Fregata Ariel Research Articles

Cyclone Ilsa in April 2023 led to significant seabird mortality on Bedout Island

On 13 April 2023, Cyclone Ilsa crossed Bedout Island in the Timor Sea off Western Australia’s remote north coast. Extensive damage was done to the entire island, with all coastal vegetation stripped clear from the island’s surface. Here we use repeated aerial and ground-based transect surveys of Bedout’s important seabird populations during 17 April – 21 July 2023 and Monte Carlo modelling to estimate total mortality for three species. We estimate that 80–90% of the populations of three seabird species (Masked Booby Sula dactylatra bedouti, Brown Booby S. leucogaster, and Lesser Frigatebird Fregata ariel) were killed in the storm, with only 40 breeding Masked Booby (a putative endemic subspecies) recorded on the island 15 weeks later. The frequency and intensity of such storms is likely approaching a threshold beyond which Bedout’s seabirds cannot readily recover, with cyclones hitting the island, on average, every seven years in recent decades. We discuss the implications for Bedout Island, and for wildlife conservation more broadly in the face of increasing, climate-driven storms and impacts documented worldwide.

The marine avifauna of Matthew and Hunter Islands, two remote volcanoes of the New Hebrides chain

The marine avifauna of Matthew and Hunter Islands, two remote volcanoes of the New Hebrides chain Breeding birds recorded on Matthew and Hunter Islands in the tropical southwestern Pacific between 1973 and 2018 are summarised from a compilation of reports, for which various methods were used for counting seabirds. These methods included line transects, or direct observations using telescope or binoculars, or exhaustive counts, depending on the species observed and its nesting habitat. Population size estimates and reproductive periods are given. The total number of seabird species recorded breeding on the two islands was n = 14. This total includes seabird species breeding on both islands (n = 7): black-winged petrel Pterodroma nigripennis, wedge-tailed shearwater Ardenna pacifica, red-tailed tropicbird Phaethon rubricauda, masked booby Sula dactylatra, brown booby S. leucogaster, brown noddy Anous stolidus, and grey noddy A. albivitta. Hunter island also harbours a small colony of Herald petrel Pterodroma heraldica, and colonies of lesser and great frigatebirds (Fregata ariel and F. minor), red-footed booby S. sula and, black noddy A. minutus and white tern Gygis alba. Matthew Island harbours a large colony of sooty tern Onychoprion fuscatus; an undetermined storm petrel may also breed there. Differences between the two islands regarding community composition of seabirds are explained by the absence of trees on Matthew Island and the presence of the Polynesian rat Rattus exulans on Hunter Island. Brown noddies bred exclusively during the austral summer, as did black-winged petrels and wedge-tailed shearwaters, while the Herald petrel and the two frigatebirds seemed to preferentially breed in the winter. The red-tailed tropicbird, the three boobies, the grey noddy and the sooty tern appeared to reproduce year-round. Disturbance caused by human activities was irregular but devastating to seabird colonies. The diversity and abundance of seabird species breeding on these islands makes them regionally important sites for conservation. Key words: Seabird, Population, Reproduction, Threats, Polynesian rat; Helicopters

Transboundary priorities for protection of frigatebird non-breeding habitat in a heavily impacted region

Species that inhabit spatially-distinct regions at different stages of their lifecycle pose challenges to conservation managers, particularly when distributions span international or jurisdictional boundaries. Despite the importance of non-breeding habitat to the persistence of individuals and species, there remains limited information on the habitat requirements of many species during the non-breeding period. We used Global Positioning System tracking devices to determine the non-breeding movements of Great Frigatebirds, Fregata minor, and Lesser Frigatebirds, F. ariel, across much of Southeast Asia. These data were analysed with MaxEnt modelling to identify important habitat features for non-breeding frigatebirds and inform priorities for targeted conservation measures. Models with the greatest predictive performance were influenced strongly by bathymetry. Predicted habitat suitability was greatest in shallow waters. Similarly, warmer waters had greater predicted suitability during the wet season. We also identify 45 roosting sites that form an important component of the habitat used by non-breeding frigatebirds in this region. The existing marine protected area (MPA) network contains only a small proportion of habitat identified as suitable or optimum for non-breeding frigatebirds. This is of particular concern given that some parts of the region’s marine environment are among the most heavily human-impacted in the world. Our findings can be used to implement spatially-targeted conservation measures such as education campaigns focusing on bycatch reduction and subsidies for bycatch reduction methods (e.g., streamer lines) for fisheries operating in suitable and optimum habitat. They could also inform placement of additional MPAs to maintain habitat integrity in areas we identified as suitable or optimum habitat, particularly when these habitats occur in close proximity to roosting sites. Such approaches will likely provide benefits to frigatebird populations tracked in the present study as well as those dispersing to the study region from other ocean basins.

Species Rank For the Critically Endangered Atlantic Lesser Frigatebird (Fregata trinitatis)

The Atlantic Lesser Frigatebird (Fregata trinitatis) is elevated to a separate species from Fregata ariel of the Indo-Pacific based on plumage differences and greater robustness of the rostrum and wing bones. The species now occurs only on the remote South Atlantic island of Trindade (South Trinidad) over 1,100 km east of mainland Brazil, although fossils establish that it once also occurred at St. Helena. Fregata trinitatis no longer breeds on the main island of Trindade and is only known to nest with certainty on a small rocky islet on the southern coast, where there may be fewer than 20 breeding pairs.

Post-breeding dispersal of frigatebirds increases their exposure to mercury

Migration and dispersal can expose wildlife to threats in different parts of their range, particularly for localized anthropogenic threats. Wildlife exposure to metal contaminants may correlate with local anthropogenic emissions. Feather mercury concentrations of adult and juvenile Lesser Frigatebirds (Fregata ariel) and Great Frigatebirds (F. minor) were determined for individuals breeding in the eastern Indian Ocean. Low mercury concentration in juveniles relative to adults, higher mercury concentration in adult females than adult males, and a trend for Lesser Frigatebirds to have higher mercury concentration than Great Frigatebirds implicate non-breeding ground exposure as the major influence on mercury burden. Aspects of foraging ecology are congruent with high exposure occurring in inshore waters of the non-breeding range, particularly in the South China Sea. These findings highlight the need for tighter mercury emission regulations in southeast Asia to minimise the potential threat to frigatebirds and other species dependent on marine resources including humans.

Resource partitioning between species and sexes in Great Frigatebirds and Lesser Frigatebirds

ABSTRACT Seabirds inhabiting large, multispecies colonies face intraspecific and interspecific competition for prey and this often results in foraging strategies that partition resources. Here, we identified mechanisms that facilitate partitioning of resources between 2 congeneric tropical seabirds, Great Frigatebirds (Fregata minor) and Lesser Frigatebirds (F. ariel), for which traditional research methods have documented high levels of resource overlap. Stable isotope analysis (SIA) indicated that throughout the breeding cycle, male and female Great Frigatebirds consumed prey with higher δ15N compared to male Lesser Frigatebirds. This trend was not significant when comparing δ15N values of male and female Great Frigatebirds to female Lesser Frigatebirds. During the breeding period, GPS tracking and SIA indicated considerable spatial overlap among species and sexes. This contrasted with SIA of samples that provide insight into nonbreeding resource acquisition because these indicated that male Great Friga...

Interpopulation resource partitioning of Lesser Frigatebirds and the influence of environmental context

Conspecific individuals inhabiting nearby breeding colonies are expected to compete strongly for food resources owing to the constraints imposed by shared morphology, physiology, and behavior on foraging strategy. Consequently, colony‐specific foraging patterns that effectively partition the available resources may be displayed. This study aimed to determine whether intraspecific resource partitioning occurs in two nearby colonies of Lesser Frigatebirds (Fregata ariel). A combination of stable isotope analysis and GPS tracking was used to assess dietary and spatial partitioning of foraging resources during the 2013 and 2014 breeding seasons. These results were compared to vessel‐derived estimates of prey availability, local primary productivity, and estimates of reproductive output to suggest potential drivers and implications of any observed partitioning. Isotopic data indicated a more neritic source of provisioned resources for near‐fledged chicks at an inshore colony, whereas their offshore counterparts were provisioned with resources with a more pelagic signal. Deep pelagic waters (>200 m) had higher availability of a preferred prey type despite a trend for lower primary productivity. Differences in foraging ecology between the two populations may have contributed to markedly different reproductive outputs. These findings suggest environmental context influences dietary and spatial aspects of foraging ecology. Furthermore, the effect of colony‐specific foraging patterns on population demography warrants further research.

Breeding seabird populations in Brazilian oceanic islands: historical review, update and a call for census standardization

In recent decades, several seabird populations have declined globally due to anthropogenic activities. In Brazil, 14 seabird species breed at four oceanic islands and one atoll: the Abrolhos, Fernando de Noronha, and Sao Pedro and Sao Paulo (SPSPA) archipelagos; the Trindade/Martin Vaz Islands; and the Atol das Rocas. Seven species are listed as nationally threatened by extinction. This study aimed to present new information on breeding seabird populations in Brazilian oceanic islands, compile all available data previously published and, when possible, to provide updated information on population estimates from censuses carried out sporadically at different islands between 2006 and 2013. Based on new data and the thorough review provided here, of the 35 seabird breeding populations analysed, 14% were increasing (as Red-billed Tropicbird Phaethon aethereus , Magnificent Frigatebird Fregata magnificens and Brown Noddy Anous stolidus in Abrolhos), 11% were decreasing (as Brown Booby Sula leucogaster in Atol das Rocas and Great Frigatebird Fregata minor in Trindade Island), 23% were stable (as White-tailed Tropicbird Phaethon lepturus in Fernando de Noronha and Brown Noddy and Black Noddy Anous minutus in Sao Pedro and Sao Paulo Archipelago), and the remaining 49% were unknown or not possible to evaluate. The Red-footed Booby ( Sula sula ) is locally extinct in Trindade Island, however there are colonies of only a few individuals of other species, such as the Audubon's Shearwater Puffinus lherminieri and Red- billed Tropicbird in Noronha, Black Noddy in Martin Vaz, and Great ( Fregata ariel trinitatis ) and Lesser ( F. m. nicoll i) Frigatebirds in Trindade, that may become extinct soon. Censuses at distinct periods of the breeding cycles and protocols were highly variable, making temporal comparisons difficult. These results indicate an urgent need for long-term studies to improve the scenario to assess seabird population trends based on comparable methodologies, in order to determine trends in the future.

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.

Frigatebirds on Aldabra Atoll: population census, recommended monitoring protocol and sustainable tourism guidelines

SummaryWe report the results of a survey of breeding Greater Frigatebird Fregata minor and Lesser Frigatebird F. ariel on Aldabra Atoll, a UNESCO World Heritage site in the Seychelles archipelago, which hosts the largest breeding population of frigatebirds in the Indian Ocean. All four colonies across the atoll were surveyed in 2011 and 2012 by counting adults on nests and chicks, and calculating the number of fledged birds. The breeding population in 2011 consisted of approximately 4,400 pairs of Greater Frigatebird and 6,600 pairs of Lesser Frigatebird. This is a potential increase of at least 10% since the last comparable surveys in 1976/77 and 2000. However, 2012 populations were considerably less than in 2011, highlighting significant annual variation and the need for more data. We also report a new breeding colony on the island of Picard, which was last reported to host breeding frigatebirds a century ago. We outline recommendations for future frigatebird monitoring on Aldabra and elsewhere and revisions to tourist regulations resulting from the census.

Breeding Avifauna of the Chesterfield Islands, Coral Sea: Current Population Sizes, Trends, and Threats

