BIRD MIGRATION OVER THE MALTESE ISLANDS

The present paper is based on data obtained during several years' observations and three recent surveys. Little has previously been published on migration through the Maltese Islands. The geographical, vegetational and climatic factors of the islands are discussed in so far as they affect the migrants. Visible migration is seen with anticyclonic weather and westerly winds. Birds are found grounded after night migration in cyclonic weather with southwesterly or easterly winds, much larger numbers and variety being seen with the latter. When there is a deterioration in the weather during the night, a large influx of birds is seen on the following morning, and in addition large flocks of migrating Turtle Doves are seen. Several trans-Saharan migrants may pass in smaller numbers during autumn than spring, but the difference may be more apparent than real because in early autumn the birds may depart after only a very short stay, and a few conspicuous species are absent or scarce. By contrast several species which winter north of the Sahara pass only or in much larger numbers during autumn, and these more than make up for those which are absent or rare. There is no evidence from bird ringing that in spring Malta regularly gets birds from Tunisia, at any rate from that part covered by the ringing stations (Cap Bon, Enfidaville, Gabes). The migrants which pass through Malta probably originate from an area in North Africa around Tripoli and some way westwards of it. During autumn the bulk of recoveries is from eastern European countries with a smaller percentage from northern and central Europe. Several species or groups of species are dealt with individually. In the discussion stress is laid on the very close relationship between migration and weather, especially the wind component. The comparatively small numbers of birds seen at Malta probably form part of a larger movement travelling on a broad front. It is argued that the large “falls” of migrants in bad weather result from drift acting on a mass passing mainly to one side or the other of the islands. Since much larger densities are seen with easterly than with westerly winds, it follows, if the hypothesis of drift be correct, that the numbers of birds travelling to the east of Malta are larger than those to the west of it. Moreover, since day migrants are seen with westerly winds and the bulk of night migrants with easterly ones, it is inferred that day migrants normally pass to the west, and the bulk of night migrants to the east, of the Maltese Islands. A parallel is drawn between the autumn migration and the performance of racing pigeons which are flown from the north and NE at this season.     

Altitude choice by night migrants in a desert area predicted by meteorological factors

The height distribution of nocturnal migrants in southern Israel was determined by con-ically scanning the sky with the pencil-beam of an X-band radar at different elevation angles. Altitudinal profiles of meteorological parameters were derived from radio sondes launched at midnight and from pilot balloons launched every 4 h. A model to predict the height distribution of birds by means of meteorological variables was developed by assuming that the observed proportions of birds within a height zone, compared with the neighbouring height zones, reflect the degree of the birds' preference for that height zone. Only one among the variables included in the multiple regression analysis proved to have a significant influence on the height distribution of migrants: the difference of tailwind speed between height zones. Simulations with 1000 birds choosing altitudes by means of the night's altitudinal profile of tailwind speed closely traced the observed distributions. The fact that all the other meteorological factors which were previously suggested to have an influence on the flight range in trans-desert migration were not selected as relevant factors is discussed. The following basic information on nocturnal bird migration in the Negev is provided as a background for the statistical analysis: Directions of migration are within very narrow limits. During the first hour after take-off, 60% of autumn migrants and 75% of spring migrants are climbing, with vertical speeds of 0.1–2 m per s and 0.1–4 m per s, respectively. During the rest of the night, climbing and descending birds are in nearly equal proportions. Thus, there is a high potential of sampling atmospheric conditions at different altitudes. Height distributions in spring and autumn show the influence of the trade wind situation, autumn migrants making use of the northerly winds at low levels in spite of high temperatures, while spring migrants tend to reach the southwesterly winds at higher levels.     

