Evening Flight Research Articles

Camera-based automated monitoring of flying insects in the wild (Camfi). II. flight behaviour and long-term population monitoring of migratory Bogong moths in Alpine Australia.

The Bogong moth Agrotis infusa is well known for its remarkable annual round-trip migration from its breeding grounds across eastern and southern Australia to its aestivation sites in the Australian Alps, to which it provides an important annual influx of nutrients. Over recent years, we have benefited from a growing understanding of the navigational abilities of the Bogong moth. Meanwhile, the population of Bogong moths has been shrinking. Recently, the ecologically and culturally important Bogong moth was listed as endangered by the IUCN Red List, and the establishment of a program for long-term monitoring of its population has been identified as critical for its conservation. Here, we present the results of two years of monitoring of the Bogong moth population in the Australian Alps using recently developed methods for automated wildlife-camera monitoring of flying insects, named Camfi. While in the Alps, some moths emerge from the caves in the evening to undertake seemingly random flights, filling the air with densities in the dozens per cubic metre. The purpose of these flights is unknown, but they may serve an important role in Bogong moth navigation. We found that these evening flights occur throughout summer and are modulated by daily weather factors. We present a simple heuristic model of the arrival to and departure from aestivation sites by Bogong moths, and confirm results obtained from fox-scat surveys which found that aestivating Bogong moths occupy higher elevations as the summer progresses. Moreover, by placing cameras along two elevational transects below the summit of Mt. Kosciuszko, we found that evening flights were not random, but were systematically oriented in directions relative to the azimuth of the summit of the mountain. Finally, we present the first recorded observations of the impact of bushfire smoke on aestivating Bogong moths - a dramatic reduction in the size of a cluster of aestivating Bogong moths during the fire, and evidence of a large departure from the fire-affected area the day after the fire. Our results highlight the challenges of monitoring Bogong moths in the wild and support the continued use of automated camera-based methods for that purpose.

Drivers affecting habitat use in Afrotropical hipposiderid and pteropodid bats

AbstractAssessing how bats respond to habitat attributes requires an integrative approach to reliably predict direct community‐level effects. We focused on hipposiderid and pteropodid bats because of their diverse resource use patterns, body size ranges, and dispersal abilities. We combined an array of bat species‐level characteristics with key forest stand characteristics that may covary with habitat use. Twelve stations were sampled in the Lomami and Yangambi landscapes, Democratic Republic of the Congo. We investigated whether species‐level flight ability of bats and forest stand characteristics can affect bat commuting flights and community‐level estimates of both species detection and habitat occupancy. We captured bats for 108 trap‐nights. Three sampling events (early evening, middle of the night, and early morning) were replicated for each survey night. Hipposiderids showed an early evening flight peak, while flight activity of pteropodids was constant throughout the night, but increased around the middle of the night. Species capture probability decreased with higher wing loading in hipposiderids and was negatively correlated with higher wing aspect ratio in pteropodids. Forest occupancy of hipposiderids increased along the gradient towards waterways, while pteropodid occurrence was not directly linked to measured forest stand variables. This suggests a consequence of habitat patterns at larger spatial scales, which would need clarifying through additional data collection. We discuss these findings in terms of resource‐use strategies of clutter‐tolerant and clutter‐intolerant species. We argue that the occurrence of specific bat species and their habitat use patterns can serve as surrogate measures of ecosystem health.

The evening crepuscular host-seeking activity of Anopheles mosquitoes in northeast Brazil.

Studies on the timing of anopheline host-seeking are important for understanding mosquito ecology, behaviors, and possible role in disease transmission. To study the evening crepuscular host-seeking activity of anophelines and the effects of moonlight, anopheline mosquitoes were collected with light traps settled in a livestock area in the Brazilian Cerrado region. Traps (Silva traps) were placed next to animal enclosures at 1.5 m asl. The research was divided in 2 experiments: the first experiment (12 nights) comprised 2 trapping periods, one from 6 PM to 7 PM and one from 7 PM to 6 AM, and the second experiment (16 evenings) divided in three 20-min intervals based on the 3 twilight phases (civil: 6-6:20 PM; nautical: 6:20-6:40 PM; and astronomical: 6:40-7 PM). A total of 2,815 anopheline mosquitoes and 9 species were found. The main species were Anopheles triannulatus s.l., An. argyritarsis, An. goeldii, and An. evanse. Host-seeking mosquitoes were more frequently active during the first hour after sunset, with a significant peak in the second 20-min interval. After that, a decrease in the number of individuals was observed from the astronomical twilight onwards. Moonlight did not affect the evening flight activity of anophelines. By using LED-based passive light traps, the evening arrival time of anophelines at blood-feeding sites was demonstrated, and it may be a key time window for malaria vector control interventions.

Relating weather radar data to migrating waterfowl abundance in the Rainwater Basin of Nebraska

AbstractWaterfowl migrations are large‐scale events that involve millions of birds moving over broad geographic extents, which make them difficult to quantify and study. Historically, wildlife managers have relied mostly on field surveys, such as visual counts from the ground or air that sample at small spatial or temporal extents, or both. Combining field surveys with remote sensing data comprehensively collected over large spatial extents at high temporal frequency may improve the study of migrating waterfowl distributions. We tested the strength of the relationship between broad‐scale weather surveillance radar data and fine‐scale field surveys of waterfowl abundance at wetlands within the Rainwater Basin of Nebraska, USA, from 2017–2019. Radar reflectivity of waterfowl at the peak exodus of evening flights was positively correlated with diurnal waterfowl count data, although there was unexplained variation in the relationship. The association was also very similar across various time scales ranging from daily to monthly averages of waterfowl abundance. We suggest that human‐based ground surveys can calibrate and leverage more comprehensive remote sensing data to get a broad understanding of waterfowl distributions during migration. Several confounding factors, such as spatial displacement between radar and survey observation, individual variation in orientation and body size, and identification of avian species sampled by radar, remain on the path to improving radar‐based waterfowl estimates.

Cold wintering of coastal birds in the source and upper reaches of the Angara river: Changes in abundance and species structure in the conditions of a sharp climate warming

Based on long-term research (1972-2023) and analysis of literature data, materials on the dynamics of the number and species structure of wintering shorebirds and waterfowl on cold wintering in the source and upper reaches of the Angara River (up to the town of Usolye-Sibirskoye) are presented. This is the largest cold wintering of coastal birds in Eastern Siberia – up to 55.0-60.0 thousand birds, the formation of which is due to very specific conditions of the upper reaches of the Angara River. This is the thermal refugium of the Upper Angara region, which ensures the accumulation of birds at the end of migration in more favorable areas of this region. It is divided into two sections: the first stretches from the source of the Angara River to the village of Taltsy, the second from the Irkutsk hydroelectric dam to the town of Usolye-Sibirskoye, and in warm winters slightly below it. On the basis of special works on the study of the dynamics of the number and species structure of birds, special methods have been developed: accounting on ice holes, accounting during the evening flight of birds to the lake Baikal (during cold periods) and accounting using a hovercraft (SVP) (during periods of severe climate warming). The basis of wintering birds is the Goldeneye Bucephala clangula (from 95.0% to 98.5% of their total species structure). However, the structure of secondary species can increase dramatically and we have noted new species that have never been found here before. The collected materials allow us to understand the reasons that determine the dynamics of the number and species structure of coastal birds in the “cold” wintering grounds of Inner Asia in the conditions of a sharp warming of the climate

The clock gene, period, influences migratory flight and reproduction of the oriental armyworm, Mythimna separata(Walker).

The oriental armyworm, Mythimna separata, is a major long-distance migratory insect pest of grain crops in China and other Asian countries. Migratory flights and reproductive behavior usually occur at night, regulated by a circadian rhythm. However, knowledge about the linkages between adult flight, reproduction, and clock genes is still incomplete. To fill this important gap in our knowledge, a clock gene (designated Msper) was identified and phylogenetic analysis indicated that the encoded protein (MsPER) was highly similar to PER proteins from other insect species. Quantitative RT-PCR assays demonstrated that significantly different spatiotemporal and circadian rhythmic accumulations of mRNA encoding MsPER occurred during development under steady 14h:10h light:dark conditions. The highest mRNA accumulation occurred in adult antennae and the lowest in larvae. Msper was expressed rhythmically in adult antennae, relatively less in photophase and more entering scotophase. Injecting small interference RNA (siRNA) into adult heads effectively knocked down Msper mRNA levels within 72h. Most siRNA-injected adults reduced their evening flight activity significantly and did not exhibit a normal evening peak of flight activity. They also failed to mate and lay eggs within 72h. Adult mating behavior was restored to control levels by 72h post injection. We infer that Msper is a prominent clock gene that acts in regulating adult migratory flight and mating behaviors of M.separata. Because of its influence on migration and mating, Msper may be a valuable gene to target for effective management of this migratory insect.

Evaluation of vertical and horizontal distribution of particulate matter near an urban roadway using an unmanned aerial vehicle.

Measurement of traffic emissions has gained a lot of interest in recent times due to its contribution to urban pollution. This paper reports the outcome from an unmanned aerial vehicle (UAV) based measurement of PM concentration near an urban roadway at Kolkata, India. A total of 54 flights were carried out for simultaneous measurements of PM1, PM2.5 and PM10 mass concentration and meteorological parameters in vertical as well as in horizontal direction. Results for the vertical flight up to 100 m showed that the PM1, PM2.5 and PM10 concentrations at higher altitudes are less (mean; 24.6, 39.9 and 103.8 μg m-3) compared to the respective ground level concentrations (mean; 26.3, 50.4 and 201.9 μg m-3). For all the three particle sizes, the majority of the cases of higher PM concentration at higher altitudes happened during the evening flight. Low mixing height and low wind speed are suggested to be the reasons for the poor dispersion of pollutants in the evening. While there was a 7-10% fall of fine particles (PM1 and PM2.5) mass concentrations up to 90 m away from the road, no trend could be seen for PM10. The random forest model to predict the UAV/Ground concentration ratio showed high accuracy (R2 = 0.82-0.95) for all three particle sizes. This is an important finding from this study, which shows how UAV measurement data can be used to generate models that can predict the higher altitude concentrations from the ground based measurements.

Aircraft observations and sub‐km modelling of the lake–land breeze circulation over Lake Victoria

AbstractThe lake–land breeze circulation over Lake Victoria was observed in unprecedented detail with a research aircraft during the HyVic pilot flight campaign in January 2019. An evening and morning flight observed the lake and land breezes respectively under mostly dry conditions. The circulation was observed at various heights along a transect across the lake and onshore in Tanzania. Profiles of the lower troposphere were recorded by dropsondes over the lake and land. Convection‐permitting MetUM simulations with different horizontal grid‐spacings (including sub‐km) were run for the flight periods. During the evening flight, the aircraft crossed the lake breeze front over land at 1627 LT, approximately 50 km to the east of the lake shore, recording a 6 gkg decrease in specific humidity and reversal in wind direction over 5 km. During the morning flight, a shallow land breeze was observed across the eastern shore at 0545 LT. At least one region of increased and deeper moisture (previously seen in simulations but never observed) was sampled over the lake surface between 0527 and 0855 LT. This bulge of moisture was likely formed from the lifting of near‐surface moist air above the lake by low‐level convergence. The observations and model simulations suggest that low‐level convergence occurred at the leading edge of the land breeze, which had detached from the main land breeze and independently propagated westward across the lake with wave‐like characteristics. The MetUM simulations were able to reasonably reproduce the lake breeze front, bulge feature, and its propagation, which is a major achievement given the sparse observational data for model initialisation in this region. However, some timing, resolution and boundary‐layer depth biases require further investigation. Overall, this pilot campaign provided an unprecedented snapshot of the Lake Victoria lake–land breeze circulation and motivates a more comprehensive field campaign in the future.

Vertical profiling of black carbon and ozone using a multicopter unmanned aerial vehicle (UAV) in urban Shenzhen of South China

Existing studies on vertical profiling of black carbon (BC) and ozone (O3) were mainly conducted in the rural areas, leading to limited knowledge of their vertical distributions in the urban area. To fill this knowledge gap, vertical profiling (0–500 m and 0–900 m, AGL) of BC and O3 was conducted in a highly urbanized area of Shenzhen in subtropical South China using a multicopter unmanned aerial vehicle (UAV) platform. In total 32 flights were conducted from the 10th to 15th, December 2017 (winter campaign) and 42 flights from the 19th to 28th, August 2018 (summer campaign) with 4 time slots per day, including morning, afternoon, evening, and midnight. In general, equivalent BC (eBC) concentration decreased as the height increased with an overall slope of −0.13 μg m−3 per 100 m in the winter campaign and −0.08 μg m−3 per 100 m in the summer campaign. On the contrary, an increase of O3 level with altitude was observed (7.8 ppb per 100 m). Absorption Ångström exponent (AAE) exhibits a slightly increasing trend with height. Seasonality of eBC vertical profiles was observed in morning, afternoon and midnight flights, but not for evening flights. The analysis showed the shape of vertical profiles of eBC and O3 can be affected by planetary boundary layer height (PBLH) and air mass origin. Calculated heating rates due to BC show distinct seasonal variability for morning but not for afternoon, because of the counteracting effects by solar irradiance in the subtropical afternoon and eBC concentration in urban South China influenced by the monsoon climate.

Impact of the COVID-19 pandemic on commercial airlines in the United States and implications for the kidney transplant community.

Many deceased-donor and living-donor kidney transplants (KTs) rely on commercial airlines for transport. However, the coronavirus-19 pandemic has drastically impacted the commercial airline industry. To understand potential pandemic-related disruptions in the transportation network of kidneys across the United States, we used national flight data to compare scheduled flights during the pandemic vs 1-year earlier, focusing on Organ Procurement Organization (OPO) pairs between which kidneys historically most likely traveled by direct flight (High Volume by direct Air transport OPO Pairs, HVA-OPs). Across the United States, there were 39% fewer flights in April 2020 vs April 2019. Specific to the kidney transportation network, there were 65.1% fewer flights between HVA-OPs, with considerable OPO-level variation (interquartile range [IQR] 54.7%-75.3%; range 0%-100%). This translated to a drop in median number of flights between HVA-OPs from 112 flights/wk in April 2019 to 34 in April 2020 (P<.001), and a rise in wait time between scheduled flights from 1.5hours in April 2019 (IQR 0.76-3.3) to 4.9hours in April 2020 (IQR 2.6-11.2; P<.001). Fewer flights and longer wait times can impact logistics as well as cold ischemia time; our findings motivate an exploration of creative approaches to KT transport as the impact of this pandemic on the airline industry evolves.

Evaluating the Use of Drones Equipped with Thermal Sensors as an Effective Method for Estimating Wildlife

ABSTRACTDrones equipped with thermal sensors have shown ability to overcome some of the limitations often associated with traditional human‐occupied aerial surveys (e.g., low detection, high operational cost, human safety risk). However, their accuracy and reliability as a valid population technique have not been adequately tested. We tested the effectiveness of using a miniaturized thermal sensor equipped to a drone (thermal drone) for surveying white‐tailed deer (Odocoileus virginianus) populations using a captive deer population with a highly constrained (hereafter, known) abundance (151–163 deer, midpoint 157 [87–94 deer/km2, midpoint 90 deer/km2]) at Auburn University's deer research facility, Alabama, USA, 16–17 March 2017. We flew 3 flights beginning 30 minutes prior to sunrise and sunset (1 morning and 2 evening) consisting of 15 nonoverlapping parallel transects (18.8 km) using a small fixed‐wing aircraft equipped with a nonradiometric thermal infrared imager. Deer were identified by 2 separate observers by their contrast against background thermal radiation and body shape. Our average thermal drone density estimate (69.8 deer/km2, 95% CI = 52.2–87.6), was 78% of the mean known value of 90.2 deer/km2, exceeding most sighting probabilities observed with thermal surveys conducted using human‐occupied aircraft. Thermal contrast between animals and background was improved during evening flights and our drone‐based density estimate (82.7 deer/km2) was 92% of the mean known value. This indicates that time of flight, in conjunction with local vegetation types, determines thermal contrast and influences ability to distinguish deer. The method provides the ability to perform accurate and reliable population surveys in a safe and cost‐effective manner compared with traditional aerial surveys and is only expected to continue to improve as sensor technology and machine learning analytics continue to advance. Furthermore, the precise replicability of autonomous flights at future dates results in methodology with superior spatial precision that increases statistical power to detect population trends across surveys. © 2020 The Wildlife Society.

Modeling Migratory Flight in the Spruce Budworm: Circadian Rhythm

The crepuscular (evening) circadian rhythm of adult spruce budworm (Choristoneura fumiferana (Clem.)) flight activity under the influence of changing evening temperatures is described using a mathematical model. This description is intended for inclusion in a comprehensive model of spruce budworm flight activity leading to the simulation of mass migration events. The model for the temporal likelihood of moth emigration flight is calibrated using numerous observations of flight activity in the moth’s natural environment. Results indicate an accurate description of moth evening flight activity using a temporal function covering the period around sunset and modified by evening temperature conditions. The moth’s crepuscular flight activity is typically coincident with the evening transition of the atmospheric boundary layer from turbulent daytime to stable nocturnal conditions. The possible interactions between moth flight activity and the evening boundary layer transition, with favorable wind and temperature conditions leading to massive and potentially successful migration events, as well as the potential impact of climate change on this process, are discussed.

Advance purchase behaviors of air passengers: A continuous logit model

Modeling the advance purchase behaviors of air passengers is essential when airlines develop revenue management strategies. Therefore, this study empirically investigates advance purchase behaviors based on the air ticket transaction data by using a continuous logit model. The estimation results show that advance purchase behaviors are significantly affected by price, price uncertainty, time of day (morning, afternoon and evening flight), days of week (flight on Friday), months of year (peak or off-peak seasons), and consecutive holiday. Accordingly, different pricing strategies should be used for different flights to maximize revenue.

Evaluation of an unmanned aircraft system for detecting surrogate caribou targets in Labrador

Regular, standardized population inventories have been suggested as an important component to the recovery of declining populations of boreal caribou (Rangifer tarandus caribou). Current survey methods typically employ manned aircraft, which can be noisy, expensive to operate, and dangerous for the people conducting the surveys. Small unmanned aerial systems (UAS) have garnered attention as a promising alterative to conducting aerial surveys in manned aircraft. Our research investigates the feasibility of using an UAS to conduct aerial surveys and determine which factors affect the detection of surrogate caribou targets, and hence may affect detection of real caribou. In the fall of 2013, we tested the capabilities of the Brican TD100E, a small, electric-powered fixed-wing UAS, to fly beyond visual line of sight near Goose Bay, Labrador. Seven surveys were done using different flight paths to collect aerial images of 26 surrogate caribou targets placed in six different habitats. Mixed effects logistic regression models were used to evaluate how habitat type, distance of the target from the image centerline, photo analysts’ experience level, flight time, and the target contrast against the landscape influenced the detection of surrogate caribou targets. We found that habitat type, target contrast, and the flight time affected target detection. Overall, 77.5% of the targets were detected; the odds of a photo analyst detecting a target in open habitat were roughly 10.5 times higher than in burned habitat and 42 times higher than in heavy forest. Target detection was influenced by the contrast of the target against the landscape, where a higher corrected integrated density was associated with greater target detection. The detection of targets was 87% during evening flights and 75% for morning flights. This study was the first of its kind to successfully fly a UAS beyond line of sight over land for non-military applications in North America and the findings of our research will provide an evaluation for using UAS to survey caribou in the future.

Population trends over 50 years of a Pied Imperial-Pigeon breeding colony on North Brook Island, a tropical Great Barrier Reef island, Australia

The Pied Imperial-Pigeon (Ducula bicolor) is a summer migrant to northern Australia, and nests colonially on many islands of the Great Barrier Reef, Queensland. Numbers are perceived to have declined as a result of large-scale shooting in the past and clearing of their mainland feeding grounds. To obtain evidence of any population changes, 1–10 counts were made each breeding season of the evening flight from the mainland to a nesting colony on North Brook Island. The counts began in 1965 and have continued for 50 years. The count represents one individual of a pair that visits the mainland to feed and returns in the evening. In the 1965–66 breeding season, the December count (the count used to compare years) was 4692 birds. Over the following three seasons, numbers declined to a low of 1451 birds in 1968–69; this decline was attributed to shooting of up to 1100 birds at a time. Large-scale shooting stopped in 1968 and was followed by a steady exponential increase (y = 3370.4e0.0908x in numbers over 23 years to 29 818 birds in the 1992–93 season. Numbers have fluctuated between ∼25 000 and 35 000 individuals over the following 18 years. A tropical cyclone of extreme intensity affected the pigeons’ breeding site on North Brook Island and their mainland feeding areas in February 2011. In the following breeding season of 2011–12, numbers fell to 5311, but recovered to 21 088 in the 2012–13 season. The dramatic drop in numbers was attributed to the pigeons moving elsewhere for the 2011–12 season. It is predicted that the post-cyclonic number of 21 088 will take 4 years to recover to 30 000. The counts are a simple and somewhat coarse measure of population trends, but provide a population baseline for more sophisticated studies on the movements of pigeons and their responses to long-term changes in habitat and climate.

Mapping Wintering Waterfowl Distributions Using Weather Surveillance Radar

The current network of weather surveillance radars within the United States readily detects flying birds and has proven to be a useful remote-sensing tool for ornithological study. Radar reflectivity measures serve as an index to bird density and have been used to quantitatively map landbird distributions during migratory stopover by sampling birds aloft at the onset of nocturnal migratory flights. Our objective was to further develop and validate a similar approach for mapping wintering waterfowl distributions using weather surveillance radar observations at the onset of evening flights. We evaluated data from the Sacramento, CA radar (KDAX) during winters 1998–1999 and 1999–2000. We determined an optimal sampling time by evaluating the accuracy and precision of radar observations at different times during the onset of evening flight relative to observed diurnal distributions of radio-marked birds on the ground. The mean time of evening flight initiation occurred 23 min after sunset with the strongest correlations between reflectivity and waterfowl density on the ground occurring almost immediately after flight initiation. Radar measures became more spatially homogeneous as evening flight progressed because birds dispersed from their departure locations. Radars effectively detected birds to a mean maximum range of 83 km during the first 20 min of evening flight. Using a sun elevation angle of −5° (28 min after sunset) as our optimal sampling time, we validated our approach using KDAX data and additional data from the Beale Air Force Base, CA (KBBX) radar during winter 1998–1999. Bias-adjusted radar reflectivity of waterfowl aloft was positively related to the observed diurnal density of radio-marked waterfowl locations on the ground. Thus, weather radars provide accurate measures of relative wintering waterfowl density that can be used to comprehensively map their distributions over large spatial extents.

Reduced-impact logging and temporal activity of understorey bats in lowland Amazonia

Because global timber demands continue to threaten tropical rain forests, identification of sustainable-use forest management protocols that meet human needs while preserving biodiversity is critical. Reduced-impact logging (RIL) protocols are increasingly common in the tropics and may be a viable option for sustainable forest use; however, few studies have documented faunal responses to RIL. Moreover, evaluations of abundance or diversity may not be sufficient for a comprehensive understanding of faunal responses to human activities, especially in the short-term. We assessed the effects of RIL on the temporal activity patterns of abundant bats in lowland Amazonian rain forest. More specifically, we characterized temporal patterns of activity, overlap of temporal activity, and dispersion of activity modes for seven abundant bat species and for four common bat guilds in RIL forest and in undisturbed forest in Tapajós National Forest, Pará, Brazil. Temporal activity of aerial insectivores, nectarivores, and gleaning animalivores did not change in response to RIL. In contrast, three of five species of frugivores and frugivores as a group changed their patterns of temporal activity in response to RIL. RIL had a greater effect on temporal activity of frugivores that foraged in the understorey than on frugivores that foraged in multiple forest strata. Overlap of temporal activity of frugivores was greater than expected by chance in undisturbed forest, but was random in RIL forest. Changes in activity may be a response to a combination of increased predation risk and reduced distances of early evening flights between day roosts and feeding areas in RIL forest compared to undisturbed forest.

