Continental-scale patterns in diel flight timing of high-altitude migratory insects.

Many insects depend on high-altitude, migratory movements during part of their life cycle. The daily timing of these migratory movements is not random, e.g. many insect species show peak migratory flight activity at dawn, noon or dusk. These insects provide essential ecosystem services such as pollination but also contribute to crop damage. Quantifying the diel timing of their migratory flight and its geographical and seasonal variation, are hence key towards effective conservation and pest management. Vertical-looking radars provide continuous and automated measurements of insect migration, but large-scale application has not been possible because of limited availability of suitable devices. Here, we quantify patterns in diel flight periodicity of migratory insects between 50 and 500 m above ground level during March-October 2021 using a network of 17 vertical-looking radars across Europe. Independent of the overall daily migratory movements and location, peak migratory movements occur around noon, during crepuscular evening and occasionally the morning. Relative daily proportions of insect migration intensity and traffic during the diel phases of crepuscular-morning, day, crepuscular-evening and night remain largely equal throughout May-September and across Europe. These findings highlight, extend, and generalize previous regional-scale findings on diel migratory insect movement patterns to the whole of temperate Europe. This article is part of the theme issue 'Towards a toolkit for global insect biodiversity monitoring'.

Does a high social status confer greater levels of trust from groupmates? An experimental study of leadership in domestic horses.

In collective movements, specific individuals may emerge as leaders. In this study on the domestic horse (Equus ferus caballus), we conducted experiments to establish if an individual is successfully followed due to its social status (including hierarchical rank and centrality). We first informed one horse about a hidden food location and recorded by how many it was followed when going back to this location. In this context, all horses lead their groupmates successfully. In a second step, we tested whether group members would trust some leaders more than others by removing the food before the informed individual led the group back to the food location. In addition, two control initiators with intermediate social status for which the food was not removed were tested. The results, confirmed by simulations, demonstrated that the proportions of followers for the unreliable initiator with highest social status are greater than the ones of the unreliable initiator with lowest social status. Our results suggest an existing relationship between having a high social status and a leadership role. Indeed, the status of a leader sometimes prevail at the detriment of the accuracy of the information, because an elevated social status apparently confers a high level of trust.

Exclusion in the field: wild brown skuas find hidden food in the absence of visual information.

Inferential reasoning by exclusion allows responding adaptively to various environmental stimuli when confronted with inconsistent or partial information. In the experimental context, this mechanism involves selecting correctly between an empty option and a potentially rewarded one. Recently, the increasing reports of this capacity in phylogenetically distant species have led to the assumption that reasoning by exclusion is the result of convergent evolution. Within one largely unstudied avian order, i.e. the Charadriiformes, brown skuas (Catharacta antarctica ssp lonnbergi) are highly flexible and opportunistic predators. Behavioural flexibility, along with specific aspects of skuas' feeding ecology, may act as influencing factors in their ability to show exclusion performance. Our study aims to test whether skuas are able to choose by exclusion in a visual two-way object-choice task. Twenty-six wild birds were presented with two opaque cups, one covering a food reward. Three conditions were used: 'full information' (showing the content of both cups), 'exclusion' (showing the content of the empty cup), and 'control' (not showing any content). Skuas preferentially selected the rewarded cup in the full information and exclusion condition. The use of olfactory cues was excluded by results in the control condition. Our study opens new field investigations for testing further the cognition of this predatory seabird.

micrObs - A customizable time-lapse camera for ecological studies.

Camera traps for motion-triggered or continuous time-lapse recordings are readily available on the market. For demanding applications in ecology and environmental sciences, however, commercial systems often lack flexibility to freely adjust recording time intervals, suffer from mechanical component wear, and can be difficult to combine with auxiliary sensors such as GPS, weather stations, or light sensors. We present a robust time-lapse camera system that has been operating continuously since 2013 under the harsh climatic conditions of the Antarctic and Subantarctic regions. Thus far, we have recorded over one million images with individual cameras. The system consumes 122 mW of power in standby mode and captures up to 200,000 high-resolution (16 MPix) images without maintenance such as battery or image memory replacement. It offers time-lapse intervals between 2 s and 1 h, low-light or night-time power saving, and data logging capabilities for additional inputs such as GPS and weather data.

The invisible cues that guide king penguin chicks home: use of magnetic and acoustic cues during orientation and short-range navigation.

King penguins (Aptenodytes patagonicus) live in large and densely populated colonies, where navigation can be challenging because of the presence of many conspecifics that could obstruct locally available cues. Our previous experiments demonstrated that visual cues were important but not essential for king penguin chicks' homing. The main objective of this study was to investigate the importance of non-visual cues, such as magnetic and acoustic cues, for chicks' orientation and short-range navigation. In a series of experiments, the chicks were individually displaced from the colony to an experimental arena where they were released under different conditions. In the magnetic experiments, a strong magnet was attached to the chicks' heads. Trials were conducted in daylight and at night to test the relative importance of visual and magnetic cues. Our results showed that when the geomagnetic field around the chicks was modified, their orientation in the arena and the overall ability to home was not affected. In a low sound experiment we limited the acoustic cues available to the chicks by putting ear pads over their ears, and in a loud sound experiment we provided additional acoustic cues by broadcasting colony sounds on the opposite side of the arena to the real colony. In the low sound experiment, the behavior of the chicks was not affected by the limited sound input. In the loud sound experiment, the chicks reacted strongly to the colony sound. These results suggest that king penguin chicks may use the sound of the colony while orienting towards their home.

Flying at no mechanical energy cost: disclosing the secret of wandering albatrosses.

Albatrosses do something that no other birds are able to do: fly thousands of kilometres at no mechanical cost. This is possible because they use dynamic soaring, a flight mode that enables them to gain the energy required for flying from wind. Until now, the physical mechanisms of the energy gain in terms of the energy transfer from the wind to the bird were mostly unknown. Here we show that the energy gain is achieved by a dynamic flight manoeuvre consisting of a continually repeated up-down curve with optimal adjustment to the wind. We determined the energy obtained from the wind by analysing the measured trajectories of free flying birds using a new GPS-signal tracking method yielding a high precision. Our results reveal an evolutionary adaptation to an extreme environment, and may support recent biologically inspired research on robotic aircraft that might utilize albatrosses' flight technique for engineless propulsion.

Orientation in a crowded environment: can King Penguin (Aptenodytes patagonicus) chicks find their creches after a displacement?

For seabird species, the presence of conspecifics in a crowded breeding colony can obstruct locally available orientation cues. Thus, navigation to specific locations can present a challenging problem. We investigated short-range orientation in King Penguin (Aptenodytes patagonicus) chicks that live in a large and densely populated colony. The two main objectives were to determine whether chicks displaced to a novel location away from the colony (i) can orient towards the colony and return to their crèche and (ii) rely on visual or non-visual cues for orientation. To address these questions, a circular arena was constructed 100 m away from the colony. Chicks were released in the arena during the day and at night. After the orientation experiment in the arena, chicks were allowed to return to their home crèche, if they could. Our results showed that, during day trials, chicks preferred the half of the arena closer to the colony, but not at night. However, at night, birds spent more time on ;the colony half' of the arena if the wind blew from the colony direction. When animals were allowed to leave the arena, 98% of chicks homed during the day but only 62% of chicks homed at night. Chicks that homed at night also took longer to find their crèche. The experiments suggest that King Penguin chicks can find their crèche from a novel location. Visual cues are important for homing but, when visual cues are not present, animals are able to make use of other information carried by the wind.

Age-dependent use of local and global landmarks during escape: experiments using Columbian ground squirrels.

How animals utilize their space often changes during ontogeny, perhaps resulting from alternative use of orientation mechanisms. This study investigated whether landmark-based navigation mechanisms were age-dependent in Columbian ground squirrels (Spermophilus columbianus). In field tests, young (1-2 years old) and adult (3-6 years old) animals had to find an escape burrow when either local, global, or both types of landmarks were obstructed. The comparison of escape times between age groups revealed that adult squirrels found escape burrow faster than young animals if global landmarks were available. However, if only local landmarks were present, young squirrels outperformed older animals. The comparison of escape time within each age group showed that obstruction of global or local landmarks lengthened escape time of adult squirrels. In contrast, young animals had longer escapes only when local landmarks were obstructed. The results suggested that the use of different types of landmarks was age specific.