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.     

ON THE BIRDS OF MOROCCO

Fifteen months were spent in Morocco. A few ecological aspects of the country are described, together with their influence on the dispersal of birds in winter. Some winter visitors are listed and discussed, several species were much commoner in the winter of 1962/63 than in 1963/64, in some cases presumably as a result of the cold weather in Europe, although in others not obviously so. Cold-weather movements of gulls, Lapwings and Cranes were observed. Individuals of species that are normally trans-Saharan migrants winter in Morocco in small numbers. Spring migration in southeast Morocco is excluded from discussion, but autumn migration in western Morocco is summarized and compared with existing data. The systematic list is devoted largely to winter visitors and passage migrants, but resident species are listed when new localities, breeding data or field notes warrant their inclusion. Six species not hitherto recorded in Morocco, were seen.     

NOTES ON BIRDS IN THE GAMBIA

Recent observations in The Gambia have shown that the status of many species has changed in the last forty or fifty years and have provided data on the local breeding seasons for a number of birds. Several species have been found for the first time in this part of West Africa. The various birds concerned are given in a systematic list, together with notes on all the Palaearctic migrants so far recorded from The Gambia. Organized research is recommended on several lines: on the sequence of food sources, especially through the long and severe dry season, when Palaearctic birds are added to resident and when some African species breed. The bird ecology of the mangroves remains to be worked out, and also the relative importance to birds of cleared ground and untouched "bush" at all seasons.     

THE BIRDS OF THE SANTA ELENA PENINSULA, S.W. ECUADOR

A systematic account is given of the birds of the Santa Elena peninsula in S.W. Ecuador, based on three years observations (1954-7) and a collection of 425 skins. The status of individual species is decribed and the different elements of the avifauna discussed, viz. the Equatorial arid fauna, Nearctic migrants, sea-birds, and other wide-ranging forms and waterfowl. Seasonal movements of species of the Equatorial arid fauna are indicated in greater detail than has been previously known. The effect of a recently constructed reservoir on the bird life is mentioned. More detailed knowledge of the occurrence of species from the cold Humboldt current is provided. Several additions to the Ecuadorian list are given, and some birds recorded which were hitherto unknown or very rarely recorded from the west coast of S. America. Various matters of taxonomy affecting races of birds along the whole west coast of S. America are discussed.     

NOTES ON SOME MARSH BIRDS OF CAPE SAN ANTONIO,ARGENTINA*

During an 11-month study of the Black-headed Duck in eastern Argentina, observations were made on the marsh birds of Cape San Antonio, Province of Buenos Aires. These observations supplement the distributional and life history obtained by Gibson (1879–1920), Wetmore (1926) and others. The deep, fresh-water marshes characteristically are dominated by one of three plants: tules, cutgrass or cat-tails. There were surprisingly few marshes with mixtures of these plants and few marshes which showed a gradual transition from marsh to uplands. Marsh birds showed considerable adaptation in chronology of nesting and nest-site selection for the seasonal water cycle of wet springs and dry periods in the late summer and fall. Some marsh birds were involved in nesting over a longer period than is usual in Northern Hemisphere marshes. As seems characteristic of all marsh birds, cover-water edges were usual sites for nests. There were only a few species with restricted nest-site selection, and competition between closely related species was noted only among the three species of coots. A list of the marsh birds of the area is given, and comments are presented on the ecology and behaviour of selected species.     

Biometry and phenology of two sibling Phylloscopus warblers on their circum-Mediterranean migrations

The Mediterranean Sea is known as an ecological barrier for numerous migratory birds flying from European breeding grounds to African wintering sites. Birds generally avoid migration over open sea and fly over land. In the Mediterranean Basin, few land bridges or bottlenecks for migratory birds exist. The narrowest are at the western and eastern extremes: the Strait of Gibraltar and Israel. Comparative studies between these locations are extremely rare to date. Therefore, in order to elucidate the differences between the two flyways, we compared data collected simultaneously for two sister leaf warbler species, the Bonelli’s Warbler complex, Phylloscopus bonelli and Phylloscopus orientalis, at ringing stations in the western Mediterranean Basin Gibraltar, and the eastern Eilat, Israel. Data on biometrics and passage dates of individuals trapped at Gibraltar and Eilat were used, and it was found that mean arrival date of Western Bonelli’s Warblers at Gibraltar was 15 days later than Eastern Bonelli’s Warblers at Eilat. Furthermore, Western Bonelli’s Warblers had shorter wings than Eastern Bonelli’s Warblers. On the other hand, birds in Eilat were in poorer body condition than individuals in Gibraltar. The comparison between geographically distant stop-over sites contributes to furthering our understanding of the development of migration strategies across ecological barriers in sibling species. Our study showed that populations that breed in southwestern Europe migrate through Gibraltar and winter in West Africa are able to accomplish migration in comparatively good body condition. This is in contrast to those that winter in East Africa, migrate through Israel and have to endure the combined challenge of crossing the Sahel, Sahara and Sinai deserts before reaching their breeding grounds across southeast Europe and southwest Asia. Hence, the discrepancies described between the western and the eastern flyway suggest that individuals in the west, in general, migrate shorter distances, have a physiologically less demanding crossing of the North African deserts and appear to stage before their crossing the Strait of Gibraltar, a privilege unavailable to the migrants of the eastern flyway.     

