Migrating ospreys use thermal uplift over the open sea

Duriez, Olivier; Péron, Guillaume; Grémillet, David; Sforzi, Andrea; Monti, Flavio

doi:10.1098/rsbl.2018.0687

Cited by 41 publications

(82 citation statements)

References 13 publications

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“…During soaring flight, the birds stretch and do not flap their wings, allowing them to save energy while covering large distances (Sapir, Wikelski, Mccue, Pinshow, & Nathan, 2010). Usually, soaring birds avoid flying over waterbodies where thermals are typically weak and rare (but see Duriez, Peron, Gremillet, Sforzi, & Monti, 2018;Nourani, Vansteelant, Byholm, & Safi, 2020). Yet, in some cases, soaring birds are forced to switch to the metabolically demanding flapping flight (Hedenström, 1993;Norberg, 1990;Sapir et al, 2011), such as when flying over areas with low availability of thermals.…”

Section: Introductionmentioning

confidence: 99%

Causes and consequences of facultative sea crossing in a soaring migrant

et al. 2020

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Studying the causes and consequences of route selection in animal migration is important for understanding the evolution of migratory systems and how they may be affected by environmental factors at various spatial and temporal scales. One key decision during migration is whether to cross ‘high transport cost’ areas or to circumvent them. Soaring birds may face this choice when encountering waterbodies where convective updrafts are weak or scarce. Crossing these waterbodies requires flying using energetically costly flapping flight, while circumventing them over land permits energetically cheap soaring. We tested how several atmospheric factors (e.g. wind, thermal uplift) and geographic, seasonal and state‐related factors (sex and age) affected route selection in migrating white storks Ciconia ciconia. We used 196 GPS tracks of 70 individuals either crossing or circumventing the north‐easternmost section of the Mediterranean Sea, over Iskenderun Bay in southern Turkey. We found that westward and southward winds promoted a cross‐bay journey in spring and autumn, respectively, acting as tailwinds. Also, overall weaker winds promoted a sea crossing in spring. Sea crossing was associated with flapping flight and higher values of overall dynamic body acceleration and resulted in higher ground speed than travel over land. The combined environmental conditions and the effects of route selection on movement‐related energy costs and speed were likely responsible for an increase in the time spent flying and distance travelled of migrating storks that decided to cross the bay during spring. Notably, daily travel distances of spring migrants crossing the bay were 60 km longer than those of land‐detouring birds, allowing them to reach their destination faster but likely incurring a higher energetic flight cost. No such benefit was found during autumn. Our findings confirm that atmospheric conditions can strongly affect bird route selection. Consequently, migration timing, speed and movement‐related energy expenditure differed considerably between the two migratory seasons and the two route choices, highlighting a time‐energy trade‐off in the migration of white storks. A free plain language summary can be found within the Supporting Information of this article.

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Section: Introductionmentioning

confidence: 99%

Causes and consequences of facultative sea crossing in a soaring migrant

et al. 2020

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“…If we remove the negative records (Poessel et al 2018), perching and low flight are under-sampled in the final dataset (Roeleke et al 2018). To illustrate this point, we used a flight track from a migrating juvenile osprey ( Pandion haliaetus ) as it crossed the sea between the Italian mainland and Corsica (Duriez et al 2018). During a portion of that sea crossing, its Ornitela GPS unit recorded flight heights that oscillated between −2m and −7m below the sea level (Fig.…”

Section: Part 2: Field Trials Simulations and Reanalysis Of Raptor mentioning

confidence: 99%

“…These negative flight height records documented a critical time period. First, the risk of having to make a sea landing were clearly much greater in the few minutes when the osprey was flying low over the waves, compared to the rest of the sea crossing when the bird was often soaring high (Duriez et al 2018). In addition, when flying low, the bird had no other choice than to flap and therefore expend energy; whereas when higher above the sea, the bird had the option to soar and therefore spare energy.…”

Section: Part 2: Field Trials Simulations and Reanalysis Of Raptor mentioning

confidence: 99%

“…They record data even when the animals are out of sight for ground-based observers, over extensive, potentially uninterrupted periods of time, and with no uncertainty about which species or individuals are being monitored. For example, we can record raptors soaring over the high sea at night (Duriez et al 2018). However, the data that GPS and altimeters record are not error-free (D’Eon et al 2002, Frair et al 2004, Jerde and Visscher 2005, Brost et al 2015).…”

Section: Introductionmentioning

confidence: 99%

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The challenges of estimating the distribution of flight heights from telemetry or altimetry data

Péron

Calabrese

Duriez

et al. 2019

Preprint

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BackgroundGlobal positioning systems (GPS) and altimeters are increasingly used to monitor vertical space use by aerial species, a key aspect of their niche that we need to know to understand their ecology and conservation needs, and to manage our own use of the airspace. However, there are various sources of error in flight height data (“height” above ground, as opposed to “altitude” above a reference like the sea level): vertical error from the devices themselves, error in the ground elevation below the tracked animals, and error in the horizontal position of the animals and thus the predicted ground elevation below them.MethodsWe used controlled field trials, simulations, and the reanalysis of raptor case studies with state-space models to illustrate the effect of improper error management.ResultsErrors of a magnitude of 20 meters appear in benign conditions (expected to be larger in more challenging context). These errors distort the shape of the distribution of flight heights, inflate the variance in flight height, bias behavioural state assignments, correlations with environmental covariates, and airspace management recommendations. Improper data filters such as removing all negative recorded flight height records introduce several biases in the remaining dataset, and preclude the opportunity to leverage unambiguous errors to help with model fitting. Analyses that ignore the variance around the mean flight height, e.g., those based on linear models of flight height, and those that ignore the variance inflation caused by telemetry errors, lead to incorrect inferences.ConclusionThe state-space modelling framework, now in widespread use by ecologists and increasingly often automatically implemented within on-board GPS data processing algorithms, makes it possible to fit flight models directly to raw flight height records, with minimal data pre-selection, and to analyse the full distribution of flight heights, not just the mean. In addition to basic research about aerial niches, behaviour quantification, and environmental interactions, we highlight the applied relevance of our recommendations for airspace management and the conservation of aerial wildlife.

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“…Most of the landbirds capable of thermal soaring are facultative soaring migrants. These species have a lower wing area to body mass ratio with which they can sustain long bouts of flapping flight if needed, for example over open water, as in the Eleonora’s flacon Falco eleonorae and the osprey Pandion haliaetus , [11, 18].…”

Section: Introductionmentioning

confidence: 99%

Dynamics of the energy seascape can explain intra-specific variations in sea-crossing behaviour of soaring birds

Nourani

Vansteelant

Byholm

et al. 2019

Preprint

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Thermal soaring birds extract energy from the atmosphere to achieve energetically low-cost movement. When encountering regions that are energetically costly to fly over, such as open seas, they attempt to adjust the spatio-temporal pattern of their passage to maximize energy extraction from the atmosphere over these ecological barriers. We apply the concept of energy landscapes to investigate the spatio-temporal dynamics of energy availability over the open sea for soaring flight. We specifically investigated how the “energy seascape” may shape age-specific sea-crossing behaviour of European honey buzzards Pernis apivorus over the Mediterranean Sea in autumn. We found uplift potential over the sea to be the main determinant of sea-crossing length, rather than wind conditions. Considering this variable as a proxy for available energy over the sea, we constructed the energy seascape for the autumn migration season using forty years of temperature data. Our results indicate that early-migrating adult buzzards are likely to encounter adverse energy subsidence over the Mediterranean, whereas late-migrating juveniles face less adverse flight conditions, and even conditions conducive to soaring flight. Our study provides evidence that the dynamics of the energy landscape can explain intra-specific variation in migratory behaviour also at sea.

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Migrating ospreys use thermal uplift over the open sea

Cited by 41 publications

References 13 publications

Causes and consequences of facultative sea crossing in a soaring migrant

Causes and consequences of facultative sea crossing in a soaring migrant

The challenges of estimating the distribution of flight heights from telemetry or altimetry data

Dynamics of the energy seascape can explain intra-specific variations in sea-crossing behaviour of soaring birds

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