David Monticelli

Productivity of White-Tailed Tropicbird on Aride Island, Seychelles

Abstract Nine years (1989/90-2002) of data on a asynchronous pelagic seabird, the White-tailed Tropicbird (Phaethon lepturus), breeding on Aride Island, Seychelles, were used to examine: (1) annual variation in productivity and, (2) the importance of large scale (El Niño Southern Oscillation) factors in explaining productivity levels. In 2001 and 2002, we examined the influence of local scale factors (parasitism by hard ticks Amblyomma loculosum and intra- and inter-specific competition for nest-sites) on productivity. Productivity between years only ranged from 0.21 to 0.37 chicks/breeding pair, but it was nevertheless significantly and inversely correlated with the El Niño index. No influence on productivity was caused by local factors. The frequency distribution of chick deaths varied significantly with chick age in 2001 but not in 2002. Most of the chick deaths were from starvation, in particular for chicks older than 20 days. As opposed to synchronous seabird species, there were no years with total breeding failure in the White-tailed Tropicbird. This may be partly explained by their dispersed feeding in the open ocean.

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 foraging success of individual birds. Comparing similar studies, chicks of Lesser Noddies and Sooty Terns (Sterna fuscata) appeared more resistant to fluctuating food supplies than those of Roseate Terns (Sterna dougallii), indicating that, in tropical seas, slow growth and foraging farther offshore are more advantageous than faster growth and inshore feeding. Datas de Postura, Alimentação dos Filhotes e Sucesso Reprodutivo de Anous tenuirostris na Ilha de Aride, Seychelles Resumo. Neste estudo descrevemos as principais características da biologia reprodutiva (datas de postura, tamanho dos ovos, peso dos filhotes ao nascerem e sucesso reprodutivo), crescimento e padrões de alimentação dos filhotes em Tinhosa-de-barrete, Anous tenuirostris, na ilha de Aride, Seychelles, 1995–2002. Na maioria dos anos a postura ocorreu entre o fim de Maio e o fim de Junho. O sucesso de eclosão e o sucesso de sobrevivência das crias variaram significativamente entre anos, apresentando o sucesso de sobrevivência (2–92%) uma maior variação do que o sucesso de eclosão (28–91%). Uma produtividade inferior a 0,10 crias por casal reprodutor ocorreu em 25% dos anos. Em 2001, o volume dos ovos que eclodiram não diferiu significativamente do volume dos ovos que não eclodiram. O peso dos filhotes ao nascerem apresentou uma correlação significativa com o índice de volume dos ovos, mas não se obtiveram correlações entre o tamanho dos ovos e, a data de eclosão e a taxa de crescimento linear dos filhotes. Cerca de 40% dos filhotes de Tinhosa-de-barrete foram alimentados ao anoitecer. Os filhotes com idades entre 0–5 e 6–10 dias receberam significativamente menos alimento do que os filhotes mais velhos. Foram observadas variações diárias e estocásticas no sucesso de alimentação dos indivíduos. A comparação do presente estudo com estudos semelhantes, sugere que as crias de A. tenuirostris e de Sterna fuscata sejam mais resistentes a flutuações na disponibilidade de alimento do que as crias de Sterna dougallii. Isto indica que, em mares tropicais, uma menor taxa de crescimento e uma alimentação em zonas pelágicas são estratégias mais vantajosas do que uma taxa de crescimento rápida e alimentação em zonas costeiras.

Diet and foraging ecology of Roseate terns and lesser noddies breeding sympatrically on Aride Island, Seychelles

Abstract Inferences on seabird ecology from stable isotopes ratios (δ13C, δ15N) and mercury concentrations analysis of feathers have been made for temperate and polar species but are far more rare for tropical species. In this paper, we used this approach combined with analysis of regurgitations and feeding observations at colonies to examine diet segregation between Roseate Terns (Sterna dougallii) and Lesser Noddies (Anous tenuirostris) breeding sympatrically on Aride Island (Seychelles), western Indian Ocean. Our results indicated extensive overlap between the two species in trophic level and foraging area during the breeding season. Goatfish predominated (93-97%) in all diet samples of adults and chicks collected in the colonies, except in prey fed to mates by Roseate Terns, of which scad and tuna comprised 20%. The isotopic analyses of feathers replaced by adults during molt (primary and body feathers) suggested, however, that the two species differ in foraging ecology during the nonbreeding period. Roseate Tern adults had consistently lower δ15N values than Lesser Noddies which, in turn, had δ15N values comparable to those of chick feathers grown on Aride. Moreover, low but similar mercury levels were found in body feathers of Lesser Noddy adults and Roseate Tern chicks, whereas Roseate Tern adults were significantly more contaminated. Overall, these results support the hypothesis that the Lesser Noddy is largely sedentary, being associated with the same food web in the vicinity of the colonies year-round. In contrast, Roseate Terns rely on distinct prey during the molting (nonbreeding) season which may be also consistent with a change in food web (i.e., a migratory regime) although the assignment of potential wintering areas remain difficult without isotopic basemaps currently available for the Indian Ocean.

Adult Survival Of Tropical Roseate Terns Breeding On Aride Island, Seychelles, Western Indian Ocean

Abstract Survival of tropical Roseate Terns (Sterna dougallii) from the western Indian Ocean was modeled using a capture-mark-recapture dataset of 102 breeding adults ringed and resighted on Aride Island, Seychelles, from 2002 to 2007. The effect of covariates reflecting oceanographic conditions and resighting effort was also examined during the modeling. A time-invariant survival rate was best supported by our data, with annual adult survival estimated at 0.807 ± 0.033 (SE). Resighting probability was found to be influenced by sea-surface temperature (SST) anomalies, as expressed by the mean Indian Ocean Dipole mode index recorded during the nonbreeding period. Years of higher SST in the western part of the Indian Ocean in September-April (8 months) corresponded to a lower probability of resighting adults at the colony during the breeding season (May-August), which may be related to a tendency for some adults to refrain from breeding in less favorable years. Comparing our results with temperate studies, Roseate Terns breeding on Aride were found to exhibit similar survival estimates. Consequently, this study does not support the hypothesis that tropical Roseate Terns may counterbalance their lower fecundity (clutch size and breeding success) compared to their temperate and northern-hemisphere counterparts (Europe, North America, Caribbean) by relatively higher survival rates.

Long-term studies on productivity of Roseate Terns and Lesser Noddies on Aride Island, Seychelles

This paper summarises up to 16 years of data on the productivity of Roseate Terns and Lesser Noddies on Aride Island, Seychelles, in order to assess: (1) the magnitude of variation in reproductive parameters, (2) the factors influencing their breeding success, and (3) whether common factors influenced the productivity of the two species. With the exception of 2002, the productivity of Lesser Noddies on Aride Island was always higher than that of Roseate Terns. The frequent mass mortalities of chicks on Aride were more common for Roseate Terns (an almost null productivity occurred in 44% of the years) than for Lesser Noddies (productivity less than 0.10 chicks per breeding pair occurred in only 20% of the years). Hatching success of both species was positively correlated, but there was no correlation for productivity, which suggests that stochastic variation in short-term food availability affected both species differently. Our results indicate that food shortage is the main factor explaining the breeding success of both species on Aride; the impact of other factors, such as tick infestation, depended upon the extent of food shortage. The underlying causes of food shortage are difficult to predict, although annual variation in marine productivity seems to be the ultimate factor determining productivity of Roseate Terns and Lesser Noddies.

Plumage Characteristics and Return Rate of One-Year-Old tropical Roseate Terns

Abstract We report an unusually high return rate (16%) of one-year-old Roseate Terns (Sterna dougallii) to their natal colony on Aride Island, Seychelles, in 2005. Detailed accounts of these birds are provided in terms of timing of arrival, breeding status, and plumage characteristics, and compared with those of two other age classes (2-year-olds and 3 to 6 year-olds) in the same colony and with temperate populations. One-year-old individuals returned on average three weeks later than older birds and did not attempt to breed. Their immature plumage dress (‘portlandica phase’) differed from their one-year-old temperate counterparts, with most birds showing several characteristics of adults in full breeding plumage, such as red bill and red legs, long tail-streamers, and absence of a dark carpal bar. Contrary to expectations from temperate studies, nonbreeding two-year-old individuals did not retain any characteristic of the portlandica plumage, and were virtually inseparable from breeding adults. The ad hoc return rate of Roseate Tern one-year-olds found in this particular year is high compared to recapture/resighting data from colonies in temperate areas, but is comparable to observations made at other tropical (Caribbean) breeding colonies. Altogether, these findings suggest that tropical Roseate Terns are prone to return to their natal site earlier than their temperate counterparts, and show a more rapid acquisition of the adult plumage. This may be especially the case in years of good food supply conditions, since the 2005 event coincided with the two years (2004-2005) of highest marine productivity recorded in the vicinity of Aride Island over the 1997-2005 period.

Global phenological insensitivity to shifting ocean temperatures among seabirds

Reproductive timing in many taxa plays a key role in determining breeding productivity1, and is often sensitive to climatic conditions2. Current climate change may alter the timing of breeding at different rates across trophic levels, potentially resulting in temporal mismatch between the resource requirements of predators and their prey3. This is of particular concern for higher-trophic-level organisms, whose longer generation times confer a lower rate of evolutionary rescue than primary producers or consumers4. However, the disconnection between studies of ecological change in marine systems makes it difficult to detect general changes in the timing of reproduction5. Here, we use a comprehensive meta-analysis of 209 phenological time series from 145 breeding populations to show that, on average, seabird populations worldwide have not adjusted their breeding seasons over time (−0.020 days yr−1) or in response to sea surface temperature (SST) (−0.272 days °C−1) between 1952 and 2015. However, marked between-year variation in timing observed in resident species and some Pelecaniformes and Suliformes (cormorants, gannets and boobies) may imply that timing, in some cases, is affected by unmeasured environmental conditions. This limited temperature-mediated plasticity of reproductive timing in seabirds potentially makes these top predators highly vulnerable to future mismatch with lower-trophic-level resources2.Time of reproduction may be altered as the climate changes. For seabirds, it is shown that there has not been an adjustment in timing as the climate changes and the sea surface warms. This lack of plasticity could result in a mismatch with food resources.

The influence of early age at breeding on reproductive parameters of tropical Roseate Terns

At Aride Island, Seychelles, western Indian Ocean, over a period of five years (2002–2006), early-age (2–5 years) Roseate Terns Sterna dougallii nested in more concealed sites than older-age (6–7 years) birds, possibly because of a relatively lower competitive ability. Fledging success and breeding productivity were higher for older birds, but clutch size, laying date and egg volume were most influenced by marine productivity (the concentration of chlorophyll a in adjacent seas, which was assumed to reflect feeding conditions) or by an interaction between marine productivity and age. Older birds bred earlier in years when food availability was greater, but younger birds did not do so. Annual variations in environmental conditions should be taken into account when examining the effect of age on the reproductive parameters of tropical Roseate Terns.

Diet of tropical Roseate Tern chicks on Aride Island and the role of local oceanographic conditions and age of chicks on food provisioning

Abstract Small seabirds are very sensitive to changes in the availability of prey and thus may be good indicators of changes in species composition and availability of prey. However, long-term data on dietary variation is scarce for tropical tern species. This paper assembles 9 years of data on deliveries of fish prey to Roseate Tern chicks of known-age on Aride Island, the Seychelles, in the western Indian Ocean, to examine: (1) the role of intrinsic (age of chicks) and extrinsic (local oceanographic conditions) factors on chick food provisioning, and (2) the temporal variation in intake rate of chicks. Our results show low annual variability in dietary composition: 75–97% of all ingested items were goatfish (Mullidae), which agrees with previous studies showing that these form the main prey fish for the Seychelles seabird community. Intake rate of chicks varied considerably among years, from 0.86 g fish ingested chick−1 h−1 in 1997 to 3.12 g chick−1 h−1 in 2005, with poor years showing a much higher coefficient of variation than good years. Intake rate of chicks was significantly correlated with local chlorophyll-fl concentration and sea-surface temperature of the preceding 2 weeks. This suggests that food provisioning of tropical Roseate Tern chicks is sensitive to fluctuations in local oceanographic conditions that affect the availability of prey fish at a short temporal scale, and that Roseate Terns are suitable sentinel organisms to indicate local changes in environmental conditions.

Altitudinal distribution and diversity of the Mount Karthala bird community on Grand Comoro (Comoro Islands)

Despite a high degree of endemism (c. 30%) and the existence of some serious threats, the avifauna of the Comoro Islands remains poorly studied. This paper reports on a bird census conducted on Grand Comoro (Ngazidja) in the afromontane forest ecosystem of Mt Karthala. Point counts were conducted over a 3-month period (March–May 1999) in different habitat types, along an altitudinal gradient ranging from completely degraded forest plantations (400–800 m elevation) to montane forest with modified understory (800–1200 m elevation) and intact cloud forest (1200–1800 m elevation) replaced by giant heathland at highest altitudes (>1800 m elevation). I tested whether or not species diversity, bird assemblages and level of endemism differed between habitat types. Furthermore, I investigated whether temporal changes had occurred since a previous census conducted in 1985–1989. Overall, 37 species were contacted during the census. No evidence of temporal changes in species diversity indices was detected during the short time interval separating both studies (10–15 years). However, the analysis could not account for the impact of increased areas of degraded forest on specific population sizes. Mean species richness and Shannon–Wiener index per point differed with respect to habitat type, being much lower in giant heathland. Mean species richness per point differed also with respect to factor “slope”, being highest in south-western montane forest with modified understory and cloud forest. An altitudinal endemism gradient was apparent with only three endemic species characteristic of low- to mid-altitude degraded habitats, while the bulk of endemic species was restricted to intact patches of primary cloud forest (six species) and giant heathland above 1800 m (one species). These findings, combined with the recent reports on ongoing levels of forest degradation and encroachment by local human populations, suggest that the survival of endemic forest species is dependent on the designation of a nationally-supported conservation area on Mt Karthala.