摘要:

Among King PenguinsAptenodytes patagonicaat Possession Island, one of the Crozet Islands, the length of the moult period, pre‐laying period, incubating and brooding shifts were highly variable according to the year and to the stage of the breeding season. The moulting period was shorter in late breeders than in early breeders. Only half of the birds which successfully reared a chick bred the following cycle, but late in the season. Almost all these late breeders were unsuccessful. The reasons for the high variability in the breeding pattern observed in this species between years, as well as between colonies and between individuals are discussed. Breeding success was on average 30.6% and survival during the first year at sea could reach 50%. The survival of adult birds has increased during the past 10 years from 90.7% to 95.2% per annum. Despite an almost biennial breeding frequency and a very high rate of chick loss during the winter fast, the King Penguin population of Possession Island has doubled between 1966 and 1985 due to a high survival rate of adult and immature birds. The increase during the last decade in adult survival and in adult and chick condition suggests that the population increase could be the result of an improvement in food availabilit

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1992.tb08387.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The diet of King PenguinsAptenodytes patagonicaat Possession Island was studied in February 1989 by analysis of 20 stomach contents collected from adult birds, just before they fed their single chicks. The mean mass of the samples was 1.84 kg, equivalent to 15% of the unladen adult body‐mass. Fish accounted for 99.8% and squids for 0.2% by mass. The main prey were mesopelagic myctophid fish which live in dense shoals and perform a daily vertical migration. Subadults/adults ofElectrona carlsbergiand juveniles and subadults/adults ofKrefftichthys anderssonirepresented 73.7 and 13.4% of the diet by mass, respectively. No difference was found in the diet of male and female King Penguins. Comparison of individual samples suggests that these birds catch a large quantity of fish from only a limited number of shoals. The mean caloric content of the food was 7 kJ/g wet mass. The total energy requirement of each chick during its initial period of growth was estimated to amount to 328,000 kJ, equivalent to 55 kg of food. The rate at which energy was delivered to the chick was calculated to be 50 W during this perio

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1992.tb08388.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

From 1986 to 1988, 30 Spanish Imperial Eagle Aquila adalbertinestlings, equipped with radio transmitters, were studied in Doñana National Park, southwestern Spain, to evaluate factors that determine when the young become independent. The results support the view that the dependence period is composed of two different periods, each representing almost half the total, and so the variations produced in one affect the overall period. The first part of the dependence period begins with leaving the nest and ends with the first soaring flight. The duration of this period is related to the physical condition of the young. The second period extends from the first soaring flight to the date of independence. Its duration is strongly related to hatching date. The young are not forced to become independent because of parental aggression. Aggressive behaviour allows the parent to evaluate the flight capacity of the young

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1992.tb08389.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

KittiwakesRissa tridactyla(683 chicks and 64 adults) were examined for ectoparasites in three breeding areas: Isle of May (Firth of Forth, Scotland; eight colonies of approximately known age of occupation on natural sites), North Shields and Gateshead (Tyne and Wear, England; well established colonies of known age on buildings). All the 208 ticks collected wereIxodes uriae.On the Isle of May, a colony which had only been established for 7 years was already infested by ticks. Tick incidence increased significantly with the length of colonization of the area during the first 30 years. Age of colonization did not have an effect after 30 years. In Gateshead only a single adult among the 127 birds examined had a tick. No ticks were found on the 106 chicks born at North Shields checked in 1987 or in 1988. However, among nine visiting newly‐fledged chicks from neighbouring colonies caught at the North Shields colony, six had either ticks or scars of previous infestation. Some visiting chicks remained for several days in the host colony and were even fed by the owners of visited nests.Ixodes uriaemay thus spread from one colony to another during visits of newly‐fledged infested chicks to neighbouring colonies. The absence of any infestation in old colonies (38 years in North Shields and 17 years in Gateshead) on buildings that are regularly visited by newly fledged infested chicks, suggests that buildings may lack the rock refuges necessary for tick survival from one year to the next. In this respect Kittiwake colonies on buildings are rather atypi

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1992.tb08390.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The total energy metabolized (TME) by nestling birds, from hatching to fledging, scales asM1.06, with body‐mass at fledging (M) explaining 97% of the variation in TME. After statistically removing the effects of body‐mass, multiple‐regression analysis reveals that 69% of the variation in TME is explained by nestling developmental rate, expressed as the time to fledging (tfl, days). Togethertfland M explain 99% of the variation in TME for the 30 species considered (Mrange 9.7 to 3700 g).Peak daily metabolized energy (DME, kJ/day), the maximum rate at which parents must provision their nestlings, scales with fledging mass as M0.78. Body‐mass explains 96% of the variation in nestling peak DME, with 37% of the residual variation being attributable to the time taken to fledge (tfl). Together,tflandMexplain 97% of the variation in peak DME. An examinination of residuals indicates that adaptive modifications in nestling energetics are attained principally through changes in growth rate, which affect TME and peak DME oppositely. Doubling nestling growth rate increases peak DME by 61%, but decreases total nestling energy demand (TME) by 77%. This opposing effect complicates evolutionary interpretations of avian reproductive p

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1992.tb08391.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Evidence of breeding during the dry season is given for 31 species of lowland birds in montane and semi‐montane areas in western Cameroon. At least 17 of these species are shown to breed in the wet season at lower altitudes in West Africa. This reversal of breeding season may be due to the unusually heavy rainfall and high humidities which cause temperatures to decrease more rapidly with altitude than on mountains with drier climates. Low temperatures and heavy rainfall during the wet season prevent almost all montane species from breeding then, and affect similarly the lowland birds whose ranges overlap with those of montane birds. Breeding seasons of some lowland species in Cameroon have previously been considered prolonged, but separation of breeding records by altitude reveals clear seasonalit

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1992.tb08392.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The Reed WarblerAcrocephalus scirpaceusis a largely monogamous insectivorous passerine in which males and females provide equal care by day to eggs and chicks. Polygyny occurs occasionally, with males leaving one female unaided. When females were temporarily removed from three recently‐completed clutches their males deserted and resumed the high song levels typical of unmated males. Males may desert either because they are physically incapable of incubation or because the energy expenditure needed for a male to return to an equivalent stage in the breeding cycle is much lower than for a female to do so. Widowed females (n = 7), however, continued the breeding attempt alone, with similar incubation levels but higher provisioning rates than those of control females. In three out of four mid‐season broods raised by lone females all fertile eggs were reared to healthy fledglings (in the fourth brood the female died), while only one of four late‐season nests produced any fledglings (which were underweight). Late‐season control nests were as successful as earlier ones. Loss of male help led to starvation of chicks, but caused no adverse effects during incubation. This explains the small changes in widows' sitting levels during incubation, but much greater effects after hatching. Females may need male help to rear late broods (but not early broods) as days are shorter and food is scarcer. Males may normally help at nests, even those in the mid‐season, because in stressful spells (even for a few days) such help is vital for successful breeding but in good periods it costs the ma

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1992.tb08393.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

In many populations of birds there is a seasonal change in the mean mass of eggs in the clutch. This might be caused by seasonal changes in the costs of egg‐production, or changes in the benefits of laying eggs of different size. In the BlackbirdTurdus merulathe mean mass of an egg correlated specifically with the air temperature during the period when it was predicted to be undergoing rapid follicular growth. There was no residual effect of date or day‐length on egg‐mass when statistically controlling for temperature during the period of rapid yolk synthesis, yet temperature still had a significant effect when controlling for date or day‐ length. Thus the seasonal increase in egg‐mass appears to be due to changes in the cost of egg‐production, not changes in the benefits of laying larger eggs. However, I could find no effect of food supply during laying on the mean mass of eggs in the clutch, either using an indirect measure of food availability, rainfall, or in a food‐supplementation experiment. This could be because females responded to extra food by laying earlier, and probably larger, clutches, rather than by increasing egg‐mass. The effect of temperature on egg‐mass increased through the laying sequence and there was a small seasonal increase in the mass of the last‐laid egg compared with the mean of the other eggs in the clutch. I propose that the mean mass of the last‐laid egg relative to the clutch mean, which can characterize a species or population, could evolve in response to the environmentally‐caused variance in the mass of the last‐laid egg: when the variance is high, the mean may have to be high to avoi

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1992.tb08394.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Begging activity in broods of MagpiesPica picawas measured as the average total number of begging nestlings and the number of nestlings giving begging calls between 5 and 9 days since the first nestling hatched. There was considerable between‐brood variation in begging activity relative to day‐to‐day variation within broods. Predation between 7 and 20 days of age was more frequent among those broods which had not previously suffered from brood reduction due to nestling starvation. Broods which were preyed upon showed significantly higher levels of begging activity than broods of a comparable size that were not preyed upon. In addition, the time elapsed from hatching to predation showed a negative correlation with the total number of begging nestlings. Within broods, those nestlings with the highest begging motivation (measured as the latency to respond when stimulated) seemed to be more readily taken by predators. These results confirm the existence of costs associated to begging in the form of an enhanced risk of being detected by pred

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1992.tb08395.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1992.tb08396.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY