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.     

Field studies of avian nocturnal migratory orientation I. interaction of sun,wind and stars as directional cues

Tracking radar and visual observation techniques were used to observe the orientation of free-flying passerine nocturnal migrants in situations in which potentially usable directional cues were absent or gave conflicting information. When migrants had seen the sun near the time of sunset and/or the stars, they oriented in appropriate migratory directions even when winds were opposed. Under solid overcast skies that prevented a view of both sun and stars, the birds headed downwind in opposing winds and thus moved in seasonally inappropriate directions. The data point to the primacy of visual cues over wind direction, with either sun or stars being sufficient to allow the birds to determine the appropriate migration direction.     

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.     

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.     

Nocturnal migratory songbirds adjust their travelling direction aloft: evidence from a radiotelemetry and radar study

In order to fully understand the orientation behaviour of migrating birds, it is important to understand when birds set their travel direction. Departure directions of migratory passerines leaving stopover sites are often assumed to reflect the birds'' intended travel directions, but this assumption has not been critically tested. We used data from an automated radiotelemetry system and a tracking radar at Falsterbo peninsula, Sweden, to compare the initial orientation of departing songbirds (recorded by radiotelemetry) with the orientation of songbird migrants in climbing and level flight (recorded by radar). We found that the track directions of birds at high altitudes and in level flight were more concentrated than the directions of departing birds and birds in climbing flight, which indicates that the birds adjust their travelling direction once aloft. This was further supported by a wide scatter of vanishing bearings in a subsample of radio-tracked birds that later passed an offshore radio receiver station 50 km southeast of Falsterbo. Track directions seemed to be more affected by winds in climbing compared with level flights, which may be explained by birds not starting to partially compensate for wind drift until they have reached cruising altitudes.     

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.     

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     

Optimal use of wind by migrating birds: combined drift and overcompensation

Migrating birds may save flying time by allowing themselves to be partially drifted by strong winds at high altitude and correcting for the displacement at low altitude under relatively weaker winds. This behaviour will be favourable with strong upper winds and with wind direction approx. 30 ° to 90 ° in relation to the goal direction (following side winds). Radar observations of drift in high altitude bird migration and visual records of low altitude overcompensation are compatible with the optimal flight behaviour of migrants at high and low altitude, respectively, as predicted from this hypothesis.     

MIGRATION OF THE NORTHWESTERN EUROPEAN POPULATION OF THE CUCKOO CUCULUS CANORUS, AS SHOWN BY RINGING

The migration of the Cuckoo Cuculus canorus is described from recoveries of ringed birds. Young birds begin to migrate in August and most go southwards by September—those in continental Europe move southeast, south or southwest, while those from the British Isles move southeast. In spring, migrants arrive in Europe in April/May, second-(calendar) year birds doing so later than post-second-year birds. In autumn old birds depart in advance of first-year birds; and the individual bird may move stepwise through Europe. Old birds showed a marked tendency to return to the same places inhabited in previous breeding seasons, and birds ringed as nestlings subsequently tended to return to the general vicinity of the natal site.     

Ontogenetic Behavior and Migration of Gulf of Mexico Sturgeon, Acipenser oxyrinchus desotoi, with Notes on Body Color and Development

We observed Suwannee River Gulf sturgeon, Acipenser oxyrinchus desotoi, in the laboratory and found free embryos (first interval after hatching) hid under rocks and did not migrate. Thus, wild embryos should be at the spawning area. Larvae (first interval feeding exogenously) initiated a slow downstream migration, and some juveniles (interval with adult features) continued to migrate slowly for at least 5 months, e.g., a 1-step long larva-juvenile migration. No other population of sturgeon yet studied has this migration style. A conceptual model using this result suggests wild year-0 sturgeon have a variable downstream migration style with short-duration (short distance) migrants and long-duration (long distance) migrants. This migration style should widely disperse wild fish. The model is supported by field studies that found year-0 juveniles are widely dispersed in fresh water to river km 10. Thus, laboratory and field data agree that the entire freshwater reach of river downstream of spawning is nursery habitat. Foraging position of larvae and early juveniles was mostly on the bottom, but fish also spent hours holding position in the water column, an unusual feeding location for sturgeons. The holding position of fish above the bottom suggests benthic forage in the river is scarce and fish have evolved drift feeding. The unusual migration and foraging styles may be adaptations to rear in a river at the southern limit of the species range with poor rearing habitat (low abundance of benthic forage and high summer water temperatures). Suwannee River Gulf sturgeon and Hudson River Atlantic sturgeon, A. o. oxyrinchus, are similar for initiation of migration, early habitat preference, and diel migration. The two subspecies differ greatly for migration and foraging styles, which is likely related to major differences in the quality of rearing habitat. The differences between Atlantic sturgeon populations show the need for geographical studies to represent the behavior of an entire species.     

Morning flight behavior of nocturnally migrating birds along the western basin of Lake Erie

Many species of birds that normally migrate during the night have been observed engaging in so‐called morning flights during the early morning. The results of previous studies have supported the hypothesis that one function of morning flights is to compensate for wind drift that birds experienced during the night. Our objective was to further explore this hypothesis in a unique geographic context. We determined the orientation of morning flights along the southern shore of Lake Erie's western basin during the spring migrations of 2016 and 2017. This orientation was then compared to the observed orientation of nocturnal migration. Additionally, the orientation of the birds engaged in morning flights following nights with drifting winds was compared to that of birds following nights with non‐drifting winds. The morning flights of most birds at our observation site were oriented to the west‐northwest, following the southern coast of Lake Erie. Given that nocturnal migration was oriented generally east of north, the orientation of morning flight necessarily reflected compensation for accumulated, seasonal wind drift resulting from prevailingly westerly winds. However, the orientation of morning flights was similar following nights with drifting and non‐drifting winds, suggesting that birds on any given morning were not necessarily re‐orienting as an immediate response to drift that occurred the previous night. Given the topographical characteristics of our observation area, the west‐northwest movement of birds in our study is likely best explained as a more complex interaction that could include some combination of compensation for wind drift, a search for suitable stopover habitat, flying in a direction that minimizes any loss in progressing northward toward the migratory goal, and avoidance of a lake crossing.     

SPRING MIGRATION THROUGH SOUTHEAST MOROCCO

Very few quantitative data existed for the spring migration of birds across the Sahara desert. Observations covering 105 days in spring 1963–66 were made at Defilia, on the extreme northern fringe of the desert in southeast Morocco. The physical features and climate of the area are described, with brief reference to neighbouring desert zones. The birds recorded are listed in weekly or part-weekly totals, followed by subspecific and other comments on selected species.
The movements of migrants are summarized, together with the effects of adverse winds on migration; very bad weather along the northern desert fringe may contribute to the late arrival of some species in the British Isles (and presumably elsewhere in Europe) in spring by causing delays and heavy mortality. Most visible migration was northeastward or eastward, but substantial westward movements of hirundines took place.
Comparison is made with migration through other areas in Morocco and Algeria, both from existing literature and from previously unpublished data, which provide evidence of broad-front migration across the entire width of the Moroccan Sahara. Birds recorded in northwest Algeria in 1966 are listed, together with notes on physical features, climate and field observations. Many terns and waders were recorded at Daiat Tchiour, including some predominantly coastal species, which suggests that the latter were migrating on a great-circle track from winter quarters in West Africa across the Sahara to their breeding grounds in Siberia.
Recoveries of ringed birds are discussed; some of these, together with records of species well west of their normal migratory range, suggest that birds may be subject to lateral displacement by winds when crossing the Sahara, leading to considerable annual variation in species and numbers of birds recorded on the northern desert edge, even in the same place.     

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.     

