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Data from: The secret life of oilbirds: new insights into the movement ecology of a unique avian frugivore
(2012-03-15) Holland, Richard A.; Wikelski, Martin; Kuemmeth, Franz; Bosque, Carlos
Background: Steatornis caripensis (the oilbird) is a very unusual bird. It supposedly never sees daylight, roosting in huge aggregations in caves during the day and bringing back fruit to the cave at night. As a consequence a large number of the seeds from the fruit they feed upon germinate in the cave and spoil. Methodology/Principal Findings: Here we use newly developed GPS/acceleration loggers with remote UHF readout to show that several assumptions about the behaviour of Steatornis caripensis need to be revised. On average, they spend only every 3rd day in a cave, individuals spent most days sitting quietly in trees in the rainforest where they regurgitate seeds. Conclusions/Significance: This provides new data on the extent of seed dispersal and the movement ecology of Steatornis caripensis. It suggests that Steatornis caripensis is perhaps the most important long-distance seed disperser in Neotropical forests. We also show that colony-living comes with high activity costs to individuals.
Data from: The effect of feeding time on dispersal of Virola seeds by toucans determined from GPS tracking and accelerometers
(2012-03-20) Kays, Roland; Jansen, Patrick A.; Knecht, Elise M.H.; Wikelski, Martin; Vohwinkel, Reinhard
NOTE: A corrected version of this dataset is available. See doi:10.5441/001/1.f32gn841. ABSTRACT: 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 spatio-temporally 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 from: Homing pigeons only navigate in air with intact environmental odours: a test of the olfactory activation hypothesis with GPS data loggers [partial dataset]
(2012-03-29) Gagliardo, Anna; Ioalè, Paolo; Filannino, Caterina; Wikelski, Martin
NOTE: A corrected version of this dataset is available. See doi:10.5441/001/1.2sr7mm39. ABSTRACT: A large body of evidence has shown that anosmic pigeons are impaired in their navigation. However, the role of odours in navigation is still subject to debate. While according to the olfactory navigation hypothesis homing pigeons possess a navigational map based on the distribution of environmental odours, the olfactory activation hypothesis proposes that odour perception is only needed to activate a navigational mechanism based on cues of another nature. Here we tested experimentally whether the perception of artificial odours is sufficient to allow pigeons to navigate, as expected from the olfactory activation hypothesis. We transported three groups of pigeons in air-tight containers to release sites 53 and 61 km from home in three different olfactory conditions. The Control group received natural environmental air; both the Pure Air and the Artificial Odour groups received pure air filtered through an active charcoal filter. Only the Artificial Odour group received additional puffs of artificial odours until release. We then released pigeons while recording their tracks with 1 Hz GPS data loggers. We also followed non-homing pigeons using an aerial data readout to a Cessna plane, allowing, for the first time, the tracking of non-homing homing pigeons. Within the first hour after release, the pigeons in both the Artificial Odour and the Pure Air group (receiving no environmental odours) showed impaired navigational performances at each release site. Our data provide evidence against an activation role of odours in navigation, and document that pigeons only navigate well when they perceive environmental odours.
Data from: Homing pigeons only navigate in air with intact environmental odours: a test of the olfactory activation hypothesis with GPS data loggers [full dataset]
(2012-04-01) Gagliardo, Anna; Ioalè, Paolo; Filannino, Caterina; Wikelski, Martin
A large body of evidence has shown that anosmic pigeons are impaired in their navigation. However, the role of odours in navigation is still subject to debate. While according to the olfactory navigation hypothesis homing pigeons possess a navigational map based on the distribution of environmental odours, the olfactory activation hypothesis proposes that odour perception is only needed to activate a navigational mechanism based on cues of another nature. Here we tested experimentally whether the perception of artificial odours is sufficient to allow pigeons to navigate, as expected from the olfactory activation hypothesis. We transported three groups of pigeons in air-tight containers to release sites 53 and 61 km from home in three different olfactory conditions. The Control group received natural environmental air; both the Pure Air and the Artificial Odour groups received pure air filtered through an active charcoal filter. Only the Artificial Odour group received additional puffs of artificial odours until release. We then released pigeons while recording their tracks with 1 Hz GPS data loggers. We also followed non-homing pigeons using an aerial data readout to a Cessna plane, allowing, for the first time, the tracking of non-homing homing pigeons. Within the first hour after release, the pigeons in both the Artificial Odour and the Pure Air group (receiving no environmental odours) showed impaired navigational performances at each release site. Our data provide evidence against an activation role of odours in navigation, and document that pigeons only navigate well when they perceive environmental odours.
Data from: Thieving rodents as substitute dispersers of megafaunal seeds
(2012-06-27) Jansen, Patrick A.; Hirsch, Ben T.; Emsens, Willem-Jan; Zamora-Gutierrez, Veronica; Wikelski, Martin; Kays, Roland
The Neotropics have many plant species that seem to be adapted for seed dispersal by megafauna that went extinct in the late Pleistocene. Given the crucial importance of seed dispersal for plant persistence, it remains a mystery how these plants have survived more than 10,000 y without their mutualist dispersers. Here we present support for the hypothesis that secondary seed dispersal by scatter-hoarding rodents has facilitated the persistence of these large-seeded species. We used miniature radio transmitters to track the dispersal of reputedly megafaunal seeds by Central American agoutis, which scatter-hoard seeds in shallow caches in the soil throughout the forest. We found that seeds were initially cached at mostly short distances and then quickly dug up again. However, rather than eating the recovered seeds, agoutis continued to move and recache the seeds, up to 36 times. Agoutis dispersed an estimated 35% of seeds for >100 m. An estimated 14% of the cached seeds survived to the next year, when a new fruit crop became available to the rodents. Serial video-monitoring of cached seeds revealed that the stepwise dispersal was caused by agoutis repeatedly stealing and recaching each other’s buried seeds. Although previous studies suggest that rodents are poor dispersers, we demonstrate that communities of rodents can in fact provide highly effective long-distance seed dispersal. Our findings suggest that thieving scatter-hoarding rodents could substitute for extinct megafaunal seed dispersers of tropical large-seeded trees.
Data from: East with the night—longitudinal migration of the Orinoco Goose between Manú National Park, Peru and the Llanos de Moxos, Bolivia
(2012-10-08) Davenport, Lisa C.; Nole, Inés; Carlos, Nancy
We report on the intra-Amazonian migration of a pair of Orinoco Geese (Neochen jubata) from Manú National Park, Peru. The species is Critically Endangered in Peru, so a major aim of the study was to aid conservation planning by learning the wet season location of the country's last known breeding population. We captured a breeding pair on October 27, 2010, and fitted the birds with Microwave Telemetry, Inc. GPS/Argos satellite PTT's. The pair migrated ~655 km from Manú National Park to the Llanos de Moxos, Bolivia (Dept. of Bení) in a predominantly longitudinal migration, reaching their final destination on December 23, 2010. Major movements (>5 km per time period) were almost exclusively at night and were undertaken with and without moonlight. Foraging areas used at stopovers in the Llanos de Moxos were remarkably limited, suggesting the importance of grazing lawns maintained by the geese and other herbivores, possibly including cattle. Orinoco Geese are resident in the Llanos de Moxos year-round, so the Manú geese represent a partial migration from the Bení region. We hypothesize that cavity nest limitation explains the partial migration of Orinoco Geese from the Llanos de Moxos.
Data from: Animal behavior, cost-based corridor models, and real corridors
(2013-07-02) LaPoint, Scott; Gallery, Paul; Wikelski, Martin; Kays, Roland
Corridors are popular conservation tools because they are thought to allow animals to safely move between habitat fragments, thereby maintaining landscape connectivity. Nonetheless, few studies show that mammals actually use corridors as predicted. Further, the assumptions underlying corridor models are rarely validated with field data. We categorized corridor use as a behavior, to identify animal-defined corridors, using movement data from fishers (Martes pennanti) tracked near Albany, New York, USA. We then used least-cost path analysis and circuit theory to predict fisher corridors and validated the performance of all three corridor models with data from camera traps. Six of eight fishers tracked used corridors to connect the forest patches that constitute their home ranges, however the locations of these corridors were not well predicted by the two cost-based models, which together identified only 5 of the 23 used corridors. Further, camera trap data suggest the cost-based corridor models performed poorly, often detecting fewer fishers and mammals than nearby habitat cores, whereas camera traps within animal-defined corridors recorded more passes made by fishers, carnivores, and all other non-target mammal groups. Our results suggest that (1) fishers use corridors to connect disjunct habitat fragments, (2) animal movement data can be used to identify corridors at local scales, (3) camera traps are useful tools for testing corridor model predictions, and (4) that corridor models can be improved by incorporating animal behavior data. Given the conservation importance and monetary costs of corridors, improving and validating corridor model predictions is vital.
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, David J.; 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 from: Oceanic navigation in Cory’s shearwaters—evidence for a crucial role of olfactory cues for homing after displacement
(2013-07-16) Gagliardo, Anna; Bried, Joël; Lambardi, Paolo; Luschi, Paolo; Wikelski, Martin; Bonadonna, Francesco
Pelagic birds, which wander in the open sea most of the year and often nest on small remote oceanic islands, are able to pinpoint their breeding colony even within an apparently featureless environment, such as the open ocean. The mechanisms underlying their surprising navigational performance are still unknown. In order to investigate the nature of the cues exploited for oceanic navigation, Cory's shearwaters, Calonectris borealis, nesting in the Azores were displaced and released in open ocean at about 800 km from their colony, after being subjected to sensory manipulation. While magnetically disturbed shearwaters showed unaltered navigational performance and behaved similarly to unmanipulated control birds, the shearwaters deprived of their sense of smell were dramatically impaired in orientation and homing. Our data show that seabirds use olfactory cues not only to find their food but also to navigate over vast distances in the ocean.
Data from: In search of greener pastures: using satellite images to predict the effects of environmental change on zebra migration
(2013-08-01) Bartlam-Brooks, Hattie L.A.; Harris, Stephen
Historically, ungulate migrations occurred in most grassland and boreal woodland ecosystems, but many have been lost due to increasing habitat loss and fragmentation. With the rate of environmental change increasing, identifying and prioritizing migration routes for conservation has taken on a new urgency. Understanding the cues that drive long-distance animal movements is critical to predicting the fate of migrations under different environmental change scenarios and how large migratory herbivores will respond to increasing resource heterogeneity and anthropogenic influences. We used an individual-based modeling approach to investigate the influence of environmental conditions, monitored using satellite data, on departure date and movement speed of migrating zebras in Botswana. Daily zebra movements between dry and rainy season ranges were annotated with coincident observations of precipitation from the Tropical Rainfall Measuring Mission data set and Moderate Resolution Imaging Spectroradiometer-derived normalized difference vegetation index (NDVI). An array of increasingly complex movement models representing alternative hypotheses regarding the environmental cues and controls for movement was parameterized and tested. The best and most justified model predicted daily zebra movement as two linear functions of precipitation rate and NDVI and included a modeled departure date as a function of cumulative precipitation. The model was highly successful at replicating both the timing and pace of seven actual migrations observed using GPS telemetry (R2 = 0.914). It shows how zebras rapidly adjust their movement to changing environmental conditions during migration and are able to reverse migration to avoid adverse conditions or exploit renewed resource availability, a nomadic behavior which should lend them a degree of resilience to climate and environmental change. Our results demonstrate how competing individual-based migration models, informed by freely available satellite data, can be used to evaluate the weight of evidence for multiple hypotheses regarding the use of environmental cues in animal movement. This modeling framework can be applied to quantify how animals adapt the timing and pace of their movements to prevailing environmental conditions and to forecast migrations in near real time or under alternative environmental scenarios.
Data from: Flexibility of continental navigation and migration in European mallards
(2013-10-11) Matthes, Doris; Latorre-Margalef, Neus; Schmidt, Andreas; Waldenström, Jonas; Wikelski, Martin; van Toor, Mariëlle L.
The ontogeny of continent-wide navigation mechanisms of the individual organism, despite being crucial for the understanding of animal movement and migration, is still poorly understood. Several previous studies, mainly conducted on passerines, indicate that inexperienced, juvenile birds may not generally correct for displacement during fall migration. Waterbirds such as the mallard (Anas platyrhynchos, Linnaeus 1758) are more flexible in their migration behavior than most migratory songbirds, but previous experiments with waterbirds have not yet allowed clear conclusions about their navigation abilities. Here we tested whether immature mallard ducks correct for latitudinal displacement during fall migration within Europe. During two consecutive fall migration periods, we caught immature females on a stopover site in southeast Sweden, and translocated a group of them ca. 1,000 km to southern Germany. We followed the movements of the ducks via satellite GPS-tracking and observed their migration decisions during the fall and consecutive spring migration. The control animals released in Ottenby behaved as expected from banding recoveries: they continued migration during the winter and in spring returned to the population’s breeding grounds in the Baltics and Northwest Russia. Contrary to the control animals, the translocated mallards did not continue migration and stayed at Lake Constance. In spring, three types of movement tactics could be observed: 61.5% of the ducks (16 of 26) stayed around Lake Constance, 27% (7 of 26) migrated in a northerly direction towards Sweden and 11.5% of the individuals (3 of 26) headed east for ca. 1,000 km and then north. We suggest that young female mallards flexibly adjust their migration tactics and develop a navigational map that allows them to return to their natal breeding area.
Data from: Migratory connectivity and population specific migration routes in a long-distance migratory bird
(2013-12-17) Trierweiler, Christiane; Klaassen, Raymond H.G.; Drent, Rudi H.; Exo, Klaus-Michael; Komdeur, Jan; Bairlein, Franz; Koks, Ben J.
Knowledge about migratory connectivity, the degree to which individuals from the same breeding site migrate to the same wintering site, is essential to understand processes affecting populations of migrants throughout the annual cycle. Here, we study the migration system of a long-distance migratory bird, the Montagu's harrier Circus pygargus, by tracking individuals from different breeding populations throughout northern Europe. We identified three main migration routes towards wintering areas in sub-Saharan Africa. Wintering areas and migration routes of different breeding populations overlapped, a pattern best described by ‘weak (diffuse) connectivity’. Migratory performance, i.e. timing, duration, distance and speed of migration, was surprisingly similar for the three routes despite differences in habitat characteristics. This study provides, to our knowledge, a first comprehensive overview of the migration system of a Palaearctic-African long-distance migrant. We emphasize the importance of spatial scale (e.g. distances between breeding populations) in defining patterns of connectivity and suggest that knowledge about fundamental aspects determining distribution patterns, such as the among-individual variation in mean migration directions, is required to ultimately understand migratory connectivity. Furthermore, we stress that for conservation purposes it is pivotal to consider wintering areas as well as migration routes and in particular stopover sites.
Data from: Great flexibility in autumn movement patterns of European Gadwalls (Anas strepera)
(2013-12-18) Gehrold, Andrea; Wikelski, Martin
The annual migration cycle of waterbirds often involves several distinct movement stages, for example within-winter movements or the moult migration during summer, which require a high degree of individual flexibility in migration direction. Here, we investigate whether such flexibility is a common characteristic of waterbird migration by analysing movement behaviour of a dabbling duck, the gadwall Anas strepera, during the little studied, intermediate autumn period. The tracking of individuals via satellite transmitters (n = 7) as well as the ring re-encounter analysis of three European gadwall populations (Germany, England, Russia) revealed that autumn movements were multidirectional. Furthermore, the comparison with winter re-encounters suggested that autumn movements were partly independent of the movements towards subsequently used south to southwestern wintering areas. Some individuals even travelled long distances north- or eastwards. Accordingly, some autumn locations were characterized by a harsh climate, thus serving as temporary staging sites but necessitating further movements when wetlands freeze during winter. The occurrence of such detours or reversals of migration was confirmed by the transmitter data. Inter-individual variability in distance and direction of autumn movements was found for both sexes and age-classes indicating that gadwalls, in general, followed flexible movement strategies. Based on the extent of multidirectional autumn movements, we hypothesize important benefits of such flights and suggest that the analysis of year-round movement patterns of individual animals during their distinct life-history stages is essential to understand how they can successfully reproduce and survive.
Data from: Commuting fruit bats beneficially modulate their flight in relation to wind
(2014-03-18) Dechmann, Dina K.N.; Fahr, Jakob; Wikelski, Martin
NOTE: An updated and larger version of this dataset is available. See https://doi.org/10.5441/001/1.k8n02jn8. ABSTRACT: When animals move, their tracks may be strongly influenced by the motion of air or water, and this may affect the speed, energetics and prospects of the journey. Flying organisms, such as bats, may thus benefit from modifying their flight in response to the wind vector. Yet, practical difficulties have so far limited the understanding of this response for free-ranging bats. We tracked nine straw-coloured fruit bats (Eidolon helvum) that flew 42.5+17.5km (mean + s.d.) to and from their roost near Accra, Ghana. Following detailed atmospheric simulations, we found that bats compensated for wind drift, as predicted under constant winds, and decreased their airspeed in response to tailwind assistance such that their groundspeed remained nearly constant. In addition, bats increased their airspeed with increasing crosswind speed. Overall, bats modulated their airspeed in relation to wind speed at different wind directions in a manner predicted by a two-dimensional optimal movement model. We conclude that sophisticated behavioural mechanisms to minimize the cost of transport under various wind conditions have evolved in bats. The bats’ response to the wind is similar to that reported for migratory birds and insects, suggesting convergent evolution of flight behaviours in volant organisms.
Data from: Environmental drivers of variability in the movement ecology of turkey vultures (Cathartes aura) in North and South America
(2014-04-14) Bildstein, Keith L.; Barber, David; Bechard, Marc J.
NOTE: An updated and larger version of this dataset is available. See https://doi.org/10.5441/001/1.f3qt46r2. ABSTRACT: Variation is key to the adaptability of species and their ability to survive changes to the Earth’s climate and habitats. Plasticity in movement strategies allows a species to better track spatial dynamics of habitat quality. We describe the mechanisms that shape the movement of a long-distance migrant bird (turkey vulture, Cathartes aura) across two continents using satellite tracking coupled with remote-sensing science. Using nearly 10 years of data from 24 satellite-tracked vultures in four distinct populations, we describe an enormous amount of variation in their movement patterns. We related vulture movement to environmental conditions and found important correlations explaining how far they need to move to find food (indexed by the normalized difference vegetation index) and how fast they can move based on the prevalence of thermals and temperature. We conclude that the extensive variability in the movement ecology of turkey vultures, facilitated by their energetically efficient thermal soaring, suggests that this species is likely to do well across periods of modest climate change. The large scale and sample sizes needed for such analysis in a widespread migrant emphasizes the need for integrated and collaborative efforts to obtain tracking data and for policies, tools and open datasets to encourage such collaborations and data sharing.
Data from: Evidence for pre-mnemonic, perceptual neglect of environmental features in hippocampal lesioned pigeons during homing
(2014-07-31) Gagliardo, Anna; Pollonara, Enrica; Coppola, Vincent J; Santos, Carlos David; Bingman, Verner P.
