Trans-Sahara migrants select flight altitudes to minimize energy costs rather than water loss

Schmaljohann, Heiko; Liechti, Félix; Bruderer, Bruno

doi:10.1007/s00265-009-0758-x

Cited by 90 publications

(131 citation statements)

References 61 publications

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“…(Liechti and Schaller, 1999;Schmaljohann et al, 2008b), which is higher than the maximum flight altitude considered in this study. Furthermore, bounding flyers did not prefer different flight altitudes due to differences in body size and mass but simply selected the altitude with the best meteorological conditions for their migratory flights (Bruderer et al, 1995b;Liechti et al, 2000;Schmaljohann et al, 2008c;Schmaljohann et al, 2009). Although we cannot categorically exclude any size effect on flight altitude, the substantial changes in wingbeat frequency and air speed are a result of behavioural adjustments of the birds to changing meteorological conditions, mainly air density.…”

Section: Sources Of Possible Errorsmentioning

confidence: 99%

“…Birds are highly selective for favourable wind conditions during migratory flights (Liechti, 2006;Schmaljohann et al, 2008c;Schmaljohann et al, 2009). The prevailing trade and anti-trade wind system over western Africa leads to migration at high altitudes in spring but low altitudes in autumn (Schmaljohann et al, 2007;Schmaljohann et al, 2008c;Schmaljohann et al, 2009).…”

Section: Wingbeat Frequencymentioning

confidence: 99%

“…Every night migrants crossing the Sahara are confronted with similar environmental conditions. Based on the fact that flight altitude of migrating birds is primarily governed by wind conditions (Liechti, 2006;Schmaljohann et al, 2008c;Schmaljohann et al, 2009), we presume that, at least within morphologically similar groups of birds (swifts, songbirds), the distribution of flight altitudes is governed by atmospheric conditions and not by species-specific flight levels. With the tracking radar 'Superfledermaus' we recorded the echo signature of birds, i.e.…”

Section: Introductionmentioning

confidence: 99%

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Adjustments of wingbeat frequency and air speed to air density in free-flying migratory birds

Schmaljohann

Liechti

2009

Journal of Experimental Biology

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Section: Sources Of Possible Errorsmentioning

confidence: 99%

Section: Wingbeat Frequencymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Adjustments of wingbeat frequency and air speed to air density in free-flying migratory birds

Schmaljohann

Liechti

2009

Journal of Experimental Biology

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“…Nocturnally migrating passerines have been recorded at a range of altitudes up to and over 5000 m (Liechti and Schaller 1999, Liechti and Schmaljohann 2007, Schmaljohann et al 2009), but in some instances a significant number of birds have been found to migrate in the lower altitudes, below 1500 m above ground level (agl; Able 2004, Mabee et al 2006, Longcore et al 2008, Schmaljohann et al 2008, Dokter et al 2011. Depending on site, this range of lower flight altitudes may occur in one season only (Schmaljohann et al 2009) or during both spring and fall movements (Bruderer 1997).…”

Section: Introductionmentioning

confidence: 99%

“…Depending on site, this range of lower flight altitudes may occur in one season only (Schmaljohann et al 2009) or during both spring and fall movements (Bruderer 1997). Migrants will typically climb to altitudes where they encounter favorable winds, which are used to maximize flight ranges on a given amount of fuel stores (Klaassen et al 2012, Marques et al 2014.…”

Section: Introductionmentioning

confidence: 99%

Comparing pre- versus postoperational movement of nocturnal migrants around a wind energy facility in northeast British Columbia, Canada

d'Entremont¹,

Hartley²,

Otter³

2017

ACE

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[2011][2012]. Data was collected during the peak periods of spring and fall passerine migration in each year. We measured bearing and altitude of nocturnal migrants, as well as the average number of migrants flying in the airspace closest to the wind turbines. Using weather data on wind direction and strength during the periods of monitored migration, we calculated flow-assistance of wind in aiding migration.Although there was greater flow-assistance to movement in spring over fall migration, we did not find a significant difference between the preoperational and operational periods in flow-assisted flight. The altitude at which migrants flew did differ with development phase of the wind facility; migrants flew at higher altitudes during years when the turbines were operational compared to preoperational years. Although the proportion of migrants detected in the airspace 0-150 m above ground level (agl), coinciding with turbine height, did not differ with season or operational phase of the installation, there was a reduction in the proportion of migrants in the airspace just above turbines (151-300 m agl) when turbines were operational. In general, though, the overall altitudes used by migrants were typically higher than turbine height, so the adjustments we documented would only further reduce what appear to be already low levels of collision risk at this particular facility. We discuss possible reasons why this facility appeared to induce low collision risk to migrants, and how this might inform siting decisions of other wind facilities. Comparaison des déplacements d'oiseaux migrateurs nocturnes avant et après la construction d'un parc d'éoliennes dans le nord-est de la Colombie-Britannique, CanadaRÉSUMÉ. Nous avons utilisé deux radars de navigation maritime, à tableau ouvert et pouvant enregistrer des données, afin de suivre les microdéplacements d'oiseaux migrateurs nocturnes sur le site d'un projet de parc d'éoliennes dans le nord-est de la ColombieBritannique en périodes préopérationnelle (2008-2010) et opérationnelle (2011-2012). Les données ont été récoltées durant les périodes de pointe de la migration des passereaux au printemps et à l'automne chaque année. Nous avons mesuré la position et l'altitude des migrateurs nocturnes, et le nombre moyen de migrateurs volant dans l'espace aérien le plus près des éoliennes. Au moyen de données météorologiques sur la direction et la force du vent durant les périodes de migration suivies, nous avons calculé l'apport du vent pour faciliter la migration. Même si l'apport du vent était plus élevé pour les déplacements au printemps qu'à l'automne, nous n'avons pas trouvé de différence significative pour les déplacements facilités par le vent entre les périodes préopérationnelle et opérationnelle. L'altitude à laquelle les migrateurs ont volé a varié pendant la construction du parc d'éoliennes; les migrateurs ont volé à des altitudes plus élevées durant les années où les éoliennes étaient en opération comparativement aux années preopérationnelles. Même si la proportio...

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Determinants of spring migration departure dates in a New World sparrow: Weather variables reign supreme

Byrd,

Talbott,

Smiley

et al. 2024

Ecology and Evolution

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Numerous factors influence the timing of spring migration in birds, yet the relative importance of intrinsic and extrinsic variables on migration initiation remains unclear. To test for interactions among weather, migration distance, parasitism, and physiology in determining spring departure date, we used the Dark‐eyed Junco (Junco hyemalis) as a model migratory species known to harbor diverse and common haemosporidian parasites. Prior to spring migration departure from their wintering grounds in Indiana, USA, we quantified the intrinsic variables of fat, body condition (i.e., mass ~ tarsus residuals), physiological stress (i.e., ratio of heterophils to lymphocytes), cellular immunity (i.e., leukocyte composition and total count), migration distance (i.e., distance to the breeding grounds) using stable isotopes of hydrogen from feathers, and haemosporidian parasite intensity. We then attached nanotags to determine the timing of spring migration departure date using the Motus Wildlife Tracking System. We used additive Cox proportional hazard mixed models to test how risk of spring migratory departure was predicted by the combined intrinsic measures, along with meteorological predictors on the evening of departure (i.e., average wind speed and direction, relative humidity, and temperature). Model comparisons found that the best predictor of spring departure date was average nightly wind direction and a principal component combining relative humidity and temperature. Juncos were more likely to depart for spring migration on nights with largely southwestern winds and on warmer and drier evenings (relative to cooler and more humid evenings). Our results indicate that weather conditions at take‐off are more critical to departure decisions than the measured physiological and parasitism variables.

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Trans-Sahara migrants select flight altitudes to minimize energy costs rather than water loss

Cited by 90 publications

References 61 publications

Adjustments of wingbeat frequency and air speed to air density in free-flying migratory birds

Adjustments of wingbeat frequency and air speed to air density in free-flying migratory birds

Comparing pre- versus postoperational movement of nocturnal migrants around a wind energy facility in northeast British Columbia, Canada

Determinants of spring migration departure dates in a New World sparrow: Weather variables reign supreme

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