Anna Gagliardo

How animals navigate using single or several sensory modalities remains disputed. Humans often use distant landmarks such as mountain peaks as visual cues for orientation. Whether animals can also rely on distant visual cues while excluding other modalities, such as smell or visual maps, is difficult to test under natural conditions. We investigated this by releasing trained homing pigeons above thick ground fog from a plane. Birds were first trained to home individually from two ground sites, each ~15 km from their loft. Subsequently, trained individuals were released from a plane ~400 m above the terrestrial release sites during sunny conditions. This was followed by two experimental release conditions above continuous ground fog. Above the fog, pigeons cannot use a map or olfactory location cues, but may potentially use magnetic cues. When all landmarks were hidden by ground fog, pigeons showed poor orientation, tortuous flight paths, and descended through the fog within four min, advancing only ~0.1 km (0.1% of the distance) towards home. They subsequently waited for solar cues to continue homing. By contrast, when distant landmarks (alpine mountain tops) were visible, pigeons maintained strong homeward orientation, flying for 20 min and covering 96% of the distance to home, similar to ground-level controls (17 min, 80%). These results demonstrate that when known olfactory cues or local maps are excluded, distant landmarks—but not magnetic cues—enable efficient short-distance homing in experienced pigeons.

Bird flocks frequently generate human–wildlife conflicts, resulting in safety and health hazards, and economic losses. Remotely controlled, raptor‐like robots have recently emerged as potentially effective deterrence tools, exploiting the innate collective escape response of birds to their predators and hence avoiding the emergence of habituation, but field tests are still scanty. We tested the effectiveness of a robotic falcon (RobotFalcon [RF]) as a deterrence tool for feral pigeons Columba livia breeding and feeding in a cattle farm (~500 individuals) and black‐headed gulls Chroicocephalus ridibundus night‐roosting in a wastewater treatment plant (~8000 individuals). We analysed collective behavioural responses during 10‐min RF exposure trials mimicking natural predator attacks and assessed deterrence effectiveness (change in the number of birds) at different temporal scales (immediate response—within‐trials and returning post‐trials; short‐term response—across 5–8 successive daily exposures). We also evaluated medium‐term deterrence effectiveness by quantifying gull flight activity using a marine radar for ~10 days after RF exposure trials. The RF induced consistent collective behavioural responses, similar to real avian predators. The frequency of collective behaviours decreased both within‐ and across trials, mainly because flocks rapidly abandoned the target sites. Pigeons decreased both during and increasingly across trials, abandoning the target site soon after trial onset. However, most pigeons returned within 30 min after the end of trials, and individuals returning post‐trials decreased only slightly (13%) across trials. The RF triggered massive gull displacements during trials, with a faster reaction in the last trial days compared to initial ones, and individuals returning post‐trials decreased markedly (94%) across trials. Night flight activity showed a large (40%) decrease post‐ compared to pre‐trial days, suggesting persistent deterrence effects. Practical implication. The RF is a valuable tool to deter birds from gathering in flocks in contexts where human–wildlife conflict may arise, based on robust evidence and field tests under different conditions. Yet, its effectiveness may depend on the importance of resources used by the target flocking species at the exposure site. Predator‐like robots provide unique advantages related to animal welfare, consistency of deterrence protocols and effective management of human–wildlife conflicts.

Homing pigeons rely on familiar landscape features in learning a visual map, which is orchestrated by the forebrain visual Wulst and hippocampus. Recent global positioning system tracking studies showed that pigeons with damage to the visual Wulst or hippocampus exhibited a still poorly understood, persistent oscillatory flight behaviour, unlike intact pigeons whose oscillations decrease with experience. To evaluate whether landscape heterogeneity influences the extent of these oscillations, we compared the flight behaviour of both intact and Wulst-lesioned pigeons when flying over the sea versus land. Regardless of treatment, pigeons exhibited less oscillatory flight behaviour over the homogeneous landscape of the sea. Further releases from familiar and unfamiliar sites tested whether oscillatory flight behaviour may be influenced by the level of familiarity with the landscape. Indeed, intact pigeons reduced their oscillatory behaviour as landscape familiarity increased. In contrast, Wulst-damaged pigeons persisted in displaying robust oscillatory flight behaviour regardless of the level of landscape familiarity, suggesting that previously experienced landscapes remained relatively unfamiliar to them. The data support the hypothesis that oscillatory flight behaviour reflects active visual scanning, most pronounced over novel, heterogeneous landscapes, contributing to visual map learning. Further, the data suggest a crucial role of the forebrain Wulst for such learning.

Functional asymmetries of the avian visual system can be studied in monocularly occluded birds, as their hemispheres are largely independent. Right and left monocularly occluded homing pigeons and control birds under binocular view have been trained in a food localisation task in an octagonal outdoor arena provided with one coloured beacon on each wall. The three groups were tested after the removal of the visual beacons, so to assess their sun compass learning abilities. Pigeons using the left eye/right hemisphere system exhibited slower learning compared to the other monocular group. During the test in the arena void of visual beacons, the three groups of birds, regardless of their visual condition, were generally able to identify the training sector by exclusively relying on sun compass information. However, the directional choices of the pigeons with the left eye/right hemisphere in use were significantly affected by the removal of the beacons, while both control pigeons and birds with the right eye/left hemisphere in use displayed unaltered performances during the test. A subsample of pigeons of each group were re-trained in the octagonal arena with visual beacons present and tested after the removal of visual beacons after a 6 h fast clock-shift treatment. All birds displayed the expected deflection consistent to the sun compass use. While birds using either the left or the right visual systems were equally able to learn a sun compass-mediated spatial task, the left eye/right hemisphere visual system displayed an advantage in relying on visual beacons.

Muskrats (Ondatra zibethicus) are competent intermediate hosts for Echinococcus multilocularis, are frequently infected with this zoonotic cestode, and have even been proposed as a target species to monitor endemicity levels of this parasite. However, their contribution to maintaining the parasitic lifecycle is still unclear. To obtain data on infection frequency and reproductive potential, 280 muskrats from the Grand Duchy of Luxembourg were examined for cestode larvae in the years 2013–2017. Based on morphological and molecular identification, Echinococcus multilocularis was found at a prevalence of 14.6%. Other metacestodes were Hydatigera kamiyai, with a prevalence of 45.7%, Taenia martis with 8.9%, Taenia polyacantha with 5.0%, and Versteria mustelae, which was found in 0.7% of all muskrats. More than 80% of E. multilocularis-infected muskrats contained fertile metacestodes with a mean number of >300,000 (and up to 1,609,816) protoscoleces, which is by far the highest reproductive potential known from any intermediate host species in Europe. Temporal analysis of E. multilocularis prevalence within the study period (and in comparison with earlier data) strongly indicates a robust increase in the studied area. Host age seemed to be an important risk factor for infection, as well as co-infections with Hydatigera kamiyai. A preference for the right medial lobe of the liver as the location of E. multilocularis metacestode was observed. Intraspecific genetic variation among 89 discrete E. multilocularis metacestodes was non-existent based on 300–1590 bp sections of cox1. This is a stark contrast to H. kamiyai, of which nine haplotypes were found on a short 318 bp section of cox1, resulting in genetic diversity in the small country of Luxembourg at a similar level than previously reported from large stretches of Europe and northern Asia.