Seabird Density Research Articles

Comparing an estimate of seabirds at risk to a mortality estimate from the November 2004 Terra Nova FPSO oil spill

On 21 November 2004, about 1000 barrels of crude oil were accidentally released from the Terra Nova FPSO (floating production, storage and offloading) onto the Grand Banks, approximately 340 km east-southeast of St. John’s, Newfoundland. We estimated the number of vulnerable seabirds (murres ( Uria spp.) and dovekies ( Alle alle)) at risk from this incident by multiplying observed densities of seabirds with the total area covered by the slick, estimated at 793 km 2. A mean density of 3.46 murres/km 2 and 1.07 dovekies/km 2 on the sea surface was recorded during vessel-based surveys on 28 and 29 November 2004, with a mean density of 6.90 murres/km 2 and 13.43 dovekies/km 2 combining those on the sea and in flight. We calculated a mean of 9858 murres and dovekies were at risk of being oiled, with estimates ranging from 3593 to 16,122 depending on what portion of birds in flight were assumed to be at risk. A mortality model based on spill volume was derived independently of the risk model, and estimated that 4688 (CI 95%: 1905–12,480) birds were killed during this incident. A low mortality estimate based strictly on spill volume would be expected for this incident, which occurred in an area of relatively high seabird densities. Given that the risk and mortality estimates are statistically indistinguishable, we estimate that on the order of 10,000 birds were killed by the Terra Nova spill.

Pelagic habitat of seabirds in the eastern tropical Pacific: effects of foraging ecology on habitat selection

A central tenet of ecology is the quantification of species-habitat relationships in order to explain spatial variability in the distribution and abundance patterns of animals. We quantified habitat preferences for 6 tropical seabird species representing a phylogenetically and ecologically diverse group within the eastern tropical Pacific (ETP). Seabird censuses were conducted aboard NOAA research vessels from August to November of 1989 and 1990 using 300 m strip transect meth- ods. Simultaneously with the seabird censuses and from the same ships, oceanic habitat was quanti- fied by measuring sea surface temperature, salinity, and chlorophyll, as well as thermocline depth and strength. We quantified seabird habitat using generalized additive models fitted with forward and backward selection algorithms based on minimizing the Akaike information criterion (AIC). In general, seabird habitat models performed well in explaining spatial variability in abundance, reduc- ing the null deviance to ranges between 42.8 and 73.5%, and predicting seabird density patterns with an accuracy ranging from 56.6 to 80.5%. Relative abundance of the species modeled affected the outcome: the higher the abundance, the more robust the fit. Seabirds feeding on fishes and squids associated with habitats characterized by deep (>100 m) and strong (>2°C 10 m -1 ) thermoclines, while planktivorous species preferred habitat characterized by shallower thermoclines with cooler surface temperatures (<25°C) and a less stratified water column. Thus, seabirds in different feeding guilds have clear and distinct habitat preferences within the ETP. We propose thermocline topo- graphy as a key variable in predicting distribution and abundance of seabirds in this area, probably due to its influence on the availability of seabird prey.

Mapping sea bird densities over the North Sea: spatially aggregated estimates and temporal changes

AbstractIn the Dutch sector of the North Sea, sea bird densities are recorded bi‐monthly by using airborne strip‐transect monitoring. From these data we try to estimate: (i) high‐resolution spatial patterns of sea bird densities; (ii) low‐resolution spatial‐average bird densities for large areas; and (iii) temporal changes in (i) and (ii), using data on Fulmaris glacialis as an example. For spatial estimation, we combined Poisson regression for modelling the trend as a function of water depth and distance to coast with kriging interpolation of the residual variability, assuming spatial (co)variances to be proportional to the trend value. Spatial averages were estimated by block kriging. For estimating temporal differences we used residual cokriging for two consecutive years, and show how this can be extended to analyse trends over multiple years. Approximate standard errors are obtained for all estimates. A comparison with a residual simple kriging approach reveals that ignoring temporal cross‐correlations leads to a severe loss of statistical accuracy when assessing the significance of temporal changes.This article shows results for Fulmaris glacialis monitored during August/September in 1998 and 1999. Copyright © 2005 John Wiley &amp; Sons, Ltd.

Physical and biological variables affecting seabird distributions during the upwelling season of the northern California Current

Abstract As a part of the GLOBEC-Northeast Pacific project, we investigated variation in the abundance of marine birds in the context of biological and physical habitat conditions in the northern portion of the California Current System (CCS) during cruises during the upwelling season 2000. Continuous surveys of seabirds were conducted simultaneously in June (onset of upwelling) and August (mature phase of upwelling) with ocean properties quantified using a towed, undulating vehicle and a multi-frequency bioacoustic instrument (38–420 kHz). Twelve species of seabirds contributed 99% of the total community density and biomass. Species composition and densities were similar to those recorded elsewhere in the CCS during earlier studies of the upwelling season. At a scale of 2–4 km, physical and biological oceanographic variables explained an average of 25% of the variation in the distributions and abundance of the 12 species. The most important explanatory variables (among 14 initially included in each multiple regression model) were distance to upwelling-derived frontal features (center and edge of coastal jet, and an abrupt, inshore temperature gradient), sea-surface salinity, acoustic backscatter representing various sizes of prey (smaller seabird species were associated with smaller prey and the reverse for larger seabird species), and chlorophyll concentration. We discuss the importance of these variables in the context of what factors seabirds may use to find food. The high seabird density in the Heceta Bank and Cape Blanco areas indicates them to be refuges contrasting the low seabird densities currently found in most other parts of the CCS, following decline during the recent warm regime of the Pacific Decadal Oscillation.

Nitrogen ecophysiology of Heron Island, a subtropical coral cay of the Great Barrier Reef, Australia.

Coral cays form part of the Australian Great Barrier Reef. Coral cays with high densities of seabirds are areas of extreme nitrogen (N) enrichment with deposition rates of up to 1000 kg N ha-1 y-1. The ways in which N sources are utilised by coral cay plants, N is distributed within the cay, and whether or not seabird-derived N moves from cay to surrounding marine environments were investigated. We used N metabolite analysis, 15N labelling and 15N natural abundance (δ15N) techniques. Deposited guano-derived uric acid is hydrolysed to ammonium (NH4+) and gaseous ammonia (NH3). Ammonium undergoes nitrification, and nitrate (NO3-) and NH4+ were the main forms of soluble N in the soil. Plants from seabird rookeries have a high capacity to take up and assimilate NH4+, are able to metabolise uric acid, but have low rates of NO3- uptake and assimilation. We concluded that NH4+ is the principal source of N for plants growing at seabird rookeries, and that the presence of NH4+ in soil and gaseous NH3 in the atmosphere inhibits assimilation of NO3-, although NO3- is taken up and stored. Seabird guano, Pisonia forest soil and vegetation were similarly enriched in 15N suggesting that the isotopic enrichment of guano (δ15N 9.9‰) carries through the forest ecosystem. Soil and plants from woodland and beach environments had lower δ15N (average 6.5‰) indicating a lower contribution of bird-derived N to the N nutrition of plants at these sites. The aquifer under the cay receives seabird-derived N leached from the cay and has high concentrations of 15N-enriched NO3- (δ15N7.9‰). Macroalgae from reefs with and without seabirds had similar δ15N values of 2.0-3.9‰ suggesting that reef macroalgae do not utilise 15N-enriched seabird-derived N as a main source of N. At a site beyond the Heron Reef Crest, macroalgae had elevated δ15N of 5.2‰, possibly indicating that there are locations where macroalgae access isotopically enriched aquifer-derived N. Nitrogen relations of Heron Island vegetation are compared with other reef islands and a conceptual model is presented.

BLACK-BROWED ALBATROSSES FORAGING ON ANTARCTIC KRILL: DENSITY-DEPENDENCE THROUGH LOCAL ENHANCEMENT?

