摘要:

Summary.A study ofPuffinus Iherminierion Plaza Island, Galápagos, showed that, although eggs were laid in all months, there were marked peaks and troughs of laying. Intervals between successive layings varied with the success or failure of the first egg, an average of nine months for successful pairs, eight months for pairs which lost a young, and 6–5 months for those which failed to hatch an egg. However the breeding success did not influence the time between the end of one breeding attempt and the next laying. This suggests that birds were breeding as quickly as possible. The critical factor preventing more frequent breeding appeared to be the time required to replace the wing and tail feathers.Details are given of the breeding biology, all aspects of which were strongly influenced by frequent and unpredictable food shortages. The average incubation period was 49 days but this was prolonged by temporary desertion due to food shortages. Chick growth and fledging periods (62 to 100 days) were variable. There was no well–defined desertion period and birds were experimentally induced to feed young for up to 120 days.Overall nesting success was low (26%) and adult survival between breeding attempts was high (92–95%).Food, planktonic fish larvae and Crustacea, appeared to be rarely abundant and details are given of the effect of food shortage on the breeding.The breeding synchrony was brought about by food shortages. The ultimate factor controlling breeding appeared to be the availability of food for egg formation and there was no possibility of birds timing breeding so that young were being fed at a time of food abundance.A comparison is made of the breeding of eightPuffinuss

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1969.tb02523.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

Summary.A brief description of the islands is followed by an account of the 13 surviving endemic land‐birds, based largely on the results of the Bristol Seychelles Expedition 1964–65.The whole of the Seychelles avifauna could possibly be derived from Madagascar, but anomalous distributions suggest that some species colonized the Seychelles from the northeast, eitheren routefor Madagascar, or independently of the Madagascan colonists.The Seychelles birds show insular evolutionary characteristics in colour and size, and some are extremes of their taxa.Endemic and introduced birds are listed in the appendix, with a Summary of their present and former distributions. A list of vagrant land‐birds is inc

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1969.tb02524.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

Summary.The rather similar ringed ploversCharadrius hiaticulaandC. semipalmatusrepresent essentially allopatric, circumpolar populations which overlap in the breeding season only in a narrow zone in the eastern Canadian Arctic.In eight fiords on eastern Baffin Island,semipalmatuswas the more numerous by a factor of almost three. Both plovers occurred together, although not in equal numbers, in the same wide range of habitats.Pair formation in both plovers apparently took place at the same time, but for more than half of the individuals, not in the same geographic area. The majority of thehiaticulaindividuals arrived after mostsemipalmatut, and the late arrivinghiaticulaappeared to be paired upon reaching Baffin Island. There was an overlap in their arrival times of about five days. Mixedhiaticula‐semipalmatuscourtship groups occurred during this period. Pair forming activities ofhiaticulaandsemipalmatusappeared similar but were not studied closely.Analysis of the non‐overlapping territories of two populations suggested that the plovers did discriminate one type from the other for there was a tendency for unlike pairs to nest side by side. The significance of this odd pattern is not known.Analysis of the mensural and plumage characteristics of adult plovers from the overlap zone seemed to indicate that gene flow between the two was absent and that they were behaving as distinct species. However, mixed pairs occurred in five out of eight fiords. Considering the populations of all fiords, the number of mixed pairs found (20) was significantly greater than theoretical expectation, which allowed for an occasional mixed mating since a choice of mate was not always possible.All mixed matings produced mixed broods. The young were eitherhiaticulaorsemipalmatus.No intermediates occurred. Moreover, 10 pairs in which both birds were pheno‐typically “semipalmatus”produced bothsemipalmatusandhiaticula‐typechicks. No intermediates were detected. Egg and chick mortality probably prevented the detection of more such cases. Allhiaticulaxhiaticulamatings produced onlyhiaticula‐typechicks. The inheritance data indicated thathiaticulaandsemipalmatusare morphs of a single polymorphic species.If a switch gene is operating, it may have originally controlled only toe‐webbing, and the other differences may have accumulated as the result of geographic isolation. That differences in plumage pattern and body size are greatest where separation was probably longest supports this hypothesis.One possible model consideredsemipalmatus‐typeindividuals to be either SS or Ss andhiaticula‐types to bess.Accordingly, allsemipalmatus‐typesinvolved in mixed matings withhiaticula‐types would have beenSsindividuals because all such matings produced chicks of both types.Circumstantial evidence suggested that during the last 80 years, the relative number of the two types in the overlap area has shifted in favour of thesemipalmatus‐type. This might have been the result of selective factors intr

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1969.tb02525.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

Summary.Because of its homogeneity, both taxonomical and ecological, the sea‐bird family Alcidae constitutes an appropriate group for the study of adaptive radiation. This radiation involves mainly the acquisition of specialized feeding habits and the consequent specialization of the various species of the family at different trophic levels.The plankton‐feeders, exemplified by the Least AukletAethia pusilla,have a relatively wide beak with a fleshy tongue and a broad palate with numerous denticles. The fish‐feeders, exemplified by the RazorbillAlca torda,have a narrow bill, a certain degree of tongue cornification and few, but sharp and regularly arranged palatal denticles. A few species, including the puffins and one auklet(Cyclorrhynchus),have characteristics intermediate between these extremes and feed partly on fish and partly on plankton.Body‐size in the predator is related to the size of the prey and these relations are examined within the family. Within a group with similar adaptations, species which are alone in their niche in their area tend to be of intermediate body size for that group. Finally, though the family may exhibit a series of parallel trends in bill shape when the bill is considered as a social releaser, it exhibits a gradation in shape and structure (adaptive radiation) when considered as a food‐get

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1969.tb02526.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

Summary.Pelecanus onocrotalus roseusis known to breed more or less regularly in Africa at Lake Shala, Ethiopia; Lake Rukwa, Tanzania; St. Lucia Bay, Natal; Abou Tougour, Chad; Kapsikis, Northern Cameroons; and Wase Rock, Nigeria; and has been observed or reported breeding at Mweru Marsh, Zambia; Lake Ngami, Botswana; Seal and Dyers Islands, South Africa; and Lake Natron, Tanzania. The Shala colony, after Lake Rukwa's, is the largest known breeding colony in Africa and is probably of crucial importance to the species in Africa.For successful breeding regular colonies of P.onocrotalusmust have an assured supply offish and an inaccessible breeding site. These conditions are met at the Lake Shala colony.Assuming that a Great White Pelican consumes about 10% of body weight or about 900‐1,200 g per day, the Lake Shala breeding colony with 7,500‐12,000 pairs would consume about 3,140‐5,040 tonnes in the breeding seasons.The partially unsuccessful breeding of perhaps 10,000 pairs at Lake Natron in 1962 is described. Failure was attributed to sudden failure of the food supply.Breeding of the Great White Pelican on Lake Shala takes place throughout the year although there is a peak of numbers breeding from December to the end of March, which is in the dry season. Observations recorded in this paper cover two full breeding seasons, 1965‐6 and 1966‐7.Although during the peak period of breeding the flock at Shala is made up of 2,500‐5,000 pairs, this mass is composed of smaller units, each made up of 300‐1,200 pairs, laying more or less together with little overlap from one group to the next.Three changes occur in the plumage of the Great White Pelican towards the onset of the breeding season: (a) the development of a knob or swelling on the forehead at the base of the beak with associated expanses of brightly‐coloured bare skin, pinkish yellow in males and bright orange in females; (b) the development of a crest; and (c) the development of a yellowish band across the chest or larger areas of darker brown in the plumage.Four distinct colour‐types of breeding plumage were observed: the dark‐brown type, the brown‐breasted type, the yellow‐banded type, and the type with scarcely any suggestion of a breast patch. No correlation was found between plumage type and sex, size, length of bill or any other obvious physical feature.Group display and individual displays of the adults are described. There appears to be no special pre‐copulation display.Elaborate nests are not prepared; the male collects the nesting material, and both sexes build the nest. Nests are small, 35–60 cm in diameter (averaging 46‐4 cm), and close together (364 nests averaged 1–55/m2).Average clutch‐size is 1–88. Incubation begins with the first egg; both sexes incubate; the incubation period is probably about 38 days.The fledging period is 65–70 days, of which about the first 28–30 days are spent in the nesting area. After that the young form into groups or “pods”.The development of the young is described. When it is very small it is fed by either parent several times each day. When the young is 30–35 days or older, it is probably fed less than once per day.The bright red nail‐like tip of the adult's upper mandible serves to direct the begging movements of the young chick, and it probably holds the liquid food on which the chick feeds.It is suggested that pod formation of young both in the middle of the day and at night possibly helps to avoid extremes of temperature, either of heat or cold.Parents recognise their own chicks; and young pelicans, at a later stage, recognise their parents. Indiscriminate feeding of young does not occur inP. o. roseus.Adults often are quiescent but not asleep at night. Activity is stimulated by the earliest light, and most pelicans begin leaving the island by 09.30‐10.00 hrs. Most departures and arrivals take place from about 10.00 to 16.00 hrs.The distance from which food is brought to the colony is not known for certain, but most birds probably fly to and from Lake Abiata. It is not known where the young go once they leave the colony; most do not fly to the obvious place, Lake Abiata.Although difficult to determine, we suggest that the breeding success of the pelicans is on the average less than one young per nest. Egyptian Vultures were the most important predators at the colony, but all forms of predation together accounted for less than 10% of the nesting losses.The timing of breeding in relation to food supply, climatic factors and inaccessibility of the breeding site is discussed. Inaccessibility appears to override seasonal factors, but in permanently inaccessible sites the peak of breeding is in the dry season.It is suggested that the Great White Pelican nests in discrete breeding units within th

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1969.tb02527.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1969.tb02528.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1969.tb02529.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1969.tb02530.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1969.tb02531.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1969.tb02532.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY