摘要:

SummaryA 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 s

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1963.tb01586.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

SummaryArrivals 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

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1963.tb01587.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

SummaryThe main passerine arrivals and departures in the Outer Hebrides in autumn are (i) S.E. from Iceland, presumably of Wheatears and Meadow Pipits in September and of Redwings in October; (ii) E.S.E. from Greenland, mainly of Wheatears; (iii) slightly west of south from the Faeroes; and (iv) with drift by easterly winds, of thrushes and drift‐migrants between west and south from Norway, (v) One W. movement was also recorded.Arriving migrants flew too low over the sea the sea during the second part of the night to be detected by radar, but rapidly gained height at dawn, at which time drifted Continental migrants re‐oriented S.S.W. and S.S.E. (from W.S.W.), but Icelandic and Greenland birds evidently did not change direction.In autumn, the presumed Wheatears, Meadow Pipits and Redwings were far less deterred from setting out by moderate head‐wings or strong cross‐winds than similar birds in Norfolk. But in spring nearly all the sizeable movements occurred with following or light winds.There were three main times of departure from Lewis in autumn, at nightfall (presumed night‐migrants), some two hours before sunrise (presumed night‐migrants again) and around sunrise (diurnal migrants).The presumed Icelandic Wheatears and Meadow Pipits, and until mid‐October the presumed Redwings, departed on the same S.E. heading as that on which they arrived. But after mid‐October the Redwings left almost due south, perhaps a re‐determined heading. On one night in late October about one‐fifth of the presumed southward departure went northwest, apparently because the birds mistook the rising moon for the set sun. Presumed Greenland Wheatears left on the same heading as that on which they arrived, but Continental thrushes, which must have arrived W.S.W., left S.S.W. on subsequent nights.The movements of non‐passerine birds are briefly discussed.In spring, the incomplete observations refer primarily to N.W. departures of Redwings, waders and geese, with some departures N.N.E., presumably for the Faeroes, others E., probably of Blackbirds, and yet others S.E., probab

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1963.tb01588.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

SummaryBased on about 425 nest records, made personally, and 150 supplied by previous observers, the breeding of 36 species of birds in Iraq is described. For 26 species the data are scanty, being less than 20 records each; but more material is available for the rest, which allows the discussion to be divided into sections for nest‐site, nest, eggs, clutch‐size, incubation and nestling period, breeding success and breeding period. Three‐quarters of the species discussed breed in Europe and about a third of these reach Britain. Wherever possible a comparison is made between breeding biology in Iraq and Europe or elsewhere. The most complete comparisons are forStreptopelia decaoctoandPica pica.ForS. decaoctothe results are discussed in the light of the expansion across Europe, the greater breeding success, longer breeding period and different habitat probably being the main factors in this spread. The performance ofP. picain Europe and Iraq is closely similar. Other species for which some interesting comparisons can be made arePterocles alchata, Hirundo rustica, Hippolais pallidaandPrinia gracilis,Knowledge of the breeding of water birds in Iraq is poor, but evidence is given to show that some species (e.g.Himantopus himantopus) may be required to be opportunists in their breeding, due to the variable and fluctuating water conditions which now exist in central Iraq.The general breeding season in central Iraq is discussed. For most species it is shown to be from March to June, usually being advanced by one to two months over that of the same species in Europe, but otherwise not differing in the number of broods or in behaviour. This is correlated with the shorter and earlier spring period of growth in Iraq. Certain species which are seed‐eaters (e.g. Columbidae) nest later and for a longer period, as in Europe, while the specializedPteroclesare adapted to breed in the heat of the summer. There is evidence that breeding at Mosul and northern Iraq generally starts about one or two weeks later than near

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1963.tb01589.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

Goodwin (1962) has commented upon the capricious, variable nature of the two plumages of the cock Red AvadavatAmandava amandava.At any time of the year cocks in the ‘red’ nuptial plumage can be found, but birds moulting into the ‘hen’ type post‐nuptial (eclipse) plumage occur most frequently between December and February. In captivity, the annual rhythm is upset and is inconsistent from year to year. In my experimental colony, all the cocks moulted into their post‐nuptial plumage during March 1962 and donned their nuptial plumage in the following May, only to effect a complete change again by early in October. A year previous to this, in October 1961, they were still in their full ‘red’,

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1963.tb01590.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

These observations were made at Vom (9° 50′ N., 8° 50′ E.), which lies on the central plateau of Nigeria at an altitude of about 4,000 feet, in the Guinea Savannah vegetational zone. The small residential area of Vom is round the periphery of the cone of an extinct volcano. The gardens have varying numbers of tall trees (mainly eucalyptus species) and ornamental shrubs. In the immediate vicinity is open grassland, with small forestry reserves and deep water‐courses filled with varying amounts of dense bushy veg

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1963.tb01591.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

San Ambrosio Island, together with San Felix 17 miles to the NNW, and the smaller González Islet form the San Felix Group situated on Lat. 26° 20'S and Long. 80° W. These islands, like all the others scattered off the Chilean coast, are outcrops of volcanic origin which emerge from depths as great as 10,000–14,000 feet below sea level. They lie 500 miles west of the port of Chañaral and about the same distance due north of Juan Fernandez (Robinson Crusoe) Island. As they lack fresh water and lie off the regular navigation routes, civilization has passed them by and, except for occasional visits by lobster fishermen, has left them uninha

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1963.tb01592.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

On 27 April 1958, while my wife and I were watching a party of 20–30 Mottled SwiftsApus aequatorialisover a dam ten miles west of Nairobi, Kenya, we repeatedly heard quite a loud “prrrpt‐prrrpt‐prrrpt”. We discovered that the swifts were making this noise by spreading and slightly depressing their tails and moving them sideways so that the outer feather was almost parallel with the wing. The ‘leading’ feather thus projected into the slipstream was quite clearly seen to vibrate at the same time as the noise was heard. We watched this performance for about half an hour and noted that the tails were invariably turned to the right; we were both using binoculars. We saw that several birds were performing in this manner but it did not appear to be in connection with any display towards any other particular member of the party. The sexes of the Mottled Swift are indistinguishable in the field. The ‘drumming’ took place in the early part of the dive towards the surface of the dam from which the birds were drinking on the wing; it did not appear to cause any deflection o

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1963.tb01593.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1963.tb01594.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1963.tb01595.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY