Many birds make migratory flights lasting several days. Migrants do not only repeatedly make small-scale shifts in altitude; some of them also climb and sink several thousand metres in a diel cycle. This is a seemingly energetically costly behaviour, adding to an already high energetic cost of flight. Here, we describe the climbing and sinking behaviour of migratory great snipes, Gallinago media, and discuss whether their diel altitude cycle could represent an additional energy cost to their migration. Making use of tracking data from multisensor data loggers, we quantified altitude variation and compared climb and sink rates from non-stop migratory flights lasting up to 4 days (84 h). In general, great snipes climb and sink at comparatively slow rates, averaging 0.21 m s-1 and -0.22 m s-1, respectively, almost invariably within ±0.7 m s-1, and hardly ever close to a theoretical maximum climb rate of 1.8 m s-1. Great snipes do not climb faster at night than in the day and climb and sink rates are similarly low for all long non-stop flights. The additional cost of shifting flight altitude for great snipes is apparently negligible compared with the cost of forward flight (<1%). This is largely explained by the birds flapping during a slow descent, thereby turning most of the potential energy built up during previous climbs into aerodynamic work. We conclude that the overall cost of shifting flight is probably low for most migratory birds, given that climb and sink rates are low.

Polygamous birds with lek-mating breeding systems often show site fidelity to display sites, leading to spatio-temporal stability of traditional leks that can persist for decades. Here, we used a mark-recapture framework to study between-year lek fidelity among adult male and female Gallinago media (Great Snipe), for two distinct breeding populations in Eastern Europe and Scandinavia. We evaluated the effects of individual body size, lek size, and distance among leks on the probability of changing lek between seasons. Moreover, we were able to obtain more precise estimates of annual survival for G. media beyond previously obtained population parameters from a single lek and for males only. G. media had a low but stable annual apparent survival across both sexes and breeding populations (S = 0.571 +/- 0.019 SE). Birds showed high between-year fidelity to their leks, as we detected a relatively low probability of changing leks between seasons (Psi = 0.18 +/- 0.019 SE). Despite pronounced differences in breeding behavior between sexes, as well as habitat differences between breeding populations, they did not influence lek fidelity, and neither did individual body size nor distance between leks. However, birds at larger leks were less likely to move elsewhere in the following years. Understanding the drivers of lek changing behavior provides insights into the evolution of a lek mating strategy, and accounting for site fidelity is crucial for studying population dynamics and space use patterns. Taking the inherent limitations of estimates based on mark-capture models into account, our estimates of annual survival and site fidelity for G. media can be used to inform management decisions and conservation strategies. Return rates to the same breeding site in different seasons vary among mating systems in waders. Monogamous birds tend to be more site faithful than polygamous ones, but in lekking species, both sexes are often highly faithful to the leks. We studied Gallinago media (Great Snipe) in two distinct breeding populations to measure both annual survival and lek fidelity, using long-term ringing data. We found that G. media rarely switch leks between breeding seasons, and high lek fidelity is shared by both sexes and both breeding populations of this species. Site fidelity likely explains how traditional leks can be in the same place for decades, frequently exceeding the lifespan of a single individual. Given the low annual survival estimates of adults, the information on lek locations must be easily accessible for the first-time breeders, additionally facilitating stability of traditional lekking sites. Las aves pol & iacute;gamas con sistemas reproductivos basados en leks suelen mostrar fidelidad al sitio de exhibici & oacute;n, lo que conduce a la estabilidad espacio-temporal de leks tradicionales que pueden persistir durante d & eacute;cadas. Aqu & iacute; utilizamos un enfoque de marcado-recaptura para estudiar la fidelidad interanual a los leks en machos y hembras adultos de Gallinago media en dos poblaciones reproductivas distintas de Europa oriental y Escandinavia. Evaluamos los efectos del tama & ntilde;o corporal individual, el tama & ntilde;o del lek y la distancia entre leks sobre la probabilidad de cambiar de lek entre temporadas. Adem & aacute;s, pudimos obtener estimaciones m & aacute;s precisas de la supervivencia anual de G. media m & aacute;s all & aacute; de los par & aacute;metros poblacionales previamente obtenidos a partir de un & uacute;nico lek y solo para machos. Gallinago media present & oacute; una supervivencia aparente anual baja pero estable en ambos sexos y poblaciones reproductivas (S = 0.571 +/- 0.019 EE). Las aves mostraron una alta fidelidad interanual a sus leks, ya que detectamos una probabilidad relativamente baja de cambiar de lek entre temporadas (Psi = 0.18 +/- 0.019 EE). A pesar de las marcadas diferencias en el comportamiento reproductivo entre sexos, as & iacute; como de las diferencias de h & aacute;bitat entre las poblaciones reproductivas, estos factores no influyeron en la fidelidad al lek, ni tampoco lo hicieron el tama & ntilde;o corporal individual o la distancia entre leks. Sin embargo, las aves en leks m & aacute;s grandes tuvieron menor probabilidad de desplazarse a otros sitios en los a & ntilde;os siguientes. Comprender los factores que determinan el cambio de lek proporciona informaci & oacute;n sobre la evoluci & oacute;n de la estrategia reproductiva basada en leks, y considerar la fidelidad al sitio es crucial para estudiar la din & aacute;mica poblacional y los patrones de uso del espacio. Teniendo en cuenta las limitaciones inherentes de las estimaciones basadas en modelos de marcado-recaptura, nuestras estimaciones de supervivencia anual y fidelidad al sitio para G. media pueden utilizarse para orientar decisiones de manejo y estrategias de conservaci & oacute;n.

Migratory songbirds have an internal circannual genetic programme that controls the timing and extent of migratory flight activity, as demonstrated by experiments with birds held in cages. We used multisensor data loggers to record the timing and duration of all migratory flights during the annual cycle of 15 free-living individuals of red-backed shrikes Lanius collurio. Annual actograms unexpectedly revealed that the nocturnal migratory flights of the shrikes were organized in a highly structured way, with flights aggregated into segments that could be readily identified for all individuals, showing low variability and thus high consistency between individuals. These results suggest that the execution of migratory flights is under a high degree of control according to a rather detailed internal travelling plan for the annual migration cycle. Potentially, the control of migratory flight under natural conditions depends on a complex feedback process where external cues associated with the geographic, temporal and nutritional situation of the bird are required for the internal programme to properly regulate the successive segmental flight steps of the migratory journey. This would mean that the internal/genetic programme for control of bird migration is much more dynamic and complex than hereto assumed.

Light-level geolocators were used to record the annual migration cycles of black terns Chlidonias niger (9 individuals, 11 journeys) and common terns Sterna hirundo (7 individuals, 11 journeys) breeding in southernmost Sweden. The black terns used two different non-breeding (Oct-Mar) regions along the Atlantic coast of Africa, either north of the equator between Senegal and Liberia (3 individuals) or south of the equator between Gabon and northern Namibia (5 individuals). All the common terns travelled to non-breeding quarters south of the equator, mainly along the coasts of Namibia and South Africa. One juvenile common tern was tracked during the first twenty months of its life. This bird spent its first northern winter in South Africa, after which it migrated north of the equator to spend the northern summer as a one-year-old non-breeder in tropical waters off Ghana, after which it returned to South Africa for its second northern winter. This record demonstrates that one-year-old terns may undertake extensive intra-African migration to distant over-summering areas. Comparing geolocator results from Swedish and Dutch black tern populations indicate that they have similar migration habits, with a possible tendency of relatively more individuals migrating south of the equator in the more northerly Swedish population (leap-frog migration). Comparing geolocator and ringing results among common tern populations indicates a fascinating and complex pattern of scale-dependent geographic segregation and intermixing along the coasts of Africa.

Abstract Background Small songbirds respond and adapt to various geographical barriers during their annual migration. Global flyways reveal the diverse migration strategies in response to different geographical barriers, among which are high-elevation plateaus. However, few studies have been focused on the largest and highest plateau in the world, the Qinghai–Tibet Plateau (QTP) which poses a significant barrier to migratory passerines. The present study explored the annual migration routes and strategies of a population of Siberian Rubythroats (Calliope calliope) that breed on the north-eastern edge of the QTP. Methods Over the period from 2021 to 2023, we applied light-level geolocators (13 deployed, seven recollected), archival GPS tags (45 deployed, 17 recollected), and CAnMove multi-sensor loggers (with barometer, accelerometer, thermometer, and light sensor, 20 deployed, six recollected) to adult males from the breeding population of Siberian Rubythroat on the QTP. Here we describe the migratory routes and phenology extracted or inferred from the GPS and multi-sensor logger data, and used a combination of accelerometric and barometric data to describe the elevational migration pattern, flight altitude, and flight duration. All light-level geolocators failed to collect suitable data. Results Both GPS locations and positions derived from pressure-based inference revealed that during autumn, the migration route detoured from the bee-line between breeding and wintering grounds, leading to a gradual elevational decrease. The spring route was more direct, with more flights over mountainous areas in western China. This different migration route during spring probably reflects a strategy for faster migration, which corresponds with more frequent long nocturnal migration flights and shorter stopovers during spring migration than in autumn. The average flight altitude (1856 ± 781 m above sea level) was correlated with ground elevation but did not differ between the seasons. Conclusions Our finding indicates strong, season-dependent impact of the Qinghai–Tibet Plateau on shaping passerine migration strategies. We hereby call for more attention to the unexplored central-China flyway to extend our knowledge on the environment-migration interaction among small passerines.

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 degrees C-8.8 degrees C in great reed warblers and 4.8 degrees C-5.4 degrees 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

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. 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. 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. 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.

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.

ABSTRACT Avian migrants may fly at a range of altitudes, but usually concentrate near strata where a combination of flight conditions is favourable. The aerial environment can have a large impact on the performance of the migrant and is usually highly dynamic, making it beneficial for a bird to regularly check the flight conditions at alternative altitudes. We recorded the migrations between northern Europe and sub-Saharan Africa of European nightjars Caprimulgus europaeus to explore their altitudinal space use during spring and autumn flights and to test whether their climbs and descents were performed according to predictions from flight mechanical theory. Spring migration across all regions was associated with more exploratory vertical flights involving major climbs, a higher degree of vertical displacement within flights, and less time spent in level flight, although flight altitude per se was only higher during the Sahara crossing. The nightjars commonly operated at ascent rates below the theoretical maximum, and periods of descent were commonly undertaken by active flight, and rarely by gliding flight, which has been assumed to be a cheaper locomotion mode during descents. The surprisingly frequent shifts in flight altitude further suggest that nightjars can perform vertical displacements at a relatively low cost, which is expected if the birds can allocate potential energy gained during climbs to thrust forward movement during descents. The results should inspire future studies on the potential costs associated with frequent altitude changes and their trade-offs against anticipated flight condition improvements for aerial migrants.

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.

Organisms in the wild are faced with multiple threats and a common response is a change in behaviour. To disentangle responses to several threats, we exposed two differently sized species of the freshwater invertebrate Daphnia to solar ultraviolet radiation (UVR) and predation from either moving pelagic or benthic ambush predators. Using an advanced nanotechnology-based method, we tracked the three-dimensional movements of those mm-sized animals at the individual level. Each behavioural trial was performed both under conditions resembling night (no UVR) and day (UVR) and we examined patterns of the depth distribution and swimming speed by Daphnia across three treatments: no predator (control); bottom-dwelling damselfly (Calopteryx sp.); and fish (stickleback, Pungitius pungitius) predators. We also quantified the actual predation rate by the two predators on the two Daphnia species, Daphnia manga and Daphnia pulex. We show that individual Daphnia are able to identify predators with different feeding habitats, rank multiple and simultaneously occurring risks and respond in accordance with the actual threat; complex responses that are generally associated with larger animals. In a broader context, our results highlight and quantify how a cocktail of everyday threats is perceived and handled by invertebrates, which advances our understanding of species distribution in space and time, and thereby of population dynamics and ecosystem function in natural ecosystems.

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.

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.

Every year, billions of seasonal migrants connect continents by transporting nutrients, energy, and pathogens between distant communities and ecosystems. For animals that power their movements by endogenous energy stores, the daily energy intake rates strongly influence the speed of migration. If access to food resources varies cyclically over the season, migrants sensitive to changes in daily energy intake rates may adjust timing of migration accordingly. As an effect, individuals adjusting to a common temporal cycle are expected to approach synchrony in foraging and movement. A large-scale periodic pattern, such as the dark-light cycle of the moon, could thus synchronize migrations across animal populations. However, such cyclic effects on the temporal regulation of migration has not been considered. Here, we show the temporal influence of the lunar cycle on the movement activity and migration tactics in a visual hunting nocturnal insectivore and long-distance migrant, the European nightjar, Caprimulgus europeaus. We found that the daily foraging activity more than doubled during moonlit nights, likely driven by an increase in light-dependent fuelling opportunities. This resulted in a clear cyclicity also in the intensity of migratory movements, with occasionally up to 100% of the birds migrating simultaneously following periods of full moon. We conclude that cyclic influences on migrants can act as an important regulator of the progression of individuals and synchronize pulses of migratory populations, with possible downstream effects on associated communities and ecosystems.

Among the many unique flight behaviours of Common Swifts Apus apus, the most puzzling may be their ascents to high altitudes during both dusk and dawn. Twilight ascents have been hypothesized to be functionally related to information acquisition, including integration of celestial orientation cues, high-altitude visual landmarks and sampling of weather conditions. However, their exact purpose remains unknown. We tracked Common Swifts with tracking radar at their breeding grounds in southern Sweden, and present evidence that during the dusk ascent and dawn descent they often occur in flocks, whereas during the dusk descent and dawn ascent phase they do not. This flocking behaviour suggests that swifts may benefit from conspecific interactions during twilight ascents and descents, possibly through more robust cue acquisition and information exchange in groups, or extending social behaviour also seen in screaming parties before dusk.

Flight activity recorders have recently confirmed that alpine and common swifts spend the majority of their non‐breeding period on the wing, which may last 6–10 months. Here we test the hypothesis that the closely related pallid swift, a species with a breeding distribution around the Mediterranean, lead a similar aerial life‐style during its migration and wintering periods. The pallid swift usually lays two clutches in one season and therefore spends more time in the breeding area than the common swift. We successfully tracked four pallid swifts with data loggers that record light for geolocation and acceleration every 5 min to monitor flight activity. The birds wintered south of the Sahel in west Africa from the Ivory Coast to Cameroon. The pallid swifts spent the majority of their non‐breeding time in flight, especially the first two months after leaving the breeding area in autumn, while a few landing events occurred during the winter. The total time grounded was < 1%, similar to that of the common and alpine swifts. The mass specific flight metabolic rate of swifts is similar to the average non‐breeding metabolic rate of a long distance terrestrial migrant, suggesting swifts are not more likely to procure oxidative damage as a consequence of continuous flight than other migrants. The open airspace used by swifts may provide a relatively safe habitat that explain the high survival rate found in swifts.

1. Advances in information technology are increasing the use of radar as a tool to investigate and monitor bird migration movements. We set up a field campaign to compare and validate outputs from different radar systems. 2. Here we compare the pattern of nocturnal bird migration movements recorded by four different radar systems at a site in southern Sweden. Within the range of the weather radar (WR) Angelholm, we operated a "BirdScan" (BS) dedicated bird radar, a standard marine radar (MR), and a tracking radar (TR). 3. The measures of nightly migration intensities, provided by three of the radars (WR, BS, MR), corresponded well with respect to the relative seasonal course of migration, while absolute migration intensity agreed reasonably only between WR and BS. Flight directions derived from WR, BS and TR corresponded very well, despite very different sample sizes. Estimated mean ground speeds differed among all four systems. The correspondence among systems was highest under clear sky conditions and at high altitudes. 4. Synthesis and applications. While different radar systems can provide useful information on nocturnal bird migration, they have distinct strengths and weaknesses, and all require supporting data to allow for species level inference. Weather radars continuously detect avian biomass flows across a wide altitude band, making them a useful tool for monitoring and predictive applications at regional to continental scales that do not rely on resolving individuals. BirdScan and marine radar's strengths are in local and low altitude applications, such as collision risks with man-made structures and airport safety, although marine radars should not be trusted for absolute intensities of movement. In quantifying flight behaviour of individuals, tracking radars are the most informative.

Billions of animals are adapted to a travelling life, making regular return migrations between more or less distant living stations on Earth by swimming, flying, running or walking (Figure 1). Extremely long migrations are completed annually by whales between calving areas in warmer waters and feeding areas at higher latitudes in either hemisphere. The longest oceanic migrations among sea turtles and fish are often undertaken by younger immature individuals during a period of several years before they start their more regular return visits to breeding and spawning sites. Among adult leatherback turtles, intervals of several years between successive breeding events leave enough time for extremely long journeys. Famous among bird migrants are arctic terns, showing the longest known annual migration circuit of about 50,000 km. Bar-tailed godwits breed in Alaska and winter in New Zealand and make the longest known non-stop flapping flights, lasting more than two hundred hours and covering up to 12,000 km across the Pacific Ocean. Their total annual migration circuit extends over 30,000 km covered in three main flights (Figure 1). Although diapause with hibernation as egg, pupae, larvae or adult is an important strategy among insects, there are also examples of impressive migrations. Monarch butterflies complete an annual circuit up to 9,000 km in North America in four generations (for more detail, see the review by Steven Reppert in this issue), and the globe skimmer (a dragonfly) presumably exploits the monsoon rains in India and rainy seasons in southern and equatorial Africa in a 15,000 km circuit in four generations (Figure 1). In comparison with swimmers and flyers, animals that migrate by running or walking cover shorter distances. Caribous migrate between boreal forest and tundra over a total distance of not much more than 1000—2000 km per year. Zebras make the longest migrations in Africa, covering at least 500 km, which is just a little bit longer than the well-known wildebeest migration circuit in Serengeti.

Recent advances in tracking technology are based on the use of miniature sensors for recording new aspects of individual migratory behaviour. In this study, we have used activity data loggers with barometric and temperature sensors to record the flight altitudes as well as ground elevations during stationary periods of migratory songbirds. We tracked one individual of red‐backed shrike and one great reed warbler along their autumn migration from Europe to Africa. Both individuals performed their migration stepwise in travel segments and climbed most metres during the passage across the Mediterranean Sea and the Sahara Desert and least metres during the first flight segment in Europe. The great reed warbler reached its highest flight altitude of 3950 m a.s.l. during the travel segment from Europe to west Africa, while the red‐backed shrike reached 3650 m a.s.l as maximum flight altitude during its travel segment from Sahel to southern Africa. Both individuals used both lowlands and highlands for resting periods along their migrations. Furthermore, temperature decreased with increasing altitude during migratory flights for both individuals, highlighting the potential to determine flight duration from temperature measurements. Finally, we discuss how barometric data could be used to investigate birds’ responses to changes in air pressure as a cue for departures on migratory flights. This new technique, i.e. using a miniature data logger with barometric pressure sensor to estimate flight altitudes and ground elevations, will open up new avenues for research and importantly advance our understanding on how small birds behave during migratory flights.