Wikelski, Martin

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Now showing 1 - 10 of 55
  • Data package
    Data from: Pigeons remember visual landmarks after one release and rely upon them more if they are anosmic
    (2020-09-24) Gagliardo, Anna; Pollonara, Enrica; Wikelski, Martin
    Anosmic birds' homing ability is impaired when challenged to navigate over unfamiliar areas. Nevertheless, anosmic pigeons, Columba livia, show unimpaired navigation when released within a familiar area, suggesting that they may rely on familiar visual landmarks for navigation. However, direct evidence for the reliance on familiar visual landmarks during homing in anosmic birds has never been provided. In this study we tracked pigeons subjected singly to one training flight from each of three locations. Prior to their second release from each site, half of the birds were made anosmic while the others were not manipulated. The level of route fidelity was analysed separately for three phases of the homing process, in which familiar visual cues may have different relevance and may be used within different cognitive strategies: (1) ‘Initial decision making’; (2) ‘En route navigation’; (3) ‘Local navigation around home’. Compared to control birds, the anosmic birds flew significantly closer to previously overflown locations in the ‘En route navigation’ phase, while no difference in route fidelity emerged during phases (1) and (3). Our results showed that a single experience is sufficient for pigeons to learn release site features, and that familiar visual landmarks constitute a critical source of navigational information in olfactorily deprived birds during the homing process.
  • Data package
    Data from: The gateway to Africa: what determines sea crossing performance of a migratory soaring bird at the strait of Gibraltar?
    (2020-03-08) Santos, Carlos David; Silva, João Paulo; Muñoz, Antonio-Román; Onrubia, Alejandro; Wikelski, Martin
    (1) Large bodies of water represent major obstacles for the migration of soaring birds because thermal updrafts are absent or weak over water. Soaring birds are known to time their water crossings with favourable weather conditions and there are records of birds falling into the water and drowning in large numbers. However, it is still unclear how environmental factors, individual traits and trajectory choices affect their water crossing performance, this being important to understand the fitness consequences of water barriers for this group of birds. (2) We addressed this problem using the black kite (Milvus migrans) as model species at a major migration bottleneck, the Strait of Gibraltar. (3) We recorded high‐resolution GPS and triaxial accelerometer data for 73 birds while crossing the Strait of Gibraltar, allowing the determination of sea crossing duration, length, altitude, speed and tortuosity, the flapping behaviour of birds and their failed crossing attempts. These parameters were modelled against wind speed and direction, time of the day, solar irradiance (proxy of thermal uplift), starting altitude and distance to Morocco, and age and sex of birds. (4) We found that sea crossing performance of black kites is driven by their age, the wind conditions, the starting altitude and distance to Morocco. Young birds made longer sea crossings and reached lower altitude above the sea than adults. Crosswinds promoted longer sea crossings, with birds reaching lower altitudes and with higher flapping effort. Birds starting at lower altitudes were more likely to quit or made higher flapping effort to complete the crossing. The location where birds started the sea crossings impacted crossing distance and duration. (5) We present evidence that explains why migrating soaring birds accumulate at sea passages during adverse weather conditions. Strong crosswinds during sea crossings force birds to extended flap‐powered flight at low altitude, which may increase their chances of falling in the water. We also showed that juvenile birds assume more risks than adults. Finally, the way in which birds start the sea crossing is crucial for their success, particularly the starting altitude, which dictates how far birds can reach with reduced flapping effort.
  • Data package
    Data from: Towards a new understanding of migration timing: slower spring than autumn migration in geese reflects different decision rules for stopover use and departure
    (2016-02-25) Kölzsch, Andrea; Kruckenberg, Helmut; Glazov, Peter; Müskens, Gerhard J.D.M.; Wikelski, Martin
    According to migration theory and several empirical studies, long-distance migrants are more time-limited during spring migration and should therefore migrate faster in spring than in autumn. Competition for the best breeding sites is supposed to be the main driver, but timing of migration is often also influenced by environmental factors such as food availability and wind conditions. Using GPS tags, we tracked 65 greater white-fronted geese Anser albifrons migrating between western Europe and the Russian Arctic during spring and autumn migration over six different years. Contrary to theory, our birds took considerably longer for spring migration (83 days) than autumn migration (42 days). This difference in duration was mainly determined by time spent at stopovers. Timing and space use during migration suggest that the birds were using different strategies in the two seasons: In spring they spread out in a wide front to acquire extra energy stores in many successive stopover sites (to fuel capital breeding), which is in accordance with previous results that white-fronted geese follow the green wave of spring growth. In autumn they filled up their stores close to the breeding grounds and waited for supportive wind conditions to quickly move to their wintering grounds. Selection for supportive winds was stronger in autumn, when general wind conditions were less favourable than in spring, leading to similar flight speeds in the two seasons. In combination with less stopover time in autumn this led to faster autumn than spring migration. White-fronted geese thus differ from theory that spring migration is faster than autumn migration. We expect our findings of different decision rules between the two migratory seasons to apply more generally, in particular in large birds in which capital breeding is common, and in birds that meet other environmental conditions along their migration route in autumn than in spring.
  • Data package
    Data from: The Environmental-Data Automated Track Annotation (Env-DATA) System: Linking animal tracks with environmental data
    (2013-07-03) Cruz, Sebastian; Proaño, Carolina B.; Anderson, Dave; Huyvaert, Kate; Wikelski, Martin
    Background: The movement of animals is strongly influenced by external factors in their surrounding environment such as weather, habitat types, and human land use. With advances in positioning and sensor technologies, it is now possible to capture animal locations at high spatial and temporal granularities. Likewise, scientists have an increasing access to large volumes of environmental data. Environmental data are heterogeneous in source and format, and are usually obtained at different spatiotemporal scales than movement data. Indeed, there remain scientific and technical challenges in developing linkages between the growing collections of animal movement data and the large repositories of heterogeneous remote sensing observations, as well as in the developments of new statistical and computational methods for the analysis of movement in its environmental context. These challenges include retrieval, indexing, efficient storage, data integration, and analytical techniques. Results: This paper contributes to movement ecology research by presenting a new publicly available system, Environmental-Data Automated Track Annotation (Env-DATA), that automates annotation of movement trajectories with ambient atmospheric observations and underlying landscape information. Env-DATA provides a free and easy-to-use platform that eliminates technical difficulties of the annotation processes and relieves end users of a ton of tedious and time-consuming tasks associated with annotation, including data acquisition, data transformation and integration, resampling, and interpolation. The system is illustrated with a case study of Galapagos Albatross (Phoebastria irrorata) tracks and their relationship to wind, ocean productivity and chlorophyll concentration. Our case study illustrates why adult albatrosses make long-range trips to preferred, productive areas and how wind assistance facilitates their return flights while their outbound flights are hampered by head winds. Conclusions: The new Env-DATA system enhances Movebank, an open portal of animal tracking data, by automating access to environmental variables from global remote sensing, weather, and ecosystem products from open web resources. The system provides several interpolation methods from the native grid resolution and structure to a global regular grid linked with the movement tracks in space and time. The aim is to facilitate new understanding and predictive capabilities of spatiotemporal patterns of animal movement in response to dynamic and changing environments from local to global scales.
  • Data package
    Data from: Shared decision-making drives collective movement in wild baboons
    (2015-06-19) Crofoot, Margaret C.; Kays, Roland; Wikelski, Martin
    NOTE: An updated and larger version of this dataset is available. See ABSTRACT: Conflicts of interest about where to go and what to do are a primary challenge of group living. However, it remains unclear how consensus is achieved in stable groups with stratified social relationships. Tracking wild baboons with a high-resolution global positioning system and analyzing their movements relative to one another reveals that a process of shared decision-making governs baboon movement. Rather than preferentially following dominant individuals, baboons are more likely to follow when multiple initiators agree. When conflicts arise over the direction of movement, baboons choose one direction over the other when the angle between them is large, but they compromise if it is not. These results are consistent with models of collective motion, suggesting that democratic collective action emerging from simple rules is widespread, even in complex, socially stratified societies.
  • Data package
    Data from: The effect of feeding time on dispersal of Virola seeds by toucans determined from GPS tracking and accelerometers
    (2016-01-12) Kays, Roland; Jansen, Patrick A.; Knecht, Elise M.H.; Vohwinkel, Reinhard; Wikelski, Martin
    Seed dispersal is critical to understanding forest dynamics but is hard to study because tracking seeds is difficult. Even for the best-studied dispersal system of the Neotropics, Virola nobilis, the dispersal kernel remains unknown. We combined high-resolution GPS/3D-acceleration bird tracking, seed-retention experiments, and field observations to quantify dispersal of V. nobilis by their principal dispersers, Ramphastos toucans. We inferred feeding events from movement data, and then estimated spatiotemporally explicit seed-dispersal kernels. Wild toucans moved an average of 1.8 km d^-1 with two distinct activity peaks. Seed retention time in captive toucans averaged 25.5 min (range 4-98 min). Estimated seed dispersal distance averaged 144 +/- 147 m, with a 56% likelihood of dispersal >100 m, two times further than the behaviour-naive estimate from the same data. Dispersal was furthest for seeds ingested in the morning, and increased with seed retention time, but only up to 60 min after feeding. Our study supports the long-standing hypothesis that toucans are excellent dispersers of Virola seeds. To maximize seed dispersal distances trees should ripen fruit in the morning when birds move the most, and produce fruits with gut-processing times around 60 min. Our study demonstrates how new tracking technology can yield nuanced seed dispersal kernels for animals that cannot be directly observed.
  • Data package
    Data from: Olfaction and topography, but not magnetic cues, control navigation in a pelagic seabird: displacements with shearwaters in the Mediterranean Sea
    (2015-10-27) Pollonara, Enrica; Luschi, Paolo; Guilford, Tim; Wikelski, Martin; Bonadonna, Francesco; Gagliardo, Anna
    Pelagic seabirds wander the open oceans then return accurately to their habitual nest-sites. We investigated the effects of sensory manipulation on oceanic navigation in Scopoli’s shearwaters (Calonectris diomedea) breeding at Pianosa island (Italy), by displacing them 400 km from their colony and tracking them. A recent experiment on Atlantic shearwaters (Cory’s shearwater, Calonectris borealis) breeding in the Azores indicated a crucial role of olfaction over the open ocean, but left open the question of whether birds might navigate by topographical landmark cues when available. Our experiment was conducted in the Mediterranean sea, where the availability of topographical cues may provide an alternative navigational mechanism for homing. Magnetically disturbed shearwaters and control birds oriented homeward even when the coast was not visible and rapidly homed. Anosmic shearwaters oriented in a direction significantly different from the home direction when in open sea. After having approached a coastline their flight path changed from convoluted to homeward oriented, so that most of them eventually reached home. Beside confirming that magnetic cues appear unimportant for oceanic navigation by seabirds, our results support the crucial role of olfactory cues for birds’ navigation and reveal that anosmic shearwaters are able to home eventually by following coastal features.
  • Data package
    Data from: European free-tailed bats use topography and nocturnal updrafts to fly high and fast
    (2021-02-04) O'Mara, M. Teague; Amorim, Francisco; McCracken, Gary F.; Mata, Vanessa; Safi, Kamran; Wikelski, Martin; Beja, Pedro; Rebelo, Hugo; Dechmann, Dina K.N.
    During the day, flying animals exploit the environmental energy landscape by seeking out thermal or orographic uplift, or extracting energy from wind gradients. However, most of these energy sources are not thought to be available at night because of the lower thermal potential in the nocturnal atmosphere, as well as the difficulty of locating features that generate uplift. Despite this, several bat species have been observed hundreds to thousands of meters above the ground. Individuals make repeated, energetically costly high-altitude ascents, and others fly at some of the fastest speeds observed for powered vertebrate flight. We hypothesized that bats use orographic uplift to reach high altitudes, and that both this uplift and bat high-altitude ascents would be highly predictable. By superimposing detailed three-dimensional GPS tracking of European free-tailed bats (Tadarida teniotis) on high-resolution regional wind data, we show that bats do indeed use the energy of orographic uplift to climb to over 1,600 m, and also that they reach maximum sustained self-powered airspeeds of 135 km h−1. We show that wind and topography can predict areas of the landscape able to support high-altitude ascents, and that bats use these locations to reach high altitudes while reducing airspeeds. Bats then integrate wind conditions to guide high-altitude ascents, deftly exploiting vertical wind energy in the nocturnal landscape.
  • Data package
    Data from: Longer days enable higher diurnal activity for migratory birds [greater white-fronted geese]
    (2021-03-24) Kölzsch, Andrea; Müskens, Gerhard J.D.M.; Moonen, Sander; Kruckenberg, Helmut; Glazov, Peter; Wikelski, Martin
    (1) Seasonal geophysical cycles strongly influence the activity of life on Earth because they affect environmental conditions like temperature, precipitation, and daylength. An increase in daylight availability during summer is especially enhanced when animals migrate along a latitudinal gradient. Yet, the question of how daylength (i.e. daylight availability) influences the activity patterns of long‐distance, latitudinal migrants is still unclear. (2) Here, we ask whether migration provides benefits to long‐distance migrants by enabling them to increase their diurnal movement activities due to an increase in daylight availability. To answer this question, we tested whether four vastly different species of long‐distance migratory birds--two arctic migrants and two mid‐latitude migrants--can capitalise on day length changes by adjusting their daily activity. (3) We quantified the relationship between daily activity (measured using accelerometer data) and day length, and estimated each species' daily activity patterns. In addition, we evaluated the role of day length as an ultimate driver of bird migration. (4) All four species exhibited longer activity periods during days with more daylight hours, showing a strong positive relationship between total daily activity and day length. The slope of this relationship varied between the different species, with activity increasing 1.5‐fold on average when migrating from wintering to breeding grounds. Underlying mechanisms of these relationships reveal two distinct patterns of daily activity. Flying foragers showed increasing activity patterns, i.e. their daytime activities rose uniformly up to solar noon and decreased until dusk, thereby exhibiting a season‐specific activity slope. In contrast, ground foragers showed a constant activity pattern, whereby they immediately increased their activity to a certain level and maintained this level throughout the day. (5) Our study reveals that long days allow birds to prolong their activity and increase their total daily activity. These findings highlight that daylight availability could be an additional ultimate cause of bird migration and act as a selective agent for the evolution of migration.
  • Data package
    Data from: Black kites of different age and sex show similar avoidance responses to wind turbines during migration
    (2021-01-24) Santos, Carlos David; Ferraz, Rafael; Muñoz, Antonio-Román; Onrubia, Alejandro; Wikelski, Martin
    Populations of soaring birds are often impacted by wind-power generation. Sex and age bias in turbine collisions can exacerbate these impacts through demographic changes that can lead to population decline or collapse. While several studies have reported sex and age differences in the number of soaring birds killed by turbines, it remains unclear if they result from different abundances or group-specific turbine avoidance behaviours, the latter having severer consequences. We investigated sex and age effects on turbine avoidance behaviour of black kites (Milvus migrans) during migration near the Strait of Gibraltar. We tracked the movements of 135 individuals with GPS data loggers in an area with high density of turbines and then modelled the effect of proximity of turbines on bird utilization distribution (UD). Both sexes and age classes showed similar patterns of displacement, with reduced UD values in the proximity of turbines and a clear peak at 700–850 m away, probably marking the distance at which most birds turn direction to avoid approaching the turbines further. The consistency of these patterns indicates that displacement range can be used as an accurate proxy for collision risk and habitat loss, and should be incorporated in environmental impact assessment studies.