Annoyance responses to stable and changing aircraft noise exposure

This article reports the two extensive aircraft noise annoyance surveys subsequently carried out among residents in the vicinity of Zurich Airport in 2001 and 2003 in order to update and validate existing exposure-effect relationships for aircraft noise and annoyance in Switzerland. Logistic and polynomial approximations of the exposure-annoyance relationships for both the years 2001 and 2003 are presented for the L(dn), L(den), and L(A,eq24) noise metrics. The results confirm other recently published international research and provide further evidence that community annoyance due to aircraft noise has increased over the past decades. Between the two survey years, a considerable amount of early morning and late evening flight operations have been relocated to use an other runway than before; thus both the effects of a recent step decrease and recent step increase on the exposure-annoyance relationship could be investigated. Residents that experienced a step increase elicited a quite pronounced over-reaction of annoyance which correlated with the magnitude of the change. Two logistic regression models are provided to forecast the effects of changes in exposure during shoulder hours in the early morning and the late evening.

Why does diurnal mass change not appear to affect the flight performance of alarmed birds?

To survive, animals need to trade-off gaining energy with the avoidance of predation. In small birds, this trade-off is thought to be mass dependent because increased mass is expected to reduce maximum flight performance during escape from predators. For large mass changes, flight performance during escape follows the inverse relation predicted by Newtonian physics but apparently not for small mass changes. I investigated three possible explanations for this apparent breach of Newtonian physics. In a study of free-living great tits, Parus major, I found no significant change in flight performance in relation to diurnal mass change. First, the novel design of the experiment rules out various potential confounding factors common to previous experiments as an explanation. Second, I used the work–energy theorem from physics to show that birds did the same amount of work in morning and evening escape flights. This indicates that the birds were maximizing their flight performance and rules out physiological compensation to increased mass as an explanation. Third, by calculating the evening flight performances predicted by Newtonian physics for each individual in my experiment, I show that the level of diurnal mass change present in both this and previous studies could not be expected to produce a statistically significant change in flight performance. The results suggest that an effect of diurnal mass gain on alarmed flight speed would be undetectable with the sample sizes used so far.

Aircrew Fatigue in Trans‐Atlantic Morning and Evening Flights

The aim of the investigation was to compare sleepiness and sleep on westward morning and evening flights. Seven morning‐crew pilots and seven evening‐crew pilots participated. Data were collected before, during, and after outward‐bound (westward) and homeward‐bound (eastward) flights across six time zones. A sleep/wake diary (with repeated sleepiness and performance ratings) and wrist actigraphy were used for data collection. Maximum sleep was obtained after return and minimum sleep before the outward‐bound flights. Actigraphy measures and sleep efficiency over the course of the study showed no significant differences between the morning and evening crews. There was a trend for a significant effect of morning vs. evening flight for time with heavy eyelids, with the homeward‐bound flight showing more time with heavy eyelids. There were no significant differences between morning and evening crews with regard to napping during the flight. The duration of wakefulness was longer for the evening flight crew. There were significant interactions for Karolinska sleepiness scale (KSS) self‐ratings on both the outward‐bound and homeward‐bound flights, and KSS was elevated during a considerable portion of the evening flights. Rated performance showed a significant time effect, but there was no difference in self‐ratings between morning and evening crews. Evening flights involve higher levels of sleepiness than morning flights, presumably because of the close proximity in time to the circadian trough of alertness.