bluuebunny/crossref_metadata_2025_split huggingface dataset:
The daily pattern of autumn bird migration in the northern Sahara
Authors: BIEBACH HERBERT , FRIEDRICH WOLFGANG , HEINE GEORG , JENNI LUKAS , JENNI‐EIERMANN SUSANNE , SCHMIDL DIETER 
Published: April 2008

The temporal pattern of migration by passerine birds during the night, and their arrival during the day at the Egyptian coast and in the northern Sahara Desert was investigated. The mean direction of nocturnal migration at the coast was south‐southeast, while at all desert sites it was south‐southwest.Birds arrived at the Egyptian coast only during the second half of the night which is explained by the fact that no birds could have taken off from the Mediterranean Sea. At least some of the birds landed at the coast where they spent the day before taking off shortly after sunset. These birds passed the desert sites at the expected time of day assuming a ground speed of 18 m per second. However, the origin of the birds passing the desert sites early at night is unclear. They must either have spent the day in the desert north of the study sites or they had overflown the Egyptian coast in the afternoon without landing.The landing of birds during the day at the desert sites was bimodal. This pattern of arrival is explained either by some birds having landed at the Egyptian coast in the early morning before continuing, or by deteriorating conditions later in the day during flight or when resting in the desert, that obliged them to seek shelter at the desert sites.A correlation between the number of migrants observed during the night and the number of resting birds in the desert on the following day suggests that an unknown proportion of birds might regularly use an intermittent migratory strategy that includes rest periods by day when crossing the desert, whereas others might adapt a non‐stop migratory strategy.
Winter movements and habitat use by Cabot's Tragopans Tragopan caboti in southeastern China
Authors: YOUNG L. , ZHENG G. M. , ZHANG Z. W. 
Published: April 2008

The endangered Cabot's Tragopan Tragopan caboti is endemic to the lower montane forests of southeastern China. Three individuals in Wuyanling Natural Reserve were radiotracked over the winter of 1987/88 to study their movements and habitat use. Home ranges varied from 2.9 to 20.0 ha, declining in size in December.Marked individuals used areas with thick undergrowth, a greater percentage of bare ground, proximity to water sources and a gentle slope. Also selected were areas containing an abundance of fallen nuts of Lithocarpus sp., Cyclobalanopsis (= Quercus) sp. and the seed capsules of Schima superba. The tree Daphniphyllum macropodum was important for roosting and the leaves and fruits were eaten.Conservation of the Cabot's Tragopan will depend on protection of its remaining forest habitat, including habitat management to ensure the continued availability of the essential habitat features identified in this study.
Effects of density‐dependence and weather on population changes of English passerines using a non‐experimental paradigm
Authors: GREENWOOD JEREMY J. D. , BAILLIE STEPHEN R. 
Published: April 2008

The Common Birds Census documents changes in the populations of the more abundant British land birds. Here we analyse the CBC data for various English passerines to discover the separate effects of weather and of density‐dependent feedback on their annual population changes. Density dependence is generally apparent in the data from woodland plots, less so in those from farmland. There are clear effects of weather, particularly in farmland. Prolonged snowfall in winter reduces populations of most species; frost and low temperatures appear much less important. Rainfall in March and April increases numbers censused in the spring but this may be an artefact. We discuss ways in which analyses such as these should be taken forward.We consider whether this work is respectable science, arguing that monitoring through the CBC goes much further than mere surveillance of numbers, that such monitoring is important in wildlife management, and that density dependence is not a bankrupt paradigm. Long‐term data gathering is an essential part of ecological science, even in programmes not designed at the outset to test specific hypotheses.
Sex‐biased mortality in the Lesser Black‐backed Gull Larus fuscus during the nestling stage
Authors: GRIFFITHS R. 
Published: April 2008

Theory predicts that skewed progeny sex ratios should be relatively common in vertebrate populations. In most birds this has proved hard to substantiate due to the difficulties associated with identifying the sex of large samples of chicks. This study reports the success of a new molecular DNA technique in determining the sex of 601 newly‐hatched Lesser Black‐backed Gulls Larus fuscusThere was no evidence of any adaptive sex ratio within broods. Male chicks were found to be disproportionately large and to grow at a faster rate than females. The overall sex ratio changed significantly from 0.484 (male/male + female) at hatching to 0.399 by fledging, probably due to male susceptibility to starvation. Mortality also increased significantly with hatching order, an effect often observed in species like the Lesser Black‐backed Gull where hatching is asynchronous. I discuss the possibility that hatching asynchrony may in fact be a strategy employed to prevent excessive skews developing in progeny sex ratio whenever variable differential mortality is likely.The results appear to vindicate Fisher's (1930) hypothesis which predicts the overproduction of the ‘cheaper’ sex. However, as the skewed sex ratio may be determined more by unpredictable environmental factors, such as food supply and weather conditions rather than parental strategy, this interpretation should be treated with caution.
Effects of DDT on the Fish Eagle Haliaeetus vocifer population of Lake Kariba in Zimbabwe
Authors: DOUTHWAITE R. J. 
Published: April 2008

Twenty clutches were collected from nests of Fish Eagles Haliaeetus vocifer at Lake Kariba, Zimbabwe, and a small dam nearby in 1989‐90. Unaltered DDT, and metabolites DDD and DDE, were found in every egg. Mean levels of σDDT(= DDT + DDD + DDE) generally varied from 14 to 49 mg/kg dry weight per clutch, but 113–223 mg/kg dry weight were found in clutches from the eastern end of the lake and the mouth of the Sengwa River. SDDT and DDE levels were significantly correlated with the Ratcliffe Index of eggshell thickness. Comparison with museum specimens showed that the Ratcliffe Index has declined by 11% since 1936‐41 due to a significant fall in shell weight. Eggshell thinning exceeded 20% at the eastern end of the lake.Aerial surveys in 1987 and 1990 found that hatching success along the southern lakeshore exceeded 72%, but chicks were seen in fewer than half the nests at the eastern end. However, the density of breeding pairs was greatest here.Residue levels have increased by about 8% since 1980, rising more steeply in areas recently sprayed for tsetse fly control and falling in others. The threat from DDT may now be receding as regional use has declined and will end, for tsetse fly control, by 1995. None was used for this purpose in 1991. Mercury levels in adult birds were very high and may pose a significant risk.The breeding population may be limited by availability of safe nest sites. Chicks are sometimes eaten by people. Settlement along the lakeshore is increasing and safe sites are becoming scarcer as dead trees in the lake collapse and large trees onshore are destroyed by elephants.
The attendance and absence of adult Kittiwakes Rissa tridactyla from the nest site during the chick stage
Authors: COULSON J. C. , JOHNSON M.P. 
Published: April 2008

In recent years there have been indications that the attendance of Kittiwakes Rissa tridactyla at the nest whilst containing young has changed, possibly influenced by food shortage. This paper examines the attendance of parents at the nest at North Shields, England, at a time when the breeding success was high and there was no indication of food shortage. It was evident that there was considerable variation in the attendance of individual parents, and chicks were left alone for the first time between 9 and over 40 days after hatching. Chicks were left alone overnight more frequently than during the day; this is related to the much longer overnight feeding trips by the parents.The recording method used in this study gave a continuous trace of the presence of each adult, and it has been used to calculate the errors made from spot observations.
Diet and habitat use of the Dotterel Charadrius morinellus in Scotland
Authors: GALBRAITH H. , MURRAY S. , DUNCAN K. , SMITH R. , WHITFIELD D. P. , THOMPSON D. B. A. 
Published: April 2008

The feeding ecology of Dotterel Charadrius morinellus adults and chicks was studied on three Scottish breeding areas. On the basis of 2324 prey items identified from 234 faeces, we show that (i) birds feed selectively and (ii) age‐related and seasonal differences in food selection occur.The diet comprised mainly beetles (Coleoptera), sawflies (Symphyta) and the adults and larvae of Tipula montana. The faeces of adult Dotterel contained a high proportion of beetles, whereas chick faeces had more soft‐bodied prey. However, when T. montana adults emerged en masse (every second year) both adults and chicks took more tipulids. On one area, larval T. montana comprised much of the diet soon after the birds arrived on their breeding grounds and just before leaving in autumn. The preferred feeding habitats were flat or gently sloping Racomitrium lanuginosum or Juncus trifidus heaths or the transition zone between moss heath and montane bog. Dwarf‐shrub, grass‐dominated and single bog communities were avoided. The preferred feeding habitats were those in which pitfall trap catches of the main prey were highest. A close juxtaposition of montane bog and R. lanuginosum heaths met the feeding requirements of both chicks and adults, respectively. Recent changes in the breeding distribution of Dotterel in Britain may be related to de‐ terioration in feeding and breeding habitat due to overgrazing by sheep and greater habitat acidification.
Immediate and delayed effects of a gale in late spring on the breeding of the Shag Phalacrocorax aristotelis
Authors: AEBISCHER N. J. 
Published: April 2008

At the beginning of May 1982, a westerly gale destroyed or damaged 49% of 761 Shag Phalacrocorax aristotelis nests on the exposed west side of the Isle of May, southeast Scotland; 518 nests on the sheltered east side acted as controls against which to assess subsequent effects of the gale on Shag reproduction and recruitment.On sites affected by the gale, 90% of pairs rebuilt their nest and laid a second clutch, on average 18 days after the loss of the first one. First‐time breeders nested closer to the sea, suffered greater damage to their nests, and deserted their damaged nests more readily after the gale than did experienced ones; a quarter of potential recruits to the west side were deterred from breeding in that year.By the end of the season, the number of chicks fledged per pair was 31% lower on the west side than on the east. The difference was caused partly by nest desertion, partly by greater hatching failure of full clutches in apparently undamaged nests and especially by lower fledging success of pairs that renested. Irrespective of breeding experience, delayed early breeders produced more chicks than late breeders nesting at the same time, showing that late breeders were of poorer intrinsic quality than early breeders. This was one reason for a seasonal decline in Shag productivity, although environmental factors also played a role.During April‐July, gales like that of May 1982 occur on average once every 5 years on the Isle of May. Despite the disruption that they may cause to nesting Shags, the impact on the long‐term growth of the colony is small.
Latitudinal variation in the body‐size of Sparrowhawks Accipiter nisus within Britain
Authors: WYLLIE I. , NEWTON I. 
Published: April 2008

On the basis of Sparrowhawks Accipiter nisus found dead in various parts of Britain during 1979–1991. wing‐length was found to provide the most reliable index of overall body‐size because it gave the best and most consistent correlations with five other measures of body‐size.A marked latitudinal trend in the body‐size of Sparrowhawks was found within Britain, with birds of each sex and age group increasing in size from south to north, in line with Bergmann's Rule. For each successive degree of latitude (approximately 110 km), wing‐length increased by an average of 0.86 mm in adult males and O.75 mm in adult females. No obvious west‐east trend in body‐size was found within Britain.
Relationship between breeding and wintering ranges in Palaearctic‐African migrants
Authors: NEWTON I. 
Published: April 2008

During the northern winter, Palaearctic migrant species are not evenly distributed within sub‐Saharan Africa. Species numbers are greatest in a belt of savannah, lying south of the Sahara, and decline southwards. For any one latitude, species numbers are also greater in the east of Africa than in the west. Only about 3% of 187 species winter exclusively south of the equator, but other species migrate from north to south during the course of the northern winter.For 62 Palaearctic species which winter entirely in Africa, the areas of breeding and wintering ranges are strongly correlated. With some exceptions, species with the largest breeding ranges also have the largest wintering ranges. However, in 69% of species, the breeding range is larger than the wintering range, whereas in 31% of species the wintering range is larger. On average, the wintering ranges of 57 landbird species cover about two‐thirds the area of their breeding ranges, and in many species only parts of the wintering range may be occupied at any one time. This implies that the per area carrying capacity of African wintering areas is greater than that of Eurasian breeding areas.The general correlation between the sizes of breeding and wintering ranges may have its basis in ecology, with generalists able to occupy wider areas than specialists in both breeding and winter quarters. At the same time, the correlation may result partly from an effect of numbers on range size, in that species which have a wide range at one time of the year may then achieve large numbers which occupy a wide range at the other time of year.
Body size establishes the scaling of avian postnatal metabolic rate: an interspecific analysis using phylogenetically independent contrasts
Authors: WEATHERS WESLEY W. , SIEGEL RODNEY B. 
Published: April 2008

The avian postnatal metabolic rate literature is reviewed using power equations,Y = aMb,to describe the relation between postnatal resting metabolic rate (RMR) and chick body mass (M) for 25 species. In altricial species, the relation between RMR andMfrom hatching to fledging can be described by a single power equation, whereas in most nonaltricial species two such equations are needed, one for chicks weighing less than about 25% of mature mass (Ma) and a second for larger chicks. For altricial chicks and larger nonaltricial chicks, the body‐mass exponent,b,of 25 intraspecific power equations ranged from 0.25 to 1.67 and varied inversely withMa. The scaling of postnatal RMR is thus unlike that of either adult or hatchling metabolism in that it is size dependent. We examined the relationship between intraspecificbandMausing Felsenstein's independent contrasts method to control for statistical complications due to the hierarchical nature of phylogenetic relationships. This “phylogenetic regression” technique yielded the relationb= 1.6Ma‐015, in which mature mass explained 38% of the variation inb.The mass exponent of this equation (‐0.15) did not differ significantly from that determined by nonphylogenetic methods (‐0.17).In altricial chicks and larger nonaltricial chicks, the scaling coefficient,a,of the interspecific power equations varied with adult mass according to the phylogenetically determined relationa(kj/h) = 0.0052Ma0.65and was higher in fed than in fasted chicks. Equations derived in this analysis permit one to estimate the RMR of a growing chick from its mass and adult body mass and provide a basis for evolutionary and ecological comparisons.
Differences in reproductive success and parental qualities between habitats in the Great Tit Parus major
Authors: RIDDINGTON R. , GOSLER A. G. 
Published: April 2008

Reproductive success and parental attributes of Great Tits Parus major nesting in good and poor habitats were compared to investigate whether they differed and, if so, whether parental or environmental variation contributed most to the differences.Monitored over 3 years, clutches in mature woodland were started earlier, were larger and produced larger broods of heavier chicks than those in marginal habitats such as gardens and hedgerows. Fledging success was significantly higher in woodland in 2 of the 3 years although egg weights were lower. Parents nesting in different habitats were very similar in body‐size although those in woodland were in better condition. The prey delivered to nestlings in woodland was of significantly higher quality than that delivered in marginal habitats. Furthermore, the heritability of body‐size (tarsus‐length) was higher in woodland, suggesting that the environment limits nestling growth in poorer habitats. Reproductive success was considerably lower in poor habitats and appears to be constrained primarily by environmental quality, although this may operate partly through its affect on parental body condition.
Diagnosing causes of bird population declines
Authors: GREEN R. E. 
Published: April 2008

The value to bird conservation of determining the causes of population declines is considered and the diagnostic methods available are reviewed, with examples. Diagnosis of the cause or causes of a decline in bird numbers is likely to be helpful in deciding the priority of conservation actions, though actions which aim to reverse the changes in external conditions which caused the decline need not be the most effective in initiating recovery.The methods for diagnosing causes of declines in bird numbers with the widest application make use of comparisons between geographical areas or time periods with different trends. Correlations between trends in numbers and measurements of external factors are examined across areas or periods or both. The danger of spurious correlations is minimized by drawing up a list of plausible causes based on studies of the natural history of the species. The effects of all of these candidates should be examined, subject to availability of data. The consistency of observed changes over time, or differences among areas, in survival rate or breeding success with the postulated demographic mechanism of the decline should be examined.Conclusions based on correlations across geographical areas between trends in numbers and external factors may be misleading if birds are able to move between the areas selected for comparison and if their pattern of settlement depends upon external factors thought to be implicated in the decline.Manipulative experiments should be carried out to test conclusions drawn from correlative studies. However, it must be recognized that the capacity of birds to move between areas means that experiments may measure effects of manipulations on settlement patterns or distribution rather than population size. Experiments that appear well designed in terms of controls and replication may be misleading when applied to the conservation of bird populations if their geographical scale is inappropriate.
Eggs, egg formation and the timing of breeding
Authors: PERRINS C. M. 
Published: April 2008

The eggs of birds contain all the nutrients necessary for the developing embryo. The female has to obtain these nutrients, and while in some species these may be gathered and stored over a period of time, in many species they seem to be obtained on a daily basis. Obtaining the calcium necessary for the eggshell may pose special problems for some species, which may have to give up valuable feeding time in order to search for calcium.Egg size varies considerably, even within species, and the reasons for this are not clear. In the Great TitPants major,large eggs produce nestlings which have a higher chance of hatching, surviving to fledging and surviving after fledging. However, large eggs require the female to acquire more nutrients to form them, and large chicks may sometimes be at a disadvantage. The amount of energy required to form a larger egg often seems small unless the metabolic costs of egg formation are taken into account.
Consequences of a female‐biased sex‐ratio in a socially monogamous bird: female‐female pairs in the Roseate Tern Sterna dougallii
Authors: Nisbet Ian C.T. , Hatch Jeremy J. 
Published: April 2008

In the socially monogamous gulls and terns, female‐biased sex ratios are sometimes revealed by the occurrence of ‘supernormal clutches’, which are usually attended by female‐female pairs or other multi‐female associations. We studied these phenomena in the endangered Roseate TernSterna dougalliiat Bird Island, USA, from 1970 to 1995. DNA‐techniques were used to sex breeding adults in 1992–94.Supernormal clutches (with three or four eggs) have comprised 1–7% of all Roseate Tern clutches at Bird Island since at least 1970, probably increasing in frequency since 1980. Supernormal clutches were spatially clustered; most were laid late in the peak period of nesting during each season. More than 80% of supernormal clutches and at least 7% of normal clutches were attended by multi‐female associations; most of these were female‐female pairs, with a few trios (male + two females, or three females) and one quartet (four females). More than half of the multi‐female associations attended normal clutches. Some female‐female pairs were maintained for up to five years. The age‐distribution of females mated to females did not differ significantly from that of females mated to males. Females mated together usually laid eggs synchronously (±2 days). Such females laid fewer eggs than females mated to males (means 1.20 versus 1.73), and had lower fertility and hatching success (about 46% versus 98%); they were less successful in raising young from eggs that did hatch (means 58% versus 73%), but this difference was not significant. Their overall breeding success was much lower (about 0.34 fledglings per female versus 1.35). The sex‐ratio of breeders was about 127 females to 100 males; about 20% of breeding females did not have male mates. Female Roseate Terns that do not obtain male mates appear to be of low phenotypic ‘quality’ ‐ based on late laying, small clutches and small eggs. Our data support the hypothesis that such females have a higher fitness if they mate with each other and raise a few young than if they do not breed at all.