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1.
Geographical variation in measurements and colouration among populations and subspecies of White-tailed Tropicbirds Phaethon lepturus , including birds from Europa Island (southern Mozambique Channel] was examined worldwide. Two groups were distinguished: the 'large subspecies' (lepturus and fulvus from the Indian Ocean, catesbyi from the western Atlantic Ocean) and the 'small subspecies' (ascensionis from the central and eastern Atlantic Ocean, dorotheae from the Pacific Ocean, and the birds from Europa Island). No clinal variation was found in the Indian Ocean, the birds from Europa Island being the only 'small' ones. This population also had a high frequency of golden morphs, a feature that does not exist elsewhere in the western Indian Ocean. These results indicate that Europa's population is isolated from all nearby colonies in the Indian Ocean, and does not belong to any of the two previously known subspecies of the area. It also differs from the birds of the two small subspecies by the frequency of the colour morphs and the distribution. Consequently, we propose to treat this population as a previously undescribed subspecies, endemic to Europa Island, for which we propose the name Phaethon lepturus europae. Geographical isolation of Europa Island and oceanic conditions in the Mozambique Channel are discussed to explain the isolation of this population.  相似文献   

2.
ABSTRACT Population size and trends are demographic parameters that can be used to help determine the threat of extirpation or extinction of bird populations and in determining management strategies. Chapada Flycatchers (Suiriri islerorum) are endemic to the Cerrado region of Brazil, dependent on open cerrado habitat, defend large territories, and their populations seem to be declining. From 2003 to 2007, we analyzed demographic parameters of a declining population of Chapada Flycatchers, using the rate at which territories became vacant and the size of the breeding population to ascertain the status of the population, and evaluated the relative contributions of apparent annual survival and recruitment rates to these trends. Territories became vacant at a mean rate of 13% per year, and 32% of all territories were vacated during our study. The current breeding population (20 pairs) was at least seven times smaller than the estimated carrying capacity of the reserve (141 territorial pairs). Estimated apparent annual survival probabilities (0.77 for breeders; 0.67 for nonbreeders) based on model averaging were comparable to those reported for other Neotropical passerines. Survival rates did not differ between the sexes and the estimated recruitment rate was 0.21. In many species, adult survival is the factor that most strongly influences population growth rates. However, the population of Chapada Flycatchers we studied is declining despite high annual survival rates, with low and variable breeding success probably causing the decline. Our results improve our understanding of the possible role of adult survival and breeding success in the decline of populations of small passerines in isolated reserves in the tropics.  相似文献   

3.
JAN KOMDEUR 《Ibis》1996,138(3):485-498
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.  相似文献   

4.
Understanding the effects of environmental variations on ecosystems is a major topic in ecology. In this study, we estimated demographic parameters of a seabird population, the thin-billed prion (Pachyptila belcheri) at Kerguelen Islands, and then tested for relationships with inter-annual variations of climatic indices, using long-term capture–recapture data. The annual adult survival probability was 0.825±0.009 and the breeding success was 0.519±0.090. Sea surface temperature anomalies were negatively related with breeding success. By contrast, winter sea ice concentration in the Antarctic seasonal ice zone seemed to negatively influence adult survival. This suggests a connection between sub-Antarctic and Antarctic ecosystems. The actual context of large climatic changes in the Austral Ocean seems to explain a large part of the decreasing trends observed for both the breeding success and the adult survival. Thus, a decrease of the population size of thin-billed prions at Kerguelen could be strongly suspected in the near future.  相似文献   

5.
Tropical cyclones are renowned for their destructive nature and are an important feature of marine and coastal tropical ecosystems. Over the last 40 years, their intensity, frequency and tracks have changed, partly in response to ocean warming, and future predictions indicate that these trends are likely to continue with potential consequences for human populations and coastal ecosystems. However, our understanding of how tropical cyclones currently affect marine biodiversity, and pelagic species in particular, is limited. For seabirds, the impacts of cyclones are known to be detrimental at breeding colonies, but impacts on the annual survival of pelagic adults and juveniles remain largely unexplored and no study has simultaneously explored the direct impacts of cyclones on different life‐history stages across the annual life cycle. We used a 20‐year data set on tropical cyclones in the Indian Ocean, tracking data from 122 Round Island petrels and long‐term capture–mark–recapture data to explore the impacts of tropical cyclones on the survival of adult and juvenile (first year) petrels during both the breeding and migration periods. The tracking data showed that juvenile and adult Round Island petrels utilize the three cyclone regions of the Indian Ocean and were potentially exposed to cyclones for a substantial part of their annual cycle. However, only juvenile petrel survival was affected by cyclone activity; negatively by a strong cyclone in the vicinity of the breeding colony and positively by increasing cyclone activity in the Northern Indian Ocean where they spend the majority of their first year at sea. These contrasting effects raise the intriguing prospect that the projected changes in cyclones under current climate change scenarios may have positive as well as the more commonly perceived negative impacts on marine biodiversity.  相似文献   

