicuous copulation, which precludes a morning mating, and to a demonstrated asymmetry of twilight activity in birds. The whole integrated spatio‐temporal cycle is attributable to evolutionary pressure to minimize the impact of predators, demonstrated to include birds, bats, wasps, and spiders, and probably also dragonflies, mice and shrews; the pre‐existing dawn flight is permissive to the evolution of sessile male displays during the evening lek. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 305–319.     

Field observations of Ostrinia nubilalis eclosion and post‐eclosion activity of females around their natal plants

Abstract The early part of the post‐eclosion, pre‐mating period were examined under field conditions for Ostrinia nubilalis. Post‐eclosion behavior of 25 and 21 females during the first and second flight periods were observed until they left their natal site. Summer generation larvae were reared under field conditions and the timing of adult eclosion was observed. Eclosion occurred at two times during the day, peaking before dawn and before dusk; 46% of females and 56% of males eclosed during the morning period and the rest eclosed during the evening period. After eclosion, females spent 30–60 min expanding their wings. Their typical behavior was to remain calmly on their natal site. None of the females exhibited calling behavior before leaving. All females left their natal sites sometime before dawn. The probability of leaving increased with time. Leaving rates were not significantly different between females of the first and second flight. These field observations indicate that females have several possibilities for pre‐mating movement, which might allow females to move out from their natal field before mating. In addition, we also discuss the influence of pre‐mating movements in relation to the rate of Bacillus thuringiensis (Bt) resistance evolution.     

Early outflying and late homeflying in the Indian pygmy bat under natural conditions

The outflying and homeflying activity pattern of a colony of the Indian pygmy bat Pipistrellus mimus occupying a tunnel was studied under natural conditions. Before leaving the tunnel for foraging, the bats made circling flights outside to sample the environmental light conditions. The onset and end of activity was related to the times of sunset and sunrise respectively. The onset of flight during evening commenced after sunset from mid-September to mid-April, before sunset during the rest of the year. Onset of activity occurred at higher light intensities compared to light intensities prevailing during the return flight to the roost in the morning. The duration of activity time showed a curvilinear relationship with the duration of the night. The phase relationship between onset and end of activity, and sunset and sunrise, showed marked seasonal variations in the values of Ψ_onset, Ψ_end, and Ψ_midpoint. However, such changes in the phase angle properties did not obey Aschoff's seasonal rule. Based upon the data obtained on the onset and end of activity patterns for five species of bats, including the data from this study, we report that P. mimus is the earliest to set out for foraging in the evening and among the last to return home in the morning. This might be due to dusk and dawn peaks in activity of the prey insects.     

Seasonal and diel plasticity of song type use in individual ovenbirds (Seiurus aurocapilla)

Animal communication is an important aspect of ecology across taxa, and there is a growing area of research that examines how animals plastically adjust their signals to account for both abiotic and biotic factors. Song type use and the temporal plasticity of song have been described in many bird species, but as of yet, few studies have examined how song type use may change across both seasonal and diel timeframes, and no studies have considered individual-level variation in plasticity. Using a hierarchical framework, we examined temporal patterns of primary and flight song use in ovenbirds (Seiurus aurocapilla; N = 21 individuals). We recorded ovenbird songs (N = 99,259) with autonomous recorders over 24-hr periods once per week across a breeding season near Sault Ste. Marie, Canada. As predicted, the occurrence and frequency of both song types significantly decreased over the season and showed temporal separation over diel periods. Primary songs peaked at dawn and declined throughout the day, while flight songs peaked at dusk and night. Our results support that primary songs have multiple functions as they remained more frequent during dawn and morning across the breeding season, while flight songs likely serve an intersexual function as they decreased similarly for all diel periods as mating opportunities decreased. Individuals were consistent in how frequently they sang their primary songs, but not their flight songs, suggesting that flight songs are more plastically expressed. We highlight the importance of examining plasticity in animal communication at the individual level as we show that males significantly differed in both their song behaviours (random intercepts) and the seasonal plasticity (random slopes) in these behaviours. Integrating themes such as song type use, temporal plasticity, and individual variation will be important for examining the evolutionary mechanisms that shape animal communication systems.     

Basis for Diel Variation in Nitrogenase Activity in the Marine Planktonic Cyanobacterium Trichodesmium thiebautii

Natural populations of the nonheterocystous marine cyanobacterium Trichodesmium thiebautii exhibit a diel periodicity in nitrogenase activity (NA). NA “turns on” near dawn and “turns off” near dusk, independent of photic conditions. Chloramphenicol (CAP) and ammonium prevented turn on of NA in T. thiebautii when added to samples collected before dawn but were progressively less effective in inhibiting NA in samples collected later in the morning. In samples collected after turn on, activities declined with time with both CAP and ammonium treatments, with ammonium having a stronger effect. In contrast, CAP added to samples collected in late afternoon prolonged NA, compared with controls, which turned off. Direct analysis of the presence of the Fe protein of nitrogenase in T. thiebautii by using a Western immunoblot procedure found a strong protein band present in samples collected after 0800 h through the late evening but little or no Fe protein in samples collected within the 2 to 4 h preceding dawn. We conclude that the diel cycle of NA in T. thiebautii results from de novo synthesis of nitrogenase each morning and from the inactivation and degradation of nitrogenase in the late afternoon and night.     

Circadian and solar clocks interact in seasonal flowering

The plant maintains a 24‐h circadian cycle that controls the sequential activation of many physiological and developmental functions. There is empirical evidence suggesting that two types of circadian rhythms exist. Some plant rhythms appear to be set by the light transition at dawn, and are calibrated to circadian (zeitgeber) time, which is measured from sunrise. Other rhythms are set by both dawn and dusk, and are calibrated to solar time that is measured from mid‐day. Rhythms on circadian timing shift seasonally in tandem with the timing of dawn that occurs earlier in summer and later in winter. On the other hand, rhythms set to solar time are maintained independently of the season, the timing of noon being constant year‐round. Various rhythms that run in‐phase and out‐of‐phase with one another seasonally may provide a means to time and induce seasonal events such as flowering.     

DIEL PATTERNS IN LIGHT ABSORPTION AND ABSORPTION EFFICIENCY FACTORS OF ISOCHRYSIS GALBANA (PRYMNESIOPHYCEAE)1

The chl a specific absorption coefficients [a* (λ), m²·mg chl a ^{? 1}] were examined in chemostat culture of the Prymnesiophyceae Isochrysis galbana (Parke) under a 12:12‐h light:dark cycle at low light (75 μmol photons·m ^{? 2}·s ^{? 1}) and high light (500 μmol photons· m ^{? 2}·s ^{? 1}) conditions. Other associated measurements such as pigment composition, cell density, and diameter as the measure of cell size were also made at the two light regimes every 2 h for 2 days to confirm the periodicity. A distinct diel variability was observed for the a* (λ) with maxima near dawn and minima near dusk. The magnitude of diel variation in a* (440) was 15% at low light and 22% at high light. Pronounced diel patterns were observed for cell size with minima near dawn and maxima near dusk. The magnitude of diel variation in cell size was 9.3% at low light and 21% at high light. The absorption efficiency factors [Q _a (440)] were determined by reconstruction using intracellular concentrations of pigments and cell size. The Q _a (440) also showed a distinct diel variability, with minima near dawn and maxima near dusk. The diel variation in a* (λ) and Q _a (λ) was primarily caused by changes in cell size due to growth, although there was some influence from diel variations in the intracellular pigment concentrations. The results presented here indicated that diel variation in a* (λ) was an important component of the optical characterization of phytoplankton.     

Dietary Benefits of Twilight Foraging by the Insectivorous Bat Hipposideros speoris1

