Can wind help explain seasonal differences in avian migration speed?

A bird's ground speed is influenced by the wind conditions it encounters. Wind conditions, although variable, are not entirely random. Instead, wind exhibits persistent spatial and temporal dynamics described by the general circulation of the atmosphere. As such, in certain geographical areas wind's assistance (or hindrance) on migratory flight is also persistent, being dependent upon the bird's migratory direction in relation to prevailing wind conditions. We propose that, considering the western migration route of nocturnal migrants through Europe, winds should be more supportive in spring than in autumn. Thus, we expect higher ground speeds, contributing to higher overall migration speeds, in spring. To test whether winds were more supportive in spring than autumn, we quantified monthly wind conditions within western Europe relative to the seasonal direction of migration using 30 years (1978–2008) of wind data from the NCEP/NCAR Reanalysis dataset. We found that supporting winds were significantly more frequent for spring migration compared to autumn and up to twice as frequent at higher altitudes. We then analyzed three years (2006–2008) of nocturnal migratory ground speeds measured with radar in the Netherlands which confirmed higher ground speeds in spring than autumn. This seasonal difference in ground speed suggests a 16.9% increase in migration speed from autumn to spring. These results stress the importance of considering the specific wind conditions experienced by birds when interpreting migration speed. We provide a simple methodological approach enabling researchers to quantify regional wind conditions for any geographic area and time period of interest.     

Confronting the winds: orientation and flight behaviour of roosting swifts, Apus apus

Swifts, Apus apus, spend the night aloft and this offers an opportunity to test the degree of adaptability of bird orientation and flight to different ecological situations. We predicted the swifts' behaviour by assuming that they are adapted to minimize energy expenditure during the nocturnal flight and during a compensatory homing flight if they become displaced by wind. We tested the predictions by recording the swifts' altitudes, speeds and directions under different wind conditions with tracking radar; we found an agreement between predictions and observations for orientation behaviour, but not for altitude and speed regulation. The swifts orientated consistently into the head wind, with angular concentration increasing with increasing wind speed. However, contrary to our predictions, they did not select altitudes with slow or moderate winds, nor did they increase their airspeed distinctly when flying into strong head winds. A possible explanation is that their head-wind orientation is sufficient to keep nocturnal displacement from their home area within tolerable limits, leaving flight altitude to be determined by other factors (correlated with temperature), and airspeed to show only a marginal increase in strong winds. The swifts were often moving "backwards", heading straight into the wind but being overpowered by wind speeds exceeding their airspeed. The regular occurrence of such flights is probably uniquely associated with the swifts' remarkable habit of roosting on the wing.     

Birds: blowin’ by the wind?

Migration is a task that implies a route, a goal and a period of time. To achieve this task, it requires orientation abilities to find the goal and energy to cover the distance. Completing such a journey by flying through a moving airspace makes this relatively simple task rather complex. On the one hand birds have to avoid wind drift or have to compensate for displacements to reach the expected goal. On the other hand flight costs make up a large proportion of energy expenditure during migration and, consequently, have a decisive impact on the refuelling requirements and the time needed for migration. As wind speeds are of the same order of magnitude as birds’ air speeds, flight costs can easily be doubled or, conversely, halved by wind effects. Many studies have investigated how birds should or actually do react to winds aloft, how they avoid additional costs or how they profit from the winds for their journeys. This review brings together numerous theoretical and empirical studies investigating the flight behaviour of migratory birds in relation to the wind. The results of these studies corroborate that birds select for favourable wind conditions both at departure and aloft to save energy and that for some long-distance migrants a tail-wind is an indispensable support to cover large barriers. Compensation of lateral wind drift seems to vary between age classes, depending on their orientation capacities, and probably between species or populations, due to the variety of winds they face en route. In addition, it is discussed how birds might measure winds aloft, and how flight behaviour with respect to wind shall be tested with field data.     

Optimal wind patterns for biological production in shelf ecosystems driven by coastal upwelling

Major upwelling systems around the world provide marine productivity and fishery yield out of proportion to their area. Upwelling winds have the counteracting effects that stronger winds upwell more nutrients to the surface for higher production, but they also transport that production off continental shelves where it may not be consumed by shelf-dwelling species. Because the patterns of wind fluctuations vary in these systems, we determined the conditions for maximal biological production using a simple conveyor belt model. The conditions are that: (1) the average cross-shelf velocity produced by the winds be the value that provides the maximum production with constant winds and (2) that the wind pattern be periodic with period equal to the cross-shelf transport time that results from maximizing production with constant winds. Examination of an example using winds in central California indicated wind patterns optimal for phytoplankton occurred more frequently than those for zooplankton.     

The experience of wind in early and medieval Chinese medicine

Two terms for wind prevail in Chinese medical texts and practice: qi and feng . Shigehisa Kuriyama noted that qi usually referred to regular and feng to unruly winds. This is not contested in this paper, but it considers these connotations of wind a characteristic of qi and feng in late imperial China in particular, and calls for an account that is more sensitive to historical change. Based on a study of twenty-five medical case histories in the 105th chapter of the Records of the Historian ( Shi ji , c. 86 BCE) and related texts, it suggests that in the third and second century BCE qi generally designated internal and feng external winds. Both alluded to the spirit world: qi -breaths tended to be associated with shen -spirits, feng -winds with gui -ghosts, although there were overlaps. Breathing techniques, with their emphasis on regularity, were developed for stabilizing the mind and appeasing the emotions, while feng -winds, associated with the fecundity-enhancing weather conditions of wind and rain, were a generative principle of procreation. By medieval times, the violent and unruly aspects of wind, and their destructive potential, started to be emphasized. Accordingly, feng -winds became the main aetiology of madness, which in early texts had been rising heat and hot bloodedness.     

BEHAVIOR OF RED-TAILED HAWKS IN A WIND TURBINE DEVELOPMENT

Abstract: Birds flying within windfarms can be killed when they collide with wind turbines. Raptors, especially red-tailed hawks (Buteo jamaicensis), are more susceptible to collisions than other birds, which may be attributable to their specific foraging and flight behavior. To more fully understand the problem, and to reduce raptor mortality, it is necessary to acquire more information on habitat use and flight behavior by raptors inhabiting windfarms. Between June 1999 and June 2000, we watched raptors for 346 hours in the Altamont Pass Wind Resource Area, the largest windfarm in North America. We recorded flight behavior in relation to characteristics of the topography such as slope aspect, elevation, and inclination and in relation to various weather variables including wind speed and wind direction. We found that red-tailed hawk behavior and their use of slope aspect differed according to wind speed. Hawks perched more often in weak winds than in strong. Red-tailed hawks were more likely to soar during low wind conditions and kite during strong wind, particularly on hillsides that faced into the wind as opposed to hillsides shielded from the wind. This is likely a result of their use of deflection updrafts for lift during flight. During our study, when winds were strong and from the south-southwest, kiting behavior occurred on south-southwestern facing slopes with inclines of greater than 20% and peak elevations greater than adjacent slopes. Accordingly, mitigation measures to decrease red-tailed hawk fatalities should be directed specifically to these areas and others fitting this general model. Wind farm managers can power down turbines at the top of these hazardous slopes when they pose the greatest danger—when winds are strong and facing perpendicularly to the slope.     

Wind Conditions and Pollen Deposition in a Mixed Deciduous Forest

Pollen deposition in a mixed deciduous forest in South Jutland, Denmark, was studied by means of pollen analyses (Andersen, 1970) and pollen collectors. In this connection it was important to know the wind conditions outside and inside the forest. Wind velocities and wind directions in the flowering seasons were measured at 2 stations in a 3-year period. High wind velocities prevail above the forest in spring and summer. At such wind velocities the difference in loss of large and small pollen grains by filtration in the tree tops is reduced. The winds inside the forest tend to turn into the direction of easiest flow. The velocities are about 20% of the outside wind before and 12–15% after the leafing. Single pollen grains released from the trees will be carried wide distances before deposition in the spring, and it is suggested that the tree pollen falls to the ground rather in aggregates or included in rain-drops.     

A RADAR STUDY OF THE AUTUMN MIGRATION OF WOOD PIGEONS COLUMBA PALUMBUS IN SOUTHERN SCANDINAVIA

The migration of Wood Pigeons in southern Scandinavia was studied from 21 September to 10 October 1971 and from 16 September to 15 November 1972 using radar stations supplemented with observations from an aircraft and a network of ground observers. By far the largest quantities of Wood Pigeons migrated after cold front passages with northwesterly to northeasterly tailwinds. Most birds departed on a few days, apparently as a consequence of strong preference for tailwind situations. With northwesterly winds a proportionately high migratory activity was recorded in the Kattegatt area. With northeasterly winds activity was higher in the Baltic area. This allowed the Wood Pigeons to make maximal use of the tailwind component, and their ground speed usually exceeded 80 km/h. The calculated mean air speed was 60 km/h. Their dependence on tailwind was particularly strong when the birds were engaging in long sea-crossings, such as across the Kattegatt. Different coastlines affected the geographical pattern of migration in different ways. Frequently Wood Pigeon flocks flew almost parallel to the coast but some distance off shore, until they finally departed. The deflective force of coastlines was greatest when the birds' ground speed was low, that is, under headwind conditions or in calm weather. Mean track directions measured over two areas in northern Skane, called Inland W and Inland E, situated about 60 km apart, differed by 11, those over the western area being directed more to the south than those over the eastern. No significant correlation with wind directions was found in these areas. Combining data from the whole land area, however, track directions were found to vary from day to day in significant correlation to the wind direction. Mean track directions over the Baltic agreed with those over Skane, but both differed significantly from those over the Kattegatt. Both over the Baltic and over the Kattegatt directions were significantly correlated with wind directions, and showed greater variation than track directions over land. Daily track differences over the Baltic resulted both from differences taking place over the land, and from real wind deflection (drift). Both over the land and over the sea heading directions were correlated with wind directions, suggesting compensatory efforts on the part of the birds. On three days extensive fog covered much of the study area. Wood Pigeons continued to migrate, but certain aberrations in their behaviour were noted. Over land migration was relatively heavier in the west with northwesterly winds and in the east with northeasterly winds. The correlation demonstrated between wind direction and the mean track direction was based upon the fact that populations with different inherent primary directions made up different proportions of the migrating cohorts under different wind conditions (pseudo-drift). The incomplete compensation for wind deflection over the sea is ascribed to the lack of visual orientation cues. The more accurate orientation possible over land suggests one reason for the birds' reluctance to flights across the open sea. When mean track directions of Wood Pigeons in different parts of southern Scandinavia were related to the migratory goals of these birds, it was found that they have to change their primary direction in the course of their journey from breeding to wintering areas.     

Wind as a negative factor in human comfort and its implications for planning

In all comfort formulae the wind appears as a positive factor with low velocities not exceeding 10 m/s. To date most researchers have ignored the negative effect which strong winds can have on man's comfort. Although they are not destructive, such winds blowing continuously for many hours of the day, over long periods of the year may have a negative effect on human comfort. Therefore, until a formula is developed which incorporates high wind velocities as a possible negative factor, the many comfort indices will not fulfill their role in objectively ascertaining man's comfort. Examples are cited from Israel. The most dominant region is the Jordan Rift Valley and its southern extension to the Gulf of Elat. This region is now undergoing intensive development and the strong winds are a factor which must be considered in regional planning, in settlement location and in their detailed planning.     

The bodily winds in ancient India revisited

This paper examines the historical development of the doctrine of the five bodily winds ( prā a s) in the early Sanskrit literature of Yoga and Āyurveda. Special attention is paid to the Indian's understanding of the connection between atmospheric wind and bodily breath and the role of wind in the human body. The paper traces the evolution of the Indian concept of breath. Originally, wind and breath were used metaphorically to indicate life. Breath was subsequently classified into five types by early ascetics who used breath-control in their practice of Yoga; and these same five breaths were eventually utilized by the Āyurvedic medical thinkers to establish a sophisticated doctrine of wind and its function in the body.     

Migration of the painted lady butterfly, Vanessa cardui, to north-eastern Spain is aided by African wind currents

1. Thousands of records of migratory butterfly species such as Vanessa cardui flying just above ground-level on fixed compass bearings have led to the common belief that these insects migrate within the so-called 'flight-boundary layer', where movements are relatively independent of the wind. 2. Given the selective advantages of windborne migration and the existence of a number of observations of flights of V. cardui from the upper levels of the atmosphere, we tested the hypothesis that migration from North Africa to southern Europe in this species is influenced by synoptic-scale wind currents. 3. Even with modern technology, it is extremely difficult to observe high-altitude flights directly, so we rely on an indirect approach that examines whether or not arrival peaks in north-eastern Spain are associated with winds blowing from Africa. 4. Arrivals of V. cardui were determined for the spring period (1 March-27 June, 1997-2006) at 79 sites in the Catalan Butterfly Monitoring Scheme. Wind patterns were described on the basis of synoptic-scale maps, transport models and back-trajectories calculated for each day of the spring period. 5. We found a strong association between migration and winds from North Africa, both for the whole data set (1997-2006; chi(2) = 4.7, P = 0.03) and for a restricted data set that excludes years in which the species was very scarce (chi(2) = 7.26, P = 0.007). 6. Episodes of massive northward migration within the species' flight-boundary layer also coincided with spells of winds from North Africa, suggesting a connection between low-altitude (observational) and high-altitude flights (inferred from wind patterns). 7. Finally, on the assumption that migration in V. cardui is windborne, a source-receptor transport model applied to spring abundance data in north-eastern Spain enables us to identify the most probable population source areas in North Africa.     

The importance of interactions between meteorological conditions when interpreting their effect on the dispersal of pollen from homogeneously distributed sources

The interaction between different meteorological conditions recorded in Badajoz (SW Spain) over a 13-year period has been studied. The results were used for analysis of the effect of these conditions on atmospheric concentrations of Plantago and Brassicaceae pollen grain. For both types of pollen there was a positive effect of NE winds and a negative effect of SW winds which could not be explained by the location of the sources, because these species are very abundant all around the sampling station. The two effects were interpreted on the basis of the action of these winds on temperatures and relative humidity, because these conditions physically and biologically directly determine the concentrations of these types of pollen. Wind from the west is associated with an increase of wind speed and a decline in calm periods; wind from the south is associated with increased rainfall and humidity; wind from the opposite directions is associated with a decrease in these meteorological conditions. These main associations can explain the variation in pollen concentration, although there are also variations in seasons and years. These types of pollen also behave differently, so wind speed reduces the concentration of pollen from Plantago but increases it from Brassicaceae. Beyond the immediate application of the analysis to this specific case, there is a clear interest in observing the interaction between meteorological factors to gain a broader perspective for interpretation of the results of aerobiological studies aimed at determining the effect of these factors on the release and transport of particles into the air.     

Wind and temperature controls on Alexandrium blooms (2000–2007) in Thau lagoon (Western Mediterranean)

Since 1998, blooms of Alexandrium catenella/tamarense in the lagoon of Thau developed regularly each autumn, reaching a maximum of several millions cells per liter in 2004. By contrast, spring blooms occurred only twice (in 2000 and 2007). During these periods, sea surface temperatures (SST) and the wind patterns appear to impact the bloom occurrences much more than the apparent limiting resources such as inorganic nutrients. The analysis of SST and wind from April to June and September to November (from 2000 to 2007) indicates first that there has to be an initial wind stress in order to resuspend the cysts buried in the sediment. Blooms then occur after a period of weak winds (<4 m s⁻¹) and of stable SST close to 20 °C (±2 °C). Those conditions appear to be most favorable for germination of Alexandrium cysts and its ensuing vegetative growth. This period of stability (a few days to a few weeks) allows the development of the inoculum from the cyst's germination, its cohesion because of reduced hydrodynamics, and development of vegetative cells that are sensitive to agitation. Strong winds during 1–2 day periods can interrupt the bloom dynamics by dispersing (advection due to southeasterly winds) and/or eliminating (turbulence due to northwesterly winds) the vegetative cells. In the spring, under the same conditions of optimal SST, strong wind episodes dominate and those, as well as biological factors very likely lead to a lower occurrence of blooms relative to the fall situation.     

