摘要:

Summary.The eyes and ears of birds are compared with those of man so far as the existing state of knowledge allows, and an attempt is made to correlate resemblances and differences with the evolutionary history and the functional requirements of the present day. It is shown that the characteristic shape of the central fovea of the bird's retina cannot be accounted for by supposing that it increases acuity; it is more likely a device for emphasizing angular movements. A brief account of Menner's theory of the pecten is given.In default of any satisfactory physiological data, an attempt is made to assess the indirect evidence relating to the frequency range and discriminative power of a bird's ear. The conditions for the unambiguous determination of the direction of a sound source are discussed and it is suggested that the asymmetry of the ears of owls is correlated with an enhanced directional sensitivity which, in turn, is related to the dependence of owls on hearing rather than sight in their hunting.Reference is made to the senses of smell and touch in birds. And there is a brief discussion of the problems of “time” and “direction”

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1948.tb01686.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1948.tb01687.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

Summary.Agapornis, an African genus of parrots allied toLoriculusof Asia, has usually been classified in nine species.Their geographical, altitudinal and ecological ranges are described and their temperature relations are worked out. There is a general agreement with Bergmann's rule.Only two of the Agapornids appear to be in any respect ecologically specialized: toA. swinderniana, the only one confined to tropical evergreen forest, the seeds of figs may be an essential food; andA. pullariais more or less completely dependent on the nests of arboreal insects for nesting‐sites. The other seven Agapornids are birds of dry country with a wide range of food and are indiscriminate hole‐nesters.All nine birds are practically allopatric. The four closely allied birds in East Africa, which produce fertile hybrids very freely in captivity, seem nowhere actually to meet in nature. Certain vegetation types, especiallyBrachystegia‐Isoberliniawoodland, appear to be an effective barrier, for reasons not clear.Comparisons are made of colour, size and proportions, degree of sexual dimorphism, juvenile plumages, hybridization and breeding biology. Special points of interest are:—1The existence of well‐developed sexual dimorphism and juvenile plumage in some Agapornids and their total absence in others.2The development of contrasting eye‐rings; in two forms from feathers, in four others from naked white skin; that is, using two different physiological bases.3The persistence of certain features in the tail pattern throughout the genus, in contrast to the variability of other parts of the plumage.4The existence of two pairs of allopatric forms, each consisting of one pink‐headed and one containing more melanin; but the distribution of the melanin being very different in the two “melanic” forms.5The fact that some forms ofAgapornis carrytheir nesting‐material in their contour feathers (a habit otherwise known only inLoriculus) and others do not.Although certain of the tectonic and climatic changes in Pleistocene Africa would, by sundering populations, have facilitated evolution of the existing forms, the isolating mechanism so provided seems inadequate.Most of the Agapornids fall into two groups, the older comprising the West African, Abyssinian and Madagascar forms. Main trends of evolution in the genus have been to eliminate (a) the habit of carrying material in the contour feathers, and (b) sexual dimorphism, partly by “grading up” the female plumage of the fore‐parts and partly by eliminating the black under wing‐coverts of the male.A proper picture of relationships within the genus demands the use of the newer taxonomic categories, cline, semispecies and superspecies, in addition to the species and subspecies.The genus provides a good field for genetical analysis. At least five sharply characterized forms, including subspecies, semispecies and full species, readily produce fertile hybrids, and one of the five has the habit of carrying mater

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1948.tb01688.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1948.tb01689.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

Summary.1 In winter, in England, the Robin chiefly frequents cultivated land and the wood‐edge, but a few occur in the interior of woods. In summer, proportionately more frequent the interior of woods.2 The Robin associates with man to a much greater extent in England than on the Continent of Europe. It seems first to have appeared round human habitations in winter, breeding being a later development.3 The Robin suffers severely in hard winters, census figures being given in Table 2. During a cold spell, the woods may temporarily become empty of Robins, but it is not known whether most of these birds have died or moved out.4 The Robin is “dimorphic”, some individuals migrating and others residing for the winter, the proportion in each class differing in different parts of Europe according to the severity of the winter. The activities of man have probably changed the proportion of residents to migrants in England.5 Young Robins commonly disperse to breed between 1 and 4 miles from their place of birth, but only 5 per cent, have been found more than 8 miles from their birth‐place. Once a Robin has taken up a territory, it rarely moves more than a mile, only 3 per cent, being found 1–3 miles away and another 3 per cent, over 10 miles away.6 The expectation of life for a Robin is about one year, and there is a suggestion that this figure is lower for north European migrants than for British birds.7 The Robin eats a great variety of small invertebrates, which are chiefly detected from a perch as they move on the ground or litter below the bird. Seeds and fruits are also taken.8 Particularly in hard weather, the Robin follows mammals or large birds which break up the ground, thereby rendering insects available to it.9 In winter the Robin probably has no serious food competitors. In summer it takes many geometrid larvae, as do titmice and warblers, but this food is probably superabundant.10 The Sparrowhawk is the only serious predator of the Robin.11 The external parasites are listed.12 More than 60 per cent, of adult Robins die each year. Winter food shortage is thought likely to be the chief mortality factor. Population control is briefly discussed.13 There is no real evidence that territorial behaviour controls population density or that it is important in e

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1948.tb01690.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1948.tb01691.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1948.tb01692.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1948.tb01693.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1948.tb01694.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1948.tb01695.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY