bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial organization of the North Island Brown Kiwi Apteryx australis mantelli: sex, pairing status and territoriality
Authors: TABORSKY BARBARA , TABORSKY MICHAEL
Published: April 2008

In Waitangi State Forest, 51 North Island Brown Kiwi Apteryx australis mantelli were tagged with radio transmitters and observed for an average of 2.3 months. All females and the majority of males were paired and maintained territories of 6.7 and 5.5 ha, respectively. Territories overlapped widely between partners but only narrowly with those of paired neighbours. Unpaired males had territories of 12.8 ha and extensively overlapped those of paired males. Territories were maintained by long distance calls and rare aggressive encounters. Males were more territorial than females. Within pairs, males called 1.5 times more often than females and initiated most pair calls. 60% of female calls were responses to their mates. Observers could often induce aggressive behaviour (calling, fast approach) in male kiwi (by playback, for example) but hardly ever in females. Kiwi territoriality cannot be explained by the distribution and availability of food and shelter sites, but seems to serve mainly a reproductive function.
Quantitative analysis of the use of discards from squid trawlers by Black‐browed Albatrosses Diomedea melanophris in the vicinity of the Falkland Islands
Authors: THOMPSON K. R.
Published: April 2008

In the past decade, a major trawl fishery for the squid Loligo gahi has developed in the vicinity of Beauchêne Island, an internationally important breeding site for the Black‐browed Albatross Diomedea melanophris. The breeding season diet of this albatross in the Falklands and its use of discards generated by the Loligo fishery were investigated. Albatross chicks are fed extensively on commercially exploited species of squid and fish including Loligo gahi and southern blue whiting Micromesistius australis. The quantity of waste generated by the Loligo fishery amounts to c. 5% of the reported catch and just over 50% of this waste, mainly Loligo and nototheniid fish, is scavenged by adult Black‐browed Albatrosses. The total quantity scavenged during the chick rearing period amounts to 1000–2000 tonnes per year. This is equivalent to 10–15% of the total food requirement of the breeding Black‐browed Albatross population on Beauchene Island during the period when the fishery is operating. Although the Loligo fishery currently provides a significant quantity of food to these albatrosses, its net effect may be detrimental to them, as it is a much greater predator of Loligo stocks than the albatrosses are estimated to have been prior to the fishery's development.
Brood adoption and deceit among African Marsh Harriers Circus ranivorus
Authors: SIMMONS ROBERT
Published: April 2008

Complete adoption of unrelated broods by foster parents is surprisingly common among birds and the behaviour appears to be maladaptive in several species. In a small, marked, southern African population of African Marsh Harriers Circus ranivorus, studied over 4 years, a young male took over the complete parenting (provisioning and defence) of an unrelated brood, and several times fed the brood in preference to the soliciting maternal parent. This female then deserted and deceitfully courted (out of season) a third male, whose provisioned food she took to feed to her own young. Since the adopting male retained the territory and bred successfully for at least two further years, he suffered no expected loss in fitness and hence this case of fostering was neither maladaptive nor apparently altruistic.
Factors affecting nest‐site choice and reproductive success of Curlews Numenius arquata on farmland
Authors: BERG ÅKE
Published: April 2008

Nest‐site choice and reproductive success of Curlews Numenius arquata in different habitats were studied at a mixed farmland site (grasslands and flooded tilled fields relatively common) and at an arable farmland site (dry tilled fields more dominant than at the mixed site) in central Sweden. At both sites Curlews preferred to nest on grassland and fallow fields, where hatching success was higher than on tillage fields. Nests were also situated further away from forest edges than random sites, but hatching success did not vary with distance to the forest edge. Only 35.6% of the pairs were estimated to hatch young. The main cause of nest loss was predation and the second most important factor was destruction by farming practices, which was an important factor in tillage early in season. Surprisingly, nest survival was higher at the arable than at the mixed farmland site, probably being an effect of the increased proportion of fallowing during recent years. Mortality of chicks was 79.7% before fledgling age (both sites combined) and, surprisingly, chick survival was lower on meadows than on arable fields and leys. The mean production of young was only 0.25 fledglings per pair, which is lower than in areas less affected by farming practice. The low production of young is probably an important factor in the decline of Curlew populations on Swedish farmland. On bogs 1.4 fledglings per pair were produced, indicating that reproductive success of Curlews is higher in more natural habitats.
Seasonal, size‐ and age‐related patterns in body‐mass and composition of Purple Sandpipers Calidris maritima in Britain
Authors: SUMMERS R. W. , UNDERHILL L. G. , NICOLL M. , RAE R. , PIERSMA T.
Published: April 2008

The masses of 3229 Purple Sandpipers Calidris maritima from Britain were analysed for differences related to age, season and size. First‐year birds were lighter by 2 g. There was only a slight increase in mass in mid‐winter, in contrast to other waders wintering in Britain, suggesting that Purple Sandpipers are less at risk to cold weather and food shortages. Their winter fat reserves were low but their breast muscles were relatively larger than other small waders wintering in Britain. Their plumage was slightly heavier and their breast and belly feathers were longer. There was a large increase in mass in May by first‐year and adult birds prior to migration. The ‘long‐billed’ population showed a greater relative increase in May, compared with the ‘short‐billed’ population, perhaps reflecting different migration distances.
Habitat selection by breeding Curlews Nwnenius arquata on mosaic farmland
Authors: BERG ÅKe
Published: April 2008

Territory establishment and habitat use by breeding Curlews Numenius arquata were studied during 1987 and 1988 on mosaic farmland (dominated by dry tillage) at two sites in central Sweden. Curlews preferred to breed in areas with a high proportion of grassland, close to rivers, while dry tillage was avoided. Territories at my study site were larger (mean = 4 5.2 ha) than in areas consisting entirely of grassland. Territory size seemed to depend on the spatial distribution of grasslands, which suggests that habitat fragmentation forces Curlews to establish larger territories in modern farmland than in areas of grassland. The number of territories in patches of grassland was correlated with patch area, and unoccupied patches were more isolated than occupied patches. However, patch area was a more important factor than isolation, since large patches (> 3 5 ha) were always occupied. Sown grassland was used significantly more than expected for foraging early in the season, possibly indicating the strong influence of the nutritional requirements in the pre‐breeding period on territory establishment. Habitat selection when foraging seemed to be less important late in the season, since there was no significant habitat preference then. During this period distance to the nest site seemed to be more important than habitat, sinced the preferred foraging fields (including fields of all habitats used more than expected by area) were situated closer to nests than the less preferred fields, probably an adaptation to the high nest predation risk. The same fields were mostly preferred in the pre‐breeding period also, suggesting that nests were built close to good foraging areas.

My results indicate that the decline of the Swedish Curlew population since 1950 is caused by changes in land use, resulting in decreased grassland area and increased habitat fragmentation, which probably have affected both breeding and foraging possibilities negatively.
Prey species and nutritive value of food fed during summer to King Penguin Aptenodytes patagonica chicks at Possession Island, Crozet Archipelago
Authors: CHEREL YVES , RIDOUX VINCENT
Published: April 2008

The diet of King Penguins Aptenodytes patagonica at 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 of Electrona carlsbergi and juveniles and subadults/adults of Krefftichthys anderssoni represented 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 period.
Regulation of the period of postfledging dependence in the Spanish Imperial Eagle Aquila adalberti
Authors: FERRER MIGUEL
Published: April 2008

From 1986 to 1988, 30 Spanish Imperial Eagle Aquila adalberti nestlings, 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.
Effects of supplementary food on density‐reduced breeding in an African eagle: adaptive restraint or ecological constraint?
Authors: SIMMONS ROBERT E.
Published: April 2008

Increased population density often reduces reproductive output in breeding birds, but the underlying mechanisms (adaptive restraint v reduced food resources) behind decreased productivity are poorly understood. Here I correlatively and experimentally investigated the roles of food, breeding density, latitude, altitude and rainfall in limiting productivity of Wahlberg's Eagles Aquila wahlbergi throughout Africa. Breeding success in equatorial and subtropical Africa (0°–30°S) was highly density‐dependent but showed no latitudinal or rainfall‐related trends. Pairs in dense populations produced half as many young annually as pairs in low‐density populations. Density (but not rainfall or latitude) also explained much of the geographic variation in the mean proportion of pairs attempting to breed each year and the incidence of two‐egg clutches.

Breeding within populations was consistent with these density‐dependent trends: incidence of two‐egg clutches increased in a declining population, and productivity was inversely related to breeding density and rainfall combined. To determine if reduced food resources accounted for reduced output in dense populations, eight pairs were food supplemented: supplementary food failed to induce nonbreeding pairs to breed: nor did it induce earlier laying or increase egg size or clutch‐size. Population density itself was unrelated to two correlates of food resources, rainfall and latitude. I conclude that population density influences most aspects of breeding in Wahlberg's Eagles, and reduced food resources do not appear to explain these trends. Hence, adaptive restraint may account for decreased annual reproduction in this species.
Pre‐nesting feeding selectivity of Pink‐footed Geese Anser brachyrhynchus in artificial grasslands
Authors: FOX A. D.
Published: April 2008

The pre‐nesting feeding ecology of Pink‐footed Geese Anser brachyrhynchus was studied in southern Iceland in April and May 1989–1992. Extensive surveys showed that prior to movement to their nesting areas in the interior, Pink‐footed Geese fed mainly on intensively managed grasslands of the southern lowlands. Faecal analysis showed that geese feeding in hayfields foraged almost exclusively on the most commonly reseeded species, Timothy grass Phleum pratense, which made up the majority (41% by number of green shoots) of new growth in studied hayfields. Dropping counts, as an indicator of goose use, were highly significantly correlated in all years with density of growing Phleum shoots in individual field units. Geese showed a response in feeding patterns to changes in Phleum density as a result of reseeding patterns. Analysis of forage quality in 1991 showed that Phleum shoots had a higher protein content than all other grasses present in hayfields, with the exception of Deschampsia caespitosa. The latter species showed similar levels of protein, but its tussocky nature precluded effective grazing by the geese. Phleum was similar in fibre content to other common grasses. Based on removal of tagged plants, geese grazed predominantly on the youngest leaves of Phleum, which also had higher protein content and lower fibre than older leaves and attached dead leaves, which were rarely taken by geese. Geese grazed shorter length classes of youngest leaves, which showed higher protein content than longer, older terminal leaves. Recently created grassland habitat has increased the opportunities for female geese to supplement their reserves during the crucial prelude to clutch initiation by selecting the highest quality plant species and the most nutritious parts of that forage.
Variations in bird abundance in tropical arid and semi‐arid habitats
Authors: POULIN BRIGITTE , LEFEBVRE GAETAN , McNEIL RAYMOND
Published: April 2008

Temporal variation in bird abundance was studied during a complete annual cycle in a thorn scrub, a thorn woodland and a deciduous forest in northeastern Venezuela. Abundance of site‐attached and transient birds from different feeding guilds was determined by mist‐netting at 2‐week intervals. Diets were investigated by regurgitated samples. The overall avifauna was characterized by a low number of species but they were present all year despite showing strong seasonal fluctuations in abundance. The number of bird species and individuals peaked before and after the reproductive period. These high values probably were associated with movement of species feeding on plant food during the late dry season and the post‐breeding dispersion of juveniles. Bird richness and abundance were lowest during the breeding season and in the early dry season when food abundance was low. Birds from different feeding guilds showed distinct patterns of seasonal abundance which tended to be similar at all three sites. Transient birds represented a large portion of the avifauna, particularly in nectarivores, frugivores and granivores during the dry season. We used a canonical correspondence analysis to demonstrate that bird abundance was correlated with breeding activity, rainfall seasonality and food abundance, with the influence of each parameter varying according to feeding guilds, spatial behaviour of individuals and habitats. Despite a great turnover in the occurrence of the diverse food types available, species composition remained strikingly constant during the year, with birds responding to seasonal changes primarily through a generalist feeding habit and a highly variable rate of transience.
Annual survival of Sparrowhawks Accipiter nisus breeding in three areas of Britain
Authors: NEWTON I. , WYLLIE I. , ROTHERY P.
Published: April 2008

Annual survival of breeding female Sparrowhawks Accipiter nisus was estimated by a capture‐recapture procedure in three different areas, Eskdale and Annandale in southern Scotland and Rockingham Forest in east‐central England.

In Eskdale, where the breeding population remained fairly stable during a 19‐year study, annual survival averaged 59% (s.e. = 4%). In Annandale, where the breeding population declined during a 10‐year study, annual survival averaged 66% (s.e. = 4%). In Rockingham, where the breeding population increased during an 11‐year study, annual survival averaged 72% (s.e. = 4%). In this area, survival declined during the study as numbers rose. The apparent density‐dependence in survival was therefore confounded with a time trend.

In all three areas, annual variations in survival were negatively related to the number of rain days during October‐April, but the relationship was significant only in Eskdale. This area had the longest run of data and the greatest variation in the number of winter rain days. The relationship with rain days could partly account for the differences in mean survival between areas, with lowest survival in the wettest area and highest survival in the driest.
Juvenile dispersal behaviour and natal philopatry of a long‐lived raptor, the Spanish Imperial Eagle Aquila adalberti
Authors: FERRER MIGUEL
Published: April 2008

The dispersal behaviour of 30 radio‐tagged young Spanish Imperial Eagles Aquila adalberti was studied in southwestern Spain in 1986–1990. The dispersal process involved first departure from the natal population, exploratory movements, temporary settlements and returns to the natal population. The dispersal process lasted for the whole of the immature period studied, and behaviour was radically different from that displayed by territorial adults. Movements between temporary settling areas and the natal population occurred continually throughout the dispersal period. Return to the natal population could be used by the young to explore the possibilities for pair formation where a vacancy may have occurred in the breeding population.
Comparative diurnal and nocturnal foraging behaviour and energy intake of premigratory Grey Plovers Pluvialis squatarola and Whimbrels Numenius phaeopus in South Africa
Authors: TURPIE JANE K. , HOCKEY PHILIP A. R.
Published: April 2008

Estimates of the energy budgets of nonbreeding waders (Charadrii) have frequently been hampered by ignorance of the birds' nocturnal activities. During the premigratory period (March), Grey Plovers Pluvialis squatarola and Whimbrels Numenius phaeopus at the Zwartkops estuary, South Africa, foraged throughout the nocturnal as well as the diurnal low‐tide period. Although both species continued to forage visually at night, they exhibited behavioural changes to compensate for the reduced visibility. Both species foraged more slowly at night, taking fewer steps per minute, and Grey Plovers paused for longer to search for prey. Prey items were sighted from shorter distances at night than during the day. Energy intake rates, however, did not differ significantly by day and night for either species, and both achieved over 40% of their daily low‐tide period intake at night. The energy intake rates and total daily intake of Grey Plovers, which fed exclusively on the study area, exceeded allometrically predicted values.
Breeding of waders (Charadrii) and Brent Geese Branta bernicla bernicla at Pronchishcheva Lake, northeastern Taimyr, Russia, in a peak and a decreasing lemming year
Authors: UNDERHILL L. G. , PRŶS‐JONES R. P. , SYROECHKOVSKI E. E. , GROEN N. M. , KARPOV V. , LAPPO H. G. , ROOMEN M. W. J. VAN , RYBKIN A. , SCHEKKERMAN H. , SPIEKMAN H. , SUMMERS R. W.
Published: April 2008

During summer 1991, lemmings occurred at high densities in Arctic tundra at Pronchishcheva Lake in the northeastern Taimyr Peninsula, whereas, in 1992, lemming densities were substantially lower and decreased further during the summer. In 1991, avian predators such as Snowy Owls Nyctea scandiaca, gulls and skuas bred well; Arctic foxes Alopex lagopus were rarely observed in the study area but bred in the immediate vicinity. In both years there was a late thaw, but this did not deter breeding by birds. The insect food supply for waders showed similar patterns of abundance in both years. In 1991, 73 nests of nine species of wader were found within a 14‐km2 study area, and Dark‐bellied Brent Geese Branta bernicla bernicla nested in association with Snowy Owls. The overall density of wader nests was estimated to be 7 per km2. Clutches disappeared at only two wader nests and no Brent Goose nests, and the Mayfield estimate of the daily probability of predation for waders was 0.0022. In contrast, the daily probability of predation was 0.20 in 1992, when there was a similar breeding density of waders. Arctic foxes were seen searching for food daily within the study area, and fox droppings were found associated with nests taken by predators. The predicted scenarios for peak and decreasing lemming years (the Roselaar‐Summers hypothesis), i.e. low predation and high nest success in the peak year and high predation and low nest success in the decreasing year, therefore occurred.
The effect of direct supplementary feeding of nestlings on weight loss in female Great Tits Parus major
Authors: JOHNSTON ROSS D.
Published: April 2008

Experimentally hand‐feeding nestlings of enlarged (+3 nestlings) broods reduced female weight loss during the nestling period in a single‐brooded Great Tit Parus major population in Scotland but did not affect nestling size. The result is consistent with the existence of a trade‐off in parental care between reproductive costs and benefits.
Effects of habitat fragmentation on the timing of Crested Tit Parus cristatus natal dispersal
Authors: LENS LUC , DHONDT ANDRE A.
Published: April 2008

Crested Tit Parus cristatus young from first broods dispersed 1 week later if they were born in small isolated pine plots (‘habitat fragments’) compared with individuals in a large pine forest (‘continuous habitat’). This delay in dispersal was caused by an extended period between fledging and dispersal. In second broods, the delay was even longer due to the interbrood interval being 9 days longer in habitat fragments. As nestlings in habitat fragments had a lower body‐mass, and age at dispersal was negatively correlated with nestling body‐mass within each nest, the postponed dispersal from fragments might be explained partly by a lower body‐mass. Alternatively, postponed dispersal from fragments could result from a barrier effect caused by reluctance to cross inhospitable habitat.

Immigration by young from first broods into habitat fragments was delayed by approximately 3 weeks, and proportionally more second brood emigrants were recovered in this type of habitat. These results are in agreement with the hypothesis that fragments are second‐choice habitat. Early immigrants into continuous habitat had a higher probability of settlement in winter flocks compared with late ones, independent of condition or age. Therefore, Crested Tits born in habitat fragments probably have a lower chance of settling in first‐choice habitat.
Family break‐up in Black and Red Kites Milvus migrans and M. milvus: is time of independence an offspring decision?
Authors: BUSTAMANTE* JAVIER
Published: April 2008

I observed the natural process of family break‐up in 13 families of Black Kites Milvus migrans and five families of Red Kites M. milvus in which fledglings had been individually marked. In other broods, I performed experiments which modified the parental investment fledglings received by supplementing nests of both species with food or transferring Black Kite chicks to nests with younger or older chicks of the same species.

The time of family break‐up in the Black Kite is mainly an offspring decision which is not affected by an artificial increase of parental investment. The duration of the post‐fledging period was not increased in Black Kites that were given supplementary food. Chicks transferred to nests with a younger chick did not extend the post‐fledging period, nor did chicks transferred to nests with an older chick shorten the post‐fledging period. In Red Kites, parental investment seemed to have more influence on the timing of the family break‐up. Red Kite adults invested less as parents than did Black Kites during the post‐fledging dependence period, and in nests where supplementary food was given, Red Kite fledglings stayed attached for a longer period.
Effects of prey abundance on the foraging behaviour, diving efficiency and time allocation of breeding Guillemots Uria aalge
Authors: MONAGHAN P. , WALTON P. , WANLESS S. , UTTLEY J.D. , BLJRNS M.D.
Published: April 2008

The foraging behaviour of Guillemots Uria aalge at sea was compared between 2 years of radically different food abundance. Radio telemetry was used to determine foraging locations and diving patterns. In the poor compared with the good food year, foraging trips were much longer, the birds foraged more than six times further from their breeding sites, they spent over five times as much time diving when at sea and their estimated energy expenditure was twice as great. Time spent foraging in the poor food year was at the expense of time spent sitting at the colony. The duration of a foraging trip was a poor indicator of distance travelled but a good indicator of the amount of time spent diving. Mean dive durations, surface pause durations and interbout periods did not differ between years, but individuals made more than four times as many dives per diving bout in the poor food year. Surface pause lengths did not vary with water depth in either year. In the poor food year, birds made shorter surface pauses for a dive of a given duration than in the good food year, possibly accepting a lactic acid debt in order to maximize searching time, The duration of the interbout period was positively related to the number of dives in the previous bout, and dives tended to get shorter in long diving sequences, suggesting possible exhaustion effects. These data demonstrate that breeding Guillemots have the capacity to adjust their foraging behaviour and time budgets in response to changes in food abundance, but this flexibility was not sufficient to compensate fully for the very low food abundance experienced by birds in this study.
Distribution of shorebirds at the Berg River estuary, South Africa, in relation to foraging mode, food supply and environmental features
Authors: KALEJTA B. , HOCKEY P.A.R.
Published: April 2008

Foraging densities of Curlew Sandpipers Calidris ferruginea and Grey Plovers Pluvialis squa‐tarola at the Berg River estuary, South Africa, are examined in relation to prey and habitat attributes.

There is a substantial overlap in the prey species eaten by Curlew Sandpipers and Grey Plovers, but the distribution patterns of the two species within the estuary could not be explained by the same prey attributes.

The distribution of tactilely foraging Curlew Sandpipers was determined largely by the numerical abundance of nereid worms. They foraged preferentialiy on muddy rather than sandy substrata, but their distribution could not be explained on the basis of substratum penetrability. The density of visually foraging Grey Plovers was correlated with the biomass, rather than abundance, of the larger of the two common nereids on the estuary. The favoured foraging area of Grey Plovers had a high vegetation cover, but their foraging dispersion was not influenced by substratum type.

The energy intake rates of Curlew Sandpipers were broadly inversely related to their foraging density, although the rate of prey capture was maximal at high prey density. These birds may use neighbour success rates in selecting foraging sites. Energy intake rates of Grey Plovers were very consistent across the estuary, suggesting that individuals occupy or defend areas which provide access to comparable food resources.
Determination of clutch‐size in the Kentish Plover Charadrius alexandrinus
Authors: SZÉKELY T. , KARSAI I. , WILLIAMS T. D.
Published: April 2008

We studied the clutch‐size distribution of Kentish Plover Charadrius alexandrinus in 1991 and 1992 and tested three hypotheses for determination of clutch‐size: egg‐formation ability of females, incubation ability of parents and nest predation. Variation in clutch‐size was small: 71 out of 74 clutches had three eggs (coeff. var. = 7%). Females spent more time foraging (51 ± 6%) pre‐laying and during egg‐laying than their mates (39 ± 5%). However, we concluded that egg‐formation was not constrained by food availability because 77% and 100% of clutches were initiated before the peaks of prey density and of prey mass, respectively. Furthermore, the number of clutches initiated and completed over time was unrelated to prey density. By experimentally reducing and enlarging clutches, we found that enlarged clutches of four eggs took longer to hatch (24.8 ± 0.9 days) than control clutches of three (21.6 ± 0.7 days). Eggs of enlarged clutches also lost weight more slowly during incubation in both years compared with control clutches. No difference was found in the incubation behaviour or weight loss of parents between reduced, control and enlarged clutches. We found no evidence to support the nest predation hypothesis, since neither the proportion of nests predated nor the number of chicks hatched was different between reduced, control and enlarged clutches. The results of this study are most consistent with the incubation ability hypothesis, although the parental ability hypothesis has remained untested.
Diet, prey‐size selection and intake rates of Black‐tailed Godwits Limosa limosa feeding on mudflats
Authors: MOREIRA FRANCISCO
Published: April 2008

This paper describes aspects of the winter feeding ecology of Black‐tailed Godwits Limosa limosa on an intertidal mudflat in the Tagus estuary, Portugal. Their diet consisted mainly of the bivalve mollusc Scrobicularia plana, which represented 88% of the ingested biomass. The remaining 12% was the worm Nereis diversicolor and, occasionally, the snail Hydrobia ulvae. Ingested Scrobicularia varied between 10 and 20 mm in length, and all size classes of Nereis present in the sediment, except those smaller than 20 mm, were preyed upon. A change in dietary composition occurred over the winter, probably in response to changes in the availability of Nereis and small Scrobicularia. Intake rates averaged 74.9 mg dry weight per minute, which corresponded to a net energy intake of 1.21 kJ per min.
Intraspecific brood‐parasitism and dispersal in fledgling Sparrowhawks Accipiter nisus
Authors: FRUMKIN RON
Published: April 2008

The progeny of early‐nesting Sparrowhawks Accipiter nisus have a higher survival rate than those of late nesters. To ascertain the reasons for greater survival in early‐season Sparrowhawk fledglings, I studied post‐fledging dispersal behaviour in this species by direct observations and radio‐tracking during 3 years in Rockingham Forest, Northamptonshire, U.K.

Post‐fledging brood‐parasitism was found among early‐dispersed young of both sexes.

Early‐dispersed young spent up to 6 days being fed by the parents of other fledged, but still dependent, broods, as far as 6 km from their own nests.

Three broods were provided with supplementary food for 4 weeks, starting 1 week before expected dispersal. These young dispersed when significantly older than young from control broods. In both groups, males dispersed, on average, 3–4 days earlier than females. The ultimate dispersal age of young in control broods was negatively correlated with their rate of mass gain during the nestling period. Unlike the young of the control broods, fledglings in broods with augmented food were usually silent.

These findings offer an explanation for why Sparrowhawk young that disperse early in the season survive better than those which disperse late.
Interinsular variations in the spring and summer diet of the Raven Corvus corax in the Canary Islands
Authors: NOGALES M. , HERNANDEZ E. C.
Published: April 2008

This paper presents the first data on the diet of the Raven Corvus corax in the Canary Islands, based on analysis of 2315 pellets collected from all of the islands and islets in the archipelago. The Ravens on three groups of island showed differences in diet, but in all cases the diet was clearly omnivorous, both in its qualitative and quantitative composition. It is evident that a broadening of the Raven's trophic niche has occurred in comparison with those living in continental areas. While the diet has a strong plant component on the wetter islands (frequency of occurrence > 87%), an appreciable animal component in the diet (principally vertebrates) is more frequent on the drier islands of the archipelago (frequency of occurrence > 96%). The composition of the plant component of the diet varied markedly from one island to another. Remains of refuse are more commonly found in the Raven's diet on the central and western islands. We concluded that while the animal diet is essential from the bioenergetic point of view, the vegetation diet is only a complementary food source. The Raven plays an important role in seed dispersal among the different habitats within each island.
Competition and egg‐weight in the Great Tit Parus major
Authors: PERRINS C. M. , McCLEERY R. H.
Published: April 2008

The mean weight of eggs in clutches of the Great Tit Parus major varies markedly between clutches. Eggs are lighter in years of high density of breeding pairs than in years of low density, but egg weight is also inversely correlated with the density of breeding Blue Tits Parus caeruleus.
Breeding dispersal and site‐fidelity in three monogamous wader species in the Western Isles, U.K.
Authors: JACKSON DAVID B.
Published: April 2008

Adult and post‐natal breeding‐dispersal movements of Redshank Tringa totanus, Dunlin Calidris alpina and Ringed Plover Charadrius hiaticula were quantified in west Scotland. Data from 373 returning birds marked as breeding adults and 142 returning birds marked as chicks are presented. Unlike most previous studies, this study measured dispersal movements up to 40 km and attempted to overcome distance‐related biases. For each species, adult males were significantly more nest site‐faithful between years than were adult females. Likewise, first‐time breeding males bred significantly closer to their natal site than did females. The settlement intensity per unit area of habitat showed marked differences between species, age classes and sex in the relative attractiveness of potential areas at different distances to settling birds. Adult dispersal was negatively and significantly related to breeding success in the previous year and positively related to capture on the nest in the previous year. Dispersal movements of adult Ringed Plover breeding on unstable cultivated habitats were significantly related to habitat quality (measured in terms of nest survival) and were always to habitat of better or equal quality.
A new genus and species of perdicine bird (Phasianidae, Perdicini) from Tanzania; a relict form with Indo‐Malayan affinities
Authors: DINESEN LARS , LEHMBERG THOMAS , SVENDSEN TENS OTTO , HANSEN LOUIS A. , FJELDSÅ JON
Published: April 2008

A very distinctive perdicine bird was discovered in July 1991 during fieldwork in montane evergreen forests in parts of the Udzungwa Mountains in Tanzania which were so far ornithologically unexplored. The bird is described here as a new genus and species with affinities to the hill‐partridges Arborophila of the Indo‐Malayan region. The relict occurrence in Africa of taxa with affinities to Oriental biota is discussed.
Pelagic communities of seabirds in the South Atlantic Ocean
Authors: VEIT RICHARD R.
Published: April 2008

This paper presents quantitative analyses at the community level of the spatial dispersion of 44 species of pelagic birds in the South Atlantic Ocean. I have examined the extent to which assemblages of pelagic bird species are influenced by the combined influences of the abundances of other species and the physical structure of the pelagic environment. Results are based upon strip transects collected from oceanographic research vessels during the four consecutive austral summers of 1982–1986.

The distributions of most seabird species were statistically independent of the distributions of other species. Species assemblages, however, did occur and were correlated with the physical structure of the ocean. The study area was divided into four zones, each defined by a distinctive assemblage of birds. Physical oceanography proved to be important in determining the species composition of each zone. These relationships were apparent despite the potentially confounding influence of large numbers of immatures and non‐breeding adults.
Courtship feeding in Ospreys Pandion haliaetus: a criterion for mate assessment?
Authors: GREEN DAVID J. , KREBS ELIZABETH A.
Published: April 2008

In many bird species males provision their mates prior to egg‐laying. Courtship feeding has been suggested to function in several ways: to advance laying date by improving female condition, to induce a female to copulate or to allow a female to assess her mate. The role of courtship feeding in Ospreys Pandion haliaetus was investigated in British Columbia, Canada. Courtship feeding rate affected the probability of a pair initiating a clutch. Pairs that laid eggs had higher rates of courtship feeding than pairs that did not lay eggs in both 1991 and 1992. Male courtship feeding rate also correlated negatively with the duration of the courtship period. Experimentally increasing the amount of food available to females prior to egg‐laying resulted in a nonsignificant reduction in the duration of the courtship period. This study found no evidence to support the suggestion that female Ospreys trade copulations for food during the courtship period; only 63 of 385 copulations observed were associated with feeds, and courtship feeding rate did not correlate with the copulation rate of a pair. Male provisioning rates, however, were predictable; courtship feeding rate correlated with both male delivery rate to the nest when chicks were 1–2 weeks old and mean brood growth rate. Female Ospreys therefore may be able to predict the quality of subsequent paternal care using courtship feeding rate. As predicted if optimal hatching asynchrony is dependent on food availability, mean brood growth rate, an indirect measure of male parental care, was negatively correlated with hatching asynchrony. This suggests that female Ospreys may manipulate hatching asynchrony in response to male courtship feeding rate, thereby maximizing the productivity of their brood at predicted food levels.
Effects of supplemental feeding and female age on timing of breeding in the Alpine Accentor Prunella collaris
Authors: NAKAMURA MASAHIKO
Published: April 2008

Supplemental food in the form of millet seed was provided to 1‐year‐old and older (2:2‐year‐old) female Alpine Accentors Prunella collaris, and the effect on timing of breeding was studied over four breeding seasons in central Japan. Only 1‐year‐old females responded to the supplemental food: additional food advanced their settlement date, the onset of the development of a cloacal protuberance and laying date. In contrast, no effect of the experimental feeding was found on the timing of breeding in older females and they invariably bred earlier than 1‐year‐old females. Having settled on the breeding grounds, females developed the cloacal protuberance and retained it for about 1 month until the last egg in the first clutch was laid. The development period of the protuberance corresponded to the copulation period. Because the copulation period was not shortened by extra food and no significant difference occurred in either of the two age classes, it is necessary for earlier breeding birds to accumulate the nutrients needed to form the protuberance as well as the eggs. Although older females relied less on supplemental food, they were significantly heavier and formed the cloacal protuberance earlier than 1‐year‐old females. One‐year‐old females depended more heavily on supplemental food than did older ones and the duration between settlement date and the onset of development of the protuberance of 1‐year‐olds was reduced by additional food. These results raised the possibility that older females fly from their wintering grounds carrying some food reserves which they can use for forming the protuberance, while 1‐year‐old females collect the food needed for forming it on the breeding grounds.
Survival and non‐breeding of adult Common Guillemots Una aalge
Authors: HARRIS M. P. , WANLESS S.
Published: April 2008

Annual survival of colour‐ringed Common Guillemots Uria aalge with at least 1 year of breeding experience was measured in five study areas on the Isle of May, southeast Scotland from 1982 to 1993. Annual survival averaged 94.9%. There were no significant sex, year or area differences. Between 5% and 10% of the birds known to be alive in any year did not breed, and on average such birds appeared to survive less well (87%) than breeders (95%). Non‐breeding did not occur randomly within the population, and 6% of birds accounted for 47% of the cases of non‐breeding. It appeared that non‐breeding in Common Guillemots on the Isle of May was socially induced with most cases occurring after an individual had lost its site.
Systematics of the Soft‐plumaged Petrel Pterodroma mollis (Procellariidae): new insight from the study of vocalizations
Authors: BRETAGNOLLE VINCENT
Published: April 2008

The taxonomic status of the populations of the polytypic Soft‐plumaged Petrel Pterodroma mollis is controversial. Previous taxonomic studies used morphological characters (measurements and colouration) and univariate statistics. In this study, I add the use of multivariate statistics on morphological (biometry and colouration) and behavioural characters (vocalizations) of the petrels. Vocalizations are especially relevant in nocturnal burrowing petrels (such as the Soft‐plumaged Petrel) and act as behavioural isolating mechanisms. The analysis, based on 535 calls from seven of the 11 known breeding localities of the species, showed that physical parameters of the call did not overlap at all between breeding localities in the northern and southern hemispheres but did so within each hemisphere. Conversely, the morphological analysis, based on morphometries from ten localities, displayed wide and significant intra‐hemisphere variation, whereas there was no consistent difference between northern and southern parts of the breeding range. Thus analysis of the two sets of characters gave contradictory results. Calls, owing to their role in species‐specific recognition in these birds, should be given priority over other characters for species separation. I suggest that only two species should be recognized, Pterodroma mollis and Pterodroma feae, with three subspecies each. I also examined behavioural affinities between P. mollislfeae groups and other gadfly petrels and found that P. mollis/feae were closest to Pterodroma cahow, whilst Pterodroma hasitata on the one hand and Pterodroma phaeopygia and Pterodroma externa (which may comprise two species instead of one) on the other belong to other groups of gadfly petrels.
The frequency distribution of bird body weights: aquatic and terrestrial species
Authors: GASTON KEVIN J. , BLACKBURN TIM M.
Published: April 2008

The frequency distribution of the log‐transformed body‐weights of the world's bird species is right‐skewed. The reasons for this skew are unknown. Aquatic bird species are on average heavier and have a less skewed distribution of weights than would be expected if they were a random sample from the overall weight distribution. Conversely, terrestrial species on average weigh less, and their weight distribution is more skewed. This is partly a phylogenetic effect; species of aquatic and terrestrial birds belong to different families. These differences suggest factors which may be important determinants of the overall weight distribution of birds.
Survival of Herring Gull Larus argentatus chicks: an experimental analysis of the need for early breeding
Authors: BROUWER ALEWIJN , SPAANS ARIE L. , DE WIT ALLE A. N.
Published: April 2008

In 1985 and 1990, we manipulated the hatching date of Herring Gulls Larus argentatus by exchanging complete clutches between pairs which had started egg laying on different dates in the season. The aim was to investigate whether the observed seasonal decline in Hedging success can be explained by laying date. In both years, fledging success of advanced pairs followed the natural seasonal trend, supporting the date hypothesis. However, in both years, Hedging success of delayed pairs remained as high as that of control pairs with the same original hatching date as the foster parents, supporting the parental quality hypothesis. These data suggest that the delayed pairs may have compensated for less favourable environmental conditions. Although conspecific predation was the main direct cause of chick mortality, food shortage probably indirectly determined the mortality rate. A model of fledging success in relation to the timing of egg laying predicts that when food is abundant the optimal hatching date coincides with the mean hatching date of the colony (synchronization advantage). When food is less abundant, early breeders have the highest fledging success.
Territory and group living in the polygynandrous Alpine Accentor Prunella collaris
Authors: NAKAMURA MASAHIKO
Published: April 2008

The spacing system of Alpine AccentorsPrunella collariswas studied on the summit of Mt. Norikura in central Japan for five breeding seasons. This species lived in groups (mean 7.2 individuals), sharing large areas of their individual home ranges within which all activities occurred. Membership of a group was closed and stable within a breeding season. The group home ranges overlapped little with each other, and antagonistic behaviour, including communal defence, was observed at the boundaries. Each female established an exclusive area around her own nest which she defended against other females (but not males) within the shared home range, but her activities (feeding, singing and mating) were observed over the whole of the group home range. Members of the same group moved around and fed together within the home range during the prebreeding season, but individual birds tended to become more solitary as the breeding season progressed. These results suggest that the primary breeding unit of Alpine Accentors is a group consisting of five to ten members who share a group territory which contains all the resources necessary for living and breeding, but this species is not a typical social one in which all members move around together within their group territory.