This paper reports on post-1991 census data and on the breeding phenology of seabirds of the Chesterfield-Bampton and Bellona groups of coral islets in the Coral Sea. In total, 13 resident bird species were observed [Wedge-tailed Shearwater (Puffinus pacificus), Masked Booby (S. dactylatra), Brown Booby (Sula leucogaster), Red-footed Booby (S. sula), Lesser Frigatebird (Fregata ariel), Great Frigatebird (F. minor), Black Noddy (Anous minutus), Brown Noddy (A. stolidus), Crested Tern (Sterna bergii), Sooty Tern (S. fuscata), Fairy Tern (S. nereis), Black-naped Tern (S. sumatrana), and Buff-banded Rail (Gallirallus philippensis)]. Segregation for nesting habitat was similar to that previously observed on other coral-reef islets of the Coral Sea. Breeding periods were either in the winter (Masked and Red-footed Boobies, Frigatebirds, Fairy Tern) or in the summer (Wedge-tailed Shearwater, Black and Brown Noddies, Crested and Black-naped Terns) or year-round (Brown Booby). Sooty Terns bred twice a year (summer and spring), but this was not consistent across years. Estimates of breeding population sizes for the whole Chesterfield-Bampton and Bellona groups are proposed for Wedge-tailed Shearwater (90,000 to 106,000 breeding pairs), Masked Booby (280–500 pairs), Brown Booby (3,800–5,800 pairs), Redfooted Booby (7,200–7,300 pairs), Lesser Frigatebird (1,600 pairs), Great Frigatebird (350–480 pairs), Black Noddy (29,000–45,000 pairs), Brown Noddy (15,000–23,000 pairs), Crested Tern (80–100 pairs), Sooty Tern (11,000–46,000 pairs), and Black-naped Tern (70–90 pairs). Interannual fluctuation in breeding population size was apparent in Wedge-tailed Shearwater. Over the last 30 yr, an increase in Brown Booby abundance was noted, whereas declines are suspected for the Fairy Tern and Buff-banded Rail. Among the threats to nesting seabirds are stress and other disturbances caused by human frequentation, including poaching of seabird chicks and introduced mice.

Foraging habitats of the seabird community of Europa Island (Mozambique Channel)

We investigated the foraging habitats of the winter breeding community of tropical seabirds from Europa Island (Mozambique Channel) in September 2003. We focused our study on the dominant species of this austral community, the sooty tern (Sterna fuscata), the red-footed booby (Sula sula), and the frigatebirds, including the great (Fregata minor) and the lesser frigatebirds (F. ariel). We considered the at-sea distribution and abundance of these species in relation to chlorophyll concentration, sea-surface temperatures, sea-surface height anomalies, depth of the thermocline, distance to the colony, and presence of surface marine predators, flying fishes and other seabirds. Although the marine environment where seabirds foraged was oligotrophic, it presents the best feeding opportunities for seabirds for the area in winter. Our study demonstrates that the winter-breeding seabird species of Europa Island tend to forage in productive waters in association with other marine predators when possible. Sooty terns and frigatebirds were widely distributed in the whole study area, whereas red-footed boobies were not found farther than 160 km from their colonies and were associated with relatively productive waters. Sooty terns and red-footed boobies were aggregated where flying fishes were abundant. The presence of other marine predators was associated with larger multispecies feeding flocks than when no association occurred. Sooty terns, which are numerically dominant at Europa and adopted network foraging, seem to be catalysts of feeding events, and represented a good target for the other foraging species, especially frigatebirds. However, when possible, frigatebirds favour association with flocks of red-footed boobies.

Sex-specific chick provisioning and kleptoparasitism in the Least Frigatebird, Fregata ariel

We examined sex-specific patterns of provisioning behaviour and kleptoparasitic host-use in the Least Frigatebird Fregata ariel. We aimed to determine, first, whether sex-specific kleptoparasitism, either at sea, or adjacent to the breeding colony, is an important source of food for chick provisioning and, second, whether observed behaviour is consistent with the expectation that sexual size-dimorphism in resource-poor environments consistently results in sex-specific divergence of foraging behaviour. We observed sex-specific differences in the time of day that adult frigatebirds provision chicks but no differences in the overall provisioning rate between sexes. We also observed no sex-specific kleptoparasitism via simultaneous monitoring of provisioning by Least Frigatebirds and Masked Boobies. Sex-specific differences in prey types attacked at the colony were observed, but these conflicted with predictions based on previous studies and were directly correlated with diural patterns of adult frigatebird attendance. Overall, we suggest that sexual differences in foraging behaviour in Least Frigatebirds are minimal and relate to either the use of different risk-sensitive foraging strategies by each sex, or are a consequence of body size differences in independently foraging sexes. While our results must be considered preliminary, we believe they provide justification for further critical examination of mechanisms of sex-specific behavioural divergence in seabird taxa.

