Data from: Soaring across continents: decision-making of a soaring migrant under changing atmospheric conditions along an entire flyway
| Main Authors: | Vansteelant, Wouter, Shamoun-Baranes, Judy, McLaren, James D., van Diermen, Jan, Bouten, Willem, Vansteelant, Wouter M. G., McLaren, James |
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| Format: | info dataset |
| Terbitan: |
, 2016
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| Subjects: | |
| Online Access: |
https://zenodo.org/record/5009449 |
Daftar Isi:
- (1) Thermal soaring birds reduce flight-energy costs by alternatingly gaining altitude in thermals and gliding across the earth's surface. To find out how soaring migrants adjust their flight behaviour to dynamic atmospheric conditions across entire migration routes, we combined optimal soaring migration theory with high-resolution GPS tracking data of migrating Honey Buzzards Pernis apivorus and wind data from a global numerical atmospheric model. (2) We compared measurements of gliding air speeds to predictions based on two distinct behavioural benchmarks for thermal soaring flight. The first being a time-optimal strategy whereby birds alter their gliding air speeds as a function of climb rates to maximize cross-country air speed over a full climb-glide cycle (Vopt). The second a risk-averse energy-efficient strategy at which birds alter their gliding air speed in response to tailwinds/headwinds to maximize the distance travelled in the intended direction during each glide phase (Vbgw). (3) Honey Buzzards were gliding on average 2.05 ms-1 slower than Vopt and 3.42 ms-1 faster than Vbgw while they increased air speeds with climb rates and reduced air speeds in tailwinds. They adopted flexible flight strategies gliding mostly near Vbgw under poor soaring conditions and closer to Vopt in good soaring conditions. (4) Honey Buzzards most adopted a time-optimal strategy when crossing the Sahara, and at the onset of spring migration, where and when they met with the best soaring conditions. The buzzards nevertheless glided slower than Vopt during most of their journeys, probably taking time to navigate, orientate and locate suitable thermals, especially in areas with poor thermal convection. (5) Linking novel tracking techniques with optimal migration models clarifies the way birds balance different trade-offs during migration.
- Flight measurements, wind data and theoretical speeds for thermal-soaring Honey BuzzardsHoney Buzzards were tracked with high-resolution GPS-loggers, measuring 3D positions every 10 seconds during two cycles of 30 minutes each on every day spent on migration during autumn 2012 and spring 2013. Based on running average of vertical speeds we distinguished climbing from gliding events. We then extracted the location, altitude and time at which birds started/ended each climb and each glide, and created one record for every climbing-gliding cycle that was completely covered by high-resolution measurements. Based on these data we calculated distances travelled, track direction, altitude gained/lost, duration, ground speeds, climb/sink rates from the start to the end of every climb, of every glide and across every full climbing-gliding cycle. We then determined wind conditions to the start of each glide by linearly interpolating wind estimates from the ECMWF deterministic forecast model (2.5x2.5 degrees, 3 hour resolution). By combining tracking data with wind data we could determine determine the heading and air speed achieved during every climb, glide and climbing-gliding cycle. Finally, we generated an aerodynamic model of a Honey Buzzard in thermal-soaring flight based following Pennycuick 2008 (see also original paper) to compute the theoretical minimum-sink speed (Vms), optimal air speed (Vopt), best-gliding air speed (Vbg) and best-gliding air speed in head-/tailwinds (Vbgw) for a Honey Buzzard (assuming mass = 1kg, wing span = 1.3m, wing area = 0.26m-squared, other parametrizations see Vansteelant et al. 2016). By comparing real gliding air speeds (Va) with theoretical benchmarks for time-optimal (Vopt) and risk-averse (Vbgw) flight, we calculated a measure of risk-averison (RAFI). All calculations were implemented in R version 3.1. Detailed descriptions of all columns are provided in the readme.txt file. Note that all distance are measured in meters, time differences in seconds and speeds are noted in meters per second.Vansteelant-etal-JAB-Dryad.xlsx