MIGRATION ACROSS THE SOUTHERN NORTH SEA STUDIED BY RADAR PART 5. MOVEMENTS IN AUGUST, WINTER AND SPRING, AND CONCLUSION

Arrivals of gulls S.W. seem almost confined to late July.
In August, the main movements are W. by day and night of Lapwings and S.S.E. by night of warblers. Sand Martins migrated at dawn directly from a large roost at 34 m.p.h.
In midwinter, migration occurred in at least one direction almost every morning and night. "Hard-weather movements" west or south are initiated primarily by easterly or northerly winds respectively, and not by cold. The corresponding return movements, which sometimes follow immediately, arc initiated primarily by westerly or southerly winds respectively, but warmth has an influence in February. In midwinter, various species are evidently ready to travel in either the autumn or the spring direction, and wind-direction is the paramount factor determining which occurs.
The big eastward departures in March and April occur mainly with westerly winds and in warm weather, both factors being important, but proportionately more departures occur against strong head or cross-winds than in autumn. The general weather situation has no direct influence.
Starlings migrated directly from their roosts on a few mornings each spring, normally at sunrise but on one occasion some did so much earlier.
In late April and May the chief movements are N.N.W. arrivals and onward passages of British summer visitors, N.E. departures of shore-birds, and N.N.E. departures of small passerines, presumably en route between Iberia and Norway. These movements occur mainly with southerly winds, but sometimes against the wind.
"Reversed movements" W. or S.S.E. are much more frequent in spring than has previously been supposed. They occur exclusively with easterly or northerly winds respectively (like the midwinter movements).
The frequency of each migratory movement throughout the year is summarized in Table 6.
The main findings of the 5-year study are reviewed under four heads in the Conclusion.     

10. PROCEEDINGS OF THE SEVENTEENTH ANNUAL GENERAL MEETING OF THE S.A. ORNITHOLOGICAL SOCIETY HELD IN THE COMMITTEE ROOM OF THE PUBLIC LIBRARY. JOHANNESBURG,AT 3 P.M., SATURDAY, 8TH MARCH. 1947

Bruderer, B. 1994. Nocturnal bud migration in the Negev (Israel) a tracking radar study. Ostrich 65: 204–212.

The present publication summarizes the methodological possibilities of tracking radar and describes some features of nocturnal migration at two sites in the Negev, which include anwers to basic questions of bird migration. The directions of spring and autumn migration were practically opposite; only the headings in spring indicated some more compensation for stronger westerly winds. The volume of nocturnal spring migration was only about 65% of autumn migration, which may be an indication of mortality outside tie breeding area. Highest densities of migration at the two radar sites in the Negev Highlands (450 m above sea level) and in the Arava Valley (150 m below sea level) indicated flightlevels adjusted to atmospheric conditions aloft, and not to round level. Due to the trade-wind system, the birds heading southward in autumn flew mainly below flew mainly above 1500 m above sea level, while in spring they tended to make use of the anti-trades at higher altitudes. The decisive factor for altitude choice was the speed of tailwind in spring and autumn; other factors, such as temperature, humidity and pressure had no significant influence on the altitude distributions. With respect to the question of non-stop or intermittent flight across large desert areas, the data show that between the eastern deserts of Egypt and the Sinai/Negev complex the nocturnal migrants maintained their schedule of nocturnal flight and diurnal rest. A few exceptions of nocturnal migrants continuing migration at high altitudes into the day were identified mainly as heron- and gull-type birds. The proportion of waders and waterfowl identified by wing-beat pattern in nocturnal migration is nearly the same at both sites, indicating broad-front migration across the desert. The numbers of birds with continuous wingbeats is, however, so large compared to available estimates of waders and waterfowl wintering in Africa that careful reconsideration of the underlying assumptions in the radar and field estimates is necessary.     

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.     

RAPTOR MIGRATION ACROSS THE STRAITS OF GIBRALTAR

The visible migration of birds of prey at Gibraltar is analysed from records kept throughout the spring passages of 1967–70 and the autumn passages of 1967–69. In early spring most visible passage is noted in the afternoons, whereas radar observations by Houghton (1970) indicate passage in the mornings. Later in the year an additional burst of visible passage sometimes occurs in the early morning, but it is concluded that most morning movements take place above visible range. Visible migration is recorded on most days of westerly wind during the migration seasons at Gibraltar. Passage is rarely seen when the winds are easterly. It is argued that under the latter conditions a strong upcurrent of air (standing wave) is formed over Gibraltar, and that this carries nearly all migrants above visible range.
Observations of visible passage elsewhere in the Straits suggest that, in spring, raptors of all species cross on a broad front from Tangier to Ceuta, except Honey Buzzards, which probably cross chiefly near Ceuta. In autumn, all species from northern Europe cross chiefly between Tarifa and to the east of Gibraltar, while birds from western Iberia probably cross mainly near Tarifa.
The periods of passage of the common migrant species are summarised.
On the basis of visual observations and published radar results, it is argued that raptors can compensate for lateral drift by the wind and so fly on chosen courses; but that in very strong cross-winds, e.g. the easterly Levanters, they may have to let themselves be drifted off-course.     

Seasonal variation in migration strategies used to cross ecological barriers in a nearctic migrant wintering in Africa

Ecological barriers such as oceans, mountain ranges or glaciers can have a substantial influence on the evolution of animal migration. Along the migration flyway connecting breeding sites in the North American Arctic and wintering grounds in Europe or Africa, nearctic species are confronted with significant barriers such as the Atlantic Ocean and the Greenland icecap. Using geolocation devices, we identified wintering areas used by ringed plovers nesting in the Canadian High‐Arctic and investigated migration strategies used by these nearctic migrants along the transatlantic route. The main wintering area of the ringed plovers (n = 20) was located in western Africa. We found contrasting seasonal migration patterns, with ringed plovers minimizing continuous flight distances over the ocean in spring by making a detour to stop in Iceland. In autumn, however, most individuals crossed the ocean in one direct flight from southern Greenland to western Europe, as far as southern Spain. This likely resulted from prevailing anti‐clockwise winds associated with the Icelandic low‐pressure system. Moreover, the plovers we tracked largely circumvented the Greenland icecap in autumn, but in spring, some plovers apparently crossed the icecap above the 65°N. Our study highlighted the importance of Iceland as a stepping‐stone during the spring migration and showed that small nearctic migrants can perform non‐stop transatlantic flights from Greenland to southern Europe.     

Towards a new understanding of migration timing: slower spring than autumn migration in geese reflects different decision rules for stopover use and departure

According to migration theory and several empirical studies, long‐distance migrants are more time‐limited during spring migration and should therefore migrate faster in spring than in autumn. Competition for the best breeding sites is supposed to be the main driver, but timing of migration is often also influenced by environmental factors such as food availability and wind conditions. Using GPS tags, we tracked 65 greater white‐fronted geese Anser albifrons migrating between western Europe and the Russian Arctic during spring and autumn migration over six different years. Contrary to theory, our birds took considerably longer for spring migration (83 days) than autumn migration (42 days). This difference in duration was mainly determined by time spent at stopovers. Timing and space use during migration suggest that the birds were using different strategies in the two seasons: In spring they spread out in a wide front to acquire extra energy stores in many successive stopover sites (to fuel capital breeding), which is in accordance with previous results that white‐fronted geese follow the green wave of spring growth. In autumn they filled up their stores close to the breeding grounds and waited for supportive wind conditions to quickly move to their wintering grounds. Selection for supportive winds was stronger in autumn, when general wind conditions were less favourable than in spring, leading to similar flight speeds in the two seasons. In combination with less stopover time in autumn this led to faster autumn than spring migration. White‐fronted geese thus differ from theory that spring migration is faster than autumn migration. We expect our findings of different decision rules between the two migratory seasons to apply more generally, in particular in large birds in which capital breeding is common, and in birds that meet other environmental conditions along their migration route in autumn than in spring.     

THE VISIBLE MIGRATION OF RAPTORS OVER THE MALTESE ISLANDS

Whilst the large migrations of raptors at the Bosphorus and at the Straits of Gibraltar have been documented in some detail, the movements which take place across the Mediterranean itself have been neglected. This paper reports observations of the visible migration of raptors over the Maltese Islands during 1969–73. The largest numbers of raptors were recorded both in spring and autumn during contrary winds or overcast conditions. Normally very few were seen before the early afternoon at either season, in spite of the much shorter minimum sea-crossing in autumn. Large passages occurred in winds with easterly or westerly components. It is therefore concluded that eastward drift does not greatly affect the numbers seen in Malta, as had been suggested by De Lucca (1969); rather that most influxes occurred in the late afternoon during unfavourable meteorological conditions. At other times most migration was probably above the visible range. The number of raptors observed on passage in the Maltese Islands was small compared with movements at the Bosphorus or at Gibraltar. Nevertheless, the numbers of the narrow-winged species (i.e., Ospreys, harriers and falcons) compare favourably with records at the narrow crossings. The only large soaring species commonly seen in Malta was the Honey Buzzard. Evidence is presented which suggests that the volume of Honey Buzzard migration across the central Mediterranean may be much larger than was formerly realized.     

Loop migration in adult marsh harriers Circus aeruginosus,as revealed by satellite telemetry

Loop migration among birds is characterized by the spring route lying consistently west or east of the autumn route. The existence of loops has been explained by general wind conditions or seasonal differences in habitat distribution. Loop migration has predominantly been studied at the population level, for example by analysing ring recoveries. Here we study loop migration of individual marsh harriers Circus aeruginosus tracked by satellite telemetry. We show that despite a generally narrow migration corridor the harriers travelled in a distinct clockwise loop through Africa and southern Europe, following more westerly routes in spring than in autumn. We used the Normalized Difference Vegetation Index (NDVI) to identify potential feeding habitat in Africa. Suitable habitat seemed always more abundant along the western route, both in spring and autumn, and no important stopover site was found along the eastern route. Observed routes did thus not coincide with seasonal variation in habitat availability. However, favourable habitat might be more important during spring migration, when the crossing of the Sahara seems more challenging, and thus habitat availability might play an indirect role in the harriers’ route choice. Grid‐based wind data were used to reconstruct general wind patterns, and in qualitative agreement with the observed loop marsh harriers predominantly encountered westerly winds in Europe and easterly winds in Africa, both in autumn and in spring. By correlating tail‐ and crosswinds with forward and perpendicular movement rates, respectively, we show that marsh harriers are partially drifted by wind. Thus, we tentatively conclude that wind rather than habitat seems to have an overriding effect on the shape of the migration routes of marsh harriers. General wind conditions seem to play an important role also in the evolution of narrow migratory loops as demonstrated for individual marsh harriers.     

VISIBLE MIGRATION IN THE BRITISH ISLES: A REVIEW

This paper aims to bring together the chief observations that have been recorded so far on visible migration in the British Isles.
The autumn movements that have been seen on the various coasts, and inland, are briefly described, and the few spring observations are summarized.
Maps show the directions which migrating Corvidae, Starlings, Chaffinches and Skylarks have been seen to take in autumn, and there is some discussion of the autumn movements of these four species. The observed movements of some of the other chief passerines, and of the Wood-pigeon, Stock-dove and Lapwing, are more briefly mentioned.
Some of the differences in the migratory behaviour of different species are mentioned, and some of the most obvious gaps in knowledge of visible migration in the British Isles are pointed out.     

SPRING MIGRATION OVER PUERTO RICO AND THE WESTERN ATLANTIC, A RADAR STUDY

Migration over Puerto Rico was recorded by time-lapse filming of the display of a long-range surveillance radar on 40 days and 37 nights in the period 2 March-29 May 1971. Moderate density movements occurred every night; low density movements occurred on most days. Many birds, primarily passerines, took off from Puerto Rico each evening at 20–45 minutes after sunset.
Almost all birds flew to the west, NW or north. Birds were seen approaching from the direction of the Windward Islands and Venezuela, over Puerto Rico, and departing towards the Bahamas and eastern coast of the U.S. Uni- and multivariate analyses showed that the number of birds departing W-N each evening was positively correlated with following winds.
There is less night-to-night variation in the amount of migration at Puerto Rico than in eastern North America. However, this is apparently the result of less variable weather in the tropics, not the result of any lesser degree of meteorological selectivity by the migrants.
The tracks of the birds were correlated with wind direction. Birds moved WNW-NW with NE side winds but NW-NNW with SE following winds. The tracks were rarely exactly downwind. The variance amongst the directions of individual birds at any given time was usually small and not correlated with cloud cover or magnetic disturbances. The estimated headings of the birds varied from day to day in a pattern suggesting adjustment of headings to compensate at least partially for lateral wind drift.
In autumn many birds approach Puerto Rico from the north or even east of north; in spring few birds moved in the opposite directions. This difference in routes takes advantage of prevailing wind patterns.     

Radar observations of passerine migration over Frankfurt and Hannover, Germany

Summary The direction of the autumn and spring migration of short- and long-distance migrants over Frankfurt and spring migration of short-distance migrants over Hannover were studied by radar. For long-distance migrants, a comparison with results obtained from the Swiss Lowland revealed no difference in the direction of autumn migration but a 35° difference in the direction of spring migration. In Frankfurt the migration was more northerly. The difference in the migratory direction of short-distance migrants between central Germany and the Swiss Lowland ranged from 10° to 15° in spring and to 9° in autumn. The direction of spring migration can be understood as a simple 180° reversal of autumn migration in short-distance migrants, but not in long-distance migrants. The difference in the direction of the migratory axis (about 30°) among long-distance migrants between autumn and spring indicates that such birds follow different routes during their two seasonal, migratory journeys. The short- and long-distance migrants flew a similar direction in autumn. In spring, the short-distance migrants flew considerably more easterly compared to long-distance migrants. Wind influences, because of the seasonality of cyclonic weather systems, was much more likely to affect the migration of short-distance migrants in both autumn and spring. The effect of strong crosswinds on the direction of spring migration was examined.

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Zusammenfassung Mittlere Zugrichtung und Windeinfluß auf Herbst- und Frühjahrszug von Kurz- und Langstreckenziehern wurden über Frankfurt und über dem Raum Hannover (nur Frühjahrszug) mit Hilfe von Radarbeobachtungen untersucht. Der Vergleich mit Ergebnissen vom Alpenrand ergab übereinstimmende Mittelrichtungen für den Herbstzug der Langstrecken-zieher, aber eine deutliche Differenz für dem Frühjahrszug (35°). In Frankfurt war der Zug stärker nach N gerichtet. Die Unterschiede bei den Kurzstreckenziehern betrugen im Frühjahr 10° bzw. 15° und im Herbst 9°. Der Frühjahrszug kann als Richtungsumkehrung des Herbstzuges bei den Kurzstreckenziehern, aber nicht bei den Langstreckenziehern interpretiert werden. Die Differenz zwischen den Zugachsen von Herbst- und Frühjahrszug betrug 30°. Sie wird als Indiz für unterschiedliche Zugrouten auf dem Herbst- und Frühjahrszug gewertet. Kurz- und Langstreckenzieher hielten auf dem Herbstzug ähnliche Zugrichtungen ein. Im Frühjahr zogen die Kurzstreckenzieher wesentlich stärker nach E als die Langstreckenzieher. Der Windeinfluß machte sich wegen der Saisonalität der Zyklonentätigkeit sowohl beim Frühjahrs- als auch beim Herbstzug der Kurzstreckenzieher stärker bemerkbar als bei den Langstreckenzieher. Der Einfluß der starken Seitenwinde auf die Richtungen des Frühjahrszuges wurde untersucht.

     

THE NIGHTLY INITIATION OF PASSERINE MIGRATION IN SPRING: A DIRECT VISUAL STUDY

The nightly initiation of migration of passerine birds was studied during a spring season in coastal Louisiana. A horizontally-directed portable ceilometer placed on a tower illuminated birds as they took off from or landed in the trees. Daily censuses were conducted to supplement nocturnal observations. Local weather conditions were continuously monitored at the site of the study. Appreciable numbers of migrants landed in the woods on the coast almost every day, the first birds usually appearing between 10.30 and 11.00 hrs, and the last about 16.00 hrs. On two occasions birds were seen landing after dark. The migrants usually became quiet by about 18.00 hrs and the first bird was usually seen leaving the trees just over an hour later. The exodus usually peaked between 19.10 and 19.15 hrs, 40 to 45 minutes after sunset. The time of initiation of nocturnal migration was not significantly affected by immediate weather factors. The duration of the exodus varied widely, and was related to the number of individual birds in the census area. On some occasions grounded migrants stayed overnight, but only when there had been an active cold front over the Gulf. No local weather conditions examined were found to be directly inhibitory to nocturnal migration. Birds departed singly and without preliminary activity. Wind direction influenced the initial orientation of the migrants. With southerly winds, 57% of the birds seen flying across the beam initially headed toward the Gulf, while with northerly winds only 19% initially flew in this direction.     

Life history events of the Eurasian sparrowhawk Accipiter nisus in a changing climate

Current climate change has been found to advance spring arrival and breeding dates of birds, but the effects on autumn migration and possible responses in the distribution of wintering individuals are poorly known. To thoroughly understand the consequences of climate change for animal life histories and populations, exploration of whole annual cycles are needed. We studied timing of migration (years 1979–2007), breeding phenology (1979–2007) and breeding success (1973–2007) of Eurasian sparrowhawks Accipiter nisus in Finland. We also investigated whether the migration distance of Finnish sparrowhawks has changed since the 1960s, using ringing recovery records. Since the late 1970s Finnish sparrowhawks have advanced their spring arrival, breeding and autumn departure considerably, but the migration distance has not changed. Early migrants, who are the ones with the highest reproductive success, show the strongest advance in the timing of spring migration. In autumn, advanced departure concerns young sparrowhawks. Late autumn migrants, who are mainly adults, have not advanced their migration significantly. The sparrowhawk is the most common bird of prey and the main predator of most passerines in Finland. Therefore, changes in sparrowhawk migration phenology may affect the migration behaviour of many prey species. The breeding success of sparrowhawks has increased significantly over the study period. This is however more likely caused by other factors than climate change, such as reduced exposure to organochlorine pollutants.     

