bluuebunny/crossref_metadata_2025 huggingface dataset:
Breeding populations of the Hobby Falco subbuteo on farmland in the southern Midlands of England
Authors: FULLER R. J. , BAKER J. K. , MORGAN R. A. , SCROGGS R. , WRIGHT M.
Published: April 2008

Site occupancy, dispersion, density and nest sites of Hobbies Falco subbuteo were studied in two areas of farmland in the English southern Midlands between 1975 and 1983. Nesting ranges were identified within which Hobby nests were regularly found but which contained only one pair of birds in any one year. Breeding was not proved in all nesting ranges in every year. Within nesting ranges, birds sometimes used the same nest in consecutive years but nests were also commonly found more than 1 km apart in consecutive years. The mean nearest‐known‐neighbour distance between simultaneously occupied breeding sites was 4 6 km (range 20‐9.6 km) and the minimum estimated densities of Hobbies in the two study areas were 3.8 and 4.8 nesting ranges/100 km. Small inter‐nest distances, less than 30 km, were recorded only in the area with the lowest density. Hobbies nested in old Crow Corvus corone nests in a wide range of tree species but prior to the onset of Dutch elm disease, elms Ulmus spp. were probably used almost exclusively in one of the areas. It is concluded that substantial numbers of Hobbies nest on farmland north of the River Thames, outside what has been traditionally regarded as the main range of the species, and that previous published estimates of the size of the British population have been far too low.
Reproductive endocrinology of the Wandering Albatross Diomedea exulans in relation to biennial breeding and deferred sexual maturity
Authors: HECTOR J. A. L. , CROXALL J. P. , FOLLETT B. K.
Published: April 2008

The reproductive endocrinology of the Wandering Albatross Diomedea exulans was studied at South Georgia to investigate the potential endocrine correlates of biennial breeding and of the acquisition of sexual maturity. Gonads of breeding birds and of known‐age immature birds of both sexes were examined by laparoscopy throughout the period that they were at the nest site. Blood samples, subsequently analysed to determine concentrations of luteinizing hormone (LH), prolactin, progesterone, testosterone and oestradiol‐17/i, were obtained from samples of breeding birds of both sexes at regular intervals from first arrival until the chicks fledged nearly a year later. Before laying in December, breeding birds had mature testes and ovarian follicles and high concentrations of LH, prolactin and sex steroids. Gonadal regression and a rapid drop in hormone levels (except for LH in females) occurred in early incubation (January). Testes (and follicles to a lesser extent) enlarged in mid‐incubation, coinciding with high levels of LH and increases in prolactin and testosterone. Gonads finally regressed completely near hatching time. LH, prolactin and testosterone remained at low levels throughout chick rearing (April to November), but females had several periods of active progesterone and oestradiol secretion, and progesterone was detectable in males only late in the chick‐rearing period. Although some changes in hormone levels are difficult to explain, the patterns are fairly typical of temperate birds. The persistence of progesterone secretion in both female breeders and non‐breeding ‘immature’ birds is viewed as part of a mechanism inhibiting an ovary from becoming vitellogenic. Although testis size and testosterone concentrations increased with age in immature males (of ages 4–10 years), birds of 5 years and older are probably physiologically mature, even though breeding does not start until they are 7 years of age and only half an age group has bred by an age of 11 years. Immature females (of age 4–7 years) had undeveloped follicles, very low oestradiol concentrations but high progesterone levels, providing further support for the role of this hormone in inhibiting gonadotropin secretion. The condition of the female is therefore probably decisive in determining when a pair first attempts to breed but it is unknown what factors initiate normal ovarian development.
The relationship between dominance behaviour, bill size and age group in Greater Sheathbills Chionis alba
Authors: SHAW P.
Published: April 2008

A dominance hierarchy developed within a wintering flock of Greater Sheathbills which fed regularly at a concentrated artificial food source. Each bir's dominance position was determined from the proportion of interactions in which it was displaced, and from the number of other birds which it was seen to displace.

Most dominant birds were known to be over 6 or 7 years of age. They had larger bills than their subordinates had and initiated displacement interactions more often. After each interaction the displacer resumed feeding more quickly than the bird it displaced. Although dominant birds had a higher average peck rate, they did not maintain a higher body mass throughout the winter, nor did they show a higher survival rate than their subordinates.
Behaviour and breeding biology of the cooperatively breeding Grey‐backed Fiscal Shrike Lanius excubitorius in Kenya
Authors: ZACK STEVE
Published: April 2008

Grey‐backed Fiscal Shrikes Lanius excubitorius were studied over a 2j year period near Lake Naivasha, Kenya. Grey‐backs are cooperative breeders, with group sizes ranging from two to II. Only one pair breeds per group, with all other group members aiding in the rearing of young. The study population ranged from 64 to 79 individuals that occurred in from 13 to 16 groups. Non‐breeding helpers made up to 66% of the population, with male helpers being more numerous overall than females. The annual survival rate was 65%, with no differences detected between the survival of males and females, or of breeders and helpers. Only male helpers were observed to acquire breeding status within the natal territory. Some female helpers acquired breeding positions in territories adjacent to their natal territories. Group territorial displays occurred throughout the year but were most pronounced prior to breeding during rainy periods. Reproductive success was very low, with only 14.5% of the recorded breeding attempts leading to fledged young. Large groups (four or more birds) had greater reproductive success than small groups, but many factors other than, or in addition to, group size may have influenced this pattern. The breeding male contributed the most food to the incubating female and to the nestlings. Male helpers and the breeding female contributed more to nestlings than did female helpers. Observations on the post‐fledging period indicate that socialization and establishment of dominance may be of importance in group‐living species living in a restricted ecological and social setting.
Population status of Common Guillemots Uria aalge at a colony in western Alaska: results and simulations
Authors: MURPHY EDWARD C. , SPRINGER ALAN M. , ROSENEAU DAVID G.
Published: April 2008

Colony‐wide boat‐based censuses suggest that numbers of Common Guillemots at Bluff, Alaska declined markedly in the late 1970s and remained low until 1983. Annual land‐based counts of study plots since 1979 generally showed no trend. However, numbers declined substantially in one study area between 1978 and 1983. Reproductive success varied considerably among years and was highest in moderately warm summers. Simulation analyses suggest that the changes in numbers cannot be attributed to changes in reproductive success several years previously. Thus, factors affecting survival, presumably in winter, are apparently implicated in the declines.
Prey profitability for adult Grey Herons Ardea cinerea and the constraints on prey size when feeding young nestlings
Authors: MOSER M. E.
Published: April 2008

Patterns of handling time and profitability are examined for adult Grey Herons feeding on carp, eels and catfish. Handling times generally increased with prey size but were influenced markedly by the morphology and behaviour of the prey. Profitability was highest for carp (max. 0.9 g/s for 15–20 cm fish), lowest for catfish (max. 0.05 g/s) and intermediate for eels (max. 0.1 g/s). Nestlings were unable to ingest the sizes of fish most profitable for the adults to consume until aged 20 days; by the age of 30 days, they could consume the full size‐range of prey taken by the adults. In order to feed their young chicks, adults must therefore either select smaller prey, or break their large prey into smaller pieces. The diet of nestling Grey Herons in the Camargue is examined for evidence to support or refute the former hypothesis.

Young nestlings (≤20 days) regurgitated smaller carp than old nestlings (> 20 days). Comparison of prey types in the diet of the two groups showed that small prey species occurred significantly more often in the diet of young chicks, while the converse was true for larger prey species. The occurrence of particular prey types in the diet only of young chicks suggests that adults may forage in more marginal, shallower water (where small prey are probably more abundant) to meet the requirements of their brood during the early part of the nestling phase. The second hypothesis, that the adults break down large prey into smaller pieces, was not examined, although evidence from other studies suggests that this does occur; both mechanisms may therefore be important.
The breeding biology of White‐tailed Tropicbirds Phaethon lepturus at Cousin Island, Seychelles
Authors: PHILLIPS N. J.
Published: April 2008

During 1981–1983 the population of White‐tailed Tropicbirds Phaethon lepturus at Cousin Island, Seychelles, bred aseasonally and asynchronously. The mean interval between consecutive successful breeding attempts was 273 days. Most individuals nested in the same site, and with the same partner, in successive attempts, but 7‐5% of nest sites were used by more than one pair; 21 % of pairs which lost eggs, and 13% of those which lost chicks re‐nested. Incubation lasted 40–41 days, with a mean incubation shift length of 6‐6 days. Fledging periods varied between 67 and 89 days (mean 76‐5 days). Mean fledging weight was not significantly greater than the average weight of breeding adults.

Fledging success was 36%. Many of the 39% of eggs which failed to hatch probably did so as a result of exposure to the sun's heat, following temporary desertion by adults which were themselves heat‐stressed during incubation. Of the 41 % of chicks which died, most died young; many were probably killed by crabs Ocypode spp. Not more than 10% of all nest failures were due to nest site competition. A few chicks probably starved to death.

At the time of the study, both food and nesting sites were evidently in excess. A considerable increase in the size of the population will be possible before density‐dependent control mechanisms begin to operate.
Inter‐ and intraspecific competition for nest holes in a population of the Collared Flycatcher Ficedula albicollis
Authors: GUSTAFSSON LARS
Published: April 2008

Field experiments with nest boxes show that nest holes are a limiting factor on the local population size of the Collared Flycatcher Ficedula albicollis. When this limiting resource occurs with different types that are quality related there is intraspecific competition among males for the best nest boxes, with bigger males being the better competitors. Population dynamics of Great Tit Parus major and Blue Tit P. caeruleus when compared with Collared Flycatchers suggests that there is strong interspecific Competition for available nest holes. This is also shown by removal experiments.
Individual differences in bait‐fishing by the Green‐backed Heron Ardeola striata associated with territory quality
Authors: HIGUCHI HIROYOSHI
Published: April 2008

Individual differences were found in the feeding sites, frequency of bait fishing, and fishing success in three individual Green‐backed Herons in southern Japan. The differences in the use of bait fishing and in fishing success seemed to be related primarily to differences in feeding sites, which were associated with territory quality. Bait fishing was used most frequently by the individual which fished often in open water with fewer suitable rocks, where the heron has to overcome the handicap of being easily seen by fish. Bait fishing was least common in the individual which fished most often from high branches. The leaves and twigs dropped from high branches rarely reached the spot the heron intended, and the fishing success was low. Individuals probably also differed in their skill at bait fishing.
Why are some birds polyterritorial?
Authors: SLAGSVOLD TORE , LIFJELD JAN T.
Published: April 2008

Whether a male bird is mono‐ or polyterritorial may be determined by several factors, but a polyterritorial system tends to be found when territories are easy to defend, male competition is not great and the period of defence is short.
Temporal and spatial patterns in the abundance of wintering Red‐breasted Mergansers Mergus serrator in an estuary
Authors: RICHNER HEINZ
Published: April 2008

Tidal, temporal and spatial aspects in the abundance of wintering Red‐breasted Mergansers in the Ythan estuary, northeast Scotland, were investigated. The number and location of birds were examined in relation to four variables: tidal cycle and tidal range, and month and time of day. A significant increase in the numbers of this piscivorous bird occurred as the winter progressed. Numbers were highest in early morning and then decreased significantly during the day. Spring tides were favoured over neap tides and a significant increase in numbers was recorded between low tide and high tide. The lower part of the estuary was preferred over the upper part with no detectable shift in the preference occurring in relation to any of the four variables.
Salinity as a constraint affecting food and habitat choice of mussel‐feeding diving ducks
Authors: NYSTRÖM K. G. KENNETH , PEHRSSON OLOF
Published: April 2008

Observations of freshwater drinking in Eiders feeding primarily on mussels led us to hypothesize that the highly saline sea water enclosed in mussels could cause salt‐related dehydration problems in the ducks, since they consume entire mussels. The proportion of sea water increases with increasing mussel size. Smaller duck species are more sensitive to the higher salt content of larger mussels than are larger ducks; however, salt stress may be avoided by feeding in habitats with lower salinity, by feeding on less salty food items, by utilizing smaller mussels, by drinking fresh water, or by employing low energy foraging techniques. A possible evolutionary strategy for solving the salt problem might be to increase body mass, enabling ducks to utilize larger mussels without passing an upper salt consumption limit. At the same time, foraging on larger mussels is more economical. Although large size facilitates the utilization of brackish and marine environments, it may be selected against in ducks breeding in fresh water, where fish competition may reduce optimal food item size. In conclusion, salinity is an important habitat barrier in both breeding and overwintering diving ducks, but there are various ways of crossing this barrier. To understand better how ducks utilize their habitats, however, it is necessary to measure habitat salinity levels and the size of both ducks and their preferred and less‐preferred food types.
The flightless period of free‐living male Teal Anas crecca in northern Sweden
Authors: SJÖBERG KJELL
Published: April 2008

A total of 126 flightless adult male Teal was caught in 1982 and 1983 in a moulting area in northern Sweden (63° 53′N). The birds were weighed and the stage of development of their primaries and secondaries measured. During the flightless period, the weight of the birds decreased by an average of 10% in 1982 and 19% in 1983. This weight decrease allows the birds to fly before their primaries and secondaries are full‐grown. The weight loss is considered to be an adaptation making it possible, for example, for lighter birds to escape predators sooner after moulting. Birds varied greatly in the dates at which they initiated their flightless period, that is, from the end of June to the end of July. Thus, it is probable that both local birds and birds from distant breeding grounds were present in the moulting area.
Interspecific variation in growth of British pigeons Columbidae
Authors: ROBERTSON HUGH A.
Published: April 2008

Growth patterns of nestling Collared Doves Streptopetia decaocto, Woodpigeons Columba palumbus, Feral Pigeons C. livia and Stock Doves C. oenas, in Britain were compared. Open‐nesting Collared Doves and Woodpigeons left the nest at about 60% of adult weight, hole‐nesting Stock Doves at adult weight, and partial hole‐nesting Feral Pigeons at an intermediate stage. Other species of pigeons and doves studied to date also fit this pattern. Stock Dove nestlings reared in nest‐boxes reached heavier weights and left the nest later than those in more exposed sites. These results were correlated with differential predation pressure on open‐ versus hole‐nesting birds.
The use of otoliths as indicators of Little Penguin Eudyptula minor diet
Authors: GALES R. P.
Published: April 2008

The validity of using otoliths from stomach contents quantitatively to determine the number and size of fish consumed was tested on Little Penguins. They were fed different meal sizes of known number and size of fish and the stomach contents were recovered after various time intervals. There were no differences in estimates of original fish size when calculated from otolith length or weight. Rate of digestion of otoliths tended to decrease with increased meal size but increased with time after ingestion. Digestion of otoliths proceeds rapidly and, if ignored, estimates of numbers of fish consumed and of original fish size can be significantly underestimated. This problem can be partially solved by inspection of otolith condition and restricting calculations of fish size to otoliths unaffected by digestion. Many factors introduce variations into rate of otolith degradation and further species‐specific studies are required before appropriate correction factors can be applied.
The social organization and behaviour of the Hoatzin Opisthocomus hoazin in central Venezuela
Authors: STRAHL STUART D.
Published: April 2008

The social organization and behaviour of the Hoatzin Opisthocomus hoazin, a cooperatively‐breeding folivorous bird, was studied in the central plains (llanos) of Venezuela. In this area Hoatzins nested in communal social units of two to eight individuals. Units were usually composed of a breeding pair and up to six helpers at the nest. Helpers, usually offspring retained from the previous years' nesting, aided in all breeding activities of their social unit except egg production. On the study site, Hoatzin units defended extremely small, all‐purpose territories along watercourses during the rainy (breeding) season, but migrated up to 2 km to areas with permanent water during the dry season. Nesting extended from early May to October. Nest and egg measurements and growth rates of young are provided. Nesting success was low (27%), primarily due to predation by Cebus olivaceus and several other species. Annual survival of adults and young was high. Young did not breed during their first year; 90% of yearlings remained on their natal territories as helpers. Females appear to be the dispersing sex. The results are discussed in relation to previous work on the Hoatzin. The demography of the study population fits the criteria for several recent theories regarding the evolution of cooperative breeding in birds.
Fine structural basis of the cutaneous water barrier in nestling Zebra Finches Poephila guttata
Authors: MENON GOPINATHAN K. , BAPTISTA LUIS F. , ELIAS PETER M. , BOUVIER MICHELE
Published: April 2008

Transepidermal water loss was studied in nestlings, fledglings and adults of the xerophylic Zebra Finch Poephila guttata. Nestlings lose little water (2–4 ppm/0–5 cm2/h) through the skin as compared to adults (60–70 ppm/0–5 cm2/h). Light and electron microscopic examination of the skin sections of both age classes revealed an abundance of lipids in the form of vacuoles and large multigranular bodies in the epidermis of nestlings, but few such lipid bodies in the epidermis of adults. Some of the disc‐like contents of granular bodies appear to be extruded into the intercellular spaces. Based on earlier studies with mammals and reptiles, it is concluded that epidermal lipids are the basis of the integumentary permeability barrier in nestlings.
The vocalizations of the Christmas Island Warbler Acrocephalus aequinoctialis, an island endemic
Authors: MILDER SHARON L. , SCHREIBER RALPH W.
Published: April 2008

We describe the vocalizations of the Christmas Island Warbler Acrocephalus aequinoctialis, endemic to Christmas and Washington Islands, central Pacific Ocean, in the absence of other land birds and natural predators. Its vocal signals are simple when compared to most Acrocephalus. We explain this simplicity as the result of a lack of interspecific interactions, a monogamous life style, large permanent territories, open dry habitat and limited interaction among neighbouring individuals.
Attendance patterns and behaviour in relation to experience and pair‐bond formation in the Wandering Albatross Diomedea exulans at South Georgia
Authors: PICKERING S. P. C.
Published: April 2008

Recruitment of Wandering Albatrosses Diomedea exulans to the breeding population at South Georgia took between 2 and 8 years after they first returned to their natal colony. In successive seasons, from first return to pairing, the date of arrival became earlier and the number of days spent ashore and the time spent interacting with other birds increased. Pairing birds arrived earlier and spent more time ashore than birds of similar experience which did not pair in that season. In the season following pairing they returned at the same time as breeding birds, but most did not breed; when ashore they spent much of their time alone or with their partner at the nest site. They left in mid‐season before other non‐breeders and bred the following season. Some birds accomplished this process by spending much time (50–60 days) ashore in two or three seasons but most birds spent a similar total time ashore spread over more seasons. Until the season prior to breeding, the number of birds of the opposite sex with whom interactions occurred was proportional to the amount of time spent ashore. There was, therefore, considerable scope for inter‐individual assessment of potential partners before interactions were confined essentially to a single partner in the season before the first breeding attempt.
Re‐use of courtship nests for quick remating in the polygynous Fan‐tailed Warbler Cisticola juncidis
Authors: UEDA KEISUKE
Published: April 2008

In a population of Fan‐tailed Warblers Cisticola juncidis near Osaka, Japan, the males were polygynous, building a succession of elaborate courtship nests within their territories, and advertising them to females. Nest desertion by females frequently occurred early in the breeding cycle. Deserted nests were generally left untouched, but 17 out of 88 territorial males cleaned and re‐used 20 of 79 nests deserted by females for their next courtship. The frequency of nest re‐use increased with season. Of the re‐used nests six (300%) were re‐occupied by secondary females. Newly built nests were preferred to the ‘second‐hand’ nests, probably because new nests were likely to last longer. Breeding success did not differ between the two categories of nests. In males, nest re‐use seems to save time and energy expenditure for additional mating.
Territorial behaviour of the Robin Erithacus rubecula: the importance of vegetation density
Authors: HOELZEL A. RUS
Published: April 2008

Robin Erithacus rubecula territories were mapped in an isolated copse of mixed deciduous woodland. An index of vegetation density, measured at numerous randomly chosen sites within the copse, was found to be higher in areas occupied by Robins. Both vegetation density and territory area were compared with measures of breeding success. In all cases vegetation density was correlated with breeding success and territory area was not. Possible evolutionary advantages to defending areas with dense vegetation are discussed.
Evidence for cuckoldry in the Great Tit Parus major
Authors: NORRIS K. J. , BLAKEY J. K.
Published: April 2008

We estimated the frequency of cuckoldry (the proportion of offspring resulting from extra‐pair copulations) in Great Tits Parus major using heritability estimates based on the resemblance of offspring tarsus‐length to that of their parents. Our results suggest that cuckoldry occurs and may be relatively common in certain years.
The breeding biology of Black GuillemotsCepphus gryllein Shetland
Authors: EWINS PETER J.
Published: April 2008

The breeding biology of Black GuillemotsCepphus gryllewas studied from 1982 to 1984 in Shetland, on islands lacking introduced mammalian predators. Adult survival (94%), clutch size (1.75‐1.92) and breeding output (1.05‐1.34 young fledged per breeding pair) were very high, indicating that conditions were relatively favourable on the islands studied. The timing of breeding varied significantly between years and was somewhat later than in other temperate parts of the range. In 1984 food was probably more readily available (possibly due to better weather conditions) in the pre‐breeding period, which enabled more inexperienced birds to reach the condition threshold for breeding. It is likely that these birds tended to lay single‐egg clutches in more open sites which were more susceptible to egg predation by crows. Nest‐site quality and food availability were the key determinants of breeding productivity.
Clutch‐size variation in the Pied Flycatcher Ficedula hypoleuca
Authors: JÄRVINEN ANTERO
Published: April 2008

Variation in clutch‐size of the Pied Flycatcher Ficedula hypoleuca was studied simultaneously in relation to latitude, longitude, altitude, laying date and habitat, using data from 103 areas from north Africa to north Norway (latitudinal range about 3900 km). Clutch‐size variation was significantly related to altitude and habitat, small clutches being laid at high altitude and in coniferous forests. In contrast to some earlier studies, latitudinal or longitudinal clutch‐size trends were not found.
Incubation rhythm in the Fulmar Fulmarus glacialis: annual variation and sex roles
Authors: HATCH SCOTT A.
Published: April 2008

I monitored the incubation schedules of Fulmars Fulmarus glacialis in an Alaskan colony by observing nests where the male and female were of different colour phases. Complete shifts of up to 16 days were recorded; the average shift in mid‐incubation was 4–6 days. Mean shift length was inversely correlated with hatching success in 5 years, suggesting that Fulmars adjusted their foraging patterns to annual differences in food availability. Males assumed the larger share (55%) of incubation on average, and a larger share in years with lower hatching success. Serial correlation in the length of incubation shifts had two components—the influence of prior shift lengths on time spent foraging and individual variation. Failure of the male to relieve the female soon after laying resulted in a few breeding failures and egg losses were associated with exceptionally long shifts throughout incubation.
The influence of age and sex on wing‐tip pattern in adult Black‐headed Gulls Larus ridibundus
Authors: ALLAINE DOMINIQUE , LEBRETON JEAN‐DOMINIQUE
Published: April 2008

A discriminant equation based on bill‐depth and total head‐ and bill‐length is provided to sex adult Black‐headed Gulls Larus ridibundus. This equation is used to sex birds of known age. Relationships between age and morphometrics and between age and the black extent on the wing are then investigated both in males and females. Size of birds did not change with age but the black extent on the wing tended to decrease with age in both sexes. The tendency to become lighter with age may he an expression of senescence.
Factors influencing family rupture and parent‐offspring conflict in the Black Kite Milvus migrans
Authors: BUSTAMANTE JAVIER , HIRALDO FERNANDO
Published: April 2008

