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Satellite Telemetry (satellite + telemetry)
Selected AbstractsHAUL-OUT ACTIVITY OF RINGED SEALS (PHOCA HISPIDA) DETERMINED FROM SATELLITE TELEMETRYMARINE MAMMAL SCIENCE, Issue 1 2002E. W. Born Abstract The haul-out activity of 15 ringed seals (Phoca hispida) equipped with satellite-linked radio transmitters was studied in NW Greenland (ca. 73°-78°N). Between 19 June 1997 and 30 June 1999, telemetry data on haulout activity were obtained by the "Land-Sea-Reporter" (LSR), "Time-at-Depth" (TAD), and "Timelines" (TIM) systems housed within the satellite transmitters. The haul-out activity (% of total time hauled out) reported by the TIM system, which is specifically designed for collecting haul-out data, was about 1.4 times higher than that inferred from the LSR, but only about 0.7 of that inferred from TAD data. The TIM were used to describe haul-out activity. A total of 1,011 d with TIM were obtained (64.5% of a total of 1,568 "seal-days" monitored) representing data from nearly an entire annual cycle. No differences were found in percentage of time hauled out per month among various age categories. At all seasons the haul-out time showed considerable individual variation. There were no trends in percentage of time hauled out per month during late summer, fall, and winter (August-February). During the High Arctic winter darkness (November-January) the percentage of haul-out per month ranged between 3.9% in an adult (SD = 2.44, range: 1.1%-5.7%, n= 3 mo) and 15.7% in a subadult (SD = 1.95, range: 13.7%-17.6%, n= 3 mo). From late March there was a significant increase in haul-out time. Between 1 and 30 June, when aerial surveys of basking ringed seals usually are conducted, the haul-out time (% per day) increased from about 25% to about 57%. No tendencies in diel haul-out activity were revealed. [source] Migration of hawksbill turtles Eretmochelys imbricata from Tortuguero, Costa RicaECOGRAPHY, Issue 3 2005Sebastian Troëng The hawksbill turtle Eretmochelys imbricata is a widely distributed and critically endangered species that feeds on sponges and fills an important ecological role in the coral reef ecosystem. At Tortuguero, Costa Rica, trend analyses indicate considerable decline in nesting estimated at 77.2,94.5% between 1956 and 2003, as a result of excessive turtle fishing. We analyzed flipper tag returns, satellite telemetry and genetic samples to determine movements and habitat use of adult female Tortuguero hawksbills. Tag returns and satellite telemetry show hawksbills migrate to foraging grounds in Nicaragua and Honduras. Genetic analysis indicates the hawksbills may also migrate to Cuban, Puerto Rican, and possibly Mexican waters. We conclude hawksbills represent an internationally shared resource. There is a close correlation between tag recapture sites, hawksbill foraging grounds and coral reef distribution. Caribbean coral reef decline may reduce food availability and negatively impact hawksbill turtles. Conversely, hawksbill decline may shift the balance on coral reefs by reducing predation pressure on sponges and hence make coral reefs less resilient to natural and anthropogenic threats. Strategies aiming to conserve hawksbills and coral reefs must consider both the extensive hawksbill migrations and the close relationship between the species and the coral reef ecosystem. [source] How well can animals navigate?ENVIRONMETRICS, Issue 4 2006Estimating the circle of confusion from tracking data Abstract State-space models have recently been shown to effectively model animal movement. In this paper we illustrate how such models can be used to improve our knowledge of animal navigation ability, something which is poorly understood. This work is of great interest when modeling the behavior of animals that are migrating, often over tremendously large distances. We use the term circle of confusion, first proposed by Kendall (1974), to describe the general inability of an animal to know its location precisely. Our modeling strategy enables us to statistically describe the circle of confusion associated with any animal movements where departure and destination points are known. For illustration, we use ARGOS satellite telemetry of leatherback turtles migrating over a distance of approximately 4000,km in the Atlantic Ocean. Robust features of the model enable one to deal with outlying observations, highly characteristic of these types of data. Although specifically designed for data obtained using satellite telemetry, our approach is generalizable to other common kinds of movement data such as archival tag data. Copyright © 2005 John Wiley & Sons, Ltd. [source] Post-fledging behaviour in Golden Eagles Aquila chrysaetos: onset of juvenile dispersal and progressive distancing from the nestIBIS, Issue 2 2006ALVARO SOUTULLO Thirteen juvenile Golden Eagles Aquila chrysaetos were tracked during their first year of life using satellite telemetry. Distances to the nest attained during that period and the age at the onset of juvenile dispersal were explored. The performance of nine different criteria to determine that age was analysed. In general, after a brief period of restricted movements around the nest, the average distance to the nest increased with time. Maximum distances to the nest ranged between 57.7 and 184.3 km, and were considerably greater in females (mean ± sd, 138.5 ± 44.5 km) than in males (70.5 ± 14.0 km). No sex difference was observed in the age at which that distance was attained (males: 329 ± 32 days, females: 312 ± 20 days). The onset of juvenile dispersal took place around the fifth month of life (September in Spain). Eight of the nine criteria provided similar results, suggesting that in Spain dispersal starts when birds are between 140 and 180 days old, and that the post-nestling period lasts between 60 and 120 days. For future studies, to determine the age at which the onset of juvenile dispersal occurs, we recommend the use of either the first day on which individuals were located beyond the mean distance between nests of different pairs (10 km in our study area), or the date of the record midway between the first and the last location recorded during the month in which the maximum variability in the distance to the nest was observed. [source] Robust hierarchical state,space models reveal diel variation in travel rates of migrating leatherback turtlesJOURNAL OF ANIMAL ECOLOGY, Issue 5 2006IAN D. JONSEN Summary 1Biological and statistical complexity are features common to most ecological data that hinder our ability to extract meaningful patterns using conventional tools. Recent work on implementing modern statistical methods for analysis of such ecological data has focused primarily on population dynamics but other types of data, such as animal movement pathways obtained from satellite telemetry, can also benefit from the application of modern statistical tools. 2We develop a robust hierarchical state,space approach for analysis of multiple satellite telemetry pathways obtained via the Argos system. State,space models are time-series methods that allow unobserved states and biological parameters to be estimated from data observed with error. We show that the approach can reveal important patterns in complex, noisy data where conventional methods cannot. 3Using the largest Atlantic satellite telemetry data set for critically endangered leatherback turtles, we show that the diel pattern in travel rates of these turtles changes over different phases of their migratory cycle. While foraging in northern waters the turtles show similar travel rates during day and night, but on their southward migration to tropical waters travel rates are markedly faster during the day. These patterns are generally consistent with diving data, and may be related to changes in foraging behaviour. Interestingly, individuals that migrate southward to breed generally show higher daytime travel rates than individuals that migrate southward in a non-breeding year. 4Our approach is extremely flexible and can be applied to many ecological analyses that use complex, sequential data. [source] Loop migration in adult marsh harriers Circus aeruginosus, as revealed by satellite telemetryJOURNAL OF AVIAN BIOLOGY, Issue 2 2010Raymond H. G. Klaassen Loop migration among birds is characterized by the spring route lying consistently west or east of the autumn route. The existence of loops has been explained by general wind conditions or seasonal differences in habitat distribution. Loop migration has predominantly been studied at the population level, for example by analysing ring recoveries. Here we study loop migration of individual marsh harriers Circus aeruginosus tracked by satellite telemetry. We show that despite a generally narrow migration corridor the harriers travelled in a distinct clockwise loop through Africa and southern Europe, following more westerly routes in spring than in autumn. We used the Normalized Difference Vegetation Index (NDVI) to identify potential feeding habitat in Africa. Suitable habitat seemed always more abundant along the western route, both in spring and autumn, and no important stopover site was found along the eastern route. Observed routes did thus not coincide with seasonal variation in habitat availability. However, favourable habitat might be more important during spring migration, when the crossing of the Sahara seems more challenging, and thus habitat availability might play an indirect role in the harriers' route choice. Grid-based wind data were used to reconstruct general wind patterns, and in qualitative agreement with the observed loop marsh harriers predominantly encountered westerly winds in Europe and easterly winds in Africa, both in autumn and in spring. By correlating tail- and crosswinds with forward and perpendicular movement rates, respectively, we show that marsh harriers are partially drifted by wind. Thus, we tentatively conclude that wind rather than habitat seems to have an overriding effect on the shape of the migration routes of marsh harriers. General wind conditions seem to play an important role also in the evolution of narrow migratory loops as demonstrated for individual marsh harriers. [source] Improving the analysis of movement data from marked individuals through explicit estimation of observer heterogeneityJOURNAL OF AVIAN BIOLOGY, Issue 1 2010Fränzi Korner-Nievergelt Ring re-encounter data, in particular ring recoveries, have made a large contribution to our understanding of bird movements. However, almost every study based on ring re-encounter data has struggled with the bias caused by unequal observer distribution. Re-encounter probabilities are strongly heterogeneous in space and over time. If this heterogeneity can be measured or at least controlled for, the enormous number of ring re-encounter data collected can be used effectively to answer many questions. Here, we review four different approaches to account for heterogeneity in observer distribution in spatial analyses of ring re-encounter data. The first approach is to measure re-encounter probability directly. We suggest that variation in ring re-encounter probability could be estimated by combining data whose re-encounter probabilities are close to one (radio or satellite telemetry) with data whose re-encounter probabilities are low (ring re-encounter data). The second approach is to measure the spatial variation in re-encounter probabilities using environmental covariates. It should be possible to identify powerful predictors for ring re-encounter probabilities. A third approach consists of the comparison of the actual observations with all possible observations using randomization techniques. We encourage combining such randomisations with ring re-encounter models that we discuss as a fourth approach. Ring re-encounter models are based on the comparison of groups with equal re-encounter probabilities. Together these four approaches could improve our understanding of bird movements considerably. We discuss their advantages and limitations and give directions for future research. 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