Showing papers by "Willem Bouten published in 2014"

Optimal orientation in flows: providing a benchmark for animal movement strategies

Abstract: Animal movements in air and water can be strongly affected by experienced flow. While various flow-orientation strategies have been proposed and observed, their performance in variable flow conditions remains unclear. We apply control theory to establish a benchmark for time-minimizing (optimal) orientation. We then define optimal orientation for movement in steady flow patterns and, using dynamic wind data, for short-distance mass movements of thrushes (Turdus sp.) and 6000 km non-stop migratory flights by great snipes, Gallinago media. Relative to the optimal benchmark, we assess the efficiency (travel speed) and reliability (success rate) of three generic orientation strategies: full compensation for lateral drift, vector orientation (single-heading movement) and goal orientation (continually heading towards the goal). Optimal orientation is characterized by detours to regions of high flow support, especially when flow speeds approach and exceed the animal's self-propelled speed. In strong predictable flow (short distance thrush flights), vector orientation adjusted to flow on departure is nearly optimal, whereas for unpredictable flow (inter-continental snipe flights), only goal orientation was near-optimally reliable and efficient. Optimal orientation provides a benchmark for assessing efficiency of responses to complex flow conditions, thereby offering insight into adaptive flow-orientation across taxa in the light of flow strength, predictability and navigation capacity.

Optimizing acceleration-based ethograms: the use of variable-time versus fixed-time segmentation

Abstract: Animal-borne accelerometers measure body orientation and movement and can thus be used to classify animal behaviour. To univocally and automatically analyse the large volume of data generated, we need classification models. An important step in the process of classification is the segmentation of acceleration data, i.e. the assignment of the boundaries between different behavioural classes in a time series. So far, analysts have worked with fixed-time segments, but this may weaken the strength of the derived classification models because transitions of behaviour do not necessarily coincide with boundaries of the segments. Here we develop random forest automated supervised classification models either built on variable-time segments generated with a so-called ‘change-point model’, or on fixed-time segments, and compare for eight behavioural classes the classification performance. The approach makes use of acceleration data measured in eight free-ranging crab plovers Dromas ardeola. Useful classification was achieved by both the variable-time and fixed-time approach for flying (89% vs. 91%, respectively), walking (88% vs. 87%) and body care (68% vs. 72%). By using the variable-time segment approach, significant gains in classification performance were obtained for inactive behaviours (95% vs. 92%) and for two major foraging activities, i.e. handling (84% vs. 77%) and searching (78% vs. 67%). Attacking a prey and pecking were never accurately classified by either method. Acceleration-based behavioural classification can be optimized using a variable-time segmentation approach. After implementing variable-time segments to our sample data, we achieved useful levels of classification performance for almost all behavioural classes. This enables behaviour, including motion, to be set in known spatial contexts, and the measurement of behavioural time-budgets of free-living birds with unprecedented coverage and precision. The methods developed here can be easily adopted in other studies, but we emphasize that for each species and set of questions, the presented string of work steps should be run through.

Effect of wind, thermal convection, and variation in flight strategies on the daily rhythm and flight paths of migrating raptors at Georgia's Black Sea coast

Abstract: Every autumn, large numbers of raptors migrate through geographical convergence zones to avoid crossing large bodies of water. At coastal convergence zones, raptors may aggregate along coastlines because of convective or wind conditions. However, the effect of wind and thermal convection on migrating raptors may vary depending on local landscapes and weather, and on the flight strategies of different raptors. From 20 August to 14 October 2008 and 2009, we studied the effect of cloud development and crosswinds on the flight paths of raptors migrating through the eastern Black Sea convergence zone, where coastal lowlands at the foothills of the Pontic Mountains form a geographical bottleneck 5-km-wide near Batumi, the capital of the Independent Republic of Ajaria in southwestern Georgia. To identify key correlates of local aggregation, we examined diurnal variation in migration intensity and coastal aggregation of 11 species of raptors categorized based on size and flight strategies. As reported at other convergence zones, migration intensity of large obligate-soaring species peaked during the core period of thermal activity at mid-day. When clouds developed over interior mountains and limited thermal convection, these large obligate-soaring species aggregated near the coast. However, medium-sized soaring migrants that occasionally use flapping flight did not aggregate at the coast when clouds over the mountains weakened thermal convection. Numbers of alternate soaring-flapping harriers (Circus spp.) peaked during early morning, with these raptors depending more on flapping flight during a time of day with poor thermal convection. Small sparrowhawks (Accipiter spp.) aggregated at the coast during periods when winds blew offshore, suggesting aggregation caused by wind drift. Thus, weather conditions, including cloud cover and wind speed and direction, can influence the daily rhythm and flight paths of migrating raptors and, therefore, should be accounted for before inferring population trends from migration counts.

Can wheatears weather the Atlantic? Modeling nonstop trans-Atlantic flights of a small migratory songbird

Abstract: Oceans represent extreme ecological barriers for land birds. Yet the Northern Wheatear (Oenanthe oenanthe leucorhoa), a 25-g songbird, negotiates the North Atlantic Ocean twice yearly between Canadian natal and sub-Saharan wintering grounds. Each autumn, these migrants appear to have 2 options: (1) a detour via Greenland, Iceland, and/or Europe to reduce the extent of open-ocean flights or (2) an astonishing nonstop flight of 4,000–5,000 km without resting opportunities between eastern Canada and northwestern Africa. We assessed the feasibility and reliability of nonstop trans-Atlantic migration of Northern Wheatears from Canada to Africa using an individual-based model incorporating flight costs and autumnal wind data from 1979 to 2011. Prevalent wind conditions were supportive of nonstop migration, especially at high altitudes and when winds at departure were favorable. For modeled individuals with high fuel loads, flying at altitudes of ∼3,000 m, successful nonstop trans-Atlantic flights reach...

GPS-logger onderzoek aan Buizerds helpt vogelaanvaringen op militaire vliegvelden te voorkomen

Abstract: Op de hele wereld is de aanwezigheid van vogels op en rond vliegvelden een probleem voor de vliegveiligheid, waarbij sommige vogelsoorten meer risico opleveren dan andere. Om de kans op ongelukken te verkleinen worden landingsterreinen vogelonaantrekkelijk beheerd, worden vogels verjaagd en soms gevangen en verplaatst of afgeschoten. Informatie over terreingebruik en gedrag van de vogels kan helpen zulke maatregelen effectiever en ecologisch duurzamer te maken. In deze pilotstudie werden voor dit doel 12 Buizerds gevolgd met GPS_loggers op de militaire vliegvelden van Leeuwarden Fr en Eindhoven NB. The presence of birds at and near airfields is a constant problem for flight safety all around the world. To minimize the risk of bird strikes, airfields practice wildlife management policies, including habitat modification and bird scaring techniques. To efficiently manage these populations a thorough understanding of their ecology and local behaviour is needed. Tracking birds with GPS devices can offer valuable insight into a species' biology and ecology, but has not yet been applied in the context of aviation safety. In the present pilot study, 12 Common Buzzards (six at each location) were tagged with UvA bird tracking GPS devices (www.uva-bits.nl) to monitor their movements and activities on the military airfields of Leeuwarden and Eindhoven in the Netherlands, from May 2009 to the end of 2010 (Tab. 1). Sufficient data was obtained for only three breeding birds at Leeuwarden and two non-breeding birds at Eindhoven. Home ranges of three breeding birds at Leeuwarden measured 46.6 ± 24.0 ha (Tab. 2), were defended and overlapped only slightly. Home ranges of non-breeding birds at Eindhoven overlapped with nest locations of breeding birds (Fig. 2). Non-breeding birds also occasionally left their local home ranges to make long trips (Fig. 3). The breeding birds spent nearly 100% of their time at the airfield, with one bird crossing the runway more or less frequently, and in 11% of cases within 5 minutes of an aircraft passage. One of the non-breeding birds crossed the runway relatively often, and in 49% of cases in close proximity to moving aircraft. This individual was finally killed in a bird strike. Although sample sizes were small, the data suggest that experienced local breeding birds form less of a bird strike risk than unexperienced non-breeding birds. Thus, to reduce bird strikes it might be better to not remove local breeding birds as they will be replaced by less experienced individuals. This pilot study forms a basis for further research in the context of behavioural ecology, conservation biology, and flight safety

Eerste resultaten van het jaarrond volgen van Blauwe Kiekendieven broedend in het Oost-Groningse akkerland

Abstract: Blauwe Kiekendieven zien we tegenwoordig vaker in de winter dan in de zomer. Het gaat uitermate slecht met de Nederlandse broedvogels en als er niets gebeurt zullen we de soort binnen afzienbare tijd als broedvogel verliezen. De voormalige bolwerken op de Waddeneilanden zijn zo goed als verlaten. Een hoopvolle ontwikkeling vormt de vestiging van de Blauwe Kiekendief in het Oost- Groningse akkerbouwgebied. In 2012-2013 werden drie van deze broedvogels uitgerust met UvA-BiTS GPS-loggers. A small breeding population (3-5 pairs) of Hen Harriers recently established in the east of the province of Groningen, the Netherlands, in large scale arable farmland. We equipped three adults, two males and one female, with UvA-BiTS GPS loggers to study home ranges and habitat use throughout the year (Fig. 1). One breeding male could be tracked during two subsequent summers (late nestling phase in 2012, prebreeding and incubation phase in 2013 (Fig. 2)). Although he nested in the same area, he used different home ranges in these subsequent years (overlap only 21%). Habitat use was similar between years. Most time was spent in (winter) cereals (60%) and grassland (22%), two crops that dominate in the study area (availability is 42 and 24%, respectively). Moreover, set-aside habitats, which are especially created and managed for breeding harriers, were preferred (4% used, 1% available). One breeding pair was tracked after their nest failed (Fig. 4). These non-breeding birds occupied much smaller summer home ranges. In addition, they used set-aside habitat much more intensively (up to 22%), until the start of the cereal harvest when they switched to using cereal stubbles. During the summer the female made three subsequent trips to Northwest Germany (Fig. 3). One male spent the winter in Spain, in an agricultural area near Olivenza (Fig. 6). Autumn and spring migration took 98 and 14 days, including 81 and 1 stopover days, respectively. The other individuals (one male and one female) spent the winter near the breeding area (Fig. 5). Loggers could not record positions during mid-winter as solar panels could not keep the batteries charged. Habitat use in winter was dominated by grassland (62%). Set-aside was also preferred (5%). The female made an 8-day mid-winter excursion to a nearby wetland area (Weerribben, Fig. 5).

Nieuwe ontdekkingen en mogelijkheden in het onderzoek aan Scholeksters dankzij het UvA Bird Tracking Systeem

Abstract: This paper reports on new discoveries and new possibilities due to the deployment of the UvA Bird Tracking System (UvA-BiTS; Bouten et al. 2013) in our investigations of the behavioural ecology of Oystercatchers. This GPS tracker is powered by solar cells and not only stores GPS locations, but also measurements with a tri-axial accelerometer, which can be used to infer behaviour (Shamoun-Baranes et al. 2012; fig. 4). Since 2008, 72 Oystercatchers were fitted with such GPS trackers. Contrary to our expectations, Oystercatchers breeding in the polder of Ameland, where they can feed on earthworms and tipulid larvae, continued to visit the Wadden Sea mudflats throughout the breeding season, just like birds breeding on the saltmarsh of Schiermonnikoog (Fig. 1). We were equally surprised to learn that the breeding populations on both islands included migrants. Whereas many breeding birds remained within 10 km of the breeding territory throughout the winter (Fig. 2), a minority moved much greater distances to a clearly distinct wintering area (Fig. 4). Fidelity to a particular wintering area was high, irrespective of distance moved. We also show examples of the potential of UvA-BiTS to address important scientific questions. Young birds must find a good place to learn how to survive and Fig. 5 shows the behaviour of such a bird: it stays for several months in a particular location and then moves to a new location. Once an individual is sufficiently proficient at surviving, it can enter the competition for breeding territories as a club-bird, usually at the age of three years. Figure 6 compares the ranging behaviour of a non-breeder to that of a breeder at the height of the breeding season.

On the transferability of rule sets for mapping cirques using Object- based feature extraction

Abstract: Cirques are complex landforms resulting from glacial erosion and occur in the mountains of western Austria at various topographic levels. After deglaciation they may potentially hold climate proxies, are showcases of vegetation regrowth and play an important role in the regulation of mountain hydrology. Our objective is to develop a workflow to test an object-based rule-set that decomposes LiDAR DEMs into the main cirque components: divide, cirque headwall, cirque floor and into the sub-component cirque lake by using stratified segmentation and classification. One cirque cluster was used to train the classification settings, which were tested in a second cirque cluster. Classification results and accuracy of both clusters were compared. We conclude that the transferability of rule sets for the extraction of cirque components is promising, but that younger depositional and erosional landforms may influence correct cirque component extraction. Fine-tuning of rule sets and integration of additional data is necessary to discriminate cirques moraines and cirque thresholds, as these sub-components highly depend on variations in local cirque development.

movement strategies Optimal orientation in flows: providing a benchmark for animal

Abstract: Cite this article: McLaren JD, Shamoun-Baranes J, Dokter AM, Klaassen RHG, BoutenW. 2014 Optimal orientation in flows:providing a benchmark for animal movementstrategies. J. R. Soc. Interface 11: 20140588.http://dx.doi.org/10.1098/rsif.2014.0588Received: 3 June 2014Accepted: 30 June 2014Subject Areas:biogeography, computational biology,environmental scienceKeywords:flow orientation, animal navigation, migration,lateral drift, optimization, movement ecologyAuthor for correspondence:James D. McLarene-mail: j.d.mclaren@uva.nl