Phylogeography of colonially nesting seabirds, with special reference to global matrilineal patterns in the sooty tern (Sterna fuscata)

Sooty tern (Sterna fuscata) rookeries are scattered throughout the tropical oceans. When not nesting, individuals wander great distances across open seas, but, like many other seabirds, they tend to be site-faithful to nesting locales in successive years. Here we examine the matrilineal history of sooty terns on a global scale. Assayed colonies within an ocean are poorly differentiated in mitochondrial DNA sequence, a result indicating tight historical ties. However, a shallow genealogical partition distinguishes Atlantic from Indo-Pacific rookeries. Phylogeographic patterns in the sooty tern are compared to those in other colonially nesting seabirds, as well as in the green turtle (Chelonia mydas), an analogue of tropical seabirds in some salient aspects of natural history. Phylogeographic structure within an ocean is normally weak in seabirds, unlike the pronounced matrilineal structure in green turtles. However, the phylogeographic partition between Atlantic and Indo-Pacific rookeries in sooty terns mirrors, albeit in shallower evolutionary time, the major matrilineal subdivision in green turtles. Thus, global geology has apparently influenced historical gene movements in these two circumtropical species.     

Spatial and temporal variation in mercury contamination of seabirds in the North Sea

Once the moult patterns have been taken into account, feather methylmercury levels can be used to accurately measure the mercury burdens of seabirds. We used body feathers from live seabirds and from museum collections to examine geographical and temporal patterns of mercury contamination in the North Sea. This approach identifies an increase in mercury concentrations in seabirds of the German North Sea coast during the last 100 years, especially high levels during the 1940s, and reduced contamination in the last few years. Comparisons among populations suggest that some increases in mercury levels are predominantly due to local pollution inputs, as on the German coast, while in other areas deposition from jet stream circulation of global contamination may be the major contributor. Mercury levels are far higher in seabirds from the German North Sea coast than in populations from the north and west North Sea or from most areas of the North Atlantic. We advocate the use of museum collections of birds for studies of long-term changes in levels of mercury contamination.     

Variability in δ15N, δ13C and Kjeldahl nitrogen of soils from islands with and without seabirds in the Marlborough Sounds, New Zealand

Nutrients brought to land by seabirds may provide important subsidies to terrestrial ecosystems. We measured the total Kjeldahl nitrogen (TKN) and carbon and nitrogen isotope ratios of soils from islands with and without seabirds in the Marlborough Sounds, New Zealand to investigate one means by which seabirds may influence island ecosystem function. Isotope analysis revealed a seabird influence in island soils on the seabird-inhabited islands. However, significant differences in TKN were not related to seabird presence or absence. Pre-existing differences between the islands and high productivity even in the absence of seabirds were concluded to be the reasons for the lack of measurable seabird influence on nitrogen levels.     

Seabird predation by great skuas Stercorarius skua– intra‐specific competition for food?

Competition for food is widely cited as an important cost of coloniality among birds and much of the evidence in support of this hypothesis comes from studies of colonial piscivorous seabirds. However, for generalist seabirds able to switch between different prey types, the role of food availability in relation to colony size is unclear. Here we investigate patterns of the consumption of seabird prey in relation to colony size in a generalist seabird, the great skua Stercorarius skua, in Shetland, UK. At the population level skuas feed mainly on sandeels Ammodytes marinus and fishery discards, but respond to declines in fish availability to facultatively prey on other seabirds. By comparing the consumption of seabirds among seven different sized colonies, including one colony with artificially reduced numbers of skuas (Fair Isle), we investigate whether consumption of seabird prey is influenced by skua population size, while simultaneously measuring seabird prey availability. Data from five years also enables us to investigate the influence of annual variation in environmental conditions on seabird consumption. Using measures of body condition and reproductive performance we investigate the consequences of living in different sized colonies, which may provide insight into ultimate costs of nesting at high population density. Skua diets varied among colonies and the proportion of seabird prey in the diet was inversely related to skua colony size, despite similar per capita numbers of seabirds across colonies. At the colony where their numbers were artificially suppressed, skuas consumed a greater proportion of seabirds per capita. Highly significant year effects in seabird predation were observed but the pattern among colonies remained consistent over time. Two measures of adult body condition (pectoral muscle index and mean corpuscular volume) revealed that adult great skuas were in poorer condition at the largest colony (Foula), but reproductive performance did not alter significantly among colonies. This study provides evidence that intra‐specific competition among skuas may limit opportunities for obtaining seabird prey, which may be particularly important during periods of poor availability of sandeels and fishery discards, and has implications for assessing the impact of skuas on seabird populations.     

Seabirds colonized Ny-Ålesund, Svalbard, Arctic ~9,400 years ago

A 118-cm-long and well-preserved sediment profile in a paleo-notch, which was formed by ocean wave action before rising to the terrace, was collected from the first terrace of Ny-Ålesund, Svalbard, Arctic. The bottom of this profile was dated as 9,400 years B.P. based on two radiocarbon dates of fossil mollusc shell fragments. The organic material in the sediment was identified by δ¹³C_org–C/N plot and δ¹⁵N_org characteristics to be predominantly composed of seabird guano, which was transported from the ocean via preying and excreting by seabirds. These results indicate that seabirds have inhabited Ny-Ålesund since 9,400 years B.P. after Kongsfjorden was completely deglaciated. This is the first report on Holocene seabird occupation on Ny-Ålesund and it provides the foundation for understanding the ecological history of seabirds in Svalbard in Holocene.     

Seabird nutrient subsidies alter patterns of algal abundance and fish biomass on coral reefs following a bleaching event

Cross‐ecosystem nutrient subsidies play a key role in the structure and dynamics of recipient communities, but human activities are disrupting these links. Because nutrient subsidies may also enhance community stability, the effects of losing these inputs may be exacerbated in the face of increasing climate‐related disturbances. Nutrients from seabirds nesting on oceanic islands enhance the productivity and functioning of adjacent coral reefs, but it is unknown whether these subsidies affect the response of coral reefs to mass bleaching events or whether the benefits of these nutrients persist following bleaching. To answer these questions, we surveyed benthic organisms and fishes around islands with seabirds and nearby islands without seabirds due to the presence of invasive rats. Surveys were conducted in the Chagos Archipelago, Indian Ocean, immediately before the 2015–2016 mass bleaching event and, in 2018, two years following the bleaching event. Regardless of the presence of seabirds, relative coral cover declined by 32%. However, there was a post‐bleaching shift in benthic community structure around islands with seabirds, which did not occur around islands with invasive rats, characterized by increases in two types of calcareous algae (crustose coralline algae [CCA] and Halimeda spp.). All feeding groups of fishes were positively affected by seabirds, but only herbivores and piscivores were unaffected by the bleaching event and sustained the greatest difference in biomass between islands with seabirds versus those with invasive rats. By contrast, corallivores and planktivores, both of which are coral‐dependent, experienced the greatest losses following bleaching. Even though seabird nutrients did not enhance community‐wide resistance to bleaching, they may still promote recovery of these reefs through their positive influence on CCA and herbivorous fishes. More broadly, the maintenance of nutrient subsidies, via strategies including eradication of invasive predators, may be important in shaping the response of ecological communities to global climate change.     

Populations and trends of Canadian Arctic seabirds

Canada’s eastern Arctic (Nunavut and Arctic Quebec—Nunavik, N of 60°) supports large numbers of seabirds in summer. Seabird breeding habitat in this region includes steep, rocky coasts and low-lying coasts backed by lowland sedge-meadow tundra. The former areas support colonial cliff- and scree-nesting seabirds, such as murres and fulmars; the latter inland or coastal seabirds, such as terns, gulls and jaegers. The region supports some 4 million breeding seabirds, of which the most numerous are thick-billed murres (Uria lomvia; 75%), black guillemots (Cepphus grylle; 9%), northern fulmars (Fulmarus glacialis; 8%) and black-legged kittiwakes (Rissa tridactyla; 6%). The majority of Arctic seabirds breed in a small number of very large colonies (>10,000 birds), but there are also substantial numbers of non-colonial or small-colony breeding populations that are scattered more widely (e.g. terns, guillemots). Population trends among Canadian Arctic seabirds over the past few decades have been variable, with no strongly negative trends except for the rare ivory gull (Pagophila eburnea): this contrasts with nearby Greenland, where several species have shown steep declines. Although current seabird trends raise only small cause for concern, climate amelioration may enable increased development activities in the north, potentially posing threats to some seabirds on their breeding grounds.     

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.     

Stress in seabirds: causes, consequences and diagnostic value

We describe a range of anthropogenic stressors thatimpact seabirds, review the effects of these stressorson individuals and populations and discuss the roleand value of seabirds as monitors of marine ecosystemhealth. Stressors described are restricted to thosewhich affect seabirds directly or indirectly throughthe marine environment; we have not dealt withterrestrially based stressors such as introducedmammalian predators or loss of habitat, which canpotentially affect seabirds whilst breeding. Wediscuss three broad categories of stress in seabirds.Marine pollutants (including biologicallynon-essential heavy metals, oil, organic pesticidesand polychlorinated biphenyls (PCBs), and plastics),industrial fisheries (further divided into the effectsof depletion of prey stocks and direct mortality), andclimate change. Additionally we highlight the role ofseabirds as monitors of marine ecosystem health,taking the example of long-term mercury contaminationas a case study. We conclude that seabirds are exposedto an increasing array of potential stressors, andthat the impact of a particular source of stress onseabirds varies markedly between species in relationto foraging and breeding ecology. The most seriousthreat to seabirds is direct mortality of adultsresulting from industrial and commercial fishingactivities. In some cases this is a significant threatto individual populations or even entire species.     

Basal metabolic rates of North Atlantic seabirds

Basal metabolic rates (BMR) were measured for 11 species of North Atlantic seabirds, ranging in size from the Kittiwake Rissa tridactyla to the Gannet Sula bassana. BMRs for all species were higher than those predicted from the allometric equations of Lasiewski and Dawson (1967), Aschoff and Pohl (1970) and Ellis (1984). The equations of Ellis (1984), incorporating a latitude correction, and of Bennett and Harvey (1987), involving deviations by seabird families from a general avian trend line, gave predictions for BMR which were closer to, but respectively lower and higher than, those observed in this study. BMR for seabirds in Scotland (55–60^oN) is described by the equation: BMR (kj/d) = 2.30W⁰⁷⁷⁴. The principal sources of variability in BMR amongst seabirds and the selective forces shaping the differences between seabirds and most other birds with lower BMRs remain unclear but deserve further study.     

Associations between seabirds and cetaceans: a review

(1) Seabird-cetacean associations involve many genera.
(2) Some seabirds/cetaceans associate with more species than others, e.g. minke and pilot whales, Common dolphins and porpoises amongst cetaceans, and gannet & kittiwake amongst seabirds. Killer whale, sperm whale, shag and cormorant have not been recorded in associations, in the N.E. Atlantic.
(3) All observed associations would be predicted on the basis of the diets of the associated species.
(4) Most associations are probably opportunistic or incidental, as a result of concentration of shared prey.
(5) Some species, however, may associate more regularly, e.g. minke & pilot whales, Common dolphin and porpoise amongst cetaceans and gannet amongst seabirds. It is not possible to say which derives benefit from the association, but on theoretical grounds it is most likely to be the seabird.
(6) Minke and pilot whales may drive towards the surface food normally out of reach of seabirds, particularly Procellariformes. Common dolphins feed by herding fast-moving fish shoals into tight groups which will be a more concentrated food source for diving sea-birds, such as gannets, and make food more accessible to other species. Porpoises may achieve the same result with inshore shoals of sprats and sand eels, particularly for auks and kittiwakes, and terns.     

Status,trends, and patterns of covariation of breeding seabirds at St Lazaria Island,Southeast Alaska, 1994–2006

Aim We examined patterns of covariation among piscivorous and planktivorous seabirds breeding at St Lazaria Island in order to evaluate their responses to interannual changes in sea surface temperature, a variable that affects marine food webs. In addition, we evaluated seabird population trends for responses to decadal‐scale changes in the marine ecosystem. Location St Lazaria Island, Sitka Sound, Alaska. Methods Established seabird monitoring protocols for the Alaska Maritime National Wildlife Refuge were followed in estimating population trends, the timing of nesting events and the reproductive success of eight species of seabirds between 1994 and 2006. Results  Population increases were noted for storm‐petrels (Oceanodroma furcata and O. leucorhoa), rhinoceros auklets (Cerorhinca monocerata) and glaucous‐winged gulls (Larus glaucescens). We found no population trend for pelagic cormorants (Phalacrocorax pelagicus), but it appeared that populations of common (Uria aalge) and thick‐billed (U. lomvia) murres and of tufted puffins (Fratercula cirrhata) declined. We detected no linear trends in either breeding chronology or reproductive success over the study period for any seabird. All species of piscivorous seabirds apparently responded similarly to environmental cues as there was a positive covariation among species in the timing of nesting. Piscivores tended to nest earlier, and most species had higher rates of reproductive success in years with relatively warm spring sea temperatures. In contrast, planktivorous Leach’s storm‐petrels (O. leucorhoa) tended to nest earlier when spring and summer sea temperatures were relatively cool. Clearly, seabirds at St Lazaria were responding to interannual changes in sea temperatures near the breeding colony, probably as a result of effects on the food webs. Main conclusions Every seabird species we monitored at St Lazaria exhibited significant population trends between 1994 and 2006. For most species there appeared to be a relationship between both the timing of nesting and reproductive rates and spring or summer sea surface temperatures. Responses at both decadal (populations) and interannual (timing and reproductive success) scales make seabirds useful candidates for helping to monitor change in the marine environment.     