Many Antarctic seabirds depend on prey that are patchy, cryptic, ephemeral, and unpredictable in location. These predators typically employ two alternative behavioral strategies for locating resource patches: direct visual or olfactory detection, and indirect detection (local enhancement) by sighting other predators that are already exploiting a patch. We developed a model of direct detection and local enhancement in seabirds that predicts how foraging success varies with behavioral strategy, seabird densities, and prey swarm density and detectability. Application of the model to Black-browed Albatrosses foraging for Antarctic krill near South Georgia suggests that local enhancement is generally a highly effective foraging strategy, and that the fraction of time albatrosses spend in feeding flocks should show strong interactions between prey and conspecific densities. To test these predictions, we analyzed survey data collected near South Georgia in January-March 1986. Our analysis suggests a strong Allee-type density dependence in foraging success that was qualitatively and quantitatively consistent with model predictions. This density dependence suggests a potential for destabilizing patterns of resource utilization and reproductive suc- cess in Black-browed Albatrosses that may have important implications for conservation of albatrosses and other Antarctic species.

Plant communities along environmental gradients of high‐arctic mires in Sassendalen, Svalbard

Abstract. The wet to moist bryophyte‐dominated vegetation of Sassendalen, Svalbard, was classified into seven communities. These communities were grouped into (1) Cardamino nymanii‐Saxifragion foliolosae marsh; (2) Caricion stantis fen; (3) Luzulion nivalis snowbed – including manured vegetation corresponding to moss tundras. All communities have a basically arctic distribution. Marshes are developed in habitats with a water table above the bryophyte vegetation surface and fens on sites with a water table level high above the permafrost but below the bryophyte surface. Moss tundras normally have no standing water table, but in Sassendalen they have a low water table due to their development on less steep slopes than in their normal habitat near bird cliffs.CCA confirms that the standing water level is the prime differentiating factor between the alliances, while aspect favourability and permafrost depth differentiate between the fen communities and temporary desiccation is important for the Catoscopium nigritum community. Carex subspathacea is a characteristic fen species in the absence of other Carex species dominating elsewhere in the Arctic. Arctic marshes are linked to an extremely cold environment. They have a very low species diversity with a few species dominating; Arctophila fulva, Pseudocalliergon trifarium, Scorpidium scorpioides and Warnstorfia tundrae are character species. Moss tundra as defined here appears to be restricted to Svalbard and, probably, neighbouring Novaya Zemlya. This may be due to the absence of rodents and the high seabird density, which is related to the mild sea currents reaching further to the north here and which implies manuring of surrounding ecosystems. Manuring in a very cold environment produces moss carpets with a thin active layer and accumulation of thick peat layers without a standing water level. In Sassendalen the role of arctic seabirds is replaced by Svalbard reindeer which are nonmigratory and are concentrated to favourable grazing areas where their manuring effect is intense. Their long‐term manuring effect probably explains the occurrence of moss tundras in this weakly rolling landscape where seabird colonies are absent.

Winter seabird distribution and abundance off south-western Greenland, 1999

South-western Greenland constitutes an internationally important wintering area for many seabird species. Several species of management concern have a predominantly near-coastal distribution, though available information about seabird numbers is mostly confined to offshore waters. Here we report on extensive aerial surveys conducted in March 1999, covering the coastal waters (up to 15-20 km from the mainland coast) and fjords of south-west Greenland. The most widespread and numerous species were estimated as 463 000 common eiders (Somateria mollissima), 153000 king eiders (S. spectabilis), 125000 thick-billed murres (Uria lomvia), 94 000 long-tailed ducks (Clangula hyemails), and 12 000 black guillemots (Cepphus grylle). A total of 19 bird species were recorded. The estimates for common eider and long-tailed duck approximately represent the entire winter population in south-western Greenland while estimates for the other species represent only an unknown proportion since their distribution continues further offshore. Waters around Nuuk and within the Julianehåbsbugten (Julianehåb Bay) area were identified as areas of high seabird density. A large proportion of the common eider population was aggregated in the fjord systems (22%), calling attention to the importance of fjords for this species. In contrast, pelagic seabird species appear to be absent from the fjords. The large winter population of common eider reveals the importance of south-western Greenland as a key wintering area for the eastern Canadian breeding population. The western Greenland breeding population is the only other contributor, probably amounting to no more than 15 000 pairs.

Response of seabirds to thermal boundaries in the tropical Pacific: the thermocline versus the Equatorial Front

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 219:275-289 (2001) - doi:10.3354/meps219275 Response of seabirds to thermal boundaries in the tropical Pacific: the thermocline versus the Equatorial Front Larry B. Spear1,*, Lisa T. Ballance2, David G. Ainley1 1H. T. Harvey & Associates, 3150 Almaden Expressway, Suite 145, San José, California 95118, USA 2Ecology Program, National Oceanic and Atmospheric Administration/National Marine Fisheries Service, Southwest Fisheries Science Center, 8604 La Jolla Shores Drive, La Jolla, California 92037, USA *E-mail: spearlarry@yahoo.com ABSTRACT: Our 10 yr study is the first to associate seabirds with oceanic boundaries, or fronts, in tropical oceans. It addresses the semi-permanent Equatorial Front, hereafter Œfront¹, a vertical boundary lying between the South Equatorial Current (SEC) and North Equatorial Countercurrent (NECC) in the eastern tropical Pacific (ETP). We also consider the subsurface, horizontal thermal boundary created by the thermocline. Our study area included the front and the north and south boundaries of the SEC and NECC respectively, between 100 and 145°W. Our data were based on 45 north-south crossings of this area. The intensity of the front differed with season and phase of the El Niño Southern Oscillation (ENSO). Densities of planktivorous seabirds, higher at the front than in the SEC or NECC, increased with front intensity (i.e., during autumn/La Niña). Densities of piscivorous seabirds were unaffected by the front, but were related to depth and intensity of the thermocline. Piscivore densities were highest in the NECC, and higher during spring than autumn. Furthermore, they were higher in the western part of the study area, i.e., when and where the thermocline was deepest and most stratified. We suggest that the difference in patterns observed for the tropical planktivorous versus piscivorous seabirds reflects processes that affect the distribution and availability of their respective prey. Zooplankton are concentrated in the surface layer by physical processes that structure the front. Prey fish, on the other hand, are made available by foraging tuna, which drive them to the ocean surface. As a result, the distribution of the piscivorous seabirds is closely tied to that of schooling surface-feeding tunas, that are most abundant in the NECC. Other studies have shown that tunas spend most of their time near the thermocline. We suggest that this, along with the patterns observed among the piscivorous seabirds, indicate that the tuna¹s prey aggregate near the thermocline. Specifically, most tropical squid and small fishes perform vertical movements to the surface at night. A deeper thermocline, such as that of the NECC, is likely to be attractive to these animals for hiding during the day (when the tuna and birds forage) because of the lack of light at depth, and because of the enriched O2 content of the cold-water layer lying immediately below the warmer surface layer. Hence, by searching on a horizontal plane near the boundary created by a deep, well stratified thermal structure, schooling tuna, and thus piscivorous seabirds, are likely to find concentrations of prey more readily than equally abundant prey dispersed throughout a less stratified water column. KEY WORDS: Seabird · Planktivore · Piscivore · Equatorial Front · Thermocline · Tropical Pacific · Southern Oscillation Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 219. Online publication date: September 10, 2001 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2001 Inter-Research.

Species Composition, Abundance, and Distribution of Seabirds along the Northeastern Coast of Sakhalin

Seabirds were counted in September 1998 from the research vessel Professor Khromovand a motorboat in Pil'tun and Lunskii bays and in the contiguous areas of the eastern Sakhalin shelf. Data on the species composition, abundance, and distribution of seabirds are presented. A fairly high species diversity and significantly high density of seabirds were recorded in Pil'tun and Lunskii bays, which are the main areas where they concentrate during the summer months.

Spatial Dynamics of Regional Wintering Populations of Seabirds in the Gradient of Winter Climatic Conditions

The current publication attempts to overview the results of offshore studies of seabirds in the eastern part of the Baltic Proper during the last decade specifically concentrating on ecological analysis of drastically changing population volumes and maximal density trends of the most representative ecological groups of wintering seabirds in the gradient of winter climatic conditions. Significant fluctuations in maximal seabird density levels were found in different phases of the gradient of winter climatic conditions indicating possibly different survival strategies of dominating species and ecological groups of wintering seabirds. Generally the negative impact of extreme winter climatic conditions was evident in the case of all seabird species studied, manifesting itself either through a dramatic decline of feeding resources, or worsening of foraging conditions in typically preferable shallow coastal marine aquatories.

Summer at-sea distribution of seabirds and marine mammals in polar ecosystems: a comparison between the European Arctic seas and the Weddell Sea, Antarctica

The summer at-sea distribution of seabirds and marine mammals was quantitatively established both in Antarctica (Weddell Sea) and in the European Arctic: Greenland, Norwegian and Barents seas. Data can directly be compared, since the same transect counts were applied by the same team from the same icebreaking ship in both regions. The main conclusion is that densities of seabirds and marine mammals are similar in open water and at the ice edge from both polar regions, while the presence of Adélie penguins, minke whales and crabeater seals in densities more than one order of magnitude higher in Antarctic pack-ice must reflect a major ecological difference between both polar systems. The ecological implications of these observations are discussed, especially concerning important primary and secondary (krill) productions under the Weddell Sea pack-ice.

Distribution, abundance and associations of seabirds in the Beagle Channel, Tierra del Fuego, Argentina

We studied the distribution and abundance of seabirds along the Beagle Channel during February and March 1997. We examined the distribution and abundance, following the strip transects methodology, of species and their relation with habitat and foraging strategy of the birds. We divided the study area into six zones a priori. We made 20 trips aboard tourist vessels. The species most abundant in the study area were the imperial cormorant, dolphin gull, kelp gull, black-browed albatross, South American tern and Chilean skua. We concluded that seabirds were distributed non-randomly in the marine environment of the Beagle Channel. The shallow waters present the largest seabird density in the Beagle Channel. The Islas Bridges zone had the highest total density of seabirds, followed by the Bahia Ushuaia zone. The first zone holds colonies of most of the seabird species nesting in the channel. The presence of seabirds in the Bahia Ushuaia zone is influenced by the Islas Bridges zone itself, from where breeding birds come, and also by Ushuaia city, the port and the open garbage dump, where birds that feed on carrion can find alternative sources of food. The distribution of species in the whole study area was related to the foraging strategies, interactions with other species and characteristics of the habitat. We identified three groups of bird species and four independent species by cluster analysis. The first group included the black-browed albatross and the Magellanic penguin, which were associated with deep waters. In the second group the imperial cormorant and Chilean skua were associated with shallow waters along the study area, especially in the Islas Bridges zone where these species breed. Lastly, the kelp gull and southern giant petrel formed interspecific groups on the coast in places influenced by humans. The independent species numbered four. The rock cormorant associated with shallow waters in kelp bed areas. Showing a completely different foraging behaviour from the rest of the species, the dolphin gull occurred in shallow waters in the Islas Bridges zone associated with sea lions' and cormorants' colonies. Diving petrels were associated with deep waters on the west side of the channel. The South American tern was distributed all along the study area.

Marine birds and mammals of the Pacific Subarctic Gyres

The importance of the subarctic gyres of the North Pacific Ocean to marine birds and mammals is poorly known because of a paucity of data spanning appropriate scales of time and space. The little information that is available indicates the western subarctic gyre (WSAG) is more productive than the eastern subarctic gyre (ESAG). In summer the WSAG supports a greater density and higher biomass of seabirds than the ESAG, including at least two species that are more abundant at nesting colonies in the eastern subarctic. Perhaps most revealing of the seabird distributions in this regard is that of southern hemisphere shearwaters ( Puffinus spp. ) that overwinter in the North Pacific. Their biomass is an order of magnitude greater than that of any northern hemisphere species and is three-fold greater in the WSAG than in the ESAG. Several species of cetaceans also appear to be, or to have been prior to commercial depletions, more abundant in the WSA. Among the many prey species consumed by marine birds and mammals, squids and fishes in the family Myctophidae predominate overall. Other forage species, notably euphausiids, Pacific saury ( Cololabis saira) and Atka mackerel ( Pleurogrammus monopterygius) are important at times to certain species. The principal exceptions to this generalization are baleen whales and small seabirds that consume zooplankton. Interannual and decadal-scale variability in the physical environment and food web production affect seabirds and marine mammals at sea and at coastal breeding locations around the margins of the gyres.

Declining thick-billed murre Uria lomvia colonies experience higher gull predation rates: an inter-colony comparison

Avian predators of colonial-nesting seabirds preferentially attack individuals nesting alone or on the edge of groups, apparently because they can forage without being struck by defending neighbours. If nesting densities of colonial seabirds declined, predators are predicted to have fewer foraging constraints and consequently a greater impact on seabird reproduction. Thus, avian predation could prevent the recovery of seabird populations once sources of adult mortality have been removed. To test these predictions, glaucous gull Larus hyperboreus predation rates, foraging mode selection and murre nest-site selection at an expanding thick-billed murre Uria lomvia colony (Coats Island, Canada) were compared with those at declining murre colonies in Northwest Greenland (Timmiak, Kingittoq). At Coats Island, most cliff ledges were densely occupied by breeding murres so that gulls could not forage extensively on foot. Gulls relied on wind when foraging (>10 km/h), which enhanced their aerial maneuverability and enabled them to reach nest sites on narrow ledges that were poorly defended. In contrast, glaucous gulls at Kingittoq foraged on foot regardless of wind conditions because broad ledges supported small breeding groups of murres. This resulted in higher attack and predation rates of murres at low wind speeds at Kingittoq. At Timmiak, which had experienced the greatest population declines, murres nested at high densities on narrow ledges or in crevices inaccessible to gulls. It was concluded that lower nesting densities at declining colonies reduce the risk of injury for gulls during attack and that this increases predation rates at low wind speeds. These findings suggest that seabird population declines that result from human-induced mortality (e.g. over-harvest) can increase the impact of avian predators on seabird reproduction and potentially, slow the recovery of colonies.

Spatial variation in seabird density at a shallow sea tidal mixing front in the Irish Sea

The distributions of Manx shearwater, guillemot, razorbill, fulmar, and kittiwake were examined in relation to sea surface temperature and salinity at the Irish Sea Front in an attempt to understand the manner in which the front is utilized by seabirds. Bird distribution data were collected from 19 crossings of the front along five transects during July 1990. The spatial distributions of the seabirds were analysed by exploratory variography and the application of generalized additive models. The distributions of Manx shearwater, guillemots, and razorbills were associated with the front. A degree of spatial partitioning was also evident that suggested these species were adopting diVerent strategies for the utilization of resources at the front. Comparison with previous studies suggests that the relationship between the seabirds and the Irish Sea Front has been consistent over a period of several years, indicating that the front is a predictable resource for seabirds.

Influence of hydrography, fishing activity, and colony location on summer seabird distribution in the south-eastern North Sea

Possible determinants of the distribution of 11 species of seabird in the south-eastern North Sea were investigated in July 1993 and 1994. During ship transects in both years, seabird distribution, trawling activity, and hydrographic parameters (salinity, temperature, stratification/mixing, water depth, water clarity) were measured. Analysis of environmental and seabird density variables by principal component analysis revealed seven components, explaining 71% of the variance found in all variables. The most important components were: (1) a land–sea gradient combining hydrographic properties and distance to land/nearest colony; (2) trawler abundance; and (3) a factor linked to water stratification and surface temperature. Distance to colony had a significant influence on the densities of all nine breeding species considered. Flight radii differed considerably between the species. Densities in the vicinity of trawlers were particularly high in black-headed gulls (Larus ridibundus), herring gulls (L. argentatus), and great black-backed gulls (L. marinus). Black-headed gulls and herring gulls had the highest proportion of ship-followers of the total number of seabirds at sea; no ship-followers at all were found in Sandwich terns (Sterna sandvicensis), common/Arctic terns (S. hirundo/paradisaea), or guillemots (Uria aalge). Surface salinity, transparency, and thermal stratification were apparently the most important hydrographic properties, characterizing distinct water masses. Cluster analysis revealed a group of four offshore species (Fulmarus glacialis, Uria aalge, Rissa tridactyla, Larus fuscus) and seven inshore species (Larus ridibundus, L. canus, L. marinus, L. argentatus, Sterna sandvicensis, S. hirundo/paradisaea). Relations between important abiotic parameters and seabird diet are discussed.

Flight speed of seabirds in relation to wind speed and direction

We studied flight speed among all major seabird taxa. Our objectives were to provide further insight into dynamics of seabird flight and to develop allometric equations relating ground speed to wind speed and direction for use in adjusting seabird density estimates (calculated from surveys at sea) for the effect of bird movement. We used triangulation at sea to estimate ground speeds of 1562 individuals of 98 species. Species sorted into 25 “groups” based on similarity in ground speeds and taxonomy. After they were controlled for differences inground speed, the 25 groups sorted into eight major “types” on the basis of response to wind speed and wind direction. Wind speed and direction explained 1664% of the variation in ground speed among seabird types. For analyses on air speed (ground speed minus apparent wind speed), we divided the 25 groups according to four flight styles: gliding, flap‐gliding, glide‐flapping and flapping. Tailwind speed had little effect on air speed of gliders (albatrosses and large gadfly petrels), but species that more often used flapping decreased air speed with increase in tailwinds. All species increased air speeds significantly with increased headwinds. Gliders showed the greatest increase relative to increase in headwind speed and flappers the least. With tailwind flight, air speeds were greatest among species with highest wing loading for each flight style except gliders, which showed no relationship. For headwind flight, species with higher wing loading had higher air speeds; however, the relation was weaker in flappers compared with species using some amount of gliding. In contrast, analyses for air speed ratio (i.e. difference between air speed in acrosswinds [with no apparent wind] and speed flown into headwinds, or with tailwinds, divided by speed acrosswind) revealed that among species using some flapping, and with lower wing loading (surface‐feeding shearwaters, small gadfly petrels, storm petrels, phalaropes, gulls and terns), adjusted air speeds more than those with higher wing loading (alcids, “diving shearwaters”, “Manx‐type shearwaters”, pelicans, boobies and cormorants). As a result, most flappers of low wing loading flew much faster than Vmr (the most energy efficient air speed per distance flown) when flying into headwinds. We suggest that better‐than‐predicted gliding performance with acrosswinds and tailwinds of large gadfly petrels, compared with albatrosses, resulted from a different type of “soaring” not previously described in seabirds.

SEABIRD TRANSECT SAMPLING DATA PROCESSING AND HANDLING SYSTEM

Abstract Standard seabird offshore sampling techniques (Tasker et al., 1984; Webb, Durinck, 1992) assume that line transect of 300 m width is basically used for counting birds sitting on the water surface, whereas “snapshot” method is used for counting flying birds at strongly fixed intervals of time. All the birds counted using the above mentioned combination of methods are used for further calculations of seabird densities at some fixed intervals of time. There are several applications developed in Europe by the leading teams of marine ornithologists for calculation of average densities of seabirds recorded using the transect sampling method. Usually those are specific routines working within the environment of the most popular database management systems. Such a simplified approach often does not ensure a completely automatic process of data analysis and requires much additional effort of operators (recording ships position at selected intervals of time, multiple repetition of certain procedures while ...

Assessing the Vulnerability of Seabirds to Oil Pollution: Sensitivity to Spatial Scale

Area Vulnerability Scores (AVSs) are a measure of the potential impact that oil pollution in an area of sea might have on seabird populations. They are used in the United Kingdom and the Republic of Ireland as a conservation tool, principally to inform the decision making processes related to the licensing of oil exploration at sea and to responses to oil pollution incidents. AVSs are currently calculated and mapped at a scale of 15' latitude x 30' longitude grid squares. Patterns of seabird distribution are known to be scale dependent and the same is also true for oil pollution. This suggests that the physical interactions between oil pollution and seabirds may also be dependent on spatial scale. We consider the sensitivity to spatial scale of the vulnerability that is determined by the interactions between oil pollution and seabirds and examine the scale dependent variation in vulnerability, as de- fined by AVS. The results demonstrate scale dependence in AVS and some features of its spatial distribution. These are decreasing heterogeneity in AVS with increasing spatial scale, and the presence of some spatial structure at a scale 20-30 km which could not be detected when estimating AVS at larger scales. These patterns in vulnerability are a consequence of scale dependence in the spatial distribution of seabird density. In addition an increase in scale resulted in a tendency to overestimate AVS which also lead to an apparent expansion in size of the higher vulnera- bilities such as those around the coast. These results were an artifact of the calculation of AVS. The results of this study have implications for the way in which we use AVS and other similar measures to assess vulnerability. They suggest that calculation of AVS should be done on a fine spatial scale, however, bird density data are not available at the appropriate spatial resolution without combining data over an extended temporal scale which runs the risk of distorting the spatial patterns. These effects may be mitigated by calculating AVS on a spatially stratified basis, at high resolution in the areas of high density and coverage, and at low resolution in areas of low densities and low coverage.