Seabird Density Research Articles

Distribution of seabirds in the Lower Estuary and Gulf of St Lawrence (Canada) during summer

We investigated the abundance and distribution patterns of a range of seabird species in the Lower Estuary and Gulf of St Lawrence in the western North Atlantic Ocean using ship-based surveys during the summers of 2007, 2008 and 2009. This area is known to be of particular importance for several seabird and cetacean species. We analysed distribution and abundance of common seabird species in mid and late summer, and estimated total numbers for the Southern Gulf, which was most intensively surveyed. Northern Gannets Morus bassanus were overall most abundant and widespread. Our at-sea estimate of 150,000 birds for the Southern Gulf constitutes 64% of the North American breeding population, rendering the site one of the most important areas for this species worldwide during this period. Our at-sea estimates suggest that according to the 1% threshold of the Ramsar Convention considerable proportions of the Canadian breeding population of Razorbills Alca torda (5-11%), Common Guillemots Uria aalge (2-3%), Black-legged Kittiwakes Rissa tridactyla (2-4%) and Black Guillemots Cepphus grylle (1-2%) use the Southern Gulf. Relative to their biogeographic populations, at-sea totals were also considerable in American Herring Gulls Larus smithsonianus (3-4%), Great Black-backed Gulls L. marinus (1-4%) and Great Northern Divers Gavia immer (1-4%). Areas of high seabird densities and multispecies aggregations (hotspots) occurred around the Gaspé Peninsula (Northern Gannets, alcids, Black-legged Kittiwakes, Larus gulls), in the Northwestern Gulf, along the Lower North Shore (near St Mary's Islands), along the west coast of Newfoundland (Bay of Islands to St Georges Bay), in Cabot Strait, around Cape Breton Island and the Magdalen Islands, as well as west and east of Prince Edward Island.

Structure and variability of the marine-bird community in the northeastern Chukchi Sea

We examined the seasonal and interannual variation in the marine-bird community and its relationship to physical oceanography in the northeastern Chukchi Sea in 2008–2010 as part of a multi-year, interdisciplinary study. We sampled 3 study areas, each ∼3000km2, located in the offshore northeastern Chukchi Sea: Klondike, Burger, and Statoil. We quantified the marine habitat by measuring strength of stratification, depth of the mixed layer, and temperature and salinity in the upper mixed layer. The total density of seabirds was the highest in 2009, when warm (5–6°C), moderately saline (31–31.5) Bering Sea Water (BSW) extended across Burger and Klondike at all depths. Bird density was generally higher in Klondike than in Burger in 2008 and 2009; densities did not differ significantly among study areas in 2010, when BSW covered all 3 study areas. The relative abundance of alcids in all study areas combined increased from 2008 to 2010. Klondike was numerically dominated by alcids and tubenoses in all years, whereas Burger was numerically dominated by larids and tubenoses in 2008 and by alcids in 2009 and 2010; Statoil also was numerically dominated by alcids in 2010. Least auklets, crested auklets, and northern fulmars were positively associated with strong stratification and high salinity (>31) in the upper mixed layer, characteristics that indicated the presence of BSW. Phalaropes were positively associated with salinity but negatively associated with stratification, suggesting that well-mixed water provides better foraging opportunities for these surface-feeding planktivores. The distribution and abundance of marine birds, particularly the planktivorous species, is influenced by advective processes that transport oceanic species of zooplankton from the Bering Sea to the Chukchi Sea. This transport apparently differed among years and resulted in a broader northeastward intrusion of Bering Sea Water and greater total abundance of planktivorous seabirds in the region in 2009 than in 2008 or 2010.

Organochlorine contaminants in coastal marine ecosystems of southern Alaska: Inferences from spatial patterns in blue mussels (Mytilus trossulus)

We measured the concentrations and chemical structures of persistent organochlorines (OCs) in blue mussels (Mytilus trossulus) from 44 sites across southwest and southeast Alaska in an effort to determine both the sources of these compounds and the extent to which this region might be contaminated. High PCB concentrations were detected at Amchitka, Adak, and Unalaska Islands (83, 430, and 2800μgkg−1 dry weight, respectively) in the Aleutians with relatively low concentrations elsewhere (7.1–51μgkg−1 dry weight). Heavy PCB congener profiles (indicative of localized point sources) characterized the high concentration sites whereas distinctly lighter congener profiles (indicative of atmospheric transport) characterized the lower concentration sites. Elevated PCB concentrations at Adak were restricted to a small area along the island’s eastern shore, suggesting either limited dispersion or rapid dilution of these compounds. More uniform chlorinated pesticide concentrations among the collection sites suggests that these compounds are entering the Aleutian ecosystem from distant sources. Pesticide concentrations correlated significantly with seabird density across the islands we sampled, thus identifying biological transport as a delivery mechanism of these compounds to the Aleutian archipelago. Our findings do not implicate persistent organochlorines as a significant factor in the recent pinniped and sea otter population declines across southwest Alaska.

Seabird predation on Arctic cod during summer in the Canadian Arctic

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 450:219-228 (2012) - DOI: https://doi.org/10.3354/meps09561 Seabird predation on Arctic cod during summer in the Canadian Arctic Jordan K. Matley1, Aaron T. Fisk2, Terry A. Dick1,* 1Department of Biological Sciences, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada2Great Lakes Institute for Environmental Research, University of Windsor, Windsor, Ontario N9B 3P4, Canada *Corresponding author. Email: terrydick09@gmail.com BSTRACT: Seabirds feed heavily on Arctic cod Boreogadus saida during the summer in the Canadian Arctic but little is known of the interactions among birds while foraging and the factors that drive feeding behaviour. The objective of this study was to describe the relationship between seabirds and Arctic cod in a productive feeding area distant from breeding colonies. Transect surveys were completed using standardized count protocols to determine the density of seabirds in Allen Bay, Cornwallis Island, Nunavut. Shore-based observation sites determined seabird foraging behaviour associated with the presence of schools and environmental variables. The density of birds (156 birds km−2) was high compared to that of other locations in the Canadian Arctic. Several bird species were more active early in the morning and with winds from the south, possibly due to an increase in Arctic cod feeding on zooplankton at the surface. Northern fulmars Fulmarus glacialis and black-legged kittiwakes Rissa tridactyla captured Arctic cod directly from the water; however, they lost nearly 25% of captures to glaucous gulls Larus hyperboreus and parasitic jaegers Stercorarius parasiticus. These kleptoparasitic seabirds benefited the most in Allen Bay obtaining as much as 8 times more Arctic cod than species capturing cod directly. Northern fulmars captured 3 times more Arctic cod from schools, and black-legged kittiwakes captured similar proportions of schooling and non-schooling cod. We conclude that non-schooling Arctic cod are as important as schooling cod as an energy source for seabirds in nearshore areas, such as Allen Bay, during the summer. KEY WORDS: Boreogadus saida · Schooling · Kleptoparasitism · Foraging · Black-legged kittiwake · Northern fulmar · Glaucous gull Full text in pdf format PreviousNextCite this article as: Matley JK, Fisk AT, Dick TA (2012) Seabird predation on Arctic cod during summer in the Canadian Arctic. Mar Ecol Prog Ser 450:219-228. https://doi.org/10.3354/meps09561Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 450. Online publication date: March 29, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Distance Sampling to Estimate the Abundance of Birds with Sector and Radial Radar Detection Methods

Distance sampling, a widespread method in ecology, can be applied to estimate seabird abundance from a radar detection image. As the radar was placed on the seashore, the detections were not equally spread in the radar image, but clustered at the side of the sea. Sector and radial method are two primary methods to get samples from the whole image by collecting the data that were detected in the sectors or on the radial lines, and different sub-sampling methods would lead to different errors of the estimations. This paper builds two models respectively on sector data and radial data based on the assumption that the birds are uniformly distributed horizontally in this area, and uses this model to calculate the seabird density with a given example of radar detection as well as to compare the errors between these two methods. The seabird density estimated with sector data is 987 per square kilometer with large errors coming from the nonuniform patterns of birds. While, combined with the deviation mainly caused by the size of birds, the radial method achieved a density of 876 objects per square kilometer. Considering the nonuniform patterns for the sea birds, radial method is the optimal method to give a stable and reliable measurement and estimation the bird abundance, especially with a modified model where the size of bird taken into account. This radial sampling method can substitute to the method that takes all the detections of the radar image into account in estimating seabird abundance.

