摘要:

SummaryThe Giant Coot is generally a local and sparse bird in Andean lakes at 3100–5000 m. One of the localities found by the author, Lake Lagunillas in southern Peru, contained 600–650 nesting pairs increasing the known population markedly. The enormous offshore nests are completely open to view. They begin as floating structures but as they increase in size, rest on the bottom like islands. Since the central parts of large nests turn into compact peat, they are probably used for years in succession. Thriving breeding populations may require extensive shallows with dense weeds such asMyriophyllumandPotamogetonat the water surface. New materials are added to the high nest‐rim as long as pairs have young and this serves as a continuing food supply for the chick, permitting them to stay dry and sheltered during bad weather.The threat behaviour differs markedly from that of other coots studied. The main breeding season is in the austral winter when there is intense cold every night, with second broods in spring and some laying at other seasons. Development appears very slow. Territorial adults seem sedentary and flightless. It is assumed that the species disperse through nocturnal flights, probably by immatures which have not yet obtained full w

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1981.tb04047.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SummaryInvestigations on the feeding ecology of Wigeon were carried out in winter 1978–79 at the species' most important inland wintering habitat in Britain. The study area included 287 ha of grassland, about one‐sixth of the Washes, which is grazed by cattle and sheep until late autumn. In winter the area is partly or fully flooded. The number of Wigeon increased to 11 200 in January but cold weather in February, with snow and frozen flood water, forced the birds to leave, only 600 staying in the reserve. In March up to 4000 birds were again present.The distribution of the population within the refuge depends on whether the habitat is dry pasture with only a few ponds, partly flooded, fully flooded or covered with snow and frozen flood water. Under dry or slightly wet conditions 98% of the Wigeon were grazing (October to January), while under partly flooded conditions (February and March) 42%, fed on water. With increasing water depth, upending was used by 13%, while 45% of the population moved to the barrier banks, grazing there in March. The feeding method can change within a few hours with increasing water depth.The diurnal activity pattern varies during the wintering period. A lower percentage of morning feeding occurred after flights back from feeding outside the refuge and under frozen conditions. The feeding activity was higher at mid‐day with a slight decrease towards dusk. The average diurnal feeding activity was 71% (October to April), with a maximum of 90% in November.Wigeon feed diurnally and nocturnally. During a 24 h period in March they were foraging for 15 h 40 min; by day 81% of the time was spent feeding, while at night only 48%.Standing crop measurements showed that the biomass of green vegetation declined significantly outside enclosures due to Wigeon usage. Pasture land should be grazed at different intensities by cattle and sheep before the arrival of the ducks. Inland reserves should include such pasture together with some standing water where the birds are undisturbed. The use of inland pastures can compensate for the loss of coastal hab

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1981.tb04048.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SummaryClutches of Red Grouse eggs were collected from the wild and subsequent hatching and rearing done in standard conditions in captivity. Variations in chick survival from one clutch to another in the same year were related to differences in hatch weight. Hatch weight was determined only partly by egg size. Weight loss between laying and hatching was related to survival independently of egg size. Variation in this weight loss obscured any simple relationship between egg size and survival, except in eggs laid by captive hens.Intrinsic differences amongst hens caused some variations in laying date, egg size, hatch weight and chick survival. Variations in egg size and hatch weight accounted for less than half the variation in survival; other unmeasured intrinsic factors were also important.Big clutches hatched earlier than small ones. The commonest clutches were of seven and eight eggs, with six and nine frequent. Very big clutches of ten or more eggs were infrequent and chicks from them sometimes survived worse than from smaller clutches.As in other species, the commonest clutch sizes were not the most productive. There was no simple relationship between egg size and clutch size.

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1981.tb04049.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SummaryThis study presents data on the roosting and feeding behaviour of Pied Wagtails around Oxford, England. During the winter of 1977–78, from two to 1200 wagtails roosted in aPhragmitesreed‐bed. Use of this roost was greatest during mild, windless weather and the birds apparently used alternate roosts during harsh weather. Movement between roosts sometimes occurred between sunset and sunrise. Morning ‘departure group’ size, number leaving per unit time and diversity of departure directions increased with roost size. Wagtails quickly left the vicinity in the morning. In the afternoon, they joined one or more pre‐roost gatherings before entering the roost for the night. Behaviour upon arrival at the roost was variable: birds might enter the reeds quickly or circle in large groups before landing. Aerial revolutions and generally ‘restless’ behaviour often accompanied increases in roost size.Wagtail feeding rates varied significantly between and within habitats. Number of wagtails feeding on the flooded Port Meadow, located 2–3 km south of the main roost, varied from about five to over 60 on different days; these numbers were not correlated with feeding rates. In contrast, the number of birds feeding at a sewage farm was nearly constant all winter. Some wagtails show high fidelity to feeding areas but others do not. Five short‐term food supplementation experiments indicated that wagtails knowledgeable about a dense food source are not followed in the morning by naive birds.Results of this study are discussed in relation to the predation, physiology and information centre hypotheses that have been suggested to explain communal roosting in birds. I conclude that the communal roosting system of Pied Wagtails has physiological and anti‐predator functions. Wagtails appear to choose certain roosts because of the protection that they provide from adverse cl

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1981.tb04050.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SummaryThis paper discusses the relative position of cooperative polyandry among models for the evolution of both polyandry and cooperative breeding. Cooperative polyandry is described as the situation where more than one male and one female breed as a group with males sharing equally in copulations and the care of one set of young. Sequential and simultaneous polyandry are defined to show how they differ from cooperative polyandry. These systems generally are characterized by the care of only one parent for each set of young, a trait which is in sharp contrast to cooperative polyandry. An argument is made that the present models for the evolution of polyandry cannot be expanded to include the cooperatively polyandrous species. Instead, the cooperative traits of cooperative polyandry fit within the array of characteristics of cooperative (communal) breeding. General characteristics of all cooperative species (monogamous, promiscuous and polyandrous) are reviewed and possible reasons for the evolution of equal‐status males are discussed. A plea is made for the unification of evolutionary models dealing with mating systems and cooperative system

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1981.tb04051.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SummaryThe food and dispersion of Great Argus were studied in two West Malaysian forested areas from 1975 to 1978. Invertebrates on the litter surface lived at low density and were typically large and solitary; those beneath the litter were abundant but typically tiny and colonial. Great Argus feed mainly on fallen fruit but rely for protein on the large, solitary litter‐surface invertebrates and were never seen scratching for food.Adult males maintain small, discrete home ranges in which they forage alone. Much of their time is spent resting, which reduces energy expenditure. Females also forage alone and may be similarly inactive. Great Argus are very large and their requisite large invertebrate prey cannot be obtained beneath the litter; scratching has been eliminated as a foraging technique. A strategy of litter‐surface searching necessitates solitariness, to avoid intraspecific feeding competition. The large size of Great Argus is related to a low rate of energy turnover and energy conservation by prolonged resting. Both sexes are probably territorial during the breeding season and larger territories then may limit population dens

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1981.tb04052.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1981.tb04053.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1981.tb04054.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1981.tb04055.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1981.tb04056.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY