摘要:

Summary.Observations were made on Rook and Jackdaw migrations by a number of British ornithologists in Germany during the years 1942‐45, chiefly at Dössel, Westphalia; Sagan, Silesia; and Eichstätt, Bavaria.The two species were found to migrate jointly, flocks being either mixed or of Rooks alone. Rooks outnumbered Jackdaws by about nine to one, except in the opening days at both seasons.Comparative statements are given of the dates, duration and peaks of some spring and autumn passages, and of recorded numbers. Two main waves of migrants were usually apparent.Two principal kinds of passage were noticed–“high passage”, in which flocks flew above 600 ft. and in good formation, and “low passage”, in which birds straggled below 100 ft., often in long “processional streams”. The highest flocks flew at 3000 ft. at least. Both kinds of passage were interrupted by halts on the ground, and the diving method of descent for this purpose and the methods of departure after halts are characteristic. The most interesting behaviour was “gyration”, in which the birds flew round and round collectively in slowly ascending spirals before setting course. The several activities of descent, take‐off and direct passage fluctuated considerably throughout daylight, and the pattern of these fluctuations in spring at Dossel corresponded approximately with the pattern in autumn at Eichstatt. Marked intensity of descent in early morning suggests the possibility of night flying, of which, however, there was no direct evidence. The call of migrants was distinct from that of residents.It is suggested that “gyration” enables birds which have temporarily lost sense

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1949.tb02232.x

出版商:Blackwell Publishing Ltd    

年代:1949

数据来源: WILEY

摘要:

Summary.1Notes on the history and former fowling of the Rock Dove on Nolsoy, Faeroe Islands, are given.2The population (normally 50–60 pairs) is polymorphic, the mutants showing a tendency towards melanism and having mantle and wing‐coverts spotted black. These occur in the ratio 1: 7 of the normal type when the population is at its peak, but seem less able to survive a severe winter, so that the proportion falls steeply to 1: 15–20 birds. The existence of polymorphism is noted in other widely‐separated populations, and the incidence of the partial melanism is discussed in the light of data available for 19 broods. The character is thought to be recessive, and more than one gene may be concerned.3Nesting‐sites are described and observations on the breeding‐biology are given, comparisons being drawn with Lees' work on Cromarty birds. Breeding is confined to the summer and is not spread over the whole year (as in Cromarty), and two broods of two young, with a very low mortality, are usual. Young remain on or near the nest for five weeks, but are not tolerated near the new nest by the parent if a second clutch is being incubated. Otherwise they are accompanied and fed for several days after fledging.4Flocking, roosting and feeding habits and bathing procedure are described; stomach contents for April–May, May–September and December–March are noted, seeds ofRutnexproviding much of the food. The population is greatly reduced by severe winter weather, and is now (1947)

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1949.tb02233.x

出版商:Blackwell Publishing Ltd    

年代:1949

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1949.tb02234.x

出版商:Blackwell Publishing Ltd    

年代:1949

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1949.tb02235.x

出版商:Blackwell Publishing Ltd    

年代:1949

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1949.tb02236.x

出版商:Blackwell Publishing Ltd    

年代:1949

数据来源: WILEY

摘要:

Summary.1Nestling RobinsErithacus rubeculawere weighed once each day from hatching until leaving the nest. Such regular visits largely eliminated the fear and premature flight reactions normally found in young Robins in the later stages in the nest.2Nestling weight increases extremely rapidly from hatching until about day 8 or 9, when the nestling may weigh ten times what it did at hatching. After about day 9 the weight stays approximately constant until the young leave the nest.3There are extremely marked individual differences (up to 80%) in the weights of young of the same age under natural conditions. Members of the same brood sometimes differ much, and sometimes only very little, in weight.4Round Oxford in 1946 and 1947 size of brood appeared to have no influence on the weight of the individual nestlings. However, it is possible that both years provided unusually favourable conditions of feeding for young Robins.5In 1947 the young in the two earliest broods to hatch died much below weight after a few days, apparently because caterpillars had not yet hatched in sufficient numbers to provide enough food for them.6The secondary coverts normally split open on day 6‐5, the primaries on day 7‐5. This happens irrespective of the body‐weight of the nestling. The nestling period also seems independent of body‐weight.7There were a few late developers, in which the wing feathers split open one or two days late. These individuals were at first low in weight, but continued to put on weight for one or two days after the age at which most nestlings had stopped.8The feeding visits of parent Robins to nestlings 7–14 days old varied from 3 to 33 visits per hour, averaging 13‐8 per hour. Broods of large size appeared to be visited rather more often than broods of small size, but the feeding rate did not increase proportionately to the greater number of young.9Reactions to predators near the nest are described.10The young can defaecate up to 7 % of the body‐weight. In the later stages in the nest, fsecal pellets were removed at an average rate of 0.8 per nest

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1949.tb02237.x

出版商:Blackwell Publishing Ltd    

年代:1949

数据来源: WILEY

摘要:

Summary.1Broods of nestling Robins were weighed at Avoch, Ross‐shire, in 1946 and 1947.2The average weight of eggs near hatching was 2–41 grams and of new‐born chicks 1 ′72 grams.3Nestlings increased steadily to 17‐8 grams at day 10, with small increases or decreases thereafter till fledging at days 12–15.4Irregularities and lateness in reaching normal weight are considered to be due to bad weather affecting food supply in North Scotland in 1946 and 1947.5Late‐season broods fledged at higher weight per nestling than early broods.6Broods of four and five young had the highest average weight per nestling.7A few observations were made of the behaviour of parents in regard to incubation, nest routes, food, and the attempted rem

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1949.tb02238.x

出版商:Blackwell Publishing Ltd    

年代:1949

数据来源: WILEY

摘要:

Summary.A more exact terminology than that current is suggested for behaviour having the effect of deflecting intruders from a bird's nest or chicks. The general term “diversionary display” is used to describe all such activities, and a distinction is made between “distraction display” and displacement activities having a diversionary function. Various sub‐categories of distraction display are distinguished–injury‐simulation, chick‐simulation, eccentric deportment and advertising distraction display. Attention is called to the possibility that a number of displacement activities habitually performed when an intruder menaces the nest or chicks may have divers

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1949.tb02239.x

出版商:Blackwell Publishing Ltd    

年代:1949

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1949.tb02240.x

出版商:Blackwell Publishing Ltd    

年代:1949

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1949.tb02241.x

出版商:Blackwell Publishing Ltd    

年代:1949

数据来源: WILEY