Although bats are nocturnal, many species emerge from roosts to forage during twilight, despite a presumed high risk of predation at this time. Here, we describe twilight foraging by a maternity colony of Schneider's leafnosed bat (Hipposideros speoris) in the dry zone of Sri Lanka and determine the dietary benefits of such behavior. Bats usually began foraging during dusk, sometimes before sunset, and also foraged during twilight in the morning. Mean use of available twilight by four radio‐tagged bats was 75 percent. Twilight foraging made up, on average, 47 percent of the total foraging time of these bats (range = 25–96%), although twilight consisted of only 12 percent of the available time between sunset and sunrise the next morning. Eight species of potential predators (7 birds and 1 mammal) were observed within a 1 km radius of the colony, of which 5 species are predicted to regularly capture bats. Bats took a wide diversity of prey (11 insect orders, including at least 27 families, and spiders) that ranged in wing length from 2.0 to 54.0 mm. Major orders in the diet were Coleoptera, Lepidoptera, and Diptera. Prey of secondary importance included Hemiptera, Hymenoptera, Isoptera, and Neuroptera. Bats captured large numbers of insects that were only available or had marked peaks in abundance during twilight. These groups included small, swarming insects (especially flies) that have peaks in flight activity at dusk and dawn, large diurnal species (especially dragonflies) that have crepuscular activity, and winged termites that emerge in swarms at dusk. Access to these insects was a clear benefit of twilight foraging.     

Seasonal trend in movement directions at dawn and dusk: a study on crow and white herons

Crows (Corvus splendens) and white herons (Ardea alba) inhabit the agricultural landscapes nearby human habitats which represent dynamic ecosystem and show seasonal crop patterns. We studied the movement pattern in these birds at dawn and dusk, during solstices (December and June) and equinoxes (March and September). The movement directions were changed from uniform at dawn to a concentrated distribution at dusk all along the season suggesting that morning movements are more exploratory than evening with seasonal differences. Differential use of directions in December than June could be the effect of temperature, food availability or wind direction and speed. During breeding, less number of directions used suggests that birds might be moving towards the directions having high probability of food availability. It is likely that avian dispersal in space and time is dependent on the food availability however, further studies are required to be carried out.     

Long-term influence of simulated territorial intrusions on dawn and dusk singing in the Winter Wren: spring versus autumn

Males of many songbird species have peaks of singing activity at dawn and dusk. Singing during those twilight periods can function in territory proclamation, and males are suggested to adjust song output to the level of intruder pressure. We used song playback during the breeding season to simulate intrusions into territories of male Winter Wrens (Troglodytes troglodytes) shortly after dawn. We then compared male singing behaviour during the dawn and dusk chorus before and 1 day after the simulated intrusion. One day after the playback, male Wrens increased their song output before sunrise, which confirms our results from a previous study on dawn singing in autumn territories. At dusk, on the evening following the playback, males slightly increased song output after sunset, but singing activity at dusk was generally very low. We found no significant changes of song output after sunrise, before sunset, and between 2 days of control without playback. These results are consistent with the hypothesis that dawn and dusk singing is important for territory defence in spring. Unlike in autumn, however, increased singing in spring at dawn and dusk could also serve to defend other resources such as fertile mates or to strengthen the pair bond after a territorial challenge. In comparison with the results on autumnal singing, male Wrens started singing earlier at dawn during the breeding season, and they generally sang more songs at dawn and immediately after playback. The increase in absolute numbers of songs sung in the morning after playback seemed greater in spring than in autumn; however, the proportional increase relative to overall song output was similar in both seasons.     

Non‐Parametric Entrainment by Natural Twilight in the Microchiropteran Bat,Hipposideros Speoris Inside a Cave

The study aimed to determine the influence of repeated natural dawn and dusk twilight pulses in entraining the circadian flight activity rhythm of the microchiropteran bat, Hipposideros speoris, free‐running in constant darkness in a natural cave. The bats were exposed to repeated dawn or dusk twilight pulses at eight circadian phases. All bats exposed to dawn twilight pulses were entrained by advancing transients, and the stable entrainment was reached when the onset of activity occurred about 12 h before the lights‐on of the pulses, irrespective of the initial phase at which the bats were exposed to twilight. All bats exposed to dusk twilight pulses, however, were entrained by delaying transients, and the stable entrainment was reached when the onset of activity occurred about 1.6 h after the lights‐on of the pulses. The entrainment caused by dawn and dusk twilight pulses is discussed in the context of the postulated two photoreceptors: the short wavelength sensitive (S) photoreceptors mediating entrainment via dusk twilight, and the medium wavelength sensitive (M) photoreceptors mediating entrainment via dawn twilight.     

Diel activity of the pink shrimp Penaeus duorarum

Twelve juvenile pink shrimp, Penaeus duorarum Burkenroad, were tested individually for 3-day periods in electronic shuttleboxes to determine their diel patterns of locomotor activity, in relation to a natural summer photoperiod. Nocturnal activity was twice that exhibited during the daytime; however, a bimodal pattern was evident with crepuscular peaks occurring at dawn and dusk. The dusk peak was more pronounced, with activity increasing markedly before sunset (indicative of an endogenous circadian rhythm component), and continuing during the initial hours of darkness, gradually declining later during the night with a secondary peak at dawn falling off to minimal activity during daylight. Crepuscular activity (mean of dawn and dusk) was twice the nocturnal average.     

How can Asphalt Roads Extend the Range of In Situ Polarized Light Pollution? A Complex Ecological Trap of <Emphasis Type="Italic">Ephemera danica</Emphasis> and a Possible Remedy

When an artificial surface (e.g. an asphalt road) reflects strongly and horizontally polarized light as water bodies do in the nature, polarotactic aquatic insects, like the creek-dwelling Ephemera danica mayflies easily become deceived. After swarming above the creek surface, E. danica females begin their upstream compensatory flight and can be deflected at bridges with an asphalt road and continue their flight above the road surface. Thus, the water-mimicking optical signal of the road may deceive water-seeking polarotactic mayflies and lead them to distant, polarized-light-polluting surfaces, which elicit anomalous oviposition. On an asphalt road crossing a creek, we deployed polarizing insect traps at different distances from the bridge. The traps captured E. danica mayflies and their catch numbers indicated that these mayflies originated from the direction of the bridge, proving that they followed the track of the road. Our results suggest that distant polarized-light-polluting objects along an asphalt road can trap mayflies emerging from a creek crossing the road. The combination of an asphalt road and a man-made in situ (local) polarizing surface forms a complex ecological trap, being capable of luring aquatic insects from greater distances. To eliminate the oviposition of dangered polarotactic aquatic insects emerging from a creek onto the asphalt road crossing the creek, we suggest to deploy strongly and horizontally polarizing water-filled black trays along the edge of the road during the swarming period. Thus, the eggs of the deceived insects can be moved back to the creek in order to assist the conservation of the offspring-generation.     

Daily activity patterns of coyotes (Canis latrans) in a tropical deciduous forest of western Mexico

We studied the activity patterns of the coyote (Canis latrans) in a tropical deciduous forest in the Mexican Pacific coast over 3 years. Fifteen coyotes (six females, nine males) were fitted with radio-collars equipped with activity sensors to determine the influence of seasonality (dry vs. wet), gender (males vs. females) and diel intervals (dusk, night, dawn, and day) on activity patterns. We found differences in activity patterns between diel intervals, but the only pair of diel intervals that showed significant differences was dawn (more active) vs. day (less active). We found no differences due to sex or season on any of the four studied diel intervals. Coyote activity patterns in this tropical forest could be responding to prey availability, human avoidance or thermoregulation.     

Contrasting diel activity and feeding patterns of four species of carnivorous stoneflies

1. The hypothesis under test was that larvae of Dinocras cephalotes (Curtis), Perla bipunctata Pictet, Isoperla grammatica (Poda), and Perlodes microcephalus (Pictet) differed markedly in their diel activity and feeding patterns. Mature larvae collected about 1 month prior to adult emergence were used either for gut analyses or for observations of their activity and feeding patterns in three stream tanks with natural substrata and glass bottoms, so that activity could be observed above and below the substratum. A dull red light was used for observations in the dark. Food (larvae of Ephemeroptera, Simuliidae, and Chironomidae) was provided in excess. 2. Larvae for gut analyses were taken 1 h before dusk or dawn (n = 30 larvae per species for each day or night sample). The only species with food in the gut for the day samples was P. microcephalus. All species fed at night, the mean number of prey per larva being very similar for D. cephalotes, P. bipunctata, and I. grammatica but significantly higher for P. microcephalus. Most prey were insect larvae, especially Simuliidae and Chironomidae. 3. Diel activity patterns of single larvae differed interspecifically but not intraspecifically. Larvae of D. cephalotes and P. bipunctata were rarely active during the day; their activity increased at dusk and decreased at dawn, and was highest during the night; their success at prey capture was highest at dusk and dawn, with an ambush rather than a search strategy. Isoperla grammatica was rarely active during the day, most active at dusk and dawn when prey capture was highest, using a search strategy, and less active for the rest of the night. Perlodes microcephalus was active during the day, but only below the substratum, and very active from dusk to dawn with a high prey‐capture success, using a search strategy. These experiments provided support for the hypothesis under test. The discussion concludes that the results could also help to explain known differences in growth rate and the length of the life‐cycle in these four species.     

Interplay of temperature and light influences wild guppy (Poecilia reticulata) daily reproductive activity

In this study we investigated the environmental regulation of daily reproductive activity of guppies (Poecilia reticulata). We observed male guppy reproductive behaviour for 17 days over three time periods (dawn, noon, and dusk) while recording natural variation in water temperature and light level. Water temperatures recorded during the experiments were highly variable (up to 7 °C per day), and there was a recurring pattern in daily variation for both light and temperature. Levels of activity were highest at dawn and similarly low during noon and dusk, but reproductive behaviour was recorded throughout the day. Mixed‐effects models indicate that light and temperature affect reproductive behaviour differently at different times of the day, and can also have opposing effects. We suggest that the environmental heterogeneity of streams in Trinidad has led to a broad thermal tolerance, and has contributed to the high level of phenotypic plasticity in the guppy and its success as an invasive species. Furthermore, our results show that daily variation in temperature and its interaction with light should be considered in future studies of guppy reproductive behaviour. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 511–520.     

Flocking behaviour in the twilight ascents of Common Swifts Apus apus

Among the many unique flight behaviours of Common Swifts Apus apus, the most puzzling may be their ascents to high altitudes during both dusk and dawn. Twilight ascents have been hypothesized to be functionally related to information acquisition, including integration of celestial orientation cues, high‐altitude visual landmarks and sampling of weather conditions. However, their exact purpose remains unknown. We tracked Common Swifts with tracking radar at their breeding grounds in southern Sweden, and present evidence that during the dusk ascent and dawn descent they often occur in flocks, whereas during the dusk descent and dawn ascent phase they do not. This flocking behaviour suggests that swifts may benefit from conspecific interactions during twilight ascents and descents, possibly through more robust cue acquisition and information exchange in groups, or extending social behaviour also seen in screaming parties before dusk.     

Patterns of daily flight activity in onitine dung beetles (Scarabaeinae: Onitini)

Different species of African dung beetles emerge from the soil at characteristic times of the day to fly and colonize the freshly-deposited dung of mammalian herbivores. Onitine dung beetles in their natural habitat displayed one of five distinctive daily flight behaviours: dusk crepuscular (Onitis alexis Klug, O. caffer Boheman, O. fulgidus Klug, O. tortuosus Houston, O. vanderkelleni Lansberge, O. westermanni Lansberge); dusk/dawn crepuscular (O. pecuarius Lansberge and O. viridulus Boheman); dusk/dawn crepuscular and nocturnal (O. aygulus (Fabricius), O. mendax Gillet, O. uncinatus Klug); late afternoon-dusk and dawn-early morning [Heteronitis castelnaui (Harold)]; or diurnal flight activity [O. belial (Fabricius), O. ion (Olivier)]. These diagnostic daily flight behaviours span a light intensity range of over 6 orders of magnitude and have been retained in selected species introduced into Australia. Ambient light intensity appears to be the primary determinant of the daily flight period in onitine dung beetles. Because the dung of mobile herbivores is rapidly exploited by onitine species for feeding and breeding purposes, different flight behaviours result in a spatial and temporal partitioning of species in the local dung beetle community. The timing of flight may contribute to, or lead to avoidance of, competition between species which may ultimately affect colonization success. Many onitines show a strong preference for dung of specific herbivores, which may further reduce interspecific competition. All crepuscular-nocturnal species examined raised their thoracic temperatures endothermically to between 35°C and 40°C before the onset of flight. In O. aygulus the thoracic temperature excess was as large as 19.3°C. The thermal threshold below which the frequency of flight onsets drops off rapidly is about 12°C for O. aygulus and 17°C for O. alexis and O. pecuarius. Radiant loss of body heat during cool nights and dawns may explain why smaller species (<0.4 g body weight), in particular, are adapted behaviourally so that they fly only during the day or early dusk.