bluuebunny/crossref_metadata_2025 huggingface dataset:
Surprise as a winter hunting strategy in Sparrowhawks Accipiter nisus, Peregrines Falco peregrinus and Merlins F. columbarius
Authors: Cresswell Will
Published: April 2008

Sparrowhawks Accipiter nisus, Peregrines Falco peregrinus and Merlins Falco columbarius were studied hunting Redshanks Tringa totanus, Dunlins Calidris alpina and Skylarks Alauda arvensis over three winters on a small Scottish estuary. Most Sparrowhawk and Merlin hunts consisted of a single attack (mean = 1.0 and 1.1, respectively), whereas Peregrine hunts often consisted of several attacks (mean = 1.8). Most hunts were short (<1 min), but Peregrine and Merlin hunts occasionally lasted over 5 min. In general, all three raptor species attacked by surprise, although Peregrines were more likely to make nonsurprise attacks. Prey attacked were usually initially very close to the raptor (<100 m); Peregrines attacked prey most often at long distances (>500 m). Chase lengths were mostly <5 second in length, although Peregrines, and particularly Merlins hunting Skylarks, often chased for several minutes. Peregrines attacked most prey in flight from flight, while Merlins and Sparrowhawks attacked birds on the ground with a flight from a perch. All three raptor species preferentially attacked larger Dunlin flocks, but Peregrines also favoured single birds. Capture rates of Redshanks and Dunlins were similar for the three raptor species (C. 10%), but for Skylarks, capture rate by Merlins was much higher (12%) than by Sparrowhawks (3%) or Peregrines (0%). Capture rates were highest when raptors attacked by surprise, particularly for a Peregrine hunting in the first minute of arrival on the study site if no Peregrines had been hunting there for the previous hour (16% success for the first minute compared with 2% in subsequent minutes). Sparrowhawks were more successful when attacking small rather than large Dunlin flocks. The use of short surprise attacks interspersed with long periods of inactivity was common to the three raptor species and was interpreted as a strategy to minimize the amount of energy and risk involved in hunting during the nonbreeding season.
Waterbirds and substrate quality of the Pichavaram wetlands, southern India
Authors: Nagarajan R. , Thiyagesan K.
Published: April 2008

The water and mud characteristics of the six types of wetlands in Pichavaram were compared in order to determine whether the habitat of waterbird species was characterized by them. Waterbird species richness was most influenced by mud phosphorus levels. Variation in water pH was the principal factor that determined waterbird diversity. The water level mainly determined the density of waterbirds. Levels of pH and nitrites in the water also appeared to influence significant variations in waterbird diversity and density, respectively. Bottom substrate variables, viz. pH and phosphorus levels, were also significantly correlated with the density and richness of waterbirds, respectively. Water quality factors, viz. pH and nitrite and mud pH and phosphorus, were correlated with the abundance, while water depth was correlated with the accessibility of prey to the birds.
Behavioural and molecular evidence for specific status of light and dark morphs of the Herald Petrel Pterodroma heraldica
Authors: Brooke M. de L. , Rowe G.
Published: April 2008

The Herald Petrel Pterodroma heraldica has an extensive subtropical breeding range across the width of the Pacific Ocean. It occurs in dark and light morphs, and, at most breeding colonies, the latter is more numerous. However, on Henderson Island, one of the Pitcairn Islands of the Central Pacific, the dark morph is more numerous. During a field study at Henderson Island, we found evidence of reproductive isolation between light and dark Herald Petrels. The morphs bred and courted assortatively. They also tended to breed in different parts of the island (dark birds nearer the coast) and at slightly different seasons (dark birds mostly in the austral winter, light birds more evenly throughout the year) and uttered different calls. Together, these data strongly suggested that the morphs are distinct species. This conclusion was supported by sequence data from a 307‐base pair region of the cytochrome b gene of the mitochondrial genome. When birds of both morphs from Henderson and light morphs from Ducie Atoll (345 km west of Henderson) were sampled, five haplotypes were restricted to light Herald Petrels: they did not occur in dark birds. In contrast, three haplotypes were restricted to dark Herald Petrels on Henderson Island. Thus, the haplotypes of the two morphs were mutually exclusive, further indicating reproductive isolation between them. We propose that the white‐bellied form should retain the name Herald Petrel P. heraldica, while the dark‐bellied form should be granted specific status as the Henderson Petrel Pterodroma atrata (Mathews 1912). The name atrata derives from a description written by Solander on Cook's first voyage. Molecular data from Round Island Petrels Pterodroma arminjoniana confirmed the close relationship between this form and heraldica. However, arminjoniana and atrata did not share sequences for the cytochrome b region studied.
The annual cycle of wing‐moult and breeding in the Wattled Starling Creatophora cinerea
Authors: CRAIG A. J. F. K.
Published: April 2008

Moult, breeding and seasonal occurrence of the Wattled Starling Creatophora cinerea throughout its range in Africa are reviewed based on data from museum specimens and the published literature. Neither moult nor breeding follows a rigid seasonal pattern, although there are some regional differences, and overlap between moult and breeding is unlikely. The regular occurrence of interrupted wing‐moult may be associated with nomadic movements rather than opportunistic breeding.
Nestling growth and mortality of Pied Flycatchers Ficedula hypoleuca in relation to weather and breeding effort
Authors: SIIKAMÄKI PIRKKO
Published: April 2008

The growth pattern and mortality of young Pied Flycatchers Ficedula hypoleuca were studied to focus on the mechanisms and constraints behind the widely studied optimization of clutch size. The clutch sizes were modified, and the growth and survival of chicks from different clutch sizes were monitored along with the prevailing weather during the nestling period to detect the effect of weather on reproductive success. The weather conditions during the feeding period of the nestlings varied within a season as well as between breeding seasons. The prevailing weather markedly affected both the growth rate and the survival of chicks, yet, the effects of weather on growth were not greater in enlarged clutches. The impact of adverse weather was more pronounced in the later phases of nesting, when the food demand of a brood was highest. Brood reduction and total nest losses were more likely during extensive rainfall during the nestling phase and also in the enlarged clutches. Thus, weather is a very important determinant of reproductive success in this species. Weather conditions during the breeding season are unpredictable, however, and therefore brood reduction through sibling competition is a mechanism whereby brood size can be adjusted to the level the parents can rear under the prevailing conditions.
Behaviour and parental care of Skylark Alauda arvensis chicks
Authors: POULSEN JOHN GRYNDERUP
Published: April 2008

I studied parental care and fledgling dispersion of Skylarks Alauda arvensis during the last 4 days of the nestling period and the first 4 days after the nestlings left the nest but before they were able to fly. The study compared parental care in three different crop types: spring barley, grass and set‐aside. Both parents made more provisioning trips and delivered more food to fledglings than to nestlings. Fledglings received fewer items per trip than did nestlings. Feeding distances did not differ between nestling and post‐Hedging periods for any crop type. This suggests that fledging was associated with a change in parental foraging strategies. Parental care differed between broods from different crop types. During the last 4 days of the nestling period, the feeding frequencies were 3.4 trips per young per hour in spring barley fields, 5.8 in grass and 7.3 in set‐aside. The mean distances to the feeding area were 233 m in spring barley fields, 155 m in grass and 120 m in set‐aside. The load size of provisioning trips was significantly higher in set‐aside than in spring barley and grass. During the first 4 days after fledging, the feeding frequencies were 2.2 successful trips per young per hour in spring barley fields, 4.1 in grass and 5.1 in set‐aside. The feeding distances were 210 m in spring barley fields, 162 m in grass and 120 m in set‐aside. Load size of provisioning trips was significantly higher in set‐aside than in spring barley and grass. The mean dispersion of fledglings was significantly greater in fields of spring barley compared with grass fields and set‐aside.
Prey preparation by adult Great Tits Parus major feeding nestlings
Authors: BARBA EMILIO , LóPEZ J. ALBANO , GIL‐DELGADO JOSÉ A.
Published: April 2008

Some birds prepare food items before giving them to their nestlings. We studied the relationships between the degree of prey preparation and prey size, nestling age, brood size and time of season. We estimated the degree of preparation of 513 animal prey items, taken by using neck collars, brought to nestling Great Tits Parus major. Prey preparation increased with prey size and decreased as the nestlings grew older, as brood size increased and as the season progressed. Other factors, such as nutrient concentration (through removal of low‐quality or deleterious parts) or palatability (considering scaly moth forewings unpalatable), seem also to be important in determining prey preparation. Our results suggest that the degree of prey preparation is a compromise between the benefits gained by the nestlings (ingestion and digestion of prey is facilitated) and the costs to the parents (mainly time allocated to prey preparation).
Age‐related survival in female Sparrowhawks Accipiter nisus
Authors: NEWTON I. , ROTHERY P. , WYLLIE I.
Published: April 2008

Long‐term capture‐recapture of female Sparrowhawks Accipiter nisus nesting in three different areas enabled age‐related survival rates to be calculated, after correcting for age‐related and annual variations in recapture frequency. The data provided strong evidence for an improvement in survival rates in the first 3 years of life and for a decline in the last 5–6 years, during a maximum life span of around 10 years. The decline in survival among older birds was attributed to senescence. At all ages, survival rates were higher in the English area, where breeding numbers were rapidly increasing, than in two Scottish areas, where breeding numbers were stable or declining. The precise pattern of change in survival rates with age may vary between areas, according to prevailing circumstances.
Provisioning and growth rates of nestling Fulmars Fulmarus glacialis: stochastic variation or regulation?
Authors: HAMER K. C. , THOMPSON D. R.
Published: April 2008

The pattern of chick feeding in the Fulmar Fulmarus glacialisat St Kilda, Scotland, was examined by repeated weighing of chicks throughout 14 consecutive days during the first half of the chick‐rearing period in 1994. After correcting for metabolic weight losses, the sizes of positive mass increments between weighings were used to assess meal sizes and feeding frequency for each chick. Individual meals fed to chicks averaged 80.8 g (s.d. ± 21.0 g), or approximately 10% of adult mass. Each chick received 0 to 4 meals per day, with an average of 1.9 meals per chick per day, giving an average interval of around 25 h between meals delivered by each parent. The distribution of time intervals between feeds for each chick (whether single or double meals) followed a negative exponential function with a maximum value of 80 h. These results are not compatible with the idea that the purpose of large fat deposits in procellariiform chicks is to guarantee survival over long intervals between feeds. Over 14 days, the chicks' mean daily food requirements for zero‐growth increased from 98 g to 160 g. This corresponded with an increase in feeding frequency but not meal size. Chicks with lower scores for body condition after feeding by both parents received more meals during the subsequent 16 h and had shorter intervals to the next feed, indicating that adults regulated feeding frequency in accordance with chick condition at the previous feed. This does not agree with the hypothesis that lipid accumulation by nestling Procellariiformes is a response to stochastic variation in food delivery associated with an absence of regulation. In view of the diversity of growth and feeding patterns present among the Procellariiformes, it is possible that lipid accumulation in this group does not have a unitary explanation.
Intermittent breeding in Cory's Shearwater Calonectris diomedea of Selvagem Grande, North Atlantic
Authors: MOUGIN J.‐L. , JOUANIN CHR. , ROUX F.
Published: April 2008

Every year, 10% of the breeding population of Cory's Shearwater Calonectris diomedea of Selvagem Grande, between the Canaries and Madeira (30d̀09'N, 15d̀52'W), fail to breed. These “sabbatical” periods can last up to 7 years but typically last 1 year in 58% of the cases, with an average of 1.7 years. Both sexes are involved, and most are young breeding birds. The frequency and duration of the absences decrease with the increase of breeding experience. During the year preceding the absence, the breeding success, mate fidelity and nest site fidelity of the breeding birds are the same as those of their sabbatical congeners. During the sabbatical absence, the former mate is also absent in just less than half of the cases. Of those present, two‐thirds are at the same nest site and one‐third at another nest site. On the return of the “missing” birds, the fidelity both to the former mate and the former nest site is low, and more so if the length of the absence has been over 1 year, because the former mate and the former nest site are then seldom available. Divorce is frequent and the breeding success is low. Comparisons with other Procellariiformes reveal few differences in the intermittent breeding except for the proportions involved, which are six times greater for some species than for others.
Flight behaviour of seabirds in relation to wind direction and wing morphology
Authors: SPEAR LARRY B. , AINLEY DAVID G.
Published: April 2008

We studied flight direction relative to wind direction (hereafter referred to as “flight direction”), the relation between wing morphology and flight behaviour and interspecies relationships in flight behaviour among all major seabird taxa. We calculated wing loading and aspect ratios for 98 species from 1029 specimens. Species were sorted into 13 groups on the basis of similarity in patterns of flight direction. The primary flight direction of Pelecaniformes and Charadriiformes was into and across headwinds. The most common flight direction of Procellariiformes was across wind. Seabirds avoided flying with tailwinds. Wing loading and aspect ratios were positively correlated in Procellariiformes, Pelecaniformes and alcids but negatively correlated in larids. In Procellariiformes, incidence of headwind flight and that of tailwind flight were significantly correlated with wing loading and aspect ratio; species with higher wing loading and aspect ratios flew more often into headwinds and less often with tailwinds. In contrast, the proportion of Pelecaniformes and Charadriiformes flying with tailwinds increased significantly with increased wing loading. Our results demonstrate a close link in seabirds between flight behaviour, wing morphology and natural history patterns in terms of distribution, colony location, dispersal and foraging behaviour.
Nonbreeding and nests without eggs in the Lesser Black‐backed Gull Larus fuscus
Authors: O'CONNELL M. J. , COULSON J. C. , RAVEN S. , JOYCE S.
Published: April 2008

Estimates of the number of breeding Lesser Black‐backed Gulls Larus fuscus at the Tarnbrook Fell gullery, Lancashire, have been made from annual counts of nests since 1981. During all of these surveys, the mean percentage of nests which did not contain eggs has been remarkably constant from year to year (54%± 1.9%). A study of specific nests at the colony in 1992 showed that the great majority of these “empty” nests did not subsequently receive eggs. in 1993, a study of a sample of territory‐holding gulls was made on a 0.41‐ha study plot to investigate and to quantify the occurrence of empty nests. Of the 62 pairs that defended a territory and constructed a complete nest, 27% subsequently failed to produce eggs. These birds attended their territory as a pair significantly less frequently than pairs that produced clutches and achieved significantly fewer apparently successful mountings. Sixty percent of pairs constructed more than one nest, and 58% of all nests built received no eggs. The construction of empty nests was not found to be related to the density of nesting gulls. Since 1981, estimates of the number of gulls in the colony have been based on the assumption that one nest represents one pair of gulls. This has been shown not to be the case, and a correction multiplier of 0.61 must be applied to counts of nests at the colony to obtain an estimate of the number of breeding gulls.
Adaptive variation in the foraging behaviour of Grey Plover Pluvialis squatarola and Whimbrel Numenius phaeopus
Authors: TURPIE JANE K. , HOCKEY PHILIP A. R.
Published: April 2008

Between‐site variation in the diet and foraging behaviour of a fixed‐method forager, the Grey Plover Pluvialis squatarola, and a versatile forager, the Whimbrel Numenius phaeopus, was examined and compared at nine tropical and south temperate sites. Grey Plover always foraged in a run‐stop‐search manner but changed the emphasis of components of this behaviour in response to prey type. Whimbrel foraged tactilely or visually and readily changed foraging speed and habitat. Both species ate a variety of prey species depending on their availability. The diet of Grey Plover was dominated by small prey, polychaetes and crabs, and Whimbrel ate mostly crabs, with Whimbrel being the more specialized in prey choice. The broader diversity of prey types consumed by Grey Plover was attributed to limitations imposed by obligate visual foraging, whereas the flexible foraging behaviour of Whimbrel allowed the latter to concentrate their efforts on the most profitable prey. Grey Plover appeared to have a density upper limit, determined by their stereotyped foraging behaviour. Whimbrel densities varied greatly in response to prey type and foraging method. Foraging effort could not be predicted from measurements of instantaneous daytime energy intake rates, and reasons for the lack of this relationship are discussed.
Climb and flight speeds of shorebirds embarking on an intercontinental flight; do they achieve the predicted optimal behaviour?
Authors: PIERSMA THEUNIS , HEDENSTRÖM ANDERS , BRUGGEMANN J. HENRICH
Published: April 2008

Most Arctic‐breeding waders wintering in West Africa cover the first 4000 km of their northward journey in spring by a single flight to western Europe. We examined the extent to which waders economize their flight behaviour during departure by comparing climb rates and forward flight speeds with predictions based on flight mechanic theory and the relevant morphological measurements made of birds collected on the site. With an optical range finder, we followed 98 wader flocks on their departure from Banc d'Arguin in Mauritania. We also measured wind speed and direction at different altitudes by tracking helium‐filled balloons and thus were able to deduce airspeeds from groundspeeds of the departing flocks. Of the nine species examined, six showed the predicted negative relationship between climb rate and airspeed, although only one was statistically significant. By normalizing the data, we found a statistically significant negative correlation across all species. Although 17% of the observed climb rates were greater than the predicted theoretical maximum, the average observed climb rate was lower than the predicted optimum and the average observed airspeed was higher. The absolute deviations of climb rates from theory may have been because of the existence of pockets of rising and sinking air at the boundary of desert and ocean. That the absolute deviations in average climb rate and airspeed followed the predicted negative relationship is in accordance with the current theory of flight mechanics.
The role of male territories in the mating system of the Yellow‐shouldered Widowbird Euplectes macrourus
Authors: SAVALLI UDO M.
Published: April 2008

The territorial system and breeding biology of the Yellow‐shouldered Widowbird Euplectes macrourus (Ploceidae) was investigated in western Kenya. Yellow‐shouldered Widowbirds had a resource‐defence polygynous mating system: males defended large (mean = 0.95 ha) territories and built the coarse framing for the nests in tall grass. Males had up to five females nesting per territory. Females provided nearly all parental care except for a territorial male seen feeding a fledgling: the first observation of paternal care in the wild for this genus. There was considerable variation in territory size, but the cause of this variation remains unknown: territory size was not related to potential indicators of territory quality, such as grass height and abundance, did not relate to male morphology (mass, size and ornament size) or territorial behaviour (boundary displays and singing) and did not affect female preferences. Although resources (territories and nests) were defended by the males, observations that males frequently fed outside their territories and formed communal roosts during the breeding season suggest that this species represents a transitional stage between typical resource‐defence polygyny and lek breeding.
Adaptive significance of the mega‐billed form in the polymorphic Black‐bellied Seedcracker Pyrenestes ostrinus
Authors: SMITH THOMAS B.
Published: April 2008

The polymorphic African estrildid finch, the Black‐bellied Seedcracker Pyrenestes ostrinus, exhibits extreme large‐billed variants in transition zones between forest and savanna. Using field data collected between 1983 and 1995 at six sites in Cameroon, I examined the adaptive significance of bill size in this mega‐billed form. In comparison with small and large morphs, body size increased more rapidly in the mega‐billed form, a trend that is consistent with some other species of finches subject to avian predators in open habitats and that suggests aerodynamic constraints imposed by larger bills are compensated by increased body size. Although additional research is required, preliminary results indicate mega‐billed birds may interbreed with other bill morphs and may therefore represent a third distinct morph rather than a distinct species.
Diving behaviour of the Shy Albatross Diomedea cauta in Tasmania: initial findings and dive recorder assessment
Authors: HEDD APRIL , GALES ROSEMARY , BROTHERS NIGEL , ROBERTSON GRAHAM
Published: April 2008

The diving behaviour of the Shy Albatross Diomedea cauta was investigated using archival time‐depth recorders (TDRs) and maximum depth gauges (MDGs). Data from birds carrying multiple devices and from diving simulations indicated that the degree of correspondence between TDRs and MDGs varied with the dive depth, duration and frequency, as well as with body placement. The MDGs were the most reliable when the diving depth was greater than 0.5 m, when the diving frequency was low and when gauges were placed on the birds' backs. The TDRs were used during late incubation and early chick rearing in 1994. Fifty‐two dives (0.4 m) were recorded during 20 foraging trips of 15 individuals. The majority of dives were within the upper 3 m of the water column and lasted for less than 6 s. However, dives to 7.4 m and others lasting 19 s were recorded. The albatrosses dived between 07.00 h and 22.00 h, with peaks in their diving activity near midday and twilight. Mean diving depth varied throughout the day. with the deepest dives occurring between 10.00 h and 12.00 h. Two dive types were identified on the basis of the relationship between dive depth and descent rate. Plunge dives were short (5 s), and the birds reached a maximum depth of 2.9 m. Swimming dives were both longer and deeper. The characteristics of Shy Albatross plunge dives were similar to those of gannets Morus spp., which are known to be proficient plunge divers. Swimming dives suggest that Shy Albatrosses actively pursue prey underwater.
Nest site characteristics, duration of use and breeding success in the Guillemot Uria aalge
Authors: HARRIS M. P. , WANLESS S. , BARTON T. R. , ELSTON D. A.
Published: April 2008

The fate of all eggs laid by Guillemots Uria aalge in seven study areas on the Isle of May was recorded in 12 consecutive seasons. The average success at each site was related to its physical characteristics, bird density, position on the cliff and availability of suitable habitat for ticks. The numbers of neighbours and walls, type of site, slope where the egg was incubated and distance from the top of the cliff all had a significant effect on both hatching and breeding success. Potential tick habitat had no significant effect. Much variation in hatching and breeding success remained unexplained. Sites used when the colony was less than half its current size and most frequently in the period 1984–1995 were the most successful. Since an average Guillemot pair remains together at a site for only 3–4 years. the consistently high success of many sites over a period of 10–12 years suggests that the most used sites were occupied by a succession of high‐quality birds.
Effects of ectoparasites on the Sand Martin Riparia riparia nestlings
Authors: ALVES MARIA ALICE SANTOS
Published: April 2008

The effects of ectoparasites on the body mass of Sand MartinRiparia riparianestlings were experimentally tested. Chicks from nests treated with a pesticide to kill arthropod ectoparasites were heavier than chicks from control nests, indicating that ectoparasitism may be a cost for Sand Martins.
Spring habitat use and feeding behaviour of Steller's Eider Polysticta stelleri in Varangerfjord, northern Norway
Authors: FOX A. D. , MITCHELL CARL
Published: April 2008

The distribution and abundance of Steller's Eider Polysticta stelleri were studied in Varangerfjord, Norway, in May 1995, immediately prior to the birds' departure for the breeding areas. Almost 80% of the variance in Steller's Eider numbers was explained by a regression model based upon low tide beach width, suggesting strong selection for gently shelving coastal profiles. Such habitat is common but restricted in Varangerfjord and is rare along surrounding coastlines where the species is more scarce. The majority of Steller's Eider and the Common Eider Somateria mollissima were recorded within 200 m of the coast, in contrast to the King Eider Somateria spectabilis, which tended to be more than 200 m from the shore. More detailed observations at one study site showed that Common and Steller's Eiders fed in different ways and in separate areas, despite similar proximity to the shore, although the two species did aggregate together to roost at high tide, particularly during the daytime. Steller's Eider showed a strong tidal rhythm in activity by day and night, roosting at high tide, diving offshore on the ebb and flow tides but resorting to algal beds and sandy‐mud beaches to feed at low tide.
Blackcaps Sylvia atricapilla stopping over at the desert edge; inter‐ and intra‐sexual differences in spring and autumn migration
Authors: IZHAKI IDO , MAITAV ASAF
Published: April 2008

Spring and autumn Palaearctic‐African migration patterns of Blackcaps Sylvia atricapilla during stopover at Elat, Israel, showed that males appeared significantly earlier than females during spring but not during autumn migration, suggesting that in males there is a stronger drive to reaching breeding territories early. The difference in mean appearance dates between sexes in spring tended to be greatest in years when the males appeared earliest. Longer spread of passage (the dates between which the central 50% of individuals were captured) for each sex in spring was found in years with an early mean passage datebut was significant only for females. These observations suggest that the timing of Blackcap migration is governed not only by endogenous factors but also by exogenous factors, and when the environmental conditions are unfavourable, the differences in passage dates between sexes decrease and the passage lengths shorten. The early individuals (both males and females) that stopped over at Elat in spring were those with relatively small body size (as indicated by relatively short wings) and relatively large fat reserves and in good body condition (as indicated from fat score and body mass/wing‐length ratio). No differences in body size between early and late transients were detected during the autumn migration, but late birds of both sexes carried larger fat reserves. These phenomena may be explained either by leap‐frog migration or by differential fitness among wintering males and females or both, with only the fittest Blackcaps being capable of an early departure. These individuals probably face much less intensive intra‐ and interspecific competition with residents and other transients in stopover sites than do later transients.
Influence of cave structure, microclimate and nest harvesting on the breeding of the White‐nest Swiftlet Collocalia fuciphaga germani in Viêtnam
Authors: PHACH NGUYÊN QUANG , VOISIN JEAN‐FRANCOIS
Published: April 2008

In Viêtnam, most White‐nest Swiftlet Collocalia fuciphaga colonies (80% of the colonies in Da Nang and 58% in Khanh Hoa provinces), and all large ones, were found in caves with wide openings where the sea entered far inside and waves may wash away numbers of nests. In dry caves above sea level, air with a relative humidity below 70% may cause many nests to fall from the walls. Breeding success was strongly influenced by nest harvesting and was especially low in the third and fourth clutches. The best harvesting method is to collect the nests twice a year, and the first harvest should occur only when the first 10–15% of the nests have eggs. The second harvest should be made when second clutch fledglings have left the nest. The later the first harvest occurs, the lower are the ability of the swiftlets to rebuild second nests and the productivity of second clutches.
The need for continued scientific collecting; a geographic analysis of Mexican bird specimens
Authors: PETERSON A. TOWNSEND , NAVARRO‐SIGÜENZA ADOLFO G. , BENÍTEZ‐DÍAZ HESIQUIO
Published: April 2008

The geographic and spatial distribution of more than 221,000 bird specimens collected in Mexico was analyzed on a grid of 1d̀ blocks to assess adequacy of representation of the country's avifauna in world systematic collections. Frequency distributions of specimens per block, specimens per species expected in blocks and total specimens per species were all severely right‐skewed, with a few blocks well sampled but most represented by very few specimens. Overall, seven scattered blocks out of about 240 were considered well sampled. The best sampled species in the country (House FinchCarpodacus mexicanus) and the best sampled Mexican endemic species (Russet Nightingale‐thrushCatharus occidentalis) were characterized by uneven and inadequate spatiotemporal sampling, especially in autumn, when plumages are generally fresh and most useful for studies of geographic variation; sampling for a species close to the median of the distribution (Great Black‐hawkButeogallus urubitinga) was scattered and inappropriate for statistical analysis. Results suggest strongly that sampling of Mexican birds is incomplete, that continued scientific collecting is needed to complete knowledge of the country's avifauna and that similar collecting efforts will be necessary throughout much of the tropics
Inter‐ and intra‐specific dominance relationships and feeding behaviour of Golden Eagles Aquila chrysaetos and Sea Eagles Haliatetus albicilla at carcasses
Authors: HALLEY D. J. , GJERSHAUG J. O.
Published: April 2008

The behaviour of Golden Eagles Aquila chrysaetos and Sea Eagles Haliceetus albicilla scavenging on artificially laid out carcasses in coastal Sør‐Trøndelag Province, Norway, was studied during two winters (totalling 640 h of observations) and the intervening summer (430 h). Neither species fed at carcasses in summer. Although smaller, Golden Eagles were strongly dominant over Sea Eagles in direct competition for carcass access. In Sea Eagles, females dominated males, while in Golden Eagles, few conflicts between birds of known sex were observed. Age effects were weak and not statistically significant in both species. Conflicts for carcass access tended to be most escalated between Golden Eagles and least escalated between Sea Eagles, with interspecific conflicts intermediate. Most conflicts were won by the aggressor, suggesting that birds were generally able to assess relative dominance before launching an attack. Young eagles fed longer at a carcass than older individuals in both species, suggesting that young eagles may have been hungrier or less efficient feeders. Sea Eagles waited longer than Golden Eagles between arrival in the immediate carcass area and feeding at the carcass. This effect was greater when the carcass was already occupied but also occurred when no other eagle was already present. While interspecific competition for carrion did not appear to have important consequences for the two species in coastal Norway, in western Scotland, where Sea Eagles are currently re‐establishing, carrion is important in the diet of both species all year round. Interspecific competition for this resource may therefore play a role in determining the ultimate realized niche (and therefore numbers) of the two species in Scotland in the longer term.
Age‐specific patterns of reproduction in White‐tailed and Willow PtarmiganLagopus leucurusandL. lagopus
Authors: WIEBE KAREN L. , MARTIN KATHY
Published: April 2008

Although many studies report a difference in reproductive success between old and young birds, little is known about how, why and when productivity changes as individuals age. We examined age‐dependent reproduction in two bird species that inhabit harsh tundra environments: White‐tailed PtarmiganLagopus leucurusin alpine areas and Willow PtarmiganLagopus lagopusin subarctic Canada. We evaluated reproductive performance in the light of three hypotheses: constraint, restraint and selection. Using cross‐sectional and longitudinal data, we observed significant age effects in seven of the eight life history and behavioural traits examined for the two species. However, the pattern of age effects variedconsiderably across life history stages; younger birds generally had smaller clutches, later laying dates and poorer spring body condition, but the nesting success did not vary with age. Brood‐rearing and renesting abilities were greater for older parents. The oldest age class of White‐tailed Ptarmigan showed reproductive senescence for laying date and clutch size but fledged such a large proportion of the brood that they had the highest overall production of any class. It thus appears that parental experience can compensate for reduced physical ability to produce eggs. Annual mortality rates for breeding females were U‐shaped for White‐tailed Ptarmigan, with higher rates for young and old birds, but mortality did not change with age in Willow Ptarmigan. Overall, the two species differed in the presence of age dependence for only two traits (renesting ability and annual survival). Age‐dependent effects were generally greater for White‐tailed Ptarmigan than for Willow Ptarmigan. The patterns of mortality and fecundity we observed in ptarmigan provide general support for the constraint hypothesis of reproductive performance. By examining discrete stages of reproduction, we identified the life history stages where age effects occur and propose proximate mechanisms responsible for these effects.
Locally stable wintering numbers in the Oystercatcher Haematopus ostralegus where carrying capacity has not been reached
Authors: GOSS‐CUSTARD JOHN D. , ROSS JOHN , McGRORTY SELWYN , DURELL SARAH E. A. le V. dit , CALDOW RICHARD W. G. , WEST ANDREW D.
Published: April 2008

Since 1976, the numbers of OystercatchersHaematopus ostraleguswintering on the Exeestuary have fluctuated independently of the substantial increase over the same period in the numbers wintering in Britain as a whole. While this might imply that the carrying capacity of the Exe has been reached, closer examination suggests not. Over a sample of the years studied, Oystercatcher numbers on the main MusselMytilus edulisfeeding areas increased even though the mussel bed quality remained unchanged, food abundance decreased and disturbance on some important beds increased. There was some redistribution of birds between mussel beds, apparently linked to the increased bird numbers and to a relative improvement in the food supply on two preferred mussel beds. The increase in Oystercatcher numbers on the main feeding areas over a period in which the feeding conditions did not improve suggests that carrying capacity was not reached on the mussel beds themselves and, therefore, on the estuary as a whole.
Sexual dimorphism and tail‐length in widowbirds and bishopbirds (Ploeeidae: Euplectes spp.): a reassessment
Authors: CRAIG ADRIAN J. F. K. , VILLET MARTIN H.
Published: April 2008

No evidence for sexual selection in the evolution of tail‐length or wing‐length in widow birds and bishopbirds (genus Euplectes) was found when the methods used by previous authors were applied to a larger set of data. Nuptial tail‐length dimorphism scaled with body size dimorphism except in Euplectes progne, and interpopulation variation in taillength could be explained by genetic drift alone. Wing‐length appears to be under stabilizing selection and scales allometrically with body size, with no relation to tail‐length unless E. progne is included in the analysis.
Vocal begging by nestlings and vulnerability to nest predation in Meadow Pipits Anthus pratensis; to what extent do predation costs of begging exist?
Authors: HALUPKA KONRAD
Published: April 2008

Models of the evolution of parent‐offspring communication and of brood size assume that the noisy begging by the young is costly in terms of predation. The present study was designed to investigate cause‐and‐effect relations between the behaviour of the offspring and adult Meadow Pipits Anthus pratensis and the risk of nest predation. Harriers (Circus spp.), which can use auditory signals, were the main predators in the study area. I found that the intensity of vocal begging by broods did not influence their survival, despite the fact that the proportion of time that parents sacrificed to nest guarding declined with increased begging and some broods readily begged if a stimulus resembling the approaching parent was produced. The lack of fitness penalties for noisy broods was attributed to the following factors: (1) the open habitat was easy to scan, and parents silenced the young before feeding them if a predator was close (this adaptation was demonstrated in an experiment) and (2) parent birds could not deter harriers searching for prey, and therefore nest guarding did not influence the probability of nest detection. Pitfalls in the interpretation of relations between the vocal begging and the vulnerability to nest predation are discussed.
Flocking behaviour of foraging birds in a neotropical rain forest and the antipredator defence hypothesis
Authors: THIOLLAY JEAN‐MARC , JULLIEN MATHILDE
Published: April 2008

Randomly encountered foraging birds were recorded in a primary rain forest of French Guiana (13,550 records of 216 species), together with their size, diet and habitat use, to assess the relative frequencies of different types of flocking behaviour and some of their ecological correlates. Overall, 42% of birds foraged singly, primarily carnivores (raptors), nectarivores (hummingbirds) and lek‐mating frugivores (manakins, some cotingas). For‐aging in pairs (26.6%) was widespread, notably among insectivores in the 17–32‐g size class. The remaining 31.4% of records were birds in groups of different composition and function, including, in order of decreasing frequency, (1) multispecies upper canopy flocks (83 member species identified)—the largest and most mobile associations of small insectivores, nectarivores and frugivores, mostly tanagers; (2) understorey mixed species flocks of small insectivores, at midlevels of closed forest interior, with 12 core, obligate members and 74 occasional species, mostly active foliage or bark gleaners and probers sharing a unique set of ecological characteristics; (3) monospecific groups (29 species), either gregarious foragers but solitary breeders (large frugivores in canopy) or also breeding colonially or several permanently group living cooperative breeders; (4) opportunistic gatherings of frugivores at fruiting trees (at least 40 species); (5) army ant followers near ground of closed understorey (29 species of mid‐ to large‐sized insectivores); (6) followers of Red‐throated Caracaras Daptrius americanus (23 species, usually canopy frugivores entering understorey with caracaras); (7) two raptors following monkeys. Attributes of vulnerability to predators defined by habitat structure (vegetation density or openness) and foraging behaviour (conspicuousness, speed, degree of vigilance) were important determinants of flocking propensity, at least in flocks that were not attracted by a particular food source. The results suggest that the permanent mixed‐species flocks in the mature forest under‐storey may be an antipredator defence to compensate for the conspicuousness and reduced vigilance resulting from active foraging behaviour in semi‐open vegetation, where early detection of predators is difficult.
Habitat selection and breeding success in Yellow‐legged Gulls Larus cachinnans
Authors: BOSCH MARC , SOL DANIEL
Published: April 2008

The habitat selection and breeding performance of Yellow‐legged Gulls Larus cachinnans were studied in the Medes Islands colony, northeastern Spain, during 1995 and 1996. Of the three main habitats on the islands (shrubs, grass and bare areas), gulls first occupied those with the highest percentage of tall vegetation. Gulls tended to select nest sites with 20–75% cover despite great differences in the cover in the habitats and territories, suggesting that the presence of a suitable nest site may play a major role in the choice of breeding habitat. Nest‐site tenacity did not influence the preferences of gulls at any level since the same pattern of choice was observed in an area subjected to annual culls (i.e. where most of the breeding pairs were culled annually and replaced by naive birds). In spite of great differences in the physical characteristics of the habitats, little difference was found in breeding performance of the gulls between habitats. Gulls nesting in the least preferred habitat (i.e. mainly bare) had smaller clutches than those nesting in the other two habitats, possibly as a result of their later seasonal laying. Despite the similar breeding success in different habitats, gulls did not seem to distribute according to the ideal free model reported for Herring Gulls Larus argentatus since the density in the preferred habitat (i.e. shrubs) was never higher than in the other two. We suggest that the habitat selection by Yellow‐legged Gulls within the colony could follow an ideal despotic distribution.
Body size variation in Audouin's Gull Larus audouinii; a density‐dependent effect?
Authors: RUIZ XAVIER , GONZÁLEZ‐SOLÍS JACOB , ORO DANIEL , JOVER LLUIS
Published: April 2008

A significant decrease in the body size of Audouin's Gulls Larus audouinii breeding at the Chafarinas Islands is reported. The decrease in linear measurements in the current breeding population ranged from 2.5% to 5.6% in males and from 0.61% to 4.4% in females. This was detected when assessing the reliability of a sex‐discriminating function derived for the same colony 13 years earlier. When applied to the current population, this function failed to predict the sex of a large proportion of males (44%). The relative decrease in mean size was significantly greater in males than in females for culmen, nalospi and tarsus lengths, while for bill depth at culmen, wing length and body mass the relative decrease was similar in both sexes. Since the extent of differences depended on sex, these differences cannot be attributed to a systematic between‐observer bias. Mean body size reduction might be either the result of a greater proportion of small breeding birds in the current population, because of increased availability of nesting sites (competition relaxation hypothesis), or an outcome of environmental factors affecting growth parameters (environmental constraint hypothesis). According to the first hypothesis, the changes observed would be associated with higher variability values. Conversely, if the second is true, the degree of variability should be similar. Since there are no significant differences in the degree of variability shown in the two data sets, our results support the second hypothesis. The environmental constraint acting via growth parameters is probably related to the increase in the number of Audouin's Gull breeding pairs while food availability was depleted. Our data suggest that changes in the duration of the growth period, rather than in the growth rates themselves, are involved in the body size differences found.
Latitudinal trends, population size and habitat preferences of the Damara Tern Sterna balaenarum on Namibia's desert coast
Authors: SIMMONS ROBERT E. , CORDES IMKE , BRABY ROD
Published: April 2008

The Damara Tern Sterna balaenarum is a rare, near‐endemic breeder along the southwestern coast of Africa. Found predominantly in Namibia, its world population was once believed to be 4000 birds. Population surveys in the northern Namib Desert have recently estimated that 12,000 adults exist. The aims of this study were to (1) determine the population status along the southern coast, thereby completing Namibian surveys, (2) assess latitudinal trends (over 10d̀) in relation to ocean upwellings for the entire coast and (3) determine breeding habitat preferences. This was completed in 1994 and 1996 using random sampling techniques. Survey squares of 1 km2, randomly plotted on 1:50,000 maps, were located in the desert with a Global Positioning System (GPS) unit and searched for breeding terns. A total of 1780 km2 was sampled in the southern desert and extrapolations indicated that about 1450 adult terns occur in this region. This gives a global population estimate of 13,500 adult Damara Terns. Significant habitat preferences were apparent with terns nesting most often on gravel plains in the north but switching to salt pans in the south. Lower salt pan temperatures in the south may account for these trends. The peak density was in central areas (23|dGS) with a decreasing density north and south along Namibia's 1470 km‐coast. This is parallel to recent findings for linear shorebird densities and macro‐invertebrate density. This suggests that primary productivity of the Benguela is highest in the central regions and not where the upwellings occur 400 km south. We propose a delayed blooming effect to account for these trends and conclude that this diminutive tern is influenced in many aspects of its life history by Namibia's cold offshore upwellings.