6.
Matthieu Le Corre 《Ostrich》2013,84(3-4):155-159
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. New data are provided on the breeding phenology of the two species of booby. Finally, the importance of this island for the conservation of seabirds in the western Indian Ocean is discussed.  相似文献   

7.
Migratory behavior varies extensively between bird taxa, from long distance migration to purely sedentary behavior. Variability in migratory behavior also occurs within taxa, where individuals within some species, or even populations, show mixed strategies. The same variability occurs in seabird species. We examined the migratory behavior of distinct populations of great frigatebirds Fregata minor in three distant oceanographic basins. Great frigatebird populations showed extensive variation in post‐breeding migratory behavior. Birds from Europa Island (Mozambique Channel) made long‐distance migration to numerous distinct roosting sites in the Indian Ocean, New Caledonia birds made shorter distance migrations to roosting sites in the southwestern Pacific Ocean, and Galapagos birds were resident within the archipelago year round. Juvenile birds from Europa Is. and New Caledonia dispersed widely whereas Galapagos juveniles were resident year round. The migratory behavior of Europa Is. and New Caledonia resulted in complete separation of foraging grounds between breeding adults, non‐breeding adults, and juveniles, whereas in the Galapagos the overlap was complete. We suggest that population variability in migratory behavior may have arisen because of different environmental conditions at sea, and also depends on the availability of suitable roosting sites on oceanic islands. The results also highlight the capacity of frigatebirds to remain airborne most of the time even outside the breeding season when they have to molt.  相似文献   

8.
Berruti, A., Cooper, J. & Newton, I.P. 1995. Morphometrics and breeding biology of the Whitechinned Petrel Procellaria aequinoctialis at sub-Antarctic Marion Island. Ostrich 66: 74–80.

Aspects of adult morphometrics and the breeding biology of the summer-breeding Whitechinned Petrel at sub-Antarctic Marion Island, southern Indian Ocean, are given, based on a study conducted in 1980/91, along with additional observations on breeding success made in 1990191. It is concluded that Whitechinned Petrels at Marion Island are similarly sized and breed in a similar manner to other studied populations of the nominate race. The eradication of cats at Marion Island in 1991 should now lead to a slow population recovery.  相似文献   

9.
Climate models forecast increasing climatic variation and more extreme events, which could increase the variability in animal demographic rates. More variable demographic rates generally lead to lower population growth and can be detrimental to wild populations, especially if the particular demographic rates affected are those to which population growth is most sensitive. We investigated the population dynamics of a metapopulation of 25 colonies of a semi-arid bird species, the sociable weaver Philetairus socius, and how it was influenced by seasonal weather during 1993–2014. We constructed an integrated population model which estimated population sizes similar to observed population counts, and allowed us to estimate annual fecundity and recruitment. Variance in fecundity contributed most to variance in population growth, which showed no trend over time. No weather variables explained overall demographic variation at the population level. However, a separate analysis of the largest colony showed a clear decline with a high extinction probability (0.05 to 0.33) within 5 years after the study period. In this colony, juvenile survival was lower when summers were hot, and adult survival was lower when winters were cold. Rainfall was also negatively correlated with adult survival. These weather effects could be due to increased physiological demands of thermoregulation and rainfall-induced breeding activity. Our results suggest that the dynamics of the population on the whole are buffered against current weather variation, as individual colonies apparently react in different ways. However, if more and increasingly extreme weather events synchronize colony dynamics, they are likely to have negative effects.  相似文献   

10.
Although Grey-headed Albatrosses Thalassarche chrysostoma are usually regarded as biennial breeders, taking a year off following a successful breeding attempt, a small proportion of successful birds attempt to breed annually. This proportion was higher at Marion Island (5.4%) than at Bird Island, South Georgia (1.0%), suggesting that conditions are more favourable at Marion Island. This hypothesis is supported by higher average breeding success and shorter lags following both successful and failed breeding attempts at Marion Island. Factors favouring reproduction at Marion Island may include reduced intraspecific competition (given the much smaller breeding population) and/or more predictable food supply (owing to production of meso-scale eddies associated with the Indian Ocean Ridge). Although annual breeding appeared to increase the risk of adult mortality, with several birds that attempted to breed annually found dead the following year, at least some birds greatly enhanced their reproductive output, with one male raising five chicks in five successive years. Contrary to life-history theory, there was no evidence that older birds were more likely to attempt annual breeding because of declining reproductive value.  相似文献   

11.
The numbers of Black-browed Albatrosses Diomedea melanophrys and Grey-headed Albatrosses D. chrysostoma at Campbell Island, New Zealand, have declined dramatically since the 1940s. Black-browed Albatross numbers went into a steep decline in the 1970s and, since at least 1984, have been increasing slightly at average rates of 1.1% and 2.1% per annum at two colonies. The long-term downward trend in numbers of the Grey-headed Albatross has continued into the 1990s, averaging annually between 3.0% and 4.8% per annum at different colonies. A demographic study carried out between 1984 and 1996 indicates that Black-browed and Grey-headed Albatrosses have similarly high annual adult survival rates (0.945 and 0.953, respectively). Black-browed Albatrosses breed for the first time at a younger average age than do Grey-headed Albatrosses (10 years and 13.5 years, respectively), have a higher average breeding success (0.663 compared with 0.397 for the latter species) and are annual breeders whereas Greyheaded Albatross show a typical biennial pattern of breeding. Both show low survival from fledging to first breeding; averaging 0.186 and 0.162 for Black-browed and Grey-headed Albatrosses, respectively. Both species are accidentally killed in the Japanese long-line fishery for tuna Thunnus sp. in the Australasian region. The steep decline of Black-browed Albatross numbers in the 1970s was concomitant with the development of this fishery in the foraging region of the Campbell Island birds. Currently, the slight increase in numbers is due to high adult survival rates and breeding success, and is coincident with a great reduction in long-line fishing. With stable and high adult survival rates, it is expected that future population trends will be mainly influenced by the recruitment rates. The continuous decline in Grey-headed Albatross numbers since the 1940s, before long-line fishing developed in this region, indicates that natural environmental processes contributed to the downward trend in breeding numbers. Modelling indicates that Grey-headed Albatross numbers will continue to decrease with the present demographic parameters. A comparison between the species breeding at different sites shows that differing environmental conditions influence demographic characteristics.  相似文献   

12.
The movements and behavior of many taxa of seabirds during the non‐breeding season remain poorly known. For example, although studies conducted in the Pacific and Indian oceans suggest that White‐tailed Tropicbirds (Phaethon lepturus) seldom fly more than a few thousand kilometers from nest colonies after breeding, little is known about the post‐breeding movements and behavior of a subspecies of White‐tailed Tropicbirds (P. l. catesbyi) that breeds on islands in the North Atlantic Ocean. Our objective, therefore, was to use light‐based geolocators to identify the ranges and pelagic activities of White‐tailed Tropicbirds from Bermuda during the non‐breeding periods in 2014–2015 (= 25) and 2015–2016 (= 16). Locations were estimated based on changes in light intensity across time, and pelagic activities were determined based on whether geolocators attached to leg bands were wet (i.e., birds resting on the water's surface) or dry (i.e., birds in flight). In 2014, birds spent late summer (July–September) near Bermuda and the British Virgin Islands; by mid‐September, most (= 17; 68%) birds took a direct easterly route to the Sargasso Sea. In 2015, most post‐breeders (= 15; 94%) flew east from Bermuda and to the Sargasso before the end of late summer. For both years combined, fall and winter (October–February) ranges extended as far west as North Carolina and as far east as the mid‐Atlantic Ridge. In both years, all birds were located between Bermuda and the British Virgin Islands during the spring (April–May). All birds then flew north to Bermuda in both years, with variations in timing, during April and May. We also found extensive overlap in the ranges of males and females during the non‐breeding season in both years. During the non‐breeding season, White‐tailed Tropicbirds spent 5% of night periods and 41% of day periods in flight in 2014; in 2015, birds spent 8% and 42% of night and day periods, respectively, in flight. Tropicbirds spent more time flying during the day because they hunt by day, detecting prey on the wing by sight. Overall, our results suggest that White‐tailed Tropicbirds that breed in Bermuda are diurnal, nomadic wanderers that range over an extensive area of the Atlantic Ocean during the non‐breeding season.  相似文献   

13.
The Príncipe Autonomous Region is recognised as a marine biodiversity hotspot, although little is known about the status of its marine fauna. It holds most breeding seabirds of the tropical eastern Atlantic Ocean. Based on anecdotal accounts of increased fishing and seabird harvesting, regular monitoring of seabird populations is considered a priority. Therefore, a survey of Príncipe’s seabird colonies was conducted in 2017. The results revealed that the more accessible seabird colonies have disappeared. Around Príncipe, Boné de Joquei is the present main stronghold for Brown Boobies Sula leucogaster and White-tailed Tropicbirds Phaethon lepturus. The Tinhosas islands hold an estimated 300 000 seabirds, predominantly Sooty Terns Onychoprion fuscatus, but also Brown Boobies, Black Noddies Anous minutus and Brown Noddies Anous stolidus. Long-term multi-annual monitoring is needed to understand the breeding phenology of each species and to better assess population trends. Ensuring a protective status for both Tinhosas and the seabirds under national legislation is a key priority for future conservation policy in São Tomé and Príncipe.  相似文献   

14.
The white-chinned petrel (Procellaria aequinoctialis) is the seabird most often killed on longlines in the Southern Ocean and is listed as vulnerable to extinction. We estimated the population breeding at the Prince Edward Islands, the last breeding site for the nominate subspecies that lacks a recent population estimate. White-chinned petrel burrows are largely confined to deep, muddy soils, usually on slopes below 200?m, but locally up to 420?m. After correcting for count bias, Marion Island has an estimated 29,900 nests (95?% CI 27,700–32,400). Burrow occupancy rates at the start of the incubation period were 65?% during one-off surveys, but repeat surveys found that at least 73?% of burrows were occupied and 87?% of burrows showed signs of occupancy. This suggests that there were roughly 24,000 occupied nests on Marion Island (95?% CI 20,000–28,000). A more cursory survey on Prince Edward Island yielded 14,700 burrows, suggesting that there are 9,000–15,000 occupied nests. The nominate subspecies of white-chinned petrel occupies approximately 974,200 nests (95?% CI 678,000–1,286,000), with the Prince Edward Islands, the third most important breeding site, after South Georgia and Kerguelen. Assuming that populations breeding at islands in the Atlantic and Indian Oceans winter in different regions, the impact of fishery bycatch is likely to have had a greater impact on the Indian Ocean population. The Marion Island survey provides a baseline against which future population changes can be assessed.  相似文献   

15.
P. JOUVENTIN  J. MARTINEZ  J. P. ROUX 《Ibis》1989,131(2):171-182
A small population of the 'Great Albatrosses' has been discovered on Amsterdam Island (Indian Ocean) and described in 1983 as a new species: Diomedea amsterdamensis (Roux et al. 1983). We present here data on the biometry, plumage variability and preliminary results of a long-term study on the breeding cycle and population dynamics of this relict population. The current population is estimated at 65 birds including 21 breeding pairs.  相似文献   

16.
Aim  To examine the exploitation, recovery and current status of green turtles ( Chelonia mydas ) nesting at Ascension Island.
Location  Ascension Island (UK) (7°57' S, 14°22' W), South Atlantic Ocean.
Methods  We analysed records of the harvest of green turtles nesting at Ascension Island between 1822 and 1935, illustrating the decline in numbers over this period. Using a deterministic age-class structured model we predict the initial number of breeding females present in the population prior to the recorded harvest and compare this to our estimate of the current population based upon our recent annual surveys (1999–2004).
Results  Prior to 1822 we estimate the nesting population of green turtles to have been at least 19,000–22,000 individuals in order for the population to have survived the level of harvest recorded. From recent data (1999–2004), we estimate the current breeding population of green turtles at this site to be 11,000–15,000 females. Our results illustrate a dramatic recovery of the population, which is still increasing exponentially and shows no evidence of slowing, suggesting it has not reached 50% of its carrying capacity.
Main conclusions  We estimate that, since the 1970s, the Ascension Island population of green turtles has increased by 285% and question the recent listing of this species as endangered by the IUCN (World Conservation Union), in particular in the Atlantic Ocean, where 75% of the populations assessed by the IUCN are increasing. Indeed, we estimate the global population of this species to be in excess of 2.2 million individuals. We suggest that the IUCN's global listing process detracts attention from those populations that are truly threatened with extinction and should not, in its present form, be applied to globally distributed long-lived species such as marine turtles.  相似文献   

