A GIS‐based decision‐making approach for prioritizing seabird management following predator eradication

Given that 29% of seabird species are threatened with extinction, protecting seabird colonies on offshore islands is a global conservation priority. Seabirds are vulnerable to non‐native predator invasions, which reduce or eliminate colonies. Accordingly, conservation efforts have focused on predator eradication. However, affected populations are often left to passively recover following eradications. Although seabirds are highly mobile, their life history traits such as philopatry can limit passive recolonization of newly predator‐free habitat. In such cases, seabird colonies can potentially be re‐instated with active restoration via chick translocations or social attraction methods, which can be risky and expensive. We used biogeographic and species‐specific behavioral data in the Hauraki Gulf, New Zealand, a global hotspot of seabird diversity and predator eradications, to illustrate the use of geographic information systems multi‐criteria decision analysis to prioritize islands for active seabird restoration. We identified nine islands with low observed passive recovery of seabirds posteradication over a 50‐year timeframe, and classified these as sites where active seabird management could be prioritized. Such spatially explicit tools are flexible, allowing for managers to choose case‐specific criteria such as time, funding, and goals constrained for their conservation needs. Furthermore, this flexibility can also be applied to threatened species management by customizing the decision criteria for individual species' capacity to passively recolonize islands. On islands with complex restoration challenges, decision tools that help island restoration practitioners decide whether active seabird management should be paired with eradication can optimize restoration outcomes and ecosystem recovery.     

Tick infestation of chicks in a seabird colony varies with local breeding synchrony,local nest density and habitat structure

Parasites are a major risk for group‐living animals and seabirds are notoriously susceptible to ectoparasite infestations because they commonly nest in dense colonies. Ticks parasitize seabirds across all biogeographical regions and they can be particularly harmful to nestlings, but the ecological factors that affect their transmission to chicks are little studied and poorly understood. Here we show that abundance of tick larvae in blue‐footed booby Sula nebouxii broods varies with local nest synchrony and density, and also with habitat structure: abundance increased with local breeding synchrony, was linearly and quadratically related to local nest density, and was highest toward the southern end of the study area which has suitable (boulder‐rich) habitat for ticks. Also, with increasing chick age infestation first increased and then declined. The results of this study highlight how local physical and social environmental factors influence infestation of seabird nestlings by ticks.     

Long‐term population dynamics reveal that survival and recruitment of tropical boobies improve after a hurricane

Variability in population numbers is a central issue in evolutionary ecology and also in biodiversity conservation. However, for most seabirds this information is lacking and tropical populations are virtually unstudied. Long‐term studies are warranted because world's seabird populations exhibit an overall declining trend since 1950. Using data spanning 23 yr, we investigated how adult survival, local recruitment, and their relative contributions to population growth (λ) vary over time in the blue‐footed booby Sula nebouxii, a long‐lived locally foraging seabird that breeds in tropical waters. In addition, we investigated whether booby demographic rates exhibit the same declining trend observed in other seabirds, whether these rates are impacted by hurricanes, and whether these potential impacts differ between sexes. Our analysis of 4608 capture–recapture histories revealed that survival and recruitment were nearly equal between males and females, exhibited a declining trend over the last 23 yr, and in both sexes, these vital rates improved after a hurricane. The declining trend in recruitment was slightly more attenuated in males. These results add to the current evidence for an overall declining trend in world's seabird populations and extend its confirmation to the warm eastern tropical Pacific. Moreover, they provide the first evidence that hurricanes may favor natural populations. As a result of the declining trend and variation in survival and recruitment, λ exhibited a slight decline and substantial variation over the 23 yr. However, most λ values were equal to or higher than 1, and the long‐term average indicates population increase. The ability of blue‐footed boobies to maintain a positive population balance despite of negative trends in their vital rates might result from canalization of adult survival (the vital rate that contributes most to λ and shows lower variation compared to recruitment) against environmental variability.     

Integrating invasive mammal eradications and biodiversity offsets for fisheries bycatch: conservation opportunities and challenges for seabirds and sea turtles

The removal of invasive mammals from islands is one of society’s most powerful tools for preventing extinctions and restoring ecosystems. Given the demonstrable high conservation impact and return on investment of eradications, new networks are needed to fully leverage invasive mammal eradications programs for biodiversity conservation at-large. There have been over 800 invasive mammal eradications from islands, and emerging innovations in technology and techniques suggest that island area will soon no longer be the limiting factor for removing invasive mammals from islands. Rather, securing the necessary social and economic capital will be one main challenge as practitioners target larger and more biologically complex islands. With a new alliance between conservation practitioners and the fisheries sector, biodiversity offsets may be a promising source of capital. A suite of incentives exists for fisheries, NGOs, and governments to embrace a framework that includes fishery bycatch offsets for seabirds and sea turtles. A bycatch management framework based on the hierarchy of “avoid, minimize, and offset” from the Convention on Biological Diversity would result in cost-effective conservation gains for many threatened seabirds and sea turtles affected by fisheries. Those involved with island conservation and fisheries management are presented with unprecedented opportunities and challenges to operationalize a scheme that will allow for the verifiable offset of fisheries impacts to seabirds and sea turtles, which would likely result in unparalleled marine conservation gains and novel cross-sector alliances.     

Anti‐predator behaviour in a procellariid seabird: Wedge‐tailed shearwaters do not respond to the odour of introduced ship rats

Seabirds are particularly vulnerable to introduced alien mammalian predators, especially invasive rats, which are the main contributors to seabird extinction and endangerment in many places worldwide. However, this appears context‐dependent because, paradoxically, cases of apparent long‐term coexistence between rats and some species of seabird have been reported for centuries, in various locations. Among seabirds, procellariiforms are known to have developed a range of olfactory‐driven behaviours, such as partner recognition and homing. Olfaction could be an effective means of recognizing and thereafter avoiding invasive predators. However, the role of olfaction in predation risk assessment has not yet been examined in any procellariiform. Here, we investigated, through a Y‐maze experiment, whether the wedge‐tailed shearwater (Puffinus pacificus) avoided the odour of one of the most damaging alien predators on islands, the ship rat (Rattus rattus). The experiment was conducted in different ecological contexts on three neighbouring islets off New Caledonia having different communities of invasive rats. Contrary to our expectations, the wedge‐tailed shearwater either did not detect or did not avoid the odour of the ship rat, despite about 175 years of coexistence between rats and shearwaters in New Caledonia. These findings highlight the need for further investigations (across species, across sites) into the factors underpinning the paradox between high vulnerability and the surprising long‐term coexistence between procellariid seabirds and alien invasive rats.     

Could specialization to cold‐water upwelling systems influence gene flow and population differentiation in marine organisms? A case study using the blue‐footed booby,Sula nebouxii

Aim We assessed population differentiation and gene flow across the range of the blue‐footed booby (Sula nebouxii) (1) to test the generality of the hypothesis that tropical seabirds exhibit higher levels of population genetic differentiation than their northern temperate counterparts, and (2) to determine if specialization to cold‐water upwelling systems increases dispersal, and thus gene flow, in blue‐footed boobies compared with other tropical sulids. Location Work was carried out on islands in the eastern tropical Pacific Ocean from Mexico to northern Peru. Methods We collected samples from 173 juvenile blue‐footed boobies from nine colonies spanning their breeding distribution and used molecular markers (540 base pairs of the mitochondrial control region and seven microsatellite loci) to estimate population genetic differentiation and gene flow. Our analyses included classic population genetic estimation of pairwise population differentiation, population growth, isolation by distance, associations between haplotypes and geographic locations, and analysis of molecular variance, as well as Bayesian analyses of gene flow and population differentiation. We compared our results with those for other tropical seabirds that are not specialized to cold‐water upwellings, including brown (Sula leucogaster), red‐footed (S. sula) and masked (S. dactylatra) boobies. Results Blue‐footed boobies exhibited weak global population differentiation at both mitochondrial and nuclear loci compared with all other tropical sulids. We found evidence of high levels of gene flow between colonies within Mexico and between colonies within the southern portion of the range, but reduced gene flow between these regions. We also found evidence for population growth, isolation by distance and weak phylogeographic structure. Main conclusions Tropical seabirds can exhibit weak genetic differentiation across large geographic distances, and blue‐footed boobies exhibit the weakest population differentiation of any tropical sulid studied thus far. The weak population genetic structure that we detected in blue‐footed boobies may be caused by increased dispersal, and subsequently increased gene flow, compared with other sulids. Increased dispersal by blue‐footed boobies may be the result of the selective pressures associated with cold‐water upwelling systems, to which blue‐footed boobies appear specialized. Consideration of foraging environment may be particularly important in future studies of marine biogeography.     

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.     

Measuring nocturnal seabird activity and status using acoustic recording devices: applications for island restoration

ABSTRACT Nocturnal burrow‐nesting seabirds breeding on isolated oceanic islands pose challenges to conventional monitoring techniques, resulting in their frequent exclusion from population studies. These seabirds have been devastated by nonnative predator introductions on islands worldwide. After predators are eradicated, recovery has been poorly quantified, but evidence suggests some nocturnal seabird populations have been slow to return. We evaluated the use of automated acoustic recorders and call‐recognition software to investigate nocturnal seabird recovery after removal of introduced Arctic foxes (Alopex lagopus) in the Aleutian Archipelago, Alaska. We compared relative seabird abundance among islands by examining levels of vocal activity. We deployed acoustic recorders on Nizki‐Alaid, Amatignak, and Little Sitkin islands that had foxes removed in 1975, 1991, and 2000, respectively, and on Buldir, a predator‐free seabird colony. Despite frequent gales, only 2.9% of 2230 recording hours from May to August of 2008 and 2009 were unusable due to wind noise. Recording quality and call recognition model success were highest when recording devices were placed at sites offering some wind shelter. We detected greater vocal activity of Fork‐tailed (Oceanodroma furcata) and Leach's (O. leucorhoa) storm‐petrels and Ancient Murrelets (Synthliboramphus antiquus) on islands with longer time periods since fox eradication. Also, by detecting chick calls in the automated recordings, we confirmed breeding by Ancient Murrelets on an island thought to be abandoned due to fox predation. Acoustic monitoring allowed us to examine the relative abundance of seabirds at remote sites. If a link between vocalizations and population dynamics can be made, acoustic monitoring could be a powerful census method.     

Commercial fisheries,inter‐colony competition and sea depth affect foraging location of breeding Scopoli's Shearwaters Calonectris diomedea

The distribution of seabirds at sea is influenced by physical, ecological and anthropogenic factors such as sea depth, prey distribution, intra‐specific competition and commerical fishing activities. We quantified the foraging habitat preferences of Scopoli's Shearwater Calonectris diomedea in the Mediterranean Sea. We analysed habitat preferences in relation to a suite of physical and ecological variables including sea depth, net primary production and distance to other colonies (as a proxy of intra‐specific competition). Since the Mediterranean is heavily impacted by commercial fisheries, we also incorporated the distance to fishing harbours in our analyses as a proxy of the availability of discards which are a potential feeding source for Scopoli's Shearwater. Foraging birds preferred shallower waters and avoided areas close to other colonies, thereby reducing interactions with conspecifics. We also found that long‐distance trips were undertaken to areas close to fishing harbours, suggesting that these represented particularly profitable locations to compensate for the greater travelling costs involved. No differences in foraging between the sexes were recorded. This study improves our understanding of the at‐sea distribution and habitat preference of a seabird inhabiting the over‐exploited Mediterranean Sea. Our results support growing evidence that seabirds exhibit complex relationships with commerical fishing activities, which must be considered when planning conservation programmes.     

Facilitative interactions among the pelagic community of temperate migratory terns,tunas and dolphins

We studied habitat and behavioral interactions among the marine community of top pelagic predators over the Atlantic continental shelf, observed from shipboard surveys off the northeastern United States. We hypothesized that foraging seabirds, specifically common terns Sterna hirundo and roseate terns S. dougallii, associate positively with the distribution and abundance of large, easily‐detected subsurface marine predators, as a result of facilitative interactions. Few rigorous tests examine the effect of interspecific interactions on seabird distributions, though many papers note the importance of environmental influences. Fewer, still, assess facilitation, defined as positive interactions among multiple taxa (birds, fish, mammals), where individuals use foraging neighbors for improved prey detection or enhanced prey availability. Our use of spatiotemporal‐structured Bayesian hierarchical models allowed us to test for fine‐scale associations of common and roseate terns with aggregations of tunas and cetaceans, and with standard oceanographic parameters. High tern abundance was linked to relatively high tuna densities and low dolphin densities, as well as high sea surface temperatures, shallow water, and proximity to shore. The fact that terns foraged when in the presence of tunas or relatively dense dolphin pods supports our hypothesis that the mechanism behind this spatial association involves positive interspecific interactions (attraction), a phenomenon that has been described but rarely quantified. This study reveals that community structure depends on static and dynamic covariates alike, ranging from bathymetry to the movement of other guild members. To improve the efficacy of predictive modeling, ecosystem approaches to applied conservation management should integrate not only habitat, but also behavior and community factors into analyses, especially in the case of marine spatial planning.     

Yellow crazy ants (<Emphasis Type="Italic">Anoplolepis gracilipes</Emphasis>) reduce numbers and impede development of a burrow-nesting seabird

Yellow crazy ants (Anoplolepis gracilipes) are a significant threat to biodiversity due to a rapidly expanding range and the potential to disrupt ecosystem interactions at multiple trophic levels. Extirpation of ground-nesting seabirds subsequent to yellow crazy ant invasion has been reported anecdotally. Yellow crazy ant control is difficult and resulting positive effects on nesting seabirds is undocumented. We report the effects of ant invasion and subsequent control on burrow-nesting seabirds following the invasion of more than half of a 1.25-ha wedge-tailed shearwater (Ardenna pacifica) colony located on eastern O‘ahu. The number of active seabird burrows in invaded areas dropped from 125 in 2006 to 6 in 2010, with no corresponding decline in active burrows in adjacent, uninvaded areas. Ant control efforts in 2011 reduced ant densities by more than 97% and resulted in a substantial increase in active burrows (43 in 2011). In invaded areas, burrows appeared to be abandoned by adults prior to egg-laying. Chicks surviving in invaded areas exhibited mild to severe developmental abnormalities, and overall had shorter culmens, tarsi and wingchords, smaller eye diameters, and lower weights than chicks outside invaded areas. We conclude that yellow crazy ants constitute a significant, and likely underestimated, risk to ground-nesting seabirds. Loss of seabird nesting colonies can have significant effects on nutrient inputs, and can bring about shifts in plant communities and faunal composition. Range expansion of yellow crazy ants is expected and ant/seabird interactions are likely to increase.     

Keeping it regular: Development of thermoregulation in four tropical seabird species

The thermoregulatory capacity of a species can determine which climatic niche it occupies. Its development in avian chicks is influenced by numerous factors. Furthermore, it is suggested that altricial chicks develop their thermoregulatory capacity post-hatching, while precocial chicks develop aspects of this in the egg. We investigated the development of thermoregulation of four co-occurring seabird species in the Seychelles; namely white, ground-nesting white-tailed tropicbirds (Phaethon lepturus) and tree-nesting fairy terns (Gygis alba); and dark plumaged, tree-nesting lesser noddies (Anous tenuirostris) and ground- and tree-nesting brown noddies (A. stolidus). White-tailed tropicbirds have semi-altricial chicks, while the remaining species have semi-precocial chicks. Cloacal temperatures (T_b) were measured at five day intervals from newly hatched chicks and compared over time, and with adult T_bs. Initial T_bs of all chicks, except fairy terns, were lower than those taken when chicks were older. Brooding cessation generally coincided with feather development, as did an increase in T_b. Mean chick T_b was significantly lower than mean adult T_b for all species, but only white-tailed tropicbird and brown noddy chicks in tree nests differed significantly from mean adult T_b when chick T_b at five day intervals were considered. There was a significant interactive effect of nest site and age on brown noddy chick T_b, but chick colour did not have a significant effect on T_b. However, brown noddy chicks on dune crests maintained a constant T_b sooner than chicks in tree nests. Our results demonstrate that tropical seabird species have a more delayed onset of thermoregulatory capabilities when compared with those in temperate environments, perhaps as nest sites are less thermally challenging. Nest microhabitats and behavioural thermoregulation, are likely more important during early chick development for these species.     

Invasive rats and seabirds after 2,000 years of an unwanted coexistence on Mediterranean islands

In the Mediterranean, the survival of endemic long-lived seabirds despite the long-standing introduction of one of the most damaging alien predator, the ship rat (Rattus rattus), on most islands constitutes an amazing conservation paradox. A database gathering information on approximately 300 Western Mediterranean islands was analyzed through generalized linear models to identify the factors likely to influence ship rat presence and to account for how ship rat presence and island characteristics may have driven the presence and abundance of seabirds. Our review showed that few Mediterranean islands remain rat-free. At the regional scale, rat presence was only a limiting factor in the abundance of the smallest seabird, the storm petrel (Hydrobates pelagicus), while the distribution and abundance of the three shearwaters were more influenced by island characteristics. We hypothesized that the long-term persistence of these seabirds may have been facilitated by the various biogeographical contexts of Mediterranean islands, likely to provide intra-island refuges.     

Optimizing survey effort for burrow‐nesting seabirds

ABSTRACT Regular monitoring of seabird populations is necessary to improve our understanding of their responses to environmental change and inform conservation management. However, given the difficulty in accessing remote breeding sites and the limited resources typically available to land managers, conducting regular, extensive surveys of seabird populations is often not feasible. Our objective was to determine the minimum survey effort required to obtain accurate and precise population estimates of Short‐tailed Shearwaters (Ardenna tenuirostris) and Little Penguins (Eudyptula minor), two abundant burrowing seabird species in southeastern Australia, by comparing bootstrapped means and confidence intervals under different sampling regimes on four islands. We found that, in many cases, survey effort (the proportion of transects and quadrats along transects surveyed) could be reduced. For Short‐tailed Shearwaters, reducing the number of transects resulted in a maximum difference of 15% between the means at full survey effort and two levels of reduced survey effort. Means differed by <3% when we halved the number of quadrats. For Little Penguins, reducing the number of transects and quadrats by 50% resulted in differences of 7–40% and 4–34%, respectively, between the full and reduced survey effort means. Confidence intervals generally increased with decreasing survey effort for both species. Differences in required survey effort between the two species in our study may have been due to differences in burrow distribution on islands, with Short‐tailed Shearwater burrows generally uniformly distributed on each island and Little Penguin burrows typically occurring in patches. These would be influenced by island‐specific characteristics in concert with habitat preferences, population size, and seasonal variation in seabird abundance. Stratified sampling did not increase survey accuracy and simulations showed that large reductions in survey effort could be made under a pseudo‐random sampling regime, with mean abundance estimates similar at most levels of survey effort. For both species, reducing the proportion of pseudo‐random quadrats to 50% and 25% of the full survey effort produced confidence intervals of 12% and 21%, respectively, of the maximum, whereas a survey effort of 10% produced confidence intervals of up to 36% of the maximum for both species. A pseudo‐random sampling regime would maximize survey efficiency because considerably fewer quadrats would be required and allow development of more efficient sampling protocols and regimes.     

Evaluating the statistical power of detecting changes in the abundance of seabirds at sea

There has been considerable recent concern about the plight of seabirds globally, as many species have declined substantially. In the UK there are statutory needs to monitor seabirds at sea, particularly in light of new offshore areas being designated for conservation and plans for major offshore wind farm developments. However, the extent to which at‐sea surveys are capable of detecting changes in abundance and options for improving survey protocols have received little attention. We investigate the power of detecting changes in numbers using at‐sea surveys. Using data collected as part of a visual aerial seabird survey programme that covered areas of ‘Round 2’ offshore wind farm developments in UK waters, we quantify the variability and characterize the statistical properties of count data. By generating random datasets with the same properties as real data, we estimated the power of being able to detect various declines (50, 33, 25, 15 and 10%) and assessed the effects of survey duration and frequency and of spatial scale and variability in bird numbers. The results indicate that the survey design protocols used for the UK ‘Round 2’ offshore wind farm visual aerial seabird survey programme do not provide adequate means of detecting changes in numbers, even when declines are in excess of 50% and assumptions regarding certainty are relaxed to < 80%. Extending the duration, frequency and spatial extent of surveys would increase the probability of detecting changes, but not to a desirable level (e.g. > 0.8). The primary reason why there is a low probability of being able to detect consistent directional changes is that seabird numbers fluctuate greatly at any given location. Means of explaining this fine‐scale variability are required, especially if small changes in populations are to be detected. Incorporating hydrodynamic variables into trend analysis might increase the power of detecting changes. Failure to detect changes in seabird numbers should not be taken to mean that no changes are occurring.     

Detectability and visibility biases associated with using a consumer‐grade unmanned aircraft to survey nesting colonial waterbirds

Surveys of colonial‐nesting waterbirds are needed to assess population trends and gain insight into the health of wetland ecosystems. Use of unmanned aerial systems (UAS) for such surveys has increased over the past decade, but possible sources of bias in surveys conducted with UAS have not been examined. We examined possible visibility biases associated with using a UAS to survey waterbird colonies in cypress‐tupelo watersheds and coastal island habitats in Texas in 2016. We used known numbers of four waterbird decoy types, including Black Skimmers (Rynchops niger), terns, and white‐ and dark‐plumaged herons, to estimate their detectability in each habitat. Six observers independently counted decoys from aerial imagery mosaics taken with a consumer‐grade, off‐the‐shelf quadcopter drone. We used generalized linear mixed‐effects models to estimate detection probabilities of each decoy type. Black Skimmers at the coastal island had a detection probability of just 53%. Detectability of both white‐ and dark‐plumaged herons was lower in the canopied cypress‐tupelo habitat than the coastal island. In addition, cloud cover > 50% further reduced detectability of white heron decoys in cypress‐tupelo habitat. Use of the double‐count method yielded biased‐low abundance estimates for white‐ and dark‐plumaged herons in canopied sites, suggesting that habitat differences were a greater source of bias than observer error. Black Skimmers were the only decoy type to be imperfectly detected at the coastal island, a surprising result given the stark contrast of their plumage with their sand and shell nesting substrate. Our results indicate that UAS‐derived photographic surveys are prone to low detection probabilities at sites where vegetation occludes nests. In habitats without canopy, however, UAS surveys show promise for obtaining accurate counts of terns, white herons, and dark herons.     

Nests of the brown booby (Sula leucogaster) as a potential indicator of tropical ocean pollution by marine debris

Seabirds collect debris primarily nearby breeding sites, and thus they may be used to monitor these pollutants in the ocean. This study aimed to investigate the prevalence of marine debris used as nesting materials by the brown booby (Sula leucogaster) and to test the species selectivity to debris type and color in two coastal islands of Brazil. We found marine debris in 61% of the brown booby nests on both islands. Fishing gear and hard plastic were the most frequent types of debris. Higher prevalence of fishing gear was found on the island with greater fishery activity. Similarly, hard plastic was the most frequent type of debris in nests and adjacent beach environment. The frequency of debris in brown booby nests can be a potential indicator of the abundance of specific items in surrounding marine waters. Monitoring debris in brown booby nests in a long-term may provide a better understanding of the species⿿ selectivity for specific debris. Furthermore, the impacts of debris in seabird nests at population level remain an overlooked threat that may reduce the quality of nesting habitats. We showed that brown booby nests are widely impacted by marine debris and that these organisms are exposed to this form of pollution from the beginning of their life.     

The biology of terns nesting at Aldabra Atoll, Indian Ocean, with particular reference to breeding seasonality

Five species of tern breed on Aldabra Atoll (09° 24' S; 46° 20' E). The Caspian tern Sterna caspia and Crested tern S. bergii feed exclusively in very shallow reef/lagoon water, the Fairy tern Gygis alba and Brown noddy Anous stolidus feed out at sea, and the Black-naped tern Sterna sumatrana is intermediate in its foraging. Both of the shallow-water species lay during the south-east monsoon season, the Caspian tern from April to August and the Crested tern from June to August, but the Crested tern also lays in December and January. The remaining three species have extended laying periods largely circumscribed by the north-west monsoon season from November to March. Breeding population size of the Caspian tern is in the low tens and of the Brown noddy in the low thousands, with the other species each numbering in the hundreds. The distribution and abundance of the nine species of tern breeding within the Seychelles ( sensu lato ) vary on the different island groups in a manner interpretable in terms of depth of the surrounding waters. Systematic differences between the central Seychelles and Aldabra groups in timing of breeding by terns which feed out at sea may be associated with seasonal latitudinal movement of the divergence zone between the South Equatorial Current and the Equatorial Counter-current, acting via correlated latitudinal shifts of prey species and game-fish abundance.     

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.     

Chick‐provisioning behaviour of two shearwaters breeding in south‐eastern Australia

The chick‐provisioning behaviour of the short‐tailed shearwater Puffinus tenuirostris and the wedge‐tailed shearwater Puffinus pacificus was investigated in a mixed colony on Montague Island, New South Wales, Australia, over two breeding seasons. This colony is located at opposite edges of the breeding distribution of the two species. Frequent weighing techniques were used to determine chick feeding frequency, feed timing, meal size, chick weight loss and indices of food conversion efficiency of the chicks. Short‐tailed shearwater parents fed their chicks larger more infrequent meals than wedge‐tailed shearwater parents. Short‐tailed shearwater chicks demonstrated higher food conversion efficiencies and lower weight loss than wedge‐tailed shearwater chicks, indicating either differences in diet or metabolic rates. The feeding frequency in wedge‐tailed shearwaters also fluctuated more widely than for short‐tailed shearwaters over the two breeding seasons. Despite the fact that the timing of the breeding cycle on Montague Island is almost identical for the two species, these differences in chick provisioning are probably a result of differences in prey type and location, so they may help explain variations in annual breeding success and limits to the distribution of the two species.