Aride Island Research Articles

LAYING DATE, CHICK PROVISIONING, AND BREEDING SUCCESS OF LESSER NODDIES ON ARIDE ISLAND, SEYCHELLES

Abstract We describe the main reproductive characteristics (laying date, egg size, hatchling mass, and breeding success), chick growth, and patterns of provisioning in Lesser Noddies (Anous tenuirostris) on Aride Island, Seychelles, 1995–2002. The bulk of the population laid eggs between late May and late June in most years. Both hatching and fledging success varied significantly between years, with fledging success (2–92%) more variable than hatching success (28–91%). Productivity of less than 0.10 chicks per breeding pair occurred in 25% of the years. In 2001, egg volume did not differ significantly between hatched and unhatched eggs. Chick mass at hatching was significantly correlated with an egg volume index, but there were no correlations between egg size and either hatching date or linear growth rate. Around 40% of the Lesser Noddy chicks were fed at dusk. Chicks aged 0–5 and 6–10 days received significantly less food than older chicks. There was evidence of daily and stochastic variation in the for...

Intraspecific Aggression by Roseate Tern Adults on Chicks in a Tropical Colony

Acts of aggression by Roseate Tern (Sterna dougallii) adults on conspecific chicks were examined on Aride Island, Seychelles, from 13 June-10 July 1998. Data were used to examine two hypotheses to explain adult aggression towards chicks: (1) the adoption avoidance hypothesis, and (2) the feeding unfamiliar chicks hypothesis. Throughout the entire nestling development, adults pecked mostly unattended chicks (96%). The intensity of pecking was higher on b-chicks than on a-chicks and 72% of the pecking acts were on chicks that were on their own nests. During each pecking act, young chicks (0-6 days) were pecked by a greater number of adults than were old chicks (>6 days). When pecked, young chicks moved significantly greater distances away from nests than did old chicks (1.41 ± 1.92 m vs. 0.18 ± 0.42 m). Of the 23 chicks killed by adults, 11 were a-chicks, representing 8.5% of the a–chicks in the study area. Parents sometimes rescued a-chicks, but did not attempt to rescue b-chicks from adult attacks. Chicks that died had moved significantly greater distances away from nests than chicks that survived (2.8 ± 2.5 m vs. 0.3 ± 0.67 m). This study presents evidence that both hypotheses may be important in explaining intraspecific adult aggression by Roseate Terns on chicks. In particular, the feeding unfamiliar chicks hypothesis may be invoked to explain the significant negative correlation between daily intensity of adult aggression and the amount of food delivered to chicks. The adoption avoidance hypothesis may explain why b-chicks were disproportionately involved in pecking in relation to a-chicks. Adult aggression is an additive factor of chick mortality, operating mostly on days of food shortage.

Spatial Patterns of Breeding Parameters in Tropical Roseate Terns Differ from Temperate Seabirds

Abstract This paper addresses the hypothesis that parental quality, expressed in terms of nest location, determines differences in breeding parameters between colonies and colony areas. I compared hatching date, egg size, egg shape, clutch size, breeding success and chick growth of Roseate Terns (Sterna dougallii) on the tropical Aride Island, Seychelles between: a) central pairs of an old colony, b) peripheral pairs of the same colony, c) pairs of old small sub-colonies and c) pairs of a recently formed colony. The breeding parameters at the small, old colonies were similar to those of the large, old colony and significantly different from those of the new colony, suggesting that parental quality is more closely related to sub-colony age than to sub-colony size. In 1998, a good breeding season, egg size was similar between all study areas, but clutch size in the new colony was significantly larger than that in the center of the old colony and the small sub-colonies. However, breeding success was signific...

Trends in Seabird Numbers on Aride Island Nature Reserve, Seychelles 1988-2000

Abstract Count data for twelve species of seabird from Aride Island Nature Reserve, Seychelles were reviewed from 1988 to 2000. The numbers of six of the ten breeding species remained relatively stable during the period, while those of one species, the White-tailed Tropicbird (Phaethon lepturus) underwent a 60% decline. Roseate Tern (Sterna dougallii) numbers significantly declined between 1987 and 1993, followed by a significant increase between 1994 and 2000. Current count data for Audubon’s Shearwater (Puffinus l’herminieri) and the Wedge-tailed Shearwater (P. pacificus) are insufficient to establish trends. The maximum annual count of roosting non-breeding frigatebirds (Fregrata spp.) increased steadily throughout the period. The island has internationally important numbers of breeding seabirds (330,000-720,000 pairs per annum), including the largest known colony of Audubon’s Shearwater, the largest colony of the declining Roseate Tern in Seychelles, and the largest known colony of the nominate subspe...

Influence of local and large-scale weather events and timing of breeding on tropical roseate tern reproductive parameters

We analysed the effects of local- (sea-surface temperature (SST) and windspeed) and large- (multivariate El Nino index) scale weather conditions and timing of breeding on reproductive parameters of tropical roseate terns Sterna dougallii on Aride Island, Seychelles, using up to 17 years of data. The size of the breeding population and initiation of breeding were negatively and positively correlated, respectively, with both SST and the multivariate El Nino index for the laying season (May- June). It is the first time that an El Nino index obtained for the Pacific Ocean is shown to be correlated with reproductive parameters of seabirds in the Indian Ocean. Hatching success decreased signifi- cantly with later initiation of breeding. Virtually no chicks fledged when breeding started in June (40% of the years monitored). We suggest that oceanographic conditions over a relatively large scale have an influence on tern arrival date to the breeding grounds and that SST around the breeding colony influences the number of birds that attempt to breed. Despite the influence of factors such as predatory fish on food availability, this influence appears to be overridden by the importance of weather events and oceanographic conditions, which are likely to determine marine productivity. This study suggests that ecosystem-level phenomena appear to be important in shaping the popula- tion dynamics of tropical roseate terns.

Male Seychelles warblers use territory budding to maximize lifetime fitness in a saturated environment

In cooperatively breeding species, helping at the nest and budding off part of the natal territory have been advanced as strategies to increase fitness in an environment that is saturated with territories. The importance of helping or territory budding as a determinant of lifetime reproductive success (LRS) has been debated because the potential benefits of both strategies could not be separated. Here we test the causes and the immediate and future fitness consequences of single dispersal decisions taken by male Seychelles warblers (Acrocephalus sechellensis). Males breeding in high-quality territories (high food abundance) have significantly higher LRS than similar-aged males budding off part of the parental territory. Initially, budders have a low reproductive success (because of limited food resources or absence of a breeding partner). However, they have a long life span and inherit high-quality territories through site dominance, by which they gain higher LRS than breeders on low-quality territories, helpers, or floaters. Experimental creation of male breeding territory vacancies showed that most young males became budders because of intense competition for high-quality territories. The translocation of warblers to the previously unoccupied Aride Island shows that males behave according to the expected fitness benefits of each dispersal strategy. In the absence of competition for territories on Aride, all young males bred in high-quality territories. However, after saturation of high-quality habitat with territories, most males became budders rather than breeders on low-quality habitat, helpers, or floaters. Key words: Acrocephalus sechellensis, budding, dispersal, helping, lifetime reproductive success, Seychelles warbler, territory inheritance. [Behav Ecol 12:706–715 (2001)]

Activity Patterns and Effect of Ticks on Growth and Survival of Tropical Roseate Tern Nestlings

Abstract Patterns of abundance of the seabird tick Amblyomma loculosum and their effects on Roseate Tern (Sterna dougallii) nestling growth, fledging age, and survival are described on Aride Island, Seychelles, in 1997–1999. Female ticks attached to nestlings from 4 to 14 days (to engorge) whereas male ticks attached for 1–3 days. The linear growth rate of birds carrying female ticks (0.24 g/day) was significantly different from that of nonparasitized nestlings of the same age and similar (or even lower) hatching weight (4.07 g/day). Parasitized nestlings that fledged did so 5.2 days later than nonparasitized nestlings of similar age. Only 37.5% of the nestlings infested with female ticks fledged compared with 83.3% of the noninfested nestlings. During the successful 1998 breeding season, around 100 nestlings died from tick infestation (24.3% of the nestling deaths). Ticks appeared to accelerate nestling mortality during periods of food shortage. Despite an annual difference of two weeks in the timing of breeding of the Roseate Terns between 1997 and 1998, adult ticks parasitized nestlings in July, with an infestation peak occurring between 8–12 July in both years. However, in 1997, nestlings were parasitized at a younger age, suggesting that ticks (nymph stage) must attach to Roseate Tern adults as soon as they make a nest scrape (usually in May). Ironically, the frequent breeding failures of the Roseate Terns will result in lower infestation levels in subsequent years, which will benefit the birds.

Seasonal variation in reproductive measures of tropical Roseate Terns Sterna dougallih previously undescribed breeding patterns in a seabird

Seasonal variation in egg‐laying, egg size, hatching success, hatchling mass, fledging success and chick growth of Roseate Terms Sterna dougallii breeding on Aride Island (Seychelles), Indian Ocean, were studied in 1997 and 1998. I investigated to what extent two patterns, common in a range of species, were followed by tropical Roseate Terns: (a) seasonal decrease in clutch size, egg size and breeding success and (b) an increase in breeding success with increasing egg weight. In 1997 (a poor year), the earliest nesting birds laid significantly smaller eggs, and chicks were lighter at hatching than those of peak nesting birds. The mean clutch size, of 1.04 eggs, showed no seasonal variation and no ‘b’‐eggs hatched. In 1998 (a good year) the earliest nesting birds laid eggs of similar size and their chicks were of similar weight to those of peak nesting birds. Mean clutch size, of 1.25 eggs, increased significantly through the season and about 60% of the ‘b’‐eggs hatched. In 1997, hatching success was 57% whereas in 1998 it was 80%. In both years, breeding success declined significantly through the season. The fact that the earliest breeding birds laid smaller eggs in a poor year and smaller clutches in a good year is in marked contrast to a range of other species, and to temperate‐nesting Roseate Terns. Egg volume explained about half of the variance in hatchling mass in both years, but only 15% of the variation in linear growth rate. Hatching date was the only variable with a significant effect on fledging success. Roseate Terns on Aride seemed to sacrifice egg size and clutch size for earliness of laying. Presumably it is a strategy of older birds to lay as early as possible and may be regarded as a response of tropical Roseate Terns to breeding under relatively poor, and seasonally declining, food conditions.

ACTIVITY PATTERNS AND EFFECT OF TICKS ON GROWTH AND SURVIVAL OF TROPICAL ROSEATE TERN NESTLINGS

Abstract Patterns of abundance of the seabird tick Amblyomma loculosum and their effects on Roseate Tern (Sterna dougallii) nestling growth, fledging age, and survival are described on Aride Island, Seychelles, in 1997–1999. Female ticks attached to nestlings from 4 to 14 days (to engorge) whereas male ticks attached for 1–3 days. The linear growth rate of birds carrying female ticks (0.24 g/day) was significantly different from that of nonparasitized nestlings of the same age and similar (or even lower) hatching weight (4.07 g/day). Parasitized nestlings that fledged did so 5.2 days later than nonparasitized nestlings of similar age. Only 37.5% of the nestlings infested with female ticks fledged compared with 83.3% of the noninfested nestlings. During the successful 1998 breeding season, around 100 nestlings died from tick infestation (24.3% of the nestling deaths). Ticks appeared to accelerate nestling mortality during periods of food shortage. Despite an annual difference of two weeks in the timing of ...

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

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

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

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

CHARACTERISTICS OF FORAGING HABITATS AND CHICK FOOD PROVISIONING BY TROPICAL ROSEATE TERNS

Abstract I studied tropical Roseate Terns (Sterna dougallii) on Aride Island, Seychelles, between 1997–1999. Productivity in 1998 was 0.58 fledglings/breeding pair, and in 1999 no young fledged. Roseate Terns on Aride concentrated their foraging along the coastline exposed to prevailing winds, with flock size over this area being significantly correlated with amount of food offered to chicks. In 1998, Lesser Noddies (Anous tenuirostris) were present in 91% of the Roseate Tern flocks, but in 1999 occurred in only 32%. During the 1998 successful breeding season, Roseate Terns were associated with dense flocks of Lesser Noddies over predatory fish, whereas during the 1999 failure season most Roseate Tern flocks were either monospecific or mixed with Fairy Terns (Gygis alba), and without predatory fish. The mean flock size of Roseate Terns (82 vs. 6 birds) and the rate of foraging attempts (8.3 vs. 2.8 attempts min−1) were significantly greater in association with predatory fish. Mullidae (Parupeneus or Mullo...

Predation risk affects trade-off between nest guarding and foraging in Seychelles warblers

The fitness costs of egg loss for Seychelles warblers (Acrocephalus sechellensis) on Cousin Island are considerable because warblers have a single-egg clutch and no time to lay a successful replacement clutch. On the islands of Cousin and Cousine, with equal densities of Seychelles fodies (Foudia sechellarum), nearly 75% of artificial eggs placed in artificial nests were predated by fodies after 3 days. On Aride Island with no fodies present, loss of artificial eggs was not observed. Female warblers incubate the clutch, and male warblers guard the clutch when females are absent. Deterrence of fodies by male warblers is efficient: loss rate of eggs from unattended warbler nests was seven times as high as from attended nests, and the more nest guarding, the lower the egg loss and the higher the hatching success. Egg loss is independent of the amount of incubation by females. There is no trade-off between incubating and foraging by females. Nest guarding competes with foraging by males, and this trade-off has a more pronounced effect on egg loss when food availability is low The transfer of breeding pairs from Cousin to either Cousine with egg-predating fodies or to Aride without fodies allowed us ro experimentally investigate the presumed trade-off between nest guarding and foraging. On Cousine, individual males spent the same amount of time nest guarding and foraging as on Cousin, and egg loss was similar and inversely related to rime spent nest guarding as on Cousin. Males that guarded their clutch on Cousin did not guard the clutch on Aride bur allocated significantly more time to foraging and gained better body condition. Loss of warbler eggs on Aride was not observed. Time allocation to incubating and for-aging by individual females before and after both translocations remained the same.

Nest-Site Selection by Roseate Terns Breeding on Aride Island, Seychelles

Estudo comparado dos impactes ambientais dos aproveitamentos hidroelectricos do Alto Coa e do Baixo Sabor

Habitat use by Seychelles sooty terns Sterna fuscata and implications for colony management

The relationship between sooty tern Sterna fuscata nest densities and vegetation characteristics of the breeding colonies was investigated on four islands in the Seychelles. Nest densities were greatest in areas with a vegetation cover of 30–50%, and areas that provided these conditions were generally dominated by pourpier Portulaca oleracea. On Aride Island, sooty terns nested at low density under an enclosed tree canopy but on the other islands nests were generally in the open, among sparse vegetation. On Desnoeufs Island, where eggs are harvested commercially for human consumption, sooty terns avoided nesting in dense areas of epi bleu Stachytarpheta jamaicensis, an introduced plant whose success on the island may be related to egg exploitation. Management of colony vegetation, especially the control of introduced aggressive species, and the encouragement of optimum conditions for nesting, could increase the numbers of nesting sooty terns and their reproductive output, helping to buffer them against adverse effects of human activity. Appropriate protection of sooty tern colonies can also benefit rarer and more vulnerable seabirds and turtles that share nesting islands.

Hybridization between Madagascan Red Fody Foudia madagascariensis and Seychelles Fody Foudia sechellarum on Aride Island, Seychelles

SummaryOn islands where populations of the endemic Seychelles Fody Foudia sechellarum and the introduced Madagascan Red Fody F. madagascariensis coexist, previous studies have concluded that the two species are reproductively isolated. On Aride Island, Seychelles, one female F. sechellarum became established within a population of F. madagascariensis and produced at least two hybrid offspring. This paper describes the first known case of hybridization between the two species and highlights the possible biological consequences.

Breeding of the Seychelles Magpie Robin Copsychus sechellarum and implications for its conservation

The total population of the Seychelles Magpie Robin Copsychus sechellarum declined from 38–41 birds in 12–13 territories in 1977–1978 to 17–21 birds in eight to nine territories in 1988–1990 and was entirely confined to Fregate Island (210 ha) in the Seychelles. After a successful cat eradication program in 1981–1982, recruitment improved, although the abandonment of agriculture had caused a reduction in the amount of feeding habitat and hence in the carrying capacity of the island. The population declined because of the failure of recruitment to compensate for the annual adult mortality. Foraging activity of the Magpie Robin was greater in high‐quality territories (measured by soil invertebrates available), leading to increased reproductive success. Through supplementary feeding, five times as many recruits were produced. Of the 11.5 potential annual breeding recruits, 5.3 are required to compensate for adult mortality, and the other 6.2 recruits can be regarded as “surplus” contributing to an increase. Magpie Robins prefer to breed in rotten trees, which are a scarce resource. The greater the distance between the nest site and feeding areas, the less time was spent in incubation and nest guarding, resulting in greater egg loss. Because of lack of suitable areas for establishing territories, many young Magpie Robins became “floaters”. Nest disturbance, both by these floaters and by the introduced Indian Mynah Acridotheres tristis, had adverse effects on the breeding success of robins. A recovery plan has been designed to save the Magpie Robin. Territories have been improved for feeding (by tree planting) and for breeding (by providing nestboxes and reducing nest disturbances). Given the vulnerability of one small island, the presence of surplus birds (supported mainly by supplementary food) and the suitability of neighbouring Aride Island (68 ha), successful translocations to this island took place in 1992 and 1994. Given the presence now of 47 individuals on two islands, it is hoped that the species will pull back from the brink of extinction.

Wariness of Caiman Populations and Its Effect on Abundance Estimates

Acknowledgments.-This research was partly funded by a Penn Chemicals Travel Grant Fund. We would like to thank Dr. James Cadbury and Mr. Adrian Skerritt, RSNC, Aride Island Trustees for permission to work on the island; Mr. Robert Lidstone-Scott, Phillippa Bond and Oglivy for assistance and information while working on the island; Mr. Norman Simmonds, Dept of Agriculture, Scotland; Dr. Peter Jones, Plant Science, U.C.C. and Dr. Tom Gittings, Dept. of Zoology, U.C.C. for statistical advice; Miss Lynn Ballard, Miss Ruth Richards and Mr Alan Browne, Dept. of Zoology, U.C.C. for assistance in the preparation of results, and Dr. Drew Gardner for comments on an earlier draft of this manuscript.

Flora of Aride Island, Seychelles

Flora of Aride Island, Seychelles

Conserving the Seychelles warbler Acrocephalus sechellensis by translocation: a transfer from Cousin Island to Aride Island : J. Komdeur, I. D. Bullock & M. R. W. Rands, Bird Conservation International, 1(2), 1991, pp 177–185

We sampled bryophytes in 52 rapids in regulated and unregulated north Swedish rivers to quantify effects of flow regulation on taxonomic richness and abundance of bryophytes. Predictive models based on the conditions at unregulated sites were used to predict richness and abundance at impacted sites and the residuals were used as a measure of the effect of regulation.Taxonomic richness was 22% lower than predicted at sites with reduced flow and 26% at sites with regulated but unreduced flow. The overall abundance of bryophytes was not significantly different from predicted. However, an analysis of the five most abundant species showed that the abundances of two species, Fontinalis antipyretica and F. dalecarlica, was lower than predicted at sites with reduced flow, while the abundance of Blindia acuta and Schistidium agassizii was higher than predicted at sites with regulated but unreduced flow.