Thomas Alerstam’s research while affiliated with Lund University and other places

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Publications (187)


(a) Migratory routes of satellite‐tracked adult common cuckoos (n = 13). For each individual cuckoo, lines connect the longest stationary period in each region. Sites used by cuckoos during stationary periods (Duration ≥ 3 days) throughout the annual loop migration are indicated with different colours (Breeding = blue, Europe‐Autumn = red, Sahel = yellow, Winter = green, West‐Africa = orange, Europe‐Spring = light blue). Positions within a 25 km radius were considered as the same stopover. (b) Examples of the variation in geographic distribution of locations (latitude and longitude according to y‐ and x‐axes, respectively) in different years at revisited sites (definition of site in methods). Symbols show one location as recorded by satellite telemetry from each 10 h transmission period during the bird's stay (≥ 7 days) at the site, with different colours for locations from different years. (a) no. 36487, breeding site, (b) no. 36332, Europe autumn, (c) no. 62608, Europe autumn and (d) no. 115591, Sahel. Note that in (c) the site was not visited in year 2, representing a case of a gap year (in b and d birds were only tracked for three years 1–3).
(a) Proximity to previously used sites across different regions. Proportion of individuals (a) visiting and (b) using a site within a certain distance (5, 25, 50 km) from a site used in a previous year (three days duration; 25 km range). (b) Variation across regions and phases of the migratory cycle in the probability of adult common cuckoos staying on average within 50 km from a site visited (Duration ≥ 7 days) in a previous year. Black bars show the proportion of cases when a site was revisited out of the total number of possible revisits.
Variation across regions and phases of the migratory cycle of adult common cuckoos in the distance to a previous year's position. Lower values of distance from previous year position indicate a stronger site fidelity and vice‐versa. All study individuals are included (n = 13) and each individual often had more than one separate stay in each region. The sample size of stopover positions (where the bird stayed ≥ 3 days) for which site fidelity was calculated differed between the stationary periods (Breeding = 21 Europe‐Autumn = 40, Sahel = 61, Winter = 84, West‐Africa = 19, Europe‐Spring = 12). Boxplots show minimum values, first quartile, median, third quartile and maximum values.
Relationship between duration of a stopover (days) used by adult common cuckoos and distance from a previous year's position in the three staging areas considered for the analyses (Europe‐Autumn, Sahel, Winter). Each data point consists of the duration of a stay in a previous year and the average minimum distances between positions in the two years during the duration of the stopover in the previous year. All study individuals are included (n = 13) and each individual often had more than one separate stay in each region. Lower values of distance from the sites visited in the previous year by the individual indicate a stronger site fidelity at a stopover site (where the bird stayed for ≥ 3 days); positions within a 25 km radius were considered as one stopover. Points from individual no. 128297 are shown in grey.
Recurrence, fidelity and proximity to previously visited sites throughout the annual cycle in a trans‐Saharan migrant, the common cuckoo
  • Article
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March 2024

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145 Reads

Carlotta Bonaldi

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Most migratory birds return every year to the same breeding sites and some species show a similarly high fidelity to wintering grounds as well. Fidelity to stopover sites during migration has been much less studied and is usually found to be lower. Here, we investigate site fidelity and distance to previously visited sites throughout the annual cycle in the common cuckoo, a nocturnal trans‐Saharan migrant, based on satellite‐tracking data from repeated annual migrations of thirteen adult males. All birds (100%) returned to the same breeding grounds, with a median shortest distance of only 1 km from the locations in previous year. This was in strong contrast to a much lower and much less precise site fidelity at non‐breeding sites during the annual cycle: In only 18% of the possible cases in all non‐breeding regions combined, did the cuckoos return to within 50 km of a previously visited non‐breeding site, with no significant differences among the main staging regions (Europe in autumn, Sahel in autumn, wintering in Central Africa, West Africa in spring, Europe in spring). The shortest distance to a previously visited non‐breeding site differed among the staging regions with median shortest distances for the longest stopovers of 131 km [2;1223] (median [min;max]) in Europe, 207 km [1;2222] in Sahel in autumn and 110 km [0;628] in Central Africa. The distance to a previously visited staging site decreased with the time spent at the stopover in a previous year. Understanding the drivers of recurrence and site selection in migratory birds are important for guiding conservation efforts in this group but further studies are needed to establish whether the patterns observed in cuckoos are general among terrestrial migrants with continuous distribution of habitat.

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Solar heating may explain extreme diel flight altitude changes in migrating birds

September 2023

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97 Reads

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1 Citation

Current Biology

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.


Average daytime activity and number of hours on migration ofred-backed shrikes throughout the annual cycle, based on accelerometer data for 14 individuals. While daytime activity varied throughout the entire year, nocturnal activity (continuous flapping flight) occurred only when migrating. Solid lines illustrate a 5-day running mean for all individuals per variable (green: migrating hours; blue: daytime activity). Data points and confidence intervals for the daytime activity are shown in Fig. 2b
Daytime activity at different locations and phases of the annual cycle in red-backed shrikes. A Mean daytime activity throughout the annual cycle with migratory periods shown in colours (spring migration in blue and autumn migration in orange). Dates indicate the mean starting and finishing dates for each migratory period for all the individuals. Two dashed lines serve as guiding for daytime activity values of 20 and 50. B Same mean daytime activity values with a 95% confidence interval shown (shadowed area). Each point represents the activity value per day per individual. Autumn and spring migration are divided in three and two migratory legs respectively, shown in different colours. Dashed line shows the mean value of activity during the winter period as a reference. C The map represents the known migratory route of the same population of red-backed shrikes [52, 53]. Coloured arrows indicate migratory periods with the same colours as B. Mean activity during a stopover period is illustrated by the size of the grey circles at each stopover location
Daytime activity of red-backed shrikes at different events of the annual cycle. Between sexes, daytime activity was different only for the summer (breeding period), but statistically identical for the others. Pairwise post hoc comparison for male red-backed shrikes (n = 11) showed that all four events of the annual cycle were statistically different from each other, while for females (n = 3) only spring migration was statistically significant from all other events (Additional file 1: Table S2)
Differences in daytime activity between migratory and non-migratory days in autumn and spring migration. Red-backed shrikes were less active during migratory days compared to non-migratory days. Non-migratory days includes stopovers and “stop and go” days; while migratory days are those in which the red-backed shrikes migrated during the evening. Post-hoc Tukey HSD results are shown with stars over the boxplots showing significant differences at a level of p < 0.001
Daily daytime activity in red-backed shrikes over a 10-day period after the arrival at the breeding grounds. Red-backed shrikes showed high activity upon arrival at the breeding grounds, gradually decreasing during a 10-day period after that. Dashed line represents the regression line for all individuals. Individual regression lines are indicated in colours
Activity patterns throughout the annual cycle in a long-distance migratory songbird, the red-backed shrike Lanius collurio

December 2022

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347 Reads

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7 Citations

Movement Ecology

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.