Airborne Remote Sensing of a Biological Hot Spot in the Southeastern Bering Sea

Intense, ephemeral foraging events within localized hot spots represent important trophic transfers to top predators in marine ecosystems, though the spatial extent and temporal overlap of predators and prey are difficult to observe using traditional methods. The southeastern Bering Sea has high marine productivity along the shelf break, especially near marine canyons. At a hot spot located near Bering Canyon, we observed three foraging events over a 12 day period in June 2005. These were located by aerial surveys, quantified by airborne lidar and visual counts, and characterized by ship-based acoustics and net catches. Because of the high density of seabirds, the events could be seen in images from space-based synthetic aperture radar. The events developed at the shelf slope, adjacent to passes between the Aleutian Islands, persisted for 1 to 8 days, then abruptly disappeared. Build-up and break down of the events occurred on 24 hr time scales, and diameters ranged from 10 to 20 km. These events comprised large concentrations of euphausiids, copepods, herring, other small pelagic fishes, humpback whales, Dall’s porpoise, short-tailed shearwaters, northern fulmars, and other pelagic seabirds. The lidar and acoustic remote sensing data demonstrated that prey densities inside the events were several times higher than those outside, indicating the importance of including events in forage fish surveys. This implies a need for either very intensive traditional surveys covering large expanses or for adaptive surveys guided by remote sensing. To our knowledge, this is the first time that an Alaskan hot spot was monitored with the combination of airborne and satellite remote sensing.

Water masses, ocean fronts, and the structure of Antarctic seabird communities: Putting the eastern Bellingshausen Sea in perspective

Waters off the western Antarctic Peninsula (i.e., the eastern Bellingshausen Sea) are unusually complex owing to the convergence of several major fronts. Determining the relative influence of fronts on occurrence patterns of top-trophic species in that area, therefore, has been challenging. In one of the few ocean-wide seabird data syntheses, in this case for the Southern Ocean, we analyzed ample, previously collected cruise data, Antarctic-wide, to determine seabird species assemblages and quantitative relationships to fronts as a way to provide context to the long-term Palmer LTER and the winter Southern Ocean GLOBEC studies in the eastern Bellingshausen Sea. Fronts investigated during both winter (April–September) and summer (October–March) were the southern boundary of the Antarctic Circumpolar Current (ACC), which separates the High Antarctic from the Low Antarctic water mass, and within which are embedded the marginal ice zone and Antarctic Shelf Break Front; and the Antarctic Polar Front, which separates the Low Antarctic and the Subantarctic water masses. We used clustering to determine species' groupings with water masses, and generalized additive models to relate species' densities, biomass and diversity to distance to respective fronts. Antarctic-wide, in both periods, highest seabird densities and lowest species diversity were found in the High Antarctic water mass. In the eastern Bellingshausen, seabird density in the High Antarctic water mass was lower (as low as half that of winter) than found in other Antarctic regions. During winter, Antarctic-wide, two significant species groups were evident: one dominated by Adélie penguins ( Pygoscelis adeliae) (High Antarctic water mass) and the other by petrels and prions (no differentiation among water masses); in eastern Bellingshausen waters during winter, the one significant species group was composed of species from both Antarctic-wide groups. In summer, Antarctic-wide, a High Antarctic group dominated by Adélie penguins, a Low Antarctic group dominated by petrels, and a Subantarctic group dominated by albatross were evident. In eastern Bellingshausen waters during summer, groups were inconsistent. With regard to frontal features, Antarctic-wide in winter, distance to the ice edge was an important explanatory factor for nine of 14 species, distance to the Antarctic Polar Front for six species and distance to the Shelf Break Front for six species; however, these Antarctic-wide models could not successfully predict spatial relationships of winter seabird density (individual species or total) and biomass in the eastern Bellingshausen. Antarctic-wide in summer, distance to land/Antarctic continent was important for 10 of 18 species, not a surprising result for these summer-time Antarctic breeders, as colonies are associated with ice-free areas of coastal land. Distance to the Shelf Break Front was important for 8 and distance to the southern boundary of the ACC was important for 7 species. These summer models were more successful in predicting eastern Bellingshausen species density and species diversity but failed to predict total seabird density or biomass. Antarctic seabirds appear to respond to fronts in a way similar to that observed along the well-studied upwelling front of the California Current. To understand fully the seabird patterns found in this synthesis, multi-disciplinary at-sea investigations, including a quantified prey field, are needed.

Seabird aggregation around free-drifting icebergs in the northwest Weddell and Scotia Seas

Seabird abundances and distributions can be influenced by seasonal variations in surface productivity, winds, and other environmental factors. Recently evidence emerged that free-drifting icebergs were hotspots of biogeochemical and ecological activity. They also represent physical habitat structure both above and below the sea surface. Here we found seabird abundances that were 2 to 6 times greater within about one-half km of free drifting icebergs than the area between about one-half and one km from the iceberg edge. Aggregation was measured by surveys with an experimental design for determining potential local impacts of free-drifting icebergs on seabird density. Seabird surveys were conducted during three cruises in the Weddell Sea from 4 to 20 December 2005, 11 to 25 June 2008, and 21 March to 2 April 2009. Visual surveys were done on the vessel bridge typically for periods of five minutes facing the port or starboard side. Differences in species composition were also linked to distance from the iceberg edge for the most sampled icebergs with Daption capense exhibiting change in relative abundance. On a local scale, environmental factors such as surface productivity, air temperature, and winds were not consistently related to seabird distributions and community dynamics. The results suggest that climatically-driven variations in iceberg abundance would influence local seabird distributions with unknown impacts on regional abundances and species composition.

Macro-ecology of plankton-seabird associations in the North Pacific Ocean

In conjunction with the North Pacific Continuous Plankton Recorder program, we conducted surveys of seabirds from June 2002 to June 2007. Here, we tested the hypotheses of (i) east–west variations in coupled plankton and seabird abundance, and (ii) that surface-feeding and diving seabirds vary in their relationships to primary productivity and mesozooplankton species abundance and diversity. To test these hypotheses, we developed statistical models for 20 species of seabirds and 12 zooplankton taxonomic groups. Seabird density was highly variable between seasons, but was consistently higher in the western than eastern North Pacific. Seabird diversity was greater in the east. Zooplankton abundance did not differ between regions. We found associations at the “bulk” level between seabird density and net primary productivity, but only one association between seabirds and total zooplankton abundance or diversity. However, we found many relationships between seabird species and the abundance of different zooplankton summarized at the genus or family level. Some of these taxonomic relationships reflect direct predator–prey interactions, while others may reflect zooplankton that serve as ecological indicators of other prey, such as micronekton, upon which the birds may feed. Surface or near-surface feeding, mostly piscivorous seabirds, did not differ systematically from diving, mainly planktivorous seabirds in their zooplankton associations. Seabirds apparently respond to zooplankton taxonomic groupings more so than bulk zooplankton characteristics, such as abundance or diversity. Macro-ecological studies of remote marine ecosystems using zooplankton and seabirds as ecological indicators provide a framework for understanding and assessing spatial and temporal variations in these difficult-to-study pelagic environments.

Prognosis for ecosystem recovery following rodent eradication and seabird restoration in an island archipelago

Invasive species are widespread and can have devastating effects on biota, especially insular biota. Invasive species eradications are increasingly employed to promote island recovery to preinvasion states. However, it remains unclear if additional restoration actions may be required on islands that were once heavily reliant on seabird guano for ecosystem functions. Active seabird augmentation has been suggested as necessary to exact ecosystem recovery on contemporary timescales in some cases. I use two experiments on offshore islands in Cook Strait, New Zealand, to test the hypothesis that seabird restoration will restore island ecosystem functioning following invasive rodent removal. The first is a small-scale single-island fertilization experiment that simulates seabird recovery. This experiment tested the recovery potential of offshore islands and was used to infer the density of seabirds needed to elicit ecosystem recovery. The second is a large-scale natural experiment that takes advantage of eight islands with differing rodent eradication and seabird restoration histories. I compared ecosystem functioning variables (delta 15N, C:N ratios in soil, plants, and spiders, as well as arthropod abundance and diversity) on two islands that had rodents eradicated and two islands undergoing seabird augmentation with two control islands (never invaded by rodents) and two positive control islands (currently invaded by rodents). The results suggest that islands do have the potential for recovery given nutrient amendments, but that islands with rodents eradicated and islands undergoing seabird augmentation have not recovered most of their ecosystem function. Finer, intra-island analysis showed that seabird restoration projects have the potential to speed the recovery process, but that the projects on the studied seabird restoration islands were not advanced enough to produce island-wide recovery. The results suggest that high seabird densities (5-10 burrows/m2) are needed to promote recovery to never-invaded control levels. Seabird augmentation, through chick translocation and/or social facilitation with decoys, vocalization playbacks, and/or mirrors can supplement passive seabird recovery on islands where seabirds have been extirpated or extremely reduced by invasive predators. Such restoration efforts may be necessary to promote ecosystem recovery on contemporary timescales.

Atmospheric concentrations of ammonia and nitrogen dioxide at a tropical coral cay with high seabird density

Ecosystems with high seabird densities can receive extremely high inputs of nitrogen (N) from bird guano. Seabirds deposit up to 1000 kg N ha(-1) y(-1) on Heron Island, a tropical coral cay of the Great Barrier Reef. We quantified atmospheric concentrations of ammonia (NH(3)) and nitrogen dioxide (NO(2)) with passive air samplers at beach, woodland and forest along a gradient of low, intermediate and high bird densities, respectively. NO(2) concentrations at all studied sites were generally low (average 0.2-2.3 microg NO(2) m(-3)) and similar to other ecosystems. An exception was the main traffic zone of helicopter and barge traffic which had elevated concentrations (average 6.2, maximum 25 microg NO(2) m(-3)) comparable to traffic-intense urban areas elsewhere. Increasing average NH(3) concentrations from 0.7 to 17 microg NH(3) m(-3) was associated with greater seabird nesting density. In areas of intermediate and high bird density, NH(3) concentrations were substantially higher than those typically detected in natural and agricultural systems, supporting the notion that seabird guano is a major source of NH(3). The steep decline of NH(3) concentrations in areas with low bird density indicates that trans-island transport of NH(3) is low. NH(3) may not only be re-deposited in close vicinity of the source but is also transported vertically as concentrations above the tree canopy averaged 7.5 microg NH(3) m(-3). How much guano-derived NH(3) contributes to reefal waters via the possible transfer path water --> land --> water remains to be established. We discuss atmospheric concentrations of NH(3) and NO(2) in context of N-based gaseous pollutants and effects on vegetation.

On the importance of estimating detection probabilities from at‐sea surveys of flying seabirds

The primary and accepted method used to estimate seabird densities at sea from ships is the strip transect method, designed to correct for the effect of random directional bird movement relative to that of the ship. However, this method relies on the critical assumption that all of the birds within the survey strip are detected. We used the distance sampling method from line‐transects to estimate detection probability of a number of species of flying seabirds, and to test whether distance from the ship and bird body size affected detectability. Detection probability decreased from 0.987 (SE=0.029) to 0.269 (SE=0.035) with increasing strip half‐width from 100 to 1400 m. Detection probability also varied between size‐groups of species with strip half‐width. For all size‐groups, this probability was close to 1 for strip half‐width of 100 m, but was 0.869 (SE=0.115), 0.725 (SE=0.096) and 0.693 (SE=0.091) for strip half‐width of 300 m, a typical strip width used in seabird surveys, for respectively large, medium and small size flying seabirds. For larger strip half‐width, detection probability was higher for large sized species, intermediate for medium sized species and lower for smaller sized species. For strip half‐width larger than 100 m we suggest that more attention should be paid to testing the assumption of perfect detectability, because abundance estimates may be underestimated when this assumption is violated. Finally, the effect of the speed of travel of flying seabird on the detection probability was estimated in a simulation study, which suggests that detection probability was underestimated with increasing flying speed.

At-sea mortality of seabirds based on beachcast and offshore surveys

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 392:295-305 (2009) - DOI: https://doi.org/10.3354/meps08152 At-sea mortality of seabirds based on beachcast and offshore surveys Kelly M. Newton1,*, Donald A. Croll1, Hannahrose M. Nevins2, Scott R. Benson3, James T. Harvey2, Bernie R. Tershy1 1Center for Ocean Health, University of California Santa Cruz, 100 Shaffer Rd. Santa Cruz, California 95060, USA 2Moss Landing Marine Laboratories, 8272 Moss Landing Rd., Moss Landing, California 95039, USA 3NOAA Fisheries, 7544 Sandholdt Rd., Moss Landing, California 95039, USA *Email: newton.kelly@gmail.com ABSTRACT: Although seabird population biology is relatively well studied, little data exists on mortality at-sea. Beached bird surveys are used to identify patterns of seabird mortality, but resulting patterns are difficult to interpret without corresponding data on at-sea density. We examined seabird mortality relative to at-sea density in Monterey Bay, California over 10 yr by integrating data from monthly beachcast seabird and offshore seabird censuses. Beachcast seabird numbers were relatively constant (mean 2.82 ± 0.31 seabirds km–1) throughout the year. At-sea seabird density (mean 148.9 ± 16.12 seabirds km–2) peaked in the summer upwelling period and was least in the winter Davidson period. A principal components analysis of seasonal climatic, prey availability, and anthropogenic variables for Monterey Bay derived 3 significant principal components (PCs) (explaining 70% of variance) characterized by storm activity and low prey availability (PC1), river discharge and krill abundance (PC2), and oiling (PC3). These principal components were used in detailed analyses of the 2 most abundant seabird species and indicate that sooty shearwater Puffinus griseus relative mortality is greatest during decreased productivity and increased storm activity. While relative mortality of common murres Uria aalge cannot be explained by the derived principal components, relative mortality increased in late winter when prey availability decreased concurrent with the annual increase in reproductive stress. Beachcast seabird data is difficult to interpret in isolation; however, when linked to at-sea densities of seabirds, it becomes a powerful tool to examine the relative impacts of oceanography and direct human perturbations on seabird demography. KEY WORDS: Seabirds at-sea · Beached bird survey · Density · Mortality · Sooty shearwater · Common murre Full text in pdf format PreviousCite this article as: Newton KM, Croll DA, Nevins HM, Benson SR, Harvey JT, Tershy BR (2009) At-sea mortality of seabirds based on beachcast and offshore surveys. Mar Ecol Prog Ser 392:295-305. https://doi.org/10.3354/meps08152 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 392. Online publication date: October 19, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

Predation of seabirds by invasive rats: multiple indirect consequences for invertebrate communities

Invasive species are a global problem but most studies have focused on their direct rather than indirect ecological effects. We studied litter and soil‐inhabiting invertebrate communities on 18 islands off northern New Zealand, to better understand the indirect ecological consequences of rat (Rattus) invasion. Nine islands host high densities of burrowing procellariid seabirds that transport large amounts of nutrients from the ocean to the land. The other nine have been invaded over the past 50–150 years by rat species that have severely reduced the density of seabirds by preying on eggs and chicks. Invaded islands had lower densities of seabird burrows but deeper forest litter than did the uninvaded islands, indicative of rats reducing disturbance effects of seabirds. However, despite deeper litter on the invaded islands, eight of the 19 orders of invertebrates that we measured were significantly less abundant on invaded islands. Furthermore, three soil‐inhabiting micro‐invertebrate groups that we measured were significantly less abundant on invaded islands. These differences probably result from rats thwarting transfer of resources by seabirds from the ocean to the land. We also investigated community‐level properties of each of three test groups of invertebrates (minute land snails, spiders and soil nematodes) to illustrate this process. Spiders were equally abundant on both groups of islands, but showed lower species richness on the invaded islands. The other two groups showed no difference in species richness with island invasion status, but were more abundant on uninvaded islands. Reduced abundance of soil nematodes on invaded islands provides strong evidence of indirect consequences of seabird reduction by rats, because nematodes are unavailable to rats as prey. We predict that if rats are eradicated from islands, components of below‐ground invertebrate dependent on seabird‐mediated soil conditions may take considerable time to recover because they require subsequent seabird recolonisation.

13C and 15N enrichment in snipe (Coenocorypha spp.) from islands across the New Zealand biogeographic region

The remaining five Coenocorypha snipes are restricted to remote islands in the New Zealand archipelago, so their ecology is difficult to study directly. To ascertain habitat types and ecological interactions across the different taxa and locations, we measured the δ13C and δ15N of feathers from known individual Auckland Island snipe C. aucklandica aucklandica (Adams I., n = 12; Enderby I., n = 4; Rose I., n = 8), Chatham Island snipe C. pusilla (Rangatira, n = 10), and Campbell Island snipe (Coenocorypha undescribed sp.; n = 1). Data for Snares snipe C. a. huegeli (North East I., n = 1) came from the literature. Developmental stage (nestling, juvenile, adult) and sex were statistically indistinguishable. Although significant differences in δ13C occurred between islands, the overall range was small (mean ± standard deviation, ‐22.7 ± 0.9%o). The restricted δ13C show that the snipe we sampled occupied a consistent habitat regardless of taxa, island size, and disturbance history. Conversely, the range in δ15N was large at c. 18.5%o and implied occupation of sites with a wide range of nutrient status. The δ15N from Adams I. (mean 5.9 ± 1.7%o) was much lower than the other islands (mean 19.2 ± 2.0%o) and could only be explained by including a 15N‐depleted site not affected by seabirds or seals. Auckland Island snipe therefore integrate seabird breeding and non‐breeding areas as well as inhabiting locations with seals and high seabird densities. Consequently, Coenocorypha snipes provide connectances between marine animals on land and the wider terrestrial environment and so maybe considered for (re)‐introduction to predator‐proof mainland New Zealand restoration sites.

The importance of oceanographic fronts to marine birds and mammals of the southern oceans

During the last 30 years, at-sea studies of seabirds and marine mammals in the oceans south of the Subtropical Front have described an association with major frontal areas. More recently, the advancement in microtechnology has allowed the tracking of individuals and investigations into how these marine predators actually use the frontal zones. In this review, we examine 1) the relative importance to apex predators of the different frontal zones in terms of spatial distribution and carbon flux; 2) the processes that determine their preferential use; and 3) how the mesoscale dynamics of frontal structures drive at-sea foraging strategies of these predators. We review published results from southern waters and place them in a broader context with respect to what has been learned about the importance of fronts in oceans farther north. Some fronts constitute important boundaries for seabird communities in southern waters. At a mesoscale the maximum values of seabird diversity and abundance correspond to the location of the main fronts. At-sea surveys show a strong curvilinear correlation between seabird abundance and sea surface temperatures. High mean species richness and diversity for whales and seabirds are consistently associated with the southern water mass boundary of the Antarctic Circumpolar Current, the Subtropical Front and the Subantarctic Front; in the case of the Polar Front mean seabird densities are more variable. At small-scales, variation in seabird occurrence has been directly related to the processes at fronts in a limited number of cases. A significant positive relation was found between some plankton feeding species and frontal temperature gradient–phytoplankton variables. Telemetric studies have revealed that several apex predators (penguins, albatrosses, seals) perform long, directed foraging trips either to the Subtropical front or Polar Front, depending on locality. Seabirds with low flight costs, such as albatrosses, are able to reach fronts at long distances from colonies, showing variable foraging strategies as a function of the distances involved. Diving birds such as King penguins, that travel at a higher cost and lower speed, rely on the predictable spatial distribution of mesopelagic fish found close to the Polar Front. They may use the currents associated with eddies as oceanographic cues in the active search for frontal zones. Once in these areas they dive preferentially in and below the depth of the thermocline where catches per unit effort are high. Elephant seals concentrate foraging activity principally inside or at the boundary of cyclonic eddies. These mesoscale features appear to offer exceptional productivity favourable for foraging by various diving top predators. The connection between biophysical parameters at fronts and predators is likely to be made through biological enhancement. Top predators appear to forage at locations where prey are advected by physical processes and others where prey are produced locally. Long-term research on at-sea distributions and demographic parameters of top predators are essential to assess the consequences of potential shift in front distributions in relation to global warming. Such environmental changes would add to the impact of fish extraction by the industrial fisheries on the southern food webs.

Estimating seabird densities from vessel transects: distance sampling and implications for strip transects

Vessel-based transects have been a mainstay of seabird research for decades, yet there has been surprisingly little effort to evaluate the detectability of seabirds within strip transects. Dis- tance sampling methods offer an opportunity to quantify detectability and assess the proportions of birds on the water that may be missed during strip transects. Three summers of line-transect surveys were analyzed using the program Distance to model detection functions of 6 seabird taxa (marbled murrelet Brachyramphus marmoratus, rhinoceros auklet Cerorhinca monocerata, common murre Uria aalge, pigeon guillemot Cepphus columba, pelagic cormorant Phalacrocorax pelagicus, gulls Larus spp.). We tested the effects of covariates (year, observers, sea state, and cluster size) on detec- tion function estimation. Year and observer were the most important covariates for some but not all species. For a 300 m wide transect (150 m on either side), 20 to 80% of birds were detected, depend- ing on species, year, and observer. Detectability was highest for cormorants (60 to 90%) and fairly similar among other species (typically 40 to 60%). Sea state had a significant effect on encounter rate for murrelets suggesting that g(0), detection probability near the transect line, may be <1 when wave height increases. These data emphasize that a high proportion of birds on the water remain unde- tected during strip-transect surveys. It is important that surveys develop independent estimates of detection probability to account for detectability among species, years, observers, vessel types/speed, and viewing conditions. The application of distance sampling to seabird surveys can provide more accurate abundance and population estimates, which can improve conservation and management efforts.

Direct and indirect effects of rats: does rat eradication restore ecosystem functioning of New Zealand seabird islands?

Introduced rats (Rattus spp.) can affect island vegetation structure and ecosystem functioning, both directly and indirectly (through the reduction of seabird populations). The extent to which structure and function of islands where rats have been eradicated will converge on uninvaded islands remains unclear. We compared three groups of islands in New Zealand: islands never invaded by rats, islands with rats, and islands on which rats have been controlled. Differences between island groups in soil and leaf chemistry and leaf production were largely explained by burrow densities. Community structure of woody seedlings differed by rat history and burrow density. Plots on islands with high seabird densities had the most non-native plant species. Since most impacts of rats were mediated through seabird density, the removal of rats without seabird recolonization is unlikely to result in a reversal of these processes. Even if seabirds return, a novel plant community may emerge.

Modelling and mapping resource overlap between seabirds and fisheries on a global scale: a preliminary assessment

Coexistence of foraging seabirds and operating fisheries may result in interactions such as competition for the same prey resources. We used GIS-based modelling at a scale of 0.5 × 0.5° spa- tial cells to: (1) map the foraging distribution of seabirds; (2) predict their annual food consumption rates in a spatially explicit manner; and (3) estimate a spatially explicit seabird-fisheries overlap index. Information on population size, diet composition and foraging attributes of 351 seabird species was compiled into a Microsoft Access database. Global annual food consumption by seabirds was estimated to be 96.4 million tonnes (95% CI: 78.0 to 114.7 million tonnes), compared with a total catch of nearly 120 million tonnes by all marine fisheries. Krill and cephalopods comprised over 58% of the overall food consumed and fish most of the remainder. The families Procellariidae (albatrosses, petrels, shearwaters) and Spheniscidae (penguins) were responsible for over 54% of the overall food consumption. Seabird foraging distribution maps revealed that areas around New Zealand, the east- ern Australian coast, and the sub-Antarctic islands had high species richness. However, temperate and polar regions supported high seabird densities and most food extracted by seabirds originated there. Furthermore, maps of food consumption rates revealed that most food consumed by seabirds was extracted from offshore rather than nearshore waters and from areas where seabird-fisheries overlap was low. The resource overlap maps identified 'hotspots' of highest potential for conflict between fisheries and seabirds. Thus, this study may provide useful insight when developing management approaches for designing offshore marine conservation areas.

Community structure across a large-scale ocean productivity gradient: Marine bird assemblages of the Southern Indian Ocean

Our objective was to understand how marine birds respond to oceanographic variability across the Southern Indian Ocean using data collected during an 16-day cruise (4–21 January 2003). We quantified concurrent water mass distributions, ocean productivity patterns, and seabird distributions across a heterogeneous pelagic ecosystem from subtropical to sub-Antarctic waters. We surveyed 5155 km and sighted 15,606 birds from 51 species, and used these data to investigate how seabirds respond to spatial variability in the structure and productivity of the ocean. We addressed two spatial scales: the structure of seabird communities across macro-mega scale (1000 s km) biogeographic domains, and their coarse-scale (10 s km) aggregation at hydrographic and bathymetric gradients. Both seabird density and species composition changed with latitudinal and onshore–offshore gradients in depth, water temperature, and chlorophyll-a concentration. The average seabird density increased across the subtropical convergence (STC) from 2.4 birds km −2 in subtropical waters to 23.8 birds km −2 in sub-Antarctic waters. The composition of the avifauna also differed across biogeographic domains. Prions ( Pachyptila spp.) accounted for 57% of all sub-Antarctic birds, wedge-tailed shearwaters ( Puffinus pacificus) accounted for 46% of all subtropical birds, and Indian Ocean yellow-nosed albatross ( Thallasarche carteri) accounted for 32% of all birds in the STC. While surface feeders were the most abundant foraging guild across the study area, divers were disproportionately more numerous in the sub-Antarctic domain, and plungers were disproportionately more abundant in subtropical waters. Seabird densities were also higher within shallow shelf-slope regions, especially in sub-Antarctic waters, where large numbers of breeding seabirds concentrated. However, we did not find elevated seabird densities along the STC, suggesting that this broad frontal region is not a site of enhanced aggregation.