The importance of the vertebrate hippocampus in spatial cognition is often related to its broad role in memory. However, in birds, the hippocampus appears to be more specifically involved in spatial processes. The maturing of GPS-tracking technology has enabled a revolution in navigation research, including the expanded possibility of studying brain mechanisms that guide navigation in the field. By GPS-tracking homing pigeons released from distant, unfamiliar sites prior to and after hippocampal lesion, we observed, as has been reported previously, impaired navigational performance postlesion over the familiar/memorized space near the home loft, where topographic features constitute an important source of navigational information. The GPS-tracking revealed that many of the lost pigeons, when lesioned, approached the home area, but nevertheless failed to locate their loft. Unexpectedly, when they were hippocampal-lesioned, the pigeons showed a notable change in their behaviour when navigating over the unfamiliar space distant from home; they actually flew straighter homeward-directed paths than they did prelesion. The data are consistent with the hypothesis that, following hippocampal lesion, homing pigeons respond less to unfamiliar visual, topographic features encountered during homing, and, as such, offer the first evidence for an unforeseen, perceptual neglect of environmental features following hippocampal damage.
Data from: Temporal and contextual consistency of leadership in homing pigeon flocks
(2014-07-31) Santos, Carlos David; Neupert, Stefanie; Lipp, Hans-Peter; Wikelski, Martin; Dechmann, Dina K.N.
Organized flight of homing pigeons (Columba livia) was previously shown to rely on simple leadership rules between flock mates, yet the stability of this social structuring over time and across different contexts remains unclear. We quantified the repeatability of leadership-based flock structures within a flight and across multiple flights conducted with the same animals. We compared two contexts of flock composition: flocks of birds of the same age and flight experience; and, flocks of birds of different ages and flight experience. All flocks displayed consistent leadership-based structures over time, showing that individuals have stable roles in the navigational decisions of the flock. However, flocks of balanced age and flight experience exhibited reduced leadership stability, indicating that these factors promote flock structuring. Our study empirically demonstrates that leadership and followership are consistent behaviours in homing pigeon flocks, but such consistency is affected by the heterogeneity of individual flight experiences and/or age. Similar evidence from other species suggests leadership as an important mechanism for coordinated motion in small groups of animals with strong social bonds.
Data from: Elliptical Time-Density model to estimate wildlife utilization distributions
(2014-08-01) Wall, Jake; Wittemyer, George; LeMay, Valerie; Douglas-Hamilton, Iain; Klinkenberg, Brian
We present a new animal space-use model (Elliptical Time-Density - ETD) that uses discrete-time tracking data collected in wildlife movement studies. The ETD model provides a trajectory-based, non-parametric approach to estimate the utilization distribution (UD) of an animal, using model parameters derived directly from the movement behavior of the species. The model builds on the theory of ‘time-geography’ whereby elliptical constraining regions are established between temporally-adjacent recorded locations. Using a Weibull speed distribution fitted for an animal's movement data, a time-density value (i.e., time per unit landscape) is determined from the expectation of all elliptical regions equal to, or greater-than, the minimum bounding ellipse for a given landscape point. We tested the ETD model using a tracking dataset for an African elephant (Loxodonta africana) and compared the resulting UDs for regularly sampled, frequently recorded locations, as well as irregular random time intervals between locations and also infrequent temporal-sampling regimes, providing insight to the method's performance with different resolution data. We compared the performance of the ETD model, the Brownian Bridge Movement Model (BBMM), the Time-Geography Density Estimator (TGDE) and the Kernel Density Estimator (KDE) by calculating omission/commission errors from the predicted space-use distribution of each model relative to the true known UD of our elephant test data. The comparison was made for the 10% to 99% percentile UD model areas. The ETD90 model (i.e., ETD model parameterized using the 90% percentile value of the Weibull speed distribution) resulted in the fewest errors of commission and omission with regards to locating the true movement path at the 99% percentile UD area. The ETD model provides an improved approach for estimating animal UDs since: i) parameters are derived directly from the tracking data rather than assumed; ii) parameter values are biologically interpretable; iii) the Weibull speed distribution is adaptable to various temporal-sampling regimes; and iv) the ETD model handles the case of degenerate ellipses thus preserving landscape connectivity in the UD. Software (freeware) for calculating the ETD and a Bayesian framework for estimating the Weibull distribution speed parameters are also introduced in the paper.
Data from: Individual variation in migratory path and behavior among Eastern Lark Sparrows
(2014-08-12) Ross, Jeremy D.; Bridge, Eli S.; Rozmarynowycz, Mark J.; Bingman, Verner P.
Two general migration strategies prevail among temperate-breeding migratory songbirds of North America. Most “Eastern” birds migrate relatively directly from breeding to wintering grounds immediately after molting, whereas a substantial proportion of “Western” species depart breeding grounds early, and molt during extended migratory stopovers before reaching wintering areas. The Lark Sparrow is one of a few Western Neotropical migrants with a breeding range that extends into regions dominated by Eastern species. We sought to determine whether Eastern Lark Sparrows migrated in a manner consistent with Western conspecifics or follow typical Eastern songbird migratory patterns. To do so, we tracked individual Eastern Lark Sparrows equipped with geolocators between their breeding grounds in Ohio and their unknown wintering locations. Data from three Ohio Lark Sparrows revealed 1) individual variation in the duration and directness of autumn migrations, 2) autumn departures that consistently preceded molt, 3) wintering grounds in the central highlands of Mexico, and 4) brief and direct spring migrations. These observations suggest that eastern populations of prevailingly Western migrants, such as Lark Sparrows, may be behaviorally constrained to depart breeding grounds before molt, but may facultatively adjust migration en route.
Data from: Forecasting spring from afar? Timing of migration and predictability of phenology along different migration routes of an avian herbivore [Barents Sea data]
(2014-09-01) van der Jeugd, Henk; Osterbeek, Kees; Ens, Bruno J; Shamoun-Baranes, Judy; Exo, Klaus-Michael
1. Herbivorous birds are hypothesized to migrate in spring along a seasonal gradient of plant profitability towards their breeding grounds (green wave hypothesis). For Arctic-breeding species in particular, following highly profitable food is important, so that they can replenish resources along the way and arrive in optimal body condition to start breeding early. 2. We compared the timing of migratory movements of Arctic-breeding geese on different flyways to examine whether flyways differed in the predictability of spring conditions at stopovers, and whether this was reflected in the degree to which birds were following the green wave. 3. Barnacle geese (Branta leucopsis) were tracked with solar Argos/GPS PTTs from their wintering grounds to breeding sites in Greenland (N = 7), Svalbard (N = 21) and the Barents Sea (N = 12). The numerous stopover sites of all birds were combined into a set of 16 general stopover regions. 4. The predictability of climatic conditions along the flyways was calculated as the correlation and slope between onsets of spring at consecutive stopovers. These values differed between sites, mainly because of the presence or absence of ecological barriers. Goose arrival at stopovers was more closely tied to the local onset of spring when predictability was higher and when geese attempted breeding that year. 5. All birds arrived at early stopovers after the onset of spring and arrived at the breeding grounds before the onset of spring, thus overtaking the green wave. This is in accordance with patterns expected for capital breeders: first they must come into condition; at intermediate stopovers arrival with the food quality peak is important to stay in condition and at the breeding grounds early arrival is favoured so that hatching of young can coincide with the peak of food quality. 6. Our results suggest that a chain of correlations between climatic conditions at subsequent stopovers enables geese to closely track the green wave. However, the birds’ precision of migratory timing seems uninfluenced by ecological barriers, indicating partly fixed migration schedules. These might become non-optimal due to climate warming and preclude accurate timing of long-distance migrants in the future.

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