Variable shifts in spring and autumn migration phenology in North American songbirds associated with climate change

Monitoring studies find that the timing of spring bird migration has advanced in recent decades, especially in Europe. Results for autumn migration have been mixed. Using data from Powdermill Nature Reserve, a banding station in western Pennsylvania, USA, we report an analysis of migratory timing in 78 songbird species from 1961 to 2006. Spring migration became significantly earlier over the 46-year period, and autumn migration showed no overall change. There was much variation among species in phenological change, especially in autumn. Change in timing was unrelated to summer range (local vs. northern breeders) or the number of broods per year, but autumn migration became earlier in neotropical migrants and later in short-distance migrants. The migratory period for many species lengthened because late phases of migration remained unchanged or grew later as early phases became earlier. There was a negative correlation between spring and autumn in long-term change, and this caused dramatic adjustments in the amount of time between migrations: the intermigratory periods of 10 species increased or decreased by > 15 days. Year-to-year changes in timing were correlated with local temperature (detrended) and, in autumn, with a regional climate index (detrended North Atlantic Oscillation). These results illustrate a complex and dynamic annual cycle in songbirds, with responses to climate change differing among species and migration seasons.     

Nocturnal passerine migration without tailwind assistance

Nocturnal passerine migrants could substantially reduce the amount of energy spent per distance covered if they fly with tailwind assistance and thus achieve ground speeds that exceed their airspeeds (the birds’ speed in relation to the surrounding air). We analysed tracking radar data from two study sites in southern and northern Scandinavia and show that nocturnally migrating passerines, during both spring and autumn migration, regularly travelled without tailwind assistance. Average ground and airspeeds of the birds were strikingly similar for all seasonal and site‐specific samples, demonstrating that winds had little overall influence on the birds’ resulting travel speeds. Distributions of wind effects, measured as (1) the difference between ground and airspeed and (2) the tail/headwind component along the birds’ direction of travel, showed peaks close to a zero wind effect, indicating that the migratory flights often occurred irrespective of wind direction. An assessment of prevailing wind speeds at the birds’ mean altitude indicated a preference for lower wind speeds, with flights often taking place in moderate winds of 3–10 m/s. The limited frequency of wind‐assisted flights among the nocturnal passerine migrants studied is surprising and in clear contrast to the strong selectivity of tailwinds exhibited by some other bird groups. Relatively high costs of waiting for favourable winds, rather low probabilities of occurrence of tailwind conditions and a need to use a large proportion of nights for flying are probably among the factors that explain the lack of a distinct preference for wind‐assisted flights among nocturnal passerine migrants.     

MIGRATION IN IRAQ

Migration in Iraq is discussed on the basis of three years' experience supplemented by data from other unpublished sources and the literature.
The migration of certain passerine and near-passerine species is considered, particularly as regards comparative numbers seen in spring and autumn, and the question of their passages between breeding quarters in the Palaearctic and winter quarters in Africa, in relation to weather, geography and ecology of the Middle East. Of about 50 species discussed, half are clearly more abundant in spring, and most of the rest probably are; thus supporting the idea that such species in autumn may make longer unbroken flights than in spring. For a number of these species the nearness of the breeding quarters to Baghdad is stressed.
Exceptions are Streptopelia turtur , Alaudidae, hirundines and perhaps Motacilla flava , which are prominent, and even the only, visible daylight migrants among such small birds. These cross Iraq from east to west in autumn in vast numbers and are thought to migrate round the Fertile Crescent past Damascus, rather than fly direct towards Africa. Comparisons are made with the Mediterranean region and the rest of the Arabian peninsula, and some comments are added on the matter of broad-front and narrow-front migrations.
In an appendix the most important aspects of migration of large non-passerine birds in Iraq are discussed.     

The large-scale detoured migration route and the shifting pattern of migration in Oriental honey-buzzards breeding in Japan

We describe the detoured migration route of the Oriental honey-buzzard Pernis ptilorhyncus , showing differences between autumn and spring migration, using data from 10 adult individuals marked with satellite transmitters. In autumn, the migration routes were very similar from Japan to the south end of the Malay Peninsula. The wintering sites were distributed within the Philippines, Borneo and the Malay Archipelago. During autumn, migration of the birds had few long-term stopover sites, instead, sometimes decidedly slowing their migration rate while proceeding in a consistent direction. During spring migration, the honey-buzzards penetrated into southern China, moving north to the base of the Korean Peninsula. The birds then went south through the Korean Peninsula to reach Japan. Before travelling to China, all spring migrants stopped for several weeks in south-east Asia. The slow rate of travel in the autumn suggests that migrants were foraging and replenishing their energy reserves. Instead of a migration strategy that uses only a few long-term stopover sites, honey-buzzards may adopt a strategy based on a number of short-term stay sites.