bluuebunny/crossref_metadata_2025_split huggingface dataset:
MIGRATION ACROSS THE NORTH SEA STUDIED BY RADAR PART 1. SURVEY THROUGH THE YEAR
Authors: Lack David 
Published: April 2008

Summary.

Migration across the North Sea off Norfolk is reviewed over three years on the basis of the detection of bird echoes by radar.
Large movements are most frequent in March, April and November and least frequent in December and January.
Most movements are east between January and May, west in June and July, and west or southwest during the rest of the year, while there is also a small passage northwest in spring and southeast in autumn.
Occasional movements were observed southwest in March in cold weather, west in spring during eastward emigrations with fog or rain at sea, also a presumed drift‐migration northwest in March and possibly southwest in September, with subsequent redetermined movements heading southeast and east respectively.
The chief additions to existing knowledge based on visual evidence are (a) the huge eastward emigrations in spring, (b) the arrivals southwest, presumably direct from Scandinavia, in late autumn and (c) the presumed redetermined movements eastward after drifted arrivals.
The limicoline species in June and July, and the passerine species in late autumn, cross the North Sea primarily with easterly winds and hardly at all with westerly winds, whereas in spring they often set out against the wind. This might merely be due to a stronger migratory urge in spring than autumn, but it also seems possible that westerly winds deter migration in autumn because they are so often associated with rain and other unfavourable conditions.
RECENT EXPERIMENTS ON BIRD ORIENTATION
Authors: Kramer Gustav 
Published: April 2008

Summary.Pigeons raised in open aviaries show homeward orientation when released 100 or 150 km. away from their home aviary. Some of them (15–20%) actually return.When palisades are placed around the aviaries orientation vanishes. The palisades allow the birds free sight of the sky except for a zone of an elevation of 3° above horizon.Orientation is absent also in pigeons raised in an aviary giving view of a broad sector to the north, i.e. the direction opposite to release. These experiments are being continued.Homing pigeons were subjected to an artificial light/dark change (period 24 hours). If the artificial cycle was out of phase with the natural day/night cycle, the “internal clock” was shifted within three to four days as shown by directional responses.Basically the same deviations are shown by “shifted” pigeons taken away from home and released. What appears to be influenced by shifting is a directional response which must necessarily rest upon a previous determination of position relative to home. This preceding part of the whole orientation performance appears to be unaffected.Orientation is influenced by spatial factors, or factors related to space, of unknown nature. The observed phenomena may be tentatively subdivided into variations due to direction, site of release place, site of loft, and region.Among weather conditions, cloud cover has a significant influence upon homing orientation. Top‐class homing flights are less frequent with overcast.Homing ability is subject to an annual fluctuation. Homing is best in August and poorest in January. Parallelity to temperature is obvious throughout the year. Correlation between particular releases and temperatures prevailing at the particular occasions exists only in autumn and winter but not during the rest of the year.A correlation has also been found with interdiurnal barometric change. This correlation is scarcely perceptible at surface level, but significant at the 500 and 200‐mb. level. This correlation concerns homing performance as well as correctness of departure directions, but not scatter of departures.So far no cross relations can be established between results attained with the different ways of approach.It is thought that homing ability as shown by the domestic pigeon continues to be a problem of ornithological interest. It is assumed the same ability is possessed by wild species.
THE CONTROL OF POPULATION‐DENSITY THROUGH SOCIAL BEHAVIOUR: A HYPOTHESIS
Authors: Wynne‐Edwards V. C. 
Published: April 2008

Summary.Any given species of animal generally occurs at a higher population‐density where food is more plentiful, and vice versa; quantitative evidence points to a rather close correlation between the two. Such density differences arise from the activities of the animals themselves, and this implies that population‐density is subject to effective internal control, i.e., it is self‐regulating.A theory is put forward that, for each species, population‐densities are limited at a safe level, which will protect the food‐supply from long‐term depletion and assure its renewal for the future. Instead of competing directly for food, animals compete for conventional substitutes, e.g. territory or social position, which are capable of imposing a ceiling density at the optimum level, and can prevent it from rising to the starvation level which would endanger future resources.Such limitation by conventional means requires the existence of a social organisation. Forms of social competition supplant direct competition for food; their intensity is density‐dependent and provides the animals with an index of population‐density. This index serves as the “feed‐back” for the machinery of density‐adjustment, which operates, very broadly, through (1) direct movement (emigration/immigration), and (2) varying the birth and survival rates.
THE HOUSE SPARROW PASSER DOMESTICUS: POPULATION PROBLEMS
Authors: Summers‐Smith D. 
Published: April 2008

Summary.Two problems of House Sparrow populations are examined: the influence of habitat on numbers and the variation in a population of House Sparrows throughout the year. Available data on censuses in Great Britain enable the population to be estimated as 10 millions; censuses from several parts of the bird's range suggest that House Sparrow numbers are correlated with the human population, the ratio being 1: 5. The seasonal variation in composition of a population is estimated from observations over five years on House Sparrows breeding on a group of seventeen houses together with breeding and mortality data obtained from British Trust for Ornithology records. The population reaches a maximum at the end of July when it is slightly less than double that at the beginning of the breeding season. It is considered that numbers are controlled by food supply and the colonial behaviour of the bird.
MIGRATION ACROSS THE NORTH SEA STUDIED BY RADAR PART 2. THE SPRING DEPARTURE 1956–59
Authors: LACK DAVID 
Published: April 2008

SUMMARY1. Radar observations on the eastward emigration of winter visitors across the North Sea from East Anglia were analysed from 24 February to late April in four years.2. Bird‐echoes were most numerous around 21.00 hours, with a second smaller peak an hour after dawn. Occasionally, emigration continued throughout the 24 hours.3. The volume of emigration was influenced by (a) the internal state of the bird, (b) temperature, (c) wind‐speed, (d) rain and cloud; it was not influenced by barometric pressure, the general weather situation, or the direction of the wind as such.4. In very similar cold weather 6–13 April, there was much more emigration in 1958, after a long hold‐up, than in 1957 after much previous emigration.5. There was more emigration in warm than cold weather in February and March, but not in April or May. The threshold temperature required was higher in February than March. A marked rise or fall in temperature had no immediate effect.6. Morning migration was visible from the ground with opposed but not with following winds.7. Most height; obtained by radar were below 5000 feet, but the highest at night were not infrequently at 13,000 feet.8. The track over the sea was normally the resultant between the bird's heading and the wind, the track nearly always being north of east with a southerly wind and south of east with a northerly wind. The bird maintains its sense of direction, but apparently not its sense of position, in flight over the North Ses.9. The migrants' mean heading varied on different days between N.E. and rather south of E.S.E., while occasionally two eastward emigrations proceeded simultaneously on mean headings differing by some 25.10. Under totally overcast conditions, migrants flew at random. This means that they would gradually drift with the wind.11. Observations on Starling flocks are described.
THE EFFECT OF AGE AND DENSITY OF BREEDING BIRDS ON THE TIME OF BREEDING OF THE KimWAKE RISSA TRIDACTYLA
Authors: WHITE J. C. COULSON & E. 
Published: April 2008

SUMMARY1. Differences were recorded in the time of breeding of colonies of the Kittiwake at Marsden, Co. Durham, between 1951 and 1958 inclusive. During 1958, observations were extended to other colonies in northeast England and southeast Scotland.2. Females breeding for the first time bred 9–8 days later than those breeding for at least the fourth time.3. The age composition of the Marsden Kittiwake colonies has been estimated. The old, established, colonies always had less than 25% of the birds breeding for the first time, while the younger colonies had much higher proportions of young birds.4. The age‐compositions of the colonies and the time of breeding of birds according to previous breeding experience did not account for the differences found in the time of breeding of the colonies.5. The time of breeding was directly related to the density of breeding birds, particularly those within a radius of 5 feet of the nest.6. The maximum nest‐density was usually related to the rock structure, but in one colony the maximum density was probably determined by the minimum distance at which Kirtiwakes can tolerate their neighbours.7. The time of return to the colonies also appeared to be related to density and this suggested that the effects produced by the density of breeding birds was carried over from one year to the next.8. All the Kittiwake colonies studied completed breeding at about the same time but differed in the time that breeding commenced. The spread of breeding was apparently related to the range of densities within the colony concerned.9. It is suggested that the onset, spread and completion of breeding within a colony can be explained by the maximum density, the range in density and the presence of low‐density areas in all colonies.10. The “socia‘ stimulation” apparently operating in the Kittiwake colonies differed from that envisaged by Darling; the effective distance appeared to be short (5 feet) and tended to produce a longer breeding season.
VARIATION IN THE AFRICAN BLACK TITS, PARUS NIGER AND PARUS LEUCOMELAS
Authors: HALL B. P. 
Published: April 2008

SUMMARY1. The relationship between the Black and Grey Tits of Africa is discussed briefly.2. Variable characters in the Black Tit are listed, on which five forms can be distinguished.3. The characters, ranges and ecology of the five forms are set out, with some discussion on atypical populations within the forms, and on the variable population of central and southeastern Uganda.4. It is concluded that speciation is taking place in many populations of Black Tits and that this presents considerable difficulties in assessing the relationship between forms.5. Reasons are given for considering P. n. niger and P. n. carpi as specifically distinct from other forms. The question of whether guineensis should be considered specifically distinct from P. I. leucomelas and P. I. insignis is left open until more is known of their field characters in Uganda and Abyssinia. Similarly purpurascens is regarded as a variable race until more field study has been done.
THE BREEDING BIOLOGY OF THE SHAG PHALACROCORAX ARISTOTELIS ON THE ISLAND OF LUNDY, BRISTOL CHANNEL
Authors: SNOW BARBARA 
Published: April 2008

SUMMARY1. In the 4 years 1454–1957 the breeding population of Shags on Lundy appeared to he static. Most of the nest‐sites were used each year. Mortality was deduced from the re‐use of old nest‐sites and the return of colour‐marked birds.2. Most of the clutches were started during a period of 3 to 4 weeks in each year but dates varied by as much as 1 6 days in different years.3. Different types of ncst‐site and nest‐material are used on different parts of the island. Larger nests were more successful than smaller ones.4. The mean‐clutch size for the five years 1954–1958 was 307, varying annually by us much as 0–4 egg. Clutch‐size decreases with the advance of the season.5. Incubation starts with the second egg in c/3 but a day or more later in c/4.6. Hatching success 1954–1957 varied only between 69 and 73%. Infertility was the mam cause of hatching failure.7. Eggs were weighed and measured in 1957 and 1958. In each year the larger clutches contained larger eggs than the smaller clutches. The mean weight of eggs was greater in 1957 (when clutches were bigger) than in 1958. This was due to a higher specific gravity.8. Fledging success was 90–95%, except in 1956 when it was 67%. The heavier losses in this year appeared to be due to food shortage. Most chick losses occur in the first ten days.9. The growth of chicks was studied in 1957. Male chicks can frequently be differentiated when 30 days old by their heavier weights. The fourth chick in a brood is normally below average weight during the first half of the fledging period.10. Some marked juveniles remain on the island up to 50 days after leaving the nest. During this time they show partial dependence on their parents.11. Later clutches are less successful than early clutches. Nests situated on narrow cliff ledges were less successful than nests at other sites.
THE ZOO‐GEOGRAPHICAL AFFINITIES OF THE AVIFAUNA OF THE WESTERN CAPE PROVINCE
Authors: WINTERBOTTOM J. M. 
Published: April 2008

SUMMARY

The area considered here is that part of South Africa south of the Orange River and west of the eastern borders of Mossel Bay, Oudtshoorn, Prince Albert, Beaufort West, Victoria West, Richmond, De Aar and Philipstown.
It is considered to fall into three avifaunal divisions, winter‐rainfall area, temperate forest, and karoo.
The affinities of the first and last of these are with the Southwest Arid zone; that of the second, which exists only ii isolated patches surrounded by winter‐rainfall vegetation, with the East Coast.
No valid grounds exist for sub‐dividing the karoo into smaller areas.
Examples arc given of changes of range in recent years.
THE NEST AS A DORMITORY
Authors: Skutch Alexander F. 
Published: April 2008

SummaryAs a rule, only birds which breed in roofed nests or those built in enclosed spaces sleep in their nests when not incubating or brooding young. The chief exceptions are rails, coots, and gallinulse, which build platforms to raise them above the water or wet ground while they sleep, and Curved‐billed Thrashers, which roost on open nests in thorny cacti.The first step in the evolution of the dormitory habit appears to be sleeping in the covered breeding nest itself before the eggs are laid or after the fledglings depart. In the simplest case, only one parent occupies the breeding nest. But in a number of species, the second parent uses the nest as a dormitory even while it contains eggs and nestlings, and sometimes unmated helpers roost with the parents. A further advance is made when the fledglings are led to sleep in the nest they have just left.The next advance is the construction of special dormitories, not intended for eggs. These usually resemble the breeding nest, but differences in form or site are sometimes found, especially in tropical wrens. Only birds which make or acquire dormitories, in addition to their breeding nests, are likely to enjoy such lodges through the year. In them, self‐supporting individuals may sleep singly, or in pairs, or with their dependent offspring. In the final stage of the evolution of the dormitory habit, the young lodge with their parents long after they are self‐supporting. Often each family remains separate throughout the year; but sometimes, probably in consequence of the loss of dormitories, several families club together in the non‐breeding season. Numerous examples of each of the foregoing arrangements are given.In a harsh environment, as at high latitudes and above timberline on tropical mountains, many birds seek closed spaces for sleeping, and their lives may depend on the availability of such protection. Nevertheless, the dormitory habit is best developed in mild climates where the birds are permanently resident.
ZUGUNRUHE ACTIVITY IN CASTRATED BRAMBLINGS FRINGILLA MONTIFRINGILLA
Authors: Lofts B. , Marshall A. J. 
Published: April 2008

Summary1. Zugunruhe, a condition of nocturnal activity in caged migratory birds that is generally held to be identical to premigratory restlessness in the wild, developed in the spring in captive castrated male Bramblings Fringilla montifringilla.2. Zugunruhe occurred in intact control birds about a week before it was recorded in castrates. Intact birds became restless each evening earlier than did the castrates.3. Nevertheless, the peaks of intensity in both castrate and intact birds occurred at the same time and coincided with the period during which the bulk of the wild population migrated to their northern breeding grounds.4. In intact birds Zugunruhe occurred during the initial period of seasonal gonad modification. It waned by the time of sperm‐production when, under wild conditions, the birds would have completed their journey to their distant breeding grounds.5. The data suggest that the seasonal phenomena of migratory unrest and gonad development occur independently of each other. The remote possibility that migration is influenced by extra‐testicular androgens is mentioned.
NOTES ON THE BIRDS OF ANNOBON AND OTHER ISLANDS IN THE GULF OF GUINEA
Authors: Fry C. H. 
Published: April 2008

Summary1. A systematic list of the birds of Annobon Island in the Gulf of Guinea is presented with field notes obtained on a recent expedition, and the records are compared with those of previous ornithological visits.2. The land avifauna of Annobon has altered markedly in the last five or six decades. That the resident land‐birds provide severe competition for newly arrived immigrants is offered as the most plausible reason for the paucity of land‐birds species on the island.3. Brief ornithological notes from Sao Tom and Fernando Po are given as addenda to recent papers on the respective avifaunas.
THE ORIENTATION OF PECKING IN VERY YOUNG MAGPIE GEESE ANSERANAS SEMIPALMATA
Authors: Davies S. J. J. F. 
Published: April 2008

SummaryThe goslings of the Magpie Goose Anseranas semipalmata make co‐ordinated pecks about 40 min. after hatching. The intensity of pecking is greater by day than by night and also increases with increasing age in unfed goslings. In a series of experiments goslings tended to orientate their pecks towards high, light, green and yellow objects rather than low, dark, blue or red ones, but did not discriminate between rough and smooth objects. It is suggested that these generalized orientation tendencies suffice to direct the goslings' pecks towards potential food, the seed heads of swamp plants. A more precise innate orientation, such as is found in some gull chicks, would not confer greater protection from predation than the shelter of the breeding swamp itself provides, and might prevent the goslings from exploiting some of the available food.
MIGRATION FROM MOROCCO INTO SOUTHWEST SPAIN IN RELATION TO WEATHER
Authors: Nisbet I. C. T. , Evans P. R. , Feeny P. P. 
Published: April 2008

“We must not, I think, deny migration in general: because migration certainly does subsist in certain places, as my brother in Andalusia has fully informed me. Of the motions of these birds he has ocular demonstration”.–Gilbert White, 12 February 1771.Summary1. Migration was stuaied on the south coast of Spain between Gibraltar and Huelva during five successive springs. Systematic observations were made during a total of 11 weeks by four parties, and casual observations made by other observers have also been used.2. West of Cape Trafalgar, grounded passerine night migrants were seen in numbers only during east winds. Observations of birds crossing the moon indicated that this correlation was due to drift, and that in the absence of east winds many more birds pass over the Straits of Gibraltar than over the wider stretch of sea to the west, probably after diversion towards the Straits by the west coast of Morocco.3. The mean heading of nocturnal migrants seen crossing the moon at the Straits of Gibraltar was usually between north and N.N.E., but was N.W. on one night when clouds obscured the stars.4. Within the periods of east winds, observed migration was correlated with dry weather and rising night temperature in Morocco, but not merely with high temperature. It may also have been correlated with clear skies, but there is slight evidence that cloud cover also caused increased drift.5. Migration of raptors and storks was seen on most days. Largest numbers were seen at the east end of the Straits in west winds, and vice versa; this is probably due to drift.6. Other day‐migrants seen included Turtle Dove Streptopelia turtur, Bee‐eater Merops apiaster, Swift Apus apus, Alpine Swift A. melba, Swallow Hirundo rustica, Sand Martin Riparia riparia, and Short‐toed Lark Calandrella cinerea. Many were drifted west of the Straits, retaining their N.E. heading, but others–perhaps those breeding in western Iberia–were seen flying N.W. after crossing the Straits.7. Large numbers of Black Terns Chlidonias niger were seen flying east or N.E. on a few days of strong east wind.
OBSERVATIONS ON THE BIRDS OF BULGARIA
Authors: Mountfort Guy , Ferguson‐Lees I. J. 
Published: April 2008

SummaryThe results of an expedition to Bulgaria during May and June 1960 are described. The majority of observations were made in the eastern regions of the Danube, the Dobrudja and particularly the lakes and woods of the Black Sea coast. Although, apart from the national scientific bodies, there is as yet little apparent interest in ornithology as such in Bulgaria, the laws protecting wild birds and the provision of sanctuaries are shown to be adequate. There is, however, evidence that the populations of certain larger birds such as pelicans, vultures and eagles have declined seriously, chiefly as a result of intensive agriculture, land reclamation, the annual cutting or burning of reed‐beds or the use of poison‐bait to control wolves. Other bird species are shown to have extended their ranges and some to have increased in numbers. Comparisons are made with the observations of earlier writers. Comments on observed migration are included in the Systematic List, which embraces 220 species, of which 205 were recorded in the course of the expedition.