17.
《Journal of Ornithology》2010,151(1):51-60
Autumn postnuptial migration is critical in the dabbling duck annual cycle, when first-year birds in particular suffer high losses to natural and hunting mortality. Mortality rates in this age-class are generally unknown in Europe where winter ringing predominates. We used data from large-scale wing collections from hunters in Finland, Denmark and France to test the prediction that juvenile proportions among killed Teal (Anas crecca) would decline with distance along the flyway. As expected, this proportion decreased from 89% in Northern Finland to 58% in Western France. Potential biases linked with age determination from the wings, differential migration of age-classes, relative susceptibility to different forms hunting and gradual improvement of juvenile survival as they learn to avoid hunters could not explain the observed decline of juveniles in the shot population. This pattern was therefore considered to be genuine, the result of the cumulative depletion of first-years along the flyway, likely through hunting. On this assumption, combined with known adult monthly survival rates during August–November (94.2%), monthly juvenile survival rate was estimated at 52.8%, i.e. 14.7% (range 13.9–15.4% based on extreme values of adult survival) amongst Scandinavian juveniles reaching wintering quarters in Western France. Despite lack of precision in such estimates based on relative proportions, there is little doubt about the magnitude of autumn juvenile mortality and its consequences for the population dynamics of Teal. Lack of correlations between annual proportions of juveniles in the hunting bag and an index of Teal breeding success in Finland may result from such high and variable inter-annual mortality.  相似文献   

18.
The presence of unmarked individuals is common in mark–recapture study populations; however, their origin and significance in terms of population dynamics remain poorly understood. At Marion Island, southern Indian Ocean, where virtually all southern elephant seal Mirounga leonina pups born annually (1983–2008) were marked in a long‐term mark–resight study, large numbers of unmarked seals occur. Unmarked seals originate either from marker (tag) loss or from immigration. We aimed to identify patterns in the occurrence of marked and unmarked individuals that will allude to the possible origin and significance of the untagged component of the population, predicting that tag loss will add untagged seals to mainly adult age categories whereas migrating untagged individuals will be mostly juveniles. We fitted a generalized linear model using the factors month, year and age‐class to explain the relative abundance of untagged seals (tag ratio) from 1997 to 2009. Site usage of untagged seals relative to tagged seals was assessed using a binomial test. Untagged seals, predominantly juveniles, were present in the highest proportions relative to tagged seals during the winter haulout (tagged seals/total seals less than 0.3) and the lowest proportion (approximately 0.5) during the female breeding haulout, increasing in relative abundance from 1997 to 2009. Untagged seals were distributed evenly across suitable haulout sites while tagged seals displayed high local site fidelity and occurred in greater numbers at or near large breeding beaches. Untagged seals are considered to be mostly migrant seals that disperse from other islands within the southern Indian Ocean and haul out at Marion Island during non‐breeding haulouts in particular. Some of these seals immigrate to the breeding population, which can be a key component of the local population dynamics. We emphasize the need for mark–recapture studies to evaluate the role of the unmarked component of a population, thereby inducing a more confident estimation of demographic parameters from the marked sample.  相似文献   

19.
Infectious diseases have the potential to cause rapid declines and extinction in vertebrate populations, and are likely to be spreading with increased globalisation and climate warming. In the Southern Ocean and Antarctica, no major outbreaks of infectious diseases have been reported to date, perhaps because of isolation and cold climate, although recent evidence suggests their presence. The major threat for the Southern Ocean environment is today considered to be fishing activities, and especially controversial long-lining which is assumed to be the cause of the major decreases in albatross and large petrel populations observed recently. Here we show that the worldwide spread of avian cholera is probably the major cause of the decrease on Amsterdam Island of the large yellow-nosed albatross (Diomedea chlororhynchos) population, which was previously attributed to long-line fishing. Another pathogenic bacterium, Erysipelas, was also present. The diseases affect mainly young chicks, with a cyclic pattern between years, but also kill adult birds. The outbreak of the disease probably occurred in the mid-1980s when chick mortality increased, adult survival decreased and the population started to decrease. The diseases may be currently threatening the very rare Amsterdam albatross (D. amsterdamensis) with extinction, and are probably also affecting sooty albatrosses (Phoebetria fusca). The spread of diseases to the most remote areas of the world raises major concern for the conservation of the Southern Ocean environment.  相似文献   

20.
Southern elephant seals range extensively during regular foraging excursions. Despite this they are highly philopatric and long range dispersal is rare. At Gough Island, southern Atlantic Ocean, we observed a breeding adult male elephant seal during September 2009, which had been tagged on its natal beach at Marion Island, southern Indian Ocean, in November 1998. The individual was resighted only once on Marion Island, 6 months after tagging. This 3,860 km movement represents dispersal (and likely gene flow) between distinct populations from different elephant seal geographical provinces. Given the polygynous breeding system of this species, the presence of this single male may have a disproportionate genetic effect on the small number of southern elephant seals breeding at Gough Island.  相似文献   

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