Seabird Bycatch in Pelagic Longline Fisheries Is Grossly Underestimated when Using Only Haul Data

Hundreds of thousands of seabirds are killed each year as bycatch in longline fisheries. Seabirds are predominantly caught during line setting but bycatch is generally recorded during line hauling, many hours after birds are caught. Bird loss during this interval may lead to inaccurate bycatch information. In this 15 year study, seabird bycatch was recorded during both line setting and line hauling from four fishing regions: Indian Ocean, Southern Ocean, Coral Sea and central Pacific Ocean. Over 43,000 albatrosses, petrels and skuas representing over 25 species were counted during line setting of which almost 6,000 seabirds attempted to take the bait. Bait-taking interactions were placed into one of four categories. (i) The majority (57%) of bait-taking attempts were “unsuccessful” involving seabirds that did not take the bait nor get caught or hooked. (ii) One-third of attempts were “successful” with seabirds removing the bait while not getting caught. (iii) One-hundred and seventy-six seabirds (3% of attempts) were observed being “caught” during line setting, with three albatross species – Laysan (Phoebastria immutabilis), black-footed (P. nigripes) and black-browed (Thalassarche melanophrys)– dominating this category. However, of these, only 85 (48%) seabird carcasses were retrieved during line hauling. Most caught seabirds were hooked through the bill. (iv) The remainder of seabird-bait interactions (7%) was not clearly observed, but likely involved more “caught” seabirds. Bait taking attempts and percentage outcome (e.g. successful, caught) varied between seabird species and was not always related to species abundance around fishing vessels. Using only haul data to calculate seabird bycatch grossly underestimates actual bycatch levels, with the level of seabird bycatch from pelagic longline fishing possibly double what was previously thought.     

Marine subsidies alter the diet and abundance of insular and coastal lizard populations

We evaluated the impact of marine materials on the diet and abundance of arthropodivorous lizards inhabiting islands and the coast of the Gulf of California. Here, marine materials are brought onto land by seabirds and by tidal action, and both subsidy pathways cause arthropod abundance to increase. We evaluated Uta stansburiana (side-blotched lizard) diets in three habitats defined by having: (1) no marine subsidies available, (2) only seabird-derived subsidies, and (3) only tidal-derived subsidies. Stable isotope data indicated that lizard diets are subsidized indirectly by seabird and tidal activity. For example, in coastal areas we determined that 40% of a lizard's diet contains arthropods that have consumed algae. Such subsidies may explain why we found that lizards in coastal areas occupy a significantly higher trophic position than lizards in unsubsidized areas. We analyzed eight years of survey data on all arthropodivorous lizards to determine if diet subsidies result in increased lizard abundance. We found that lizards were more abundant in coastal areas than they were in inland habitats, and that they were more abundant on islands with seabirds than on islands without seabird populations. This study provides insight into the importance and effect of marine-derived nutrients from multiple sources on vertebrate consumers inhabiting islands and coastal areas.     

Notes on the effects of E1 Niño on the seabirds of the Mollendo district, southwest Peru, in 1983

In the austral summer of 1982–83 the cool Peru Coastal Current Zone of the Pacific Coast of South America was affected by the strongest and most prolonged incursion of the warm El Niño Current in at least 58 years. An account is given of the visual effects of the disturbance on the seabirds of the Mollendo district on the coast of southwest Peru. With one exception, local numbers of the endemic cool water species were drastically reduced, with little evidence of recovery up to April 1984. During the period when El Niño was at its height, several warm water species of seabirds, previously either virtually or completely unknown at Mollendo, were recorded.     

Climate as a driver of phenological change in southern seabirds

Seabirds are one of the most threatened groups of birds globally and, overall, their conservation status is deteriorating rapidly. Southern hemisphere countries are over-represented in the number of species of conservation concern yet long-term phenological data on seabirds in the southern hemisphere is limited. A better understanding of the implications of changes in the marine and terrestrial environments to seabird species is required in order to improve their management and conservation status. Here we conducted a meta-analysis of the phenological drivers and trends among southern hemisphere seabirds. Overall there was a general trend towards later phenological events over time (34 % of all data series, N?=?47; 67 % of all significant trends), though this varied by taxa and location. The strongest trends towards later events were for seabirds breeding in Australia, the Laridae (gulls, noddies, terns) and migratory southern polar seabirds. In contrast, earlier phenologies were more often observed for the Spheniscidae (penguins) and for other seabirds breeding in the Antarctic and subantarctic. Phenological changes were most often associated with changes in oceanographic conditions, with sea-ice playing an important role for more southerly species. For some species in some locations, such as the Little Penguin Eudyptula minor in south-eastern Australia, warmer oceans projected under various climate change scenarios are expected to correspond to increased seabird productivity, manifested through earlier breeding, heavier chicks, an increased chance of double brooding, at least in the short-term.     

Effects of invasive rats and burrowing seabirds on seeds and seedlings on New Zealand islands

Rats (Rattus rattus, Rattus norvegicus, Rattus exulans) are important invaders on islands. They alter vegetation indirectly by preying on burrowing seabirds. These seabirds affect vegetation through nutrient inputs from sea to land and physical disturbance through trampling and burrowing. Rats also directly affect vegetation though consumption of seeds and seedlings. Seedling communities on northern New Zealand islands differ in composition and densities among islands which have never been invaded by rats, are currently invaded by rats, or from which rats have been eradicated. We conducted experimental investigations to determine the mechanisms driving these patterns. When the physical disturbance of seabirds was removed, in soils collected from islands and inside exclosures, seedling densities increased with seabird burrow density. For example, seedling densities inside exclosures were 10 times greater than those outside. Thus the negative effects of seabirds on seedlings, by trampling and uprooting, overwhelm the potentially beneficial effects of high levels of seed germination, seedling emergence, and possibly seed production, which result from seed burial and nutrient additions. Potential seedling density was reduced on an island where rats were present, germination of seeds from soils of this island was approximately half that found on other islands, but on this island seedling density inside exclosures was 7 times the density outside. Although the total negative effects of seabirds and rats on seedling densities are similar (reduced seedling density), the differences in mechanisms and life stages affected result in very different filters on the plant community.     

Nutrients and seabird biogeography: Feather elements differ among oceanic basins in the Southern Hemisphere,reflecting bird size,foraging range and nutrient availability in seawater

Aim

Biodiversity hotspots in wide-ranging marine species typically overlap with regions of high productivity, which are often associated with nutrient-rich waters. Here we investigate how element concentrations in feathers vary among highly mobile seabirds in global seabird biodiversity hotspots.

Location

Southern Hemisphere.

Time period

Contemporary.

Major taxa studied

Fifteen species in the order Procellariiformes.

Methods

We collected data on the concentration of 15 elements in feathers for 253 seabirds sampled across Australia and New Zealand and compared the “fingerprint” of micronutrient element profiles to feathers of related seabirds from global hotspots using principal component analysis (PCA), cluster analysis and permutational analysis of variance (PERMANOVA).

Results

Breast feather concentrations of some elements, including aluminium, iron, cobalt, chromium, manganese, nickel, arsenic and cadmium, were tens-to-hundred-fold higher in smaller (<400 g) than larger species (≥400 g). We suggest these results reflect the dominance of pelagic crustaceans in the diet of smaller seabirds, blooms of which are influenced by input of limiting ocean nutrients. Cluster analysis revealed three broad groups of feather elements: large seabirds, and small seabirds in each of the South Pacific and South Atlantic Ocean basins. High concentrations of some elements in feathers match seawater availability and are detectable in lower-trophic feeding seabirds with local movements. Conversely, the element fingerprints of longer-distance, higher-trophic foragers, including albatrosses, do not match availability in seawater at the collection site.

Main conclusions

The feather element concentrations of shorter-range foraging, lower-trophic feeding seabirds vary significantly among ocean basins, reflecting availability in seawater, while longer-range, higher-trophic species do not. We propose that geographically diverse availability of micronutrients, in addition to primary productivity, may play an underrecognized role in seabird biogeography and intra-hemispheric migration, though more research is needed. This study has important implications, considering the role of element availability in supporting biodiversity hotspots for dispersive marine predators and for the designation of protected areas.     

No evidence for extra-pair paternity in the western gull

The genetic mating system of western gulls Larus occidentalis breeding on Southeast Farallon Island, California, was determined using multilocus DNA fingerprints of 33 chicks from 22 broods. No extra-pair paternity (EPP) was found, despite extra-pair copulations (EPCs) occurring. This suggests that paternity guards are effective, and that females gain few genetic benefits from EPCs. The EPP in western gulls concurs with that of other seabirds, reinforcing the idea that seabirds generally have a monogamous genetic mating system.