Sula Leucogaster Research Articles

Females of a polymorphic seabird dislike foreign-looking males

Sexual selection may facilitate speciation if it promotes divergence in attributes used in mate choice, causing prezygotic isolation between populations. Brown boobies, Sula leucogaster, are seabirds that can be grouped into four genetic clusters and two male plumage morphs: brown-headed sexually monomorphic and white-headed male dimorphic. The extent of white on the head (white hood) of a male may reflect parenting ability and be sexually selected. Colour morphs have been geographically isolated, but contact has been recently reported. We manipulated male hood colour in two dimorphic populations (at Islas Marietas National Park (hereafter Marietas), which is close to the contact zone of San Benedicto Island, and San Jorge Island, which is away from the contact zone) to establish whether female preference for male hoods can function as a reproductive barrier. Females from Marietas were more aggressive towards male mates whose white hoods were painted brown (allopatric-looking) than were females from San Jorge. Although experimental females from both islands courted less than females from control pairs, experimental females from Marietas were five times less likely to copulate than control females, whereas there were no differences between treatments in propensity to copulate by females in San Jorge. Thus, in the brown booby, female dislike of foreign males may function as a reproductive barrier in populations close to contact zones, where the risk of possibly maladaptive hybridization is highest.

Oxidative stress during courtship affects male and female reproductive effort differentially in a wild bird with biparental care.

Oxidative stress has been suggested as one of the physiological mechanisms modulating reproductive effort, including investment in mate choice. Here, we evaluated whether oxidative stress influences breeding decisions by acting as a cost of or constraint on reproduction in the brown booby (Sula leucogaster), a long-lived seabird with prolonged biparental care. We found that during courtship, levels of lipid peroxidation (LP) of males and females were positively associated with gular skin color, a trait presumably used in mate choice, while levels of reactive oxygen species (ROS) were higher as laying approached and in early breeding pairs. Evidence of a constraining effect of oxidative stress for females was suggested by the fact that females with higher ROS during courtship laid smaller first eggs and had chicks with lower rates of body mass gain, and higher female LP was associated with lower offspring attendance time. No evidence of an oxidative cost of parental effort was found; from courtship to parental care, levels of ROS in males and females decreased, and changes in LP levels were non-significant. Finally, using a cross-fostering experiment we found that offspring ROS was unrelated to rearing and genetic parents' ROS. Interestingly, offspring LP was positively associated with the LP during courtship of both the rearing parents and the genetic father, suggesting that offspring LP might have both a genetic and an environmental component. Hence, in the brown booby, oxidative stress may be a cost of investment in reproductive traits before egg laying and constrain females' investment in eggs and parental care.

Foraging behaviour of a declining population of Brown Boobies (Sula leucogaster) breeding in the Swain Reefs, Great Barrier Reef

The Great Barrier Reef supports significant breeding populations of tropical seabirds; however, recent evidence has indicated declines in seabird populations across some of the most important breeding sites. Evidence for the cause of these significant declines is lacking but is generally thought to result from inadequate food supplies caused by warmer sea surface temperatures associated with climate change. This paper provides the first detailed investigation into the foraging behaviour of Brown Boobies (Sula leucogaster,) a species considered to be more susceptible to climate change impacts due to reduced foraging ranges. Fifteen complete foraging trips were recorded from five individuals (three males, two females). Adults typically foraged in shallow inshore reef waters and the mean foraging trip duration was 6.8 ± 2.8 h with a mean foraging range of 14.5 ± 10.1 km and the total distance travelled being 49.5 ± 30.3 km per trip. While most foraging trips occurred during daylight hours, five (33%) trips recorded periods spent at sea at night. The preliminary results presented here suggest that further research across widely dispersed breeding sites and different species investigating the potential drivers of seabird declines in the Great Barrier Reef is warranted.

An Evaluation of the Use of Predicted Harness Spans for Correctly Fitting Leg-Loop Harnesses in Seabird Research

Abstract. Leg-loop harnesses for the attachment of telemetry devices have been used for over two decades in terrestrial bird research. Recently, the technique has been extended to waterbird applications. An equation exists for predicting the dimensions of correctly fitting leg-loop harnesses in terrestrial bird research. This equation appears robust to the varied life histories of terrestrial birds. Yet, the applicability of this equation for waterbird research has not been tested. Here, we present the dimensions of leg-loop harnesses fitted to Lesser Frigatebirds (Fregata ariel), a sexually dimorphic seabird species. For both sexes, measured harness spans were shorter than those predicted by the terrestrial bird equation. Additionally, leg-loop harnesses trialed on Brown (Sula leucogaster) and Masked (S. dactylatra) boobies were unsuitable and hence unsuccessful. Morphological and behavioral features of species suited to leg-loop harness attachment are identified.

Chewing Lice (Phthiraptera) Infesting Breeding Suliformes (Aves: Aequornithes) of the Arabian Peninsula

Despite the large diversity of the migratory and resident avifauna of the Arabian Peninsula, relatively few species have been sampled for chewing lice. In this study, three breeding species of Suliformes, Phalacrocorax nigrogularis Ogilvie-Grant & Forbes, Sula dactylatra Lesson and Sula leucogaster (Boddaert) were examined for chewing lice. Four species of chewing lice were identified, two from the suborder Amblycera (Eidmanniella albescens (Piaget, 1880) and Eidmanniella nancyae Ryan & Price, 1969) and two from the suborder Ischnocera (Pectinopygus socotranus Timmermann, 1964 and Pectinopygus sulae (Rudow, 1869)). Diagnostic characters, examined and other known hosts, an identification key, and images of hosts and chewing lice are provided.

Cannibalism by Brown Booby (Sula leucogaster) at a small tropical archipelago

Cannibalism is the total or partial consumption of a conspecific’s body or eggs, and it has been reported for many bird taxa, particularly carnivorous, colonial species, and those species that ingest fragmented prey. Here we report cannibalism by Brown Booby (Sula leucogaster) at Saint Peter and Saint Paul Archipelago, ofshore Brazil. We discussed possible causes for this behavior such as opportunistic feeding, colony sanitation and space competition for nesting places.

Subspecific identification of the Great Lakes' first Brown Booby (<em>Sula leucogaster</em>) using DNA

The first Brown Booby (Sula leucogaster) recorded in the Great Lakes basin was discovered on Lake Erie near the source of the Niagara River on 7 October 2013 by J. P. Morphologic evidence suggested that this bird was an adult female of the nominate Atlantic subspecies. We obtained genomic DNA from feces left by the bird. Mitochondrial DNA from the control region (CR2) was sequenced and compared with extensive CR2 data for Brown Booby available in GenBank; this corroborated the morphologic hypothesis. This is the first time that a vagrant bird in Canada has been identified using DNA extracted from feces.

Bernard Stonehouse (1926-2014)

Bernard Stonehouse's long and varied career commenced with pioneering studies on the breeding habits of the two species of Aptenodytes penguins. As well as undertaking fieldwork in remote places, he taught in both schools and universities, wrote academic and popular books, and latterly led a long-term study on the ecological impact of tourism in Antarctica. Stonehouse was born on 1 May 1926 at Kingston upon Hull. After learning to fly in the Fleet Air Arm he served as a meteorologist with the Falklands Islands Dependencies Survey (now British Antarctic Survey). He was posted in February 1947 to the base at Stonington Island, in Marguerite Bay, where during his second year he discovered a colony of Emperor Penguins Aptenodytes fosteri on the tiny Dion Islands. That summer the pack-ice remained solid and the base could not be relieved. Stonehouse was able to put his third, enforced, winter to good use by spending 2 months on the Dion Islands where, camped in a tent with temperatures dropping to −40 °C, he made the first detailed study of the breeding habits of the Emperor Penguin, a species that lays its egg in the middle of the Antarctic winter. After his return to Britain, Stonehouse graduated in zoology and geology at University College, London, and moved to the Edward Grey Institute of Field Ornithology at Oxford University. He received special dispensation to spend 18 months at South Georgia to study the breeding behaviour of the King Penguin Aptenodytes patagonicus. With Nigel Bonner as assistant, he set up camp in a garden shed near a large King Penguin colony and was able to elucidate the species' unusual protracted breeding season. In 1957 Stonehouse was appointed leader of the British Ornithologists' Union Centenary Expedition to Ascension Island which would study the breeding cycles and breeding seasons of 11 species of seabirds and four species of introduced landbirds living in a near tropical environment. Of particular interest were the Sooty Tern (locally Wideawake Tern) Onychoprion fuscatus, Yellow-billed Tropic Bird Phaethon lepturus, Red-billed Tropic Bird P. aethereus and Brown Booby Sula leucogaster which have unusual shorter than annual breeding cycles. The team on Ascension Island consisted of Stonehouse, his wife Sally as camp manager, Douglas Dorward and Philip Ashmole, with shorter visits by Richard Allan, Michael Cullen and Eric Duffey. Stonehouse was appointed senior lecturer at the University of Canterbury, Christchurch, New Zealand, in 1960. He was able to return to Antarctica and continue the study of penguins. Aerial surveys were used to discover new colonies of both Adélie and Pygoscelis adeliae Emperor Penguins and record annual population fluctuations. An important strand of Stonehouse's research was the impact of human activity on animal populations and he persuaded the New Zealand and American authorities to restrict visits to penguin colonies. He was also concerned about the emergence of Antarctic tourism but he soon realized that tourists had more regard for wildlife than many of the administrators and scientists working in Antarctica. In 1972 Stonehouse moved to the University of Bradford to set up a School of Studies in Environmental Sciences. Eleven years later, he moved to Cambridge and, from 1983 to 1992, was editor of the Polar Record. In 1991, he initiated Project Antarctic Conservation to investigate the development and impact of the growing shipborne tourism. He noted that ‘On the whole, the tourists have done far less damage than some of the scientists’. Bernard Stonehouse was known to his colleagues as an efficient and unflappable organizer with an aptitude for improvisation, and by his many students for his ability to make them think critically and for unselfishly sharing his own knowledge. The International Steering Committee of the International Penguin Conferences recognized him with a Lifetime Achievement Award to celebrate his achievements in a lifetime of penguin research, the New Zealand Antarctic Society awarded him their Voycey Trophy for Antarctic Conservation and he was given an honorary D.Sc. by the University of Hull. The BOU awarded Bernard the Union Medal in 1971 (Ibis 1971, 113: 404–405). He is generally credited as the true father of penguin biology.

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.

Development of Diving Abilities by Fledgling Brown Boobies (Sula leucogaster) in the Central Gulf of California, México

Abstract. Diving abilities of fledging Brown Boobies (Sula leucogaster) were characterized during the transition to independence period, and potential inter-sex differences (females are larger than males) were evaluated. Mean and maximum diving depths and mean dive duration increased gradually following the fledglings' first flights. The diving rate and the proportion of active dives (U type) increased notably between days 21 and 25 after first flight. However, maximum dive duration was not influenced by time since first flight, and none of the dive variables evaluated was influenced by sex. In Brown Boobies, acquisition of diving abilities by juveniles is a gradual process, and this can be an important driver of their extended post-fledging parental care.

Nesting Sites and Population Estimates of Seabirds and other Waterbirds of the Gulf of Chiriquí, Panamá

Abstract.— Little information exists on nesting by seabirds and coastal waterbirds in Panama. The present study of the Gulf of Chiriqui complements our previous study of nesting waterbirds of the Gulf of Panama. In April 2012, about 4,000 nests of seven species of seabirds and other colonial waterbirds were identified during a complete survey by small plane and boat within and adjacent to the Gulf of Chiriqui. Seventeen colony sites were found, 12 of which are reported here for the first time. Nesting species included Brown Booby (Sula leucogaster; the most abundant species with nearly 2,500 nests), Brown Pelican (Pelecanus occidentalis), Magnificent Frigatebird (Fregata magnificens), Bridled Tern (Onychoprion anaethetus; second nesting site for Panama), Wood Stork (Mycteria americana; third nesting site for Panama), Great Egret (Ardea alba), and Cattle Egret (Bubulcus ibis). The largest nesting site in the Gulf of Chiriqui was the Islas Ladrones, with 2,200 Brown Booby nests (the largest site for this sp...