Juvenile and adult behaviour was studied at eight nests of Black Kites Milvus migrans within the Doñana Biological Reserve, Spain. Parental investment in vigilance and defence of offspring progressively decreased during the post‐fledging dependence period. The number of feeds was also slightly reduced towards the end of the period. However, this does not seem to be the main factor which leads to juvenile independence. The fact that the family rupture is sudden and that the post‐fledging dependence period tends to shorten as the season progresses suggests that juvenile and adult migratory urgency may be as important a factor as reduced parental investment in breaking the family ties.
Birds and zoonoses
Authors: COOPER JOHN E.
Published: April 2008

Birds may harbour many organisms, some of which can be transmitted to humans (zoonoses) and domestic livestock. Certain zoonoses are of considerable importance and their control may necessitate changes in management of bird populations. If problems relating to zoonoses are to be effectively tackled there is a need for closer collaboration between ornithologists and those concerned with public health, more research on avian diseases and the collation of relevant data.
Bird behaviour and environmental planning: approaches in the study of wader populations
Authors: GOSS‐CUSTARD J. D. , le V. ditDURELL S. E. A.
Published: April 2008

Predicting the effect of changes in land‐use on bird populations requires a degree of understanding of their population dynamics which is seldom available. Such knowledge is especially difficult to acquire if the birds occupy a variety of habitats of differing quality and they are also migratory. The effects of habitat loss at a particular time of year on the year‐round population dynamics are then difficult to predict. The problem is discussed using wintering waders as examples. Unless a species can extend its present range, the initial effect of habitat loss is to increase bird density. Whether this affects population size will depend on whether bird density affects either winter survival or subsequent breeding success. Measuring such density‐dependent relationships is in practice extremely difficult in migratory populations. However, behavioural studies help in testing the key hypothesis that birth and death rates are affected by bird density, and may even allow the form of any density‐dependent functions to be deduced. Simulation modelling then allows the effects of habitat loss on the overall population dynamics to be explored. The general point is that behavioural studies play an important part in Environmental Impact Studies because behaviour is the main way in which birds respond to environmental changes and compete for limited resources, such as diminishing habitat. They are therefore likely to provide insights when making predictions about the responses of birds and populations to habitat loss.
A new species of nightjar from Zaïre
Authors: LOUETTE M.
Published: April 2008

Prigogine's Nightjar Caprimulgus prigoginei is described from a single skin collected in 1955 in Itombwe, eastern Zaïre. The species is unknown in life. Because of its distinct morphology: rather stiff feathers, small tail/wing proportion, broad head, short rictal bristles and its speckled plumage, it is considered to be without close relatives.
The effect of food on laying date and clutch‐size in Tengmalm's Owl Aegolius funereus
Authors: HÖRNFELDT BIRGER , EKLUND ULF
Published: April 2008

The breeding of Tengmalm's Owl Aegolius funereus was studied at Umeå, Sweden, during the 1984–85. Mean clutch‐size was one egg larger in 1984 than in 1985 despite the later laying in 1984. The difference in clutch‐size was related to a better food supply in 1984. Daily weight increase of females during the prelaying period showed a high negative correlation with laying date in 1985, and a high positive correlation with clutch‐size independently of laying date in 1984–85. This suggested that food eaten before and during laying had a great and direct influence on both laying date and clutch‐size. Many females increased in weight during laying and most others decreased only moderately (relative to egg weight), suggesting that body reserves were not a main source for egg production.

Late breeding females were provided with extra food during the prelaying and laying periods in 1985. Fed females weighed more, bred eight days earlier and laid one more egg than controls. At the same laying dates in mid season, and after heavy snow‐fall, clutch‐size and female weight were larger in the fed birds than in controls, but this was not so near the end of the laying season. Although the earliest of the fed late breeders weighed more, and probably were less restricted by food availability just before or during laying, they did not lay more eggs than did early breeders. This result suggested some limitation on clutch‐size that could not be overcome by the supplementary feeding. Weights of females during laying did not show any consistent relationship with clutch‐size during successive laying date intervals, suggesting that clutch‐size was not directly related to body condition.
Space and habitat use by Red KitesMilvus milvusduring winter in the Guadalquivir marshes: a comparison between resident and wintering populations
Authors: HEREDIA BORJA , ALONSO JUAN C. , HIRALDO FERNANDO
Published: April 2008

Differences in habitat selection, diet and behaviour of resident and wintering Red KitesMilvus milvuswere studied in Donana National Park, southwest Spain. Adult resident Red Kites roosted at their nests, while immature residents and wintering birds gathered at communal roosts. Individuals remained on average for two consecutive nights (range 1–8) at the same communal roost. Wintering kites spent significantly more time foraging gregariously than residents. The use of the marsh was greater by wintering kites while residents more often used the forest. Wintering birds consumed more goose carrion than the residents. Wintering kites had larger core areas, moved farther from their roost sites to feed and changed foraging areas more frequently than residents. Among residents, adult females had the smallest home ranges (core area, distances travelled and time spent flying). We suggest that Red Kites wintering in Donana occupy the marsh because it provides high food availability, and is vacated by Black KitesM. migranswhich exploit this profitable habitat during the breeding season.
Reproductive potential and output of the Bahama Parrot Amazona leucocephala bahamensis
Authors: GNAM ROSEMARIE , ROCKWELL R. F.
Published: April 2008

We evaluated reproductive investment and loss in the endangered Bahama Parrot Amazona leucocephala bahamensis using a fitness components model that corresponds to stages of the reproductive cycle. On average, a pair produced 3.6 eggs but fledged only 0.8 young, a 77% loss on their initial investment. While losses accrued throughout the cycle, they were highest during the hatching and post‐hatching stages. Partial hatching failure and total brood failure, respectively, were the primary sources of loss at these stages. These components did not change significantly over the four years of the study. Total nesting failure changed significantly over time and exacerbated losses during the incubation stage in two of the four years of the study. The implementation of a conservation management plan that would reduce total nest and brood failures is urgently needed.
Territory quality or bird quality? Factors determining breeding success in the Magpie Pica pica
Authors: GOODBURN S. F.
Published: April 2008

The effects of male, female and territory quality on eight measures of breeding performance in the Magpie Pica pica were examined using repeatability. Comparisons were made for (i) the same male or female on the same territory (ii) the same male or female on different territories during their lifetime and (iii) the same territory occupied by a different male or female. Female quality explained over 60% of the variance in clutch‐size and size of eggs laid. Male quality accounted for over 70% of a pair's breeding success within each breeding season. The differential ability of males to provision their female adequately during incubation and their chicks in the nestling period is the most likely explanation for this result. The timing of breeding appeared to be controlled primarily by territory quality, but the effect was relatively weak (19%). Although no effect of female quality on the timing of breeding was detected, this cannot be totally discounted. In addition, it is likely that environmental constraints (i.e. temperature) also exerted some influence on the date of laying. These results contrast with those of Högstedt (1980), who found that 86% of the variance in clutch‐size was due to the effects of territory quality, with only 14% of the variance attributable to female effects. Reasons for the differences are examined.
Parental provisioning in the Dunnock Prunella modularis: the effects of a variable mating system
Authors: BYLE PHILIP A. F.
Published: April 2008

The feeding rates to nestlings by adult Dunnocks Prunella modularis in monogamy, cooperative polyandry (the beta male helped) and uncooperative polyandry (where the beta male did not help) at various chick ages were examined. The presence of a helper at the nest did not lead to a significant reduction in the provisioning rate by the other parents. During the first four days of chick feeding, females in all the mating systems examined appeared to provision the chicks at a higher rate than males.
Population cycles and kin selection in Red Grouse Lagopus lagopus scoticus
Authors: MOSS R. , WATSON A.
Published: April 2008

Populations of Red Grouse Lagopus lagopus scoticus often show cyclic fluctuations in numbers. There is good evidence from previous work that, each year, densities are limited by the territorial behaviour of cocks. Therefore, changes in territorial behaviour and associated territory size might cause changes in density from one year to the next. Demographic measurements and a population experiment were consistent with a model which explained cycles as a consequence of changes in behaviour resulting from kin selection: differential behaviour between kin and non‐kin. The demographic measurements presented here covered 16 years and two cyclic‐type fluctuations, and the experiment lasted 10 years. Long‐term studies are essential if lengthy processes are to be understood reliably.
A technique which may allow accurate determination of the age of adult birds
Authors: KLOMP N. I. , FURNESS R. W.
Published: April 2008

Although many age determination techniques have been developed for four of the five vertebrate classes, none has been developed to determine ages of adult birds. Here we report a technique, involving counting endosteal layers in the tibia, that has allowed us accurately to determine the age (in years) of 12 dead birds of species in four different families, FulmarFulmarus glacialis,ShagPhalacrocorax aristotelis,RedshankTringa totanusand Great SkuaCatharacta skua,all of which had been ringed as chicks and so were of known ages up to 16 years old, but provided inaccurate results for one species, theCommonGuillemotUria aalge.Since other bird species have been found to possess endosteal layers and no species has yet been found to lack such layers, this would appear to be a technique of general applicability which could permit invaluable new work in both pure and applied fields of ornithology.
Nesting ecology of the Seychelles Kestrel Falco araea on Mahe, Seychelles
Authors: WATSON J.
Published: April 2008

The Seychelles KestrelFalco araeais an endemic species confined to several granitic islands in the Seychelles archipelago. Over the three years 1975‐77 a total of 227 nesting attempts were observed on the island of Mahe. Eggs were laid between August and October and only one brood was reared each year. Laying occurred consistently at a time of increasing food abundance and young were in the nest when food was at a maximum. Clutch‐size was invariably 2 or 3, incubation lasted 30 days, the nestling period was 38 days and the post‐nestling period about 14 weeks. In upland areas (above 200 m a.s.l.) the majority of pairs (69%) nested on cliffs and the remainder in trees. At lower elevations (below 200 m a.s.l.) most used coconut palms (46%), with smaller numbers in cliffs (28%), trees (13%) and buildings (13%). Only 19% of pairs nesting in coconut palms fledged young compared with 35% in buildings, 68% in trees and 76% in cliffs. These differences may be related to differences in predation pressure. Overall breeding success was significantly depressed in 1977 compared with 1975 and 1976. This coincided with food shortage, notably of green geckosPhelsumaspp., in 1977.
Nest predation and nestling growth rate of two lark species in the Negev Desert, Israel
Authors: SHKEDY YEHOSHUA , SAFRIEL URIEL N.
Published: April 2008

Clutch‐size, nestling growth and predation rates on eggs and nestlings in two sympatric alaudids, the Crested Lark Galerida cristata and the Desert Lark Ammomanes deserti, were studied in the Negev desert of Israel. Logistic growth constants were similar for both species, and experimental brood reduction did not accelerate the growth rate of their nestlings. It is suggested that the predation rate on nests of both species has been sufficiently high to select for maximal growth rate of nestlings. Overall probability of predation was 0.85 on a Desert Lark nest and 0.76 on a Crested Lark nest. The smaller clutch‐size of the Desert Lark (3.7) may be an adaptation to a higher predation risk, as compared to that of the Crested Lark (4.6) which is more vigilant and nests in more concealed sites.
Assessment of territory quality and its effects on breeding success in a migrant passerine, the Wheatear Oenanthe oenanthe
Authors: TYE ALAN
Published: April 2008

This paper examines how a returning migrant assesses the quality of an area as a breeding territory before the period of peak food demand and how effective the assessment is in terms of breeding success. Male Wheatears Oenanthe oenanthe return from Africa to choose territories in the Breckland of eastern England about March, females arriving shortly after males. The food supply was predictable: prey densities during the breeding period (egg‐laying to chick independence) were strongly correlated with prey densities at the same sites during the period of arrival and territory establishment. Prey densities were also related to vegetation structure, averaging highest on short turf. Male arrival date and territory size were not significantly related to prey density but were strongly related to vegetation structure, implying that birds used vegetation as an indirect clue to prey availability. Neither territory size nor nest spacing appeared to affect nest losses caused by predators. The major variations in number of young fledged (other than predation) were caused by the number of nestlings hatched and presence of a second brood. Both early arrival and an early first brood improved first‐brood success and were necessary for a second brood. Not all birds which arrived early bred early enough for a second brood. First‐brood hatching date was strongly negatively correlated with pre‐breeding prey availability but not significantly related to vegetation structure. Thus by using vegetation as a clue to habitat quality, some pairs suffered reduced breeding success. This result implies that birds may not be able adequately to assess prey density directly at the time of territory establishment. The critical period for food availability may not be the period of peak demand (nestling period), when food is relatively abundant, but is probably the pre‐breeding period when females must accumulate reserves for eggs and when the food supply is poor. Food supply during this period may determine the timing of breeding and the ability to rear a second brood, and may thus have a greater effect on breeding success.
The occurrence and performance of leucistic Barnacle Geese Branta leucopsis
Authors: OWEN MYRFYN , SKIMMINGS PAUL
Published: April 2008

The paper reports the occurrence of whitish ‘leucistic’ forms in populations of Barnacle Geese Branta leucopsis. A total of 15 (including 11 in the last 21 years) have been reported in the population breeding in Svalbard and wintering in the Solway Firth, northern Britain, whereas the two other populations, though much larger, have produced only one bird of the same type between them in the last 30 years. Leucism is controlled by a single, recessive allele.

The median lifespan of leucistic birds is 2–3 years, compared to 8–10 years for normal plumaged birds. This is because they are sought out by (illegal) hunters. There is no evidence that there is any difference in pairing or breeding performance between white and normal birds, though one male, which is still alive aged 18 years, has produced 13 young; this performance is matched fay less than 2% of normal geese.

It is suggested that the Svalbard population was established recently, from a few founders from the Siberian population; if one or two of these carried the allele controlling leucism, this would explain its much higher prevalence in this population than in the other discrete groups of Barnacle Geese.
Scaling nestling energy requirements
Authors: WEATHERS WESLEY W.
Published: April 2008

The total energy metabolized (TME) by nestling birds, from hatching to fledging, scales as M1.06, 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). Together tfl and M explain 99% of the variation in TME for the 30 species considered (M range 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, tfl and M explain 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 patterns.