Adverse wind conditions during northward Sahara crossings increase the in‐flight mortality of Black‐tailed Godwits

Long‐distance migratory flights are predicted to be associated with higher mortality rates when individuals encounter adverse weather conditions. However, directly connecting environmental conditions experienced in‐flight with the survival of migrants has proven difficult. We studied how the in‐flight mortality of 53 satellite‐tagged Black‐tailed Godwits (Limosa limosa limosa) during 132 crossings of the Sahara Desert, a major geographical barrier along their migration route between The Netherlands and sub‐Saharan Africa, is correlated with the experienced wind conditions and departure date during both southward and northward migration. We show that godwits experienced higher wind assistance during southward crossings, which seems to reflect local prevailing trade winds. Critically, we found that fatal northward crossings (15 deaths during 61 crossings) were associated with adverse wind conditions. Wind conditions during migration can thus directly influence vital rates. Changing wind conditions associated with global change may thus profoundly influence the costs of long‐distance migration in the future.     

Wind as an ecological factor

Wind has long been regarded as an important ecological factor in forests owing to the dramatic damage hurricanes can wreak. However, the long-term wind regime of a site also exerts a strong influence on the growth of trees. A relatively large amount is known about the acclimation of trees to wind but less about intra- or interspecific adaption to high winds. In fact, changes resulting from the effect of wind may have a greater effect on the ecology of forests than the more acute effects of destructive stroms. Improved understanding of the mechanical effects of wind is helping foresters manage their plantations and may help us to account better for local and geographical variations in forest ecology.     

Effects of host-odour plume altitude and changing wind velocity on upwind flight manoeuvres of a specialist braconid parasitoid

Abstract. Females of the specialist parasitoid, Microplitis croceipes (Cresson) (Hymenoptera: Braconidae), were released in a wind tunnel into host-odour plumes dispersed by winds of three velocities and winds whose speed was changed while the wasps were engaged in upwind flight. In steady winds of 61, 122 and 183 cms-^-1, wasps maintained similar 'preferred' ground speeds by adjusting their airspeed, while turning to a lesser degree as wind velocity increased. In winds of changing velocity (either increasing or decreasing within a 60–100 cm s-¹ range), wasps lowered their rate of upwind progress, leading to more tortuous tracks. During changing wind speeds longitudinal image flow decreased. Wasps flying in host-odour plumes 10 cm and 20 cm above the flight tunnel floor in a 122 cm s-¹ wind had similar ground speeds; thus their rate of ventral visual image flow varied two-fold. M.croceipes may 'aim' upwind by comparing how changes in the course angle vary with the direction of visual image flow. During changing wind velocities the relationship between changes in visual and flight muscle generated torque is ambiguous. Under these conditions most wasps cast, a manoeuvre characterized by wide lateral excursions across the wind without upwind progress. Once wind speed stabilizes, flight straightens out and upwind flight resumes.     

The effect of wind on shore gastropods

A preliminary investigation into the effect of wind on shore gastropods has been undertaken. Moderate winds displace some Monodonta lineata (da Costa) from boulders on the shore and some individuals detach within six hours in weaker winds in the laboratory (5–10 km/h, 10°C, 94% humidity). Sheltered aspects of the rock are used to minimize the effects of the wind on shores, and maintenance movements on the shore are extensive.  

Summary:

In calm conditions and in light winds Monodonta lineata is more widely dispersed about the rocks than in moderate winds when the animals are either sheltering in cracks or displaced.
Providing the rock surface is damp then animals continue to move about during emersion in light winds. On a small boulder beach animals moved as much as 4 m upshore during one tidal cycle. Only slight reorientation movements were recorded during moderate winds.
Animals withstand a windspeed of 4 km/h for six hours in a wind tunnel in a humidity of 94% at 10°C, but are displaced within an hour by 10 km/h winds in similar conditions.     