Parental care in frigatebirds : a comparison between two sympatric species

The participation of both sexes to parental care have been studied in two different frigatebird species : the Great Frigatebird (Fregata minor), exhibiting a clear sexual size dimorphism, and the Lesser Frigatebird (Fregata ariel), with little sexual size dimorphism. Our results show that Great Frigatebirds perform an unequal division of labour during the chick rearing period : males desert the nest around three months after hatching and females undertake alone the long remaining chick rearing period. On the other hand, male and female Lesser Frigatebirds share equally parental duties until the chick is able to fly. These results are discussed in the light of explicative hypotheses of Reversed Sexual Size Dimorphism.

The status of seabird colonies on the Cook Islands atoll of Suwarrow

Suwarrow (Suvorov) atoll is an important seabird breeding site in the central Pacific Ocean. However, it is not protected and is attractive to developers of potentially damaging aquaculture industries. In this paper I report the results of a survey conducted to establish the present status of Suwarrow's seabird colonies and to generate base-line data for measuring the effect of a proposed pearl-farm development. Between late July and early September 2000 the reef islets were surveyed for seabird chick numbers and age-states using a simple sampling method. In addition to Sooty Tern Sterna fuscata, populations of boobies Sula spp., noddies Anous spp., frigatebirds Fregata spp. and tropicbirds Phaethon spp. were assessed. Results showed that bird populations were maintaining levels similar to those from findings of surveys in 1992. Of particular note were globally significant numbers of Lesser Frigatebird Fregata ariel and Red-tailed Tropicbird Phaethon rubricauda. Migratory birds were observed with Bristle-thighed Curlew Numenius tahitiensis regularly seen. The well-being of bird-life on the islets appears to be indirectly proportional to the proximity of human activity, with birds not observed breeding on Anchorage Island – the islet most often visited by people.

Species and Sex-Biased Predation on Hatchling Green Turtles by Frigatebirds on Europa Island, Western Indian Ocean

Abstract Europa Island is a major breeding place for green turtles (Chelonia mydas; 0.7 to 2.4 million juvenile turtles hatch there annually), Great Frigatebirds (Fregata minor; 700 to 1100 breeding pairs), and Lesser Frigatebirds (Fregata ariel; 1000 to 1200 pairs). By visual observation, we quantified the proportions of males, females, and juveniles of both frigatebird species prospecting over the hatching sites and preying on hatchling turtles. Of 1828 juveniles observed hatching at daytime (35 separate turtle emergences), 1632 were immediately eaten by male Great Frigatebirds. Only 10 hatchlings were preyed upon by female Great Frigatebirds; the remaining 186 were captured by juvenile Great Frigatebirds. Such feeding behavior was not observed in Lesser Frigatebirds. We suggest that the sexual and species differences in hatchling turtle predation are due to size differences between the two species and between male and female Great Frigatebirds.

SPECIES AND SEX-BIASED PREDATION ON HATCHLING GREEN TURTLES BY FRIGATEBIRDS ON EUROPA ISLAND, WESTERN INDIAN OCEAN1

Europa Island is a major breeding place for green turtles (Chelonia mydas; 0.7 to 2.4 million juvenile turtles hatch there annually), Great Frigatebirds (Fregata minor; 700 to 1100 breeding pairs), and Lesser Frigatebirds (Fregata ariel; 1000 to 1200 pairs). By visual observation, we quantified the proportions of males, females, and juveniles of both frigatebird species prospecting over the hatching sites and preying on hatchling turtles. Of 1828 juveniles observed hatching at daytime (35 separate turtle emergences), 1632 were immediately eaten by male Great Frigatebirds. Only 10 hatchlings were preyed upon by female Great Frigatebirds; the remaining 186 were captured by juvenile Great Frigatebirds. Such feeding behavior was not observed in Lesser Frigatebirds. We suggest that the sexual and species differences in hatchling turtle predation are due to size differences between the two species and between male and female Great Frigatebirds.

Seabird Breeding Populations on the Far Northern Great Barrier Reef, Australia: Trends and Influences

SummaryAll available records (1977–96) of 12 species of breeding seabirds in the far northern Great Barrier Reef (between 9°S and 16°S) were examined to detect any changes, particularly in relation to effects of trawling on populations. The study area included the ‘Green Zone’ (approximately 11–12°S), closed to trawling since 1983, and the well-studied Lizard Island area (14–15°S), which is open to trawling. Seven species (Sterna bergii, S. bengalensis, S. anaethetus, S. sumatrana, Anous stolidus, A. minutus and Sula leuco- gaster) were common and widely distributed, and five species were less common or local (Sterna fuscata, S. dougallii, S. caspia, Fregata ariel and F. minor). Large annual fluctuations in numbers in particular areas are a feature of most species in this region. Sterna bergii, a trawl-discard feeder, showed a clear order of magnitude increase in numbers in the study areas that may be related to the additional food provided by the discarded trawl by-catch. Other discard-feeding species showed no definite population trends. The numbers of S. bengalensis and S. fuscata in the ‘Green Zone’ have declined since the mid-1980s, possibly due to the birds moving away from the area. Both species appear to have increased in the Lizard Island area. It is postulated that the large increases in S. bergii numbers may affect other species, by competing for food and nesting sites. The seabirds fell broadly into three breeding groups: mainly wet season (summer) nesters (Sterna bergii, S. bengalensis, S. anaethetus, S. sumatrana and Sula leucogaster); dry season (winter) nesters (Sterna caspia, Fregata minor and F. ariel), and species that may nest in almost any month of the year (S. fuscata, Anous stolidus and A. minutus). Despite pronounced seasonal peaks in breeding activity among the species, most also show some nesting activity at other times of year. This suggests that they have the potential to breed at any time and are sufficiently flexible to take advantage of the onset of suitable conditions. At present, there are no definite indications that trawl discarding directly influences breeding seasonality, but there is evidence that extra food in the form of trawl discards may influence breeding success and hence population size in some species.

Kleptoparasitism in Tropical Seabirds: Vulnerability and Avoidance Responses of a Host Species, the Red-Footed Booby

We investigated the importance of kleptoparasitism in a population of Red-footed Boobies (Sula sula) sympatric with frigatebirds (Great and Lesser Frigatebird Fregata minor and F. ariel) and identified the responses adopted by boobies. Less than 1% of the boobies lost their food by kleptoparasitism. Birds flying in a group >50 m high or after dusk were less likely to be chased than others. We compared the way boobies returned to land and the rate of successful chases in this population with another population of Red-footed Boobies where kleptoparasitic attempts were rare. Birds were more nocturnal in the former population and were better able to resist chases. These observations suggest that the coexistence of boobies with frigatebirds may have led to avoidance responses. Comparison of the behavior of the Masked Booby (Sula dactylatra) to that of the Red-footed Booby showed that the former should be more vulnerable when returning to land than the latter. Further investigations are needed on the way Masked Boobies interact with frigatebirds in a place where both coexist in large numbers and to determine if this species has adopted other avoidance tactics.

THE BREEDING SEABIRDS OF TROMELIN ISLAND (WESTERN INDIAN OCEAN): POPULATION SIZES, TRENDS AND BREEDING PHENOLOGY

Summary Le Corre, M. 1996. The breeding seabirds of Tromelin Island (western Indian Ocean): population sizes, trends and breeding phenology. Ostrich 67: 155–159. Formerly six or eight species of seabirds bred on Tromelin Island, but currently only two species do so: The Redfooted Booby Sula sula and the Masked Booby S. dactylatra. The last two species which became locally extinct, the Lesser Frigatebird Fregata ariel and the Greater Frigatebird F. minor, probably stopped breeding on the island as a consequence of human disturbance to breeding colonies. The populations of the two species of booby have opposing trends since 1954. The Masked Booby's population increased from 60 pairs in 1954 to 200–250 pairs in 1996 while the Red-footed Booby's population decreased from 500 pairs in 1968 to 130–180 pairs in 1996. The impacts of human settlement, introduced brown rats Rattus norvegicus, local extinction of the Greater Frigatebird and other factors are discussed to explain these changes in population sizes. Ne...