Male skin color signals direct and indirect benefits in a species with biparental care

Particularly in species with biparental care and low levels of extrapair paternity, sexual traits that honestly indicate phenotypic and genetic quality are expected. We investigated in the brown booby, Sula leucogaster, whether gular color displayed by males during courtship is related to direct or indirect benefits to females. We performed a cross-fostering experiment in order to identify the relative contribution of parental care and genetic effects on offspring condition. We found that rearing father gular color was positively related to parental care (offspring attendance and provisioning) and chick body mass increase, whereas the genetic father gular color was related to chick structural growth. Contrary to expectations, females paired to more colorful males laid smaller eggs and did not increase parental care. Interestingly, chicks from genetic mothers with more colorful gulars and chicks that hatched from larger eggs “begged” at higher rates to mothers than to fathers. Overall, the results suggest that male gular color may provide females with reliable information on mate genetic quality and parenting abilities.

Community of chewing lice (Phthiraptera: Amblycera and Ischnocera) parasites of resident birds at the Archipelago of São Pedro and São Paulo in northeast Brazil.

The current study describes the chewing lice community associated with seabird populations resident at the São Pedro and São Paulo Archipelago in the Atlantic Ocean in Pernambuco State, Brazil. Adults of three species of seabirds were captured using hand-nets for the collection of biometric data and specimens of ectoparasites. In total, 320 birds were examined (120 Sula leucogaster (Boddaert), Brown Booby; 120 Anous stolidus (L.), --Brown Noddy; and 80 Anous minutus Boie, Black Noddy) of which 95% were infested with 8,625 chewing lice, representing eight species of the genera Actornithophilus, Austromenopon, Eidmanniella, Pectinopygus, Quadraceps, and Saemundssonia. On S. leucogaster, Pectinopygus garbei (Pessôa & Guimarães) was more prevalent and had a mean and median intensity of infestation significantly greater than those recorded for Eidmanniella albescens (Piaget). On the two Noddies, the species of Actornithophilus and Quadraceps were significantly more prevalent and abundant than Austromenopon atrofulvum (Piaget) and Saemundssonia remota Timmermann Most of the louse species had a highly aggregated distribution, with k exponent of the negative binomial distribution ranging from 0.04 to 3.06. A weak but significant correlation was found between the abundance of chewing lice and morphometric variables (body weight, wing, beak, tail, and tarsus lengths). It is possible that high rates of infestation have a negative effect on the morphological characteristics of the hosts, including the health of the plumage. All the lice species collected--except for P. garbei (ex S. leucogaster)--were reported for the first time from Brazilian populations of these seabird species.

Marine debris is selected as nesting material by the brown booby (Sula leucogaster) within the Swain Reefs, Great Barrier Reef, Australia

Many seabirds are impacted by marine debris through its presence in foraging and nesting areas. To determine the extent of this problem, marine debris use in nest material of the brown booby (Sula leucogaster) in the Great Barrier Reef, Australia, was investigated. Nine cays were examined using beach and nest surveys. On average, four marine debris items were found per nest (n=96) with 58.3% of surveyed nests containing marine debris. The source of marine debris in nests and transects were primarily oceanic. Hard plastic items dominated both nest (56.8%) and surveyed beaches (72.8%), however only two item types were significantly correlated between these surveys. Nest surveys indicated higher levels of black and green items compared to beach transects. This selectivity for colours and items suggest these nests are not good indicators of environmental loads. This is the first study to examine S. leucogaster nests for marine debris in this location.

Resources partitioning by seabirds and their relationship with other consumers at and around a small tropical archipelago

Abstract Seabirds occupy a range of trophic levels in marine foodwebs, and as top predators, they potentially may compete with large fish for prey. Here, we examine trophic segregation among seabird species breeding on São Pedro and São Paulo Archipelago (SPSPA), in the tropical Atlantic Ocean, as well as the trophic relationships between the seabirds and pelagic fish. We used stable isotopes (δ15N, δ13C) combined with a conventional dietary analysis of brown booby (Sula leucogaster), brown noddy (Anous stolidus), and black noddy (Anous minutus) and also analysed stable isotopes in the muscles of tropical two-wing flying fish (Exocoetus volitans), blackfin tuna (Thunnus atlanticus), and common dolphinfish (Coryphaena hippurus). Brown boobies shared a similar trophic level with large predatory fish probably due to their intense consumption of flying fish, but seabirds are most likely not competing with blackfin tuna and common dolphinfish, despite relying on the same prey. Food resources seem to be abundant around SPSPA, minimizing competition. Despite relying mostly on two-wing flying fish, the three seabirds studied had non-overlapping trophic niches during the breeding period, with segregation apparently occurring by prey size. Sex-related trophic differences were not found, but age-related trophic segregation was observed in brown boobies and brown noddies. Overall, although seabirds and marine pelagic fish rely on the same prey species, the overlap in their trophic niches was limited, most likely due to an overabundant food resource, i.e. flying fish, a common prey of large predators in most pelagic tropical oceans.

Resource partitioning between incubating and chick-rearing brown boobies and red-tailed tropicbirds on Christmas Island

Background: In oligotrophic tropical marine environments, the main mechanism explaining the coexistence of sympatric seabirds is segregation by habitat or segregation by prey within the same habitat. Both types of segregation can play a role during the breeding season due to different constraints associated with different phases of the breeding cycle. By using stable isotope analyses, we investigated intra- and interspecific foraging segregation in two tropical seabird species, the red-tailed tropicbird Phaeton rubricauda and the brown booby Sula leucogaster, breeding sympatrically on Christmas Island, Indian Ocean. We compared isotopic values of δ 13 C and δ 15 N in blood from incubating and chick-rearing adults of both species. Results: The results showed small but significantly interspecific and intraspecific differences in δ 13 C and δ 15 N values. Differences in δ 13 C values suggest spatial segregation in the main foraging grounds between the two species during the breeding season as well as between incubating and chick-rearing brown boobies. In contrast, red-tailed tropicbirds probably exploited similar foraging habitats during both breeding stages. δ 15 N values did not indicate diet-related differences, neither within nor between species, suggesting a highly opportunistic feeding behavior to cope with the limited prey available in the oligotrophic marine environment. Conclusions: Competition for prey in breeding red-tailed tropicbirds and brown boobies seems to be reduced by spatial segregation enabling both species to successfully reproduce in sympatry in an oligotrophic tropical marine environment.

Predation of Greater Crested Tern (Thalasseus bergii) Eggs by Juvenile Brown Boobies (Sula leucogaster) on Ashmore Reef

As young seabirds approach independence, a range of tactics are sometimes employed in an attempt to secure additional food items prior to departing the nest. Detailed here are previously unreported kleptoparasitic and predatory behaviors of juvenile Brown Boobies (Sula leucogastei) on Ashmore Reef in the Timor Sea. From 14–20 November 2013, the number of Greater Crested Terns (Thalasseus bergii) breeding adjacent to a Brown Booby colony was reduced from 128 adults attending the colony to 59 adults. During this time, two juvenile Brown Boobies were observed depredating the eggs of the Greater Crested Terns and ingesting prey regurgitated by Greater Crested Terns. The factors that lead to this unusual foraging behavior in juvenile Brown Boobies are not known; however, low body mass and hunger may play a role. Repeated years of predation of Greater Crested Tern eggs by Brown Boobies could lead to the abandonment of this colony.

Promiscuous Brown BoobySula leucogasterFemales Perform Reverse Mounting

Reverse mounting (RM), i.e. where the female mounts the male, has been recorded in some bird species, yet the potential function of this behaviour is not clear. Here, we describe the frequency of RM in the brown booby Sula leucogaster and the behavioural context in which it occurs. We found that 12% (4 out of 33) of focal pairs performed RM. Time spent at the territory and intra-pair courtship and copulations did not differ between RM and non-RM pairs. Females that performed RM were more prone to engage in extra-pair courtship than females that did not perform RM, and male partners of females that performed RM were more likely to engage in extra-pair copulations; however, the probability of laying a clutch did not differ between RM and non-RM pairs. Hence, in the brown booby our data suggest that it is unlikely that RM plays a role during courtship by strengthening pair formation or pair bonds. The potential functional role and the mechanisms modulating RM in promiscuous females need to be further investigated.

