Tropical Seabird Research Articles

Loss of Darvic rings from Sooty Terns Onychoprion fuscatus in Seychelles

Coloured Darvic rings fitted to Sooty Terns in the Seychelles became brittle and fell off. Where birds had been ringed also with Incoloy BTO rings, the extent of loss was quantified. Darvic rings are unsuitable for long-term studies of Seychelles Sooty Terns and may be unsuitable for long-term population studies of other tropical seabirds.

Migration, wintering distribution and habitat use of an endangered tropical seabird, Barau’s petrel Pterodroma baraui

Gadfly petrels are strictly oceanic seabirds that range very far from their breeding grounds. Foraging movements outside the breeding season are poorly described. We used global location sensing (GLS) to describe the migration pathways and wintering habitats of Barau's petrels Pterodroma baraui, an endemic, endangered seabird of Reunion Island (western Indian Ocean). In 2 consecutive years, petrels migrated far eastward, up to 5000 km from their breeding colony, to the central and eastern Indian Ocean. Migration pathways, timing, and wintering areas varied little among individuals, and non-breeding areas were remarkably consistent between years. There was no sexual variation in migration patterns. Barau's petrels did not occur in the most productive areas of the Indian Ocean (Arabian Gulf and Somalia upwelling region) but instead foraged over warm oligotrophic and mesotrophic waters. Tracked birds consistently occurred in areas with relatively strong and consistent easterly winds, and avoided northern regions with weaker westerly winds. Our results indicate that Barau's petrels use an expansive wintering area between the western South Equatorial Current and the eastern Equatorial Counter Current, characterised by warm sea surface temperatures (SST) and low productivity. However, wind regimes in the Indian Ocean are strongly influenced by the Asian Monsoon; in this particular area, wind and currents may create a frontal system where prey are aggregated, increasing their accessibility for Barau's petrels. These results provide important baseline information for conservation, and are useful for the selection of potential marine reserves and the evaluation of effects of pollution or climate change on this highly threatened species.

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.

Panmixia and high genetic diversity in a Humboldt Current endemic, the Peruvian Booby (Sula variegata)

Marine ecosystems and their inhabitants are increasingly under threat from climate change, competition with humans for resources, and pollution. Species that are endemic to particular currents or regions of the world’s oceans have the potential to be at higher risk due to localized overfishing, pollution, or locally severe impacts of climate change such as more intense, or longer, El Nino Southern Oscillation events. Understanding patterns of population differentiation in endemic marine organisms may be particularly important for their conservation and persistence. Peruvian Boobies (Sula variegata) are endemic to the Humboldt Current upwelling system and have experienced population fluctuations throughout their evolutionary history due to both dramatic reduction of food supplies, and anthropogenic influence over the last ~150 years. Recent research on other members of the Sulidae indicates that populations of these primarily tropical seabirds show a high degree of genetic differentiation; however, the sister species of the Peruvian Booby, the Blue-footed Booby (S. nebouxii), exhibits only weak range-wide population genetic structure. We characterized population genetic differentiation and diversity in 153 Peruvian Boobies using sequence variation of 540 base pairs of the mitochondrial control region and seven microsatellite loci. Although we found evidence of panmixia, a signature of isolation by distance appears to exist between the five sampled colonies. We also found unexpectedly high genetic diversity given this species’ recent population decline. Our results are similar to those for the Humboldt Penguin (Spheniscus humboldti), another endemic of the Humboldt Current upwelling system.

Long-term isolation of a highly mobile seabird on the Galapagos

The Galapagos Islands are renowned for their high degree of endemism. Marine taxa inhabiting the archipelago might be expected to be an exception, because of their utilization of pelagic habitats-the dispersal barrier for terrestrial taxa-as foraging grounds. Magnificent frigatebirds (Fregata magnificens) have a highly vagile lifestyle and wide geographical distribution around the South and Central American coasts. Given the potentially high levels of gene flow among populations, the species provides a good test of the effectiveness of the Galapagos ecosystem in isolating populations of highly dispersive marine species. We studied patterns of genetic (mitochondrial DNA, microsatellites and nuclear introns) and morphological variation across the distribution of magnificent frigatebirds. Concordant with predictions from life-history traits, we found signatures of extensive gene flow over most of the range, even across the Isthmus of Panama, which is a major barrier to gene flow in other tropical seabirds. In contrast, individuals from the Galapagos were strongly differentiated from all conspecifics, and have probably been isolated for several hundred thousand years. Our finding is a powerful testimony to the evolutionary uniqueness of the taxa inhabiting the Galapagos archipelago and its associated marine ecosystems.

Unexplained recurrent features of the plumage of birds

Unexplained recurrent features of the plumage of birds

Foraging movements of great frigatebirds from Aldabra Island: Relationship with environmental variables and interactions with fisheries

Great Frigatebirds ( Fregata minor) are large tropical seabirds that rely primarily on sub-surface predators such as tunas or cetaceans to capture their prey. We studied the foraging movements of 14 Great Frigatebirds breeding on Aldabra Island (9.4°S, 46.4°E), the largest colony in the Indian Ocean. This colony is located at more than 500 km from the main fishing grounds of a very important industrial purse-seine fishery targeting surface-dwelling tunas. Despite their slow flight speeds (16 km h −1), frigatebirds are able to forage at more than 1000 km from the colonies when breeding, using 2500–4750 km long foraging loops over oceanic waters. All trips were directed to the north of the island up to the equator. Foraging bouts, indicated by reduced flight speeds, were rare and located throughout the trips. Foraging spots tended to be more frequent on higher surface chlorophyll concentration and in association with some cyclonic vortices. However, mesoscale activity is relatively weak between Aldabra and the equator and the chlorophyll variability is mostly the result of wind-mixing processes during the southwest monsoon. These results suggest that frigatebirds forage for widely distributed resources to the north of Aldabra. The northernmost foraging bouts were located in the vicinity of the purse-seine fishing grounds, but without a significant overlap between frigatebirds and tuna fleets. The results of the study are compared with those from another population at Europa Island (22.3°S, 40.3°E) where birds were foraging on predictable features, the edge of cyclonic eddies that are marked in the Mozambique Channel. We discuss the consequences of the reliance of populations on contrasted oceanographic conditions on foraging strategies and on the evolution of life histories in these long-lived animals in a changing climate, as well as the possible effects of overfishing on frigatebird populations.

Climatic influence on demographic parameters of a tropical seabird varies with age and sex

In marine ecosystems climatic fluctuation and other physical variables greatly influence population dynamics, but differential effects of physical variables on the demographic parameters of the two sexes and different age classes are largely unexplored. We analyzed the effects of climate on the survival and recruitment of both sexes and several age classes of a long-lived tropical seabird, the Blue-footed Booby (Sula nebouxii), using long-term observations on marked individuals. Results demonstrated a complex interaction between yearly fluctuations in climate (both local and global indexes, during both winter and breeding season) and the sex and age of individuals. Youngest birds' survival and recruitment were commonly affected by local climate, whereas oldest birds' parameters tended to be constant and less influenced by environmental variables. These results confirm the theoretical prediction that sex- and age-related variation in life-history demographic traits is greater under poor environmental conditions, and they highlight the importance of including variability in fitness components in demographic and evolutionary models. Males and females showed similar variation in survival but different recruitment patterns, in relation to both age and the spatial scale of climatic influence (local or global). Results indicate different life-history tactics for each sex and different ages, with birds likely trying to maximize their fitness by responding to the environmental contingencies of each year.

Comparison of trip duration, activity pattern and diving behaviour by Red-tailed Tropicbirds (Phaethon rubricauda) during incubation and chick-rearing

In the tropical marine environment food resources are scarce and often patchily distributed. Consequently, nesting tropical seabirds must balance travelling to productive areas and sharing incubation or providing food to the chick. Changes in foraging behaviour occur when adults switch from feeding only for themselves during incubation to feeding a chick and fulfilling their own energy requirements. Externally attached data-devices were used to compare the duration of foraging trips, flight activity and depth of dives of incubating and chick-rearing Red-tailed Tropicbirds (Phaethon rubricauda) on Christmas Island, Indian Ocean. Adults with chicks had a bimodal pattern of foraging, with alternating short and long foraging trips (mean duration±s.d. of short trips = 3.0 ± 4.1 h, of long trips = 57.4 ± 41.1 h), whereas incubating adults undertook only longer trips (mean duration ± s.d. = 152.9 ± 47.2 h). This strategy is stimulated by partner behaviour, rather than body mass as reported for many other seabirds, and may enable the optimisation of simultaneous food delivery to chicks and self-feeding when local resources are poor. The proportion of time spent in flight (flight activity) by adults with chicks averaged 90.1% during short trips whereas incubating birds spent only 62.4% of their trips flying. Overall mean depth of foraging dives by adults with chicks averaged 0.6 ± 0.3 m during short trips; mean maximum depth of dives by incubating adults were recorded using maximum-depth recorders and were significantly deeper at 10.7 ± 8.7 m, reaching a maximum depth of 25.6 m.

Niche partitioning among and within sympatric tropical seabirds revealed by stable isotope analysis

The low productivity and unpredictable nature of resources in tropical waters would appear to make resource partitioning among predators difficult. Yet, stable isotope data from the pre- sent study suggest that substantial resource partitioning occurs among tropical seabird communities, both between and within species. In the present study, we compared δ 13 C and δ 15 N levels among 8 sympatric tropical seabird species. For a subset of these species, we also examined isotopic levels across years, breeding periods, and sexes. When breeding and non-breeding periods were both con- sidered, we found that all species occupied distinct isotopic niches across at least one time period. Resource partitioning by age (within the same year) and year studied (for birds of the same age), within species was observed in all the species we examined. However, niche separation by sex appeared to be relatively uncommon even in sexually dimorphic species. As a group, seabirds were isotopically distinct from other marine predators. There was a strong correlation between both body mass and wing loading ratios and foraging area, as evaluated using δ 13 C levels. Cumulatively, the isotopic patterns observed are consistent with diet-based surveys of resource partitioning during the breeding period. Importantly, these data provide additional evidence to suggest that substantial niche partitioning among tropical seabird species persists even during non-breeding periods in open ocean environments, when direct diet-based surveys are difficult to conduct.

Comparative phylogeography of brown (Sula leucogaster) and red-footed boobies (S. sula): The influence of physical barriers and habitat preference on gene flow in pelagic seabirds

To test the hypothesis that both physical and ecological barriers to gene flow drive population differentiation in tropical seabirds, we surveyed mitochondrial control region variation in 242 brown boobies (Sula leucogaster), which prefer inshore habitat, and 271 red-footed boobies (S. sula), which prefer pelagic habitat. To determine the relative influence of isolation and gene flow on population structure, we used both traditional methods and a recently developed statistical method based on coalescent theory and Bayesian inference (Isolation with Migration). We found that global population genetic structure was high in both species, and that female-mediated gene flow among ocean basins apparently has been restricted by major physical barriers including the Isthmus of Panama, and the periodic emergence of the Sunda and Sahul Shelves in Southeast Asia. In contrast, the evolutionary history of populations within ocean basins differed markedly between the two species. In brown boobies, we found high levels of population genetic differentiation and limited gene flow among colonies, even at spatial scales as small as 500km. Although red-footed booby colonies were also genetically differentiated within ocean basins, coalescent analyses indicated that populations have either diverged in the face of ongoing gene flow, or diverged without gene flow but recently made secondary contact. Regardless, gene flow among red-footed booby populations was higher than among brown booby populations. We suggest that these contrasting patterns of gene flow within ocean basins may be explained by the different habitat preferences of brown and red-footed boobies.

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.

Demography and conservation of the White-tailed Tropicbird Phaethon lepturus on Aride Island, Western Indian Ocean

The White-tailed Tropicbird Phaethon lepturus breeding population of Aride Island, Seychelles, has experienced a strong decline in the recent past. To predict the future trends of the White-tailed Tropicbird population on Aride Island and understand the urgency of applying management procedures, we developed a population matrix model. We estimated White-tailed Tropicbird adult survival rate over a 12-year period and investigated whether oceanographic conditions (El Nino Southern Oscillation, ENSO, and inter-annual climate variability in the Indian Ocean, Indian Ocean Dipole, IOD) or local factors (Pisonia grandis fruiting events) potentially affect adult survival. Annual adult survival could not be linked to inter-annual variability in oceanographic conditions, but may be more influenced by Pisonia fruiting events, which, overall, accounts for 23.2% of the adult mortality. The growth rate of the population, primarily influenced by annual adult survival, was estimated to be 0.946, which indicates an annual population decline of 5.4%. At the current rate, the probability of extinction of this population would be 99% in 170 years. Management scenarios studied through Monte Carlo simulations, assuming small increments in adult survival and/or breeding success, dramatically reduce the risk of extinction of White-tailed Tropicbirds. Habitat management, in order to maintain an open canopy and little understorey vegetation, appears to be crucial for the conservation of White-tailed Tropicbirds on Aride Island, as has already been shown for other ground-nesting tropical seabirds nesting on forested islands.

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.

Testing the efficacy of a boundary fence at an important tropical seabird breeding colony and key tourist destination

Tourists have the potential to detrimentally impact breeding seabirds, particularly at popular destinations such as on the Great Barrier Reef. Michaelmas Cay is a significant seabird rookery and prime tourist destination on the reef. In 1990, Queensland Parks & Wildlife Service erected a fence to separate tourists from fragile nesting habitat. We used two independent assessments during different breeding seasons to determine the potential impacts of tourism on two pelagic seabird species breeding on the cay. In the first quasi-experiment, egg losses by sooty terns (Sterna fuscata) and common noddies (Anous stolidus) were monitored at four distances (3, 6, 18 and 36 m) from a tourist enclosure. Our second quasi-experiment involved monitoring adult provisioning rates, chick growth and chick survival of sooty terns at two locations, one adjacent to the tourist fence and one 50 m away. At plots 3–6 m from the fence, we observed higher among-week variation in egg loss but no differences in total egg loss as compared with the more distant plots. The only difference observed between plots during our second quasi-experiment was that nest predation was higher at the tourist fence plot. Our research suggests that as long as the effects observed do not influence post-fledging survival or gull predation does not impact under different conditions, current management protocols are appropriately facilitating shared usage between wildlife and the tourism industry at Michaelmas Cay.

Associations between seabirds and subsurface predators around Oahu, Hawaii

Many species of tropical seabirds rely on subsurface predators such as tuna and dol- phins to drive prey close to the ocean's surface. We observed seabird foraging events from fishing vessels around the island of Oahu, Hawaii, to determine the prevalence and relative importance of different subsurface predators to seabird foraging. Sixty-nine seabird foraging events were observed, in 62 of which the presence and/or identity of subsurface predators could be determined. Of those 62, all but two involved subsurface predators and accounted for 99.8% of all foraging birds. Skipjack tuna Katsuwonus pelamis were the predominant (81%) subsurface predator involved in seabird feed- ing events, with odontocetes Stenella attenuata and Pseudorca crassidens (8%), mahimahi Coryphaena hippurus (6%), and yellowfin tuna Thunnus albacares (2%) being less common. Wedge- tailed shearwaters Puffinus pacificus and brown noddies Anous stolidus foraged in association with tuna schools more often than would be expected by chance alone. Red-footed boobies Sula sula, in contrast, did not associate with any subsurface predator in greater proportion than what would be expected by chance. Nine additional seabird species were observed foraging in association with sub- surface predators, but not in numbers large enough for statistical analysis. This study highlights the value of regional investigations able to uncover the variable nature of seabird-subsurface-predator associations. The finding that, in Hawaii, at least 2 species of seabirds showed tight dependence on tuna underlines the need for tuna fishery management to address the potential indirect ecological effects of fishing.

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.

Comparative foraging ecology and ecological niche of a superabundant tropical seabird: the sooty tern Sterna fuscata in the southwest Indian Ocean

Over 6-million pairs of sooty terns Sterna fuscata breed once a year in the southwest Indian Ocean, mostly on three islands of the Mozambique Channel (Europa, Juan de Nova and Glorieuses) and in the Seychelles region. Seasonal reproduction in either winter or summer is the dominant strategy in the area, but non-seasonal reproduction also occurred in some places like at Glorieuses Archipelago. The feeding ecology of the sooty tern was investigated during the breeding seasons to determine whether terns showed significant differences in their trophic ecology between locations. Regurgitations were analyzed to describe the diet of individuals when breeding, and stable isotopes and mercury concentrations were used to temporally integrate over the medium-term of the trophic ecology of both adults and chicks. Overall, the diet was composed of fish, flying squid and fish larvae in different proportions. At Europa and Aride in the Seychelles, where winter reproduction occurs, large epipelagic prey like flying fish or squid dominated the diet. At Juan de Nova, sooty terns reproduce in summer and rely mostly on fish larvae. At Glorieuses (non-seasonal breeding), the diet was intermediate with fish larvae and flying squid being important prey items. The stable-carbon and nitrogen isotope values in blood confirm the differences observed in dietary analysis, and demonstrate different feeding strategies between colonies. δ13C values of feathers showed spatial segregation between birds from the Mozambique Channel and the Seychelles region. Terns from the Seychelles had also higher δ15N values. Feather δ13C values also suggest a significant shift from summer to wintering habitat for birds from Juan de Nova. This study emphasizes the high phenotypic plasticity of the species, which may explain its numerical dominance in all tropical waters of the World’s Ocean.

Resource partitioning within a tropical seabird community: new information from stable isotopes

Characteristics of the tropical oceanic environment (low productivity, little seasonality) and poor diversity of tropical seabird foraging methods and prey relative to temperate and polar spe- cies suggest that tropical seabirds overall encompass a narrow range of isotopic niches, with large overlaps among species. To test this hypothesis, we examined the stable carbon (δ 13 C) and nitrogen (δ 15 N) isotopic composition of blood and feathers of 5 seabird species from Europa Island, Mozam- bique Channel. While differences were small, blood δ 13 C and δ 15 N values characterized 5 distinct and non-overlapping trophic niches during the breeding period. Seabirds used 2 distinct foraging areas (δ 13 C), one used by sooty tern Sterna fuscata and white-tailed tropicbird Phaethon lepturus and one used by red-footed booby Sula sula and great Fregata minor and lesser F. ariel frigatebirds. Seabird species overall encompassed less than 1 trophic level (δ 15 N), which is in agreement with a diet mainly based on flying fish and squid. Feather δ 13 C and δ 15 N values showed that the trophic structure of the community was different during the breeding and non-breeding (moulting) periods, suggesting a shift in the feeding ecology when adult birds were no longer central-place foragers. The stable iso- tope method underlined sex-related (red-footed booby) and age-related (great frigatebird immatures and adults) feeding strategies. It also suggested that breeding adults could feed themselves on differ- ent prey than those given to their chicks (sooty tern). Within the tropical pelagic ecosystem, seabirds overall shared the same trophic level as large predatory fishes (albacore, yellowfin and skipjack tunas), but they had lower δ 15 N values than the deeper-dwelling bigeye tuna and swordfish. We con- clude that analyzing stable isotope values in blood and feathers appears to be a promising alternative method for investigating food and feeding ecology of tropical seabirds year round, and for determin- ing sex- and age-related differences in their foraging strategies. A limitation of the method is the lack of information on marine isoscapes; future studies aimed at isotopically characterizing the tropical marine environment could help to associate consumer signatures to geographic origins.

Effects of annual changes in primary productivity and ocean indices on breeding performance of tropical roseate terns in the western Indian Ocean

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 351:273-286 (2007) - DOI: https://doi.org/10.3354/meps07119 Effects of annual changes in primary productivity and ocean indices on breeding performance of tropical roseate terns in the western Indian Ocean David Monticelli1,2,*, Jaime A. Ramos3, Graham D. Quartly4 1Royal Belgian Institute of Natural Sciences, Section of Conservation Biology, 29 Rue Vautier, 1000 Brussels, Belgium 2Laboratory of Tropical and Subtropical Forestry, Unit of Forest and Nature Management, Gembloux Agricultural University, 2 Passage des Déportés, 5030 Gembloux, Belgium 3Institute of Marine Research (IMAR), Department of Zoology, University of Coimbra, 3004-517 Coimbra, Portugal 4National Oceanography Centre, Southampton (NOCS), Empress Dock, Southampton, Hampshire SO14 3ZH, UK *Email: dmonticelli@naturalsciences.be ABSTRACT: We assessed the influence of inter-annual changes in primary productivity and local, regional and large scale ocean indices on the breeding parameters of roseate terns Sterna dougallii on Aride Island, Seychelles, western Indian Ocean. Productivity (chicks per breeding pair), timing of breeding and clutch and egg sizes were monitored annually for 8 yr and correlated with local ocean productivity (denoted by Sea-viewing Wide Field-of-view Sensor, SeaWiFS, estimates of chlorophyll concentration, CC), sea surface temperature and indices recording the status of the Indian Ocean Dipole and of El Niño. The rate of increase in CC between mean laying date and CC peak value was positively related to roseate tern productivity and mean clutch size over the 1998 to 2005 study period. Colony productivity seemed also to be influenced by the Multivariate El Niño Index. In most years, the breeding phenology of roseate terns corresponded to the local increase in CC around Aride, and failure to adjust timing of reproduction to the timing of the phytopankton bloom decreased the probability of breeding success. This is the first study showing that a tropical seabird species is sensitive to inter-annual variations in the intensity and timing of the phytoplankton bloom, which should be connected to annual variations in the availability of its main fish prey (juvenile goatfishes). Overall, these patterns indicate that the reproduction of this top marine predator is dictated by the temporal variability in oceanographic conditions. We suggest that CC data available over the world’s oceans may be a useful tool to develop models predicting the fate of colonies of inshore feeding seabirds when other, more conventional, monitoring methods cannot be used. KEY WORDS: Sterna dougallii · Breeding · Inter-annual variation · Ocean productivity · El Niño · SeaWiFS · Seabird ecology · Indian Ocean Full text in pdf format PreviousNextCite this article as: Monticelli D, Ramos JA, Quartly GD (2007) Effects of annual changes in primary productivity and ocean indices on breeding performance of tropical roseate terns in the western Indian Ocean. Mar Ecol Prog Ser 351:273-286. https://doi.org/10.3354/meps07119 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 351. Online publication date: December 06, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.