Gygis Research Articles

Current Land Bird Distribution and Trends in Population Abundance Between 1982 and 2012 on Rota, Mariana Islands

Abstract The western Pacific island of Rota is the fourth largest human-inhabited island in the Mariana archipelago and designated an Endemic Bird Area. Between 1982 and 2012, 12 point-transect distance-sampling surveys were conducted to assess bird population status. Surveys did not consistently sample the entire island; thus, we used a ratio estimator to estimate bird abundances in strata not sampled during every survey. Trends in population size were reliably estimated for 11 of 13 bird species, and 7 species declined over the 30-y time series, including the island collared-dove Streptopelia bitorquata, white-throated ground-dove Gallicolumba xanthonura, Mariana fruit-dove Ptilinopus roseicapilla, collared kingfisher Todiramphus chloris orii, Micronesian myzomela Myzomela rubratra, black drongo Dicrurus macrocercus, and Mariana crow Corvus kubaryi. The endangered Mariana crow (x̄ = 81 birds, 95% CI 30–202) declined sharply to fewer than 200 individuals in 2012, down from 1,491 birds in 1982 (95% CI = 815–3,115). Trends increased for white tern Gygis alba, rufous fantail Rhipidura rufifrons mariae, and Micronesian starling Aplonis opaca. Numbers of the endangered Rota white-eye Zosterops rotensis declined from 1982 to the late 1990s but returned to 1980s levels by 2012, resulting in an overall stable trend. Trends for the yellow bittern Ixobrychus sinensis were inconclusive. Eurasian tree sparrow Passer montanus trends were not assessed; however, their numbers in 1982 and 2012 were similar. Occupancy models of the 2012 survey data revealed general patterns of land cover use and detectability among 12 species that could be reliably modeled. Occupancy was not assessed for the Eurasian tree sparrow because of insufficient detections. Based on the 2012 survey, bird distribution and abundance across Rota revealed three general patterns: 1) range restriction, including Mariana crow, Rota white-eye, and Eurasian tree sparrow; 2) widespread distribution, low abundance, including collared kingfisher, island collared-dove, white-throated ground-dove, Mariana fruit-dove, white tern, yellow bittern, black drongo, and Micronesian myzomela; and 3) widespread distribution, high abundance, including rufous fantail and Micronesian starling. The Mariana crow was dispersed around the periphery of the island in steep forested land-cover types. In contrast, the Rota white-eye was restricted to the high-elevation mesa. Only for the white-throated ground-dove was there a significant difference among cover types, with lower occupancy in open field than in forested areas. Vegetation was included in the best-fit occupancy models for yellow bittern, black drongo, Micronesian myzomela, and Micronesian starling, but vegetation type was not a significant variable nor included in the top models for the remaining five species: white tern, island collared-dove, Mariana fruit-dove, collared kingfisher, and rufous fantail. Given declining population trends, the Rota bird-monitoring program could benefit from establishing threshold and alert limits and identifying alternative research and management actions. Continued monitoring and demographic sampling, in conjunction with ecological studies, are needed to understand why most bird species on Rota are declining, identify the causative agents, and assess effectiveness of conservation actions, especially for the Mariana crow.

Seabird recovery and vegetation dynamics after Norway rat eradication at Tromelin Island, western Indian Ocean

Seabirds are notoriously sensitive to introduced mammalian predators and eradication programs have benefitted seabird populations and their habitats on numerous islands throughout the world. However, less evidence is available from the tropics as to the benefits of rat eradication. Here, we report the seabird recovery and vegetation dynamics on a small coralline island of the tropical western Indian Ocean, eight years after Norway rat (Rattus norvegicus) eradication. Two species of seabirds were breeding before rat eradication (red-footed and masked boobies, Sula sula and Sula, dactylatra) and, in both species, the number of breeding pairs had an apparent increase of 22–23% per year after rat eradication. Such a high annual growth rate cannot be achieved by auto-recruitment only and our data suggest that immigration from other source populations never occurred in at least one of these species. We suggest that it is rather due to a rapid increase in breeding success, which rapidly increased the observed number of breeders since birds remained in the available-for-counting-as-breeders group for much longer. Two other species, the white tern (Gygis alba) and the brown booby (Sula leucogaster) were recorded breeding in 2014. The former species has not bred on the island since 1856 and the latter has never bred on the island. Plant cover (monospecific formation of the ruderal herb Boerhavia diffusa) dramatically increased from less than 30% of surface coverage to more than 70%. Although the initial restoration project was to eradicate all introduced mammals of the island simultaneously, house mouse (Mus musculus) eradication failed. Mouse density was high 8years after rat eradication (32mice/ha in dry season and 52mice/ha in rainy season) but not higher than at a comparable tropical island of the region (Juan de Nova) where mice coexist with introduced black rats (Rattus rattus) and feral cats (Felis catus). These results are discussed in terms of the direct positive effects of rat eradication on seabirds and plants and the indirect positive effects of post-eradication seabird increase on soil manuring and vegetation recovery. Overall, our results show that on tropical islands, seabird and habitat recovery can be very rapid after rat eradication and should be implemented as a restoration tool wherever possible.

First Breeding Record of the White Tern,Gygis alba, in México

We report the first breeding record of the White Tern (Gygis alba) in México. We also provide notes on parental behavior of this species on Socorro Island, Revillagigedo Archipelago, México. We observed two adults feeding one nestling during the summer of 2012 at a nest located on the naval base on Socorro Island. The White Tern is considered a vagrant species in the Revillagigedo Archipelago. Although a breeding colony was mistakenly reported earlier, our report positively confirms for the first time the breeding status of this species in México

Predicting cetacean and seabird habitats across a productivity gradient in the South Pacific gyre

Oligotrophic regions are expected to host low densities of top predators. Nevertheless, top predators with contrasting energetic costs might respond differently to the productivity of their habitats. Predators with high energetic demands might be constrained to select the most productive habitats to meet their high energetic requirements, whereas less active predators would be able to satisfy their needs by exploiting either high or low productivity habitats. Although situated in the core of the South Pacific oligotrophic gyre, French Polynesia is characterized by a fairly marked productivity gradient from the extremely oligotrophic Australs area to the more productive Marquesas area. The aim of this study was to investigate cetacean and seabird habitats in French Polynesia in light of their general energetic constraints. We collected cetacean and seabird sightings from an aerial survey across French Polynesian waters during the austral summer 2011. We classified cetaceans and seabirds into energetic guilds according to the literature. For each guild, we built generalized additive models along with static covariates and oceanographic covariates at the seasonal and climatological resolutions. We provided regional habitat predictions for Delphininae, Globicephalinae, sperm and beaked whales, tropicbirds, grey terns, noddies, white terns, boobies, petrels and shearwaters, sooty terns and frigatebirds. Explained deviances ranged from 5% to 30% for cetaceans and from 14% to 29% for seabirds. Cetaceans clearly responded to the productivity gradient, with the highest predicted densities around the productive waters of the Marquesas. However, Delphininae and Globicephalinae, characterized by higher energetic demands, depended more strongly on productivity, showing a ratio of 1–26 and 1–31 between their lowest and highest density areas respectively, compared to the less active sperm and beaked whales (showing only a ratio of 1–3.5 in predicted densities). In contrast, seabird distributions appeared more governed by the availability of nesting and roosting sites than by energetic constraints.

Population Dynamics of Hawaiian Seabird Colonies Vulnerable to Sea‐Level Rise

Globally, seabirds are vulnerable to anthropogenic threats both at sea and on land. Seabirds typically nest colonially and show strong fidelity to natal colonies, and such colonies on low-lying islands may be threatened by sea-level rise. We used French Frigate Shoals, the largest atoll in the Hawaiian Archipelago, as a case study to explore the population dynamics of seabird colonies and the potential effects sea-level rise may have on these rookeries. We compiled historic observations, a 30-year time series of seabird population abundance, lidar-derived elevations, and aerial imagery of all the islands of French Frigate Shoals. To estimate the population dynamics of 8 species of breeding seabirds on Tern Island from 1980 to 2009, we used a Gompertz model with a Bayesian approach to infer population growth rates, density dependence, process variation, and observation error. All species increased in abundance, in a pattern that provided evidence of density dependence. Great Frigatebirds (Fregata minor), Masked Boobies (Sula dactylatra), Red-tailed Tropicbirds (Phaethon rubricauda), Spectacled Terns (Onychoprion lunatus), and White Terns (Gygis alba) are likely at carrying capacity. Density dependence may exacerbate the effects of sea-level rise on seabirds because populations near carrying capacity on an island will be more negatively affected than populations with room for growth. We projected 12% of French Frigate Shoals will be inundated if sea level rises 1 m and 28% if sea level rises 2 m. Spectacled Terns and shrub-nesting species are especially vulnerable to sea-level rise, but seawalls and habitat restoration may mitigate the effects of sea-level rise. Losses of seabird nesting habitat may be substantial in the Hawaiian Islands by 2100 if sea levels rise 2 m. Restoration of higher-elevation seabird colonies represent a more enduring conservation solution for Pacific seabirds.

Genome skimming identifies polymorphism in tern populations and species

BackgroundTerns (Charadriiformes: Sterninae) are a lineage of cosmopolitan shorebirds with a disputed evolutionary history that comprises several species of conservation concern. As a non-model system in genetics, previous study has left most of the nuclear genome unexplored, and population-level studies are limited to only 15% of the world's species of terns and noddies. Screening of polymorphic nuclear sequence markers is needed to enhance genetic resolution because of supposed low mitochondrial mutation rate, documentation of nuclear insertion of hypervariable mitochondrial regions, and limited success of microsatellite enrichment in terns. Here, we investigated the phylogenetic and population genetic utility for terns and relatives of a variety of nuclear markers previously developed for other birds and spanning the nuclear genome. Markers displaying a variety of mutation rates from both the nuclear and mitochondrial genome were tested and prioritized according to optimal cross-species amplification and extent of genetic polymorphism between (1) the main tern clades and (2) individual Royal Terns (Thalasseus maxima) breeding on the US East Coast.ResultsResults from this genome skimming effort yielded four new nuclear sequence-based markers for tern phylogenetics and 11 intra-specific polymorphic markers. Further, comparison between the two genomes indicated a phylogenetic conflict at the base of terns, involving the inclusion (mitochondrial) or exclusion (nuclear) of the Angel Tern (Gygis alba). Although limited mitochondrial variation was confirmed, both nuclear markers and a short tandem repeat in the mitochondrial control region indicated the presence of considerable genetic variation in Royal Terns at a regional scale.ConclusionsThese data document the value of intronic markers to the study of terns and allies. We expect that these and additional markers attained through next-generation sequencing methods will accurately map the genetic origin and species history of this group of birds.

Mercury levels in the feathers of breeding seabirds in the Seychelles, western Indian Ocean, from 1996 to 2005

We analysed mercury levels in the breast feathers of several breeding seabirds—White-tailed Tropicbird (Phaethon lepturus), Audubon's Shearwater(Puffinus lherminieri), Lesser Noddy (Anous tenuirostris), White Tern (Gygis alba), Sooty Tern (Onychoprion fuscata) and Roseate Tern (Sterna dougallii)—on Aride Island in the Seychelles during three periods between 1996 and 2005. Mercury concentrations tended to be higher in the second sampling period (2002–03) than the first (1996–97), particularly for inshore-feeding species. El Niño events in 1997–99 and 2002–03 might help to explain this pattern, through an increase in mercury bioavailability for seabirds that forage inshore. However, levels of mercury in tissue decreased significantly from the first period (1996–97) to the third period (2004–05) for inshore-foraging species (Lesser Noddy mean ± s.e.: 0.82 ± 0.02 mg g−1 v. 0.53 ± 0.06 μg g−1 respectively) and more wide-ranging, offshore-feeding species (Sooty Tern: 1.16–0.05 v. 0.59 ± 0.04; White-tailed Tropicbird: 1.82 ± 0.05 v. 1.43 ± 0.09). Wide-ranging species of seabirds are more likely to be useful bioindicators at large spatial scales, with such species suggesting a decreasing trend in mercury pollution in the western Indian Ocean.

Testing subspecies hypothesis with molecular markers and morphometrics in the Pacific white tern complex

To test the validity of subspecies designations of the white tern, genetic and morphological data were used to assess differences among four putative Pacific subspecies Gygis alba candida, Gygis alba rothschildi, Gygis alba pacifica, and Gygis alba microrhyncha. The origin(s) of a recent colonization of Oahu was also examined using molecular data. Samples were collected from 209 birds, representing island groups of the North and South Pacific. Culmen length and depth, longest and shortest rectrix lengths, and wing chord measurements from an earlier dataset were compared. Mitochondrial DNA variation suggests that there are no phylogenetically distinct species within the Pacific Ocean. The genetic and morphological similarity of G. a. candida and G. a. rothschildi warrants merging them into one subspecies (G. a. candida). Gygis alba microrhyncha and G. a. pacifica are distinctly smaller and larger than the other two subspecies, respectively, but are not completely diagnosable across the morphological characters examined. Although the Pacific subspecies do not exhibit reciprocal monophyly, there is significant genetic differentiation among the two South Pacific groups, G. a. microrhyncha, G. a. pacifica, and all other Pacific subspecies. This differentiation warrants treating these two South Pacific groups as separate management units, but not species or subspecies. Finally, the recently established population of white terns on Oahu shared haplotypes with all subspecies, suggesting multiple origins from populations across the Pacific and confirming contemporary gene flow. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 586–595.

Nesting success of White Terns and White-tailed Tropicbirds on Cousine Island, Seychelles

This study investigates the breeding success of two tropical seabirds that exploit dissimilar nesting habitats on Cousine Island in the Seychelles archipelago, the White Tern Gygis alba and the White-tailed Tropicbird Phaethon lepturus, which nest in trees and in crevices on the ground, respectively. Both species have a clutch of one egg. Over a 23-month study period, the outcomes of 134 nesting attempts by White Terns and 285 by White-tailed Tropicbirds were followed. White Terns produced an average of 0.4 chicks per attempt, significantly more than that of White-tailed Tropicbirds (0.25). Hatching success did not differ between the two species, but fledging success of White Terns (62%) was significantly higher than that of White-tailed Tropicbirds (43%). Nesting success of White-tailed Tropicbirds may be less successful than White Terns because their ground nests are at risk to purely terrestrial predators, in addition to predators that are both terrestrial and arboreal. Many nests of White-tailed Tropicbirds failed during the first two weeks of the incubation and nestling periods, but the reasons for this are unclear. Food availability may influence the reproductive success of both species.

Does interference competition explain why White Terns of Aride Island, Seychelles, breed predominantly when marine productivity is lower?

White Terns Gygis alba breed throughout the year on Aride Island but show a marked preference to nest during the northwest monsoon (November-March), when interspecific competition and also marine productivity are considered to be lower. In this study we investigated and compared breeding and foraging parameters of White Terns between the northwest and southeast (May-September) monsoons to assess whether interspecific competition affected foraging activity and explained the timing of breeding of White Terns. Goatfish (Mullidae) dominated the diet of White Terns and no significant differences were found in diet composition between the northwest and southeast monsoons. Similar diets and patterns of food provisioning of White Terns between the two monsoons do not support the hypothesis of strong exploitation competition during the southeast monsoon. On the other hand, foraging behaviour and frequency of capture attempts of White Terns differed between the two monsoons. The percentages of multi-species flocks with White Terns and of large flocks with more than 25 noddies Anous and terns Onychoprion were significantly higher during the southeast monsoon. Moreover, capture attempt frequencies of White Terns foraging in multi-species flocks were lower than those of solitary individuals, and both solitary and flocking White Terns had significantly lower capture attempt frequencies during the southeast monsoon in comparison with the northwest monsoon. These results suggest that interference competition depresses foraging activity of flock-foraging White Terns, particularly during the southeast monsoon, which could potentially explain why White Terns breed preferentially during the northwest monsoon. However, and despite avoiding interference competition, White Terns nesting during the northwest monsoon did not show higher breeding success than those nesting during the southeast monsoon. Other hypotheses that might explain the preference of White Terns for breeding during the northwest monsoon, such as avoidance of agonistic interactions with Lesser Noddies Anous tenuirostris at nest sites, should also be investigated.

Does interference competition explain why White Terns of Aride Island, Seychelles, breed predominantly when marine productivity is lower?

White Terns Gygis alba breed throughout the year on Aride Island but show a marked preference to nest during the northwest monsoon (November–March), when interspecific competition and also marine productivity are considered to be lower. In this study we investigated and compared breeding and foraging parameters of White Terns between the northwest and southeast (May–September) monsoons to assess whether interspecific competition affected foraging activity and explained the timing of breeding of White Terns. Goatfish (Mullidae) dominated the diet of White Terns and no significant differences were found in diet composition between the northwest and southeast monsoons. Similar diets and patterns of food provisioning of White Terns between the two monsoons do not support the hypothesis of strong exploitation competition during the southeast monsoon. On the other hand, foraging behaviour and frequency of capture attempts of White Terns differed between the two monsoons. The percentages of multi‐species flocks with White Terns and of large flocks with more than 25 noddies Anous and terns Onychoprion were significantly higher during the southeast monsoon. Moreover, capture attempt frequencies of White Terns foraging in multi‐species flocks were lower than those of solitary individuals, and both solitary and flocking White Terns had significantly lower capture attempt frequencies during the southeast monsoon in comparison with the northwest monsoon. These results suggest that interference competition depresses foraging activity of flock‐foraging White Terns, particularly during the southeast monsoon, which could potentially explain why White Terns breed preferentially during the northwest monsoon. However, and despite avoiding interference competition, White Terns nesting during the northwest monsoon did not show higher breeding success than those nesting during the southeast monsoon. Other hypotheses that might explain the preference of White Terns for breeding during the northwest monsoon, such as avoidance of agonistic interactions with Lesser Noddies Anous tenuirostris at nest sites, should also be investigated.

Comparative foraging ecology of a tropical seabird community of the Seychelles, western Indian Ocean

We studied the foraging ecology of a tropical seabird community in 2 islands of the Seychelles from 2005 to 2007. Chick dietary samples were used to compare feeding habits among species and assess inter-annual and seasonal variations in diet. Fish prey dominated the diet of the community (68 to 100%, of prey consumed), although cephalopods were present in 61.3, 40.0, 27.1 and 32.9% of the food samples from white-tailed tropicbirds, sooty terns, brown noddies and wedge-tailed shearwaters, respectively. We found high diet overlap between species (Mullidae fish being the first prey consumed [30 to 90%] for all species except for the white-tailed tropicbird [\textless2%]) but some segregation in prey length. Other important prey were Exocoetidae, Carangidae, Scombridae and Clupeidae mainly for white-tailed tropicbirds, sooty terns and brown noddies, Hemiramphidae and Coryphaenidae for white-tailed tropicbirds, and Engraulidae and fish larvae for lesser noddies and Audubon's shearwaters. Despise some inter-annual and seasonal variations in diet, these were not consistent within the community. Responses of the seabird community to an environmental perturbation that negatively affected chick growth and breeding success of lesser noddies emphasised the higher vulnerability of species with smaller foraging ranges and/or with lower ability to switch diet (lesser noddy, roseate tern) compared to less range-restricted and/or more opportunistic ones (white-tailed tropicbird, brown noddy, sooty tern, white tern). Although situated in a tropical region, the food availability in the Seychelles seems to be predictable at a large (annual) temporal scale, but highly unpredictable at a small (intra-seasonal or daily) temporal scale.

The role of stable isotopes and mercury concentrations to describe seabird foraging ecology in tropical environments

Nitrogen (δ15N) and carbon (δ13C) stable isotopes and contaminants, such as mercury, have been widely used to characterise foraging ecology of temperate and polar seabirds. In this study, for the first time, we used isotopic signatures and mercury levels of feathers and blood of eight tropical seabird species, that forage in a range-gradient between inshore and offshore areas, to describe the foraging habits of a large tropical seabird community (from two neighboring islands of the Seychelles archipelago, western Indian Ocean) during both the breeding and inter-breeding periods. Overall, we found a high overlap in both δ15N and δ13C signatures among species. The high inter-specific overlap in δ15N values was expected, given the similarities in the diet of the species from this community. However, several unexpected results, such as (1) the consistently higher δ15N signatures of white terns (Gygis alba), (2) the large variation in inter-specific differences in δ15N signatures among the sampling groups (season, age, island and tissue) and (3) the consistent low δ15N values of breeding birds during the northwest monsoon (austral summer), suggest that δ15N signatures cannot be used as indicators of seabird trophic levels in this community. The high inter-specific overlap in δ13C signatures and the absence, during the breeding season, of a δ13C gradient that follows the inshore-offshore foraging gradient within the community can be explained by the habitat homogeneity of the Seychelles continental shelf and suggest that birds forage mostly within the limits of this “plateau”. On the other hand, the similarities in δ13C values between the breeding and inter-breeding periods in species that are known to show post-breeding dispersal, strongly support the hypothesis of a lack of latitudinal variation in δ13C signatures of POM in the central Indian Ocean, and the consequent inaccuracy of δ13C values to track seabird movements within this geographic area. Inter-specific differences in mercury levels seem to be related to prey size, while consistent higher mercury concentrations in one of the studied islands suggest different island mercury-backgrounds and possible segregation in foraging areas between the seabirds of the two islands.

A phylogenetic framework for the terns (Sternini) inferred from mtDNA sequences: implications for taxonomy and plumage evolution

We sequenced 2800 bp of mitochondrial DNA from each of 33 species and 2 subspecies (35 taxa) of terns (Sternini), and employed Bayesian methods to derive a phylogeny with good branch support based on posterior probabilities. The resulting tree confirmed many of the generally accepted taxonomic groups, and led us to suggest a revision of the terns that recognizes 12 genera, 11 of which correspond to a distinct clade on the tree or a highly divergent species (1 genus was not represented in the phylogeny). As an example of how the molecular phylogeny reflects similarities in morphology and behavior among the terns, we used the phylogeny to examine the evolution of the breeding (alternate) head plumage patterns among the terns to test the hypothesis that this character is phylogenetically informative. The three basic types of head plumage (white crown, black cap, and black cap with a white blaze on the forehead) were highly conserved within clades, with notable exceptions in two white-crowned species that evolved independently among the black-capped terns. Based on the appearance of the close relatives of these exceptional species, their white crowns appear to be due to the retention of either winter (basic) plumage characteristics or perhaps juvenile characteristics when the birds molt into their breeding plumage. Examination of the evolutionary history of head plumage indicated that the white-crowned species such as the noddies ( Anous) and the white tern ( Gygis alba) are probably most representative of ancestral terns.

DISTRIBUTION, ABUNDANCE, AND BREEDING BIOLOGY OF WHITE TERNS ON OAHU, HAWAII

White Terns (Gygis alba) are common in the northwestern Hawaiian Islands, but in the main Hawaiian Islands they are found only on Oahu, where they are listed as threatened by the State of Hawaii. I censused the White Tern population on Oahu from October 2001 to January 2003, and I investigated breeding success and seasonality during monthly visits to four sites. I observed a total of 694 adult White Terns on Oahu, of which approximately 500 (72%) were breeding birds. Active nests were present during all months, but most eggs were laid from January to April (65%), with a peak in egg laying during March (22%). Nest success was 74%, and pairs produced a mean of 0.98 fledglings/year. One pair fledged successive young less than three months apart. The incubation period at one nest was 35 days, and the fledging periods at two nests were 43 and 47 days. The White Tern population on Oahu has increased from a single breeding pair in 1961 to approximately 250 pairs in 2002, a growth rate of 14% per year. White Terns on Oahu exist entirely in urban and suburban areas, and their reproduction is not inhibited by the numerous predators and sources of disturbance.

Abundance and breeding habitat of Noddies and White Terns on a relatively unmodified island in the Kingdom of Tonga

Islands in the Kingdom of Tonga have undergone severe modification since human colonisation and, as a result, the availability of optimal habitat for breeding seabirds has decreased. We collected data on the abundance of breeding Black Noddies (Anous minutes), Brown Noddies (A. stolidus) and White Terns (Gygis alba) during a short visit to Maninita Island, one of the few relatively unmodified islands in Tonga. The island was surveyed and quadrat plots were used to count trees, birds and nests, from which we described vegetation composition and structure, and obtained population estimates of the Noddies and White Terns on the island. The island's vegetation is dominated (96.8% of total basal area) by Pisonia grandis, which is used for nesting by the noddies and terns. At the time of our visit the seabird population on Maninita consisted of an estimated 2664 ± 110 noddies and 233 ± 14 White Terns. Our work illustrates the importance, to breeding seabirds, of conserving those few relatively unmodified islands that remain in the Kingdom of Tonga.

Metals in feathers of sooty tern, white tern, gray-backed tern, and brown noddy from islands in the North Pacific.

Levels of heavy metals are usually higher in adult than young birds because they eat larger, more contaminated prey, or because they have had longer to accumulate metals in their tissues. Further, levels of contaminants are usually less in birds nesting on remote, offshore islands than in birds breeding closer to mainland areas that are urbanized and industrialized. We examined the feather levels of arsenic, cadmium, chromium, lead, manganese, mercury, and selenium in adult sooty terns (Sterna fuscata), gray-backed terns (Sterna lunata), and brown noddy (Anous stolidus, and adult and young white terns (Gygis alba, from Midway Atoll, and in adult and young sooty terns and adult brown noddy from Manana Island, Hawaii (chicks of other terns were not available). We tested and rejected the null hypotheses that metal levels are not significantly different among species, ages, and locations. Despite their small size, adult white terns had the highest levels of lead, arsenic and tin. Brown noddies had the highest levels of cadmium, chromium, manganese, and selenium. Sooty and white terns had the highest levels of mercury. Sooty tern adults had significantly higher levels of cadmium, mercury, and selenium than young, while young had significantly higher levels of arsenic and manganese. White tern adults had significantly higher levels of selenium and tin than young, while young had higher levels of cadmium and mercury than adults. Except for mercury, there were significant inter-location differences within species in all heavy metals. Contrary to expectation, where the differences were great, metals generally were higher in the feathers of terns and noddies from Midway than from Manana.

Characteristics of Foraging Habitats and Chick Food Provisioning by Tropical Roseate Terns

I studied tropical Roseate Terns (Sterna dougallii) on Aride Island, Seychelles, between 1997–1999. Productivity in 1998 was 0.58 fledglings/breeding pair, and in 1999 no young fledged. Roseate Terns on Aride concentrated their foraging along the coastline exposed to prevailing winds, with flock size over this area being significantly correlated with amount of food offered to chicks. In 1998, Lesser Noddies (Anous tenuirostris) were present in 91% of the Roseate Tern flocks, but in 1999 occurred in only 32%. During the 1998 successful breeding season, Roseate Terns were associated with dense flocks of Lesser Noddies over predatory fish, whereas during the 1999 failure season most Roseate Tern flocks were either monospecific or mixed with Fairy Terns (Gygis alba), and without predatory fish. The mean flock size of Roseate Terns (82 vs. 6 birds) and the rate of foraging attempts (8.3 vs. 2.8 attempts min−1) were significantly greater in association with predatory fish. Mullidae (Parupeneus or Mulloidichthys) were the primary prey taken by Roseate Terns, and alternative sources of food were apparently scarce. The high daily variations in the amount of food brought to chicks, intermediate periods of low food delivery, and an apparent seasonal decline in the amount of food brought to the colony suggest that food is unpredictable on a daily and seasonal basis. Absence of predatory fish may explain complete breeding failures and periods of low food delivery, but the importance of other factors is unknown. Information on the ecology and movement patterns of predatory fish around Aride Island is needed to assist the conservation of the Roseate Terns.

Characteristics of Foraging Habitats and Chick Food Provisioning by Tropical Roseate Terns

Abstract I studied tropical Roseate Terns (Sterna dougallii) on Aride Island, Seychelles, between 1997–1999. Productivity in 1998 was 0.58 fledglings/breeding pair, and in 1999 no young fledged. Roseate Terns on Aride concentrated their foraging along the coastline exposed to prevailing winds, with flock size over this area being significantly correlated with amount of food offered to chicks. In 1998, Lesser Noddies (Anous tenuirostris) were present in 91% of the Roseate Tern flocks, but in 1999 occurred in only 32%. During the 1998 successful breeding season, Roseate Terns were associated with dense flocks of Lesser Noddies over predatory fish, whereas during the 1999 failure season most Roseate Tern flocks were either monospecific or mixed with Fairy Terns (Gygis alba), and without predatory fish. The mean flock size of Roseate Terns (82 vs. 6 birds) and the rate of foraging attempts (8.3 vs. 2.8 attempts min−1) were significantly greater in association with predatory fish. Mullidae (Parupeneus or Mulloidichthys) were the primary prey taken by Roseate Terns, and alternative sources of food were apparently scarce. The high daily variations in the amount of food brought to chicks, intermediate periods of low food delivery, and an apparent seasonal decline in the amount of food brought to the colony suggest that food is unpredictable on a daily and seasonal basis. Absence of predatory fish may explain complete breeding failures and periods of low food delivery, but the importance of other factors is unknown. Information on the ecology and movement patterns of predatory fish around Aride Island is needed to assist the conservation of the Roseate Terns.

Metal levels in feathers of 12 species of seabirds from Midway Atoll in the northern Pacific Ocean

Seabirds are excellent subjects for examination of heavy metals because they are long-lived, feed at different distances from land, and exhibit different trophic levels. In this paper we compare the levels of lead, cadmium, mercury arsenic, chromium, manganese, selenium, and tin in the feathers of birds nesting on Midway Atoll in the northern Pacific Ocean. We test the null hypothesis that there are no interspecific differences in the levels of metals in the feathers of the adult black-footed albatross ( Diomedea nigripes), Laysan albatross ( Diomedea immutabilis), red-footed booby ( Sula sula), great frigatebird ( Fregata minor), Bonin petrel ( Pterodroma hypoleuca), Christmas shearwater ( Puffinus nativitatis), red-tailed tropicbird ( Phaethon rubricauda), wedge-tailed shearwater ( Puffinus pacificus), brown noddy ( Anous stolidus), sooty tern ( Sterna fuscata), grey-backed tern ( Sterna lunata), and white tern ( Gygis alba), and young of some of these species. There were interspecific differences in the levels of all metals for adults. Christmas shearwater had the highest levels of lead, cadmium, selenium and manganese, but the second lowest levels of mercury. In general, metal levels were the lowest in the smallest species (white tern), but were not the highest in the largest species (black-footed albatross), except for manganese, arsenic and mercury. There was a high variance in metal levels among adults for some species, but not for others. White tern adults were variable for lead, while Christmas shearwaters were variable for lead and cadmium. Compared to the means for metals in other birds generally (after Burger, 1993), Christmas shearwaters had higher levels of lead, white terns, brown noddy, Christmas shearwater, frigatebirds and Laysan albatrosses had higher levels of cadmium, and bonin petrel, wedge-tailed shearwater, tropicbirds, frigatebirds, red-footed boobies, and both albatrosses had higher levels of mercury. Whereas the means for lead and cadmium were below the known effects levels, some individuals had levels high enough to cause adverse effects in the birds. The mean values for mercury in Bonin petrel, red-tailed tropicbird, and black-footed albatross were higher than the levels known to cause adverse reproductive and behavioral effects.