Figure 1. Schematic flight routes of Swedish male great snipes
Figure 2. The diel cycle in flight altitudes by great snipes (A-C) Flight altitudes (m a.s.l.) of great snipes during the Autumn, In-Africa, and Spring flights (Figure 1), in relation to time of day (UTC). The solid dark line and gray shading are the average flight altitude and its 95% CI, as estimated from LOESS. Approximate day (yellow) and night (gray) are shown for the average date and longitude of migration in each season. Thin gray lines denote the individual tracks. When estimating sunrise (03:43) and sunset (18:21) for the Autumn flights, we assumed an average estimated starting point for all flights of 700 km south of the breeding grounds (56.8 N, 15.0 E), on August 23. For the Spring flight the estimated sunrise (04:48) and sunset (16:55) were based on an average starting point for all flights at 0.00 N, 17.00 E, on April 17. For the In-Africa flight the estimated sunrise (05:17) and sunset (17:22) were based on an average starting point for all flights at 10.00 N, 8.00 E, on September 25. See also Figures S1-S4. (D) Frequency analysis (discrete Fourier transform) with power spectrum of variations in altitude during the long migratory flights of great snipes for Autumn (light brown; n = 13) and Spring flights (dark green; n = 5). The frequency is presented as number of cycles in altitude per 24 h. Clearly, the strongly dominating regular frequency is one altitude cycle/day. Bars indicate average power components and data are for the same flights as shown in (A) and (C). (E) Autocorrelations of hourly flight altitudes during the long migratory flights of great snipes. The time series are based on altitudes measured hourly for Autumn (solid) and Spring flights (dashed). The local correlation maxima, as indicated by the average correlation coefficient (r), that occur after ~24 and ~48 h show that the altitude at any given hour is best matched by the altitude recorded ~24 or ~48 h before (or after) that. The local correlation minima (negative correlation coefficients) that occur after ca. ~12 and ~36 h show that the altitude at any given hour is matched by an altitude at the opposite side of the altitude range ~12 or ~36 h before (or after).
Figure 3. Flight altitudes in relation to topography and air temperature (A and B) Flight altitudes (m a.s.l.) of great snipes during Autumn and Spring flights in relation to Earth's topography at estimated distances along five schematic flight routes (Figure 1; Table S3). The solid dark line and gray shading are the average flight altitude and its 95% CI, as estimated from LOESS. Thin gray lines denote the individual tracks. The topography is shown as the average (black) and maximum (gray) altitude along the approximated tracks. (C and D) Ambient air temperatures in autumn and spring at four different atmospheric pressure levels of 850, 700, 500, and 400 hPa (corresponding to altitudes as indicated in D), along the approximate Autumn and Spring flight routes #3 (Table S3). The solid dark line and gray shading are the average air temperature and its 95% CI for each pressure level, as estimated from LOESS. Thin gray lines denote the individual temperature profile for an early, average, and late timing at each pressure level. See also Figure S1.
Evaluation of factors potentially explaining the diel cycle in flight altitudes
Extreme altitude changes between night and day during marathon flights of great snipes

June 2021

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535 Reads

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37 Citations

Current Biology

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.1-6 Recent tracking of migratory birds over long distances has shown that migrants change flight altitude more commonly and dramatically than previously thought.4-8 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.


Extreme altitudes during diurnal flights in a nocturnal songbird migrant

May 2021

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357 Reads

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47 Citations

Science

High fliers Migrating from hemisphere to hemisphere is a global strategy for many bird species. Despite allowing birds to track productivity, these long-distance movements bring them in contact with inhospitable regions such as deserts and oceans. Sjöberg et al. used geolocators to monitor flight in great reed warblers ( Acrocephalus arundinaceus ) and found that when over these types of regions, this normally nocturnal migrating species flew both day and night. During the day, the birds increased the altitudes at which they flew, rising to more than 5000 meters. Such behavior may allow them to avoid heat stress or other daytime threats during migration. Science , this issue p. 646


Individual and sex‐related patterns of prolonged flights during both day and night by great reed warblers crossing the Mediterranean Sea and Sahara Desert

January 2021

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129 Reads

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8 Citations

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 4 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 vs. 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. This article is protected by copyright. All rights reserved.


Waders flying with folded legs – which species, when, where and why?

August 2020

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11 Reads

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4 Citations

Wader Study

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.


Remarkably similar migration patterns between different red‐backed shrike populations suggest that migration rather than breeding area phenology determines the annual cycle

August 2020

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189 Reads

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11 Citations

The regular fluctuation of resources across the Globe guides movements of migratory animals. To ensure sufficient reproductive output and maintain viable population sizes, migratory animals should match arrival at breeding areas with local peaks in resource availability. It is generally assumed that breeding phenology dictates the timing of the annual cycle, but this is poorly studied. Here, we use light‐level geolocator tracking data to compare the annual spatiotemporal migration patterns of a long‐distance migratory songbird, the red‐backed shrike, Lanius collurio, breeding at widely different latitudes within Europe. We find that populations use remarkably similar migration routes and are highly synchronized in time. Additional tracks from populations breeding at the edges of the European range support these similar migration patterns. When comparing timing of breeding and vegetation phenology, as a measure of resource availability across populations, we find that arrival and timing of breeding corresponds to the peak in vegetation greenness at northern latitudes. At lower latitudes birds arrive simultaneously with the more northerly breeding populations, but after the local greenness peak, suggesting that breeding area phenology does not determine the migratory schedule. Rather, timing of migration in red‐backed shrikes may be constrained by events in other parts of the annual cycle. This article is protected by copyright. All rights reserved.


Hypotheses and tracking results about the longest migration: The case of the arctic tern

August 2019

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739 Reads

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24 Citations

The arctic tern Sterna paradisaea completes the longest known annual return migration on Earth, traveling between breeding sites in the northern arctic and temperate regions and survival/molt areas in the Antarctic pack‐ice zone. Salomonsen (1967, Biologiske Meddelelser, Copenhagen Danske Videnskabernes Selskab, 24, 1) put forward a hypothetical comprehensive interpretation of this global migration pattern, suggesting food distribution, wind patterns, sea ice distribution, and molt habits as key ecological and evolutionary determinants. We used light‐level geolocators to record 12 annual journeys by eight individuals of arctic terns breeding in the Baltic Sea. Migration cycles were evaluated in light of Salomonsen's hypotheses and compared with results from geolocator studies of arctic tern populations from Greenland, Netherlands, and Alaska. The Baltic terns completed a 50,000 km annual migration circuit, exploiting ocean regions of high productivity in the North Atlantic, Benguela Current, and the Indian Ocean between southern Africa and Australia (sometimes including the Tasman Sea). They arrived about 1 November in the Antarctic zone at far easterly longitudes (in one case even at the Ross Sea) subsequently moving westward across 120–220 degrees of longitude toward the Weddell Sea region. They departed from here in mid‐March on a fast spring migration up the Atlantic Ocean. The geolocator data revealed unexpected segregation in time and space between tern populations in the same flyway. Terns from the Baltic and Netherlands traveled earlier and to significantly more easterly longitudes in the Indian Ocean and Antarctic zone than terns from Greenland. We suggest an adaptive explanation for this pattern. The global migration system of the arctic tern offers an extraordinary possibility to understand adaptive values and constraints in complex pelagic life cycles, as determined by environmental conditions (marine productivity, wind patterns, low‐pressure trajectories, pack‐ice distribution), inherent factors (flight performance, molt, flocking), and effects of predation/piracy and competition. The arctic tern is probably the animal that performs the longest known migrations. We used geolocator tracking data from a population of arctic terns from the Baltic Sea for evaluating the ecology and evolution of its long‐distance pelagic migration. We also compared with results from geolocator studies of arctic tern populations from Greenland, Netherlands, and Alaska. This comparison revealed unexpected segregation in time and space between tern populations in the same flyway.


Fig. 3 Relative energy costs (Eq. 8) for central place foraging flights in relation to wind direction for cases with different cost factors (c) associated with the carrying of a load on the inward flight. The graph shows a situation with strong wind speed (a = 0.75). See "Effects of extra flight costs (extra load) during return flights" for further explanation
Fig. 7 a Relative energy costs (Eq. 4) for central place foraging flights a given distance from the origin in relation to wind direction (with outward flight in direction β and the inward flight (180 -β) relative to wind) for flights with optimal airspeed adjustment (wind dependent V mr ) for minimization of energy cost per distance (solid lines, see "Effects of flight speed optimization") or with constant airspeed (dashed lines). The cost is expressed in relation to the round-trip energy cost in calm conditions and plotted in relation to wind direction for three different cases of wind speed (a = 0.75, 0.5 and 0.25, where a is the ratio of wind speed to the bird's optimal airspeed V mr under calm conditions; see Fig. 1 and "Central place foraging flights in a uniform wind field"). b Relative range (Eq. 6) of central place foraging flights using a given amount of energy for the round trip in relation to wind direction (with outward flight in direction β and the inward flight (180 -β) relative to wind) with optimal airspeed adjustment (wind dependent V mr ) for minimization of energy cost per distance (solid lines) or with constant airspeed (dashed lines). The range is expressed in relation to the range reached by using the same amount of energy in calm conditions and plotted in relation to wind direction for three different cases of wind speed (a = 0.75, 0.5 and 0.25, where a is the ratio of wind speed to the bird's optimal airspeed, V mr , under calm conditions; see Fig. 1 and "Central place foraging flights in a uniform wind field"). Calculations follow the R package aerodynamic model AFTP of Klein Heerenbrink, based on Klein Heerenbrink et al. (2015, 2016) with Jackdaw Corvus monedula as example species (calculations of chemical power)
Optimal central place foraging flights in relation to wind

June 2019

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182 Reads

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8 Citations

Journal of Ornithology

Many flying animals, like birds feeding their young, make commuting flights between a central place and foraging areas in the surroundings. Such central place foraging (CPF) represents a special case of foraging theory. We use simple geometry and trigonometry to analyse CPF flight performance (a round-trip cycle of outward flight from the central place and inward flight back along the reverse track) in relation to wind. In addition to considering the situation of a constant and uniform wind field, we take into account two factors that are likely to apply in many CPF situations under natural conditions: (a) that animals carry a load that will increase the energy expenditure during the inward flight and (b) that they may fly at different altitudes during out- and inward flights in the wind gradient above the ground or sea surface. Four main predictions emerge: (1) efficiency of CPF flights will be reduced with increasing wind speed, and foraging at the longest ranges is expected under low wind speeds. (2) A preference for CPF flights in crosswinds is expected in a constant and uniform wind field. (3) Carrying a load during the inward flight makes it optimal to fly with a small component of following winds during this flight while the outward flight will have a corresponding component of opposed winds. (4) With a steep wind gradient (e.g. over rough terrain) providing much shelter from wind at the lowest altitudes, predicted behaviour may change from crosswind preference to a preference for flights along the head/tailwind axis (at low altitude into headwinds and high altitude in tailwinds). Detailed tests of predictions for CPF flights in relation to wind will be important for understanding constraints and adaptations in animal responses to wind and for evaluating consequences of changing wind regimes in animal movement ecology.


Citations (82)


... Most animal flight occurs within the atmospheric boundary layer (ABL), but there is increasing evidence that waders and passerines migrate above the ABL at flight heights of 4-7 km above ground (Sjöberg et al., 2023, Sjöberg et al., 2021. Here, wind speeds tend to be stronger and more uniform due to a decrease in surface effects. ...

Reference:

How might turbulence affect animal flight in a changing world?
Solar heating may explain extreme diel flight altitude changes in migrating birds
  • Citing Article
  • September 2023

Current Biology

... Accelerometers, which record accelerations over time, allow the study of animal activities without the limitation of visibility and observer bias (Brown et al., 2013). Accelerometers can be used to record coarse flight activity patterns of birds over a complete annual cycle (Bäckman et al., 2017;Norevik et al., 2019;Macias-Torres et al., 2022). What these accelerometer studies do not show, however, is activity patterns and detailed flight performance at high temporal resolution. ...

Activity patterns throughout the annual cycle in a long-distance migratory songbird, the red-backed shrike Lanius collurio

Movement Ecology

... Recent tracking technology has revealed that some birds fly at extreme altitudes up to and above 7000 m above sea level (asl) during nonstop migration flights (Lindström et al., 2021;Sjöberg et al., 2021). An untested hypothesis put forward is that birds migrate this high above the ground to avoid encountering predators. ...

Extreme altitude changes between night and day during marathon flights of great snipes

Current Biology

... Deciding when to migrate is critical for migratory animals, who must trade off the need to accumulate reserves before taking off on the long journey with the need to leave early in order to find and take over a good habitat at the destination (van de Kerk et al. 2021). Additional sensors can be added to this device to monitor long-term acceleration, ambient pressure, temperature, etc., allowing researchers to identify different behavioral states, such as when a bird is standing, eating, and actively or passively flying (Nathan et al. 2012), as well as its flight height and body or environmental temperature (Sjöberg et al. 2021). Such an approach was employed to demonstrate the outstanding phenomenon of the Alpine swifts, which continuously fly for 200 days during migration, foraging, and resting (Liechti et al. 2013). ...

Extreme altitudes during diurnal flights in a nocturnal songbird migrant
  • Citing Article
  • May 2021

Science

... Instead, we argue that occasional daytime migration in nocturnally migrating birds is better viewed as phenotypic plasticity within the reaction norm [18] and hence should be referred to as a "tactic" [19]. Malmiga et al. (2021) used repeated tracks to show that individual great reed warblers Acrocephalus arundinaceus can alternate and carry out FDFs in one year but not the other, showcasing that it is indeed a tactic. ...

Individual and sex‐related patterns of prolonged flights during both day and night by great reed warblers crossing the Mediterranean Sea and Sahara Desert

... Late and fast arriving species exhibited a different migratory strategy, arriving at warmer temperatures closer to green-up temperature compared to the early and slow species. This is possibly due to seasonal environmental constraints in resource availability in Africa (Davies et al., 2023;Pedersen et al., 2020), as faster arrival was linked to wintering in the humid and southern zones and, therefore, required traversing more of Africa. Because they arrived in Europe later, there was a stronger pressure to rapidly progress through Europe to ensure arrival in time for peak food supply. ...

Remarkably similar migration patterns between different red‐backed shrike populations suggest that migration rather than breeding area phenology determines the annual cycle
  • Citing Article
  • August 2020

... Migratory individuals typically have longer wings to enhance their migratory flight performance, while resident individuals have shorter wings, which has been shown to increase predator avoidance through faster take-off velocity (Norberg 1995, Kullberg et al. 1996. Tarsus length has an impact on migratory flight performance due to the increase in drag associated with longer legs (Zeffer et al 2003, Lindström andAlerstam 2020). However, to our knowledge, no studies have examined the difference in tarsus length between migratory and resident WCSP. ...

Waders flying with folded legs – which species, when, where and why?
  • Citing Article
  • August 2020

Wader Study

... Still, it also involves exploring how this species covers a significant portion of the world's oceans within a year. The terns encounter a rapidly changing environment throughout this journey, with modified opportunities for finding food during breeding and wintering (Egevang et al., 2010;Thomas et al., 2019). Figure 3 depicts Arctic terns' migration routes and foraging paths, adapted from www.go2moon.com. ...

Hypotheses and tracking results about the longest migration: The case of the arctic tern

... Over the past decades, several studies documented segregation in seabird spatial distribution at sea [15], allochrony in breeding phenology [21] and dietary specializations [22]. For many pelagic seabirds, locomotor efficiency is key to optimal foraging, particularly so during the breeding season, when they are central-place foragers [23]. Yet, despite the centralplace constraint, some seabirds travel hundreds to thousands of kilometres to forage over immense ocean areas in search of ephemeral and heterogeneously distributed prey patches [24,25]. ...

Optimal central place foraging flights in relation to wind

Journal of Ornithology

... If subsampling had partly or fully failed (e.g. if only 10 out of 12 or no scores were available during an hour) during a flight period, these samples were defined as zeros and were not included to calculate flight duration. Migration starts with a period of fuelling in order to allow the first migratory flight [38]. However, in most cases the duration of this period is unknown since the bird may still be at the breeding or wintering site. ...

Faster fuelling is the key to faster migration

Nature Climate Change