Impacts of passage migrant songbirds on behaviour and habitat use of resident Sardinian Warblers Sylvia melanocephala in Gibraltar

Explanations for the coexistence of migratory and sedentary (resident) birds are much debated: some authors have suggested that migrants make use of surplus resources not exploited by residents, whereas others have recorded ecological shifts in residents during periods when migrants are present. These shifts have been ascribed to the presence of migrants but could equally reflect seasonal variation in the distribution of resources required by sedentary species. Here we assess how the abundance of migrants affects the territorial behaviour and habitat use of resident Sardinian Warblers Sylvia melanocephala at a stop‐over site on the Rock of Gibraltar. There was a significant positive relationship between the abundance of migrants and the distances moved, time spent calling and the species and functional diversity of plants used by Sardinian Warblers on a daily basis, suggesting that migrants have a significant impact on residents.     

BIRD MIGRATION AT ELAT, ISRAEL

Several years' observations at the head of the Gulf of Aqaba are summarized. Migrants occur the whole year round, but most numerously in March-April and September. Only a few of the 185 species recorded pass the winter at Elat. About 25 species are recorded more in autumn, whereas about 50 species are commoner in spring. The causes of these disparities are discussed. Thousands of soaring raptors pass through, mainly in spring. In spring only, thousands of Lesser Black-backed Gulls stream through Elat, and many rest there for a short period. Mass migration of storks occurs too, more conspicuously in spring than autumn. An attempt is made to construct the routes of these birds between Eurasia and Africa, by analysing published sight records of raptors and storks and ringing recoveries of gulls. It is suggested that many of these birds move in autumn on a wide front, which may include Arabia, but that the core of the spring passage is shifted westward and part of it is channelled through the Rift Valley north of the northern end of the Red Sea and in the areas between the rift and the Mediterranean (Fig. 4). Supporting evidence is still needed from Arabia and the coasts of the Red Sea, especially from its southern end, where birds may be concentrated at the straits of Bab-el-Mandeb, as they are over the Bosphorus. Pelicans and a few other species perform very late southerly movements. These movements involve small numbers of birds, which may belong to late-breeding populations. About 45 other species of water and shore birds have been recorded, many of which occur in winter. With the expansion of areas of artificial water, some of them have become very common. About 75 passerines, near-passerines and other migrants pass through. The numbers involved suggest that the movement is on a broad front. Out of about 50 species whose passage is adequately recorded for seasonal comparison, 30 are more common in spring. Most of these are also commoner in other eastern Mediterranean countries and in Iraq in spring, md are presumed to perform a continuous overhead flight in autumn. Cases of “loop-migration” among these species are rare.     

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.     

Timing of autumn bird migration under climate change: advances in long-distance migrants,delays in short-distance migrants

As a response to increasing spring temperature in temperate regions in recent years, populations of many plant and animal species, including migratory birds, have advanced the seasonal start of their reproduction or growth. However, the effects of climate changes on subsequent events of the annual cycle remain poorly understood. We investigated long-term changes in the timing of autumn migration in birds, a key event in the annual cycle limiting the reproductive period. Using data spanning a 42-year period, we analysed long-term changes in the passage of 65 species of migratory birds through Western Europe. The autumn passage of migrants wintering south of the Sahara has advanced in recent years, presumably as a result of selection pressure to cross the Sahel before its seasonal dry period. In contrast, migrants wintering north of the Sahara have delayed autumn passage. In addition, species with a variable rather than a fixed number of broods per year have delayed passage, possibly because they are free to attempt more broods. Recent climate changes seem to have a simple unidirectional effect on the seasonal onset of reproduction, but complex and opposing effects on the timing of subsequent events in the annual cycle, depending on the ecology and life history of a species. This complicates predictions of overall effects of global warming on avian communities.     

ORIGIN OF THE AVIFAUNA OF URBAN AND SUBURBAN SINGAPORE

A list of the commoner garden and town birds of the tropical city of Singapore is given. None of them are birds of the rain forest which formerly covered the island. The majority are coastal species the natural habitats of which were mangrove and the thin fringe of savanna along parts of the east coast of the Malayan Peninsula. The reasons for this are discussed.
The number of garden species is comparatively small and many niches appear to be vacant. These are expected to be filled mainly by open country species moving down the peninsula from Burma and Thailand along the corridors being opened up by deforestation. This process has already begun, though few species have yet reached as far south as Singapore.
The garden avifauna is unstable and numerous changes in status have occurred in the last few decades; many more are predicted.     

Beitrag zur Kenntnis des Vorkommens ostpal?arktischer Limikolen auf Mindoro, Philippinen

Summary From September 1970 till March 1972 field observations on birds were carried out on the Philippine Island Mindoro Occ., in the vicinity of the town San José. This paper deals with plovers, snipes and waders which were either on the passage, or wintering in that area. A few individuals of ten species probably remain also during sommer season in the Philippines. The evaporation lakes of the Philippine Salt Industry (PSI), the ricefields and fishponds of the adjacent National Investment and Development Corporation (NIDC), including the coast of the South China Sea and two large rivers are an important habitat for these birds. Therefore, 14 additions have been made to the avifaunal list of Mindoro Island.     

Narrow sea crossings present major obstacles to migrating Griffon Vultures Gyps fulvus

The flight behaviour of Griffon Vultures Gyps fulvus was studied at a major migration bottleneck, the Strait of Gibraltar in southernmost Spain, during the autumns of 2004 to 2007. The 14‐km‐wide sea channel significantly impeded the southern migration of the species into Africa, with many birds attempting repeated passage for weeks before crossing, and others not crossing at all and overwintering in Southern Spain. Water‐crossing attempts were restricted to times between 11:00 and 14:00 h on days with light or variable winds, or on days with strong winds from the north or west. No crossing attempts were made on days with strong winds from the south or east. Vultures attempted to cross the Strait in large flocks and never attempted to do so alone. Although 29% of the birds soared during crossing attempts, at least until they flew beyond visible range of approximately 4 km, most engaged in considerable flapping flight when attempting to cross. Overall, birds flying over water flapped more than 10 times as frequently as those flying over land prior to crossing attempts. Vultures did not flap continuously, but intermittently in brief bouts of flapping interspersed with periods of gliding or soaring flight. The number of flaps per bout over water was significantly greater than the number of flaps per bout over land. Vultures flying over water that flapped at rates of 20 flaps or more per minute typically aborted attempted crossings and returned to Spain in intermittent flapping and gliding flight. There are numerous reports of Vultures falling into the Strait and drowning while attempting to cross, as well as reports of returning Vultures collapsing on the beach having reached Spain in spring ( Barrios Partida 2006 ). Our observations indicate that passage of Griffon Vultures at the Strait of Gibraltar is limited by the species’ over‐water flapping‐flight abilities, including its inability to flap continuously for even short periods of time. We suggest that even relatively short sea crossings represent significant obstacles to migrating Vultures and discuss the implications of this limitation on the distribution and abundance of the species.     

THE WINTERING AND MIGRATION OF PALAEARCTIC PASSERINES AT KAMPALA, SOUTHERN UGANDA

Palaearctic passerines were observed and trapped over three seasons near Kampala, in southern Uganda. Passage migration and wintering are described.
Only 11 species were encountered at all frequently. Three of these were common as passage migrants only, the rest remained in numbers throughout the northern winter. Most migrants reached Kampala during October and November, but the majority of Acrocephalus warblers appeared later. Spring departure commenced at the end of March, and continued throughout April. Autumn passage was in progress from late September to December, but appreciable spring movement was confined to a period of a few weeks only.
Ringing revealed that most wintering warblers were highly sedentary, and that a high proportion of surviving birds returned to the same site in successive winters. No fewer than 12–5% of the 220 Acrocephalus warblers ringed during 1966/67 were retrapped during the following season.
Wing measurements were recorded for most migrants trapped. Plumage details were noted, and representative specimens of several species were subsequently compared with museum series. It was concluded that most migrant passerines which occurred at Kampala were of eastern origin.
Migration times were compared with those recorded for some other areas. The spring movement from southern Uganda to the Middle East tends to be more rapid than the return journey. Some species apparently spend weeks or even months of the autumn in northeast Africa before reaching the equator,     

AUTUMN MIGRATION IN SOUTHWEST PORTUGAL.

During the latter half of September observations were made at various points on the coast of southwest Portugal. A great many migrants were seen, especially close to Cape St. Vincent, belonging to species that winter only south of the Sahara. Bird-catchers were in evidence on the south coast, but not on the west. Evidence was obtained that migrants are fewest with east winds
Most of the birds seen must have been travelling in a southwesterly direction for a long way and it is necessary for their survival that they should change course on reaching the shores of the Atlantic. Any that did not do so might find a temporary refuge on the Canary Islands, but the list of regular passage-migrants there is very different from that of the birds seen commonly near Cape St. Vincent     

SPRING MIGRATION AT THE BOSPHORUS

During observations made at the Bosphorus from 23 March to 6 April 1965, 3473 raptors were seen; the majority were Spotted/Lesser Spotted Eagles and Honey Buzzards. The migration of the main species is considered in some detail and attempts are made to correlate this with the prevailing weather. Comparisons are made with the records of observers both in spring and autumn at the Bosphorus and in spring at Gibraltar. Honey Buzzards pass in spring a month later at Gibraltar than at the Bosphorus. It is suggested that this is related to the timing of spring in the breeding areas to which these birds are returning. Notes on the observations of passerine movements and a night migration of Black Storks are also included.     

QUANTITATIVE STUDY OF MIGRATION WITH 23-CENTIMETRE RADAR*

A quantitative study was made of the displays of "angels" on the screen of a 23-centimetre radar installation on Cape Cod, Massachusetts. The birds responsible for the displays were nocturnal migrants, mainly passerines.
Other things being equal, the density of angels decreased roughly exponentially with distance from the centre of the radar screen, being halved about every eight miles. The rate of decrease varied only slightly with total migration density, and could be used to estimate the total number of bird targets in the air.
Estimates obtained by this means were compared with estimates of migration density obtained from "moon-watching" observations, which were reduced by a new method of calculation which incorporates radar measurements of the height of flight. Each angel was found to correspond to between two and twelve birds. After considering and rejecting other explanations, it is concluded that many birds migrate in groups at night. There is evidence that many species (including Parulidae, Turdidae and Emberizidae) migrate in small groups, rather than a few species in large groups. Groups of passerine night-migrants are probably spread over a wide area, since it is rare to see two birds cross the moon together.
Once the average group-size has been determined in this way, radar can be used to measure the density of migration over a large area. Estimates of low migration density have a standard error about 25%, but estimates of high migration density are less accurate, and very high migration densities cannot be measured at all, although they can be accurately identified as such.
The results in this paper cannot be applied directly to other radar stations, nor to other species of birds.     

Altitudinal migration by birds: a review of the literature and a comprehensive list of species

Altitudinal migration is the seasonal altitudinal movement of birds from breeding areas to non‐breeding or wintering areas at different elevations. Although this type of migration is widely reported, questions remain concerning the number of species that perform altitudinal migration, possible variation among different taxa and geographic locations in the extent of altitudinal migration, and the foraging guilds of altitudinal migrants. We conducted an extensive bibliographic survey and compiled a list of altitudinal migrant birds worldwide. We characterized species in terms of their foraging guilds because the spatial distribution of food resources along altitudinal gradients is often evoked as a driver of bird altitudinal migration. We identified 1238 species of altitudinal migrants, ~10% of the ~10,000 extant species of birds. We found a strong geographic bias in publications focusing on avian altitudinal migration toward the United States and Costa Rica, and a paucity of studies in megadiverse regions such as the Afrotropical and Indomalayan realms, and areas in the Neotropics other than Costa Rica. We also found that most species of altitudinal migrants were invertivores rather than frugivores or nectarivores. This general pattern held true for all zoogeographic realms except the Neotropics, where nectarivores and frugivores predominated among altitudinal migrants. The prevalence of invertivore birds among altitudinal migrants is not unexpected because this is the most common foraging guild among birds worldwide. Overall, we found no prevalence of any specific foraging guild among altitudinal migrants across zoogeographic regions. The results of studies to date suggest that altitudinal migration by birds may be driven by a number of factors, including access to increased food resources for breeding or molting, weather conditions, and mating and nesting opportunities. However, to better understand the mechanisms underlying altitudinal migration, broadening the geographic scope of studies is paramount, with additional study of altitudinal migration especially needed in the megadiverse tropical regions of sub‐Saharan Africa, Southeast Asia, and South America.     

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.     

豫北黄河故道湿地岛类自然保护区鸟类区系调查

1997－1999年对豫北黄河故道湿地鸟类自然保护区的鸟类进行了调查,共记录鸟类119种,隶属16目37科,其中留鸟32种,占总数的26．89％,冬候鸟24种,占总数的20．17％,夏候鸟30种,占总数的25．21％,旅鸟占33种,占总数的27．73％,国家一级重点保护鸟类2种,二级重点保护鸟类19种,河南省重点保护的鸟类6种。