| 1. |
- Lindström, Åke, et al.
(author)
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Extreme altitude changes between night and day during marathon flights of great snipes
- 2021
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In: Current Biology. - : Elsevier BV. - 0960-9822 .- 1879-0445. ; 31:15, s. 3433-3439
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Journal article (peer-reviewed)abstract
- Summary Several factors affect the flight altitude of migratory birds, such as topography, ambient temperature, wind conditions, air humidity, predation avoidance, landmark orientation, and avoiding over-heating from direct sunlight.1, 2, 3, 4, 5, 6 Recent tracking of migratory birds over long distances has shown that migrants change flight altitude more commonly and dramatically than previously thought.4, 5, 6, 7, 8 The reasons behind these altitude changes are not well understood. In their seasonal migrations between Sweden and sub-Saharan Africa, great snipes Gallinago media make non-stop flights of 4,000–7,000 km, lasting 60–90 h.9,10 Activity and air pressure data from multisensor dataloggers showed that great snipes repeatedly changed altitudes around dawn and dusk, between average cruising heights about 2,000 m (above sea level) at night and around 4,000 m during daytime. Frequency and autocorrelation analyses corroborated a conspicuous diel cycle in flight altitude. Most birds regularly flew at 6,000 m and one bird reached 8,700 m, possibly the highest altitude ever recorded for an identified migrating bird. The diel altitude changes took place independently of climate zone, topography, and habitat overflown. Ambient temperature, wind condition, and humidity have no important diel variation at the high altitudes chosen by great snipes. Instead, improved view for orientation by landmarks, predator avoidance, and not least, seeking cold altitudes at day to counteract heating from direct sunlight are the most plausible explanations for the diel altitude cycle. Together with similar recent findings for a small songbird,6 the great snipes’ altitudinal performance sheds new light on the complexity and challenges of migratory flights.
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| 2. |
- Lindström, Åke, et al.
(author)
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Waders flying with folded legs – which species, when, where and why?
- 2020
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In: Wader Study. - : International Wader Study Group. - 2058-8410. ; 127:2, s. 1-8
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Journal article (peer-reviewed)abstract
- Waders normally fly with their legs stretched out under the tail, with their feet pointing backwards. Whereas there are a few published records of waders flying with their legs folded forward (like a passerine), with legs and feet tucked in under the belly feathers, the causes and consequences of waders flying with folded legs are poorly understood. Through searching the literature, asking ornithologists in person and through public calls, and from searching photos on the internet, we retrieved 90 records of 17 different species where one or more individuals flew with folded legs. It was most common in Spotted Redshank Tringa erythropus (in up to 10% of all birds) and Common Redshank T. totanus, but was also observed in short-legged species such as Dunlin Calidris alpina and Common Ringed Plover Charadrius hiaticula. The behaviour was recorded in most months of the year, in different age classes, in single birds as well as in flocks, at different ambient temperatures, and in both migratory flights and local move-ments. Whereas reducing heat loss at low temperatures is a likely, but not omnipo-tent, explanation for waders flying with folded legs, aerodynamics and leg muscle fatigue may also affect how waders keep their legs in flight.
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| 3. |
- Macías-Torres, Pablo, et al.
(author)
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Activity patterns throughout the annual cycle in a long-distance migratory songbird, the red-backed shrike Lanius collurio
- 2022
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In: Movement Ecology. - : Springer Science and Business Media LLC. - 2051-3933. ; 10:1
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Journal article (peer-reviewed)abstract
- Background: Long-distance migratory birds undergo complex annual cycles during which they must adjust their behaviour according to the needs and conditions encountered throughout the year. Yet, variation in activity throughout the entire annual cycle has rarely been studied in wild migratory birds. Methods: We used multisensor data loggers to evaluate the patterns of activity throughout the complete annual cycle of a long-distance migratory bird, the red-backed shrike Lanius collurio. Accelerometer data was used to identify life-history stages and to estimate levels of activity during various phases of the annual cycle. In this study, we analysed the variation in daytime activity along the annual cycle and between migratory and non-migratory days. Results: The birds’ daytime activity varied throughout the annual cycle while night-time activity was almost exclusively restricted to migratory flights. The highest daytime activity levels were observed during the breeding season, while it remained low during autumn migration and the winter period. Daytime activity differed between sexes during the breeding period, when the males showed the highest level in activity. During migratory periods, both sexes exhibited a higher daytime activity in spring compared to autumn migration, being particularly high in the final migratory leg towards the breeding ground. The birds showed a lower daytime activity on migratory days (days when a migratory flight took place during the succeeding night) than on non-migratory days during both migratory seasons. Conclusions: Activity measured during daytime results from a combination of several behaviours, and a high daytime activity during spring migration and the breeding period is possibly reflecting particularly energy-demanding periods in the annual cycle of migratory birds. The use of multisensor data loggers to track annual activity provides us with a full annual perspective on variation in activity in long-distance migratory species, an essential approach for understanding possible critical life-history stages and migration ecology.
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| 4. |
- Malmiga, Gintaras, et al.
(author)
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Individual and sex-related patterns of prolonged flights during both day and night by great reed warblers crossing the Mediterranean Sea and Sahara Desert
- 2021
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In: Journal of Avian Biology. - : Wiley. - 0908-8857 .- 1600-048X. ; 52:1
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Journal article (peer-reviewed)abstract
- A wide variety of the barrier crossing strategies exist among migrating songbirds, ranging from strict nocturnal flights to non-stop flights over a few days. We evaluate barrier crossing strategies in a nocturnally migrating songbird crossing the Mediterranean Sea and the Sahara Desert, the great reed warbler, exploring variation between the sexes and within individuals. We used data from 31 year-round light-level geolocators tracks from 26 individuals (13 males and 13 females), with four individuals tracked for 2–3.5 consecutive years. Almost all individuals (25 of 26) prolonged their flights into the day at least on one occasion. The mean duration of these prolonged flights was 19.9 h and did not differ between sexes or seasons. Fifteen birds performed non-stop flights during more than one full day and night (≥ 24 h; mean = 31.9 h; max = 55 h) in autumn and/or spring, but these flights were generally too short to cross an entire barrier (such as the Sahara Desert) in one non-stop flight. Patterns of prolonged flights showed considerable within-individual variation in females between seasons (autumn versus spring) and in both males and females between years, suggesting high individual flexibility in migration strategy. Significantly more males than females performed prolonged flights during autumn migration, but not spring, possibly reflecting sex-specific carry-over effects. We conclude that great reed warblers have the ability to conduct prolonged continuous flights for up to several nights and days, which potentially would allow them to cross the Sahara Desert in one non-stop flight. However, they typically use a mixed strategy of several nocturnal flights with intermittent stopovers in combination with 1–3 prolonged flights. Prolonged flights covered less than half (44%) of the total flight time across the barriers, and the diurnal parts of the flights covered only 18% of this time.
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| 5. |
- Sjöberg, Sissel, et al.
(author)
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Extreme altitudes during diurnal flights in a nocturnal songbird migrant
- 2021
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In: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 372:6542, s. 646-648
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Journal article (peer-reviewed)abstract
- Billions of nocturnally migrating songbirds fly across oceans and deserts on their annual journeys. Using multisensor data loggers, we show that great reed warblers (Acrocephalus arundinaceus) regularly prolong their otherwise strictly nocturnal flights into daytime when crossing the Mediterranean Sea and the Sahara Desert. Unexpectedly, when prolonging their flights, they climbed steeply at dawn, from a mean of 2394 meters above sea level to reach extreme cruising altitudes (mean 5367 and maximum 6267 meters above sea level) during daytime flights. This previously unknown behavior of using exceedingly high flight altitudes when migrating during daytime could be caused by diel variation in ambient temperature, winds, predation, vision range, and solar radiation. Our finding of this notable behavior provides new perspectives on constraints in bird flight and might help to explain the evolution of nocturnal migration.
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| 6. |
- Sjöberg, Sissel, et al.
(author)
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Solar heating may explain extreme diel flight altitude changes in migrating birds
- 2023
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In: Current Biology. - 0960-9822. ; 33:19, s. 2-4237
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Journal article (peer-reviewed)abstract
- Great reed warblers, Acrocephalus arundinaceus,1 and great snipes, Gallinago media,2 exhibit a diel cycle in flight altitudes—flying much higher during the day than the night—when performing migratory flights covering both night and day. One hypothesis proposed to explain this behavior is that the birds face additional heating by solar radiation during daytime and hence must climb to very high, and thus also very cold, altitudes to avoid overheating during daytime flights.1,2 Yet, solar heat gain in birds has been shown to drastically decrease with wind speed,3,4 and the quantitative heating effect by solar radiation on a bird flying with an airspeed of 10 m/s or more is unknown. We analyzed temperature data from multisensor data loggers (MDLs)5,6 placed without direct exposure to solar radiation on great reed warblers (the logger covered by feathers on the back) and great snipes (the logger on the leg, covered from the sun by the tail). We found that logger temperatures were significantly higher (5.9°C–8.8°C in great reed warblers and 4.8°C–5.4°C in great snipes) during the day than during the night in birds flying at the same altitudes (and thus also the same expected ambient air temperatures). These results strongly indicate that the heat balance of the flying birds is indeed affected by solar radiation, which is in accordance with the hypothesis that solar radiation is a key factor causing the remarkable diel cycles in flight altitude observed in these two long-distance migrant bird species.1,2
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