Flight dynamics of Cory’s shearwater foraging in a coastal environment

Flight dynamics theories are influenced by two major topics: how birds adapt their flight to cope with heterogeneous habitats, and whether birds plan to use the wind field or simply experience it. The aim of this study was to understand the flight dynamics of free-flying Cory’s shearwaters in relation to the wind characteristics on the coastal upwelling region of continental Portugal. We deployed recently miniaturised devices—global positioning system loggers to collect precise and detailed information on birds’ positions and motions. Prevalent winds were blowing from the north-east and adults used those winds by adjusting their flight directions mainly towards north-west and south-west, flying with cross and tail winds, respectively, and avoiding head winds. This is confirmation that Cory’s shearwaters use a shear soaring flying strategy while exploiting the environment for food: adults foraged mainly with cross winds and their ground speed was not constant during all foraging trips as it changed dynamically as a result of the ocean surface shear winds. During travelling phases, ground speed was strongly influenced by the position of the bird with regard to the wind direction, as ground speed increased significantly with increasing tail wind component (TWC) values. Adults appear to choose foraging directions to exploit ambient wind, in order to improve shear soaring efficiency (cross winding) and exploit diurnal changes in tail wind strength to maximise commuting efficiency. We report, for the first time, precise ground speed values (GPS-derived data) and computed actual flight speed values (using TWC analysis) for Cory’s shearwater.     

Avoidance response, house response, and wind responses of the sporangiophore of Phycomyces

Avoidance response: An object placed 1 mm from the growing zone of a Phycomyces sporangiophore elicits a tropic response away from the object. The dependence of this response on the size of the object and its distance from the specimen is described, as well as measurements which exclude electric fields, electromagnetic radiation, temperature, and humidity as avoidance-mediating signals. This response is independent of the composition and surface properties of the object and of ambient light. House Response: A house of 0.5- to 10-cm diameter put over a sporangiophore elicits a transient growth response. Avoidance responses inside closed houses are slightly smaller than those in the open. Wind responses: A transverse wind elicits a tropic response into the wind, increasing with wind speed. A longitudinal wind, up or down, elicits a transient negative growth response to a step-up in wind speed, and vice versa. It is proposed that all of the effects listed involve wind sensing. This proposal is supported by measurements of aerodynamic effects of barriers and houses on random winds. The wind sensing is discussed in terms of the hypothesis that a gas is emitted by the growing zone (not water or any normal constituent of air), the concentration of which is modified by the winds and monitored by a chemical sensor. This model puts severe constraints on the physical properties of the gas.     

Good Days,Bad Days: Wind as a Driver of Foraging Success in a Flightless Seabird,the Southern Rockhopper Penguin

Due to their restricted foraging range, flightless seabirds are ideal models to study the short-term variability in foraging success in response to environmentally driven food availability. Wind can be a driver of upwelling and food abundance in marine ecosystems such as the Southern Ocean, where wind regime changes due to global warming may have important ecological consequences. Southern rockhopper penguins (Eudyptes chrysocome) have undergone a dramatic population decline in the past decades, potentially due to changing environmental conditions. We used a weighbridge system to record daily foraging mass gain (the difference in mean mass of adults leaving the colony in the morning and returning to the colony in the evening) of adult penguins during the chick rearing in two breeding seasons. We related the day-to-day variability in foraging mass gain to ocean wind conditions (wind direction and wind speed) and tested for a relationship between wind speed and sea surface temperature anomaly (SSTA). Foraging mass gain was highly variable among days, but did not differ between breeding seasons, chick rearing stages (guard and crèche) and sexes. It was strongly correlated between males and females, indicating synchronous changes among days. There was a significant interaction of wind direction and wind speed on daily foraging mass gain. Foraging mass gain was highest under moderate to strong winds from westerly directions and under weak winds from easterly directions, while decreasing under stronger easterly winds and storm conditions. Ocean wind speed showed a negative correlation with daily SSTA, suggesting that winds particularly from westerly directions might enhance upwelling and consequently the prey availability in the penguins'' foraging areas. Our data emphasize the importance of small-scale, wind-induced patterns in prey availability on foraging success, a widely neglected aspect in seabird foraging studies, which might become more important with increasing changes in climatic variability.