科尔沁沙地黄榆种子散布的空间差异及规律

黄榆(Ulmus macrocarpa)是典型的风播植物, 在科尔沁沙地可以形成单一优势种林地。通过对其林下随机取样和林缘与孤立树不同方向从树基部向外的有序取样调查, 分析了黄榆林下和林缘外不同距离的种子沉降特征、林缘和孤立树种子散布方向的差异性与规律性。结果表明, 黄榆平均种子密度以林下最大, 林缘3 m处已显著减小, 林缘外随着距离增加黄榆平均种子密度呈指数减少态势, 且越远越不均匀。林缘和孤立树不同方向在26 m内, 单位面积连续分布的种子累积数量均以顺风向频率大的东北方向最多, 以逆风向频率大的西南或西方向最少。林缘和孤立树共10个方向的垂直断面从树基部向外的单位面积种子数量频度均符合Weibull分布和对数-正态分布密度函数(χ²_(α) < 0.900), 具有相同的种子散布格局。在科尔沁沙地自然条件下, 黄榆在各方向具有相同的“远距离”种子散布机制。     

Stopover and fat deposition by North American wood-warblers (Parulinae) following spring migration over the Gulf of Mexico

Summary Length of stopover and rate of weight gain (fat deposition) were studied in several species of passerine birds that stopped in southwestern Louisiana along the northern coast of the Gulf of Mexico after a trans-Gulf flight. Fatdepleted birds were more common among the birds that arrived at our study site in southwest Louisiana, though variability characterized our samples. Migrants that landed after encountering opposing winds or rain over the northern Gulf of Mexico were, on average, fatter than migrants that landed when weather was favorable for continued migration. Some of the variation in the energetic condition of arrivals may be explained by the location where migrants initiated crossings. Our simulation of flight over the Gulf of Mexico showed that with following winds a warbler can cross the Gulf of Mexico from Yucatan with fat reserves to spare, and stronger tailwinds make flights from as far south as Honduras energetically permissible. The length of stay after a trans-Gulf flight was related to the extent of fat-depletion upon arrival: lean birds stayed longer than fat migrants. Migrants stopped over for 1–7 days and replenished energy reserves at rates that varied from 0.19 g/d for Hooded Warblers (Wilsonia citrina) to 0.87 g/d for Ovenbirds (Seiurus aurocapillus). Within each species, most individuals gained weight at a rapid rate, though a few individuals lost or maintained weight during their stay.     

Within night correlations between radar and ground counts of migrating songbirds

ABSTRACT.   Studies comparing numbers of nocturnal migrants in flight with numbers of migrants at stopover sites have produced equivocal results. In 2003, we compared numbers of nocturnal migrants detected by radar to numbers of passerines observed at the Atlantic Bird Observatory in southwestern Nova Scotia, Canada. Numbers of nocturnal migrants detected by radar were positively correlated with numbers of migrants as determined by mist-netting, censuses, and daily estimated totals (daily estimates of birds present based netting and census results and casual observations) the following day. On nights with winds favorable for migration (tailwinds), the peak correlation between ground counts and radar counts the night before occurred just after sunset. On nights with unfavorable winds (headwinds), the correlation increased through the night, with a peak just before sunrise. The patterns of correlation are consistent with a scenario where birds accumulate at the coastline during periods of unfavorable wind, likely because they are not willing to cross a major ecological barrier, the Gulf of Maine. On nights with favorable winds, many birds departed, but some, possibly after testing wind conditions, apparently decided not to cross the Gulf of Maine and returned. Our results suggest that combining data collected using different methods to generate a daily estimated total provides the best estimate of the number of migrants present at a stopover site. Simultaneous studies at multiple locations where different census methods are used, making more effective use of temporal data (both from radar and diurnal counts), will more clearly elucidate patterns of flight behavior by migratory songbirds and the relationship between ground counts and counts of birds aloft.     

Nocturnal autumn bird migration at Falsterbo, South Sweden

We investigated the patterns of nocturnal bird migration in autumn 1998 at a coastal site on the Falsterbo peninsula in south-western Sweden, by means of a passive infrared device. In total 17 411 flight paths, including track direction and altitude, of migrating birds were recorded for 68 nights from August to October. Mean migratory traffic rate per night varied between 6 and 6618 birds km⁻¹ h⁻¹, with an average of 1319 birds km⁻¹ h⁻¹. Migration at Falsterbo showed a similar seasonal pattern to that reported for central Europe, with pronounced peaks of migration and intermittent periods with relatively low migratory intensities. Weather factors explained two thirds of the variance in the intensity of bird migration. During nights with intense migration, associated with weak winds, the mean track direction was close to that in central western Europe (225°). Birds usually maintained a constant heading independent of wind directions and, in consequence, were drifted by the wind. The mean orientation clearly differed from that of the nearest coastline, suggesting that the birds did not use the topography below to compensate for wind drift.     

The spring migration pattern of arctic birds in southwest Iceland, as recorded by radar

A surveillance radar in southwest Iceland was recorded by time-lapse filming in order to monitor the migration pattern of birds departing from or passing Iceland on their way to high-arctic breeding grounds in late May and early June 1988–1990. An overwhelming majority of the radar echoes from migrating bird flocks departed from Iceland but a few seemed to pass over from further south. Timing of movements and supplementary field observations indicated that mainly four species were involved, i.e. Knot Calidris canutus , Turnstone Arenaria interpres. Sanderling C. alba and Brent Goose Branta bernicla. Departures in late May from stopover sites in Iceland took place mainly in the afternoons, peaking between 1700 and 1900h in all 3 years. The departure intensity was lowest between 0100 and 1300h. Flight paths were generally straight, and the average track direction was towards the northwest (315°), suggesting that the majority of birds were heading for a transglacial migration across the Greenland icecap on their way to breeding grounds in northwest Greenland and northern Canada. Track directions varied with wind, although to a rather small degree, indicating partial drift or pseudodrift. More echoes were registered in easterly winds (tailwinds) and fewer in northerly winds than expected from random. Airspeeds were significantly slower than groundspeeds (average 17.0 and 18.7 m/s, respectively), showing that the birds more often than not benefited from tail wind assistance.     

Migration and orientation of passerine night migrants in northeast England

Evening departures of passerine migrants were watched by radar in northeast England on 193 nights in the months of August to November 1961 to 1963. It was found that migrants were not departing each night on the same heading, from which they were drifted passively by the wind, but rather were departing on similar tracks night after night. On ten nights they maintained their tracks even when the upper-air wind changed during the night. This indicates that migrants can, at least sometimes, compensate completely for the effect of the wind and fly on a fixed track, but calculations show that there are certain wind conditions when this becomes impossible.
Movements were grouped according to the months in which they took place and the tracks which they followed, and then related to variousweather factors. Migration was seen most frequently with light winds favourable to the birds'track, after a marked drop in temperature (in October/November, but not August/September), and withabsence of cloud. However, it was also recorded on 17 nights when the cloud cover was complete.
The departures of small passerines from Britain in August and September follow tracks east of south, yet the same birds reach western Iberia later in their journey. It is suggested that the direction of departure from Britain has been evolved to take advantage of the prevailing (westerly) upper-air winds. Certain warblers leave their breeding areas in Northumberland without laying down much migratory fat, yet the same species make long flights non-stop (across the Mediterranean and Sahara) later in their migrations. These migrants change froman insect to a fruit diet in autumn, and can presumably IaKdown fat more quickly the further south they travel in Europe, as the soft fruit ripens earlier in southern areas.     

Distributión de avifauna en los distintos ‘Habitats’ del Estuario Andalién,Bahia de Conceptión,Conception, Chile

In a first survey a total of 70 species of birds was found in the area of the Andalien river estuary in Chile during the years 1979 to 1981. There are four major types of habitat: the marine coastal zone, the vegetation covered coastal plain, the brackish coastal lagoons, and the mud flats aiong the river. The distribution of adaptive types of birds across these different kinds of habitat is shown qualitatively in the figs. 2 to 5. Twelve of the 70 species are migrants from North America and distant regions of South America, the remaining 58 are residents of Central Chile.