Foraging behaviour of Brown Boobies Sula leucogaster in Anguilla, Lesser Antilles: Preliminary identification of at-sea distribution using a time-in-area approach

SummarySeabird populations breeding in the UK Overseas Territories remain relatively understudied compared to UK seabird populations, despite their international importance. Here we present results from one of the first seabird tracking studies in the Caribbean region, of Brown Boobies Sula leucogaster breeding on the Important Bird Area (IBA) of Dog Island, Anguilla. Birds were tracked for 5–7 days during the chick-rearing period using GPS data loggers. We assess how representative the at-sea areas of use (utilisation distributions) identified from our sample of 16 birds are likely to be of those of the whole breeding colony, and examined the effect that grid cell size used in the ‘time-in-area’ analytical approach has on these predictions. We also assess the effectiveness of the BirdLife International’s seaward extension approach to marine IBA designation, where terrestrial IBAs are buffered a set distance using existing information on the foraging radii of the same or similar breeding species. Foraging trips were 125.3 ± 54.4 (SD) km long and lasted for 5.6 ± 1.95 hrs on average. Birds travelled into the waters of four neighbouring territories; Saint Martin, Saba, Saint Eustatius and Saint Barthelemy. Our models suggest that many more individuals would need to be tracked to fully identify important at-sea areas for this colony, although this depends on the scale that important areas are defined. Whilst a smaller grid cell size may be necessary for assessing fine-scale habitat use, a larger grid cell size may be more appropriate for marine spatial planning processes. Although the BirdLife Seaward extension approach using maximum foraging distance recorded from Brown Boobies at a Mexican colony predicted a smaller foraging area than that used by Dog Island birds this approach still incorporated at least 99% of their 50% UD, 98% of their 75% UD and 86% of the 95% UD.

Role of body size in shaping the trophic structure of tropical seabird communities

Ecological segregation among coexisting seabird species can occur due to morpho- logical and behavioral differences. This segregation is especially important as it reduces competi- tion during the breeding season, when birds are central-place foragers. Furthermore, seasonal variation in oceanographic processes may change prey availability and shape seabird community trophic structure and species isotopic niche. We used stable isotope analyses of seabird whole blood and prey muscle in 5 tropical seabird communities representing 12 species (Charadri- iformes, Phaethontiformes, Procellariiformes and Suliformes) inhabiting 5 offshore islands off Brazil from 00°55' N to 20° 30' S and 65 to 1160 km from the coast. We evaluated how community trophic structure was correlated with morphology (body mass and bill length), and we verified seasonal variation in isotopic niche in 2 communities. Overall, seabird trophic position (TP) was positively correlated with body size, with frigatebirds and boobies occupying a higher TP than noddies and terns. Structuring of seabird communities according to body size probably occurred due to consumption of prey of different sizes and TP, which contributed to niche segregation by reducing interspecific competition during the breeding season. All species showed isotopic niche segregation at 2 islands, and ~60 to 70% of species segregated at the other islands, except at Atol das Rocas, where 43% of species segregated. Niche overlap occurred mainly among closely related species at Atol das Rocas, Fernando de Noronha and Trindade. The isotopic niche and TP changed across islands for all 3 boobies (red-footed Sula sula, brown S. leucogaster and masked S. dactylatra), brown noddy Anous stolidus and red-billed tropicbird Phaethon aethereus; these factors also changed seasonally in other species, such as in magnificent frigatebird Fregata mag- nificens, brown booby, both the red-billed P. aethereus and white-tailed P. lepturus tropicbirds and both the brown A. stolidus and black Anous minutus noddies. Such changes probably occurred due to differences in prey availability, opportunistic behavior (e.g. feeding on fishery dis- cards) and/or local foraging and diet specialization.